Search

Natural self-assembled microstructured particles (diatomaceous earth) were used to develop a gas sensor paper with detection mechanism based on visible and distinct color changes of the sensor paper when exposed to volatile basic nitrogen compounds. The coating formulation for paper was prepared by applying diatomites, polyvinyl alcohol (PVOH), and pH sensitive dyes on acidic paper substrate. The surface coating was designed to allow a maximum gas flow through the diatomite sensors. The produced sensor paper was tested for sensitivity using different ammonia concentrations and we observed a sensitivity lower limit at 63 ppm. As a comparison, the results show comparable sensitivity levels to carbon nanotube based sensor technologies reported in literature. [ABSTRACT FROM AUTHOR]

For the lack of historical water ecology monitoring data and the limitations of traditional morphology-based water ecology reconstruction methods, the response mechanism of lake phytoplankton to climate change in the Tibetan Plateau remains unclear. In this study, we reconstructed the succession of phytoplankton community in Lake Gyaring, located in the northeastern Tibetan Plateau, since the 6th century by using sediment DNA metabarcoding. We found that the diversity and structure succession stages of phytoplankton community were consistent with the global temperature oscillation events, namely, the Medieval Warm Period (800–1300 CE). Little Ice Age (1300–1850 CE) and Current Warm Period (1850–2000 CE). The community structure dominated by Chlorophyta in the Medieval Warm Period gradually changed to that dominated by Bacillariophyta in the Little Ice Age. However, the Current Warm Period did not observe the dominant community structure of Chlorophyta similar to that of the Medieval Warm Period. This finding may be due to the climate change of the Current Warm Period was influenced by multiple human activities, such as increased anthropogenic aerosols, which promoted obvious weakening of the intensity of the summer monsoon, leading to decreased soil erosion and lake mixing, and thus may trigger a strikingly different aquatic ecosystem compared to that during the Medieval Warm Period. In this paper, the combination of genomics and palaeollimnology is helpful to explore the response mechanism of phytoplankton to climate change. [Display omitted] [ABSTRACT FROM AUTHOR]

• Macroscopic assessment via image analysis aimed to explore environmental trace evidence dynamics. • Transfer and persistence of soils to footwear and diatomaceous earth to clothing was tested. • Both environmental traces were retained and visually identifiable during one week of wear. • Soil type, clothing type, & body positioning significantly impacted persistence and distribution. • Recognising the presence of trace evidence is a critical first step in the forensic process. Environmental trace evidence offers useful circumstantial intelligence to link persons and scenes of forensic interest. An increasing empirical research base is dedicated towards understanding the transfer and persistence dynamics of environmental indicators including pollen, soils, and diatoms, within a diverse range of experimental frameworks. This paper presents two discrete studies exploring transfer and persistence of soils and sediments on footwear and diatomaceous earth adhered to clothing in forensically pertinent scenarios. Variables including sediment type, foot position, clothing type, and body positioning were also explored throughout. Both experiments incorporated a field-based methodology during the sampling effort. Photographs were collected of an initial transfer sample and of a retained assemblage following hours, days, and up to one-week of wear, facilitating macroscopic assessment of trace evidence dynamics. All images were processed using accessible, open-source software before spatial analysis of evidence distribution within and temporal assessment (% retention) upon each evidential surface. The results highlighted consistent loss of transferred sediment from footwear with significantly greater retention of loamy clay soil than dune sand which was absent beyond 24 h of wear. Loss was not influenced by wearer gait but was more rapid from those areas of the shoe sole in direct contact with the ground. Diatomaceous earth was retrieved from all three clothing types tested after one week – significant losses of material occurred before 48 h with a consistent assemblage identified beyond this. Denim was significantly more effective than acrylic and fleece for diatomaceous earth retention and significantly more material was lost from clothing worn on the lower body. These findings highlight the value of using visual environmental markers and a macroscopic analytical approach during the investigation of environmental trace dynamics. The methodology offers a novel, non-destructive assessment of soil and diatom transfer and persistence, complementing more extensive laboratory-based examinations to ensure the development of a well-rounded research base within the forensic sciences. [ABSTRACT FROM AUTHOR]

This paper presents recently obtained palebotanical data regarding the evolution of Lake Paleolotos in the Middle Pleistocene. Its evolution was more complicated than the development of the adjacent lakes in the coast of Peter the Great Bay (the Sea of Japan). The Middle Pleistocene lacustrine sediments accumulated in the downstream of the Tumannaya River (the most southwestern area of Primorye, Russia Far East) were studied using diatom and pollen analytical methods. We found that the Lake Paleolotos arose during Marine Isotope Stage 11 (MIS 11) and disappeared during MIS 6. For more than half of its existence (MIS 11–8), it was a freshwater oligotrophic basin with a depth of at least 20 m, with clear waters and poor organic matter content. The lake occupied most of the modern accumulative plain on the left bank of the Tumannaya River, reaching a size of at least 10–12 km across. During MIS 7–6 Lake Paleolotos turned into a shallow-water basin (its depth most likely did not exceed 1–3 m) of a eutrophic type with turbid waters rich in organic matter. Palynological data suggest that during MIS 11, 9 and 7 the area adjacent to the Lake was covered with coniferous/broad-leaved forests with presence of some thermophilic plants of North China and North Korea Flora (Castanea , Celtis , Magnolia , Tsuga and Cupressaceae). This indicates that vegetation zones were displaced by about 500–700 km to the north relative to their present position. During periods of cooling they were replaced by coniferous/small-leaved forests with the participation of shrub species of birch and alder (MIS 10) and coniferous/small-leaved forests consisted of pine, birch, and spruce with the participation of elm and oak (MIS 8 and 6). [ABSTRACT FROM AUTHOR]

This paper discusses the results of siliceous microfossils studies performed in a "staircase" of four isolation basins (33.7 m–2.9 m a.s.l.) on Big Solovetskiy Island (Solovki Archipelago, the White Sea). Diatoms were used as a primary group for paleoinferences, while chrysophyte cysts and sponge spicules also demonstrated high indicative potential. In all study lakes, the siliceous microfossils stratigraphy revealed three main stages of their evolution, i.e. large-basin, transitional and small-lake stages, each characterized by certain composition of the diatom assemblages and floristic diversity, relative abundances of chrysophyte cysts and sponge spicules, and siliceous microfossils concentrations. In the uppermost lake, glaciolacustrine environments unfavorable for aquatic biota existed during the large-basin stage. The proglacial lake stage terminated prior to ca. 10.4 cal ka BP, followed by a (semi)terrestrial episode before the transition to small-lake environments. In the other three lakes, marine environments were inferred at the earlier stage, characterized by the predominance of marine and brackish-marine diatoms, increased proportions of sponge spicules and low "cysts to diatoms" ratio. At the transitional marine-freshwater stage, mass growth of small fragilarioid diatoms and decreased abundances of spicules indicated unstable environments, while increased proportions of cysts pointed to progressive freshening of the basins. The duration of the marine-freshwater transition expectedly prolonged from ca. 200 yr in the upper basin (16.6 m a.s.l) to ca. 500 yr in the lowermost lake (2.9 m a.s.l.). The isolation from the sea took place between ca. 6.3 and 1.4 cal ka BP. At the small-lake stage, siliceous microfossils stratigraphies reflected local specifics of the basins and their catchments. We argue that besides traditionally used diatom data, relative and absolute abundances of siliceous microfossils also possess high indicative value for isolation basin studies. Our study demonstrated that marine waters on Big Solovetskiy Island never reached ca. 34 m a.s.l. during the Holocene, unlike the western coast of the Onega Bay where the Preboreal marine intrusion was recorded even at higher elevated localities. Different rates and amplitudes of shoreline displacement are thus suggested for the inner and outer parts of the Onega Bay. During the mid-Holocene Tapes transgression, before ca. 6.3 cal ka BP, the relative sea level on Big Solovetskiy Island exceeded 17 m a.s.l. The average estimated rates of the shoreline retreat during the second half of the Holocene gradually decreased from 0.28 cm year−1 to 0.2 cm year−1, indicating slowed isostatic uplift. [ABSTRACT FROM AUTHOR]

The sedimentary sequence of La Narce du Béage Basin is one of the few natural archives covering the last 18 ka cal. BP in the French Massif Central. This paper focuses on the palaeoecological reconstruction of environmental and climatic changes affecting this shallow periglacial lake from the Late-Glacial to the Early Holocene. After field surveys and geophysical mapping, two cores (cores A and D) were extracted and dated. Plant macrofossils, pollen, non-pollen palynomorphs (NPPs) and diatom assemblages were compared within the cores to study vegetation, temperature, pH, water level and ice cover changes through time. During the Oldest Dryas (18–14.75 ka cal. BP), climatic conditions were the coldest with a short ice-free season allowing the development of periphytic diatoms only (ecologically comparable to Arctic ones). A cold and dry steppe landscape – exposed to severe erosion – comprised an herbaceous and shrub flora (e.g. Artemisia , Chenopodiaceae, Helianthemum, Ephedra, Hippophaë, Juniperus). Animal presence is suggested by coprophilous fungi. Periphytic diatoms and allochtonous pollen (Cedrus) underline windy conditions, and the possible erosion of neo-formed soils. Then, during the Bølling-Allerød interstadial (14.75–12.7 ka cal. BP), the ice-free season increased and some trees/shrubs (Salix, Betula and Juniperus) established locally within open grasslands. During the Younger Dryas (12.7–11.7 ka cal. BP) cooler conditions favoured steppe taxa again (Helianthemum, Achillea, Artemisia , Caryophyllaceae, Ranunculaceae) and erosion increased. The ice cover on the lake prevailed even if the conditions were not as cold as during the Oldest Dryas. During the Preboreal (11.7–10 ka cal. BP) Isoëtes echinospora and I. lacustris developed in the eulittoral zone of the lake, which was surrounded by a swamp forest (with Betula nana and B. pubescens). Pinus sylvestris, Betula pendula, Corylus avellana and trees from the Quercetum mixtum rapidly established in the uplands. Occurrences of Gaeumannomyces and Xylomyces fungi – both phytopathogens on broadleaved trees – and decreasing herb values indirectly hint at a close forest canopy. At the beginning of the Boreal (10 ka cal. BP), aquatic and semi-aquatic taxa developed on open water due to longer ice-free seasons (diatoms, micro-algae, Alisma plantago-aquatica, Potamogeton, Typha). The final terrestrialization towards a mire occurred as a consequence of the Holocene warming and related to water chemistry changes (acidification, eutrophication). • During the last deglaciation, a very shallow lake established as demonstrated by palaeoecological data, such as epiphytic diatoms, living on rocks. • Late-Glacial steppe landscape with severe erosion, open grassland and possible mega-herbivore presence. Arctic-like conditions. • Development of shrubs or trees during the Bølling-Allerød interstadial and reduced ice-free season. • Dry and cold conditions persisted from the Younger Dryas to the Early Preboreal. Oligotrophic flora (Isoetids) established in the eulittoral zone. • During the post-glacial warming, the lake tended to acidify. Peat flora and organic matter accumulated and led to the terrestrialization of the lake. [ABSTRACT FROM AUTHOR]

• Diatoms in two springs with different surrounding land use in the Karoo compared. • Diatom indices GDI, SPI,BDI and%PTV were used to evaluate water quality. • Diatom species and indices in Great Fish River compared to historical data. • Indices at headwater site reduced ecological classification compared to previous study. This paper examines the efficacy of diatoms as bioindicators of water quality in the upper reaches of the Great Fish River following a period of reduced flow from drought conditions. Of the five sites, three were sampled three times in an 18 month period while the remaining two were sampled once. As a comparison, one headwater site within Mountain Zebra National Park, situated in the same district, was sampled. A total of 166 diatom taxa belonging to 29 genera were identified. Dominant taxa for the Great Fish River were identified as Amphora pediculus; Epithemia sorex; Nitzschia frustulum; Navicula veneta and Craticula buderi. These species, indicative of high nutrient concentrations and moderately saline to brackish conditions can tolerate low flow conditions. The Generic Diatom Index (GDI), the Specific Pollution sensitivity Index (SPI) the Biological Diatom Index (BDI) and the% Pollution Tolerant Valves (%PTV) – part of the UK Trophic Diatom Index (TDI) were used for interpretation of the results. The indices showed that this river is in poor condition. By comparison the headwater site in the Mountain Zebra National Park had Cocconeis placentula var. euglypta, Achnanthidium minutissimum and Cocconeis placentula var. lineata as dominant species and, using the same indices, the river was classified as in moderate to good condition with respect to water quality. When compared to a previous study (2010 – 2012), these sites showed a shift in dominant species indicating a change in water flow conditions and quality. [ABSTRACT FROM AUTHOR]

Abstract This paper provides an overview of stable isotope analysis (H, C, N, O, Si) of the macro- and microscopic remains from aquatic organisms found in lake sediment records and their application in (palaeo)environmental science. Aquatic organisms, including diatoms, macrophytes, invertebrates, and fish, can produce sufficiently robust remains that preserve well as fossils and can be identified in lake sediment records. Stable isotope analyses of these remains can then provide valuable insights into habitat-specific biogeochemistry, feeding ecology, but also on climatic and hydrological changes in and around lakes. Since these analyses focus on the remains of known and identified organisms, they can provide more specific and detailed information on past ecosystem, food web and environmental changes affecting different compartments of lake ecosystems than analyses on bulk sedimentary organic matter or carbonate samples. We review applications of these types of analyses in palaeoclimatology, palaeohydrology, and palaeoecology. Interpretation of the environmental ‘signal’ provided by taxon-specific stable isotope analysis requires a thorough understanding of the ecology and phenology of the organism groups involved. Growth, metabolism, diet, feeding strategy, migration, taphonomy and several other processes can lead to isotope fractionation or otherwise influence the stable isotope signatures of the remains from aquatic organisms. This paper includes a review of the (modern) calibration, culturing and modelling studies used to quantify the extent to which these factors influence stable isotope values and provides an outlook for future research and methodological developments for the different examined fossil groups. Highlights • Review of stable isotopes in the remains of aquatic organisms in lake sediments. • Stable O and Si isotopes in biogenic silica (diatoms). • Stable C and O isotopes in biogenic carbonates (ostracods, molluscs, charophytes). • Stable H, C, N and O isotopes in aquatic plant, invertebrate, and fish remains. • Outlook on controlled experiments, calibrations, taphonomic studies, and modelling. [ABSTRACT FROM AUTHOR]

This paper presents a detailed description of the lithostratigraphy of mostly contouritic deposits from the Piedra Buena Terrace (PBT), collected at water depth of 2–2.5 km. It is based upon a multi-proxy investigation of five gravity cores, including visual description and scanning, grain size distributions, microfossils and sand fraction study, supported by the analysis of high-resolution sub-bottom profiles. Two older seismic units were identified in addition to those previously described in the area. The defined lithostratigraphic units were correlated to the upper seismic units, while the age of the younger units was confirmed using AMS-14C dating. In terms of the sedimentary facies, the dark quartz-glauconitic sands, which seem to be a fingerprint of the Piedra Buena Terrace, were investigated by applying the X-ray diffraction and performing grain SEM - SE images. The sandy facies correspond to sea-level low-stands during cold glacials (MIS 2 and MIS 4), when glauconite and terrigenous material were transported from the emerged shelf down and along the Patagonian continental slope by vigorous bottom currents. The latter is confirmed by an occurrence of parts of bi-gradational sequences reported from the grain-size distributions in lithostratigraphic units 2 and 4. Units 1 and 3, represented by mostly hemipelagic calcareous ooze, were formed during warm high sea-level stages (MIS 1 and 3). Unlike Unit 1, Unit 3 also demonstrates clear contourite features, similar to Units 2 and 4. They include common bioturbation, occurrence of mottles, lenses, irregular thin layers of sand, erosional boundaries and hiatuses between and within the units, good sorting of fine sands, and microfossil reworking. Together with our previous data from canyons on the Perito Moreno Terrace and the Ameghino segment, supported by available publications from the PBT and Mar del Plata areas, this study demonstrates that the Patagonian Continental Margin could be used as a natural laboratory to investigate and better understand contourite systems. • Massive quartz-glauconite sands discovered on the PBT. • Detailed litho- and chronostratigraphy provided for ∼70 ka. • Contourite sediments identified between ∼70 and ∼14ka. • More developped glauconitization phase during glacials. • New seismic units and unconformities identified in the PBT. [ABSTRACT FROM AUTHOR]

The isolation of α-amino-β-methylaminopropionic acid from seeds of Cycas circinalis (now C. micronesica Hill) resulted from a purposeful attempt to establish the cause of the profound neurological disease, amyotrophic lateral sclerosis/parkinsonism/dementia, that existed in high frequency amongst the inhabitants of the western Pacific island of Guam (Guam ALS/PD). In the 50 years since its discovery the amino acid has been a stimulus, and sometimes a subject of mockery, for generations of scientists in a remarkably diverse range of subject areas. The number of citations of the original paper has risen in the five decades from a few to 120 within the decade 2007–2016 and continues at a high rate into the next decade. The reasons for this remarkable outcome are discussed and examples from the literature are used to illustrate the wide range of scientific interest that the original paper generated. [ABSTRACT FROM AUTHOR]

This paper investigates the 2D dielectrophoretic signature of a unicellular centric green alga, Coscinodiscus wailesii , in non-uniform electric fields. The electrokinetic response was studied as a function of applied signal frequency and voltage. The effective permittivity of the diatoms was studied through mathematical simulation resulting in analyzing the diatoms' frequency response. Three different types of dielectrophoretic responses were measured and analyzed (i) lateral displacement of cells, movement of diatoms in a particular direction based on their dielectric polarizability, (ii) dielectrophoretic force, the translational force experienced by the diatoms as a result of applied non-uniform electric fields and (iii) translational dielectrophoretic velocity, the speed at which the diatoms move either towards or away from strong electric fields. The approaches discussed in this paper will improve the predictability of the dielectric properties of the diatoms using a combination of these parameters. The calibration of the physical diatom model to the experimental data results in the estimation of their dielectrophoretic behavior depending on the geometric structure of the diatom model. This method offers a practical means of label-free manipulation of diatoms and for rapid screening for environmental effects on the dielectric properties of algal cells. [ABSTRACT FROM AUTHOR]

Antarctica is one of the most susceptible regions to climate change on Earth. Rising ocean temperatures, glacier melting, and disruptions of marine ecosystems make this polar region a focus of research on ecosystem transformation associated with ongoing climate change. Within the Antarctic ecosystem, diatoms, a key group of phytoplankton at the base of the marine food web, play a crucial role in maintaining marine ecosystem balance and functioning. Conventionally, fossil diatom assemblages have been investigated in marine sediment records to reconstruct paleoenvironmental conditions and understand climate change patterns of Antarctica. Recently, the application of ancient DNA techniques to ocean sediments (sedimentary ancient DNA, sed aDNA) has provided new insights into diatom community responses to environmental change over geological time scales. One benefit of sed aDNA analysis is that this technique can detect fragile diatom species that do not preserve well and are thus difficult to study via traditional microscopy techniques. In this paper, we review the importance of diatoms as indicators of Antarctic paleoenvironmental change, the novel use of diatom sed aDNA to assist Antarctic paleoenvironmental reconstruction, and the challenges and promises of using the sed aDNA approach. We propose that Fragilariopsis cylindrus , an extant polar diatom species, is an ideal model organism to study adaptation patterns of diatoms to changing climate due to its ecological success through time and the availability of whole-genome information for this species. Novel genetic information obtainable from ancient F. cylindrus, as well as other diatoms, will help us to better predict the evolutionary and adaptive dynamics of this important group of primary producers in the climatically vulnerable Antarctic region. • Climate change in Antarctica and the need to study this polar region. • Diatoms in Antarctic ecosystem and their role as paleoenvironmental indicators. • Using the novel technique of sedimentary ancient DNA (sed aDNA) in Antarctica. • Fragilariopsis cylindrus to study adaptation and evolution of diatoms in Antarctica. [ABSTRACT FROM AUTHOR]

Prostaglandins (Pgs) are eicosanoid lipid mediators detected in all vertebrates, in some marine invertebrates, macroalgae and in diatoms, a class of eukaryotic microalgae composing the phytoplankton. The enzymes involved in the Pgs pathway were found to be differentially expressed in two strains of the diatom Skeletonema marinoi , named FE7 and FE60, already known to produce different levels of oxylipins, a class of secondary metabolites involved in the defence of diatoms against copepod predation, with FE7 being higher producer than FE60. In the present study we investigated the response of genes involved in the production of oxylipins and Pgs, evaluating their expression after the exposure to the copepod Temora stylifera. Our results highlighted a grazer feeding preference for FE60, the strain having low oxylipins content and reduced expression of Pgs enzymes, and an impact on the gene expression of the enzymes involved in oxylipins (i.e. lipoxygenase) and Pgs (i.e. cyclooxygenase) biosynthesis, especially in FE7. A time course evaluation of the gene expression over 24 h showed an upregulation of the essential enzyme in the Pgs pathway, the cyclooxygenase, in FE60 after 6 h of exposure to the grazer, differently from FE7 where no upregulation of gene expression in the presence of copepods was revealed. These results provide preliminary indications regarding the existence of a complex involvement of the Pgs pathway in the prey-predator interaction that requires further investigations. • The copepod grazer T. stylifera shows different ingestion rates on two S. marinoi strains, with a preference for the one with lower oxylipin content. • S. marinoi strains responded differently to the presence of copepods in terms of expression of the oxylipins enzymes. • This paper provides indications regarding the existence of a complex Pgs involvement in the prey-predator interaction. [ABSTRACT FROM AUTHOR]

Lake Baiyangdian, the largest natural freshwater wetland on the North China Plain, has faced multiple stressors from anthropogenic disturbances and climate change, affecting its aquatic ecosystem over the past century. An improved understanding of the relationship between environmental stresses and ecosystem responses and the mechanisms underlying ecological shifts has significant implications for managing the aquatic ecosystem in Lake Baiyangdian. In this paper, we reconstructed the ecological changes in Lake Baiyangdian over the past 70 years based on diatom assemblages in a sediment core and identified ecological shifts by the Sequential t test Analysis of Regime-shifts algorithm (STARS) and a sequential F test. Our results revealed two ecological shifts. The first ecological shift in the diatom community occurred in approximately 1963, which was associated with the rather abrupt changes, i.e., damming in the basin. This hydrological modification prolongs hydraulic residence time and accelerates nutrient retention, consequently leading to an increase in eutrophic species. Subsequently, the second ecological shift occurred in the 1990 s, which was attributed to sustained nutrient loading due to human activity intensification as well as an increase in the regional temperature. Ongoing nutrient loading finally pushed the lake toward a driver threshold, leading to an abrupt shift in the diatom assemblage. Our study details the complex trajectories of aquatic ecosystem shifts driven by hydrological alteration, increasing nutrient loading, and climate change in Lake Baiyangdian and highlights the processes by which ecological shifts occur in response to both abrupt and gradual stressors. [ABSTRACT FROM AUTHOR]

The northwest coast of North America exhibits highly variable patterns of relative sea-level (RSL) change following the Last Glacial Maximum (LGM) that reflect proximity to the Cordilleran glacial ice loading and local rates of deglaciation. In this paper we present postglacial RSL histories for four coastal zones in a transect across northern Vancouver Island, Canada, derived from multiple proxies (isolation basin cores, geological exposures, archaeological sites, GIS-based landform interpretation), and relate these to the timing of glacial retreat after the LGM. Notably, parts of the west coast of northern Vancouver Island were ice-free by ∼18,200 years ago, earlier than much of the rest of Vancouver Island and the broader region. These four RSL reconstructions demonstrate substantial variation across the north end of Vancouver Island, which we attribute to regional differences in glacial isostatic processes. Additionally, some RSL curves reveal the likely effects of global glacial meltwater pulses. Documenting late Pleistocene and early Holocene coastline change in this region of Vancouver Island is significant for understanding the late Quaternary history of western North America more broadly: the RSL histories help delimit potential refugia and postglacial expansion of plants and animals (including humans) as the ice retreated. • We present four new relative sea level curves for Northern Vancouver Island, Canada. • RSL histories vary from east to west, related to glacio-isostatic processes. • Radiocarbon ages constrain timing of glacial retreat, landscape change. • Some parts of northern Vancouver Island have been ice-free for ∼18,200 years. • Past shoreline positions help understand postglacial expansions of plants/animals. [ABSTRACT FROM AUTHOR]

This opinion paper introduces a special series of articles dedicated to freshwater benthic algae and their use in assessment and monitoring. This special series was inspired by talks presented at the 9th International Congress on the Use of Algae for Monitoring Rivers and Comparable Habitats (Trento, Italy, 2015), the latest of a series of meetings started in 1991. In this paper, we will first provide a brief overview of phytobenthos methods in Europe. Then, we will turn towards the ‘dark side’ of phytobenthos and describe four particular problems for phytobenthos assessment in the European Union: (1) over-reliance on a single group of algae (mostly diatoms) to the exclusion of other groups; (2) relatively low adoption of benthic algae for ecological assessments in lakes; (3) absence of measures of phytobenthos abundance; (4) approaches used to define boundaries between ecological classes. Following this, we evaluate the strengths and limitations of current phytobenthos assessment methods against 12 criteria for method evaluation addressing four areas: ecological rationale, performance, feasibility of implementation, and use in communication and management. Using these criteria, we identify and discuss three general challenges for those developing new methods for phytobenthos-based assessment: a weak ecological rationale and insufficient consideration of the role of phytobenthos as a diagnostic tool and for communicating ecosystem health beyond a narrow group of specialists. The papers in the special series allow a comparison with the situation and approaches in the USA, present new methods for the assessment of ecological status and acidification, provide tools for an improved management of headwaters and petrifying springs, discuss the utility of phytobenthos for lake assessments, and test the utility of functional measures (such as biofilm phosphorus uptake capacity, PUC). [ABSTRACT FROM AUTHOR]

The goal of NASA's EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) project is to develop a predictive understanding of the fate of global ocean primary productivity and export of carbon from the surface to the deep ocean. Thorium-234 (234Th, t 1/2 = 24.1 d) was used to measure sinking particle export from an anticyclonic eddy during the EXPORTS North Atlantic cruise (May 2021) at the Porcupine Abyssal Plain. The four-week sampling period was broken into three time periods ("epochs") where 800 234Th seawater samples were collected from over 50 CTD casts with high depth resolution over the upper 500 m. Size-fractioned particulate samples were collected to determine particulate organic carbon (POC) and biogenic silica (bSi) to 234Th ratios using in situ McLane pumps. A 234Th non-steady state model shows an eddy center epoch average progression of increasing 234Th export (∼2800 ± 300 (Epoch 1; standard deviation) to 4500 ± 700 (Epoch 3) dpm m−2 d−1) out of the top 110 m of the water column over the course of the cruise (29 d). This translates into an epoch average progression of ∼11 ± 1 to 14 ± 2 mmol C m−2 d−1 of sinking POC flux, and ∼ 3 ± 1 to 6 ± 1 mmol bSi m−2 d−1 of sinking bSi flux to deeper waters at 110 m. The overall efficiency of the biological carbon pump (amount of net primary production reaching 100 m below the euphotic zone) increases from ∼10% to ∼30% throughout the sampling period. The temporal trends discussed extensively in this paper show that POC and bSi export increase during diatom bloom evolution. • A largescale 234Th non-steady state analysis builds on the use of the 234Th method. • The EXPORTS 2021 N. Atlantic field campaign captured the demise of a diatom bloom. • Increasing carbon flux values co-occurred with increasing deep biogenic silica fluxes. [ABSTRACT FROM AUTHOR]

This paper reports the third in a series of three studies of a unique aquatic phytobial consortium that developed in a polluted ditch situated near an old chromium waste landfill. The ditch is a specific ecological niche having increased loads of several chemical compounds, including extreme hexavalent chromium concentrations up to two thousand times the allowed limit (0.02 mg dm−3 in Poland) in the more polluted section B; the moderate concentrations in section A are twice the limit. We focus on the microscopic algae group of diatoms, one of the most important components of the phytobial consortium, and continue our novel attempt to analyze the bioremediation potential of the entire consortium under those environmental conditions. We used numerical methods to analyze differences in diatom biodiversity between sections A and B, and assessed the relations between diatoms and selected water chemistry properties, including hexavalent chromium, chlorides and sulphates, the latter two known to positively influence the resistance of algae to the impact of hexavalent chromium. We noted 37 diatom taxa in section A of the ditch and 30 in section B. The most frequently observed diatoms were cosmopolitan taxa and/or characteristic taxa of saline waters. Sulphates were the most important factor influencing the diatom composition in the ditch, explaining 52% of the total variability, followed by chlorides (30%) and hexavalent chromium (9%). Gomphonema acuminatum , Melosira varians and Nitzschia frustulum var. f rustulum were found to be most resistant to hexavalent chromium and were selected for further experimental studies on their biotechnological usefulness. [Display omitted] • Diatoms are an important part of algal communities found in chromate wastewater • 44 diatom taxa are recognized there • Biotechnological potential of three most resistant taxa should be analyzed further • These taxa are Gomphonema acuminatum , Melosira varians and Nitzschia frustulum [ABSTRACT FROM AUTHOR]

[Display omitted] • Heterogeneity index(H) is a structural parameter describing the distribution of species associations. • H is proposed to unveil the species turnover in community in this paper. • Eight lakes exhibit a eutrophication trend with different degrees from the 1950s. • H , species richness, evenness and Jaccard index respond differently to eutrophication. • H can serve as a complementary biodiversity metric to quantify functional diversity. Anthropogenic eutrophication in aquatic ecosystems has had significant negative effects on biodiversity and human wellbeing. Improving our understanding of the ways in which biological communities respond to eutrophication underlies biodiversity conservation, and diversity metrics like species richness and evenness are often used to assess environmental impacts on biodiversity. However, such studies mainly consider overall gain and loss, ignoring species replacement in community succession. This paper combines paleolimnology and network science to propose a heterogeneity index (H) to measure community successions by linking long-term changes in community structure with environmental stress. Eight lakes of different types in the middle and lower reaches of the Yangtze River Basin (MLYB) were selected, and we focused on diatom communities to reconstruct their ecological trajectories after significant anthropogenic impact. The combined results suggested that human impacts have caused eutrophication in each lake since the 1950s, but led to different degrees of impact on the diatom communities. In hypereutrophic lakes, diatom assemblages shifted to high-nutrient tolerance and the proportions of epiphytic-benthic species decreased, while in mildly eutrophic lakes, a switch to mild-nutrient tolerant assemblages occurred in planktonic and epiphytic-benthic species with no change in epiphytic-benthic proportions. The H of diatom communities declined in hypereutrophic lakes, but changed little in mildly eutrophic lakes after the 1950s. Meanwhile, no regular changes in diversity indicators such as richness, evenness and the Jaccard-index occurred with lake eutrophication. The ordered species turnover in nutrient-enriched diatom communities may account for the discrepancies in H and the above indices, such as ordered epiphytic-benthic species being replaced by higher nutrient-tolerant and planktonic species with no necessarily attendant reduction in species richness. By quantifying the alteration of species associations without being influenced by species diversity, the H index effectively reveals the succession of diatom communities, and can therefore serve as a complementary indicator of biodiversity. [ABSTRACT FROM AUTHOR]

The paper presents the first set of micropaleontological data from the Buor-Khaya Bay sediments in the southeastern part of the Laptev Sea, obtained from the bottom sediments through permafrost drilling. The study of diatoms and spore-pollen assemblages in Hole 1D-11 and Hole 4D-12, high-resolution seismic profiling, and lithological composition of the sediments have facilitated the identification of two different age strata formed under different conditions and dating to the Late Pleistocene and Holocene. The Pleistocene strata were composed of assorted sands with inclusions of dense dehydrated silt formed under continental conditions. The Holocene strata were composed mostly of clayey silt that had formed under transgressive conditions and significant influence of the Lena River runoff and Arctic tundra vegetation on the coast. [ABSTRACT FROM AUTHOR]

Abstract El Rincón is a highly productive area in the inner-shelf of the Argentine Sea, southern Buenos Aires Province (39°S–62.5°W; 41.5°S–60°W), regarded as the habitat for commercially valuable fish species and important for local artisanal fisheries. The aims of this work were to characterize for the first time the in situ absorption coefficient of phytoplankton (a ph (λ)) in relation to phytoplankton composition and chlorophyll- a (Chl- a) concentration, and to evaluate the satellite retrieval of a ph (443) using two atmospheric correction algorithms and three bio-optical semi-analytical algorithms in order to define which is more suitable for the study area. A total of 28 oceanographic cruises were performed between November 2013 and March 2017 and the sampling included physical variables (temperature, salinity, suspended particulate matter, SPM), Chl- a , phytoplankton absorption and composition. The phytoplankton community was mainly dominated by chain-forming diatoms from the microplankton size class (40–80%), while a single coccolithophore, Gephyrocapsa oceanica (cell diameter <10 µm) was a key component (up to 40%) of the nanoplankon. In situ Chl- a (mean 1.8 mg m−3) and a ph (443) (mean 0.052 m−1) generally covariated with no clear seasonality. Their correlation was rather low (R2 = 0.52) and with high scattering, in agreement with the high interannual variability of phytoplankton composition. Further, the relative low mean specific absorption coefficient of phytoplankton (a ph * (443), 0.032 m2 (mg Chl- a)−1) and (a ph * (676), 0.014 m2 (mg Chl- a)−1) denoted the presence of big cells and pigment packaging effect. Aside from the optical complexity of these waters, reasonable results were found using the Quasi Analytical Algorithm in retrieving a ph coefficient (R2 = 0.55, Bias = 19%) and switching the atmospheric correction algorithm depending on the distance to the coast, the depth and turbidity. The results found in this paper present for the first time the phytoplankton composition and absorption of algal material characteristics and the derived implication on the performance of bio-optical algorithms in the optically complex waters of El Rincon. Highlights • El Rincon waters are turbid and mixed, dominated by chain-forming diatoms. • The light absorption coefficient by phytoplankton coefficient is low for a given chlorophyll- a. • The traditional bio-optical algorithms (GIOP and GSM) overestimate in situ data. • The Quasi Analytical Algorithm estimates are reasonable for the study area. [ABSTRACT FROM AUTHOR]

Abstract Chaetoceros is a dominant genus of marine planktonic diatoms with worldwide distribution. Due to the difficulty of extracting setae from Chaetoceros images, automatic segmentation of Chaetoceros is still a challenging task. In this paper, we address this difficult task by regarding the whole segmentation process as unsupervised pixel-wise classification without human participation. First, we automatically produce positive (object) and negative (background) samples for follow-up training, by combining the advantages of two image processing algorithms: Grayscale Surface Direction Angle Model (GSDAM) for extracting setae information and Canny for detecting cell edges from low-contrast and strong-noisy microscopic images. Second, we develop pixel-wise training by using the produced samples in the training process of Deep Convolutional Neural Network (DCNN). At last, the trained DCNN is used to label other pixels into object and background for final segmentation. We compare our method with eight mainstream segmentation approaches: Otsu's thresholding, Canny, Watershed, Mean Shift, gPb-owt-ucm, Normalized Cut, Efficient Graph-based method and GSDAM. To objectively evaluate segmentation results, we apply six well-known evaluation indexes. Experimental results on a new Chaetoceros image dataset with human labelled ground truth show that our method outperforms the eight mainstream segmentation methods in terms of both quantitative and qualitative evaluation. [ABSTRACT FROM AUTHOR]

Abstract: Diatoms are ideal bio-indicators of water ecosystem health and can be classified into one of the trophic state indexes (TSI) according to the nutrient level. Thus, the diatoms can be used to indicate the relationship between the organisms and the environmental parameters. In order to find the correct diatom- indicator connection, we can use a certain classification algorithm directly from measure data. This process of diatom classification can be significantly improved using information technology, especially data mining tools. In this direction, this paper work present several classification models with the novel method called aggregation trees based on evenly sigmoid shaped membership function (MF). Earlier, numerous statistical approaches have been used for this purpose, which provide very useful data inside information, but they are limited to interpretation. Further improvement is made by using decision trees, which increases interpretability, but remains not resistant to over fitting and robustness on data change. The proposed method in this paper synthesizes these advantages, in terms of interpretability, resistance of over-fitting and high classification accuracy compared with classical classification algorithms. This is confirmed by the experimental evaluation. Based on these evaluation results, one model for each TSI is presented and discussed. From ecological point of view, the described method improves the water quality and sustaining bio diversity understandings of this ecosystem. The method added new ecological knowledge about the ecological indicators for certain diatoms, which have been recently discovered. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present multi-parameter data on phytoplankton community composition, and its response to storm events in the Sargasso Sea in late February and early March of 2 years (2004 and 2005). Observed physical conditions spanned a continuum from pulsed destratification/stratification to continuous mixing, with a corresponding range of phytoplankton growth responses. The pulsed destratification/stratification condition resulted in a rapid (1–2d) doubling of euphotic zone chlorophyll (Chl-a) along with a rapid succession, days timescale, from diatoms to haptophytes and then to cyanobacteria. Deep (>300m) continuous mixing led to a slow (8–9d) doubling of autotrophic biomass with no observed succession in the phytoplankton community. These different temporal responses appear to be due to differences between nutrient-limited and light-limited phytoplankton growth, although differences in grazing rates or selective grazing cannot be ruled out. Unexpectedly, we found that flow cytometrically enumerated picoeukaryotes were not accounted for in HPLC-pigment derived phytoplankton classifications and did not covary with any of the pigments quantified. Yet, the picoeukaryotes were positively related to increases in total Chl-a and increased carbon export, suggesting an important but as yet unknown role in the Sargasso Sea carbon cycle. [Copyright &y& Elsevier]

Abstract: Palaeoenvironmental reconstructions of lake sediment records have been greatly facilitated by statistical comparisons with microfossil assemblages from the surface sediments of modern lakes. These modern sub-fossil assemblages from different lakes, which are often referred to as “training-sets”, attempt to incorporate gradients of environmental parameters, such as e.g., temperature and phosphorus, are of interest for paleoenvironmental reconstruction. One major assumption of quantitative palaeoenvironmental reconstructions requires that the environmental variable to be reconstructed is, or is linearly related to, an ecologically important determinant in the ecological system of interest, and that the joint distribution with other variables in the fossil set is the same as in the training-set. The motivation for this paper is that present-day diatom species abundances in surface-sediment samples are often influenced by several environmental gradients. Partial least squares (PLS) or weighted-averaging partial least squares (WA-PLS) regression methods can be used to adjust species optima, if the additional PLS components, which are orthogonal to previous PLS components, are included. This paper tests a reproducible approach for reducing the influence of background variables within a diatom training-set to produce a “screened” training-set, which focuses on the variable of interest. In our example total phosphorus (TP) is the variable of interest. The initial training-set consists of modern Swiss lakes along an elevation gradient spanning 2005 m (334 to 2339 m a.s.l.), which follows a TP gradient from 522 to 3 μg L−1. However, high-elevation lakes are not distributed equally along the TP gradient. They are meso-oligotrophic because high-elevation eutrophic lakes are rare in Switzerland. This leads to a potential confounding effect between the elevation and the nutrient gradients. These higher elevation lakes were selectively excluded, using Monte Carlo permutation tests, until the conditional effect with respect of covariables of elevation was no longer significantly related to the relative abundance of diatoms. The initial and screened inference models for log TP were applied to fossil assemblages from varved sediments at Greifensee (Switzerland), which cover the past century. The evaluation of the reconstructions with measured TP (1954–1994) demonstrates that the smaller (screened) subset performs better than the larger, more heterogeneous, initial data-set when the same number of components are included. The slope of the relation between measured and inferred log TP changed significantly for the reconstructions using partial least squares, with one and two components, and for reconstruction using weighted averaging partial least squares with two components. According to our interpretation, the accuracy of the reconstructions improved because modern diatom abundances of the smaller subset are controlled mainly by log TP and lakes are more equally distributed along the log TP gradient. This approach of reducing the influence of background variables is applicable to other heterogeneous training-sets, such as merged training-sets, in order to homogenise the background variables and to maintain the gradient of interest. [Copyright &y& Elsevier]

Biological systems are variable and there are fundamental limits on the predictability of, e.g. phytoplankton concentrations in rivers and lakes. How does inherent uncertainties in empirical data constrain our approaches to prediction? This paper addresses this question in discussing one of the most fundamental concepts in predictive ecosystem modelling, the uncertainty in the empirical y-variable used to validate model predictions. So, the focus of this paper is not on concentrations but on coefficients of variation (CV: S.D./MV; S.D.: standard deviation, MV: mean value). The CV-values regulate the theoretically highest predictive power of models and the reliability of data used for model validations. We have collected an extensive data-base from the River Danube (at a site close to Regensburg) as a basis for these analyses. The water samples have been analysed using delayed fluorescence (DF), a technique which makes it possible to obtain compatible data on the five algal variables used in this study, green algae, diatoms, cryptophytes and blue-greens (cyanobacteria) as well as total chlorophyll. We have also compared these results on CVs with results from other river sites and lakes. This study shows that: (1) The monthly variations in CV based on data from several years show similar patterns for the five algal variables, but the CVs are generally somewhat higher for all five variables in September and October and lower in April and May. (2) The monthly CVs do not seem to be significantly related to the mean values or the flow velocity. (3) There are no significant differences in monthly CVs among the five variables, although the blue-greens may have the highest CV and cryptophytes and green algae the lowest. (4) The daily, weekly, monthly (based on individual months, e.g. January a given year), monthly (based on data from several years, e.g. January for several years) and yearly CVs increase from 0.3, 0.35, 0.55, 0.80 to 0.95, respectively, for chlorophyll (and similar values also apply to the four other algal variables). This means that it is unlikely that a model for monthly chlorophyll concentrations in rivers would yield r2-values higher than about 0.6. This information is of great importance in science and water management since it means that we can never expect to derive models that could predict monthly chlorophyll concentrations in rivers well. (5) The mean CV for chlorophyll based on all data from the Regensburg site is 0.96, which is close to the median value from 19 rivers sites in the UK. (6) The correlation between the monthly mean values and the monthly peak values were found to be strong, but this is partly spurious. [Copyright &y& Elsevier]

This paper documents ambient concentrations of nutrients in the Belgian coastal waters of the North Sea during the spring of 1996 and 1997. The paper elaborates the differences of uptake rates of oxidised nitrogen (NO3−) and reduced nitrogen (NH4 and urea) by Phaeocystis and diatoms. The nitrogen concentrations were dominated by NO3− with a maximum concentration of 30 μM (January 1997) and 40 μM (March 1996). In 1996, Phaeocystis dominated the spring biomass with a maximum of 521 μg C l−1, while maximum diatom biomass was 174 μg C l−1. In 1997, the maximum Phaeocystis spring biomass was 1600 μg C l−1 and diatom maximum biomass was below 100 μg C l−1. A maximum bacteria biomass of about 55 μg C l−1 was observed in mid-May 1996. The maximum nitrogen uptake rates were recorded during spring and were dominated by NO3− (0.005 h−1 in 1996 and 0.032 h−1 in 1997). Maximum specific NH4 uptake rates were between 0.005 h−1 in May 1996 and 0.006 h−1 in April 1997. The NO3− uptake rates displayed exponential decrease versus increasing ambient reduced nitrogen concentrations (ammonium and urea), whereas the reduced nitrogen uptake increased but never compensated the decreased nitrate uptake. The NH4 uptake kinetics of diatoms displayed lower vmax compared to Phaeocystis. Consequently, Phaeocystis showed ability to increase their NH4 uptake capacity when more NH4 became available while diatoms failed to do so, after ammonium had exceeded their saturation concentration (>1 μM). Although reduced nitrogen has a negative effect on the uptake of NO3−, Phaeocystis have more advantage than diatoms on the uptake of ammonium. This might be contributing to the biomass domination shown by Phaeocystis over extended periods in spring. [Copyright &y& Elsevier]

High-latitude permafrost peatlands are sensitive to global warming, and understanding their paleohydrological evolution is critical for assessing future hydrological and environmental changes. This paper presents a diatom record from a peat deposit covering the past 3300 years to reconstruct the moisture and acidity conditions in the Tuqiang permafrost peatland in the northern Greater Khingan Mountains of northeast China. Our findings are integrated with previously published records of plant macrofossils, palynology, and geochemistry from the same profile. From 3300 to 2800 cal yr BP, planktonic and benthic diatoms were equally abundant, indicating relatively high moisture conditions, while the low abundance of acidophilous diatoms reflects relatively high pH during this interval. Pollen data show dominance by sedges with input from the surrounding Pinus forest, while LOI data and lithology suggest that the site was a non-peat accumulating wetland. During the period 2800–1100 cal yr BP, the dominance of planktonic diatoms indicates a wetter local environment, concurrent with the dominance of peat-forming sedges (Eriophorum), indicating the development of a peatland. Between 1100 and 500 cal yr BP, a short-lived increase in acidophilous diatoms (Eunotia) marks a decrease in pH. Since 500 cal yr BP, the dominance of benthic diatoms reflects a drier environment, while a vegetation shift from an Eriophorum -dominated rich fen to a Sphagnum- and Ericaceae-dominated poor fen. An increase in Eunotia diatoms prior to the Sphagnum peak may indicate that diatoms are more sensitive to local acidified habitats than moss. Peatland development in the northern Greater Khingan Mountains was likely induced by the onset of a cooler and wetter climate starting at approximately 2800 cal yr BP, a scenario supported by regional paleoclimate records. Since 700 cal yr BP, the peatland has been affected by both anthropogenic activities and climatic changes, as a drying climate and intensified human activities around the study area reduced diatom species diversity and peat accumulation. Under the background of future global warming and enhanced human activities, the decreasing species diversity and carbon accumulation rate of peatlands in high-latitude permafrost regions need more attention. • Diatoms can indicate local moisture and acidity in permafrost peatlands. • Diatoms are likely more sensitive to microhabitats than bryophytes. • TQ peatland formed after 2800 cal yr BP caused by the cooler and wetter climate. • Rich-fen shifted to poor-fen which co-influenced by deforestation and dry climate at LIA. [ABSTRACT FROM AUTHOR]

Geological evidence of megathrust earthquakes along the Mexican Pacific coast relies predominantly on tsunami deposits. Records of coseismic relative sea-level changes are scarce even though such evidence can complement and constrain tsunami records, providing information to reconstruct past earthquake rupture dimensions to improve the earthquake hazard assessment of the region. This paper provides the first diatom-based quantitative reconstruction of coastal subsidence along the Mexican subduction zone through the analysis of coastal wetland sediments. We use the stratigraphic signature of the 1995 Colima-Jalisco earthquake (M w 8.0) as this earthquake is instrumentally well-constrained, allowing us to evaluate our findings and establish approaches to investigate earlier earthquakes. Deposits beneath the wetland Estero Potrero Grande reveal a stratigraphic sequence, < 28 cm beneath the wetland surface, that resembles a signature of rapid submergence. This sequence consists of a horizontal bed of silt with highly humified organic matter abruptly overlain by a horizontal bed of grey silt. The abrupt stratigraphic contact between the two units extends across >1 km of the wetland. Using 14C ages and 137Cs chronohorizons to build an age-depth model, we estimate the age range (1985–2003 CE) and mean age (1995 CE) of this abrupt stratigraphic contact, coincident with the year of the earthquake. Three elemental log-ratios (S/Zn, Br/Zn and Ca/Zn) indicate an abrupt increase of salinity across the stratigraphic contact, which we interpret as marsh submergence recording coseismic coastal subsidence, reflected as relative sea-level rise. Fossil diatom assemblages confirm this trend, and through quantitative approaches we estimate its magnitude (−0.06 ± 0.08 m and − 0.11 ± 0.23 m), which is comparable with coastal subsidence measured by geodetic instruments. Our records reveal a millimetric spike of sand, which we interpret as a signature of the tsunami that accompanied this great earthquake. These findings demonstrate that coastal wetland sediments from the Mexican Pacific coast can record tectonic induced relative sea-level changes. This approach can allow us to better understand the long-term spatial and temporal behavior of this subduction zone. • Deposits beneath the costal wetland Estero Potrero Grande record coastal subsidence produced by the 1995 Colima-Jalisco earthquake (M w 8.0). • The lithological expression of this event, an organic silt- silt couplet, was mapped for over 1 km across the wetland. • Elemental log-ratios and diatom assemblages are the proxies that reveal the abrupt increase of salinity conditions above the stratigraphic contact. • Through a diatom-based quantitative approach we estimate the magnitude of coastal subsidence and relative sea level changes before, during and after this earthquake. • Sediment gran size analyses reveal the occurrence of a high-energy event, interpreted as the signature of the tsunami produced by this earthquake. [ABSTRACT FROM AUTHOR]

Urban streams display consistent ecological symptoms that commonly express degraded biological, physical, and chemical conditions: the urban stream syndrome (USS). Changes linked to the USS result in consistent declines in the abundance and richness of algae, invertebrates, and riparian vegetation. In this paper, we assessed the impacts of extreme ionic pollution from an industrial effluent in an urban stream. We studied the community composition of benthic algae and benthic invertebrates and the indicator traits of riparian vegetation. The dominant pool of benthic algae, benthic invertebrates and riparian species were considered as euryece. However, ionic pollution impacted these three biotic compartments' communities, disrupting these tolerant species assemblages. Indeed, after the effluent, we observed the higher occurrence of conductivity-tolerant benthic taxa, like Nitzschia palea or Potamopyrgus antipodarum and plant species reflecting nitrogen and salt contents in soils. Providing insights into organisms' responses and resistance to heavy ionic pollution, this study sheds light on how industrial environmental perturbations could alter the ecology of freshwater aquatic biodiversity and riparian vegetation. [Display omitted] • Ionic pollution could be one of the main factor of aquatic and terrestrial communities disruption. • Higher occurrence of benthic conductivity-tolerant taxa observed after ionic pollution. • After the effluent, indicator values of plant species reflected soil salinity. • One industrial point-source pollutant may be detrimental to overall ecosystem health. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Margalef's mandala remains a key paradigm to depict phytoplankton growth strategies. • Current mandala use oversimplifies the original with a single diatom growth strategy. • Increasing observational evidence indicates a range of diatom growth strategies. • Diatoms are not limited to turbulent waters and may bloom in the stratified ocean. • Models should adopt diatom niche plasticity to predict change in ocean carbon cycling. Abstract Models used to predict future ocean ecosystem and biogeochemical behaviour depend on simplified ecological frameworks allowing the definition of plankton functional types. Foremost among such frameworks has been the mandala of Margalef. His 1978 paper has been increasingly referred to in the past decade as simplified ecological schemes have been sought to help predict the effect of climate change on phytoplankton. However, the mandala is based on an understanding of the subject that is over 40 years old, when observational studies were largely limited to the coastal ocean and to near surface waters. Furthermore, most recent reproductions of the mandala are significant oversimplifications of Margalef's original. In these simplified mandala-type constructs, diatoms, in particular, have commonly been cast as a single plankton functional type that thrive in turbulent waters and decrease in abundance with increasing stratification. On this basis, it is widely predicted that diatom productivity and hence the effectiveness of the marine biological carbon pump will decrease with climate change that is driving increased stratification of the oceans. But Margalef's original took a more refined approach and depicted diatom genera that were adapted to more stratified conditions such as those characteristic of the subtropical oligotrophic gyres. If we now draw on the vast advances in observational oceanography of recent decades it is evident that diatoms may thrive, bloom and generate significant export even in the most intensely stratified and apparently oligotrophic conditions. Indeed, some diatom species have unique adaptations to such environments. We therefore suggest that it is time to abandon oversimplified schemes and recognize the diverse ecology of diatoms. [ABSTRACT FROM AUTHOR]

This paper introduces the concept of ‘Precision Mining’ of metals which can be defined as a process for the selective in situ uptake of a metal from a material or media, with subsequent retrieval and recovery of the target metal. In order to demonstrate this concept nanoscale zerovalent iron (nZVI) was loaded onto diatomaceous earth (DE) and tested for the selective uptake of Cu from acid mine drainage (AMD) and subsequent release. Batch experiments were conducted using the AMD and nZVI-DE at 4.0–16.0 g/L. Results demonstrate nZVI-DE as highly selective for Cu removal with >99% uptake recorded after 0.25 h when using nZVI-DE concentrations ≥12.0 g/L, despite appreciable concentrations of numerous other metals in the AMD, namely: Co, Ni, Mn and Zn. Cu uptake was maintained in excess of 4 and 24 h when using nZVI-DE concentrations of 12.0 and 16.0 g/L respectively. Near-total Cu release from the nZVI-DE was then recorded and attributed to the depletion of the nZVI component and the subsequent Eh, DO and pH recovery. This novel Cu uptake and release mechanism, once appropriately engineered, holds great promise as a novel ‘Precision Mining’ process for the rapid and selective Cu recovery from acidic wastewater, process effluents and leach liquors. [ABSTRACT FROM AUTHOR]

Sediment cores obtained from two deep (>15 m) glacial lakes were analyzed in context of terrestrial vegetation development and in-lake processes from the Retezat Mountains (Southern Carpathians, Romania). Only the Holocene parts were chosen for study for testing what is the connection between geochemical changes and biotas around and in the lakes. The lakes are situated at slightly different altitudes on the northern (Lake Gales, 1990 m a.s.l.) and southern slope (Lake Bucura, 2040 m a.s.l.), respectively. Changes in geochemical composition were relatively low amplitude during the studied period (10,300–1790 and 10,300–695 cal yr BP) in both lakes, but the applicability of enrichment factor (EF) for geochemical elements and diatom ecological traits (guilds) in paleoecological reconstruction were demonstrated in this paper. The main changes have been observed at ca. 10,670–9000, 6500 and 3100 cal yr BP in geochemistry, vegetation and siliceous algal assemblages. Catchment soil stabilization was apparent from ∼9000 cal yr BP onwards, in-lake and terrestrial productivity was the highest between 9000 and 6500 cal yr BP and human impact became the dominant driver in both terrestrial vegetation and sediment geochemical changes and in-lake processes over the last ∼3400 years in both lakes. The geochemical record displayed frequent erosional events within the Holocene. The strongest soil erosions clustered around 6500–7400 and 3200-900 cal yr BP. [ABSTRACT FROM AUTHOR]

With increasing restrictions of environmental regulations and safety concerns on the traditional poisonous coatings, it is highly desirable to develop a new green anti-biofouling method in marine environment. In this paper, graphene composite coating and carbon fiber (CF) composite coating connected with high voltage pulse electric field (HPEF) were developed to inhibit the attachment of diatoms. The polarizing microscopy showed that the attachment rates of Thalassiosira and Navicula reached the lowest levels which were 0.23 cells mm −2 and 6.06 cells mm −2 on the graphene composite coating, 0.38 cells mm −2 and 4.17 cells mm −2 on the CF composite coating, under the HPEF with 1 h duration, 23.15 kHz frequency, 0.5 duty cycle and 19 kV pulse amplitude. While the attachment rates of Thalassiosira and Navicula were 21.21 cells mm −2 and 61.89 cells mm −2 on the graphene composite coating, 22.75 cells mm −2 and 62 cells mm −2 on the CF composite coating, without HPEF. Scanning electron microscopy (SEM) revealed that HPEF disintegrated the diatom cells, which could underlie the considerable inhibition of the diatom attachment by the HPEF. Additionally, the hardness, flexibility and shock resistance tests indicated that graphene and CF could considerably increase the mechanical properties of epoxy resin coating. HPEF stimulation had no obvious effect on the mechanical properties of the composite coatings. [ABSTRACT FROM AUTHOR]

Contaminant-related stress on aquatic biota is difficult to assess when lethal impacts are not observed. Diatoms, by displaying deformities (teratologies) in their valves, have the potential to reflect sub-lethal responses to environmental stressors such as metals and organic compounds. For this reason, there is great interest in using diatom morphological aberrations in biomonitoring. However, the detection and mostly the quantification of teratologies is still a challenge; not all studies have succeeded in showing a relationship between the proportion of abnormal valves and contamination level along a gradient of exposure. This limitation in part reflects the loss of ecological information from diatom teratologies during analyses when all deformities are considered. The type of deformity, the severity of aberration, species proneness to deformity formation, and propagation of deformities throughout the population are key components and constraints in quantifying teratologies. Before a metric based on diatom deformities can be used as an indicator of contamination, it is important to better understand the “ecological signal” provided by this biomarker. Using the overall abundance of teratologies has proved to be an excellent tool for identifying contaminated and non-contaminated environments (presence/absence), but refining this biomonitoring approach may bring additional insights allowing for a better assessment of contamination level along a gradient. The dilemma: are all teratologies significant, equal and/or meaningful in assessing changing levels of contamination? This viewpoint article examines numerous interrogatives relative to the use of diatom teratologies in water quality monitoring, provides selected examples of differential responses to contamination, and proposes solutions that may refine our understanding and quantification of the stress. This paper highlights the logistical problems associated with accurately evaluating and interpreting teratologies and stimulates more discussion and research on the subject to enhance the sensitivity of this metric in bioassessments. [ABSTRACT FROM AUTHOR]

Diatoms are ideal aquaculture baits because they are not only rich in products with added value, such as eicosapentaenoic acid (EPA), docosahexaenoic acid, chrysolaminarin, and fucoxanthin (Fx) but also substantial primary producers in aquaculture. It is difficult to cultivate diatoms at a high density using traditional photoautotrophy. For improving diatom growth rate, biomass, and metabolites, mixotrophy and heterotrophy employing organic carbon sources are promising. However, preparing a conventional single organic carbon source is complicated and costly. This paper reviews the diatom species that can utilize organic carbon, the types of organic carbon used by diatoms (saccharides, alcohols, carboxylic acids, nitrogenous organic carbon, phenols), and the main bottlenecks and technical means of diatom heterotrophy and mixotrophy from an aquaculture perspective. For the first time, the impact of fermented feed on diatom culture was discussed to guide the development of a more efficient and practical nutrient supplement to promote. • The fermentation feed was first used in the culture of diatoms. • The types of organic carbon sources used by diatoms are discussed comprehensively. • The effect of organic carbon on aquaculture including diatom was discussed. [ABSTRACT FROM AUTHOR]

Algal pollution in water sources has posed a serious problem. Estimating algal concentration in advance saves time for drinking water plants to take measures and helps us to understand causal chains of algal dynamics. This paper explores the possibility of building a short-term algal early warning model with online monitoring systems. In this study, we collected high-frequency data for water quality and weather conditions in shallow and eutrophic Lake Taihu by an in situ multi-sensor system (BIOLIFT) combined with a weather station. Extracted chlorophyll- a from water samples and chlorophyll- a fluorescence differentiated according to different algal classeses verified that chlorophyll- a fluorescence continuously measured by BIOLIFT only represent chlorophyll- a of green algae and diatoms. Stepwise linear regression was used to simulate the chlorophyll- a fluorescence changing rate of green algae and diatoms together (ΔChl a-f %) and phycocyanin fluorescence concentration (blue-green algae) on the water surface layer (CyanoS). The results show that nutrients (total N, NO 3 –N, NH 4 –N, total P) were not necessary parameters for short-term algal models. ΔChl a-f % is greatly influenced by the seasons, so seasonal partition of data before modeling is highly recommended. CyanoS max and ΔChl a-f % were simulated by only using multi-sensor and meteorological data (R 2 = 0.73; 0.75). All the independent variables (wave, water temperature, relative humidity, depth, cloud cover) used in the model were measured online and predictable. Wave height is the most important independent variable in the shallow lake. This paper offers a new approach to simulate and predict the algal dynamics, which also can be applied in other surface water. Image 1 • Chlorophyll-a and phycocyanin fluorescence can be predicted using online sensor data. • Wave is the leading factor for the short-term changes of algae in shallow lakes. • Nutrients are not important factors in short-term algal simulation in eutrophic lakes. [ABSTRACT FROM AUTHOR]

The growing evidence supporting a link between exposure to the naturally occurring toxin β- N -methylamino- l -alanine (BMAA) and progressive neurodegenerative diseases, has recently arisen the interest of the scientific community. Latest investigations suggest that dietary exposure to this algal toxin may have been largely underestimated. This paper reviews the state of the art regarding BMAA, with special attention paid to its neurotoxicity, its concentration levels in food, and human exposure. As for other environmental toxins, dietary intake is most likely the main route of exposure to BMAA for the general population. However, data concerning BMAA levels in foodstuffs are still scarce. It is concluded that further investigations on dietary intake and potential human health effects are clearly necessary to assess the risks to public health associated with BMAA exposure. Some critical remarks and recommendations on future research in this area are provided, which may help to identify approaches to reduce dietary BMAA exposure. [ABSTRACT FROM AUTHOR]

Sea ice is an important vehicle for sediment transport in the Arctic Ocean. On the Laptev Sea shelf (Siberian Arctic) large volumes of sediment-laden sea ice are formed during freeze-up in autumn, then exported and transported across the Arctic Ocean into Fram Strait where it partly melts. The incorporated sediments are released, settle on the sea floor, and serve as a proxy for ice-transport in the Arctic Ocean on geological time scales. However, the formation process of sediment-laden ice in the source area has been scarcely observed. Sediment-laden ice was sampled during a helicopter-based expedition to the Laptev Sea in March/April 2012. Sedimentological, biogeochemical and biological studies on the ice core as well as in the water column give insights into the formation process and, in combination with oceanographic process studies, on matter fluxes beneath the sea ice. Based on satellite images and ice drift back-trajectories the sediments were likely incorporated into the sea ice during a mid-winter coastal polynya near one of the main outlets of the Lena River, which is supported by the presence of abundant freshwater diatoms typical for the Lena River phytoplankton, and subsequently transported about 80 km northwards onto the shelf. Assuming ice growth of 12–19 cm during this period and mean suspended matter content in the newly formed ice of 91.9 mg l −1 suggests that a minimum sediment load of 8.4×10 4 t might have been incorporated into sea ice. Extrapolating these sediment loads for the entire Lena Delta region suggests that at least 65% of the estimated sediment loads which are incorporated during freeze-up, and up to 10% of the annually exported sediment load may be incorporated during an event such as described in this paper. [ABSTRACT FROM AUTHOR]

Diatom frustules are abundantly available, environmentally non-toxic natural structures that can enhance photocatalytic activity when templated with titania nanostructures. Dye molecules such as of Azo dye, when allowed to occupy spaces available within a porous diatom frustule templated titania nanostructure, get greater exposure to light photons because diatom frustules not only can collect and transmit light very efficiently through their structure but also naturally arranges the dye molecules within the structure in such a way that there is a lot of optical paths for the light photons to move within the structure and thereby exposing more dye molecules to the light. Moreover, these structures also transmit UV light, unlike ordinary glass structures and hence, enrich the degradation of the dye molecules. This paper reports the observation of breaking of Ti O anatase bonds at 800 °C to a considerable extent and consequent formation of new Ti O rutile bonds at that temperature, generating oxygen vacancies and defect states which results in lowering the band gap of diatom templated titania nanostructures. As such, diatom calcined at 800 °C with titania (DT800), containing both anatase and rutile phase (mixed phase) of nano-sized titania, showed advantageous visible light range photocatalytic activity and enhanced separation efficiency of the photo generated electron-hole pairs compared to diatom calcined at 500 °C with titania (DT500), which contain only anatase phase of nano-sized titania. [ABSTRACT FROM AUTHOR]

This paper presents a history of relative sea level (RSL) change for the last 15,000 years in the Prince Rupert region on the northern coast of British Columbia, Canada. One hundred twenty-three radiocarbon ages of organic material from isolation basin cores, sediment sequence exposures, and archaeological sites having a recognized relation to past sea levels constrain postglacial RSL. The large number of new measurements relating to past sea-level provides a well constrained RSL curve that differs in significant ways from previously published results. After deglaciation following the Last Glacial Maximum, the region experienced an isostatically-induced rapid RSL drop from as much 50 m asl to as low as −6.3 m asl in as little as a few centuries between 14,500 BP and 13,500 BP. After a lowstand below current sea level for about 2000 years during the terminal Pleistocene, RSL rose again to a highstand at least 6 m asl after the end of the Younger Dryas. RSL slowly dropped through the Holocene to close to its current position by 2000-1500 BP, with some potential fluctuations between 3500 and 1500 BP. This study highlights variation in RSL histories across relatively short distances, which must be accounted for by local RSL reconstructions such as this one. This RSL curve aided in the identification of an 8000–9000 year old archaeological site on a 10–12 m asl terrace, which is currently the earliest dated archaeological site in the area, and it provides guidance for searching for even older archaeological remains. We highlight the utility and potential of this refined RSL history for developing surveys for other archaeological sites associated with paleoshorelines. [ABSTRACT FROM AUTHOR]

Microalgae, composed of phytoplankton and benthic microalgae, are used in estuary freshwater requirement studies as they respond quickly to changes in water quality and river flow. The aim of this paper is to show how microalgae are used to determine the present ecological status of river-dominated estuaries by determining the changes in biomass and community composition from the reference state, using the ecological water requirements studies of the uMzimvubu and Orange estuaries as case studies. Microalgal chlorophyll a was used as an index of biomass, phytoplankton counts were classified into functional groups and benthic diatoms were analysed using the software OMNIDIA to determine estuarine health. The slight decrease in river flow (4%) and substantial increase in nutrients from the reference state have resulted in an estimated 28% increase in phytoplankton biomass in the uMzimvubu Estuary from reference. Frequent flooding and high average river flow limit benthic microalgal growth, and changes to species richness, abundance and community composition have been estimated to be 15%, 17% and 15%, respectively. The estuary had high benthic diatom species richness with 228 identified taxa and challenges related to the use of diatom indices are discussed. Phytoplankton abundance has increased by an estimated 28% and community composition has shifted away, ~ 35% change, from being diatom-dominated to one with more chlorophytes and dinoflagellates. The present ecological status was estimated to be 65 (C); moderately modified. Damming and abstraction of river water in the Orange River catchment has resulted in a 60% reduction in flow into the estuary. During the reference state, the river flow exceeded 50 m 3 s − 1 an estimated 73% of the time; freshwater dominated. Presently, river flow is between 5 and 20 m 3 s − 1 for 52% of the time; marine dominated. In addition, agricultural practises in the river catchment and the increased intrusion of upwelled marine water have increased the concentration of nutrients in the estuary. These conditions support the development of a productive river–estuary interface zone in the middle reaches of the estuary where phytoplankton chlorophyll a exceeds 20 μg L − 1 and is dominated by flagellates and dinoflagellates; the diatom to flagellate ratio has decreased. As anoxic events are more likely to occur with a further reduction in river flow, an increase in the proportion of cyanobacteria is likely to occur. Fewer benthic diatom taxa (68), dominated by two species, resulted in a low species richness score. Of the variables considered, a 60% increase in phytoplankton biomass was the largest; giving a present ecological status based on microalgae a score of 40 (E); highly degraded. The use of benthic diatom indices, using the programme OMNIDIA, did not provide reliable results that could be used to determine estuarine health. The South African Diatom Index and Trophic Diatom Index gave mixed results that did not correlate well with the other more established methods, contrasting with phytoplankton abundance and community structure and water quality results. However, benthic diatom species diversity results were well aligned with these parameters and will continue to be a useful tool in freshwater requirement studies. [ABSTRACT FROM AUTHOR]

Lower Jurassic grey/black horizons composed of mudstones and claystones can be found in the Polish Basin area. These horizons are interbedded in thick sandstone packets, which to date have been mostly recognised as good geothermal reservoirs. In this paper, we examined the hydrocarbon potential of the Lower Jurassic claystones and mudstones from the central part of the Polish Basin. To properly evaluate these, we described in detail the organic matter's origin and maturity, as well as the palaeoenvironmental conditions. The collected core samples were examined by geochemical (Rock-Eval pyrolysis and GC-MS) and petrological (macerals content, vitrinite, and fusinite reflectance values) analyses. The obtained results revealed that the Lower Jurassic strata have poor hydrocarbon potential and contain mostly early-mature, terrigenous organic matter. Deposition took place under dysoxic conditions of the epicontinental sea, with the serious influence of deltaic/estuarine systems. Some samples contained mature, marine organic matter dominated mostly by bacterial input. One Sinemurian/Hettangian sample contained a high contribution of algal organic matter, which can be linked with the diatoms or diatom-related organisms as C 25 HBI, 24-norcholestane and 4-desmethyl-23,24-dimethyl steranes were detected. This might represent some of the oldest geochemical evidence of diatoms or diatom-related organisms. A wide spectrum of plant-derived biomarkers was marked in most of the samples, which allowed us to find traces of conifers, bryophytes, and fungi. Evidence of palaeo-wildfires was also noted. Newly introduced Pyrolytic Input Ratio (PIR) and Fire Maceral Index (FMI) were also examined. The use of PIR in samples with higher marine organic matter input indicated that PIR is not suitable for these samples, as the obtained results were overestimated. The PIR and FMI results obtained from the Lower Jurassic samples dominated by terrigenous organic matter suggested that both indicators gave proper results, as well as those samples with lesser paleo-wildfire product input. • Lower Jurassic (J 1) strata from Polish Basin has poor hydrocarbon (HC) potential. • J 1 organic matter contains mixed type III/IV kerogen with a minor admixture of type II. • Differences in conifer distribution were noted across Lower Jurassic strata. • Algal presence was recorded at the turn of the Hettangian/Sinemurian time. • Geochemical evidence of diatom or diatom-related organism was found. [ABSTRACT FROM AUTHOR]

Worldwide the use of pesticides has increased, especially in the industry and agriculture sector even though they contain highly toxic substances. The use of pesticides has various negative effects on the aquatic ecosystem and organisms within these ecosystems. The paper aimed to assess the effects of increased concentrations of malaria vector control insecticides (Dichlorodiphenyltrichloroethane (DDT) and Deltamethrin (DTM)) on the freshwater diatom community structure using a microcosm approach as well as determine whether a mixture (DDT 1:1 Deltamethrin) exposure will have a greater influence on the diatom community when compared to single exposures of these insecticides. Diatoms were exposed to a high and low concentration (based on LC50 data for freshwater Xenopus laevis from the USEPA Ecotox database) of DDT, DTM and a mixture in lentic microcosms over a total period of 28 days. Results indicated that irrespective of exposure concentrations, DDT, DTM and a mixture had negative effects on the diatom community including functionality and vitality as these insecticides induced changes to their chloroplasts. There was an increased percentage dead cells for all exposures compared to the control, with the insecticides having a phototoxic effect on the diatom community. Exposure to the selected insecticides caused a significant decrease in some diatom metrics indicating the negative effects these insecticides have on the diatom metrics. Therefore, diatoms may prove to be useful as bio-indicators in ecotoxicology studies when assessing the effects of any insecticide exposures. [Display omitted] • First study since 1972 to asses effects of DDT on non-target diatom communities. • First study to asses effects of deltamethrin on non-target diatom communities. • Lentic microcosm exposure of a high, low and mix concentration on diatoms. • Both concentration application influenced the vitality of the diatom community. • Diatom vitality were affected by acute and chronic exposure to both pesticides. [ABSTRACT FROM AUTHOR]

Anticyclonic mesoscale eddies (ACME) have been proposed as a mechanism by which new nutrients are episodically delivered into the euphotic zone, thereby enhancing new production as well as shifting phytoplankton community structure. In this paper, we report on a 34-month sediment trap experiment at the Cape Verde Ocean Observatory (CVOO; ca. 18°N, 24°E; December 2009–October 2012), occasionally influenced by ACME passages. The typically oligotrophic, weakly seasonal particle flux pattern at the CVOO is strongly modified by the appearance of a highly productive and low oxygen ACME. Out of four recorded diatom flux maxima at CVOO, three were associated with the passage of ACMEs. The recorded diatom maxima events support the view that local ACME dynamics promotes upward nutrient supply into the euphotic zone leading to a rapid response of diatoms. This response is clearly reflected by the flux seasonality: between 40% and 60% of the total annual diatom flux at the CVOO site was intercepted in a relatively short time interval (<60 days). A highly diverse diatom community characterized the diatom fluxes throughout. Along with the ACME passages, small species of the genus Nitzschia , and Thalassionema nitzschioides var. parva dominated and delivered a major portion of the opal and organic carbon into deeper waters at site CVOO. Several pelagic, warm-water background species became dominant during intervals with low nutrient availability in the euphotic zone. Results of our interannual time-series suggest that ACMEs impact on total diatom production and the species-specific composition of the assemblage north of the Cave Verde Islands, and can strengthen the biological pump in open-ocean, oligotrophic subtropical regions of the world ocean. Our observations are useful for testing biogeochemical ocean models and will also help in improving the knowledge of processes and mechanisms behind interannual time-series of bulk components and microorganisms in pelagic and hemipelagic ocean areas. [ABSTRACT FROM AUTHOR]

Nettilling Lake (Baffin Island, Nunavut) is currently the largest lake in the Canadian Arctic Archipelago. Despite its enormous size, this freshwater system remains little studied until the present-day. Existing records from southern Baffin Island indicate that in the early postglacial period, the region was submerged by the postglacial Tyrell Sea due to isostatic depression previously exerted by the Laurentide Ice Sheet. However, these records are temporally and spatially discontinuous, relying on qualitative extrapolation. This paper presents the first quantitative reconstruction of the postglacial environmental succession of the Nettilling Lake basin based on a 8300 yr-long high resolution sedimentary record. Our multi-proxy investigation of the glacio-isostatic uplift and subsequent changes in paleosalinity and sediment sources is based on analyses of sediment fabric, elemental geochemistry (μ-XRF), diatom assemblage composition, as well as on the first diatom-based oxygen isotope record from the eastern Canadian Arctic. Results indicate that the Nettilling Lake basin experienced a relatively rapid and uniform marine invasion in the early Holocene, followed by progressive freshening until about 6000 yr BP when limnological conditions similar to those of today were established. Our findings present evidence for deglacial processes in the Foxe Basin that were initiated at least 400yrs earlier than previously thought. [ABSTRACT FROM AUTHOR]

Microalgal quantity and quality are major factors affecting bivalve larval growth. Effects of ration using bi-specific diet assemblages with varying proportions of the flagellate Isochrysis galbana and the diatom Chaetoceros neogracile were evaluated on Venerupis corrugata larval development. Response surface methodology was used to determine the optimal ration and better proportions of flagellate and diatom in the microalgal diet at different phases of larval development (early larva (< 190 μm, 10 days), 12 days, early pediveliger (15 days) and young postlarvae (26 days)). Maximum growth was obtained on day 10 for a diet of 22.5 cells μL − 1 of I. galbana , which suggests that C. neogracile was not ingested or digested by early larvae. On day 12 a maximum in the experimental domain was predicted for a diet of 22.5 cells μL − 1 of I. galbana and the lowest concentration of C. neogracile tested (30 cells μL − 1 ), as C. neogracile reduced growth of the larvae at higher concentrations. On day 15, maximum growth was found at 42.6 cells μL − 1 of C. neogracile and 27.9 cells μL − 1 of I. galbana . During metamorphosis and early postlarval growth optimal ration was 70 cells μL − 1 of a bi-specific diet in similar proportions to that previous stage of development. This novel approach to study bivalve larval nutrition allows the quality and quantity of the optimal diet to be determined. Statement of relevance This study is really relevant to the field of bivalve larval production because it defines the quality and quantity of the optimal diet for larvae of the clam Venerupis corrugata . The information provided in this paper has great applicability for clam larval production in commercial hatcheries. [ABSTRACT FROM AUTHOR]

In this paper we determine whether a realistic mixture of hydrophobic chemicals affects the growth dynamics of a marine diatom and how this effect compares to the effect of temperature, light regime and nutrient conditions. To do so, we examine the specific growth rate of Phaeodactylum tricornutum in a 72 h algal growth inhibition test using a full factorial design with three nutrient regimes, two test temperatures, three light intensities and three chemical exposures. Passive samplers were used to achieve exposure to realistic mixtures of organic chemicals close to ambient concentrations. Nutrient regime, temperature and time interval (24, 48 and 72 h) explained 85% of the observed variability in the experimental data. The variability explained by chemical exposure was about 1%. Overall, ambient concentrations of hydrophobic compounds present in Belgian coastal waters, and for which the passive samplers have affinity, are too low to affect the intrinsic growth rate of P. tricornutum. [ABSTRACT FROM AUTHOR]

The coupling of lake dynamics with catchment biogeochemistry is considered the key element controlling primary production in mountain lakes at time scales of a few decades to millennia, yet little is known on the impacts of the morphometry of lakes throughout their ontogeny. As Lake Chungará (Central Andean Altiplano, northern Chile) experienced long-term lake-level fluctuations that strongly modified its area:volume ratio, it is an ideal system for exploring the relative roles that long-term climatic shifts and lake morphometry play on biosiliceous lacustrine productivity. In this paper, we review previous data on the percent contents of total organic carbon, total inorganic carbon, total nitrogen, total biogenic silica, isotopic composition of organic matter, carbonates, and diatom frustules, as well as data on the abundance of the chlorophycean Botryococcus braunii in this lake for the period 12,400–1300 cal yr BP. We also include new data on organic carbon and biogenic silica mass accumulation rates and the diatom assemblage composition of an offshore core dated using 14 C and U/Th. Biosiliceous productivity in Lake Chungará was influenced by shifts in allochthonous nutrient inputs related to variability in precipitation. Humid phases dated at approx. 12,400 to 10,000 and 9600 to 7400 cal yr BP coincide with periods of elevated productivity, whereas decreases in productivity were recorded during arid phases dated at approx. 10,000 to 9600 and 7400 to 3550 cal yr BP (Andean mid-Holocene Aridity Period). However, morphometry-related in–lake controls led to a lack of a linear response of productivity to precipitation variability. During the late Glacial to early Holocene, lowstands facilitated complete water column mixing, prompting episodic massive blooms of a large centric diatom, Cyclostephanos cf. andinus . Thus, moderate productivity could be maintained, regardless of aridity, by this phenomenon of morphometric eutrophy during the early history of the lake. The subsequent net increase in lake level introduced modifications in the area of the epilimnion sediments versus the total volume of the epilimnion, preventing complete overturn. Surpassing a certain depth threshold at approx. 8300 cal yr BP caused cessation of the morphometric eutrophy conditions associated with Cyclostephanos cf. andinus superblooms. After 7300 cal yr BP, the lake experienced a decrease in biosiliceous productivity and a change of state that involved a stronger dependence on precipitation variability, with a lesser contribution of diatoms to the total primary productivity. Our results show that the interpretation of lacustrine paleoproductivity records as paleoclimatic archives needs to take into account the effects of changes in the epilimnion sediment area to epilimnion volume ratio in association with lake ontogeny. [ABSTRACT FROM AUTHOR]

Especially in combination with other proxies, the oxygen isotope composition of diatom silica (δ 18 O diatom ) from lake sediments is useful for interpreting past climate conditions. This paper presents the first oxygen isotope data of fossil diatoms from Kamchatka, Russia, derived from sediment cores from Two-Yurts Lake (TYL). For reconstructing Late Holocene climate change, palaeolimnological investigations also included diatom, pollen and chironomid analysis. The most recent diatom sample (δ 18 O diatom = + 23.3‰) corresponds well with the present day isotopic composition of the TYL water (mean δ 18 O = − 14.8‰) displaying a reasonable isotope fractionation in the system silica-water. Nonetheless, the TYL δ 18 O diatom record is mainly controlled by changes in the isotopic composition of the lake water. TYL is considered as a dynamic system triggered by differential environmental changes closely linked with lake-internal hydrological factors. The diatom silica isotope record displays large variations in δ 18 O diatom from + 27.3‰ to + 23.3‰ from about ~ 4.5 kyr BP until today. A continuous depletion in δ 18 O diatom of 4.0‰ is observed in the past 4.5 kyr, which is in good accordance with other hemispheric environmental changes (i.e. a summer insolation-driven Mid- to Late Holocene cooling). The overall cooling trend is superimposed by regional hydrological and atmospheric–oceanic changes. These are related to the interplay between Siberian High and Aleutian Low as well as to the ice dynamics in the Sea of Okhotsk. Additionally, combined δ 18 O diatom and chironomid interpretations provide new information on changes related to meltwater input to lakes. Hence, this diatom isotope study provides further insight into hydrology and climate dynamics of this remote, rarely investigated area. [ABSTRACT FROM AUTHOR]