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The study of sedimentary organic matter (SOM) is essential for understanding paleoenvironmental conditions and depositional settings of geological formations. This paper explores the Devonian strata of the Paraná Basin, utilizing SOM analysis to reconstruct paleoenvironments and identify global events. The Devonian period is notable for significant geological and biological changes, including mass extinctions and extensive organic-rich sediment deposition. By examining the composition, distribution, and diagenesis of SOM in this region, we aim to elucidate the paleoenvironmental dynamics and depositional history. The Devonian outcrops in the state of Mato Grosso do Sul, Brazil rocks reveal distinct depositional characteristics, when compared to those found on the eastern border of the basin. The palynofacies analysis was conducted on 59 samples from four outcrops (MS-26, MS-29, MS-30 and MS-70), which age spans from Pragian to Givetian. The main groups and subgroups of the SOM were identified: amorphous organic matter (AOM) ("amorphous organic matter" and pseudoamorphous), phytoclasts (opaques, non-opaque-non biostructured, cuticles, membranes and Spongiophyton) and palynomorphs (spores, freshwater algae, scolecodonts, chitinozoan and acritarchs). The SOM was grouped into three palynofacies associations: opaques, land-derived and marine+AOM. In the Pragian—Emsian interval (MS-26, MS-29 and MS-30), a prevalent occurrence of phytoclasts and marine microphytoplankton is noted, with their distribution exhibiting distinct alternations in each section suggesting a deposition in the marine environment ranging from onshore to offshore. In the Givetian (MS-70 outcrop), we detected a progressive increase and diversification of marine elements (e.g., acritarchs), indicating a transgressive phase probably related with the Kačák event. • Comprehension of the Devonian period within the Paraná Basin, situated in the southwestern part of Gondwana. • Paleoenvironmental reconstruction from Pragian to Givetian in SW Gondwana • Palynofacies [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]

[Display omitted] • H. rivularis spread very widely in Europe during recent decades. • H. rivularis is no longer a simple indicator for oligotrophic ecosystems. • H. rivularis occurs mainly in habitats with eu- and hypertrophic waters. • H. rivularis is a poor indicator of the good ecological status of waters. • Classification of H. rivularis as an endangered species in Poland is unfounded. Our knowledge about the size of benthic red alga populations inhabiting European freshwater ecosystems is still insufficient. For many years, in Europe, Hildenbrandia rivularis (Rhodophyta, Hildenbrandiaceae) was believed to be a very rare species of crustaceous red algae, valuable for oligotrophic system biomonitoring. In this paper, we challenge this assumption and show the phenomenon of H. rivularis expansion (i.e., from mountains and highlands to lowlands) in Europe based on detailed data from Poland. We collected over 311 records of H. rivularis occurring in rivers, streams and lakes (not typical habitats for this alga) across the country, including historical data. Here, we show the detailed distribution of this endangered species in Poland, one of the largest European countries. To examine the mechanism of H. rivularis population expansion, physicochemical data from 122 aquatic ecosystems were investigated. A comparison between three subperiods (1860–1944, 1945–1999, and 2000–2019) revealed an increase in the average abundance of the H. rivularis population in the lowlands area. However, the studied species seems to be disappearing in mountain and upland ecosystems. We found altitude and water flow and quality (i.e., alkalinity, oxygenation and biogens) to be the main determinants of H. rivularis occurrence within the study area. The results indicate that this red alga can be described as an expansive species, and its occurrence does not always indicate good water quality and fast water flow. Surprisingly, in contrast to observations from the last century, the population of H. rivularis in Poland currently occurs mainly in habitats with eu- and hypertrophic waters. We point out here that in the zone with temperate climate influence, H. rivularis is no longer an obvious indicator for oligotrophic ecosystems. We suggest that climate warming and eutrophication–reoligotrophication may have contributed to the increased spread of H. rivularis in Europe over recent decades. In addition, we see no reason to classify H. rivularis as an endangered species in Poland. This species most often inhabits anthropogenic water systems and occurs at high abundance in waters with high concentrations of biogens. For these reasons, H. rivularis is more ubiquitous than a cosmopolitan species (i.e., with a wide range of occurrence but associated with only a specific type of habitat and specific environmental parameters). Thus, the value of H. rivularis as a bioindicator for oligotrophic water ecosystems is very low. [ABSTRACT FROM AUTHOR]

For the first time polysaccharidic ulvans have been isolated from freshwater green macroalgae Ulva flexuosa and Cladophora glomerata . One of the main components of ulvan is 3-sulfated rhamnoglucuronan showing a wide range of interesting properties and being a source of rare sugars. The production of mono- and oligo-saccharides from this polysaccharide can potentially be applied in cosmetic, pharmaceutical and food industry. In this paper a new and effective method for the isolation of ulvans from freshwater algae is described. The substance has been characterized after enzymatic hydrolysis by Fourier Transform Infrared (FT-IR) spectroscopy and elemental analysis. FT-IR spectroscopy permits identification of the band characteristic of the sulfonic acid groups, specific for this kind of polysaccharides. With increasing size of the thalli, the amount of ulvans in the algae cells increases. Hence, freshwater green macroalgae U. flexuosa and C. glomerata were found as a new source of polysaccharidic ulvans that can be considered to be potentially used in medicine, pharmacy, food and cosmetic industry. [ABSTRACT FROM AUTHOR]

Algal blooms are commonly observed in freshwater and coastal areas, causing significant damage to drinking water and aquaculture production. Predictive models are effective for algal bloom forecasting and management. In this paper, an auto-regressive integrated moving average (ARIMA) model was developed to predict daily chlorophyll a ( Chl a ) concentrations, using data from Taihu Lake in China. For comparison, a multivariate linear regression (MVLR) model was also established to predict daily Chl a concentrations using the same data. Results showed that the ARIMA model generally performed better than the MVLR model with respect to the absolute error of peak value, root mean square error and index of agreement. Because the ARIMA model needs only one input variable, it shows greater applicability as an algal bloom early warning system using online sensors of Chl a . [ABSTRACT FROM AUTHOR]

This paper presents the results of a palynological investigation of an assemblage of pollen, spores and organic-walled microalgal remains from the paleosinkhole infill exposed at Górażdże, Upper Silesia, SW Poland. The results of previous palynological studies indicate that the infill was deposited in the late Miocene, probably during the more humid Tortonian stage. The sinkhole at Górażdże was filled with shallow water that periodically might have dried out or, at least, undergone seasonal warming. Green algae (Chlorophyta) such as Zygnemataceae, Botryococcus and Pediastrum , as well as Sigmopollis were major components of the algal community. The presence of planktonic algae Pediastrum and Tetraedron as well as pollen grains of aquatic plants, such as Nuphar and Nymphaea , indicate that there were extended periods of standing water. The pond was surrounded by vegetation composed of herbs and riparian forests dominated by Alnus , Salix , Ulmus , Pterocarya , Carya , and others. More dry terrains were presumably covered by mixed forests composed of Pinus , Tsuga , Picea , Quercus , Carpinus , Fagus , Betula , and others, with only a small admixture of thermophilous plants, such as Castanea . Ericaceae were presumably a component of the groundcover of the forests, or they formed their own open dwarf-shrub communities, such as bush swamps or heathlands. A high frequency of Poaceae pollen grains might reflect the development of open landscapes. The climate during the deposition of sediments in the sinkhole was warm temperate and mild, without severe winters. A comparison of the sporomorph association from the studied sinkhole with another Neogene paleosinkhole palynoflora from the neighboring Tarnów Opolski site revealed asynchronous karst development in the western part of the Upper Silesian Upland, with the infill sediments being at least middle and late Miocene in age. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of estuarine hydrodynamics and water quality comes mostly from studies of large estuarine systems. The processes affecting algae, nutrients, and dissolved oxygen (DO) in small and shallow subtropical estuaries are relatively less studied. This paper documents the development, calibration, and verification of a three dimensional (3D) water quality model for the St. Lucie Estuary (SLE), a small and shallow estuary located on the east coast of south Florida. The water quality model is calibrated and verified using two years of measured data. Statistical analyses indicate that the model is capable of reproducing key water quality characteristics of the estuary within an acceptable range of accuracy. The calibrated model is further applied to study hydrodynamic and eutrophication processes in the estuary. Modeling results reveal that high algae concentrations in the estuary are likely caused by excessive nutrient and algae supplies in freshwater inflows. While algal blooms may lead to reduced DO concentrations near the bottom of the waterbody, this study indicates that stratification and circulation induced by freshwater inflows may also contribute significantly to bottom water hypoxia in the estuary. It is also found that high freshwater inflows from one of the tributaries can change the circulation pattern and nutrient loading, thereby impacting water quality conditions of the entire estuary. Restoration plans for the SLE ecosystem need to consider both a reduction of nutrient loading and regulation of the freshwater discharge pattern. [Copyright &y& Elsevier]

Abstract: This paper presents the first record of charophytes from the Triassic sedimentary rocks of Argentina and the entire southern hemisphere. Algal remains were found in the Cerro Puntudo Formation dated as Anisian (243.8±1.9Ma). The formation is part of the Cuyana Basin, which formed as consequence of the Triassic rifting of Pangaea. The paleoenvironments represented by this succession include from bottom to top: (1) a proximal to medial alluvial fan system; (2) a distal alluvial fan deposit; (3) a braided fluvial system with small channelized bodies; (4) a distal fluvial system containing rare carbonates; and (5) a carbonate-rich lacustrine system. The lacustrine facies association corresponds mainly to carbonate microbialites with three recognized facies, namely disrupted micritic limestones (Lmd), stromatolitic limestones (Ls), and oncolitic limestones (Lo). The Lo facies is rich in oncolites formed by filamentous algae in the cortex and charophyte remains (gyrogonites) in the nucleus and is interpreted as being deposited in a carbonate-rich pond environment, perhaps sourced from springs. Filamentous algae are thought to cause the precipitation of carbonates and trigger the development of micritic coatings in the ponds. Sedimentary and paleobiologic evidence suggest minor movement of the oncolites in a ponded environment where charophytes developed. The charophyte remains found in the Cerro Puntudo Formation are gyrogonites attributed to the Porocharaceae family. All the previous records for Triassic Charophyta correspond to Laurasia in the northern hemisphere, therefore, the paleolatitudinal location of this finding allows the expansion of the paleobiogeographic distribution of the group into Gondwana. [Copyright &y& Elsevier]

Recent global spread of the freshwater alga Didymosphenia geminata (Didymo) has caused major biosecurity and freshwater management concerns. Didymo degrades river esthetics, alters ecosystems, negatively impacts recreation experiences and may require strict containment measures. This paper assesses the impact of Didymo on nonmarket values for recreational angling using a case study from New Zealand, where Didymo is extraordinarily prolific. Choice experiment data are used to fit a latent class model, identifying five distinct angler preference profiles. For the largest class of anglers the presence of Didymo had no significant effect on angling benefits. However, other classes were negatively affected. Overall, Didymo reduced fishing values by about NZ$44 per visit. Anglers were sensitive to the scale of Didymo infestation, suffering significantly higher costs when more water bodies are affected. Closure of Didymo-infected mainstem-rivers to prevent spread of Didymo resulted in a significant reduction in angler net benefits, even if the policy were 100% effective. The latent class model identified distributional implications. While three angler classes would not have significantly different benefits if mainstem-rivers were closed to prevent the spread of Didymo, two classes of anglers would be highly impacted by such a policy, particularly those who regularly fish mainstem-rivers for salmon. [Copyright &y& Elsevier]

Abstract: In this paper, the multifaceted Cr(VI) toxicity over the freshwater green alga Monoraphidium convolutum was assessed by concomitantly monitoring thiol-dependent redox balances, photosynthesis activity and growth-survival scores. Control group showed exponential growth rate at (5.78±0.29) division/day until 8th day with linear increasing chlorophyll a/protein ratios (CHLa/PROT) throughout the period. Cultures of M. convolutum were exposed for 5 days to Cr(VI) concentrations from 0 up to 100mg/L showing that CHLa/PROT ratios were sensibly affected, in agreement to the calculated LC50,48h (5.38±0.72)mg/L from the concentration-response curve of cell mortality after 48h. Regarding photosynthesis effects, Cr(VI) concentrations >1.0mg/L showed significant increases in short-term (after 2h) electron transfer rates (ETR) and quantum yields of photosystem II (Φ PSII), followed by subsequent decline of both parameters after 48 and 72h. Biochemical analyses showed that maximal GSH concentrations in algal cultures were observed upon 1mg Cr(VI)/L and higher dichromate concentrations dramatically increased the activity of antioxidant GSH-dependent enzymes ascorbate peroxidase and glutathione reductase. However, no variation was observed in the cellular GSH levels, whereas GSSG and lipid peroxidation indexes abruptly increased upon 10mg Cr(VI)/L exposure. Altogether, plant physiology, photosynthesis and biochemical data suggest that the GSH-dependent antioxidant system is capable to sustain M. convolutum viability through efficient photosynthesis activity and adequate antioxidant responses up to Cr(VI) concentrations of 1.0mg/L, when redox unbalances were first evidenced. [Copyright &y& Elsevier]

Abstract: Two questions have been posed: whether the concept of clonality may be applied to charophytes (Characeae) and whether species of the genus Chara differ in the features connected with clonal life strategy. The following criteria of clonality were established: 1/an iterative growth form characterised by a horizontal (above- or underground) axis and vertical (orthotropic) above-ground axes in the architecture of an individual, and 2/the ability of the upright axes to function independently and to regenerate the thallus. We determined the architecture of individuals as well as the ability of the vertical thallus fragments to continue growing and developing after separation from the parent thallus in Chara aspera, Chara globularis, Chara rudis and Chara tomentosa. It was found that both single-axis individuals and those made up of several (mostly 2–3) upright axes (branches) growing from the main horizontal axis occur in the populations of each of these species. The orthotropic axis of the thallus represents a module, a recurring structural unit. The modules, having been separated from the parent thalli, extend to form new vertical branches. However, the strategies of the species discussed in this paper vary in correspondence with differences in habitat. [Copyright &y& Elsevier]

Abstract: The combination of microalga-based biodiesel production and wastewater treatment is a promising approach to solve problems related to the energy crisis as well as eutrophication in bodies of water. A freshwater microalga, Chlorella ellipsoidea YJ1, with a high capacity for biomass production and lipid accumulation in secondary effluent was isolated. C. ellipsoidea YJ1 could achieve a biomass of 425mgL−1 (dry weight) in domestic secondary effluent treated with activated sludge technology; and the lipid content per unit of algal biomass was as high as 43% (w/w) in this condition. The lipid growth rate of C. ellipsoidea YJ1 in domestic secondary effluents could attain 11.4mg/L. Furthermore, after the cultivation of C. ellipsoidea YJ1, the removal efficiencies of nitrogen and phosphorus from the secondary effluent studied in this paper were more than 99% and 90%, respectively. Logistic and Monod models were used successfully to simulate the growth of C. ellipsoidea YJ1, and its maximum biomass and maximum population growth rate under different initial concentrations of nitrogen and phosphorus could be simulated and predicted using the models. . [Copyright &y& Elsevier]

The coastal plain of southern Brazil documents several environmental changes mainly related to sea-level fluctuation and climatic variations during the Quaternary. Comprehensive studies have been carried out, of local and regional scope, in order to improve the knowledge about the geological evolution of this portion of the South American. In this paper we present the results of stable isotope, palynological and palynofaciological analysis of the PSC-03 core (7744 cal yr BP – Modern) was performed to provide the sedimentary evolution of the Santa Catarina coastal plain. Palynological and palynofacies analyses revealed abundant and diversified palynological associations, including terrestrial palynomorphs (spores, pollen grains, fungi, and freshwater algae), marine elements (dinoflagellate cysts and foraminiferal linings), besides abundant phytoclasts and amorphous organic matter. Based on the combined analysis of δ13C isotopes (−20.7 ‰ to −29.6 ‰) and the C/N ratio (15.5–68) of the selected samples, we deduce that the organic matter is derived from marine phytoplankton and terrestrial C 3 plants. The integrated approach of palynofacies and stable isotopes (δ13C and C/N) analyses revealed three distinct intervals, which characterize the environmental evolution of this portion of the coastal plain. The Interval I (7744 to 2844 cal yr BP) is related to a marginal marine environment, followed by the Interval II (2857 to 2276 cal yr BP), which indicates shallow water conditions, with wetland or soggy soils, while the Interval III (2124 cal yr BP to Modern) shows a subaerial scenario, strongly influenced by arboreal forms of the Atlantic Forest. Comparisons with other sites in southeastern South America were carried out, especially from Uruguay and Argentina, showing similarities in the palynological succession, as response to broader climatic conditions. • Stable isotopes (δ13C and C/N) and palynofacies analyses are used for understanding coastal evolution of southern Brazil. • Three paleoenvironmental phases are identified within the last 7744 cal years BP. • The marine influence is evidenced between 7744 and 2884 cal years BP. • Major development of the Atlantic Forest in the area from 2124 cal years BP onwards. [ABSTRACT FROM AUTHOR]

Abstract: Precious ecological information extracted from limnological long-term time series advances the theory on functioning and evolution of freshwater ecosystems. This paper presents results of applications of artificial neural networks (ANN) and evolutionary algorithms (EA) for ordination, clustering, forecasting and rule discovery of complex limnological time-series data of two distinctively different lakes. Ten years of data of the shallow and hypertrophic Lake Kasumigaura (Japan) are utilized in comparison with 13 years of data of the deep and mesotrophic Lake Soyang (Korea). Results demonstrate the potential that: (1) recurrent supervised ANN and EA facilitate 1-week-ahead forecasting of outbreaks of harmful algae or water quality changes, (2) EA discover explanatory rule sets for timing and abundance of harmful outbreaks algal populations, and (3) non-supervised ANN provide clusters to unravel ecological relationships regarding seasons, water quality ranges and long-term environmental changes. [Copyright &y& Elsevier]

The effects of cypermethrin, a commonly used pyrethroid insecticide, were studied in small in situ enclosures situated in an eutrophic lake over an 11-day period. The experimental design used a regression principle that included three untreated controls and a gradient of six unreplicated cypermethrin concentrations, ranging from 0.01 to 6 μg/l. This paper is the second in a series of two and describes the effects on the species composition of the crustacean, rotifer, periphyton and phytoplankton communities. Multivariate ordination technique (redundancy analysis (RDA) combined with Monte Carlo permutation tests) showed that exposure to cypermethrin caused significant changes in the species composition of the communities. Changes in the structure of the communities were observed following exposure to a nominal concentration of 0.13 μg cypermethrin per litre above. The direct acute effect of exposure to cypermethrin was a rapid decrease of many species of crustacean zooplankton. The alterations in crustacean species composition were probably due to variations in susceptibility to the direct toxic effects of cypermethrin. No effects concentration (NEC) for individual zooplankton species were calculated using inverse regression and revealed that copepod nauplii were the most sensitive (NEC=0.01 μg/l) of the crustacean groups examined. The observed alterations of the species composition of the autotrophic communities as well as of the rotifers were most likely caused indirectly by cypermethrin, mediated through the direct negative effects of the insecticide on the crustacean grazers. The results of this experiment provide further knowledge about the direct and indirect effects of pesticide stress on the ecosystem level. They also show that there is a variation in sensitivity between different species of zooplankton under natural conditions and thus exemplify the necessity of multispecies approaches in the risk assessment of pesticides. [Copyright &y& Elsevier]

Coastal morphodynamics and environmental changes have been obviously altered by global warming, sea-level fluctuations, and human activities. Palynological analysis is one of the most important tools for providing information on vegetation, climate, and environmental change, which can be relatively sensitive indicators of human activity during the Holocene. However, Holocene coastal morphodynamics and palynological evidence from the Pearl River Delta and coastal areas has not been sufficiently studied. In this paper, we carry out analyses using detailed grain-size and palynological records of pollen, spores, freshwater algae, and marine dinoflagellate cysts from Borehole QZK13 in the Pearl River Estuary (PRE), southern China. The results show information relating coastal morphodynamics, vegetation evolution, climate changes, and anthropogenic activities during the Holocene based on radiocarbon chronology. In general, the PRE experienced marine transgressive processes; sea-level and the coastline tended to migrate landward between 10,700 and 4250 cal yr BP. Meanwhile, abundant arboreal pollen (mainly Castanopsis , Quercus -evergreen, Oleaceae, and Castanea) and small amounts of non-arboreal pollen (mainly Poaceae, Cyperaceae, and Artemisia) were observed in Borehole QZK13, which suggests that subtropical evergreen broadleaved forests were distributed throughout the PRE and adjacent areas, and relatively warm and moist climatic conditions were present during the early-middle Holocene. After that, there were relatively cool and wet climatic conditions, and marine regressive processes occurred in the PRE during the Late Holocene (ca. 4250–960 cal yr BP) indicated by an abrupt increase in aquatic herbs and Dicranopteris. Moreover, we hypothesize that the Neolithic "cultural fault" in the PRE is likely related to frequent storm surges induced by extreme typhoon events that occurred ca. 3000–2700 yr BP. • Grain size, pollen, spores, freshwater algae and dinoflagellate cysts from the Pearl River Estuary were investigated. • Three major phases shown by palynological results were corresponding to the changes in vegetation and climate. • We hypothesized that the Neolithic "cultural fault" is probably related to the storm surges induced by extreme typhoon events. • Natural vegetation cover has suffered large-scale destruction by ancient humans during the Late Holocene. [ABSTRACT FROM AUTHOR]

Antibiotics in water and wastewater have been determined extensively. The treatment of antibiotics in water needs evaluation of possible harmful effects on aquatic ecosystems and human health. This paper presents the toxicity evaluation of antibiotics after their treatment with ferrate (VI) (FeVIO 4 2−, Fe(VI)) in water. The antibiotics (sulfamethoxazole (SMX), erythromycin (ERY), ofloxacin (OFL), ciprofloxacin (CIP), tetracycline (TET), oxytetracycline (OXY), and trimethoprim (TMP)) were treated at pH 8.0 by applying two concentrations of Fe(VI) to have molar ratios of 5:1 and 10:1 ([Fe(VI)]:[antibiotic]). Under the studied conditions, incomplete removal of antibiotics was observed, suggesting that the treated solutions contained parent antibiotics and their transformation products. The toxicity of antibiotics without Fe(VI) treatment was tested against freshwater green alga Raphidocelis subcapitata and cyanobacterium Synechococcus elongatus , which were determined to be generally sensitive to antibiotics, with EC 50 < 1.0 mg/L. The toxicity of Fe(VI) treated solution was tested against R. subcapitata. Results found no toxicity for the treated solutions of OFL, CIP, and OXY. However, SMX, ERY, and TET remained toxic after Fe(VI) treatment (i.e., more than 75% growth inhibition of R. subcapitata). Results demonstrated that R. subcapitata may be applied to test the toxicity of antibiotics after oxidative treatments. [Display omitted] • Studied antibiotics have EC 50 < 1.0 mg/L against R. subcapitata and S. elongatus. • Excess Fe(VI) compared to antibiotics has high removal efficiency at pH 8.0 • Excess Fe(VI) treatment of antibiotics gave varied decreases in algal toxicity. • OFL, CIP, and OXY lose algal toxicity after excess Fe(VI) treatment. • SMX, ERY, TET, and their degradation byproducts remain toxic after Fe(VI) treatment. [ABSTRACT FROM AUTHOR]

The rapid industrialization has led to the generation of various organic chemicals and multi-component mixtures which affect the environment adversely. Although organic chemicals are often exposed to the environment as a form of chemical mixtures rather than individual compounds, there is insufficient toxicity data available for the chemical mixtures due to the associated complexities. Most importantly, the nature of toxicity of mixtures is completely different from the individual chemicals, which makes the evaluation more difficult and challenging. In this paper, we have developed QSAR models for various individual and mixture data sets for the prediction of the aquatic toxicity. We have used Partial Least Squares (PLS) regression as a statistical tool to build the models. The various structural features of the individual chemicals and the mixture components have been modeled against the toxicity end point pEC 50 (negative logarithm of median effective concentration in molar scale) of the aquatic organisms Photobacterium phosphoreum (marine bacterium) and Selenastrum capricornutum (freshwater algae). The mixture descriptors have been calculated by the weighted descriptor generation approach. The models were developed in accordance with OECD guidelines, and the quality of each model has been adjudged by strict validation parameters. The final models are robust, extremely predictive and interpretable mechanistically which can be used for the prediction of toxicity of untested chemical mixtures under the domain of applicability of the developed models. ga1 • We model here aquatic toxicity of mixtures of organic chemicals against two end points. • We use weighted descriptor generation strategy to calculate the mixture descriptors. • Structural features for individual chemicals are not important for the toxicity of mixtures. • The molecular bulk of mixture components enhance the aquatic toxicity. • The developed models can be helpful for data gap filling. [ABSTRACT FROM AUTHOR]

Abstract: Microalgae have received much attention for the inorganic nutrient removal in tertiary treatment of domestic wastewater. Effect of different kinds of nitrogen sources on the growth and nitrogen/phosphorus removal properties of a newly isolated freshwater microalga, Scenedesmus sp. LX1, from a low-nutrient environment condition was studied and reported in this paper. The order of specific growth rate of the microalga with different nitrogen sources was NH4-N>urea-N>NO3-N. With nitrate or urea as nitrogen source, the microalga could grow well and remove both nitrogen and phosphorus efficiently (90% nitrogen and nearly 100% phosphorus were removed). However, with ammonium as the nitrogen source, the maximum algal density was relatively low, and the nitrogen and phosphorus removal efficiencies were as low as 31.1% and 76.4%, respectively. This was caused by the inhibitory effect of algal culture''s acid pH due to H+ releasing from NH4 + during algal cultivation process. [Copyright &y& Elsevier]

• Algal input from upstream dominant the seasonal change of chl-a in Liangxi river. • In situ proliferation played an important role in algal vertical distribution. • Potential chl-a growth induced by excessive nutrient or temperature was quantified. Eutrophication in a freshwater system has mainly been studied in lakes and their upstream rivers, which are responsible to bring pollutants into the lakes. However, the influence of lakes on downstream rivers suffered massive algae from upstream lakes has not been fully studied. Our study area is Liangxi river, downstream of Taihu Lake, which is highly eutrophicated. The algae in Liangxi river has two origins: the physical transport from Taihu Lake and the in-situ proliferation. This paper aims to apply a numerical model to quantify these two processes. The model is calibrated against the measured data in 2018. This computational condition that includes both algal processes is termed as Scheme A. Then, we regarded phytoplankton as a conservative substance by turning off the phytoplankton biological process and term it as Scheme E. We selected the chl-a concentration in Hongqiao (LX2) section to represent the amount of algae in Liangxi river. The average chl-a difference in this section between Schemes A and E, Δ ae , can be used to quantify the magnitude of in-situ proliferation. The Δ ae varies seasonally, and the annual average Δ ae is 7.22 mg/m3, which is 44.7% of the amount attributed to the physical transport. Liangxi river lies in an urban area which might encounter extreme events to facilitate the in-situ proliferation, such as increased temperature and or excessive nutrient load. To quantify the level of algae under extreme situations, we design Schemes B, C and D which eliminated the limitation on algal growth by temperature, nitrogen and phosphorus respectively. Compared with the Scheme A, Schemes B, C and D observe 21.8%, 65.7%and 61.2% respectively, increase in the average algal concentration. In the vertical direction, the chl-a concentration varies between 0.8 mg/m3 and 2 mg/m3 in Scheme A, while the vertical concentration variances of chl-a in schemes B, C and D are found to be 5.56 mg/m3, 12.11 mg/m3 and 3.30 mg/m3, respectively. [ABSTRACT FROM AUTHOR]