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Verlorenvlei is a globally important RAMSAR wetland on the arid west coast of South Africa. A prolonged drought between 2016 and 2021 and increasing competition for water from the agricultural sector resulted in extremely low water levels. We used historical aerial and satellite imagery from 1942 and rainfall and water level data for the past 50 years, to assess habitat changes within the estuarine functional zone of the Verlorenvlei Estuarine Lake. Prior to the drought, lake water levels and water surface area remained stable (1113 ± 27 ha (SE)). Since then, there has been a 64% decrease in open water area, exposing 193 ha of sandbanks, of which 190.9 ha were hyper-sulfidic pyrite-rich. The water in the lower lake was hypersaline (>100), and in the middle, it was acidic (pH<3). The low water level plus sediment and nutrient input from surrounding agriculture resulted in a localised increase in reeds. Additional pressures, such as fires, have reduced the above-ground biomass of reeds and sedges, potentially altering surface morphology and reducing stored carbon. Despite flooding and filling up in June 2023, the lake remained in an acidic state (3.9-4.3). Similar low-lake level, hypersaline and acidic conditions are predicted to become more common under future climate change scenarios where aridity and extreme weather events are anticipated. Inflow of fresh water into the estuary and control of farming practices are required to keep the Verlorenvlei in a functional state, with long-term monitoring necessary to assess the ecological condition in response to restoration actions. [ABSTRACT FROM AUTHOR]

Verlorenvlei is a globally important RAMSAR wetland on the arid west coast of South Africa. A prolonged drought between 2016 and 2021 and increasing competition for water from the agricultural sector resulted in extremely low water levels. We used historical aerial and satellite imagery from 1942 and rainfall and water level data for the past 50 years, to assess habitat changes within the estuarine functional zone of the Verlorenvlei Estuarine Lake. Prior to the drought, lake water levels and water surface area remained stable (1113 ± 27 ha (SE)). Since then, there has been a 64% decrease in open water area, exposing 193 ha of sandbanks, of which 190.9 ha were hyper-sulfidic pyrite-rich. The water in the lower lake was hypersaline (>100), and in the middle, it was acidic (pH

The impact of rising atmospheric CO2 (pCO2atm) from anthropogenic activities on pH, dissolved inorganic carbon, carbonate mineral saturation, and aluminum (Al) speciation is evaluated for 18 northeastern USA lakes using polythermal, sliding activity reaction path models. pCO2atm was forced using two scenarios from the IPCC's Sixth Assessment Report in which pCO2atm attains either 600 or 1,100 ppm in 2,100. Results suggest pH will decrease 0.15 and 0.32 pH units, aCO32− ${a}_{\mathrm{C}{\mathrm{O}}_{3}^{2-}}$ will decrease 24% and 49%, and Ωaragonite will decrease 21% and 45%, respectively. These changes are of the same magnitude as those expected for the oceans. The effects of rising pCO2atm on sub‐lethal 20% effect concentrations (i.e., EC20) of Al for brook trout (Salvelinus fontinalis) are evaluated with the biotic ligand model, which indicates Al toxicity effects will increase as pH decreases. These changes could reverse gains in water quality and fisheries health achieved since implementation of the Clean Air Act. Plain Language Summary: Fossil fuel consumption, deforestation, and changing land use are all contributing to rising CO2 concentrations in the atmosphere. In addition to atmospheric warming and climate impacts, rising atmospheric CO2 will also promote acidification of ocean surface waters, which is expected to have detrimental effects on marine ecosystems. Much less is known about how rising atmospheric CO2 will impact terrestrial freshwaters such as lakes and streams. We developed reaction path models for 18 lakes from northeastern USA to investigate possible impacts of rising atmospheric CO2 and temperature on these systems. The models indicate that acidification of these lakes could be of similar magnitude to ocean acidification. The saturation state of these lakes with respect to the mineral aragonite, which is important for calcifying organisms, will also decrease. Finally, acidification will alter aluminum (Al) speciation, which could augment toxic effects from this metal on important sport fish like brook trout, possibly reversing gains made in water quality since implementation of the Clean Air Act decreased the input of strong acids via acid rain. Key Points: Rising atmospheric CO2 from anthropogenic activities will lead to acidification of lakes in the northeastern USA during the 21st centuryAcidification will alter Al speciation and lower concentrations required to cause a sub‐lethal response in 20% of the resident brook troutAnthropogenic‐sourced CO2 could reverse gains in lake water quality realized since implementation of the Clean Air Act [ABSTRACT FROM AUTHOR]

Base metal smelting in Sudbury (Ontario, Canada) resulted in marked environmental degradation starting in the late nineteenth century. The environmental legacy of intensive industrial activity remains evident in the region despite remediation efforts and recovery. Even though chironomids (Diptera: Chironomidae) are important trophic intermediates, relatively little is known about their response to base metal smelting contaminants. We examined the spatial distribution of recently deposited (i.e., modern) chironomid assemblages in 64 lakes, which we found was most related to lake depth. Further, we compared pre-1880 assemblages to recent sedimentary assemblages with a 32-lake subset. The influence of past contamination was apparent from the replacement of acid- and metal-sensitive taxa with tolerant taxa and early colonizers. In clear lakes, littoral taxa experienced the most change. Chironomid diversity appears lower in recent sediments compared to pre-impact sediments, which is in part related to the persistence of tolerant communities and the lack of recovery of acid-/metal-sensitive taxa, but may also be related to changes in biotic stressors. Spatial trends in chironomid assemblages can inform modern studies of biodiversity recovery in metal smelting regions and strengthen future inferences of how smelting emissions have influenced fish communities and deep-water habitat in the context of multiple modern stressors. [ABSTRACT FROM AUTHOR]

Abstract The impact of rising atmospheric CO2 (pCO2atm) from anthropogenic activities on pH, dissolved inorganic carbon, carbonate mineral saturation, and aluminum (Al) speciation is evaluated for 18 northeastern USA lakes using polythermal, sliding activity reaction path models. pCO2atm was forced using two scenarios from the IPCC's Sixth Assessment Report in which pCO2atm attains either 600 or 1,100 ppm in 2,100. Results suggest pH will decrease 0.15 and 0.32 pH units, aCO32− will decrease 24% and 49%, and Ωaragonite will decrease 21% and 45%, respectively. These changes are of the same magnitude as those expected for the oceans. The effects of rising pCO2atm on sub‐lethal 20% effect concentrations (i.e., EC20) of Al for brook trout (Salvelinus fontinalis) are evaluated with the biotic ligand model, which indicates Al toxicity effects will increase as pH decreases. These changes could reverse gains in water quality and fisheries health achieved since implementation of the Clean Air Act.

Major ion chemistry (2000-2009) from 208 lakes (342 sample dates and 600 samples) in class I and II wilderness areas of the Sierra Nevada was used in the Steady-State Water Chemistry (SSWC) model to estimate critical loads for acid deposition and investigate the current vulnerability of high elevation lakes to acid deposition. The majority of the lakes were dilute (mean specific conductance=8.0 ?S cm?1) and characterized by low acid neutralizing capacity (ANC; mean= 56.8 ?eq L?1). Two variants of the SSWC model were employed: (1) one model used the F-factor and (2) the alternate model used empirical estimates of atmospheric deposition and mineral weathering rates. A comparison between the results from both model variants resulted in a nearly 1:1 slope and an R2 value of 0.98, suggesting that the deposition and mineral weathering rates used were appropriate.Using anANClimit of 10 ?eq L?1, both models predicted a median critical load value of 149 eq ha?1 year?1 of H+ for granitic catchments. Median exceedances for the empirical approach and Ffactor approach were ?81 and ?77 eq ha?1 year?1, respectively. Based on the F-factor and empirical models, 36 (17 %) and 34 (16 %) lakes exceeded their critical loads for acid deposition. Our analyses suggest that high elevation lakes in the Sierra Nevada have not fully recovered from the effects of acid deposition despite substantial improvement in air quality since the 1970s. © Springer Science+Business Media Dordrecht 2013.

Increases in the concentration of dissolved organic matter (DOM) have been documented in many inland waters in recent decades, a process known as "browning". Previous studies have often used space‐for‐time substitution to examine the direct consequences of increased DOM on lake ecosystems. However, browning often occurs concomitant with other ecologically important water chemistry changes that may interact with or overwhelm any potential ecological response to browning itself. Here we examine a long‐term (~20 year) dataset of 28 lakes in the Adirondack Park, New York, USA, that have undergone strong browning in response to recovery from acidification. With these data, we explored how primary producer and zooplankton consumer populations changed during this time and what physical and chemical changes best predicted these long‐term ecosystem changes. Our results indicate that changes in primary producers are likely driven by reduced water clarity due to browning, independent of changes in nutrients, counter to previously hypothesized primary producer response to browning. In contrast, declines in calcium concomitant with browning play an important role in driving long‐term declines in zooplankton biomass. Our results indicate that responses to browning at different trophic levels are decoupled from one another. Concomitant chemical changes have important implications for our understanding of the response of aquatic ecosystems to browning. [ABSTRACT FROM AUTHOR]

Coastal ecosystems can experience acidification via upwelling, eutrophication, riverine discharge, and climate change. While the resulting increases in pCO2 can have deleterious effects on calcifying animals, this change in carbonate chemistry may benefit some marine autotrophs. Here, we report on experiments performed with North Atlantic populations of hard clams (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), bay scallops (Argopecten irradians), and blue mussels (Mytilus edulis) grown with and without North Atlantic populations of the green macroalgae, Ulva. In six of seven experiments, exposure to elevated pCO2 levels (~ 1700 μatm) resulted in depressed shell- and/or tissuebased growth rates of bivalves compared to control conditions, whereas rates were significantly higher in the presence of Ulva in all experiments. In many cases, the co-exposure to elevated pCO2 levels and Ulva had an antagonistic effect on bivalve growth rates whereby the presence of Ulva under elevated pCO2 levels significantly improved their performance compared to the acidification-only treatment. Saturation states for calcium carbonate (Χ) were significantly higher in the presence of Ulva under both ambient and elevated CO2 delivery rates, and growth rates of bivalves were significantly correlated with Χ in six of seven experiments. Collectively, the results suggest that photosynthesis and/or nitrate assimilation by Ulva increased alkalinity, fostering a carbonate chemistry regime more suitable for optimal growth of calcifying bivalves. This suggests that large natural and/or aquacultured collections of macroalgae in acidified environments could serve as a refuge for calcifying animals that may otherwise be negatively impacted by elevated pCO2 levels and depressed Χ. [ABSTRACT FROM AUTHOR]

The extended multiple linear regression technique is used to determine changes in anthropogenic carbon in the intermediate layers of the Eurasian Basin based on occupations from four cruises between 1996 and 2015. The results show a significant increase in basin‐wide anthropogenic carbon storage in the Nansen Basin (0.44–0.73 ± 0.14 mol C·m−2·year−1) and the Amundsen Basin (0.63–1.04 ± 0.09 mol C·m−2·year−1). Over the last two decades, inferred changes in ocean acidification (0.020–0.055 pH units) and calcium carbonate desaturation (0.05–0.18 units) are pronounced and rapid. These results, together with results from carbonate‐dynamic box model simulations and 129I tracer distribution simulations, suggest that the accumulation of anthropogenic carbon in the intermediate layers of the Eurasian Basin are consistent with increasing concentrations of anthropogenic carbon in source waters of Atlantic origin entering the Arctic Ocean followed by interior transport. The dissimilar distributions of anthropogenic carbon in the interior Nansen and Amundsen Basins are likely due to differences in the lateral ventilation of the intermediate layers by the return flows and ramifications of the boundary current along the topographic boundaries in the Eurasian Basin. Key Points: Rapid decadal accumulation of basin‐wide anthropogenic carbon in the Arctic and intermediate layers of the Nansen and Amundsen BasinsThe pH in the upper layers has decreased by 0.0021 ± 0.0004 per year in the Eurasian BasinTracer data and model simulations suggest that Cant accumulation is likely driven by Atlantic source waters, followed by interior transport [ABSTRACT FROM AUTHOR]

We compiled and examined 15 years (2002-2016) of high-frequency monitoring data from the National Estuarine Research Reserve System (NERRS) to characterize diel to interannual variability of pH and dissolved oxygen (DO, % saturation) across 16 diverse, shallow-water habitats along the US Atlantic, Gulf of Mexico, Caribbean, and Pacific coasts. We asked whether these systems exhibit a common pH/DO relationship, whether there were detectable interannual trends in temperature, pH, and DO within and across systems, and how pH/DO dynamics would relate to measured levels of nutrients and chlorophyll. Our analyses confirmed that large, metabolically driven, and thus concurrent fluctuations of pH and DO are a unifying feature of nearshore habitats. Moreover, we derived well-constrained relationships that predict (i) monthly mean pH or (ii) mean diel pH fluctuations across systems based on habitat mean salinity and (i) mean DO or (ii) mean diel DO fluctuations. This suggests that common metabolic principles drive diel to seasonal pH/DO variations within as well as across a diversity of estuarine environments. Yearly pH and DO anomalies did not show monotonous trends over the study period and differed considerably between sites and regions. However, weekly anomalies of means, diel minima, and diel ranges of pH and DO changed significantly over time and were strongly correlated to temperature anomalies. These general patterns lend strong empirical support to the notion that coastal acidification—in addition to being driven by eutrophication and atmospheric CO2 increases—is exacerbated simply by warming, likely via increasing community respiration. Nutrient and chlorophyll dynamics were inversely related in these shallow, well-mixed systems, but higher nutrient levels were still associated with lower pH and lower DO levels in most, but not all, systems. Our analyses emphasize the particular dynamics of nearshore habitats and the critical importance of NERRS and its system-wide monitoring program. [ABSTRACT FROM AUTHOR]

Aeolian dust is a significant source of phosphorus (P) to alpine oligotrophic lakes, but P speciation in dust and source sediments and its release kinetics to lake water remain unknown. Phosphorus K-edge XANES spectroscopy shows that calcium-bound P (Ca-P) is dominant in 10 of 12 dust samples (41-74%) deposited on snow in the central Rocky Mountains and all 42 source sediment samples (the fine fraction) (68-80%), with a lower proportion in dust probably because acidic snowmelt dissolves some Ca-P in dust before collection. Iron-bound P (Fe-P, ∼54%) dominates in the remaining two dust samples. Chemical extractions (SEDEX) on these samples provide inaccurate results because of unselective extraction of targeted species and artifacts introduced by the extractions. Dust releases increasingly more P in synthetic lake water within 6-72 h thanks to dissolution of Ca-P, but dust release of P declines afterward due to back adsorption of P onto Fe oxides present in the dust. The back sorption is stronger for the dust with a lower degree of P saturation determined by oxalate extraction. This work suggests that P speciation, poorly crystalline minerals in the dust, and lake acidification all affect the availability and fate of dust-borne P in lakes. [ABSTRACT FROM AUTHOR]

In recent decades, many aquatic ecosystems in Europe and North America have experienced reduced inputs of nutrients and acidifying substances because of improved sewage treatment and reduced emission of sulphur oxides. We evaluated the consequences of these efforts to changes in water chemistry, species richness and community composition of aquatic macrophytes in 56 lakes in Denmark around 1990 and again around 2010., Reductions in lake water concentrations of phosphorus and nitrogen were strongest in eutrophic and hypertrophic lakes, for example, lakes which had been heavily affected by domestic sewage. These changes translated into decreased algal biomass in the most eutrophied lakes. Oligo- and mesotrophic lakes did not change significantly in terms of nutrients or algal biomass. Water clarity increased across all lakes but not significantly in specific trophic lake groups. Alkalinity and pH increased significantly (up to 2 pH-units) in low-alkaline lakes, while well-buffered high-alkaline lakes (>0.5 meq/L) did not show any change., Macrophyte species richness per lake increased, on average, by 13% during the 20-year study period. The increase was strongest in species preferring nutrient-rich conditions and could be directly attributed to reductions in phytoplankton biomass in lakes of medium water clarity. The similarity among all lakes in terms of species composition increased over the study period. This development was closely related to higher average species richness and was mainly caused by recolonisation of lakes, recovering from past eutrophication, by relatively common species (e.g., Lemna trisulca, Sparganium emersum and Potamogeton berchtoldii). Higher pH in low-alkaline lakes was accompanied by a shift from acid-tolerant to more acid-sensitive species., Our results demonstrate that investment in pollution control has been successful in terms of markedly improving water quality of lakes and, with a time lag, macrophyte species richness. Although relatively common species have spread across lakes and resulted in homogenised macrophyte communities, continued efforts to reduce pollution could ensure the survival of rare specialist species and perhaps even increase their abundance in the future. [ABSTRACT FROM AUTHOR]

Ocean acidification is widely recognised to have a negative impact on marine calcifying organisms by reducing calcifications, but controversy remains over whether such organisms could cope with ocean acidification within a range of phenotypic plasticity and/or adapt to future acidifying ocean. We performed a laboratory rearing experiment using clonal fragments of the common branching corals Montipora digitata and Porites cylindrica under control and acidified seawater (lower pH) conditions (approximately 400 and 900 μatm p CO 2 , respectively) and evaluated the intraspecific variations in their responses to ocean acidification. Intra- and interspecific variations in calcification and photosynthetic efficiency were evident according to both p CO 2 conditions and colony, indicating that responses to acidification may be individually variable at the colony level. Our results suggest that some corals may cope with ocean acidification within their present genotypic composition by adaptation through phenotypic plasticity, while others may be placed under selective pressures resulting in population alteration. [ABSTRACT FROM AUTHOR]

The development of effective risk reduction strategies for aquatic pollutants requires a comprehensive understanding of toxic impacts on ecosystems. Classical toxicological studies are effective for characterizing pollutant impacts on biota in a controlled, simplified environment. Nonetheless, it is well-acknowledged that predictions based on the results of these studies must be tested over the long-term in a natural ecosystem setting to account for increased complexity and multiple stressors. Paleolimnology (the study of lake sediment cores to reconstruct environmental change) can address many key knowledge gaps. When used as part of a weight-of-evidence framework with more traditional approaches in ecotoxicology, it can facilitate rapid advances in our understanding of the chronic effects of pollutants on ecosystems in an environmentally realistic, multistressor context. Paleolimnology played a central role in the Acid Rain debates, as it was instrumental in demonstrating industrial emissions caused acidification of lakes and associated ecosystem-wide impacts. "Resurrection Ecology" (hatching dormant resting eggs deposited in the past) records evolutionary responses of populations to chronic pollutant exposure. With recent technological advances (e.g., geochemistry, genomic approaches), combined with an emerging paleo-ecotoxicological framework that leverages strengths across multiple disciplines, paleolimnology will continue to provide valuable insights into the most pressing questions in ecotoxicology. [ABSTRACT FROM AUTHOR]

D/H ratios of leaf lipids from lacustrine aquatic macrophytes have been shown to record precipitation δD values, which can reflect precipitation-weighted mean annual temperature (MAT) in the northeastern United States. Here we report a high-resolution hydrogen isotopic record from Little Pond, Massachusetts, USA, which we compare with other paleoclimate data from the region, including a similar δD record from Blood Pond, Massachusetts. Together the two datasets provide a >16 ka record of δD variability in the region, affording new insights into Holocene climate history. First, the long-term trends in δD correlate significantly with regional temperatures inferred from alkenone records from nearby areas of the North Atlantic and lake-level inferred changes in precipitation and evaporation. The long-term δD trends reflect a period of maximum regional warmth at ca. 8–6 ka after the collapse of the Laurentide Ice Sheet. Second, unlike the positive relationship between temperature and δD observed over the long-term and during early events like the Younger Dryas, we find that a series of warm and dry events at 4.9–4.6, 4.2–3.9, 2.9–2.1, and 1.3–1.2 cal kya BP coincide with negative δD excursions from the long trends. These events were likely driven by summer drought dynamics. [ABSTRACT FROM AUTHOR]

Ocean warming and acidification may substantially affect the reproduction of keystone species such as Fucus vesiculosus (Phaeophyceae). In four consecutive benthic mesocosm experiments, we compared the reproductive biology and quantified the temporal development of Baltic Sea Fucus fertility under the single and combined impact of elevated seawater temperature and pCO2 (1100 ppm). In an additional experiment, we investigated the impact of temperature (0-25°C) on the maturation of North Sea F. vesiculosus receptacles. A marked seasonal reproductive cycle of F. vesiculosus became apparent in the course of 1 year. The first appearance of receptacles on vegetative apices and the further development of immature receptacles of F. vesiculosus in autumn were unaffected by warming or elevated pCO2. During winter, elevated pCO2 in both ambient and warmed temperatures increased the proportion of mature receptacles significantly. In spring, warming and, to a lesser extent, elevated pCO2 accelerated the maturation of receptacles and advanced the release of gametes by up to 2 weeks. Likewise, in the laboratory, maturation and gamete release were accelerated at 15-25°C relative to colder temperatures. In summary, elevated pCO2 and/or warming do not influence receptacle appearance in autumn, but do accelerate the maturation process during spring, resulting in earlier gamete release. Temperature and, to a much lesser extent, pCO2 affect the temporal development of Fucus fertility. Thus, rising temperatures will mainly shift or disturb the phenology of F. vesiculosus in spring and summer, which may alter and/or hamper its ecological functions in shallow coastal ecosystems of the Baltic Sea. [ABSTRACT FROM AUTHOR]

A 3-year study of the biota of the remote mountain lakes of Amut, Balan-Tamur, and Yakondykon, situated in the Dzherginsky State Reserve in the Baikalian region of Eastern Siberia, was carried out from 2006 to 2008. Examining the biota of non-modern and non-industrialised mountain lakes allowed us to reveal its background in relation to the species composition of plankton, the main groups of benthos and fishes, production potential, and seasonal dynamics of the ecosystem's basic links. Our data on pH and biota were compared with the findings of a previous study in 1986 in order to evaluate possible changes associated with probable acidification. We observed that the lakes of the Dzherginsky State Reserve have high species diversity. Despite this, they are classed as oligotrophic water-bodies with regard to the development level of their planktonic and benthic coenoses. These lakes are not polluted by anthropogenic activity and so could be considered as a pattern of ecologically pure water-bodies. It is important to add that high mountain lakes of Pribaikalye presently serve as refuges for species that were widespread during past geological epochs. [ABSTRACT FROM AUTHOR]

Coastal time series of ocean carbonate chemistry are critical for understanding how global anthropogenic change manifests in near-shore ecosystems. Yet, they are few and have low temporal resolution. At the time series station Point B in the northwestern Mediterranean Sea, seawater was sampled weekly from 2007 through 2015, at 1 and 50 m, and analyzed for total dissolved inorganic carbon (CT) and total alkalinity (AT). Parameters of the carbonate system such as pH (pHT, total hydrogen ion scale) were calculated and a deconvolution analysis was performed to identify drivers of change. The rate of surface ocean acidification was -0.0028±0.0003 units pHT yr-1. This rate is larger than previously identified open-ocean trends due to rapid warming that occurred over the study period (0.072±0.022 °C yr-1). The total pHT change over the study period was of similar magnitude as the diel pHT variability at this site. The acidification trend can be attributed to atmospheric carbon dioxide (CO2) forcing (59 %, 2.08±0.01 ppmCO2 yr-1) and warming (41 %). Similar trends were observed at 50m but rates were generally slower. At 1m depth, the increase in atmospheric CO2 accounted for approximately 40% of the observed increase in CT (2.97±0.20 μmol kg-1 yr-1). The remaining increase in CT may have been driven by the same unidentified process that caused an increase in AT (2.08±0.19 μmol kg-1 yr-1). Based on the analysis of monthly trends, synchronous increases in CT and AT were fastest in the spring-summer transition. The driving process of the interannual increase in AT has a seasonal and shallow component, which may indicate riverine or groundwater influence. This study exemplifies the importance of understanding changes in coastal carbonate chemistry through the lens of biogeochemical cycling at the land-sea interface. This is the first coastal acidification time series providing multiyear data at high temporal resolution. The data confirm rapid warming in the Mediterranean Sea and demonstrate coastal acidification with a synchronous increase in total alkalinity. [ABSTRACT FROM AUTHOR]

Emerging environmental threats often lack sufficient governance to address the full extent of the problem. An example is ocean acidification which is a growing concern in fishing and aquaculture economies worldwide, but has remained a footnote in environmental policy at all governance levels. However, existing legal jurisdictions do account for some aspects of the system relating to ocean acidification and these may be leveraged to support adapting to and mitigating ocean acidification. We refine and apply a methodological framework that helps objectively evaluate governance, from a social-ecological systems perspective. We assess how well a set of extant US institutions fits with the social-ecological interactions pertinent to ocean acidification. The assessment points to measured legal gaps, for which we evaluate the government authorities most appropriate to help fill these gaps. The analysis is conducted on United State federal statutes and regulations. Results show quantitative improvement of institutional fit over time (2006 to 2013), but a substantial number of measured legal gaps persist especially around acknowledging local sources of acidification and adaptation strategies to deal with or avoid impacts. We demonstrate the utility of this framework to evaluate the governance surrounding any emerging environmental threat as a first step to guiding the development of jurisdictionally realistic solutions. [ABSTRACT FROM AUTHOR]

We estimated the potential economic value of recreational fisheries in lakes altered by acid pollution in the Adirondack Mountains (USA). We found that the expected value of recreational fisheries has been diminished because of acid deposition but may improve as lakes recover from acidification under low emissions scenarios combined with fish stocking. Fishery value increased with lake pH, from a low of $4.41 angler day-1 in lakes with pH < 4.5, to a high of $38.40 angler day-1 in lakes with pH > 6.5 that were stocked with trout species. Stocking increased the expected fishery value by an average of $11.50 angler day-1 across the entire pH range of the lakes studied. Simulating the future long-term trajectory of a subset of lakes, we found that pH and expected fishery value increased over time in all future emissions scenarios. Differences in estimated value among pollution reduction scenarios were small (<$1 angler day-1) compared to fish stocking scenarios (>$4 angler day-1). Our work provides a basis for assessing the costs and benefits of emissions reductions and management efforts that can hasten recovery of the economic and cultural benefits of ecosystems degraded by chronic pollution. [ABSTRACT FROM AUTHOR]

Despite their remoteness from sources of atmospheric pollutant emissions, the Afromontane tarns in the Maloti-Drakensberg region are perfect candidates to study the negative effects of acidifying atmospheric pollution, because mountain lakes are widely recognised as sentinel ecosystems, unimpacted by direct human disturbance within their catchments. Thirty-four tarns were sampled in the Maloti-Drakensberg region and most were found to be extremely sensitive to acidic deposition, as indicated by their low acid neutralising capacity. There are very few studies of freshwater critical loads for any region within South Africa. The steady-state water chemistry model (SSWC) was adapted and used to determine critical loads, whereas exceedance was estimated relative to modelled regional deposition data, in order to understand the risk of harmful effects to aquatic ecosystems. Seventy-six percent of sampled sites across the Maloti-Drakensberg would exceed critical loads even at the lowest modelled deposition levels, but there are no current measured deposition data for the region. The sensitivity of the Maloti-Drakensberg tarns needs to be considered in future policy formulation regarding acceptable levels of acidifying atmospheric pollution from South Africa’s energy sector and indicates the need for assessing aquatic ecosystem impacts in other regions of South Africa. [ABSTRACT FROM PUBLISHER]

Thousands of Swedish acidified lakes and streams have been regularly limed for about 30 years. Standard sampling of fish assemblages in lakes and streams was an important part of monitoring the trends after liming, i.e. sampling with multi-mesh gillnets in lakes (EN 14757) and electrofishing in streams (EN 14011). Monitoring data are nationally managed, in the National Register of Survey test-fishing and the Swedish Electrofishing Register. We evaluated long-term data from 1029 electrofishing sites in limed streams and gillnet sampling in 750 limed lakes, along with reference data from 195 stream sites and 101 lakes with no upstream liming in their catchments. The median year of first liming was 1986 for both streams and lakes. The proportion of limed stream sites with no fish clearly decreased with time, mean species richness and proportion of sites with brown trout ( Salmo trutta ) recruits increased. There were no consistent trends in fish occurrence or species richness at non-limed sites, but occurrence of brown trout recruits also increased in acid as well as neutral reference streams. Abundance of brown trout, perch ( Perca fluviatilis ) and roach ( Rutilus rutilus ) increased significantly more at limed sites than at non-limed reference sites sampled before and after 1986. The mean species richness did not change consistently in limed lakes, but decreased in low alkalinity reference lakes, and fish abundance decreased significantly in limed as well as in non-limed lakes. [ABSTRACT FROM AUTHOR]

The potential for atmospheric deposition of sulfur and nitrogen to affect lakes in the Northwestern USA to cause lake acidification was assessed by examining four lakes extending from southern Oregon into the central Washington Cascades. The four lakes were dilute (conductivity 2.2 to 3.6 μS/cm), low ANC (−3 to 11 μeq/L) systems, located in subalpine to alpine settings in designated wilderness areas. The four lakes were cored, dated with Pb and C, and analyzed for sediment nutrients and diatom remains. Diatom-inferred changes in chemistry were made possible through an earlier project to create a diatom calibration set for the Cascades. The three southern lakes exhibited volcanic inputs of ash or tephra, but diatom stratigraphy generally showed only modest responses to these events. None of the lakes exhibited any recent trends in diatom-inferred pH. The most significant finding with respect to paleolimnology was that Foehn Lake, WA, was formed in the twentieth century (1930 ± 7 years), likely as a result of melting of an adjacent snowfield. Current deposition was estimated using the AIRPACT-3 system, and lake chemistry was simulated using the CE-QUAL-W2 hydrodynamic model that had been modified to represent acid-base chemistry. The model simulations showed that the three southern lakes in the transect were insensitive to increases of nitrogen and sulfur until simulated increases reached 300% of current levels. Foehn Lake showed simulated declines of pH and ANC beginning at 50% increases over current deposition of S and N. The three southern lakes are resistant to changes from atmospheric deposition and other disturbances because of long hydraulic residence times, allowing internal processes to neutralize acidic inputs. [ABSTRACT FROM AUTHOR]

Since 1926, the fishes in Lake Orta, one of Italy’s deepest natural lakes, were heavily damaged by profundal hypoxia and acidification linked to oxidation of ammonia from industrial effluents and by industrial metal pollution. Of the original 28 fish species, only perch survived the lake’s contamination. Recently, the water quality of the lake has been largely restored by reductions in pollutant inputs, and a massive liming intervention. These interventions restored fish habitat, but it is unclear whether the recent fish reintroductions were successful, and the present status of the fish community is unknown. Here we reviewed the history of the Lake Orta fish assemblage. Using an extensive 2014 sampling campaign, we compared the present fish community to both its pre-pollution composition and to the assemblages of nearby un-polluted, but otherwise similar lakes, Lake Mergozzo and Lake Maggiore. While nearshore fish density now appears normal in lake Orta, the open water community remains impoverished both in numbers and in species. Epilimnetic and hypolimnetic benthic nets were dominated by perch and roach in all the three lakes, but the catch of pelagic nets differed among lakes. Perch (Perca fluviatilis), rudd (Scardinius erythrophthalmus) and brown trout (Salmo trutta) dominated in Lake Orta while shad (Alosa fallax lacustris) and coregonids (Coregonus spp.) were dominant in the open waters of the other two lakes, but missing from Lake Orta. Many fully or partially migratory species, including marble trout (Salmo trutta marmoratus), eel (Anguilla Anguilla) and barbel (Barbus plebejus) were also missing from Lake Orta, a consequence of their initial extirpation and blocked re-colonization routes along the River Strona. In comparison with both pre-pollution and contemporary reference data, the fish community of Lake Orta has not been rehabilitated. The recovery of the littoral community is complete, but cold water species such as burbot (Lota lota), Arctic charr (Salvelinus alpinus) and bullhead (Cottus gobio) are still lacking, as are the pelagic zooplanktivores European whitefish (Coregonus lavaretus) and shad, which dominate offshore communities in the reference lakes, as they did a century ago in Lake Orta. To propose priorities for fish community rehabilitation in Lake Orta, we categorized the conservation, ecological and fishing values of each missing fish species in the lake, and evaluated the cost and probability of success of the needed intervention for each species. This analysis indicated that rehabilitation of shad and European whitefish should receive highest priority.

Organism-level effects of ocean acidification (OA) are well recognized. Less understood are OA's consequences for ecological species interactions. Here, we examine a behaviourally mediated predator-prey interaction within the rocky intertidal zone of the temperate eastern Pacific Ocean, using it as a model system to explore OA's capacity to impair invertebrate anti-predator behaviours more broadly. Our system involves the iconic sea star predator, Pisaster ochraceus, that elicits flee responses in numerous gastropod prey. We examine, in particular, the capacity for OA-associated reductions in pH to alter flight behaviours of the black turban snail, Tegula funebralis, an often-abundant and well-studied grazer in the system. We assess interactions between these species at 16 discrete levels of pH, quantifying the full functional response of Tegula under present and near-future OA conditions. Results demonstrate the disruption of snail anti-predator behaviours at low pH, with decreases in the time individuals spend in refuge locations. We also show that fluctuations in pH, including those typical of rock pools inhabited by snails, do not materially change outcomes, implying little capacity for episodically benign pH conditions to aid behavioural recovery. Together, these findings suggest a strong potential for OA to induce cascading community-level shifts within this long-studied ecosystem. [ABSTRACT FROM AUTHOR]

We studied the recovery of brown trout populations from 1970 to 2010 in acidified mountain lakes with low ionic content in southwestern Norway. A total of 181 test fishing surveys with gill net series were performed in 59 lakes. We found that the most significant recovery occurred during the 1980s and early 1990s. In this period, only limited improvement in the water chemistry related to acidification, i.e., pH, was observed. However, due to a temporary increase in sea salt deposition, water conductivity almost doubled during this period. In many of the mountain lakes in the study area, the brown trout populations are restricted by ion deficit. Moreover, greater ionic strength ameliorates the effects of acidification by increasing the tolerance to H. Well-established relationships between conductivity and the relative abundance of brown trout (CPUE) explain the observed recovery. We conclude that the dynamics of the sea salt ion contribution should be taken into consideration wherever biological recovery in very diluted water qualities is being evaluated. [ABSTRACT FROM AUTHOR]

Since 1926, the fishes in Lake Orta, one of Italy's deepest natural lakes, were heavily damaged by profundal hypoxia and acidification linked to oxidation of ammonia from industrial effluents and by industrial metal pollution. Of the original 28 fish species, only perch survived the lake's contamination. Recently, the water quality of the lake has been largely restored by reductions in pollutant inputs, and a massive liming intervention. These interventions restored fish habitat, but it is unclear whether the recent fish reintroductions were successful, and the present status of the fish community is unknown. Here we reviewed the history of the Lake Orta fish assemblage. Using an extensive 2014 sampling campaign, we compared the present fish community to both its pre-pollution composition and to the assemblages of nearby un-polluted, but otherwise similar lakes, Lake Mergozzo and Lake Maggiore. While nearshore fish density now appears normal in lake Orta, the open water community remains impoverished both in numbers and in species. Epilimnetic and hypolimnetic benthic nets were dominated by perch and roach in all the three lakes, but the catch of pelagic nets differed among lakes. Perch (Perca fluviatilis), rudd (Scardinius erythrophthalmus) and brown trout (Salmo trutta) dominated in Lake Orta while shad (Alosa fallax lacustris) and coregonids (Coregonus spp.) were dominant in the open waters of the other two lakes, but missing from Lake Orta. Many fully or partially migratory species, including marble trout (Salmo trutta marmoratus), eel (Anguilla Anguilla) and barbel (Barbus plebejus) were also missing from Lake Orta, a consequence of their initial extirpation and blocked re-colonization routes along the River Strona. In comparison with both pre-pollution and contemporary reference data, the fish community of Lake Orta has not been rehabilitated. The recovery of the littoral community is complete, but cold water species such as burbot (Lota lota), Arctic charr (Salvelinus alpinus) and bullhead (Cottus gobio) are still lacking, as are the pelagic zooplanktivores European whitefish (Coregonus lavaretus) and shad, which dominate offshore communities in the reference lakes, as they did a century ago in Lake Orta. To propose priorities for fish community rehabilitation in Lake Orta, we categorized the conservation, ecological and fishing values of each missing fish species in the lake, and evaluated the cost and probability of success of the needed intervention for each species. This analysis indicated that rehabilitation of shad and European whitefish should receive highest priority. [ABSTRACT FROM AUTHOR]

Mahoney Lake in British Columbia is an extreme meromictic system with unusually high levels of sulfate and sulfide present in the water column. As is common in strongly stratified lakes, Mahoney Lake hosts a dense, sulfide-oxidizing phototrophic microbial community where light reaches the chemocline. Below this "plate," the euxinic hypolimnion is anoxic, eutrophic, saline, and rich in sulfide, polysulfides, elemental sulfur, and other sulfur intermediates. While much is known regarding microbial communities in sunlit portions of euxinic systems, the composition and genetic potential of organisms living at aphotic depths have rarely been studied. Metagenomic sequencing of samples from the hypolimnion and the underlying sediments of Mahoney Lake indicate that multiple taxa contribute to sulfate reduction below the chemocline and that the hypolimnion and sediments each support distinct populations of sulfate reducing bacteria (SRB) that differ from the SRB populations observed in the chemocline. After assembling and binning the metagenomic datasets, we recovered near-complete genomes of dominant populations including two Deltaproteobacteria. One of the deltaproteobacterial genomes encoded a 16S rRNA sequence that was most closely related to the sulfur-disproportionating genus Dissulfuribacter and the other encoded a 16S rRNA sequence that was most closely related to the fatty acid- and aromatic acid-degrading genus Syntrophus. We also recovered two near-complete genomes of Firmicutes species. Analysis of concatenated ribosomal protein trees suggests these genomes are most closely related to extremely alkaliphilic genera Alkaliphilus and Dethiobacter. Our metagenomic data indicate that these Firmicutes contribute to carbon cycling below the chemocline. Lastly, we recovered a nearly complete genome from the sediment metagenome which represents a new genus within the FCB (Fibrobacteres, Chlorobi, Bacteroidetes) superphylum. Consistent with the geochemical data, we found little or no evidence for organisms capable of sulfide oxidation in the aphotic zone below the chemocline. Instead, comparison of functional genes below the chemocline are consistent with recovery of multiple populations capable of reducing oxidized sulfur. Our data support previous observations that at least some of the sulfide necessary to support the dense population of phototrophs in the chemocline is supplied from sulfate reduction in the hypolimnion and sediments. These studies provide key insights regarding the taxonomic and functional diversity within a euxinic environment and highlight the complexity of biogeochemical carbon and sulfur cycling necessary to maintain euxinia. [ABSTRACT FROM AUTHOR]

Locating appropriate settlement habitat is a crucial step in the life cycle of most benthic marine animals. In marine fish, this step involves the use of multiple senses, including audition, olfaction and vision. To date, most investigations of larval fish audition focus on the hearing thresholds to various frequencies of sounds without testing an ecological response to such sounds. Identifying responses to biologically relevant sounds at the development stage in which orientation is most relevant is fundamental. We tested for the existence of ontogenetic windows of reception to sounds that could act as orientation cues with a focus on vulnerability to alteration by human impacts. Here we show that larvae of a catadromous fish species (barramundi, Lates calcarifer) were attracted towards sounds from settlement habitat during a surprisingly short ontogenetic window of approximately 3 days. Yet, this auditory preference was reversed in larvae reared under end-of-century levels of elevated CO[sub 2], such that larvae are repelled from cues of settlement habitat. These future conditions also reduced the swimming speeds and heightened the anxiety levels of barramundi. Unexpectedly, an acceleration of development and onset of metamorphosis caused by elevated CO2 were not accompanied by the earlier onset of attraction towards habitat sounds. This mismatch between ontogenetic development and the timing of orientation behaviour may reduce the ability of larvae to locate habitat or lead to settlement in unsuitable habitats. The misinterpretation of key orientation cues can have implications for population replenishment, which are only exacerbated when ontogenetic development decouples from the specific behaviours required for location of settlement habitats. [ABSTRACT FROM AUTHOR]

Lakes near Sudbury, Canada, have been exposed to intense acidification and metal contamination from nearby mining and smelting operations. Although lakewater p H improved substantially following the implementation of emission controls in the late 1960s, biological recovery continues to lag behind chemical recovery., We assessed the current state of biological recovery (relative to pre-impact times) using multiproxy palaeolimnological records from two nearby lake districts ( Sudbury and Killarney), both impacted by acidification but having experienced differences in metal contamination due to their respective distances from smelters., Twentieth century cladoceran shifts were most pronounced in the acidified and metal-contaminated Sudbury lakes, with assemblage changes tracking industrial activity. Chydorus brevilabris increased markedly in dominance, largely at the expense of Bosmina spp. In contrast, the Killarney lakes, with similar changes in p H but lower Cu and Ni inputs than the Sudbury lakes, experienced minimal changes within their sedimentary cladoceran assemblages., These regional differences in cladoceran impact and recovery patterns are best explained by varying levels of Cu and Ni contamination, with concentrations of these metals still exceeding provincial water quality guidelines in the Sudbury lakes. Biological recovery in these systems appears to be inhibited by persistent high metal levels., Increased lake primary production and coincident shifts in cladoceran assemblages over the past approximately 40 years in all the study lakes suggest that climate impacts may be gaining prominence as drivers of ecological change, and therefore a return to the biotic structure of the pre-smelter era is unlikely. [ABSTRACT FROM AUTHOR]

The European Union Water Framework Directive (WFD) classifies ecological status of a waterbody by the determination of its natural reference state to provide a measure of perturbation by human impacts based on taxonomic composition and abundance of aquatic species. Ruse (2010; 2011) has provided methods of assessing anthropogenic perturbations to lake ecological status, in terms of nutrient enrichment and acidification, by analysing collections of floating pupal exuviae discarded by emerging adult Chironomidae. The previous nutrient assessment method was derived from chironomid and environmental data collected during 178 lake surveys of all WFD types found in Britain. Canonical Correspondence Analysis provided species optima in relation to phosphate and nitrogen concentrations. Species found in less than three surveys were excluded from analysis in case of spurious association with environmental values. Since Ruse (2010) an additional 72 lakes have been surveyed adding 31 more species for use in nutrient status assessment. These additional scoring species are reported here. The practical application of the Chironomid Pupal Exuvial Technique (CPET) to classify WFD lake nutrient status is demonstrated using CPET survey data from lakes in Poland. [ABSTRACT FROM AUTHOR]

The Iberian Pyrite Belt, located in Southwestern Spain, represents one of the world's largest accumulations of mine wastes and acid mine drainages. This study reports the comparative microbial ecology of the water column of Nuestra Señora del Carmen acid pit lake with the extreme acidic Río Tinto basin. The canonical correspondence analysis identified members of the Leptospir ilium, Acidiphilium, Metallibacterium, Acidithiobacillus, Ferrimicrobium and Acidisphaera genera as the most representative microorganisms of both ecosystems. The presence of archaeal members is scarce in both systems. Only sequences clustering with the Thermoplasmata have been retrieved in the bottom layer of Nuestra Señora del Carmen and one station of Río Tinto. Although the photosynthetically active radiation values measured in this lake upper layer were low, they were sufficient to activate photosynthesis in acidophilic microorganisms. All identified photosynthetic microorganisms in Nuestra Señora del Carmen (members of the Chlamydomonas, Zygnemopsis and Klebsormidium genera) are major members of the photosynthetic eukaryotic community characterized in Río Tinto basin. This study demonstrates a close relationship between the microbial diversity of Nuestra Señora del Carmen pit lake and the diversity detected in the Río Tinto basin, which underlain the influence of the shared mineral substrates in the microbial ecology of these ecosystems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Extreme low water levels occurred in lakes of the Murray-Darling Basin (Australia). [•] Large areas of pyrite-containing sediments on the lake margins were exposed. [•] Rewetting resulted in acidification of surface water and metal mobilisation. [•] Neutralisation of acidification occurred via limestone dosing and lake refill. [•] Acidity persists in the sediment several years after surface water neutralisation. [Copyright &y& Elsevier]

We investigated whether algal osmotrophy in naturally acidic Lake Caviahue is an important process for acquisition of organic carbon and organic nitrogen. To accomplish this, we quantified algal assimilation of organic compounds, measured the specific growth rate and biomass yield, and documented incorporation of organic compounds by phytoplankton in situ using microautoradiography. Substrate uptake quantification and microautoradiographic investigations were performed using H-leucine, H-glucose, H-thymidine, C-aspartic acid, C-acetic acid and C-bicarbonates. The results showed that the most important species of the phytoplankton community, Keratococcus rhaphidioides and Watanabea sp., took up various sources of organic carbon and nitrogen under both light and dark conditions. They were also able to assimilate leucine, thymidine, aspartic acid and acetate under high levels of inorganic nitrogen and phosphorus, while they could use leucine, arginine, glutamine and glucose under low levels of nitrogen and phosphorus. The assimilation rates were higher in light than in darkness, and the algal specific growth rates increased when organic sources were added. We proposed that osmotrophy complements the main photosynthetic process of the phytoplankton in Lake Caviahue, which helps to overcome the scarcity of light and inorganic nitrogen and carbon in the water column. [ABSTRACT FROM AUTHOR]

Highlights: [•] The dynamic geochemistry of a lake acidification event and its management was assessed. [•] Sulfate complexes dominated the aqueous metal speciation at low pH. [•] Iron oxydroxysulfate minerals (schwertmannite, jarosite) were identified. [•] Aerial additions of limestone to the acidic water slowly returned the pH to near neutral. [•] Coating of the limestone with gypsum and metal precipitates limited its neutralisation efficiency. [Copyright &y& Elsevier]

The extraction of bitumen from the Athabasca oil sands is rapidly expanding, and emission of sulphur and nitrogen oxides has substantially increased. To determine whether lakes downwind of this development in northwest Saskatchewan have been detrimentally impacted since development of the oil sands, a paleolimnological assessment of ten lakes was carried out. Analysis of diatom valves and inferences of diatom-inferred pH indicated that emissions have not resulted in widespread chronic acidification of acid-sensitive lakes ~80-250 km east and northeast of the oil sands development around Fort McMurray and Fort Mackay. However, one of the closest sites to the development indicated a slight decline in diatom-inferred pH, but the two next closest sites, both of which had higher alkalinity, did not show any evidence of acidification. There were also no consistent trends in the concentration or flux of total or individual priority pollutants including lead, mercury, copper, zinc and vanadium. The sedimentation rates in most lakes increased since the mid-1900s, along with increased flux of both diatoms and scaled chrysophytes. Subtle changes in the species assemblages of diatoms and increased flux of diatoms and chrysophyte scales are consistent with recent climate change in this region. [ABSTRACT FROM AUTHOR]

Measurements of total iodine (I) and iodine-129 (129I) concentrations in rivers and lakes of Argentina are presented. Their latitudinal distribution can be explained by taking into account their main sources (oceanic emissions and biomass burning for I, and atmospheric nuclear tests for 129I), transport mechanisms, and fallout patterns. From the measured 129I concentrations in the studied lakes, deposition fluences for their catchment areas were estimated. These results agree with a model of the global deposition pattern due to the 129I released by atmospheric nuclear weapon tests and with other fluences reported for the southern hemisphere. In addition, the first measurements of 129I in shallow seawater from the South Atlantic Ocean are presented and discussed. [ABSTRACT FROM AUTHOR]

In recent decades, explanations for post-glacial lake acidification have focused on changing climate and biotic factors. Here we present a unique lake sediment data set combining diatom-inferred acidity reconstruction with detailed quantitative assessment of soil base dynamics that challenges this view. We show, at Kråkenes Lake in Norway, that historical development of soil mineral depletion inferred from the lake sediment record is consistent with the extent and timing of early Holocene acidification. The lake-water acidification can be fully accounted for by abiotic soil mineral depletion, suggesting a lesser role for alternative acidifying mechanisms, such as direct climate impacts and successional changes in organic acid production. There are at present few comparable data sets, but those that exist suggest similar rates of soil base depletion. As this acidification is not confined to water, abiotic mineral depletion is likely also to impact terrestrial ecosystems, and dynamic vegetation models that exclude irreversible mineral depletion will fail to capture an important element of global ecology. [ABSTRACT FROM AUTHOR]

Views expressed on the potential impact of ocean acidification range from wholesale degradation of marine ecosystems through to no discernable impact with minimal consequences. Constraining this range of predictions is necessary for the development of informed policy and management. The direct biological impacts of acidification occur at the molecular and cellular level; however, it is the expression of these effects at the population and ecosystem level that is of societal concern. Here, we consider the potential impact of ocean acidification on fisheries with particular emphasis on approaches to scaling from physiological responses to population- and ecosystem-level processes. In some instances, impacts of ocean acidification may lead to changes in the relative species composition at a given trophic level without affecting the overall productivity, whilst in other instances, ocean acidification may lead to a reduction in productivity at a given tropic level. Because of the scale at which ecological processes operate, modelling studies are required. Here, ocean acidification is situated within ongoing research into the ecological dynamics of perturbed systems, for which many models have already been developed. Whilst few existing models currently explicitly represent physiological processes sensitive to ocean acidification, some examples of how ocean acidification effects may be emulated within existing models are discussed. Answering the question of how acidification may impact fisheries requires the integration of knowledge across disciplines; this contribution aims to facilitate the inclusion of higher trophic level ecology into this ongoing debate and discussion. [ABSTRACT FROM AUTHOR]