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Beginning in the late-1800s, gold mining activities throughout Nova Scotia, eastern Canada, released contaminants, notably geogenic arsenic from milled ore and anthropogenic mercury from amalgamation, to local environments via surface water flows through tailings fields. We investigated recovery from and legacy effects of the tailings field at the Montague Gold District (~1863-1940) on nearby urban lake ecosystems using geochemical measures and zooplankton remains archived in dated sediment cores from an impact (Lake Charles) and a reference (Loon Lake) lake. Sedimentary levels of total arsenic and total mercury were used to assess mining-related inputs. Arsenic concentrations remain elevated at nearly 300 times above sediment guidelines in Lake Charles surface sediments, due to its upward mobilization from enriched sediment intervals and sequestration by iron oxyhydroxides in surficial sediments. Peak mercury concentrations at Lake Charles were eight times above sediment guidelines during the mining period, and since ~1990 have recovered to levels observed before mining began. Legacy mining impacts at Lake Charles and non-mining related environmental changes in the post-1950 sediments at both lakes have thus combined to structure assemblage compositions of primary consumers. At both lakes, assemblages of pelagic-dominated Cladocera differed (p ≤ 0.05) during the mining period compared to periods before and after mining. Taxon richness differed (p ≤ 0.01) only between the pre- and post-mining periods at mining-impacted Lake Charles and reflects long-term declines of substrate-dwelling littoral taxa. Geochemical and biological recovery have not completely occurred at Lake Charles despite the mine district's closure ~80 years ago. Our findings demonstrate that impacts of ore processing and amalgamation from historical gold mining, combined with recent watershed stressors, continue to affect sedimentary arsenic geochemistry and intermediate trophic levels of nearby, downstream aquatic habitats., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Since the implementation of large-scale lake monitoring in the ~1980s, water color and dissolved organic carbon (DOC) concentrations have increased in many northern lakes (i.e., lake browning), impacting the functioning of aquatic ecosystems. In regions that formerly experienced high levels of acid deposition, this browning trend has been largely attributed to the recovery from the impacts of past acid deposition. However, the extent to which DOC levels have now returned to naturally higher, pre-industrial conditions is still poorly understood. In this study, we assessed whether DOC levels are still influenced by acid deposition in lakes near Sudbury, Ontario, a region that has been heavily affected by sulfur dioxide emissions from local metal smelting during the 20th century. We analyzed water chemistry monitoring data (1981-2018), together with comparisons between modern and pre-industrial DOC levels inferred from sediment spectroscopy, for 51 acid-sensitive and 24 buffered reference lakes across the Sudbury landscape. Since 1981, DOC concentrations doubled in acid-sensitive lakes, with a mean increase of +1.6 mg/L, whereas in more buffered reference lakes, mean DOC levels increased by only 0.8 mg/L. Similarly, sediment-inferred DOC trends indicate that current DOC levels are, on average, ~22% below pre-industrial levels in acid sensitive systems compared to only ~10% in buffered lakes. Weakening correlations between DOC and acidification-related water chemistry variables (e.g., pH, alkalinity, metals) further indicate a diminishing influence of acid deposition on DOC in Sudbury lakes. These results highlight the strong impact that acid deposition has historically had on lake-water DOC dynamics in this region, but also suggest that DOC levels are approaching natural baseline levels in less acid-sensitive lakes, and that other drivers, such as changes in climate or vegetation cover, are now becoming the dominant controls on changes in DOC concentrations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Dissolved organic matter (DOM) concentrations have risen by a factor of two or more across much of Europe and North America during recent decades. These increases have affected the carbon cycle, light regime, drinking water treatability, and the energy and nutrient budgets of lakes and streams. However, while trends in DOM quantity are well characterised, information on how/whether qualitative properties of DOM have changed are scarce. Here, we describe over 40 years of monitoring data from a forested headwater stream in the Gårdsjön experimental catchment, southwest Sweden, which provides a unique record of biogeochemical change, including optical and stoichiometric DOM quality metrics, spanning the entire period of recovery from acidification. For the period 1980–2020 we find a 71% reduction in decadal mean sulphate concentrations, and a similar reduction in inorganic aluminium concentrations, alongside a 64% increase in dissolved organic carbon (DOC) concentrations. Over the same period, colour (absorbance at 420 nm) increased almost twice as much as DOC, whereas dissolved organic nitrogen (DON) increased by only one third as much. These results demonstrate a shift in stream water composition, with DOM becoming dominated by highly coloured, complex, nitrogen-poor compounds. This material is likely more resistant to biological degradation, but more susceptible to photochemical degradation. Changes in DOM stoichiometry could lead to intensified nitrogen and/or phosphorus limitation in surface waters, while increased colour/DOC ratios could intensify light-limitation of primary production beyond that expected from DOC increases alone. We observed increases in organic matter associated metals (iron 117%, organically complexed aluminium 85%) that exceeded the increase in DOC, consistent with their increased mobilisation by more aromatic organic matter. All observed changes are consistent with recovery from acidification being the primary driver of change, implying that past acidification, and ongoing recovery, have profoundly affected terrestrial and aquatic biogeochemistry, ecology and the carbon cycle. [ABSTRACT FROM AUTHOR]

Atmospheric acid deposition disrupted terrestrial-aquatic carbon cycling by drastically lowering dissolved organic carbon (DOC) loads in many lakes across NE North America and northern Europe during the 20th century. However, little is known about how acid deposition has altered the role of lakes as long-term carbon sinks. We present contemporary (n = 80) organic carbon accumulation rates (OCAR) and OCAR trends over the past ~ 150 years (n = 8), and other supporting infrared spectroscopic, isotopic, and elemental geochemical proxies, for lakes in and near Sudbury, Ontario, Canada – an area heavily affected by acid deposition from smelting activities in the late-19th and 20th centuries. Contemporary OCAR varied between 4.9 and 35.3 g m–2 yr–1 among study lakes (mean: 13.5±6.4 g m–2 yr–1). Sediment-inferred trends in lake-water DOC showed a strong response in DOC loadings to the effects of acid deposition during the past century, which is corroborated by increasing observed lake-water DOC concentrations (i.e., lake browning) since the 1980s. Despite these changes in DOC, as well as changes in water acidity, only lakes with direct physical watershed disturbances showed short-lived increases in OCAR, whereas OCAR changed little in remote Sudbury-region lakes with minimal direct human disturbances (mean OCAR: 14.3 ± 8.7 g m–2 yr–1). This is in stark contrast to many other northern forest lakes with minimal direct catchment disturbances that experienced significant increases in OCAR during the 20th century. Our results caution that lake browning may not be a dominant driver behind the widespread increase in organic C burial in northern lakes during recovery from acid deposition in recent decades. [ABSTRACT FROM AUTHOR]

In a natural lake of southeastern Brazil (Lake Carioca), the current scarcity of limnetic cladocerans is attributed to the predatory activity of the dipteran Chaoborus larvae. The Inverted Trophic Cascade Hypothesis (ITCH) predicted that such predation pressure intensified after the decrease in native planktivorous fish populations, due to non-native piscivorous fish introductions. However, the ITCH is mainly based on recent data obtained when the non-native piscivorous fish have already disturbed the community of this Neotropical lake. In the present study, we used a paleolimnological approach aiming to provide evidence in support of ITCH. Specifically, we evaluated: (1) whether a great numerical increase of Chaoborus larvae and a sharp decline in the number of small cladocerans (Bosminidae) occurred in the recent past of Lake Carioca, and (2) whether the Bosmina tubicen size structure changed temporally in response to the dominant predator (from planktivorous fish to Chaoborus larvae). Samples from one sediment core collected in the deepest zone of the lake were concurrently used for radiometric dating, quantification of invertebrate subfossils, and measurement of B. tubicen size attributes. The radiometric dating was based on the analysis of 210Pb. Although we recorded an evident decline of Bosmina subfossils after the introduction of non-native piscivorous fish, we did not observe an increase of Chaoborus subfossils. Significant increases in the mean lengths of carapaces and mucros of B. tubicen were detected in Lake Carioca after the dominant predation regime changed from planktivorous fish to Chaoborus larvae. Despite the statistical significance, the differences for both attributes exhibited a small effect size and likely had limited ecological implications on the dynamics of local food web. Our results support one of the assumptions of the ITCH; showing that the negative effects of non-native piscivorous fish were not restricted to their prey (native planktivorous fish), but cascaded down, reaching the lower trophic levels (small limnetic cladocerans). This finding has relevant implications for the conservation and management of biodiversity in Neotropical lakes. It reinforces the need to better plan and control activities that historically have contributed to the spread of piscivorous fish outside their original areas such as aquaculture and sport fishing. [ABSTRACT FROM AUTHOR]

This research paper focused on the monitoring of marine sites using mussels, which are highly valuable organisms in assessing environmental health. However, a significant challenge arises when determining the appropriate size of mussels for monitoring purposes. The objective of this study was to examine the levels of Cd, Pb, As, and Co in three different size classes of two mussel species, Mytilus galloprovincialis and Perna perna, collected from three sites along the Algerian coast, each exhibiting varying degrees of pollution. At each of the study sites, a total of thirty individuals from small, medium, and large size classes of mussels were collected during four different time periods. The mussels were then dissected, and the concentrations of Cd, Pb, As, and Co were measured in the entire flesh of the mussels using ICP-MS. Across the various study sites, the concentrations of cadmium, lead, arsenic, and cobalt ranged from 0.06 to 1.32 mg/kg, 0.09 to 12.56 mg/kg, 4.23 to 18.31 mg/kg, and 0.11 to 1.85 mg/kg, respectively. Interestingly, the distribution of these metals in the three different size classes of mussels followed a consistent pattern at all the study sites. Large mussels exhibited higher concentrations, while small and medium-sized mussels displayed lower levels. These findings highlight substantial spatial and temporal variations in metal concentrations within the studied sites. [ABSTRACT FROM AUTHOR]

Assemblages of infralittoral periphytic algae are understudied due partially to the historical emphasis on phytoplankton and other water-column characteristics to evaluate the integrity of lentic systems. We tested the null hypothesis that characteristics of epilithic algal assemblages at infralittoral sites in reservoirs of Middle and East Tennessee do not infer trophic state. One infralittoral site in five mesotrophic and five eutrophic reservoirs in Middle and East Tennessee was sampled to determine the relative abundance of the most common epilithic diatoms and soft algae, concentrations of epilithic chlorophyll (chl) a, and water concentrations of chl a, total phosphorus (TP), and total nitrogen (TN). The concentration of epilithic chl a correlates significantly to the concentration of TP but not to TN as determined by the probability values for Pearson's correlation coefficients. The water concentration of chl a does not correlate significantly to concentrations of TP, TN, or epilithic chl a. Trophic-state indicator values for 162 epilithic diatom taxa and 102 epilithic soft-algal taxa are calculated as the abundance-weighted average of the concentration of epilithic chl a normalized between 0 and 100. The trophic-state indicator values indicate the relationship of the abundance of algal taxa to trophic state and contribute to our limited knowledge of the effects of eutrophication on infralittoral algal taxa. Trophic-state indices are calculated as the mean abundance-weighted average of trophic-state indicator values for algal taxa of an assemblage. The index values infer the trophic state of the sites and are the first to use epilithic concentrations of chl a as opposed to water-column characteristics to indicate trophic-state optima for periphytic algae of lentic systems. The indices are easy to calculate and provide novel tools to help evaluate and monitor the trophic state of infralittoral sites in reservoirs of Middle and East Tennessee. [ABSTRACT FROM AUTHOR]

The freshwater ecological characteristics in terms of the daily inventory of thermal stratification, spatial variation of O 2 distribution, and the mobility of potentially toxic elements (PTEs) at the water sediment interface (WSI) are prudent freshwater assessment indices for water quality management protocol. The study conducted daily observations within a monsoon-influenced region, utilizing high-resolution techniques such as HR Peeper, Yellow Spring Instrument (YSI), and ZrO-Chelex diffusive gradient technology (DGT) to analyze PTEs, specifically phosphorus (P) and iron (Fe),within the water-sediment interface (WSI) under different temperatures and oxygen conditions. The 66-day field study showed that high thermal structure contributed significantly to production Fe ions and P from sediment under reductive dissolution of FeOOH. The study also revealed that P and Fe exhibited comparable spatial distribution patterns at the WSI, indicating a linked relationship between these PTEs. This correlation was reinforced by high Pearson correlation coefficients ranging from 0.7 to 0.9 (bilateral, p < 0.05) indicating that the concentrations of labile P were predominantly influenced by the release of phosphorus bound to iron. The fluxes of the PTEs were positive with a range of Fe, 3.3-81.5 mg/m 2 day and P, 0.03-0.5 mg/m 2 day showing the sediments liberated the PTEs into the benthic water. Again, high positive fluxes (Fe≈60 mg/m 2 day, P≈0.5 mg/m 2 day) for PTEs were obtained when stratification was high (anoxic conditions) and low (Fe≈5 mg/m 2 day, P≈0.08 mg/m 2 day) when stratification did not exist. This depicts that Fe/P dynamics were hinged mainly on hypoxic conditions in the benthic water under the reductive dissolution of FeOOH. The findings showed that organic materials (both solid and dissolved) correlated (> 0.7) significantly with (positive high values) Fe. This indicates that their interaction contributed to the reservoir water deterioration. However, Ca 2 ⁺ and Mg 2 ⁺ had little impact on the liberation of Fe-DOC-P from sediments due to their inability to compete with Fe for binding to DOC and P, as shown by their low correlation values. The research provides in-depth insights into the dynamics of PTEs on a daily timescale and offers valuable information for water management practices in inland reservoirs, particularly concerning the cycling of phosphorus (P) and its effects on ecosystem health., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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]

Plastic production is increasing rapidly at a global scale and microplastics are widely distributed in aquatic ecosystems and food webs. As filter feeders, bivalves present entry points for microplastics into food webs and numerous descriptive and experimental studies have addressed microplastic size selection by bivalves. However, much less is known about size selection of microplastic fibers by bivalves. This represents a gap in understanding of how microplastics impact bivalves and food webs, particularly given the numerical dominance of microplastic fibers in freshwater and marine ecosystems and in bivalve tissue. To address this gap, we tested two hypotheses: (1) the net accumulation of polyester fibers in zebra mussels (Dreissena polymoropha) is dependent on fiber size and (2) zebra mussel size impacts the amount of plastic fibers accumulated. We conducted two experiments to test these hypotheses. In the first experiment, we exposed zebra mussels to pink polyester fibers (PPF) of four different lengths (0.25–2.0 mm), offered separately. In the second experiment, we exposed mussels with PPF of three different lengths (0.25–1.0 mm) in a mixture. Both hypotheses were supported. In each experiment, PPF of the smallest size (0.25 mm) disproportionately accumulated in the mussels. In addition, PPF accumulation of 0.25 and 0.50 mm PPF increased as zebra mussel shell length increased. Our results have implications for how microplastic fibers in water columns may impact bivalves and their food webs and demonstrate that size distribution should be considered when sampling bivalves for microplastics in ecosystems. [ABSTRACT FROM AUTHOR]

Diatoms are powerful biomonitoring indicators for contemporary and past limnological conditions, provided that their environmental optima are well-defined. Surface-sediment-calibration (or training) sets are widely used to develop quantitative transfer functions linking species distributions to limnological variables. Accurate estimates of each taxon's environmental optimum benefit from a large dataset spanning a broad gradient of the variable of interest. Here, we compiled data from surface-sediment-diatom analyses from over 450 lakes in Ontario (Canada) to identify ecological optima for the province's most common taxa. The data were collected from the same laboratory using similar methods and spanned more than three decades of research (1987–2019) on 546 samples (representing 464 unique sites). We describe the ecological responses of 52 common diatom taxa to three limnological variables that are key to lake management: pH, total phosphorus (TP), and maximum lake depth. The gradients were broad (pH: 4.2–9.3; TP: 1.1–96.8 µg L−1; maximum depth: 0.7–95.0 m), enabling robust statistical analyses. We used hierarchical logistic regression modelling to identify statistically significant ecological response curves for all common taxa, and weighted averaging to identify the optima. In our dataset, 96% of common diatom taxa had significant ecological responses and optima for pH, 81% for TP, and 83% for depth. Aside from the benthic cosmopolitan Achnanthidium minutissimum complex (occurring in 88.1% of samples), the most frequently recorded taxa were planktonic, including Discostella stelligera/pseudostelligera (83.2%), Asterionella formosa (77.8%), and the Lindavia bodanica complex (76.6%). Our results illustrate the responses of diatom taxa across key limnological gradients, providing important autecological information to advance their use as bioindicators in environmental assessments. These data can be used to address management and knowledge gaps in understudied areas of Ontario where calibration sets are not available and can support research in regions with similar limnological environments and diatom communities. [ABSTRACT FROM AUTHOR]

Plastic pollution has emerged as a prominent environmental concern over recent decades, particularly due to its critical implications for seafood safety. In light of this, an investigation was conducted to assess the abundance and characteristics of microplastics (MPs) in Unio mancus Lamarck 1819, a freshwater bivalve inhabiting Atatürk Dam Lake in Türkiye. For the MPs analysis, a total of 20 U. mancus Lamarck 1819 specimens were collected from the lake, with shell lengths ranging from 7.7 to 10.1 cm and soft tissue weights varying from 21.46 to 49.1 g. The findings of this study revealed the presence of MPs-like particles in 12 out of the 20 mussels, with a total count of 42 particles. MPs concentration ranged from 0 to 9.9 MPs per individual, with an average of 1.89 ± 0.57 MPs per individual. When considering the soft tissue weight, MPs concentration ranged from 0 to 50.51 MPs per 100 g, with a mean of 6.91 ± 2.56 MPs per 100 g. µ-Raman analysis further confirmed that 90% of the particles were composed of various polymers. Among these, polypropylene (PP) constituted 40%, polyethylene (PE) accounted for 20%, polyethylene terephthalate (PET) comprised 10%, Nylon-6 constituted 10%, and cellulose represented 10% of the identified particles. Notably, fragments were the predominant shape observed in the samples, and the majority of MPs were less than 100 µm in length. This study provides valuable foundational data for establishing frequent MP monitoring routines in freshwater environments, considering that bivalves serve as key vectors of MP contamination in the context of human exposure. [ABSTRACT FROM AUTHOR]

In general, lakes provide various ecosystem services that support biotic habitats and human life. Lake Toba, the largest caldera volcanic lake in the world, has been functioning as a tourism destination and for fish farming, a fresh water source, and for power supplies. The lake has maximum depth of about 505 m. Stratification in the lake water column especially in a tropical region like Indonesia is a common phenomenon. Stratification of the lake is one important factor which will influence the next stage in the biological processes and water quality of the lake. The objective of the current study was to analyze and elucidate the stratification of Lake Toba through the variations of physical, chemical, and isotopic parameters. Water temperature, dissolved oxygen concentrations, water chemical contents, and isotopic parameters were observed periodically from 2016 until 2019. Fourteen sampling points evenly distributed across the surface of the lake were predetermined to represent the North, South, East, and West of the lake. A conductivity, temperature, and depth (CTD) device and Baro-divers were used to measure temperature and conductivity at various depths in the water column for each sampling point. The water samples for isotopic and chemical parameter measurements were collected from water depths of 0, 20, 40, 60, 80, and 100 m using a horizontal transparent acrylic water sampler at each sampling point. Some results from isotope analysis showed that all the water at all levels along the water column had undergone evaporation. Although there were some slight fluctuations, the chemical composition of the lake water was relatively homogenous up to 100 m of depth. The chemical pattern suggested that there was no other secondary process that altered the chemical composition of the lake water, thus the lake water and river water had the same facies. The stratification of Lake Toba was found to be permanent. The depth of the hypolimnion layer was consistently at about 80 m below the surface. However, the depth of the upper layer, the epilimnion, was strongly affected by the climate at the surface of the lake. [ABSTRACT FROM AUTHOR]

Laird KR, Li S, Gushulak CAC, Moir KE, Wang Y, Leavitt PR, Cumming BF. 2023. Influence of cultural eutrophication, climate, and landscape connectivity on 3 Kawartha lakes (Ontario, Canada) since the early 1800s. Lake Reserv Manage. 39:120–140. Paleolimnological analyses of 3 lakes within the Trent-Severn Waterway (TSW) were examined to evaluate the role of regional land-use practices (forestry and agriculture), climate change, and landscape position on cultural eutrophication and lake response over the past ∼200 yr. The lakes were selected to represent lake position along the chain of lakes of the TSW; these 3 lakes vary in lake-water conditions from a lower nutrient headwater lake (Cameron Lake) to more nutrient-rich sites (Pigeon and Stony lakes) downstream. Diatom-inferred total phosphorus (TP) concentrations estimate that all lakes had TP levels of ∼15 µg/L in the 1700s, which increased to ∼20–30 µg/L in the 1800s and 1900s. Significant changes in diatom and Cladocera assemblages circa the 1830s are consistent with increased water levels and elevated phosphorus conditions associated with the intensification of forest harvest, agriculture, and development of the TSW. Diatom-inferred TP levels varied among lakes since the early 1900s, declining in Cameron Lake, increasing in Pigeon Lake, and stabilizing in Stony Lake, reflective of landscape position, degree of water inflow from the northern forested regions, and responsiveness of basins to point-source nutrient reductions and climate change. Timing of changes in TP, and changes in planktonic community composition varied among lakes. Lake production (as pigments) increased coherently in 2 lakes over the past ∼20 yr, and modern algal composition (diatoms and pigments) are lake specific and unique in comparison to the last ∼200 yr, likely reflecting combined effects of climate change and changes in nutrient loading. [ABSTRACT FROM AUTHOR]

Doucet C, Johnston L, Hiscock A, Bermarija T, Hammond M, Holmes B, Smith T, Lalonde B, Parent D, Deacoff C, Scott R, Kurek J, Jamieson R. 2023. Synoptic snapshots: monitoring lake water quality over 4 decades in an urbanizing region. Lake Reserv Manage. 39: 101–119. Synoptic water quality surveys—measuring major ions, nutrients, pH, organic matter, and trace elements—have been conducted in ∼50 lakes in the Halifax Regional Municipality (Nova Scotia, Canada) once per decade since 1980. In this study, lake water quality over 40 yr was examined and urban development was evaluated as a possible driver of observed changes. More than half of the lakes experienced strong (>50%) increases in conductivity, iron, sodium, chloride, calcium, and total phosphorus (TP), and strong decreases in acidity (i.e., [H+]). Between 20% and 50% of the lakes experienced strong increases in nitrate, alkalinity, zinc, color, aluminum, dissolved organic carbon, and magnesium, and strong decreases in manganese and sulfate. In 2021, national guidelines for the protection of aquatic life were exceeded by chloride, aluminum, manganese, and arsenic in certain lakes. Land cover classification from circa 1980 and 2020 revealed that although change in urban development within the lake watersheds ranged from a decrease of 11 percentage points to an increase of 48 percentage points, the majority (90%) of watersheds experienced an increase. Urban development was associated with increased chloride, conductivity, sodium, calcium, and TP concentrations. Other parameters appear to be more influenced by hydrology, watershed characteristics, climate, and decreased acid deposition. Results highlight emerging water quality concerns, such as elevated aluminum concentrations, and increased concentrations of chloride, nutrients, and arsenic, which should be the focus of strategic monitoring and mitigation efforts. [ABSTRACT FROM AUTHOR]

Smelting activities have strongly affected the Sudbury (Ontario, Canada) region since the late-nineteenth century, leading to acidification and metal contamination of local ecosystems. Regulations restricting acid deposition were enacted in the 1970s, after which many lakes exhibited increasing pH and decreasing metal concentrations. Given the documented chemical recovery and potential emergence of new stressors, we used paleolimnological tools to assess the biological recovery processes in three previously acidified lakes, and also to reconstruct the limnological histories of two reference lakes that were relatively unaffected by acidification. Using subfossil diatoms preserved in lake sediments, we show that assemblages from the acidified lakes have not returned to their pre-disturbance conditions but became dominated by an acidophilous planktonic taxon, Asterionella ralfsii var. americana Körner, during the past few decades. Considering that this taxon has a relatively low pH optimum and is mostly found in thermally stratified waters during summers, we suspect that the legacy effects of acidification and climate warming are the main factors driving its recent prosperity. Our study suggests that biological recovery lags chemical recovery in acid-impacted systems, and a return to pre-disturbance biological assemblages may be impeded by newly emerging environmental stressors. [ABSTRACT FROM AUTHOR]

Increasing surface air temperatures and human influences (e.g., agriculture, livestock grazing, tourism) are altering lacustrine ecosystems in the South American Andean páramo, and these influences are evident in changes in the diatom-species composition in sediment cores from the region that span the last ~ 150 years. Existing studies are limited by their short temporal scales and limited spatial extent. We analyzed two sediment cores spanning the last two millennia from the northern (Laguna Piñan) and southern (Laguna Fondococha) Andean páramo of Ecuador to provide a longer-term perspective on lake dynamics. Both lakes show shifts in the dominant diatoms through time. Fondococha diatoms shifted in dominance between two Aulacoseira species and in the planktic to benthic ratio, and these shifts are interpreted as evidence of changing lake level. The inferred shifts are corroborated by changes in sediment geochemistry. Piñan shows a directional shift in the diatom assemblage over the period of the record, from benthic diatoms tolerant of high dissolved organic carbon (DOC), low pH, and low nutrients, to an assemblage characteristic of lower DOC, higher pH, nutrients and lake levels. Shifts in Piñan's diatoms are correlated with tephra layers in the sediment, suggesting that local volcanic deposition may have been responsible for altering the catchment and lake geochemistry. This is supported by relatively high δ13C values in organic matter associated with tephra layers, which become more negative up-section. Our study suggests that remote lakes in spatially heterogenous montane regions act as sentinels of different facets of environmental change and provide insights into Andean ecosystem responses to environmental perturbations. [ABSTRACT FROM AUTHOR]

Microplastics of fibrous shape are esteemed to be the most abundant micro-debris form present in the environment. Despite the occurrence of microfibers in fish may pose a risk to human health, the literature is scarce regarding studies on the contamination in commercial marine fish mostly due to methodological issues. In this study, a versatile approach, able to discriminate among natural and synthetic microfibers according to the evaluation of specific morphological features, is proposed in farmed mussels (Mytilus galloprovincialis). The approach was useful to determine that microfibers were present in 74% of mussel samples, with a mean number of 14.57 microfibers/individual, corresponding to 3.13 microfibers/g w.w. A negative correlation between the size of analysed mussels and the amount of microfibers/g w.w. was detected, showing that smaller specimens contained more microfibers than the larger ones. This work paves the way to further studies aimed to adequately assess the risk that microfibers may pose to marine biota, also considering the commercial value as seafood items of many species of the Mytilus genus and the potential implication for human exposure. [ABSTRACT FROM AUTHOR]

Our planet is being subjected to unprecedented climate change, with far-reaching social and ecological repercussions. Below the waterline, aquatic ecosystems are being affected by multiple climate-related and anthropogenic stressors, the combined effects of which are poorly understood and rarely appreciated at the global stage. A striking consequence of climate change on aquatic ecosystems is that many are experiencing shorter periods of ice cover, as well as earlier and longer summer stratified seasons, which often result in a cascade of ecological and environmental consequences, such as warmer summer water temperatures, alterations in lake mixing and water levels, declines in dissolved oxygen, increased likelihood of cyanobacterial algal blooms, and the loss of habitat for native cold-water fisheries. The repercussions of a changing climate include impacts on freshwater supplies, water quality, biodiversity, and the ecosystem benefits that they provide to society. [ABSTRACT FROM AUTHOR]

The aim of the study was to assess the distribution of heavy metals in the environmental compartments from artisanal and small-scale gold mining (ASGM) activities from Lolgorian, Kenya. The investigation was carried out using Inductively-Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Mercury (p > 0.05) (p = 0.755), arsenic (p = 0.182), and lead (p = 0.430) mean concentrations in soil, water, sediments, and ore were not significantly different. The mean mercury, lead, and arsenic concentrations in the water were 0.66 mg/L, 0.46 mg/L, and 1.25 mg/L, respectively. In sediments, the mean values of Cr (66.65 mg/kg), Zn (45.62 mg/kg), Hg (24.63 mg/kg), Pb (22.35 mg/kg), Cd (0.90 mg/kg), and Mn (613.10 mg/kg) were found to be significantly higher. A positive correlation between ore-tailings (r = 0.971109), tailings-sediment (r = 0.9441036), and ore-sediment (r = 0.9441036), was observed indicating the presence of harmful heavy metals in the environment in excess of national and World Health Organization (WHO) recommended threshold, posing a high risk of multiple human exposure pathways. [ABSTRACT FROM AUTHOR]

Evidence suggests that boreal-lake ecosystems are changing rapidly, but with variable ecological responses, due to climate warming. Paleolimnological analysis of 27 undeveloped northern forested lakes showed significant and potentially climate-mediated shifts in diatom communities and increased carbon and biogenic silica burial. We hypothesize the sensitivity of northern forested lakes to climate change will vary along two physical gradients: one reflecting direct, in-lake climate effects (propensity to thermally stratify), the other reflecting indirect watershed effects (watershed to lake-surface area ratio). We focus on the historical response of algal communities to test our two-dimensional sensitivity framework. Historical algal response was summarized by measures of diatom community turnover, changes in species and diagnostic species groups, and measures of siliceous algal and overall primary production (biogenic silica, carbon burial). Measures of algal production increased across all lake types, with carbon burial proportionately higher in polymictic lakes. Greater diatom community change occurred in deep, stratified lakes with smaller watersheds, whereas diatom species groups showed variable responses along our two-dimensional sensitivity framework. Physical characteristics of lakes and watersheds could serve as predictors of sensitivity to climate change based on paleo-indicators that are mechanistically linked to direct and indirect limnological effects of climate change. [ABSTRACT FROM AUTHOR]

Microplastics have been detected in lake environments globally, including in remote regions. Agricultural and populated areas are known to congregate several inputs and release pathways for microplastic. This study investigated microplastic (50–5000 µm) contamination in five Danish freshwater lakes with catchments dominated by arable land use. The concentrations in sediments (n = 3/site) and the zebra mussel, Dreissena polymorpha (n = 30/site), were calculated and compared with catchment characteristics and environmental parameters. Microplastic concentrations in sediment were relatively low (average 0.028 ± 0.017 items/g dry weight sediment) whilst only a single microplastic was found in the mussels (average 0.067 ± 0.249 items/10 individual). Hence, no relationship between the number of observed microplastics in sediment and mussels could be identified, nor could a relationship between concentration in sediment and environmental parameters. As all lakes studied received their water from moderate to heavily anthropogenically impacted catchments, it was expected that they would be sinks for microplastic with high bioavailability. Based on the results of the present study, D. polymorpha were found to not be contaminated by microplastics in the five study lakes. Thus, our results suggest that these mussels do not interact with microplastics at low concentrations. We speculate that the results on sediment and biota could be explained by several factors related to regional differences in plastic use, species characteristics, sampling size, and the fact that finding no microplastic is not always reported in the scientific literature. Thus, the paper provides insight into the dynamics between the catchment, lake, and biota in systems with low microplastic concentration. [ABSTRACT FROM AUTHOR]

Diatoms are universally recognized as good bio-indicators due to their high diversity and rapid response to environmental and climate changes. This paper explores whether the sedimentary diatom record from Sanjiaolongwan Maar Lake (SJML), northeastern China, reveals variations in seasonal pattern over the past 1000 years. The observed succession in diatom assemblages reveals that between 980 and 1310 CE the small-celled planktonic diatom Discostella pseudostelligera was abundant. Its relative abundance peaked during 1020–1060 CE, indicating that the duration of summer conditions over this interval was the longest within the last millennium. By contrast, the interval between 1470 and 1850 CE was marked by an increase in benthic diatoms pointing to a shortened duration of the ice-free season, and generally cold conditions. During the twentieth century warm period, the succession of eutrophic diatoms and changes in diatom cell size also reveal temperature-controlled seasonal variations in limnological conditions. The differences observed between the diatoms assemblages associated with the two warm periods indicate that the summers of the warmest part of the Medieval Climate Anomaly were longer than that of the current warm period. This result is supported by the diatom record from Erlongwan, another maar lake in the region that differs from SJML by its topographic features and in the level of human impact on its catchment. [ABSTRACT FROM AUTHOR]

Metal leachate from mine tailings has the potential to release toxic metals into the surrounding environment. A single-step extraction procedure mimicking rainwater and a three-step BCR sequential extraction procedure (acid, reducing and oxidizing conditions) were applied to gold (GMT) and silver (SMT) mine tailings. Major (Al, Ca, Fe, Mg, and Mn) and trace metals were monitored to better understand the mobility and geochemistry of these metals when exposed to various environmental leaching conditions. Rainwater extraction released only small quantities of metals, while the three-step BCR extraction was more effective in mobilizing metals from the tailings. Under the acidic conditions of BCR step 1, Ca, Mg, Cd, Cu, and Mn were released in high concentrations. The dissolution of Fe, Ca, and Mg were dominant along with Pb in step 2 (reducing conditions). In step 3 (oxidizing conditions), Fe was the most dominant species together with Co, Cu, Ni, and Se. A high fraction of Al, Be, Cr, Li, Mo, Sb, Tl, and V remained in the residue. From SMT, larger quantities of As, Ca, Cd, and Zn were released compared to GMT. The BCR extraction could be applied to tailings to predict the potential release of toxic metals from mine wastes; however, excessive amounts of Ca and Fe in the tailings could cause carry-overs and incomplete extraction and carry-overs, resulting in a misinterpretation of results. [ABSTRACT FROM AUTHOR]

The Environmental Effects Assessment Panel of the Montreal Protocol under the United Nations Environment Programme evaluates effects on the environment and human health that arise from changes in the stratospheric ozone layer and concomitant variations in ultraviolet (UV) radiation at the Earth's surface. The current update is based on scientific advances that have accumulated since our last assessment (Photochem and Photobiol Sci 20(1):1–67, 2021). We also discuss how climate change affects stratospheric ozone depletion and ultraviolet radiation, and how stratospheric ozone depletion affects climate change. The resulting interlinking effects of stratospheric ozone depletion, UV radiation, and climate change are assessed in terms of air quality, carbon sinks, ecosystems, human health, and natural and synthetic materials. We further highlight potential impacts on the biosphere from extreme climate events that are occurring with increasing frequency as a consequence of climate change. These and other interactive effects are examined with respect to the benefits that the Montreal Protocol and its Amendments are providing to life on Earth by controlling the production of various substances that contribute to both stratospheric ozone depletion and climate change. [ABSTRACT FROM AUTHOR]

We provide a photographic guide and taxonomic diagnosis of Chironomidae larval remains obtained from surface sediments and short cores of 92 waterbodies situated on the Yucatan Peninsula and in Central America, namely Mexico, Belize, Guatemala, El Salvador and Honduras. A total of 101 morphotypes belonging to 64 genera were identified. Chironominae was the most species-rich subfamily represented by 57 morphotypes of 34 genera. The most widespread and abundant genus was Goeldichironomus followed by Chironomus and Polypedilum. Orthocladiinae were represented by 26 morphotypes and 17 genera, with the most common one being Cricotopus. Remains of this subfamily were recorded in only 1 5 of the surveyed lakes. Tanypodinae included 17 morphotypes belonging to 12 genera. Labrundinia along with Ablabesmyia and Coelotanypus were the most common genera. Subfamily Podonominae was represented by the genus Parochlus. We believe that our study includes most of the Chironomidae genera of Central America and will have broad applicability for both paleolimnologists and aquatic ecologists. [ABSTRACT FROM AUTHOR]

Summary: Although protected areas (PAs) play an important role in ecosystem conservation and climate change adaptation, no systematic information is available on PA protection of high-elevation freshwater ecosystems (e.g., lakes and watersheds with glaciers), their biodiversity and their ecosystem services in the tropical Andes. We therefore combined a literature review and map analysis of PAs of International Union for Conservation of Nature (IUCN) and national systems of PAs and freshwater ecosystems. We found that seven national parks were created for water resources protection but were not designed for freshwater conservation (i.e., larger watersheds). High-value biodiversity sites have not been protected, and new local PAs were created due to water resource needs. We quantified 31 Ramsar sites and observed that PAs cover 12% of lakes, 31% of glacial lakes and 12% of the total stream length in the tropical Andes. Additionally, 120 watersheds (average area 631 km2) with glaciers and 40% of the total glacier surface area were covered by PAs. Future research into the role of PAs in ecosystem services provision and more detailed freshwater inventories within and around PAs, especially for those dependent on glacier runoff, will fill key knowledge gaps for freshwater conservation and climate change adaptation in the tropical Andes. [ABSTRACT FROM AUTHOR]

Peninsula Lake, Ontario, Canada, is a Precambrian Shield lake that has experienced many environmental stressors since European settlement of the watershed in the mid-1800s, including forest clearance, water-level management, sewage inputs, and land-use changes. The deterioration of water quality by the 1970s prompted mitigation efforts intended to reduce inputs of nutrients and untreated sewage to the lake. Paleolimnological analysis of a sediment core from Peninsula Lake, collected in 1995, revealed that efforts to address eutrophication had been somewhat successful, in that the lake had returned to oligotrophic status by the early 1990s. Nevertheless, there had been little to no improvement in inferred deepwater oxygen conditions. We used similar paleolimnological techniques on a core collected in 2014 to examine ecological responses to environmental stressors and remediation efforts in the intervening years, with a particular focus on changes in the amount of oxygenated habitat available to lake trout. Specifically, we inferred trends in volume-weighted hypolimnetic oxygen (VWHO), through analysis of sedimentary chironomid assemblages, to assess long-term changes in coldwater fisheries habitat. Potential drivers of VWHO were also investigated, and included diatom-inferred total phosphorus, spectrally derived trends in sedimentary chlorophyll a and its main diagenetic products, and lake-water dissolved organic carbon. The sedimentary chironomid assemblages indicate a long period of VWHO depletion, concurrent with known anthropogenic activities from the early twentieth century to the 1990s, followed by recent recovery to near pre-impact levels. The sedimentary diatom assemblages indicate nutrient enrichment throughout most of the twentieth century, which was also followed by a return to pre-impact conditions, albeit with recent indications of renewed nutrient enrichment. In contrast, strikingly different trajectories were observed in two other regional waterbodies that support lake trout, but experienced relatively little nutrient enrichment over the past ~ 150 years. Peninsula Lake appears to be recovering from nutrient enrichment and hypolimnetic oxygen depletion, but water quality improvements have nevertheless been accompanied by increased primary production, perhaps because climate warming has extended the ice-free season and stratification period. Therefore, instead of returning to pre-impact conditions, Peninsula Lake appears to be developing a novel ecological state. Any future improvements in lake trout habitat that result from nutrient abatement may be offset by rising temperatures. [ABSTRACT FROM AUTHOR]

The influence of lake restoration efforts on lake bottom-water conditions and varve preservation is not well known. We studied varved sediments deposited during the last 80 years along a water-depth transect in the Enonsaari Deep, a deep-water area of the southernmost Enonselkä Basin, Lake Vesijärvi, southern Finland. For the last few decades, the Enonselkä Basin has been subject to ongoing restoration efforts. Varve, elemental, and diatom analyses were undertaken to explore how these actions and other human activities affected varve preservation in the Enonsaari Deep. In contrast to most varved Finnish lakes, whose water columns have a natural tendency to stratify, and possess varve records that span thousands of years, varve formation and preservation in Lake Vesijärvi was triggered by relatively recent anthropogenic stressors. The multi-core varve analysis revealed that sediment in the Enonsaari Deep was initially non-varved, but became fully varved in the late 1930s, a time of increasing anthropogenic influence on the lake. The largest spatial extent of varves occurred in the 1970s, which was followed by a period of less distinguishable varves, which coincided with diversion of sewage from the lake. Varve preservation weakened during subsequent decades and was terminated completely by lake aeration in the 2010s. Despite improvements in water quality, hypolimnetic oxygen depletion and varve preservation persisted beyond the reduction in sewage loading, initial aeration, and biomanipulation. These restoration efforts, however, along with other human actions such as harbor construction and dredging, did influence varve characteristics. Varves were also influenced by diatom responses to anthropogenic forcing, because diatoms form a substantial part of the varve structure. Of all the restoration efforts, a second episode of aeration seems to have had the single most dramatic impact on profundal conditions in the basin, resulting in replacement of a sediment accumulation zone by a transport or erosional zone in the Enonsaari Deep. We conclude that human activities in a lake and its catchment can alter lake hypolimnetic conditions, leading to shifts in lake bottom dynamics and changes in varve preservation. [ABSTRACT FROM AUTHOR]

Lake surveys conducted in 1987–88 and 2018–19 show changes in the chemical and optical properties of Adirondack lakes recovering from acidification. Among chronically acidified lakes (1980s pH < 5.5, ANC < 0 µeq L−1), increases in pH and reductions in monomeric Al were accompanied by significant increases in light attenuation, DOC, and CDOM. DOC-specific dissolved color (CDOM:DOC) doubled over the 30-year span, and is the likely factor accounting for loss of water clarity in Adirondack lakes during recovery from acidification. Monitoring data (1994–2002) from a subset of these lakes show that reductions in light attenuation were accompanied by stronger thermal stratification and greater hypolimnetic oxygen depletion. Lakes most affected by acidification experienced greater loss of water clarity during recovery relative to moderately acidified lakes. These findings are consistent with the hypothesis that lake acidification resulted in a reduction in light attenuation by CDOM resulting in greater water clarity in acidified lakes, and that this process has been reversed following regional declines in sulfate deposition. [ABSTRACT FROM AUTHOR]

Silver mining in Cobalt (Ontario, Canada) has a long history that has left a complex environmental legacy where many lakes are contaminated with arsenic-rich mine tailings. In this exploratory survey, we examined subfossil Cladocera remains in the surface sediments of 22 lakes in the abandoned mining region to assess which environmental variables may be influencing the recent assemblage structure. Further, using a "top-bottom" paleolimnological approach, we compared the recent (top) and older (bottom) assemblages from a subset of 16 lakes to determine how cladoceran composition has changed in these lakes. Our regional survey suggests that the cladoceran assemblages in the Cobalt area are primarily structured by differences in lake depth, while site-specific limnological characteristics, including those related to past mining activities, may have limited roles in shaping the recent cladoceran compositions. The top-bottom paleolimnological analysis suggests that the cladoceran assemblages have changed in most lakes around Cobalt, however the magnitude and nature of changes varied across the study sites. As with most regional biological surveys, the responses to historical mining activities were not uniform across all sites, which further emphasizes the importance of considering site-specific limnological characteristics and multiple environmental stressors when assessing the impacts of mining pollution. [ABSTRACT FROM AUTHOR]

A multi-proxy study on a sediment core from Pedro Palo Lake, a mid-altitude endorheic Andean Lake in northern South America, was carried out to understand the effects of human activities and climate variability on tropical mountain freshwater ecosystems. Results indicate that between ~ 7980 and 4110 cal year BP the lake maintained well-mixed, mesotrophic conditions, within which a diverse planktonic and benthic diatom community flourished. From 4110 to about 2050 cal year BP, benthic diatoms almost disappeared, and the planktonic community changed to include small Discostella spp. and large Fragilaria species, suggesting higher nutrient concentrations and possibly, more turbid waters. At this time, peaks in charcoal concentration and in the sedimentary C/N ratio imply that forest fires in the watershed intensified and that more organic matter, derived from terrestrial vegetation, accumulated in the lake. This period coincides with an increase in population, and in the social, technological and agricultural complexity of indigenous peoples. We propose that anthropogenic activities, burning and deforestation, increased the nutrient load to the lake causing the observed changes in the diatom communities. After 2050 cal year BP, periphytic diatoms returned, the intensity and frequency of fires diminished, and a secondary forest grew. We infer an associated decrease in nutrients, resulting from reforestation and/or lower water levels caused by drier climates. Estimations based on the age model of the core suggest that it took approximately 30 years for the lake to change from its most degraded state in the middle Holocene to its state in the late Holocene. However, the much-reduced diversity of the diatom community after ~ 2050 cal year BP indicates that the lake did not rebound to its previous middle Holocene conditions. The record from Pedro Palo is therefore a good example of the detrimental and long-lasting effects of anthropic deforestation. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibetan Plateau region has unique meteorological characteristics, with low air temperature, low air pressure, low humidity, little precipitation, and strong diurnal variation. A two-dimensional hydrodynamic CE-QUAL-W2 model was configured for the Pangduo Reservoir to better understand the thermal structure and diurnal variation inside the reservoir under the local climate and hydrological conditions on the Qinghai-Tibetan Plateau. Observation data were used to verify the model, and the results showed that the average error of the 6 profile measured monthly from August to December 2016 was 0.1°C, and the root-mean-square error (RMSE) was 0.173°C. The water temperature from August 2016 to September 2017 was simulated by inputting measured data as model inputs. The results revealed that the reservoir of the Qinghai-Tibetan Plateau was a typical dimictic reservoir and the water mixed vertically at the end of March and the end of October. During the heating period, thermal stratification occurred, with strong diurnal variation in the epilimnion. The mean variance of the diurnal water temperature was 0.10 within a 5 m water depth but 0.04 in the whole water column. The mixing mode of inflow changed from undercurrent, horizontal-invaded flow and surface layer flow in one day. In winter, the diurnal variation was weak due to the thermal protection of the ice cover, while the mean variance of diurnal water temperature was 0.00 within both 5 m and the whole water column. Compared to reservoirs in areas with low altitude but the same latitude, significant differences occurred between the temperature structure of the low-altitude reservoir and the Pangduo Reservoir (P<0.01). The Pangduo Reservoir presented a shorter stratification period and weaker stratification stability, and the annual average SI value was 26.4 kg/m2, which was only 7.5% that of the low-altitude reservoir. The seasonal changes in the net heat flux received by the surface layers determined the seasonal cycle of stratification and mixing in reservoirs. This study provided a scientific understanding of the thermal changes in stratified reservoirs under the special geographical and meteorological conditions on the Qinghai-Tibetan Plateau. Moreover, this model can serve as a reference for adaptive management of similar dimictic reservoirs in cold and high-altitude areas. [ABSTRACT FROM AUTHOR]

Paul Colinvaux and his Ecuadorian student Miriam Steinitz-Kannan were the first modern scientists to study limnology in Ecuador in the 1960s and 1970s. Fifty years later, Steinitz-Kannan continues this research along with many collaborators, focusing on Andean, Amazonian, and Galapagos lakes, particularly their paleolimnology, physical/chemical parameters, and plankton communities. Historically, Ecuador's inland and Pacific waters were studied and described by European explorers, including Juan de Velasco, Alexander von Humboldt, and Charles Darwin. In modern times, other Europeans followed Colinvaux and Steinitz-Kannan. In the 1990s, Dean Jacobsen extended limnologic studies to Ecuadorian stream ecology, focusing on macroinvertebrates from streams covering wide environmental gradients. In the 2000s, Günter Gunkel intensively studied several Andean lakes in northern Ecuador. In the 2010s, Willem Van Colen and Ecuadorian colleagues continued limnologic research in Andean lakes located in Azuay and Imbabura provinces. The Instituto Antárctico Ecuatoriano has, and continues to, conduct limnological research in Ecuador's Antarctic territory on Greenwich Island. Going forward, Ecuadorian universities are training their students to take the research initiative, inspiring a limnologic renaissance at a critical time when the country's water resources are increasingly threatened by climate change and human impacts. [ABSTRACT FROM AUTHOR]

In recent decades, climate change in Peru's Cordillera Vilcanota has resulted in massive reductions to its cryosphere and the upslope migration of species and agriculture. Little, however, is known about the response of the region's many lakes that support local biodiversity and supply water to downstream populations. We analyzed fossil diatom assemblages in dated sediment cores from three lakes with differing morphometry and catchment characteristics to document the limnological response to climate variability over the late Holocene. The study lakes contained similar dominant diatom taxa but recorded markedly different assemblage shifts over time. The two deeper lakes, Laguna Sibinacocha (zmax = 92 m) and Chaca Cocha (zmax = 18 m), contained diatom assemblages that oscillated in dominance between benthic fragilarioids (Staurosirella pinnata, Pseudostaurosira brevistriata) and the planktonic Discostella stelligera. The Chaca Cocha diatom record closely matched the mean state changes in climate inferred from independent proxy records, whereas the record from the glacially influenced Laguna Sibinacocha did not match independent records. In contrast, the shallow study site, Lado del Quelccaya (zmax = 5 m), recorded a complacent diatom profile dominated by benthic fragilarioids with negligible planktonic taxa. The disparate diatom trajectories among the study lakes reflect variations in morphometry and glacial influence and the assemblage shifts appear best explained by climate-driven alterations to thermal stratification. These data offer insight into the primary mechanisms driving limnological change in this region and how different lake types throughout the Andes may respond to future warming. [ABSTRACT FROM AUTHOR]

While deposition of reactive nitrogen (N) in the twentieth century has been strongly linked to changes in diatom assemblages in high-elevation lakes, pronounced and contemporaneous changes in other algal groups suggest additional drivers. We explored the origin and magnitude of changes in two mountain lakes from the end of the Little Ice Age at ca 1850, to ca 2010, using lake sediments. We found dramatic changes in algal community abundance and composition. While diatoms remain the most abundant photosynthetic organisms, concentrations of diatom pigments decreased while pigments representing chlorophytes increased 200–300% since ca 1950 and total algal biomass more than doubled. Some algal changes began ca 1900 but shifts in most sedimentary proxies accelerated ca 1950 commensurate with many human-caused changes to the Earth System. In addition to N deposition, aeolian dust deposition may have contributed phosphorus. Strong increases in summer air and surface water temperatures since 1983 have direct and indirect consequences for high-elevation ecosystems. Such warming could have directly enhanced nutrient use and primary production. Indirect consequences of warming include enhanced leaching of nutrients from geologic and cryosphere sources, particularly as glaciers ablate. While we infer causal mechanisms, changes in primary producer communities appear to be without historical precedent and are commensurate with the post-1950 acceleration of global change. [ABSTRACT FROM AUTHOR]

Continuous temperature monitoring for two adjacent tropical crater lakes in Mexico at 4200 m amsl shows that the lakes have rhythmic episodes of heating and cooling with a duration of ~ 30 days during the warmest months. The episodes were caused by rise and decline of solar irradiance reaching the lake surface. One lake, El Sol, showed over each heating and cooling episode a stable mixed layer (~ 20 days) and a deeper layer with a weak thermal gradient. Temperatures below the mixed layer warmed progressively by eddy diffusion after the mixed layer formed. Stratification was followed by full mixing of the water column. Within the same crater, an adjacent second lake, La Luna, showed the same cycles of heating and cooling; it stratified daily but not over multiple days. The difference between the lakes (discontinuous polymictic, continuous polymictic) is explained by the lower transparency of El Sol, which led to greater heat uptake near the surface than the more transparent La Luna. Lower transparency of El Sol was caused by modest anthropogenic effects on total suspended solids and nutrient loading, i.e., small deviations from the natural condition of El Sol caused it to differ qualitatively from La Luna. Events observed in these lakes would not have been evident from weekly temperature records. [ABSTRACT FROM AUTHOR]

Pre-Hispanic artifacts and sacred architecture were recently discovered submerged in a large lake (Laguna Sibinacocha) in the Peruvian Andes. The underwater ruins indicate a dramatic shift in the region's hydrology but the timing and triggers of this shift remain unknown. In a novel approach blending archaeology and paleoecology, we analyzed a sediment sequence from within one of the recovered artifacts, specifically a pot from the Late Intermediate Period (~1000–1400 CE). Radioisotopic dating of discrete sediment intervals sampled from the pot show a stratigraphically intact profile that preserves a history of change at this site. The pot's basal sediment age places the timing of lake-level rise at ~1600 CE, which post-dates the end of the Inca Empire (1400–1532 CE) by several decades. The ubiquity of planktonic algae throughout the sediment profile suggests water levels remained high above the pot since its submergence. Paleoclimate data from the nearby Quelccaya ice core records indicate lake flooding followed a pronounced wet period beginning ~1520 CE. These data show the permanence of mean state changes in climate on the region's hydrology, with clear implications for the study site (an important water resource for ~500,000 people) and other lakes in the rapidly warming Andes. [ABSTRACT FROM AUTHOR]

Functional traits are ecologically relevant characteristics of species. They are relevant to community structuring in face of environmental drivers (response traits) and to ecosystem processes (effect traits). For planktonic microcrustaceans, the link between functional traits and their responses or effects is not always clear. Our objective was to review the literature on linking functional traits to environmental drivers and ecosystem processes for planktonic cladocerans and copepods. Response traits are discussed in four categories: morphological, life history, behavioral, or physiological. Temperature, predation, resources, and stressors are important drivers of morphological and life-history traits. Body size, a morphological trait, is probably the most important trait, because it responds to several environmental characteristics and is correlated with physiological traits and to zooplankton impact on ecosystems functions. In an ecosystem perspective, zooplankton is an important energy link between primary producers and secondary consumers. In trophic webs, it may control phytoplankton biomass and productivity, with consequences for whole lakes. Its influence on carbon, nitrogen, and phosphorus cycles is expected to increase with body size. Other traits may be important, but there is a lack of information. We point out the need of more functional trait research, especially with freshwater copepods and neglected tropical species. For a better understanding of natural systems, an integrative approach of multiple traits with multiple environmental drivers and ecosystem functions is necessary. [ABSTRACT FROM AUTHOR]

Sedimentary postabdominal claws, among other remains, have been used successfully in paleolimnological studies to reconstruct past environmental conditions and the distribution pattern of certain Daphnia species. However, morphological analysis of postabdominal claws has not proven adequate for the clear taxonomic differentiation among species within a complex, such as the Daphnia pulex complex. The presence of the invasive North American (NA) D. pulex lineage was recently detected in an alpine lake in the Sierra Nevada mountain range (Southeast Spain). This lineage has spread throughout Africa and the Mediterranean basin, suggesting a trend towards its increased presence in Europe. The aim of this study was to examine whether this invasive lineage could be differentiated from the native European (Eu) Daphnia pulicaria lineage based on morphological differences in postabdominal claws recovered from three alpine lakes in the Sierra Nevada. The most useful differential variables were the postabdominal claw length (PCL), ratio of distal comb length to PCL (Cldist/PCL), and number of stout spines. Thus, NA D. pulex may be identifiable by a short PCL, low Cldist/PCL value and the presence of < 5 stout spines. Because of a wide variability in PCL within the Eu D. pulicaria species and an overlap in stout spine number between the species, morphological analysis results cannot unequivocally differentiate these lineages. However, they make a useful contribution to recognition of the possible presence of this invasive lineage. The present findings assist identification of the invasive NA D. pulex lineage in potentially affected regions, facilitating reconstruction of its historic dispersion and colonization. [ABSTRACT FROM AUTHOR]

Dickson Lake, located in Algonquin Provincial Park, Ontario, is a remote, oligotrophic lake, where cyanobacterial blooms of the genus Dolichospermum (Ralfs ex Bornet & Flahault) P. Wacklin, L. Hoffmann and J. Komárek were reported for the first time in the fall of 2014, and subsequently in the late spring of 2015. To investigate the potential environmental triggers of these bloom events, we assessed long-term trends in water quality using a multi-proxy paleolimnological approach, examining sedimentary diatoms, chironomids, cladocerans, spectrally inferred chlorophyll a, and cyanobacterial akinetes preserved in a 210Pb-dated sediment core. Assemblage changes were modest in all biological proxies. A subtle increase in the abundance of warm-water chironomid taxa (Topt > 15 °C) commences in the year ~ 2000, with further increases in the most recent years of the sediment record (~ 2013–2015). End-of-summer volume-weighted hypolimnetic oxygen concentrations (CI-VWHO), inferred from chironomid remains, reveal a decline in oxygen concentrations over the last two decades coincident with the highest levels of sedimentary chlorophyll a and cyanobacterial akinetes in the sediment record. These paleolimnological findings corroborate observed reports of the onset of cyanobacterial blooms in Dickson Lake in late 2014 and are consistent with increasingly favourable bloom-forming conditions over the past few decades that are related to warmer air temperatures, sharp declines in wind speed, and a lengthening of the ice-free season by 2 weeks since 1975. It is plausible that late ice-out and a quick onset to stratification in 2014 may have resulted in incomplete spring mixing, early onset of hypolimnetic anoxia, and increased internal nutrient loading, that, occurring during a period when climate conditions were particularly ideal for cyanobacterial proliferation, may have fueled the unprecedented algal blooms in this remote lake. Collectively, the factors causing algal blooms in remote lakes such as Dickson Lake are not yet fully understood, and it is worrisome that with continued warming the triggering conditions may become a more common feature of Algonquin Park and other minimally impacted Boreal Shield lakes in the coming years. [ABSTRACT FROM AUTHOR]

Understanding and managing the responses of natural systems to climate change requires knowing whether recent changes in ecosystem structure and function are within the bounds of natural variation or whether the systems are entering new states that are unprecedented. Several recent studies of the fossil diatom record of the last ~ 150 years in Andean lakes have shown changes in diatom species composition that suggest changes in lake thermal structure in response to regional climate warming. Yet these paleolimnological records are only a few hundred years in length, so it is unclear whether the systems have entered new states, with potentially severe consequences for ecosystem structure and function, or whether current trends are within the natural variability of the systems. Here, we use a recently compiled diatom database from tropical South America to explore the regional distribution and ecological controls of selected planktic diatom taxa that are associated with warming and changes in the lake thermal structure. We also review published Andean stratigraphic records that span thousands of years to characterize the long-term dynamics of relevant planktic species in response to past climate change. The contemporary data show that many planktic taxa have broad latitudinal and elevational distributions. The distributions of several taxa are correlated with surface water temperature, but most also are correlated with pH and/or conductivity. A review of existing stratigraphic data from Andean lakes demonstrates that rapid changes in diatom abundance, including abrupt increases followed by decades to centuries of near extirpation, are a common mode of population variation for some planktic taxa. Yet the majority of these published paleolimnological investigations are of lakes that are larger and differ in nutrient status and conductivity from the small dilute systems where recent species shifts have been observed. We propose that assessing the resilience of contemporary diatom communities and, by inference, lake ecosystems is best done by generating new records from Andean lakes of varied size and chemistry that span a millennium or more and hence a broader spectrum of climate conditions, coupled with new ecological and biogeographic studies that build upon ongoing research programs in the tropical Andes. [ABSTRACT FROM AUTHOR]

Sparse monitoring of New Brunswick (Canada) lakes creates challenges for understanding mechanisms of deteriorating water quality, such as recent instances of increased cyanobacterial biomass in low-nutrient systems. To assess long-term environmental change experienced by low-nutrient, dimictic New Brunswick lakes we use sedimentary remains of algal pigments and Cladocera in dated cores from impact (prone to late-summer algal blooms, Lac Unique) and reference (no observed algal blooms, First and States) lakes. Overall, all three lakes now exhibit greater bosminid abundance and fewer daphniids, lower Cladocera richness, and smaller average cladoceran body size, although some lake-specific differences in assemblage response exist that cannot be related solely to top-down or bottom-up forces. Zooplankton trends are most pronounced at Lac Unique and First Lake, where algal production is generally greater. Across all three lakes, the only significant (IndVal: p < 0.05) cladoceran bioindicator of the post-1990 period is the pelagic bosminid group, whereas prior to ~ 1990, Daphnia longispina-complex and several littoral taxa were significant (IndVal: p < 0.05) bioindicators. These temporal shifts suggest that the smaller-bodied bosminid group may now be favored over its larger-bodied pelagic competitor Daphnia sp. in these lakes, irrespective of heterogeneous long-term algal patterns inferred from stable sedimentary pigments. We suggest that the indirect effects of climate change, principally during the spring and summer quarters in New Brunswick, may be associated with marked shifts in limnological structure, as evidenced by changes in dominant zooplankton of the pelagic zone. However, further research is needed to rule out whether or not size-selective predation, and its potential interactions with climate change and other stressors, are key mechanisms favoring increased bosminids in low-nutrient, dimictic lakes. [ABSTRACT FROM AUTHOR]

A paleolimnological approach was used at 45 mostly remote, low-nutrient lakes in New Brunswick (NB), Canada, to determine bioindicator responses and lake sensitivity to post twentieth century environmental change. From each undated core we assessed zooplankton (Cladocera) change between discrete time periods using related assemblage metrics, including the rise of Bosmina sp., cladoceran richness, and average assemblage body size. Cladocerans from a pre-industrial interval (20–20.5 cm) were compared to those from a present-day interval (0–0.5 cm). Lakes were then classified as either high- or low-sensitivity based on assemblage metrics, and sensitivity group differences in physical–chemical measures were tested for significance. Compared to pre-industrial times, Bosmina sp. relative abundance increased in 33 of 43 lakes (75% of lakes surveyed) by on average 20%. Body size and rarefied species richness of assemblages decreased significantly. These ecological shifts detected at an important intermediate trophic level are attributable to indirect effects of climate change, although we cannot rule out shifts in fish predation and littoral habitat as additional structuring factors. Eighteen lakes were classified as high-sensitivity lakes and showed significant differences in latitude, surface area, elevation, dissolved calcium and magnesium concentrations, and conductivity compared to 25 low-sensitivity lakes. In high-sensitivity lakes, richness decreased on average by 6 species and body size decreased by 0.2 mm. This study presents a historical context for constructing effective conservation and management efforts at a time of substantial environmental change in low-nutrient NB lakes. [ABSTRACT FROM AUTHOR]

The paper presents the results of time-related changes in maximum temperatures in lakes. The analysis was carried out on the basis of 9 lakes located in the northern part of Poland. The analysis was based on daily water and air temperatures in the period 1971–2015. Mann–Kendall's and Sen's tests were applied to determine the directions and rates of change of maximum air and water temperatures. The average increase of maximum water temperature in analysed lakes was found to be 0.39 °C dec–1, while the warming trend of the maximum air temperature was 0.48 °C dec–1. Cluster analysis (CA) was used to group lakes characterised by similar changes of maximum water temperature. The first group included five lakes in which the values of the maximum temperature trends were 0.41 °C dec–1. In the second cluster the average value of maximum water temperature increase was smaller than in the first cluster (0.36 °C dec–1). Comparing the results of cluster analysis with morphometric data show that in the first cluster lakes are having a greater average depth, maximum depth and water transparency in comparison to the lakes of the second cluster. The study showed significant changes in the maximum annual water temperatures in post-glacial lakes located in Poland in the years 1971-2015. The highest rate of increase in monthly maximum water temperature was recorded in April and the lowest in January and February. The value of maximum water temperature trends was lower than annual air temperature trends. [ABSTRACT FROM AUTHOR]

Lakes of the Andean páramo are critical water reservoirs for millions of people. Páramo ecosystems have experienced anthropogenic warming faster than the global average. Recent paleolimnological work from Cajas National Park (southern Ecuador) revealed striking shifts in diatoms and Cladocera linked to climate change. However, the impacts on shallow lakes (< 5 m deep), which are numerically dominant on the landscape, remain poorly understood. Here, we use paleolimnology to investigate cladoceran species changes and responses to climate change in three shallow waterbodies from Cajas. Each system supported abundant littoral Cladocera. The deepest site (~ 4 m) contained the highest proportion of pelagic taxa, while the shallowest (~ 0.3 m) contained almost exclusively littoral taxa. Cladoceran assemblages in these shallow lakes reflect littoral habitat, likely partly influenced by shifting precipitation, and in one site, construction of a small rock dam. The cladoceran assemblage shifts do not align with regional temperature increases and reduced wind speeds, contrasting the ecological responses previously recorded in nearby deeper lakes. Although these polymictic, ice-free shallow systems are not immune to climate-related change, algal and cladoceran assemblages in nearby deeper lakes are responding earlier and more sensitively to recent climate changes, largely through changes to lake thermal stratification regimes. [ABSTRACT FROM AUTHOR]

We examined the relationship between cladoceran, limnological, geological and biological variables in a recent sediment sequence to assess the cladoceran community response to flood conditions and human impacts during the last century in shallow Lake La Tembladera, on the southern coast of Ecuador. We recovered three sediment cores from central and littoral locations to analyze cladoceran subfossils and plant macrofossils. Redundancy analysis identified three environmental variables controlling the assemblage composition: the presence of non-aquatic plants, As and Be concentrations in the sediment. Before AD 1925, the surface area of the lake was smaller than it is now and the most representative cladocerans were Euryalona at lower lake levels and Leydigiopsis at relatively higher lake levels. After ca. AD 1925, anthropogenic works increased the lake level and the expanse of the littoral zone, favoring phytophilous cladocerans such as Kurzia. Around ca. AD 1990, the disposal of mining tailings contaminated with arsenic increased cladoceran sexual reproduction (total chydorid ephippia) and favored certain taxa. Our study shows the influence of anthropogenic activities on hydrologic regime, lake stage and heavy metal contamination and our results indicate the environmental trajectory of this lake, as it shifted from more natural to more impacted conditions in the last century. [ABSTRACT FROM AUTHOR]

Mine-fed waters have been rigorously studied, but most of the ecological research on mine water has been conducted in riverine systems. Lakes, however, are known to recover from pollution more slowly than riverine systems and, thus, the impacts of mine water on lakes are equally interesting. One of the most important biological components in lakes are the Cladocera, an order of crustacean zooplankton. Cladocerans are regarded as excellent indicators of environmental change and, for example, genus Daphnia is one of the most used test organisms in ecotoxicology. While in vitro tests regarding pollutants and cladocerans have been reviewed multiple times, the literature regarding the community level responses to mine pollution in natural settings is still to be better explored. The main aim of this paper is to screen and compile the current literature related to cladoceran communities and mine-induced water pollution. In addition, the applicability of cladocerans as a bioindicators group in mine water studies will be explored. This review shows that cladocerans have been studied in many cases of mining related pollution and most of the research has been conducted in North America, central Europe and Brazil. Acidity, turbidity and metals pollution are nearly equally important in shaping cladoceran communities in mining impacted lakes. The most tolerant taxa to mining pollution are Bosmina spp. and Chydorus sphaericus. The group clearly has potential as community level bioindicator/biomonitor in mining pollution studies, but challenges remain. Namely, the lack of data regarding the most sensitive taxa is a major problem when indicator value of any single species is assessed. [ABSTRACT FROM AUTHOR]