Cladoceran Assemblages Research Articles

Trends in sedimentary Cladocera and metal(loid)s from Williams Lake (Washington, USA) track ∼125 years of trans-boundary contamination from smelter emissions in the upper Columbia River valley

The lead‑zinc smelter at Trail (British Columbia, Canada) has operated continuously for ∼125 years, with long-standing concerns that transboundary metal(loid) and sulphur emissions have contaminated water bodies in both western Canada and Washington (WA), USA. To assess aquatic ecosystems affected by over a century of industrial contamination requires an understanding of pre-smelting conditions. Here, we use a dated sediment core from Williams Lake (WA), downwind of both the Trail and the short-lived LeRoi (Northport, WA) smelters, to track regional contaminant history and other environmental stressors. Specifically, we examine a selection of chemical elements, cladoceran assemblages, visible range spectroscopy-inferred chlorophyll a (VRS-Chl a) and visible near-infrared spectroscopy-inferred lake-water total organic carbon (VNIRS-TOC). Sedimentary proxies recorded the onset of smelting in 1896 CE, peak periods of aerial emissions in the early to mid-20th century, and the history of emission controls. With a few exceptions, sedimentary metal(loid)s exceeded Canadian Interim Sediment Quality Guidelines during the height of the smelting era and have declined substantially since ca. 2000 CE. The loss of metal-sensitive Cladocera and declines in primary production (VRS-Chl a) at the onset of the regional smelting era indicate a strong biological response to airborne industrial contamination. The largest cladoceran change in the sediment record was concurrent with accelerated mitigation efforts at the Trail facilities following the 1960s; however, this compositional shift was between ecologically similar daphniid taxa. Steep declines in VNIRS-TOC concentrations during the period of peak emissions at Trail suggested an increase in sulphur deposition on the landscape that reduced terrestrial carbon supply. However, the persistence of calcium-sensitive daphniids throughout the record indicates that alkaline Williams Lake had not acidified. Current cladoceran assemblages remain substantially distinct from pre-industrial communities, demonstrating how paleoecotoxicological approaches can be used to track the effects of multiple stressors in a temporally appropriate context.

Seabird inputs drive changes in Cladocera assemblages in freshwater ponds

Seabirds are biovectors that transport large concentrations of nutrients from their marine feeding areas to terrestrial breeding grounds. Here, we used subfossil cladoceran assemblages to assess if, and how, changes in the world’s largest colony of Leach’s Storm Petrels affected the structure of Cladocera assemblages over the past ~1700 years. Using sediment cores from four ponds impacted by Leach’s Storm-Petrel colonies on Baccalieu Island (NL, Canada), we observed a consistent transition in cladoceran assemblages from benthic/littoral to pelagic taxa in association with high seabird presence. This shift aligns with previously published limnological changes that tracked the growth of the colony. Compared to trends in sedimentary chlorophyll-a, pelagic cladoceran taxa lagged behind algal shifts driven by seabird activity. The main drivers of cladoceran assemblage shifts were likely alterations to the physical habitat structure and food availability driven by seabird inputs. Furthermore, deposition of calcium from seabirds may have also contributed to changing the composition of cladoceran communities. Our study provides information on food web shifts associated with seabird-driven eutrophication, which can be compared to future paleoecological studies.

Impacts of hydrologic management on the eutrophication of shallow lakes in an intensive agricultural landscape (Saskatchewan, Canada)

Abstract Hydrologic management of shallow lakes is often undertaken to prevent fluctuations in lake level, and to ensure sufficient water volume for economic, domestic, and recreational uses, but there is inconsistent evidence of whether lake‐level stabilisation through hydrological management promotes or hinders eutrophication. Here we used multi‐proxy paleolimnological assessments of water quality (sedimentary carbon, nitrogen, total phosphorus, fossil pigments), and zooplankton community ecology (fossil Cladocera assemblages), combined with Landsat‐derived estimates of lake surface area in two shallow eutrophic lakes, in the Prairies of southern Saskatchewan, Canada, to quantify how 8 decades of contrasting hydrological management strategies (continuous or intermittent) affect primary production and phytoplankton composition. Analysis revealed that irregular hydrological management of Pelican Lake led to sharp increases in primary production concomitant with lake‐level decline. In contrast, continuously managed Buffalo Pound Lake, a drinking water reservoir for regional cities, exhibited slow, persistent eutrophication over decades despite active regulation of water levels. In both lakes, strong correlations of δ 15N values with pigments from diazotrophic cyanobacteria (canthaxanthin) showed that N2‐fixation increased during eutrophication irrespective of the timing of change. Finally, variation in fossil cladoceran density and composition reflected changes in pelagic and littoral habitats (e.g., reduced macrophyte cover) due to changes in both lake level and water quality. Basin comparison shows that while hydrologic management can moderate water quality degradation due to lake‐level change, it does not prevent eutrophication when nutrient influx remains high. Given that regional water availability is forecast to decline in coming decades, we anticipate that continued hydrological management will be unavoidable and will be unable to improve water quality unless nutrient influx is also controlled.

Changes in cladoceran assemblage composition linked to early nineteenth century canal construction, land-use changes, and recent climate change in a macrophyte-dominated Ontario lake

Changes in cladoceran assemblage composition linked to early nineteenth century canal construction, land-use changes, and recent climate change in a macrophyte-dominated Ontario lake

Temporal dynamics of invertebrate community assembly in Lake Victoria since the late Pleistocene based on chitinous remains

Abstract Preserved assemblages of invertebrate remains in lacustrine sediment reveal temporal variations of community composition and environmental conditions. However, records for large tropical lakes are scarce. Lake Victoria, the largest tropical lake, has a dynamic history of changes in water level, biogeochemistry and fish community composition over the past ~17,000 cal yr BP. In order to quantify changes in the invertebrate assemblage of Lake Victoria from the late Pleistocene throughout the Holocene, we examined chitinous remains of Cladocera and larval dipterans (Chironomidae and Chaoboridae) from a sediment core (37 m water depth) dated from ~13,700 cal yr BP to present. We identified four major phases in the invertebrate assemblage throughout this period of lake history. Firstly, Chironomidae and Chaoboridae appeared at low abundances during the earliest stages of lake inundation in the late Pleistocene, at a time when Cladocera were notably absent. Secondly, chaoborids and chironomids increased in abundance during the mid‐Holocene, which coincided with high diatom production toward the end of the Holocene African Humid Period. Thirdly, starting ~4,700 cal yr BP, Alona, a predominantly littoral cladoceran genus, consistently appeared in the invertebrate assemblage alongside changes in mixing regimes and persisted throughout the late Holocene to the present. Fourthly, the arrival of both Chydorus and Bosmina longirostris marked the establishment of an abundant cladoceran assemblage at ~1,350 cal yr BP. The assemblage then gradually shifted toward the increasing dominance of B. longirostris, a planktonic cladoceran. Several of the observed changes in the invertebrate assemblage occurred concurrently with changes in climatic conditions in East Africa and diatom productivity that have been previously recorded in Lake Victoria. This multi‐millennial record of sedimentary invertebrate assemblages in Lake Victoria elucidates some of the temporal development of these communities throughout most of the dynamic modern history of the ecosystem.

Structure and heterogeneity of the Cladocera taphocoenoses in lakes of the Sredny Island (Keretsky archipelago, Kandalaksha bay of the White Sea)

Surface sediments, which were selected from various depths in three lakes of the Sredny Island (Karelia, Russia), were analyzed for subfossil Cladocera assemblages. In total at least 30 taxa remains were identified in samples of surface sediments. Predominance of cold-water littoral and cosmopolitan taxa was noted according to biotypic characteristic. Eurybiont Chydorus cf. sphaericus and typical of wetlands, the phytophilous Alonella nana, were most common in Cladocera taphocoenoses. Spatial heterogeneity was noted in subfossil Cladocera assemblages from various depths. Pelagic taxa proportion increased just as littoral taxa proportion decreased towards the center of lake. Several species remains were only found in littoral surface sediments samples.

Fatores que estimulam a eclosão de ovos de resistência e a sua contribuição para a composição das assembleias de cladóceros em lagoas temporárias tropicais

Abstract: Aim We aimed to verify the contribution of cladocerans’ resting eggs to the active communities of temporary lagoons and, through an experiment, identify which conditions induce high hatching rates. Methods Cladocera assemblages were sampled in four temporary lagoons in the Turvo River floodplain (20° 22’S and 49° 16’W), in the northwest region of São Paulo State, Brazil. Sediment samples were taken during the dry season from a depth of 5 cm, using a 4.5 cm diameter corer. Plankton samples were taken from the water column before and after the dry season. For the hatching test, two treatments were performed 1. Natural condition – without light and temperature control; 2. Controlled condition – with controlled photoperiod and temperature. Temperature, pH, conductivity, dissolved oxygen and hatching of resting eggs were monitored for two weeks. The influence of the parameters on hatching in both treatments was evaluated using Hierarchical Partition Analysis. Results Hatching of resting eggs was higher in the Controlled condition than in the Natural one. Thirty percent of species observed in the active community after flooding hatched in the laboratory test. Conductivity, pH, and dissolved oxygen were positively correlated to the hatching of some species, e.g., Ephemeroporus hybridus, Leydigiops ornata, Notoalona sculpta and Ilyocryptus spinifer. The first species to hatch were those living associated with macrophytes and at low depths. Conclusions Our results show that stable temperature and photoperiod with similar light and dark hours stimulate greater hatching of Cladocera resting eggs. Variables such as pH, conductivity and dissolved oxygen were also correlated with the hatching of some species. We observed that the first contributions to activating the community after drought came from hatching of species usually associated with macrophytes and low depth conditions.

Congruence of water column, contemporary and pre‐industrial sediment cladoceran assemblages in 85 Canadian lakes of contrasting human impact levels

Abstract Crustacean zooplankton occupy a key position as primary consumers within lake food webs, acting as early indicators of wider ecosystem shifts that can cascade to higher trophic levels. Their communities can be assessed via water column net hauls or via sediment samples containing preserved subfossil remnants from various time periods; the latter probably integrate multiple years of data, habitats within lakes, and seasonal patterns. The degree to which such samples do or do not correspond has never been assessed across a wide variety of lake types and gradients. As part of a larger sampling of over 600 lakes across lake‐rich Canada, 85 lakes were selected along a gradient of human impact, according to contemporary catchment land use, to analyse cladoceran zooplankton assemblage relatedness among snapshot water column, contemporary and pre‐industrial sediment samples. We used a combination of ordinations and matrix correlations (RV coefficients), along with partial redundancy analyses, to determine the degree to which the different sample types were comparable and whether they responded similarly to >30 environmental variables. We also compared conclusions obtained using the full cladoceran assemblages versus pelagic‐only taxa and whether our results varied according to degree of human impact. Overall, while all sample types were correlated, congruence was highest between contemporary and pre‐industrial sediment sample types. This result could arise from the under‐representation of littoral taxa in water column samples relative to those from the sediment. In high impacted catchments, however, we observed greater similarity between water column and contemporary sediment samples, as water quality stressors potentially structure assemblages in parallel directions over time. In these modern‐day sample types and among measured variables, we identified lake depth and pH as the most important structuring variables across Canada. In this first study comparing cladoceran assemblages in water column, contemporary and pre‐industrial sediments across many lakes, we conclude that water column and sediment samples respond similarly to environmental drivers but should not be considered entirely analogous or redundant.

CLADOCERA COMMUNITIES OF LAKE ARCTO-PIMBERTO (NENETS AUTONOMOUS DISTRICT) IN THE MIDDLE AND LATE HOLOCENE<a href="#FN1"><sup>1</sup></a>

The analysis of the subfossil Cladocera community in the bottom sediments from Lake Arcto-Pimberto located in the Pechora River delta (Nenets Autonomous District) was carried out. A 95-cm-long continuous core of bottom sediments was collected in the deepest part of the lake and covers approximately 6400 years of sediment accumulation during Middle and Late Holocene. 17 cladoceran taxa were identified in the studied core. Species with Holarctic and Palearctic distributions prevailed in the lake. Most of the identified subfossil remains belong to pelagic species living in the open part of the lake. Found fragments of chitinized remains of Rhynchotalona falcata and Alonopsis elongata indicate the presence of sandy soils in the water body. The samples were dominated by Bosmina (Eubosmina) longispina and Chydorus cf. sphaericus, which are evenly distributed along the continuous sediment core. We have studied the history of the development and evolution of the lake based on changing of the taxonomic composition of microcrustaceans in the bottom sediment core. The structure of the subfossil Cladocera community stayed relatively constant. The ratio of pelagic and littoral-phytophilic taxa changed slightly. Depending on the changes in the species composition of the cladoceran assemblage, the sediment core was divided into 4 ecological zones. In the early history of sedimentation in the lake, there is a small peak in the abundance of crustaceans, followed by decrease and further gradual increase towards the upper horizons of the column. Between from 5700 cal. years BP to 2100 cal. years BP there is an increase in abundance of pelagic organisms, with a decrease in abundance of littoral taxa. This marks the presence of a well-developed pelagic part of the reservoir at that time. In the upper zones, we observe the taxonomic diversity of littoral organisms and an increase in abundance of their remains. The Shannon-Weaver species diversity Index showed a simple organization of the community of subfossil Cladocera. The Pantle and Buck saprobity Index characterized the lake as oligosaprobic, this status is maintained throughout its evolution of the lake.

First Data on Species Composition and Development Cladocera (Crustacea: Branchiopoda) in Mire Ecosystems (Kaliningrad Region, Russia)

The original data on Cladocera fauna in standing-water and stream habitats of mire ecosystems were obtained for the first time in the Kaliningrad region during the research study on large raised bogs (Zehlau and Bolshoye) and drainage canals of 6 peatlands affected by peat extraction. In the studied wetland ecosystems, 41 species of Cladocera were recorded in total, including a number of rare and vulnerable taxa (Flavalona rustica, Scapholeberis microcephala, Streblocerus serricaudatus and Holopedium gibberum). The four species of Cladocera are new species for the Kaliningrad region which were not reported here before. Cladocera played a vital role in the studied bog pools and waterlogged habitats in peatlands as a key group of organisms that forms here a significant part of the zooplankton biomass due to the abundance and intensive production in the water bodies. The secondary filter feeders and predators were the most abundant in bog ecosystems. The cladoceran fauna in the intact bog ecosystems, especially the Zehlau raised bog, was the most diverse and unique. Nevertheless, the cladoceran assemblages in the disturbed ecosystems of drainage canals retained certain features of the natural water bodies. The latter fact is important in applied respect enabling to consider these canals as refugia that have potentials for natural restoration of the cladoceran fauna during the peatland rewetting programme on the Carbon Polygon in the Kaliningrad region.

Influence of cultural eutrophication, climate, and landscape connectivity on 3 Kawartha lakes (Ontario, Canada) since the early 1800s

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.

Using a multi-proxy paleolimnological approach to track the effects of multiple stressors on a naturally acidic lake from Killarney Provincial Park (Ontario, Canada)

Ruth-Roy Lake (Killarney Provincial Park, Ontario, Canada) is an ultra-oligotrophic, naturally acidic waterbody. Lakes in Killarney Provincial Park were impacted by long-range transportation of contaminants from copper-nickel smelting operations in nearby Sudbury, but recent lake monitoring indicates that Ruth-Roy Lake has been less acidic than inferred pre-industrial pH conditions. We assessed the effects of pH change, reduced sulphur emissions, and drivers of reduced acidity using biological and geochemical paleolimnological techniques. Ruth-Roy Lake experienced notable biological and chemical change over the past ~150 years. All examined proxies supported that Ruth-Roy Lake was naturally acidic but further acidified as early as ca. 1920s, with the strongest acidification signal apparent in ca. 1940s. Biological recovery in diatom and cladoceran assemblages, however, is modest. We highlight the importance of understanding reference conditions to assess ecosystem recovery and climate-mediated change in clear acidic lakes located in industrial landscapes.

Human deforestation outweighed climate as factors affecting Yellow River floods and erosion on the Chinese Loess Plateau since the 10th century

Increasing proportions of the global population are exposed to floods, including many living in the Yellow River floodplain. Since records were first kept in 602 BCE, there have been ∼1500 floods on the Yellow River, resulting in the death of millions of people. Counteracting increased flood risk requires an understanding of the relationship between climate, forest cover, erosion, and river flow. However, to assess whether the Yellow River basin is currently experiencing a period of high flood risk requires a long-term perspective. Here we use a variety of paleoenvironmental proxies (pollen, magnetic susceptibility, cladoceran assemblages) preserved in high-resolution, well-dated sediment records retrieved from an alpine lake in the middle Yellow River basin (Chinese Loess Plateau) within the agro-pastoral ecozone to examine how climatic and land-use changes affected aquatic ecosystems over the past ∼2000 years. Further, to examine changes in erosion, runoff production and flood frequency, we synthesize previously published proxy reconstructions of vegetation density, soil erosion, and dry-wet changes, as well as flood records from historical documents. We demonstrate that, following the period around the 10th century, excessive cultural deforestation outweighed climate effects and became the dominant factor that led to an unprecedented flood-rich period when drought conditions were common, cultivation expanded to meet food shortages, heavy silting raised the riverbed, and runoff and flood risk increased. These watershed changes, including enhanced soil erosion, affected the biological communities of aquatic ecosystems that led to the disappearance of planktonic cladocerans that hitherto dominated the assemblages. Increasing temperatures and weakening monsoon precipitation during the past ∼50 years, together with decreased erosion indicated by unprecedented reductions in Yellow River runoff and sediment load resulting from reforestation and damming, led to the re-establishment of planktonic cladocerans. Despite these recent changes, vegetation cover has not recovered to pre-deforestation levels, suggesting that the Yellow River is currently experiencing a high flood risk period. Our results emphasize the importance of considering vegetation–flooding relationships to help improve risk assessments and management protocols for the Yellow River.

Zooplankton assemblage structure and diversity since pre‐industrial times in relation to land use

AbstractAimWhile it is now well accepted that human activities are having pronounced effects on natural ecosystems, regional variation in the rate and magnitude of various human impacts is unclear. Moreover, the effects of land use change on natural aquatic communities have only relatively recently begun to be explored. Our goal was to understand how and where assemblages of a central food web component of freshwater lakes have changed over the course of industrialization in relation to land use.LocationCanada.Time periodPre‐1880 AD to present.Major taxa studiedCladoceran zooplankton.MethodsAs part of the Natural Sciences and Engineering Research Council (NSERC) Canadian Lake Pulse Network, we selected 101 lakes across Canada along a gradient of human impact to analyse subfossil cladoceran assemblages from sediment cores. We examined relationships between taxonomic and functional indicators of cladoceran assemblage change among lakes and through time.ResultsContemporary assemblages were taxonomically and functionally less diverse locally relative to pre‐industrial assemblages (α‐diversity) and were structured by the degree of human impact in watersheds. Local α‐diversity losses were greatest in highly impacted lakes where agriculture and pasture are prevalent. While spatial homogenization (spatial β‐diversity) did not increase since pre‐industrial times as expected, temporal turnover (temporal β‐diversity) showed a non‐significant but increasing trend in highly impacted lakes, especially in urbanized watersheds.Main conclusionsCladoceran assemblages have changed significantly over the course of the Industrial period, and especially in more highly impacted watersheds, underscoring the important role of watershed land use in shaping diversity. However, indicators of cladoceran function have remained relatively conserved over time and land use change showed little impact on β‐diversity, despite important environmental variation. Overall, this research furthers our understanding of the health status of Canadian lakes and the consequences of human activities, especially agriculture and urbanization, on lake zooplankton.

Density and Diversity Differences of Contemporary and Subfossil Cladocera Assemblages: A Case Study in an Oxbow Lake

Cladocerans are biological indicators of environmental changes. Their remains provide information on past changes in lake environments. We studied the correspondence between contemporary Cladocera assemblages and their subfossil remains from an oxbow lake. We sought to demonstrate that there were differences among the various sites of an oxbow lake with different utilization based on contemporary and subfossil Cladocera assemblages and physical–chemical variables. The oxbow lake’s two sides are used as fishing sites, where angling is the main activity. The middle site of the lake is under nature protection with high macrovegetation coverage. Contemporary and subfossil Cladocera assemblages were sampled from 21 sampling sites along the oxbow lake. Our research showed that the subfossil Cladocera assemblages had higher species richness and densities (36 taxa) than the contemporary species (29 taxa). We found one species of the Polyphemidae family only in the contemporary assemblage. Among the sites, Cladocera assemblages differed in their species composition and density. The highest densities were found in the second fishing site due to the appearance of the small-sized Bosmids. The relationship between Cladocerans and the physical–chemical variables showed that some variables, such as chlorophyll-a, biological oxygen demand, dissolved oxygen, copper, phosphide, and organic matter content, significantly affected Cladocera composition. We found that the subfossil Cladocera assemblage was significantly more diverse and abundant than the contemporary one, indicating that an integrated sampling may be sufficient to provide better results on the total species composition of the water body.

Zooplankton assemblage and body size responses to severe lake eutrophication from agricultural activities near mink farms in Nova Scotia, Canada

Abstract Mink fur farming was once a widespread agricultural activity in southwestern Nova Scotia. Freshwaters near to and downstream of several mink fur farm operations have experienced severe water quality issues, including eutrophication and recurring algal blooms. Here, we use dated lake sediments to examine trends in primary producers and primary consumers from a hypereutrophic lake to assess how cladoceran assemblages have responded to extreme eutrophication. Shifts in the dominant pelagic cladoceran taxa began in the early 1900s, coinciding with an increase in sedimentary chlorophyll-a concentrations. Notably, small-bodied bosminids decreased, while taxa such as Chydorus brevilabris and Daphnia pulex spp. dominated assemblages in recent decades. Bottom-up ecological factors, such as decades of greater primary production, were the likely drivers of assemblage shifts of primary consumers. Consistent body sizes of bosminids throughout the sedimentary record suggested that pelagic cladocerans were not influenced solely by predation pressure from macroinvertebrates or fish. This study provides evidence of large-scale ecological shifts occurring at multiple trophic levels in a hypereutrophic temperate lake with mink farming operations in its catchment.

Lake ecosystem regime shifts induced by agricultural intensification: A century scale paleolimnological investigation from the Huai River Basin (China)

Regime shifts of freshwater ecosystems driven by fast-changing multiple stressors are increasingly occurring. However, lake regime shifts across intensive agricultural landscapes are less explored, especially how different aquatic communities respond to multiple environmental forcings through time is poorly understood. Using a century scale paleolimnological record from Gaoyou Lake in the Huai River Basin, one of the most intensively cultivated areas in China, we analyzed high-resolution sedimentary subfossil pigments and cladoceran assemblages to investigate the dynamic trajectories of plankton communities and detect the potential occurrence of ecological shifts across different aquatic trophic levels. Furthermore, we explored how these shifts were driven by anthropogenic and climatic stressors, and examined the rates of ecological change through time. Our results revealed a significant ecological shift in the cladoceran community around the 1970s associated with the hydrological regulation through damming within the basin. Subsequently, a regime shift for the whole-lake ecosystem occurred in the 1990s, which was characterized by the onset of eutrophication with elevated primary production and decreased water clarity. Redundancy and variance partitioning analyses identified agricultural intensification with substantial anthropogenic nutrient loading as the main driver of lake ecological dynamics. Rising temperature played an additional role. Moreover, we detected two significant acceleration phases of lake primary productivity (in the 1990s and after the 2000s), which were asynchronous with the variability of external environmental drivers. This finding probably indicated Gaoyou Lake has switched from a slow-to a fast-response system with decreasing ecological stability. Our study offers new challenges and insights for incorporating rate-focused management strategies to minimize the risk of catastrophic ecological shifts in aquatic ecosystems.

Using diatoms to track road-salt seepage into small, shallow, softwater Ontario lakes

Since the 1950s, the widespread application of road salt for winter road maintenance and safety in cold regions has led to increased conductivity levels in many freshwater systems. Salting practices have adversely affected freshwater biota; however, the magnitude of ecological impacts may vary by species and ecosystem. Here, we examine diatom assemblage changes during the past ∼200 years from the sedimentary records of five impacted lakes (measured specific conductance values of 149–350 µS·cm−1) and a reference lake (18 µS·cm−1) located in the Muskoka River Watershed, south-central Ontario, Canada. Diatom compositional changes in the road-salt-impacted sites were consistent with increasing conductivity and increased diatom-inferred (DI)-conductivity was evident during the latter half of the 20th century in the impacted lakes, concurrent with known road-salt application. The strongest predictor of DI-conductivity changes among the six lakes was the kilometre equivalents of roads within the watershed (i.e., kilometres of road × number of lanes). Similar to changes observed in a previous study focusing on cladoceran assemblages, we conclude that even modest applications of road salt can affect diatom assemblages in softwater lakes.

Comparing recent and preindustrial cladoceran assemblages in 35 metal- and smelting-affected lakes near Sudbury (Ontario, Canada)

Abstract Base metal smelting activity around Sudbury (Ontario, Canada) has persisted for over a century, emitting metals and acidifying contaminants that affected lakes downwind of smelter stacks. Although considerable research has been directed toward the paleolimnological study of diatoms and chrysophytes in the region, relatively little comparable work has been completed on invertebrates. Here, cladoceran (Branchiopoda: Cladocera) assemblages are compared using a paleolimnological “top-bottom approach”, comparing preimpact and recent assemblages. Spatiotemporal differences were likely driven by acidification-related stressors and legacy effects of metal contamination. The replacement of the Daphnia longispina complex with the Daphnia pulex complex is attributable to diminished lake-water calcium concentrations. Increased abundances of early colonist taxa demonstrate that many acidified lakes have not fully recovered. Regional stressors further complicate recovery and the interpretation of temporal changes. Finally, clustering of recent cladoceran assemblages reflects the effects of modern multiple stressors and persistent historical stressors. This study shows that acidification history partially explains differences in cladoceran assemblages, but also that multiple stressors will likely continue to influence assemblage composition and recovery in Sudbury lakes. Defining appropriate reference conditions, considering historical and modern stressors, will be important when assessing the extent and trajectory of ecosystem recovery from widespread anthropogenic impacts.

Subfossil records of Cladocera from the tundra Lake Yambeto in the Yamal Peninsula

Abstract. We performed a paleoecological study of a 124-cm-long sediment core from Lake Yambeto (southern part of the Yamal Peninsula, Yamalo-Nenets Autonomous Okrug, Russia), which consists of a series of lake basins varying in depth (up to 6.9 m) and merged with each other. The species composition of subfossil cladocerans was analyzed: a total of 26 taxa from 5 families were identified; of them, 73% belonged the family Chydoridae, thus ranking it as the most diverse. The cladoceran assemblage was dominated by Holarctic and Palearctic species, with Bosmina (Eubosmina) longispina, Bosmina longirostris, and Chydorus cf. sphaericus as the most abundant. The mean saprobity index (1.52) characterized the lake as -mesosaprobic.