Ice-free Season Research Articles

Year-round monitoring of Arctic species of sculpin to identify residency and seasonality of movement behavior

Environments change across space and time, often requiring organisms to exhibit behavioral responses. In the Arctic, migratory consumers are motivated by spring resources to follow receding ice; however, resident species’ responses to this ephemeral productivity are less well understood. We characterized the movement behaviors of relatively sedentary Arctic species of sculpin ( Myoxocephalus spp.) in Tremblay Sound, Nunavut, Canada. Movements of individuals ( n = 60) captured during the ice-free periods of 2017–2019 were monitored year-round via an array of acoustic telemetry receivers ( n = 37). Telemetry data confirmed year-round residency within the Sound, yet sculpins were consistently more active and wider ranging during the ice-free period versus the ice-covered winters. Sequence analysis revealed distinct patterns of activity differentiated primarily by regional associations. Together, these results indicate sculpins are highly sedentary, but move more during the ice-free season, suggesting the importance of the seasonal productivity pulse to these fishes. As resident species are adapted to exploit the conditions within their local environment, sculpins provide valuable indicator species to monitor coastal and benthic Arctic ecosystems that are experiencing rapid change.

Haul-out patterns of the Baltic grey seal (Halichoerus grypus) in the suburbs of a metropolis

In this study, we investigated the haul-out patterns of the Baltic grey seal in the coastal area adjacent to the metropolitan city, Saint Petersburg, during the ice-free seasons of 2017-2022. Grey seals occupied stony banks near Kotlin Island, in the easternmost part of the Gulf of Finland. The censuses were carried out from the island shore during evening hours. The number of seals reached 70 during the survey. Contrary to the common trend reported in similar studies, the annual minimum in seal abundance (May and June) coincided with the peak of moulting. Active use of the haul-out site was observed between July and November, implying that eastward movements of the grey seals take place in the Gulf of Finland in the post-moulting period. Wind speed and sea state interfered with the seal hauling out throughout the year, whereas the relationship with air temperature varied seasonally. Cloud cover, atmospheric pressure, wind direction and sea level had no impact on the seal number, though the fluctuations in sea level reduced the haul-out space. The tendency of the seals to haul out towards and after the sunset was determined. The most frequent sources of human disturbance were light planes (0.45 ± 0.12 confidence interval, per count) and powerboats (0.41 ± 0.14 confidence interval, per count), but only the powerboats significantly decreased the seal number. We found that the seals used the banks concurrently with seabirds. The area of Kotlin Island presumably attracts the seals by the diversity of prey items in the estuary of the Neva River. Establishing of a marine protected area and physical marking of the water space around the haul-out site are recommended.

A Quantification of Heat Storage Change-Based Evaporation Behavior in Middle–Large-Sized Lakes in the Inland of the Tibetan Plateau and Their Temporal and Spatial Variations

A large number of different-sized lakes exist in the inland area of the Tibetan Plateau (TP), which are examples of the important connection between the atmosphere and hydrosphere through the analysis of lake surface convergence and evaporation processes. The evaporation level changes that occur in middle–large-sized lakes (surface area > 50 km2) in the area directly influence the regional mass and energy balance values, atmospheric boundary layer heat and humidity structures, and weather processes occurring in the lower-reach areas. The studies conducted in the literature at present, concerning lake evaporation processes, generally overlook the differences in lake heat storage behavior due to the reduced amount of data in the literature concerning lake bathymetry. According to the in situ bathymetric data obtained for 68 middle–large-sized lakes in the inner basin of the TP, in this study, we calculated their heat storage (G) change values by using the different vertical-depth water-temperature-change integral method, and we established a regression equation for the heat storage and lake surface net radiation values for 68 lakes. The evaporation rates of 134 middle–large-sized lakes larger than 50 km2 in the inland are of the TP were calculated by obtaining the G regression result and adopting it into the Penman model, as well as estimating the evaporation losses of theses 134 lakes from 2002 to 2018. The result shows that the annual average evaporation rate for these lakes is 927.39 mm/year, with an insignificant upward trend (0.10 mm/year). This method achieved good accuracy compared with the Bowen ratio method, which estimates the evaporation rate during the ice-free season, with a high correlation coefficient (R) value of 0.95 and least root mean square error (RMSE) value of 61 mm. The annual mean evaporation rate can be divided into the southern and northern lake groups along a 34°N line with a difference of 314.41 mm/year. The annual average evaporation volume of these lakes was 25.02 km3 and showed an upward trend of 0.35 km3/year. Among them, the annual average evaporation volume contribution ratio of level-1 lakes (50 km2 ≤ lake’s area < 100 km2, 61 lakes) was 14.04%, showing an upward trend, and the contribution of level-3 lakes (lake’s area ≥ 500 km2, 10 lakes) was 41.50%, showing a downward trend. There were no obvious changes in the level-2 lakes (100 km2 ≤ lake’s area < 500 km2, 63 lakes), which maintained at the same level in approximately 44.46%. Air temperature is the most important factor affecting the evaporation rate of lakes, while the lake surface area is the main factor affecting lake evaporation volume. Our study, considering the actual lake heat storage value, provides a useful reference for further improving lake water budget balance values and watershed hydrologic features in the inland closed lakes located in the TP.

Mapping vessel traffic patterns in the ice-covered waters of the Pacific Arctic

Recent climate change has caused declines in ice coverage which have lengthened the open water season in the Arctic and increased access to resources and shipping routes. These changes have resulted in more vessel activity in seasonally ice-covered regions. While traffic is increasing in the ice-free season, the amount of vessel activity in the marginal ice zone (ice concentration 15–80%) or in pack ice (>80% concentration) remains unclear. Understanding patterns of vessel activities in ice is important given increased safety challenges and environmental impacts. Here, we couple high-resolution ship tracking information with sea ice thickness and concentration data to quantify vessel activity in ice-covered areas of the Pacific Arctic (northern Bering, Chukchi, and western Beaufort Seas). This region is a geo-strategically critical area that contains globally important commercial fisheries and serves as a corridor for Arctic access for wildlife and vessels. We find that vessel traffic in the marginal ice zone is widely distributed across the study area while vessel traffic in pack ice is concentrated along known shipping routes and in areas of natural resource development. Of the statistically significant relationships between vessel traffic and both sea ice concentration and thickness, over 99% are negative, indicating that increasing sea ice is associated with decreasing vessel traffic on a monthly time scale. Furthermore, there is substantial vessel traffic in areas of high concentration for bowhead whales (Balaena mysticetus), and traffic in these areas increased four-fold during the study period. Fishing vessels dominate vessel traffic at low ice concentrations, but vessels categorized as Other, likely icebreakers, are the most common vessel type in pack ice. These findings indicate that vessel traffic in areas of ice coverage is influenced by distant policy and resource development decisions which should be taken into consideration when trying to predict future vessel-ice interactions in a changing climate.

Anthropogenic Neighborhood Impact on Bacterial and Fungal Communities in Polar Bear Feces.

Climate changes cause a dramatical increase in the ice-free season in the Arctic, forcing polar bears ashore, closer to human settlements associated with new and non-natural food objects. Such a diet may crucially transform the intestinal microbiome and metabolism of polar bears. The aim of this study was to characterize changes in the gut bacterial and fungal communities resulting from the transition to anthropogenic food objects by the means of 16S and ITS metabarcoding. Thus, rectal samples from 16 wild polar bears from the Kara-Barents subpopulation were studied. Human waste consuming resulted in a significant increase in the relative abundance of fermentative bacteria (Lactobacillaceae, Leuconostocaceae, and Streptococcaceae) and a decrease in proteolytic Enterobacteriaceae. However, the alpha-diversity parameters remained similar. Also, for the first time, the composition of the fungal community of the polar bear intestine was determined. Diet change is associated with the displacement of eurybiontic fungi (Thelebolus, Dipodascus, Candida (sake), and Geotrichum) by opportunistic Candida (tropicalis), Kazachstania, and Trichosporon. Feeding on human waste does not cause any signs of dysbiosis and probably leads to adaptive changes in the bacterial microbiome. However, the emergence of fungal facultative pathogens increases the risk of infections.

Hydrological, meteorological, and watershed controls on the water balance of thermokarst lakes between Inuvik and Tuktoyaktuk, Northwest Territories, Canada

Abstract. Thermokarst lake water balances are becoming increasingly vulnerable to change in the Arctic as air temperature increases and precipitation patterns shift. In the tundra uplands east of the Mackenzie Delta in the Northwest Territories, Canada, previous research has found that lakes responded non-uniformly to year-to-year changes in precipitation, suggesting that lake and watershed properties mediate the response of lakes to climate change. To investigate how lake and watershed properties and meteorological conditions influence the water balance of thermokarst lakes in this region, we sampled 25 lakes for isotope analysis five times in 2018, beginning before snowmelt on 1 May and sampling throughout the remainder of the ice-free season. Water isotope data were used to calculate the average isotope composition of lake source water (δI) and the ratio of evaporation to inflow (E/I). We identified four distinct water balance phases as lakes responded to seasonal shifts in meteorological conditions and hydrological processes. During the freshet phase from 1 May to 15 June, the median E/I ratio of lakes decreased from 0.20 to 0.13 in response to freshet runoff and limited evaporation due to lake ice presence that persisted for the duration of this phase. During the following warm, dry, and ice-free period from 15 June to 26 July, designated the evaporation phase, the median E/I ratio increased to 0.19. During the brief soil wetting phase, E/I ratios did not respond to rainfall between 26 July and 2 August, likely because watershed soils absorbed most of the precipitation which resulted in minimal runoff to lakes. The median E/I ratio decreased to 0.11 after a cool and rainy August, identified as the recharge phase. Throughout the sampling period, δI remained relatively stable and most lakes contained a greater amount of rainfall-sourced water than snow-sourced water, even after the freshet phase, due to snowmelt bypass. The range of average E/I ratios that we observed at lakes (0.00–0.43) was relatively narrow and low compared with thermokarst lakes in other regions, likely owing to the large ratio of watershed area to lake area (WA/LA), efficient preferential flow pathways for runoff, and a shorter ice-free season. Lakes with smaller WA/LA tended to have higher E/I ratios (R2 = 0.74). An empirical relationship between WA/LA and E/I was derived and used to predict the average E/I ratio of 7340 lakes in the region, which identified that these lakes are not vulnerable to desiccation, given that E/I ratios were < 0.33. If future permafrost thaw and warming cause less runoff to flow into lakes, we expect that lakes with a smaller WA/LA will be more influenced by increasing evaporation, while lakes with a larger WA/LA will be more resistant to lake-level drawdown. However under wetter conditions, lakes with a larger WA/LA will likely experience a greater increases in lake level and could be more susceptible to rapid drainage.

A 1300-year microfaunal record from the Beaufort Sea shelf indicates exceptional climate-related environmental changes over the last two centuries

The environments of Arctic Ocean nearshore areas experience high intra- and inter-annual variability, making it difficult to evaluate the impact of anthropogenic warming. However, a sediment record from the southern Canadian Beaufort Sea allowed us to reconstruct the impacts of climate and environmental changes over the last 1300 years along the northern Yukon coast, Canada. The coring site (PG2303; 69.513°N, 138.895°W; water depth 32 m) is located in the Herschel Basin, where high sedimentation rates (0.1–0.5 cm a−1) allowed analyses at sub-centennial to decadal resolutions. Benthic foraminiferal, ostracod, and tintinnid assemblages, as well as the stable isotope composition of the foraminifera Elphidium clavatum and Cassidulina reniforme were used as paleoclimatic and ecological indicators, while the age model was based on the combined radiometric data of 14C, 210Pb and 137Cs. From ca 700 to 1050 CE, our data suggest penetration of offshore shelf-break waters inferred by the dominance of C. reniforme followed by the relatively abundant Triloculina trihedra in the foraminiferal assemblages as both species are associated with stable saline conditions. Afterwards, the occurrence of ostracods Kotoracythere arctoborealis and Normanicythere leioderma suggests influx of Pacific-sourced waters until ca. 1150 CE. From ∼1150–1650 CE, persistent frigid waters, limited sediment supply, and low abundances of microfossils suggest cold conditions with pervasive annual sea-ice cover that may have restricted upwelling of oceanic waters. After ∼1800 CE, the co-occurrence of Tintinnopsis fimbriata and bacterial/complex organic carbon feeder foraminifera (Quinqueloculina stalkeri, Textularia earlandi and Stetsonia horvathi), suggest an increased influence of freshwater rich in particulate organic matter, which may be related to the spreading of the Mackenzie River plume and/or increased coastal permafrost erosion during longer ice-free seasons. Based on these proxy data, the shift at ∼1800 CE marks the onset of regional warming, which further intensified after ∼1955 CE, likely in response to the anthropogenic forcing.

Modeling the impacts of a changing and disturbed environment on an endangered beluga whale population

Climate change and disturbance from human activities are key threats facing many wildlife populations worldwide. The ability to quantify the effects of such threats on individual health and population dynamics is critical for effective management and conservation. We used Stochastic Dynamic Programming (SDP), a method for implementing state-dependent life history theory, to explore the impacts of changes in prey availability and anthropogenic disturbance on survival and reproductive success of Cook Inlet belugas (Delphinapterus leucas, CIB), an endangered and isolated population in decline. We predicted behavioral decisions (whether to forage, travel to a new location, or rest) of pregnant CIBs within a spatially and seasonally dynamic prey landscape. We used those decisions to explore time-activity budgets and spatial use under a variety of hypothetical environmental scenarios and estimate the resulting impacts on body condition and vital rates. In all scenarios, foraging activity was highest during summer to capitalize on abundant prey, which in the model was assumed to be eulachon (Thaleichthys pacificus) and salmonids (Oncorhynchus spp.). This resulted in large increases in blubber reserves that pregnant CIBs relied on during October to April when prey was assumed to be less abundant. Prey availability outside of summer months was still critical, as it either exacerbated or buffered against reductions in prey availability during summer months. Spatial predictions of habitat use indicated that pregnant CIBs should forage in areas used historically that now appear to be abandoned, suggesting that prey availability alone is unlikely to explain the recent range contraction of CIBs to upper Cook Inlet. Reductions in prey availability from late spring to early fall adversely affected vital rates, but intermittent disturbances that resulted in lost foraging opportunities, such as those caused by anthropogenic activities during the ice-free season, had little impact on body condition or vital rates if prey were abundant during the summer and early fall. Accurate assessment of the effects of anthropogenic disturbance on CIBs requires robust data on both disturbances and year-round prey availability, as intermittent disturbances adversely affected survival and reproductive success when they occurred in environments with reduced prey availability. Our model represents an initial effort to fill a critical information gap for informing CIB management decisions, providing insights into conditions under which reductions in vital rates might be expected and highlighting key data needed to increase the applicability of the model to this endangered population.

GTAR: a new ensemble evolutionary autoregressive approach to model dissolved organic carbon

AbstractThis article explores the forecasting capabilities of three classic linear and nonlinear autoregressive modeling techniques and proposes a new ensemble evolutionary time series approach to model and forecast daily dynamics in stream dissolved organic carbon (DOC). The model used data from the Oulankajoki River basin, a boreal catchment in Northern Finland. The models that were evolved used both accuracy and parsimony measures including autoregressive (AR), vector autoregressive (VAR), and self-exciting threshold autoregressive (SETAR). The new method, called genetic-based SETAR (GTAR), evolved through the integration of state-of-the-art genetic programming with SETAR. To develop the models, high-resolution DOC concentration and daily streamflow (as the external input for VAR) were measured at the same gauging station throughout the ice free season. The results showed that all the models characterize the DOC dynamics with an acceptable 1-day-ahead forecasting accuracy. Use of the streamflow time series as an exogenous variable did not increase the predictive accuracy of AR models. Moreover, the hybrid GTAR provided the best accuracy for the holdout testing data and proved to be a suitable approach for predicting DOC in boreal conditions.

Stratification and its consequences in two constructed urban stormwater wetlands

Stratification in constructed urban stormwater wetlands is one of the fundamental physical processes that affect hydrodynamics, transport and fate of stormwater pollutants. Adverse effects of stratification include decreasing pollutant retention capacity, causing the water at lower depths to become anoxic, degrading water quality and increasing stress on the downstream aquatic communities. The current study reports on a comprehensive field monitoring program of stratification and hydrodynamics in two ice-free seasons (May – October) in two constructed urban stormwater wetlands in Calgary, Canada, with different inlet, outlet, morphometric and vegetation designs. Despite their small sizes of 0.5 and 1.2 ha and shallow water depths of 0.8 m, stratification was strong and persistent in the wetlands. The response of stratification and mixing to atmospheric forcings (e.g., air temperature, atmospheric instability, rainfall depth, wind speed) and the impact of design characteristics (inlet/outlet design, water depth, surface area and aquatic vegetation) were examined and discussed. Thermal stratification, defined as a vertical temperature gradient >1 °C/m, was found to be significantly higher (up to ten times) near the inlets and last longer (up to twice) than in the main cells and the outlet basins due to the relatively cold summer inflows. The wetland with twice the permanent water volume and surface area and half the length-to-width ratio had denser submerged aquatic vegetation, higher (by up to 2 °C) water temperature and more severe (up to eight times) thermal stratification. Strong densimetric stratification and low wind stress on the water surface caused hypoxic conditions near the bed, potentially adversely affecting water quality and downstream aquatic communities.

Comparative Analysis of Empirical and Machine Learning Models for Chla Extraction Using Sentinel-2 and Landsat OLI Data: Opportunities, Limitations, and Challenges

Remote retrieval of near-surface chlorophyll- a (Chla) concentration in small inland waters is challenging due to substantial optical interferences of various water constituents and uncertainties in the atmospheric correction (AC) process. Although various algorithms have been developed to estimate Chla from moderate-resolution terrestrial missions (∼10–60 m), the production of both accurate distribution maps and time series of Chla has proven challenging, limiting the use of remote analyses for lake monitoring. Here, we develop a support vector regression (SVR) model, which uses satellite-derived remote-sensing reflectance spectra ( R r s δ ) from Sentinel-2 and Landsat-8 images as input for Chla retrieval in a representative eutrophic prairie lake, Buffalo Pound Lake (BPL), Saskatchewan, Canada. Validated against in situ Chla from seven ice-free seasons (N ∼ 200; 2014–2020), the SVR model outperformed both locally tuned, R r s δ -fed empirical models (Normalized Difference Chlorophyll Index, 2- and 3-band, and OC3) and Mixture Density Networks (MDNs) by 15–65%, while exhibiting comparable performance to a locally trained MDN, with an error of ∼35%. Comparison of Chla retrieval models, AC processors (iCOR, ACOLITE), and radiometric products (Rayleigh-corrected, surface, and top-of-atmosphere reflectance) showed that the best Chla maps and optimal time series (up to 100 mg m−3) were produced using a coupled SVR-iCOR system.

Community-led non-invasive polar bear monitoring in the Eeyou Marine Region of James Bay, Canada: insights on distribution and body condition during the ice-free season

Wildlife conservation is informed by detailed understanding of species demographics, habitat use, and interactions with environmental drivers. Challenges to collecting this information, particularly in remote places and on widely ranging species, can contribute to data deficiencies that detract from conservation status assessment and the effectiveness of management actions. Polar bears in James Bay face rapidly changing environmental conditions at the southern edge of their global range, but studying their ecology has been limited by community concerns about the methods typically used in polar bear research. Using a community-led and non-invasive approach, we deployed hair snare and camera trap sampling stations across 400 km of the Eeyou Marine Region in eastern James Bay. Stations collected >100 hair samples and thousands of photographs in one eight-week period that allowed for a novel investigation of this population’s distribution and body condition during the ice-free season. Polar bears were in average to above average body condition, and model selection of detections at stations revealed distance to mainland as a significant predictor of polar bear presence. Given its high potential, we suggest community-based monitoring using this method become a standard protocol to expand the scope and local leadership of polar bear research across the North.

Pond greenhouse gas emissions controlled by duckweed coverage

Freshwaters are significant contributors of greenhouse gases to the atmosphere, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Small waterbodies such as ponds are now recognized to have disproportionate greenhouse gas emissions relative to their size, but measured emissions from ponds have varied by several orders of magnitude. To assess drivers of variation in pond greenhouse gas dynamics, we measured concentrations and emissions of CO2, CH4, and N2O across 26 ponds in Minnesota, United States, during the ice-free season. The studied ponds differed in land-use, from urban stormwater ponds to natural forested ponds. The ponds were all sources of greenhouse gases, driven by large CH4 emissions (mean 704 [sd 840] mg CH4-C m−2 d−1). CO2 fluxes were variable, but on average a sink (mean −25.9 [sd 862] mg CO2-C m−2 d−1), and N2O emissions were generally low (mean 0.398 [sd 0.747] mg N2O-N m−2 d−1). Duckweed coverage on the water surfaces ranged from 0% to 100% coverage, and had the largest influence on water chemistry and greenhouse gas dynamics across the ponds. Duckweed covered ponds (ponds with greater than 85% coverage) had higher phosphorus levels and increased anoxia compared to ponds without duckweed (ponds with less than 12% coverage), leading to higher CH4 concentrations and overall greenhouse gas emissions in the duckweed ponds. Duckweed ponds had a mean emission rate in CO2 equivalents of 30.9 g C m−2 d−1 compared to 11.0 g C m−2 d−1 in non-duckweed ponds.

Effects of long-term climate trends on the methane and CO2 exchange processes of Toolik Lake, Alaska

Methane and carbon dioxide effluxes from aquatic systems in the Arctic will affect and likely amplify global change. As permafrost thaws in a warming world, more dissolved organic carbon (DOC) and greenhouse gases are produced and move from soils to surface waters where the DOC can be oxidized to CO2 and also released to the atmosphere. Our main study objective is to measure the release of carbon to the atmosphere via effluxes of methane (CH4) and carbon dioxide (CO2) from Toolik Lake, a deep, dimictic, low-arctic lake in northern Alaska. By combining direct eddy covariance flux measurements with continuous gas pressure measurements in the lake surface waters, we quantified the k600 piston velocity that controls gas flux across the air–water interface. Our measured k values for CH4 and CO2 were substantially above predictions from several models at low to moderate wind speeds, and only converged on model predictions at the highest wind speeds. We attribute this higher flux at low wind speeds to effects on water-side turbulence resulting from how the surrounding tundra vegetation and topography increase atmospheric turbulence considerably in this lake, above the level observed over large ocean surfaces. We combine this process-level understanding of gas exchange with the trends of a climate-relevant long-term (30 + years) meteorological data set at Toolik Lake to examine short-term variations (2015 ice-free season) and interannual variability (2010–2015 ice-free seasons) of CH4 and CO2 fluxes. We argue that the biological processing of DOC substrate that becomes available for decomposition as the tundra soil warms is important for understanding future trends in aquatic gas fluxes, whereas the variability and long-term trends of the physical and meteorological variables primarily affect the timing of when higher or lower than average fluxes are observed. We see no evidence suggesting that a tipping point will be reached soon to change the status of the aquatic system from gas source to sink. We estimate that changes in CH4 and CO2 fluxes will be constrained with a range of +30% and −10% of their current values over the next 30 years.

Field observations of stratification in stormwater wet ponds

Stratification is one of the fundamental physical processes that may have a significant impact on water quality in stormwater wet ponds. However, the role of thermal and chemical stratifications in governing water quality processes is not fully understood. This is in part due to the lack of detailed field measurements of sufficient governing parameters over time periods that span a wide range of environmental conditions. To fill this gap, a comprehensive 2-year field program was undertaken in two stormwater wet ponds in Calgary, Alberta, Canada, during the ice-free season from May to November in 2018 and 2019. At different locations in each pond, thermal and chemical stratifications were observed, thermocline depth and strength were determined, and continuous water velocity profiles were measured. In addition, the effect of local weather conditions on stratification, thermocline, and hydrodynamics was investigated. The results showed that the ponds had vertical water temperature differences >1 °C for 99% of the time, May to August. In addition, salt-laden inflows from road deicing salts led to strong chemical stratification up to five times stronger in the sediment forebays than in the main cells in spring. Wind-induced surface currents were insignificant, scaling at 0.3% of the wind speed with negligible impact on vertical mixing in the ponds. Our results demonstrate that the ponds' strong and prolonged stratification decreased pollutant retention capacity and caused the water at depth to become anoxic, degrading the quality of the water discharged downstream. Hence, additional consideration of stratification is required when designing new stormwater ponds.

Applying early warning indicators to predict critical transitions in a lake undergoing multiple changes.

Lakes are dynamic ecosystems that can transition among stable states. Since ecosystem-scale transitions can be detrimental and difficult to reverse, being able to predict impending critical transitions in state variables has become a major area of research. However, not all transitions are detrimental, and there is considerable interest in better evaluating the success of management interventions to support adaptive management strategies. Here, we retrospectively evaluated the agreement between time series statistics (i.e., standard deviation, autocorrelation, skewness, and kurtosis-also known as early warning indicators) and breakpoints in state variables in a lake (Lake Simcoe, Ontario, Canada) that has improved from a state of eutrophication. Long-term (1980 to 2019) monitoring data collected fortnightly throughout the ice-free season were used to evaluate historical changes in 15 state variables (e.g., dissolved organic carbon, phosphorus, chlorophyll a) and multivariate-derived time series at three monitoring stations (shallow, middepth, deep) in Lake Simcoe. Time series results from the two deep-water stations indicate that over this period Lake Simcoe transitioned from an algal-dominated state toward a state with increased water clarity (i.e., Secchi disk depth) and silica and lower nutrient and chlorophyll a concentrations, which coincided with both substantial management intervention and the establishment of invasive species (e.g., Dreissenid mussels). Consistent with improvement, Secchi depth at the deep-water stations demonstrated expected trends in statistical indicators prior to identified breakpoints, whereas total phosphorus and chlorophyll a revealed more nuanced patterns. Overall, state variables were largely found to yield inconsistent trends in statistical indicators, so many breakpoints were likely not reflective of traditional bifurcation critical transitions. Nevertheless, statistical indicators of state variable time series may be a valuable tool for the adaptive management and long-term monitoring of lake ecosystems, but we call for more research within the domain of early warning indicators to establish a better understanding of state variable behavior prior to lake changes.

Ciliates in man-made mountain reservoirs

Climate warming has multiple effects on an environment. Especially the Alpine region is affected by changing conditions, which do not only have ecological but also economic impacts in respect to winter sports tourism. Due to higher environmental temperatures and less precipitation, artificial snow making is becoming increasingly important and consequently, mountain reservoirs for water storage are built. In these systems, planktonic communities are not only influenced by the naturally harsh environmental conditions of the alpine region, but also by severe changes in water level fluctuations due to water withdrawal and re-filling within short time periods. Information on planktonic communities and species traits in such man-made water bodies is nonexistent. Here, we focused on ciliates, a group of unicellular protists known to adapt and respond rapidly to changing environmental conditions. Simultaneously, we identified abiotic and other biotic factors that shaped these microbial communities. We investigated the species composition, abundance and species traits of ciliates in eleven mountain reservoirs in the Tyrolean Alps, Austria, and hypothesized that these communities differed significantly from natural ones. The mountain reservoirs were investigated twice during the ice-free season and water chemistry, chlorophyll a, bacteria, zooplankton, and ciliates were sampled. We detected 48 ciliate taxa in total, with an average of five taxa per mountain reservoir. A wide range of abundance (summer: 24 to >15,600 Ind L−1; autumn: 38 to ∼7,500 Ind L−1) and no clear pattern in the community composition was found, most likely due to water level fluctuations and the source of water used for filling the mountain reservoirs. The ciliate abundance was significantly affected by pH, nutrients, but also water transparency and potential predators (crustaceans). Planktonic ciliates dominated the mountain reservoirs and, surprisingly, mixotrophic species, typically found in natural (alpine) lakes, were only rarely observed. Our data suggest that in these fast-changing systems, local factors seem to be more important than regional ones.

An Ecological Profile of Hydropsyche alternans (Trichoptera: Hydropsychidae) in Lake Superior, the Last Stronghold of a Once-Dominant Great Lakes Surf Zone Caddisfly.

Simple SummaryPrior to the invasion and spread of Dreissena mussels in the late 1980s, the nearshore waters of the Laurentian Great Lakes were home to diverse assemblages of native aquatic insects, including the net-spinning caddisfly Hydropsyche alternans, which occurred in rocky surf-exposed habitat throughout the system from Lake Superior downstream to Lake Ontario. These surf zone caddisflies are still abundant in the largely Dreissena-free waters of Lake Superior where the present study was conducted. They have not been reported in the lakes below Lake Superior for decades, and are presumed to have been extirpated from Dreissena-infested habitats. The ecological profile presented here documents the life history of H. alternans in Lake Superior, and reveals details of its feeding biology that shed light on the roles that surf zone net-spinners play in the native nearshore food webs of the Great Lakes. The H. alternans life history in Lake Superior begins in mid-summer shortly after oviposition, which features females swimming to surf-exposed lake bottom substrates. Larval development takes approximately 10 months, but most of it occurs during their first 100 days. Adult emergence is broadly synchronous, with large numbers present from the summer solstice through mid-July. Gut content analyses showed that larvae opportunistically feed on algal, animal, and detrital material of aquatic and terrestrial origin. δ13C and δ15N stable isotope data indicate that they function as omnivores that link coastal, nearshore, and pelagic food webs. These energetic links, and the very existence of surf zone insect assemblages in the Great Lakes, depend on the Dreissena populations in Lake Superior remaining relatively small and isolated.We studied the life history, diet, and trophic ecology of Hydropsyche alternans in four rocky sites located along the south-central coast of Lake Superior. The H. alternans life history and broad trophic niche space were similar to those of its riverine relatives. Quantitative sampling over the course of one ice-free season revealed that most individuals lived univoltine life histories that featured early to mid-summer mating, and oviposition and rapid growth and development through summer into fall. Most individuals overwintered as ultimate or penultimate larval instars. Pupation followed ice-out in the spring. Gut content sampling and δ13C and δ15N stable isotope analyses indicated that the typical larval diet is a mix of benthic, pelagic, and terrestrial food resources, including diatoms, small arthropods, sloughed periphyton, and in one site, fugal hyphae apparently of foredune origin. As a suspension-feeding omnivore that relies on waves and currents to deliver food to its nets, H. alternans larvae form energetic links between coastal, nearshore, and offshore food webs. These connections have been lost throughout the lower Laurentian Great Lakes as a consequence of the invasion and spread of Dreissena mussels.

Assessing the size at maturity, spawning, and condition of the truncate soft-shell clam (Mya truncata) of southern Baffin Island, Nunavut, Canada.

The truncate soft-shell clam Mya truncata is an important source of country food for Inuit communities across the territory of Nunavut, Canada. M. truncata also plays an important role in marine ecosystems, yet there is little understanding of their life history and condition in Canadian Arctic waters. To provide a foundation on which aspects of the life history and condition of M. truncata of Baffin Island can be monitored in the future with a changing climate and fishery development, this study estimated size at maturity and provides insights into the spawning cycle and weight-length condition indices of clams from inner Frobisher Bay and the north shore of the Hudson Strait. Male and female M. truncata exhibited similar lengths at 50% attainment of sexual maturity, 31 mm and 32 mm shell length (SL), respectively. Most (77%) of the sexually mature M. truncata collected from inner Frobisher Bay in late August and 35% of clams collected from the Hudson Strait in early September were in the ripe stage of gonadal development. These results lead us to suggest a spring spawning season and that M. truncata invest in gonadal development for the next year’s spawning during the late summer-early autumn ice-free season while phytoplankton concentrations are high. Dry bodyweight-SL relationships were used to show that M. truncata condition can differ significantly over small and large spatial scales based on plotted 95% confidence intervals.

Seasonal ice removal in the Barents Sea and its dependence on heat advection by Atlantic waters

The Barents Sea is one of the key areas in the Arctic for monitoring of climate change. Although the Barents Sea is one of the Arctic seas, it is never completely covered with ice. One of the parameters characterizing the change in the ice regime is the date of ice retreat (DOR). The study is based on ice concentration data from the NOAA / NSIDC Climate Data Record (CDR) from 1979 to 2019 and the GLORYS12V1 ocean reanalysis data from 1993 to 2019. The analysis of the spatial and temporal variability of DOR for the Barents Sea using the HDBSCAN cluster analysis method made it possible to identify areas (clusters) with the synchronous dynamics of DOR. A number of the identified areas are located on the path of the Atlantic waters (AW) in the Barents Sea, which made it possible to relate the revealed temporal variability of the DOR to the variability of the AW transport across the western boundary of the sea. Over the entire Barents Sea, after 2003, there has been a steady trend in the timing of seasonal ice removal to earlier ones. At the same time, each of the six regions identified has its own dynamics and rate of changes in DOR. A noticeable effect of the advective heat flux across the western boundary of the Barents Sea on the DOR was revealed for areas in the central and eastern parts of the sea. At the same time, for different regions, the maximum correlation coefficient is observed at different time lags (from 0 to 6 months). The value of the time lag indirectly indicates the time the thermal signal travels the distance from the western boundary of the sea to the corresponding region. The continuing trend towards an increase in the duration of the ice–free season in the Barents Sea is one of the manifestations of the growing “Atlantification” of the East Atlantic sector of the Arctic Ocean which opens up new prospects for socio–economic activity in this Arctic region.