Northern Lake Research Articles

The influence of sampling method and season on modeling of selenium into coldwater fish and implications on tissue-based water quality benchmarks.

Selenium (Se) contamination of aquatic ecosystems has led to the local extirpation of some Se-sensitive fish species. Although Se exposure occurs primarily via diet, considerable uncertainty lies in modeling Se transfer and bioaccumulation from sediment, detritus, and/or periphyton through benthic macroinvertebrates (BMI) to fish. Here we estimated Se concentrations in four coldwater fish species (northern pike, white sucker, lake whitefish, and ninespine stickleback) inhabiting boreal lakes downstream from a uranium mill in northern Canada. In addition, we evaluated the potential effects of BMI and periphyton sampling methods (artificial substrates vs. grab samples), seasons (summer vs. winter), and models (USEPA vs. Assessment of the Dispersion and Effects of Parameter Transport) on the estimated Se concentrations in fish tissue. Results were compared with site-specific benchmarks and observed Se concentrations in resident fish. In summer 2019, periphyton and BMI were sampled at 10 sampling stations (two in Vulture Lake and eight in McClean Lake) using artificial substrates (n = 4) and sediment grab samples (n = 3). In winter 2021, samples were collected in McClean Lake (n = 3) through ice holes using a sediment grab sampler. Estimated Se concentrations in fish tissue depended on the surface sediment or periphyton Se concentrations used in the models. At Vulture Lake, Se concentrations in northern pike muscle estimated using the grab sample data (17.3 ± 11.5 µg/g DW), but not the artificial substrates (34.5 ± 1.2 µg/g DW), were comparable with the observed mean concentration (19.0 ± 1.4 µg/g DW) in this species. At McClean Lake, Se body burdens in forage fish estimated using data from both sampling methods were comparable with measured data. Significantly lower mean whole-body Se concentrations were estimated for all fish species in winter (1.0 ± 0.3 µg/g DW) relative to summer (4.8 ± 1.6 µg/g DW). Further investigation is necessary to understand how potential seasonal shifts in dietary Se exposure relate to fish reproduction and early life stages. Integr Environ Assess Manag 2023;00:1-15. © 2023 SETAC.

GEOLOGICAL MARKERS OF THE UPPER PLEISTOCENE DEPOSITS IN MAIN RIVER VALLEYS OF WESTERN SIBERIA

During the second half of the 20th century by the end of the first quarter of the 21st century the problem of differentiation and correlation of the main rivers of Western Siberia (primarily the Ob and Yenisey) valleys sediments was intensively discussed. Traditionally, the regional Quaternary history of the river valleys was considered as the “terrace flight” paradigm. According to it in the Neogene-Quaternary time alluvial terraces formed by sequentially from the older upper to the younger lower ones. It was considered that terrace formed by neotectonics, paleoclimate dynamics changed the fullness of the rivers, advance of the sea and dereliction influenced on base of erosion and blocking river valley by northern glaciers. As a result, in outside glacier zone appeared barrier basins and periglacial alluvium. However, on the official maps of the Quaternary deposits the heights, age and even the number of terraces differ significantly. Nowadays a lot of data are contrary to theory about flight consistently carved cycloclimatic terraces and periglacial alluvium facies replacing the ice-dammed northern lakes in the south of Western Siberia. In the article it was performed the updated concept of the sedimental structure of the Upper Neopleistocene in the main valleys of the region and taking into account data on glacier outburst floods from intermountain area to the plain. Its intensive erosional and accumulative activity has so far been underestimated.

Evidence of summer thermal stratification in extreme northern lakes

Rapid warming in the High Arctic has induced changes in terrestrial environments that have included major recent shifts in lakes and ponds. Numerous studies exist of spatial trends in water chemistry, bioindicator groups, and paleoenvironmental change from High Arctic lakes; however, little is known about lake thermal stratification regimes at high latitudes beyond assumptions based on generalized classification schemes. Here, we report on the presence in late July 2022 of positive thermal stratification during open-water conditions in two freshwater lakes near Clements Markham Inlet, on northern Ellesmere Island. These lakes are situated in the polar desert at 82.6°N, >1000 km north of the generally accepted northern limit of summer thermal stratification. Given their location approaching the northernmost land on Earth, the thermal profiles of these lakes suggest that the occurrence of summer stratification may no longer be discounted anywhere in the Northern Hemisphere.

Initial Post-Release Performance of Cultured Cyprinus chilia Juveniles in a Shallow Lake in Southwestern China.

The post-release performance of cultured fish is crucial for understanding the viability of cultured fish and assessing the effects of stock enhancement programs. This study aimed to investigate the initial post-release performance of cultured Cyprinus chilia juveniles by examining their movement, spatial distribution, gut fullness, and gut microbiota in nature. In July 2022, a total of 20,000 C. chilia juveniles, tagged with visible implant fluorescence (VIE), were released into Qilu Lake, a shallow lake in southwestern China. Subsequently, continuous recapture was conducted at fixed recapture sites using trap nets during the first 7 days, one month and three months after release. Out of the released fish, 512 were recaptured, resulting in a recapture rate of 2.56%. The recaptured fish had a 100% tag retention rate. The majority (98.05%) of the recaptured fish were found in the recapture sites located on the eastern or western lakeshore, while only 10 fish were recaptured from the recapture sites in the northern lake area. The water depth range where the recaptured fish were found ranged from 190 to 350 cm, with most fish preferring depths less than 300 cm. The majority of the released fish migrated towards the eastern and western lakeshore, with long-distance movement (greater than 100 m) primarily occurring within the first four days after release. The level of gut fullness in the released fish initially decreased and then increased over time following release. Regarding gut microbiota, the dominant phyla observed in most samples were Firmicutes, Proteobacteria, Cyanobacteria, and Fusobacteria. Furthermore, significant variations in the dominant genera were observed across different samples. Principal coordinates analysis (PCoA) revealed clear separation between the microbial communities of pre-release and post-release C. chilia juveniles. This study demonstrated that VIE tagging was a suitable method for short-term marking of C. chilia juveniles. Lakeshores with water depths less than 300 cm were identified as preferred habitats for C. chilia juveniles. The primary adaptation period for cultured C. chilia juveniles released into the natural environment was found to be approximately 4-5 days. These findings contribute to our understanding of the post-release performance of cultured fish and may provide guidance for the management and evaluation of relevant stock enhancement programs.

Coastal archaeological site visibility problems and underwater prospects in the Northern Lake Superior Basin

AbstractThe early to middle Holocene was marked by considerable variability in lake levels in the Lake Superior Basin due to a combination of meltwater runoff, isostatic adjustment, shifting glacial margins, and climate change. These processes likely had a large impact on the preservation and visibility of coastal archaeological sites dating from the Early Period (Paleoindian) to the Middle Period (Shield Archaic). Of particular interest is the brief interval after 9300 cal. B.P. when ancestral Lake Superior dropped to its lowest level (Houghton) and human populations may have made incursions deeper into the basin. Elsewhere in the Upper Great Lakes, this period is associated with offshore archaeological sites submerged by rising water levels later in the Holocene. New geological data from the Thunder Bay, ON, region yield exceptional insight into the paleohydrology of the Houghton phase and, hence, the underwater archaeological prospects of this low water phase in the northern Lake Superior Basin. These data indicate that the lake reached its lowest level by at least ~9100 cal. B.P. but was highly unstable, at least initially, due to a combination of climate and meltwater runoff. Early underwater sites may be confined to two short, hydrologically closed, lowstands between ~9100 and 8700 cal. B.P. and would have been impacted by at least one lake transgression. Such sites, however, may still hold better potential for organic preservation and the visibility of large cultural features compared to their terrestrial counterparts. Coastal sites occupied when the lake was hydrologically closed may be especially well‐preserved due to rapid inundation before the gradual, and generally erosional, Nipissing transgression occurred.

Long-term trends in carbon and color signal uneven browning and terrestrialization of northern lakes

The widespread browning of northern lakes has been associated with long-term increases in dissolved organic carbon and color and should be linked to changes in surface water carbon dioxide, yet the long-term covariation in these three key carbon components of lake functioning remains to be assessed. We present long-term trends in dissolved organic carbon, color, and carbon dioxide from lakes, with generally positive but highly variable trends in organic carbon and a large degree of uncoupling with color and carbon dioxide. The highest rates of change in color and carbon dioxide were in lakes with greatest increasing dissolved organic carbon trends. Lakes with the lowest water retention times had greater increases and stronger coupling between all three parameters, coinciding with dominance of terrestrially derived carbon. These results suggest an uneven terrestrialization of northern lakes, where the increases and coupling in the three carbon components depends on hydrology and watershed connectivity.

Hydrobiological characteristic of small lakes in northern Karelia during the ice-covered period

The life of lakes in winter is still insufficiently studied. The purpose of this article is a comparative analysis of the quantitative development of planktonic and benthic communities and the abiotic conditions of their existence during the ice-covered period in two small (<1 km2) northern lakes that differ greatly in morphometry and the degree of water humification. A significant difference was revealed in the seasonal dynamics of plankton communities in the studied lakes. In a deeper lake with water uncolored by humus, the quantitative development of phytoplankton at the end of the ice-covered period was almost as significant as during the open-water period. It is necessary to note the rapidity of changes in under-ice phytoplankton in early spring: in April 2020, the content of chlorophyll a in water changed more than six times during a week. There was no mass development of phytoplankton under the ice in a shallow highly humified lake. The zooplankton of the studied lakes was characterized by the opposite trend. In the deep-water lake, the winter zooplankton was noticeably inferior to the summer one in terms of the level of quantitative development; in the shallow lake, a high biomass (~1 g/m2) of zooplankton was noted throughout the entire study period. The macrozoobenthos of lakes in winter, on the whole, retained the same high level of quantitative development as in the open-water period. Seasonal differences were local and were caused by the redistribution of bottom animals due to changes in the oxygen and, possibly, temperature regime of bottom waters. In particular, due to hypoxic-anoxic conditions at the end of the ice-covered period, benthic animals migrated from the profundal zone of the deep-water lake. After the ice melted and the near-bottom waters were saturated with oxygen, the profundal community quickly recovered. Thus, the quantitative development of biological communities in winter can vary greatly even in closely located lakes, in particular, it depends on the degree of humification of the water body. Given the high dynamism of phytoplankton in early spring, the assessment of the role of the under-ice period in the life of lakes, apparently, requires long-term research, including detailed observations at the end of ice-covered period.

Arctic warming drives striking twenty-first century ecosystem shifts in Great Slave Lake (Subarctic Canada), North America's deepest lake.

Great Slave Lake (GSL), one of the world's largest and deepest lakes, has undergone an aquatic ecosystem transformation in response to twenty-first-century accelerated Arctic warming that is unparalleled in at least the past two centuries. Algal remains from four high-resolution palaeolimnological records retrieved from the West Basin provide baseline limnological data that we compared with historical phycological surveys undertaken on GSL between the 1940s and 1990s. We document the rapid restructuring of algal community composition ca 2000 CE that is consistent with recent increases in regional air temperature and declines in ice cover and wind speed, that collectively altered habitats for aquatic biota. This new limnological regime initiated the first observation of scaled chrysophytes and favoured the rapid proliferation of small planktonic cyclotelloid diatoms which replaced the long-established dominance of large filamentous Aulacoseira islandica in West Basin sedimentary records. Such abrupt transformations in the primary producers of this socioecologically valuable 'northern Great Lake' may have widespread implications for the entire food web with unknown consequences for aquatic ecosystem functioning and fisheries, which First Nations, Métis and other northern communities depend upon, pointing to the need for new studies.

Urban lake water quality responses to elevated road salt concentrations

Road salt runoff from de-icing applications is increasingly impacting water quality around the globe. Excess salt (especially chloride) concentrations can negatively impact the biological, chemical, and physical properties of freshwater ecosystems. Though road salt pollution is a prevalent issue affecting many northern temperate lakes, there are few studies on how freshwater salinization interacts with other ecological stressors such as eutrophication. We investigated how chloride from road deicers influences water quality in an urban lake. We sampled a tributary and lake receiving large amounts of road salt runoff from a nearby highway in Grand Rapids, Michigan over a 20-month period. Chloride concentrations in the deepest part of the lake consistently exceeded the US EPA chloride chronic toxicity threshold of 230 mg/L, at times reaching up to 331 mg/L. These high chloride concentrations appear to be responsible for preventing part of the lake from complete mixing, and causing hypoxia in the deepest regions of the lake. Total phosphorus concentrations near the surface averaged 35 μg/L but exceeded 7500 μg/L in the deepest part of the lake, which occupies 3–5 % of total lake volume. Phosphorus release rates from the sediments were low and unlikely to be a current source of the high phosphorus concentrations. Rather, both phosphorus and chloride likely have been accumulating in the hypolimnion over a relatively long period of time. Lake management actions will require control of both internal and external phosphorus and chloride sources in the future. We recommend that phosphorus be addressed first to avoid the extremely high phosphorus concentrations from reaching the photic zone and stimulating algal blooms, which would occur if salt was removed first and the halocline broke down. Our findings and recommendations are applicable to other lakes facing similar issues.

Macroinvertebrate Response to Internal Nutrient Loading Increases in Shallow Eutrophic Lakes.

In eutrophic lakes, even if external loading is controlled, internal nutrient loading delays the recovery of lake eutrophication. When the input of external pollutants is reduced, the dissolved oxygen environment at the sediment interface improves in a season without algal blooms. As an important part of lake ecosystems, macroinvertebrates are sensitive to hypoxia caused by eutrophication; however, how this change affects macroinvertebrates is still unknown. In this study, we analysed the monitoring data of northern Lake Taihu from 2007 to 2019. After 2007, the external loading of Lake Taihu was relatively stable, but eutrophication began to intensify after 2013, and the nutrients in the sediments also began to decline, which was related to the efficient use of nutrients by algal blooms. The community structure and population density of macroinvertebrates showed different responses in different stages. In particular, the density of oligochaetes and the Shannon-Wiener index showed significant differences in their response to different stages, and their sensitivity to eutrophication was significantly reduced. Under eutrophication conditions dominated by internal loading, frequent hypoxia occurs at the sediment interface only when an algal bloom erupts. When there is no bloom, the probability of sediment hypoxia is significantly reduced under the disturbance of wind. Our results indicate that the current method for evaluating lake eutrophication based on oligochaetes and the Shannon-Wiener diversity index may lose its sensitivity.

Spatial and temporal pattern of benthic macroinvertebrate assemblages in two large Chinese freshwater lakes subjected to different degrees of eutrophication

Freshwater lakes are subjected to increasing eutrophication and algal blooms worldwide, which have dramatically impacted the aquatic biodiversity. This situation is especially true in the Yangtze River Floodplain, China. However, few researches have been focused on differences in the spatial and temporal patterns of benthic macroinvertebrates assemblages between the two adjacent lakes in this floodplain. In this study, we conducted seasonal investigations in 2021 to compare the spatial and temporal patterns of macroinvertebrates in Lakes Taihu and Lake Chaohu. Non-metric multidimensional scaling (NMDS) analyses showed Lake Taihu was found to have differences in assemblages within the lake, but Lake Chaohu was found to have uniform assemblage across the entire lake. Macrophyte-dominated lake regions (eastern Lake Taihu) were characterised by the highest species richness and diversity indices than those in other lake regions. The pollution sensitive species (e.g. EPT: Ephemeroptera, Plecoptera and Trichoptera) were only distributed in the macrophytic areas of Lake Taihu. Corbicula fluminea, polychaetes Nephtys oligobranchia and Capitella sp. were dominant in the middle central lake regions in Lake Taihu. Lake Chaohu and the northern Lake Taihu, with turbid algal-dominated state, were characterised by dominance of Oligochaetes and Chironomids. These differences were attributed to varying habitats and environmental parameters among different lake regions. Canonical correspondence analysis (CCA) demonstrated that macrophytes, chemical oxygen demand (CODMn), temperature, ammonium (NH3-N) and electric conductivity (EC) were detected as important factors influencing such macroinvertebrate assemblage patterns between these two lakes. This study contributes to the scientific knowledge of within lake habitats, community assemblages, nutrients and pollution within these lakes.

Can water release from local reservoirs cope with the droughts of downstream lake in a large river-lake system?

Lake is an important component of the Earth’s surface water bodies. Frequent and serious drought events in lakes have affected the security of regional water resources and caused the degradation of the lake ecosystem. Poyang Lake, the largest freshwater lake in China, has been suffering from increasingly severe hydrological droughts. This study simulated and investigated the effects of water release from local reservoirs in dry season on hydrological droughts in Poyang Lake based on a hydrodynamic model MIKE 21, and quantified the effectiveness of the joint operation of local reservoirs and the Three Gorges Reservoir (TGR). Major results showed that the water level of Poyang Lake during the dry period was significantly raised by the water release from local reservoirs, especially in the northern lake area. The average and the lowest lake level increased from 10.99 m to 11.18–11.59 m and from 9.97 m to 10.14–10.50 m at Xingzi station, respectively. Meanwhile, both the duration of low water and the drought severity/intensity (DS/DI) decreased significantly, with the duration decreasing from 128 days to 105–115 days for typical threshold lake level of 12.0 m, and the DS and DI decreasing from 176.6 m and 1.38 m/day to 117.6–155.3 m and 1.12–1.35 m/day, respectively. Moreover, the release oflocal reservoirs shortened the exposure duration of beach wetland, from nearly 3 months to about 1.5–2.5 months at the northern channel of Poyang Lake. The area with long exposure duration (>120 days) was also significantly reduced. In addition, the hydrodynamic simulations revealed that the joint operation of local reservoirs and the TGR further raised the average and the lowest lake level and decreased the duration of low water and drought severity and intensity. Outcomes of the study provided valuable references for mitigating lake droughts in complex river-lake-catchment system.

Seasonal variation in activity and nearshore habitat use of Lake Trout in a subarctic lake

BackgroundIn lake ecosystems, predatory fish can move and forage across both nearshore and offshore habitats. This coupling of sub-habitats, which is important in stabilizing lake food webs, has largely been assessed from a dietary perspective and has not included movement data. As such, empirical estimates of the seasonal dynamics of these coupling movements by fish are rarely quantified, especially for northern lakes. Here we collect fine-scale fish movement data on Lake Trout (Salvelinus namaycush), a predatory cold-water fish known to link nearshore and offshore habitats, to test for seasonal drivers of activity, habitat use and diet in a subarctic lake.MethodsWe used an acoustic telemetry positioning array to track the depth and spatial movements of 43 Lake Trout in a subarctic lake over two years. From these data we estimated seasonal 50% home ranges, movements rates, tail beat activity, depth use, and nearshore habitat use. Additionally, we examined stomach contents to quantify seasonal diet. Data from water temperature and light loggers were used to monitor abiotic lake conditions and compare to telemetry data.ResultsLake Trout showed repeatable seasonal patterns of nearshore habitat use that peaked each spring and fall, were lower throughout the long winter, and least in summer when this habitat was above preferred temperatures. Stomach content data showed that Lake Trout acquired the most nearshore prey during the brief spring season, followed by fall, and winter, supporting telemetry results. Activity rates were highest in spring when feeding on invertebrates and least in summer when foraging offshore, presumably on large-bodied prey fish. High rates of nearshore activity in fall were associated with spawning. Nearshore habitat use was widespread and not localized to specific regions of the lake, although there was high overlap of winter nearshore core areas between years.ConclusionsWe provide empirical demonstrations of the seasonal extent to which a mobile top predator links nearshore and offshore habitats in a subarctic lake. Our findings suggest that the nearshore is an important foraging area for Lake Trout for much of the year, and the role of this zone for feeding should be considered in addition to its traditional importance as spawning habitat.

Effect of temperature on carbon accumulation in northern lake systems over the past 21,000 years

Introduction: Rising industrial emissions of carbon dioxide and methane highlight the important role of carbon sinks and sources in fast-changing northern landscapes. Northern lake systems play a key role in regulating organic carbon input by accumulating carbon in their sediment. Here we look at the lake history of 28 lakes (between 50°N and 80°N) over the past 21,000 years to explore the relationship between carbon accumulation in lakes and temperature changes.Method: For this study, we calculated organic carbon accumulation rates (OCAR) using measured and newly generated organic carbon and dry bulk density data. To estimate new data, we used and evaluated seven different regression techniques in addition to a log-linear model as our base model. We also used combined age-depth modeling to derive sedimentation rates and the TraCE-21ka climate reanalysis dataset to understand temperature development since the Last Glacial Maximum. We determined correlation between temperature and OCAR by using four different correlation coefficients.Results: In our data collection, we found a slightly positive association between OCAR and temperature. OCAR values peaked during warm periods Bølling Allerød (38.07 g·m−2·yr−1) and the Early Holocene (40.68 g·m−2·yr−1), while lowest values occurred during the cold phases of Last Glacial Maximum (9.47 g·m−2·yr−1) and Last Deglaciation (10.53 g·m−2·yr−1). However, high temperatures did not directly lead to high OCAR values.Discussion: We assume that rapid warming events lead to high carbon accumulation in lakes, but as warming progresses, this effect appears to change as increased microbial activity triggers greater outgassing. Despite the complexity of environmental forcing mechanisms affecting individual lake systems, our study showed statistical significance between measured OCAR and modelled paleotemperature for 11 out of 28 lakes. We concluded that air temperature alone appears to drive the carbon accumulation in lakes. We expected that other factors (catchment vegetation, permafrost, and lake characteristics) would influence accumulation rates, but could not discover a conclusive factor that had a statistical significant impact. More data available on long-term records from northern lake systems could lead to more confidence and accuracy on the matter.

Does the Ice Age legacy end in Central Europe? The shrinking distributions of glacial relict crustaceans in Lithuania

Abstract Glacial relict crustaceans are characterized by their affinity for cold and well‐oxygenated waters and their limited dispersal ability. They occur in large, deep lakes of Northern and Central Europe and North America, with their distributions shaped by glaciation events. In many countries and especially along the southern distribution edge, glacial relict populations are declining as a result of eutrophication, global warming, and possible adverse interactions with invasive Ponto‐Caspian crustaceans. This study assessed the status of three glacial relict malacostracan species (the amphipods Monoporeia affinis and Pallaseopsis quadrispinosa and the mysid Mysis relicta) in Lithuania and modelled their abundance across environmental variables, including the presence of Ponto‐Caspian malacostracans. The results showed that M. affinis is probably extinct in the country, whereas M. relicta was found in only nine out of 16 locations from which it was previously recorded. The distribution of P. quadrispinosa also seems to be shrinking. The annual water renewal rate (P. quadrispinosa and M. relicta) and lake depth (P. quadrispinosa) were significantly and positively associated with the relative abundance of relict mysids and amphipods, but no association was found with lake size or with the presence of invasive Ponto‐Caspian crustaceans. Both species were less abundant in samples collected in the 21st century compared with the 20th century. Given the biogeographical and ecological importance of glacial relict crustaceans, their widespread declines are of concern and point to the deterioration of habitat quality, essential for other species with similar requirements. Urgent action is needed to improve water conditions and safeguard these communities. In cases where water quality improves, the reintroduction of extirpated relict populations should be considered. One example is Lake Drūkšiai, where these crustaceans became extinct during the operation of the Ignalina nuclear power plant but where conditions improved following the closure of the power plant in 2009.

Energy channelling, food chain length and body condition in a northern lake predator

Abstract Identifying potential links between food web structure and animal body condition is fundamental for predicting the long‐term persistence of populations under rapidly changing environments. Northern lakes, and the cold‐water adapted species that inhabit them, are particularly vulnerable to a warming climate. We explored relationships among body condition and energy channel use in lake trout (Salvelinus namaycush) and seasonal variation in food‐chain length in the Lake of Two Rivers, Ontario, Canada. Bayesian mixing models using carbon isotope values (δ13C) of essential amino acids showed that individuals utilising multiple energy channels had higher gonad mass, suggesting that dietary diversity has reproductive fitness benefits. Amino acid nitrogen isotope (δ15N) analysis revealed seasonal variation in food chain length, with extension of the food web during winter and spring and truncation of the food web during summer. Although these findings illustrate increased omnivory of lake trout during summer, there was no clear evidence that seasonal changes in food chain length had an impact on trout condition. These findings provide new insight into potential relationships between food web structure, energy flow and consumer condition in freshwater ecosystems, thereby revealing potential responses of species to shifting ecosystem states under intensifying climate change at high latitudes.

Determining Sexual Development and Size at Sexual Maturity of Sardinella tawilis and its Implications on Management

Reproductive biology is important in formulating management interventions for fish stocks. Limits on catch size are established based on the identified size at first sexual maturity of the target fish species, which can be accurately determined through histological analysis of gonads. The study investigated the reproductive characteristics of the endangered Sardinella tawilis and determined the size at first sexual maturity based on histological analysis. Between 2017 and 2018, 312 fish samples with different lengths were collected in Taal Lake's northern and southern basins. The length-weight relationship of S. tawilis shows that the species exhibits negative allometric growth. Female S. tawilis, characterized by larger sizes, are significantly more abundant in our catches than male individuals (mean sex ratio p<0.05) and exhibit an asynchronous oocyte development. Histological analysis of gonads showed that the size at sexual maturity for both male and female S. tawilis were at 75 to 79 mm FL, which was smaller than the reported size at sexual maturity based on morphological analysis. Smaller average and maximum lengths, as well as the size at first sexual maturity, could suggest that S. tawilis has experienced growth overfishing and a slowly degrading lake environment through time. Results highlighted the importance of ensuring that immature S. tawilis can enter sexual maturity and contribute to the population through reproduction. It is also highly recommended that the size of S. tawilis to be targeted by fisheries are individuals above 100 mm FL, which exhibited the highest proportion of spawning capable individuals.

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.

Temporal resolution of birth rate analysis in zooplankton and its implications for identifying strong interactions in ecology.

Expanding on Haeckel's classical definition, ecology can be defined as the study of strong and weak interactions between the organism and the environment, hence the need for identifying strong interactions as major drivers of population and community dynamics. The solution to this problem is facilitated by the fact that the frequency distribution of interaction strengths is highly skewed, resulting in few or, according to Liebig's law of the minimum, just one strong interaction. However, a single strong interaction often remains elusive. One of the reasons may be that, due to the ever-present dynamics of ecological systems, a single strong interaction is likely to exist only on relatively short time intervals, so methods with sufficient temporal resolution are required. In this paper, we study the temporal resolution of contribution analysis of birth rate in zooplankton, a method to assess the relative strength of bottom-up (food) versus top-down (predation) effects. Birth rate is estimated by the Edmondson-Paloheimo model. Our test system is a population of the cladoceran Bosmina longirostris inhabiting a small northern lake with few planktivorous predators, and thus likely controlled by food. We find that the method's temporal resolution in detecting bottom-up effects corresponds well to the species' generation time, and the latter seems comparable to the lifetime of a single strong interaction. This enables one to capture a single strong interaction "on the fly," right during its time of existence. We suggest that this feature, the temporal resolution of about the lifetime of a single strong interaction, may be a generally desirable property for any method, not only the one studied here, intended to identify and assess strong interactions. Success in disentangling strong interactions in ecological communities, and thus solving one of the key issues in ecology, may critically depend on the temporal resolution of the methods used.

Predator telemetry informs temporal and spatial overlap with stocked salmonids in Lake Huron

Double-Crested Cormorants (Phalacrocorax auratus), Walleyes (Sander vitreus), and Lake Trout (Salvelinus namaycush) are migratory predators that undergo extensive movements in Lake Huron. Stocking of juvenile salmonid fish (Oncorhynchus and Salmo sp.) is an important component of fishery management in Lake Huron and assessing the spatial and temporal extent of predator movements is a useful consideration for determining when and where to stock juvenile fish to reduce predation and maximize survival. Previous investigation indicated that some Walleyes migrate to the main basin of Lake Huron in spring from Saginaw Bay. Similarly, telemetry studies of Lake Trout movement in Lake Huron have indicated an onshore movement in the spring. We used detection histories of Walleyes implanted with acoustic transmitters tagged in Saginaw Bay and Lake Trout implanted in northern Lake Huron to estimate the arrival date of migrating adults at eight ports in Lake Huron, where hatchery reared juvenile salmonids are stocked. Satellite telemetry of Cormorants that return to nesting grounds in northern Lake Huron were used to estimate their arrival dates at the same Lake Huron ports. Arrival of Walleye at Lake Huron ports ranged from April 10th to May 7th. Cormorants arrived earlier than Walleye at most Lake Huron ports (April 11th–April 18th). Lake Trout were more variable with a range of onshore movement from March 28th to May 16th. Our results suggested stocking efforts at these ports should generally occur before April 14th to decrease predatory impact from Cormorants, Walleyes, and Lake Trout.