Factors influencing egg thiamine concentrations of Lake Ontario lake trout: 2019–2020

In the Great Lakes region, thiamine deficiency is considered a recruitment bottleneck for lake trout Salvelinus namaycush and has been correlated with the consumption of non-native alewife Alosa pseudoharengus. While alewife, the most abundant forage fish in Lake Ontario, are the predominant prey for lake trout, they also consume benthic prey such as round goby Neogobius melanostomus. Because variation in the proportion of alewife in lake trout diets is linked to variation in egg thiamine concentrations, understanding how factors such as region of capture and hatchery-strain of lake trout influence diet, are key to understanding the patterns of variation in egg thiamine concentrations observed in this species. With recent increases in natural recruitment of lake trout being observed in the western region of the lake, understanding if egg thiamine is a potential driver is crucial to the rehabilitation of lake trout. In this study, we evaluated egg thiamine concentrations in lake trout during 2019–2020. We found no significant difference in egg thiamine concentrations among regions. However, a stocked Lake Superior deepwater morphotype (Superior Klondike Wild – SKW) showed significantly higher egg thiamine concentrations compared to the lean morphotype including Seneca (SEN) and Lake Champlain Domestic (LCD) strains. An analysis of fatty acid signatures of each hatchery-strain suggested that the SKW strain consumed a higher proportion of round goby than lean strains. Overall, these results suggest that morphotypic differences in the feeding ecology of lake trout can result in biochemical changes which may influence the effectiveness of restoration efforts.     

Spatial and temporal variation in distribution of larval lake whitefish in eastern Lake Ontario: Signs of recovery?

The lake whitefish (Coregonus clupeaformis) is one of the native Lake Ontario fishes that declined severely over the past century. Recent evidence of larval lake whitefish production in a historic spawning area (Chaumont Bay) might signal a recovery of this species in New York waters. We surveyed coastal and open water areas to evaluate densities and estimate total abundance of larval lake whitefish in Chaumont Bay. Other historic spawning areas and embayments with appropriate spawning and nursery habitat were also surveyed, but only a few larvae were found outside of Chaumont Bay. Lake whitefish larvae were found in every embayment sampled within Chaumont Bay, with larval densities of nearly 600/1000 m² in some samples. Greatest abundances occurred in the northern sectors and near the mouth of the bay. Open water densities were generally less than half that of nearshore sites. The total bay-wide estimate for 2005 was approximately 644,000 lake whitefish larvae, but dropped to 230,000–400,000 in 2006 and 2007, respectively. Mean larval growth rates (0.36 mm/day) did not differ by year, but were consistently higher in early May than in late April. Lake whitefish production in Chaumont Bay is encouraging for this species, but the cause and persistence of the decline after 2005 can be determined only by continued monitoring. Other possible bottlenecks of survival may exist at juvenile and adult stages and could significantly affect recruitment dynamics. This species is sensitive to normal climatic fluctuations and increased variability associated with global climatic change could make winter nursery conditions unfavorable for this species.     

Genetic diversity and structure of lake whitefish (Coregonus clupeaformis) 100 years after closure of the commercial fishery

In small, inland fisheries even small perturbations to the ecosystem can quickly influence population abundance, size and age distribution, and genetic structure and diversity. In Lake Champlain, lake whitefish (Coregonus clupeaformis) experienced extensive commercial harvest from the mid-1800 s to1918 and habitat fragmentation due to the construction of multiple causeways between 1850 and 1899. We evaluated the influence these environmental perturbations had on lake whitefish population genetics 120 years later. We used historic catch records to determine whether fishing pressure could have been strong enough to reduce lake whitefish population abundance, and used genotype data from eight microsatellite loci to look for genetic signatures of population-sub structure and bottleneck. Catch records indicate lake whitefish were being harvested in Lake Champlain at a similar magnitude to the Great Lakes, and simulations suggest genetic diversity may have been lost as a result of harvest. However, we were unable to detect significant evidence of a genetic bottleneck, but we cannot conclusively suggest that harvest of lake whitefish did not result in a genetic bottleneck. Additionally, we found only slight evidence of population sub-structure among isolated basins, suggesting that either some gene flow among basins is possible, or that populations are just beginning to diverge and therefore differences in allele frequency were too small to detect. These data provide a perspective on effects of an inland lake commercial fishery that was closed prior to population collapse, and offer a comparison to the Laurentian Great Lakes where lake whitefish are still being harvested.     

Spatial and seasonal variation in the phytoplankton community of Lake Victoria’s Mwanza Gulf,compared to northern parts of the lake

We investigated the phytoplankton species composition and abundance in two seasons in Mwanza Gulf, Lake Victoria (Tanzania). Phytoplankton was sampled and chlorophyll a content was measured in the dry and wet seasons of 2010–2011 at three stations, from the southern land-inward end of the Gulf towards the open lake. Cyanobacteria, mostly small colonial and filamentous species (e.g., Aphanocapsa spp., Planktolyngbya spp., Merismopedia spp.) dominated at each station (76–95 %), followed by Chlorophyta (5–21 %), whereas the contribution of Bacillariophyceae was small (0–6 %). Phytoplankton densities were generally higher in the rainy season and strongly increased going land-inward from the open lake. Low abundance of N-fixing phytoplankton species suggests that N-fixation was low. The chlorophyll a content in the mouth of the Gulf was low (mean values 4–6 µg/L) compared to values reported previously. Also, chlorophyll a values (means 11–14 µg/L) at land-inward stations of Mwanza Gulf were much lower than those in the northern gulfs (Napoleon Gulf, Murchison Bay and Nyanza Gulf). Between 2002 and 2009 the phytoplankton composition of Mwanza Gulf changed from a community mostly dominated by Bacillariophyceae into a community dominated by Cyanobacteria. In the open water of Lake Victoria, Bacillariophyceae and Cyanobacteria were both abundant. Cyanobacteria dominated both in the three northern gulfs and Mwanza Gulf, but all four showed substantial differences in species and genus compositions. Phytoplankton composition and abundance in Mwanza Gulf differs in many respects from the open water of Lake Victoria and its three northern gulfs.     

The role of groundwater in loading of nutrients to a restricted bay in a Precambrian Shield lake Part 2. – Numerical modeling

Previous modeling of hydrologic and nutrient budgets of lakes in Precambrian Shield regions have generally ignored groundwater as a source of water and supplier or sink of nutrients. This paper and its companion (Part 1) address this science gap by probing the role of groundwater in the nutrient balance for a restricted bay of a Precambrian Shield lake (Lake of the Woods) that experienced extensive shoreline development in the 1990s. Based on field data (Part 1), we applied a 3D reactive transport model (FEFLOW) to simulate the fate of nutrients in a cottage septic plume in groundwater and seepage into the bay. Corresponding simulations are for chloride and septic tracers in the plume, and 1D modeling of the mass balance of one septic tracer (acesulfame) in the bay. Our results suggest that, before they reach the lake, significant portions of the septic plume contaminants are attenuated by various processes, including uptake by transpiring plants. Extrapolating, we estimate that, for annual fluxes to the bay, groundwater seepage contributes ~1–3% of the phosphorus (P) and ~2–5% of the dissolved inorganic nitrogen (DIN). The results suggest that these groundwater nutrient fluxes to the bay are derived mainly from natural background sources. In contrast, cottage septic plumes contribute a quarter of the groundwater flux of DIN to Poplar Bay, while the septic contribution of P to the bay is negligible. We estimate that the largest sources of P and DIN fluxes to Poplar Bay are influx from the open lake and atmospheric deposition.     

What controls distribution of larval and juvenile yellow perch? The role of habitat characteristics and spatial processes in a large,shallow lake

The goal of this study was to determine the relative contribution of environmental and spatial processes governing the distribution of larval and juvenile yellow perch (Perca flavescens) in two shallow embayments of a large fluvial lake on the St. Lawrence River system. We tested the hypotheses that: i) larval distribution is not related to habitat characteristics, presumably due to their relatively low swimming capacity, whereas ii) these environmental variables drive juvenile distribution, reflecting a more active habitat selection. This study is one of the first attempts to partition the relative roles of environmental and spatial factors in shaping the distribution of a freshwater fish through its early ontogeny. We show that larvae were not spatially aggregated within the embayments and that habitat characteristics, mainly related to aquatic vegetation, played an important role in explaining their distribution. In contrast, juvenile abundances were not significantly related to habitat characteristics, despite being spatially structured over multiple scales. Contrary to our predictions, habitat association was stronger for larvae than for juveniles which were aggregated independent of habitat characteristics. Increased swimming capacities may thus facilitate the aggregation of juveniles rather than strengthening their association with habitat, at least at the scales considered here (ca 3 km²). These results shed a new light on the factors governing larval and juvenile yellow perch distribution, suggesting that active habitat choice might begin earlier than previously thought.     

Spatial and temporal distributions of lake whitefish spawning stocks in Northern lakes Michigan and Huron, 2003–2008

Adult lake whitefish were tagged and released from the Big Bay de Noc (BBN) and Naubinway (NAB) stocks in northern Lake Michigan, and the Detour (DET) and Cheboygan (CHB) stocks in northern Lake Huron during 2003–2006 to describe their spatial and temporal distributions. The contemporary spatial distributions were compared with past distributions of the BBN and NAB stocks. Sixty-two percent of BBN tag recoveries occurred in Wisconsin waters during winter, spring and summer, but 83% of fall tag recoveries were made near the tagging site. Eighty-eight percent of the NAB tag recoveries were made in the management unit of tagging and 7% occurred into northern Lake Huron. Over 90% of the DET stock remained in the vicinity of the tagging sites regardless of the season, while 75% of the CHB tag recoveries were made in northwestern Lake Huron and 17% were made in Ontario. Based on regression tree analysis, there were strong stock, season, and year effects on movement distances, with weaker effects due to sex and length at tagging. Spatial distribution of the BBN stock changed from 1978–1982 to 2003–2008, but spatial distribution of the NAB stock did not. Substantial differences in movement and distribution existed among the four stocks, large seasonal differences in spatial distribution were found within some stocks, and lake whitefish exhibited strong spawning site fidelity. Present management unit boundaries are inappropriate for managing three of our four stocks, and agencies should consider developing single harvest limits for both northern Lake Huron and western Lake Michigan.     

Our current understanding of lake ecosystem response to climate change: What have we really learned from the north temperate deep lakes?

Climatic change is recognized as an important factor capable of influencing the structural properties of aquatic ecosystems. Lake ecosystems are particularly sensitive to climate change. Several long time-series studies have shown close coupling between climate, lake thermal properties and individual organism physiology, population abundance, community structure, and food-web structure. Understanding the complex interplay between climate, hydrological variability, and ecosystem structure and functioning is essential to inform water resources risk assessment and fisheries management. The purpose of this paper is to present the current understanding of climate-induced changes on lake ecosystem phenology. We first review the ability of climate to modulate the interactions among lake hydrodynamics, chemical factors, and food-web structure in several north temperate deep lakes (e.g., Lake Washington, Lake Tahoe, Lake Constance, Lake Geneva, Lake Baikal, and Lake Zurich). Our aim is to assess long-term trends in the physical (e.g., temperature, timing of stratification, and duration of ice cover), chemical (e.g., nutrient concentrations), and biological (e.g., timing of the spring bloom, phytoplankton composition, and zooplankton abundance) characteristics of the lakes and to examine the signature of local weather conditions (e.g., air temperature and rainfall) and large-scale climatic variability (e.g., ENSO and PDO) on the lake physics, chemistry and biology. We also conducted modeling experiments to quantify the relative effect of climate change and nutrient loading on lake phenology. These modeling experiments focused on the relative changes to the major causal associations underlying plankton dynamics during the spring bloom and the summer stratified period. To further understand the importance of climate change on lakes, we propose two complementary directions of future research. First, additional research is needed to elucidate the wide array of in-lake processes that are likely to be affected by the climate change. Second, it is essential to examine the heterogeneity in responses among different water bodies. The rationale of this approach and its significance for dealing with the uncertainty that the climate signals cascade through lake ecosystems and shape abiotic variability and/or biotic responses have been recently advocated by several other synthesis papers.     

Monitoring changes of snow cover,lake and vegetation phenology in Nam Co Lake Basin (Tibetan Plateau) using remote SENSING (2000–2009)

The changes of environmental factors such as snow cover, vegetation and hydrologic regime of lakes can reflect ecosystem responses to changing climate. A series of satellite imagery-based environmental data archives including variations in snow cover, vegetation phenology and lake level were mapped in the Nam Co Lake Basin for the period 2000–2009. Results of the synthesis indicate that throughout this period, the average annual snow cover was 19.87% of the total basin, and there is an obvious relation between the elevation and a clear decreasing southeast–northwest trend in snow-cover persistence. Snow mainly happens from October to May. The multi-year mean water storage of Nam Co Lake is 86.40 × 10⁹ m³, with a lake level increase of approximately 2.06 m during the study period. Vegetation phenology showed obvious variation with advanced start of season (SOS) and slightly extended duration of season (DOS). The mean DOS for the Nam Co Lake Basin was 154 days from 2000 to 2009. Affected by air temperature, the SOS dates coincided with snowmelt. The seasonal-variability of climate factors was also studied. The satellite-derived continuous and multiple datasets offer the advantage of monitoring the temporal and spatial trends of each of these metrics and mapping extensive, remote in mountainous areas with no in-situ data such as represented by the Tibetan Plateau.     

Long-term changes in hypolimnetic dissolved oxygen in a large lake: Effects of invasive mussels,eutrophication and climate change on Lake Simcoe, 1980–2012

Lake Simcoe has been influenced by multiple environmental drivers over the past decades, especially by reductions in phosphorus (P) loading, climate change, and invasive species such as dreissenid mussels (DM) which became firmly established in 1996. We examined the cumulative impact of these drivers on the volume-weighted hypolimnetic dissolved oxygen concentration (VWHDO) below 18?m at station K42 in Kempenfelt Bay during ice-free seasons from 1980 to 2012. Hypolimnetic DO depletion began in early spring when thermal stratification was observable but weak and continued throughout the ice-free season until cooling sufficiently lowered water column stability. In comparison to the pre-DM invasion period (1980–1995), mean annual VWHDO_init was 2.4?mg?L^?1 higher in the post-DM period (1996–2012), VWHDO_min was 1.54?mg?L^?1 higher and the mean duration of the depletion period (L) was 16?days longer. Mean DO depletion rate (DR) and temperature adjusted DO depletion rate (DR_adj) were slightly lower (7% and 5%, respectively) after 1996. P controls and DM had a positive effect on VWHDO, presumably by lowering productivity and diverting organic matter away from the hypolimnon. However, longer L apparently offset improvements in VWHDO_min. If lengthening of L associated with regional warming continues, then additional efforts to reduce P loads will be necessary to achieve the goal of maintaining VWHDO_min above the target of 7?mg?O₂?L^?1 throughout the summer and fall.     

Total and methyl mercury accumulation in 1994–1995 Lake Michigan lake trout and forage fish

As part of the Lake Michigan Mass Balance Project, total and methyl mercury were determined for lake trout (Salvelinus namaycush) and five forage fish species collected from Lake Michigan near Saugatuck, Michigan, and Port Washington, Sheboygan Reef, and Sturgeon Bay, Wisconsin, between 1994 and 1995. With a mean concentration of 179 ng/g wet wt., whole lake trout total mercury (Hg_T) concentrations ranged between 27.6 and 348 ng/g wet wt. For combined sites, 1–4 yrs, 5–6 yrs, 7–11 yrs, and 12–15 yrs lake trout mean Hg_T concentrations were 73.7, 130, 212, and 280 ng/g, respectively. Forage fish species alewife (Alosa pseudoharengus), bloater (Coregonus hoyi), slimy sculpin (Cottus cognatus), deepwater sculpin (Myoxocephalus thompsoni), and rainbow smelt (Osmerus mordax) had mean Hg_T concentrations of 63.8, 55.3, 36.7, 51.4, and 35.2 ng/g wet wt., respectively. With the exception of alewife, bloater, and slimy sculpin, all fish species contained approximately 100% methyl mercury (MeHg). Field bioaccumulation factors (BAF) were consistent with a Lake Michigan food chain that is more efficient at transferring MeHg to higher trophic levels than some inland lakes. This and other studies of lake trout from Lake Michigan document decreasing Hg_T concentrations in lake trout from 1971 to 1985 and constant or increasing concentrations between 1985 and 2000. These observations were supported by a similar trend in Lake Michigan Hg sediment fluxes. To our knowledge, this is the most intense two year study of mercury in fish for any Great Lake or other large fresh water system and is one of the most complete studies of mercury cycling in the Lake Michigan food chain.     

Water storage strategy in post-flood period for hongze lake based on flood utilizationEI北大核心CSCD

基于洪泽湖的地理地形特征,采用MIKE平台构建了湖泊及其蓄滞洪区联合运用的水文水动力模型,实现了对湖、陆水流运动和水量交换与控制的精细化模拟,并制定了后汛期不同蓄水时机和蓄水方案构成的蓄水策略样本库;通过丰、平、枯多种来水情景大规模的数值模拟,对不同典型年蓄水策略进行了评价和优选。结果表明:若洪泽湖后汛期来水属于丰水年系列,应于9月10—20日偏后期伺机蓄水,采用“先泄后蓄”、泄水效率较高的蓄水策略,尽量避开完整的洪水过程;若来水属于平水年系列,应于9月10—20日偏前期伺机蓄水,采用“先泄后蓄”、泄水效率较低的蓄水策略,在洪水的退水阶段起蓄;若来水属于枯水年系列,应于8月31日—9月10日起蓄,采用“先蓄后泄”的蓄水策略,泄水效率的选择应结合来水预报信息,在洪水的起涨段或中段即可拦蓄。     

Factors influencing water level changes in China’s largest freshwater lake,Poyang Lake,in the past 50 years

This study analyses the changing characteristics in the level of Poyang Lake during the period 1960–2010. Results show that the changing stage of annual lake level variations is evident, and average onset time of the lake dry season has advanced since the 1990s. Investigation indicates that the Yangtze River discharge has a greater impact on annual lake level variations than the lake’s catchment inflow. Climate change in the Yangtze River basin since the 1990s is possibly the precondition for the advance of the lake dry season, which is further aggravated by the effects of the Three Gorges Dam in the 2000s.     

A lake-wide approach for large lake zooplankton monitoring: Results from the 2006–2016 Lake Superior Cooperative Science and Monitoring Initiative surveys

Whole-lake surveys of Lake Superior were completed during late summer in 2006, 2011, and 2016 to assess lower food web conditions under the Cooperative Science and Monitoring Initiative (CSMI). These surveys used a spatially stratified probability approach based on depth to assess food web conditions within different depth zones. We evaluated differences in crustacean zooplankton biomass, rotifer density, and the community structure of both groups in nearshore (<30 m), midshore (30–100 m), and offshore (>100 m) depth zones and investigated changes in these parameters within zones over time. Although nearshore crustacean biomasses and rotifer densities were highly variable, the depth zones differed from each other based on these parameters and should be considered separately. Crustacean biomass, community structure, and vertical position were consistent over time across depth zones. The differences that did occur were within the range of known annual variability. Total rotifer densities were lower in 2016 than in 2006 in all depth zones, but the genera that contributed to the lower values were not the same across zones. Further studies are needed to know whether these differences reflect annual variability or long-term trends. Finally, we show how the depth zones used in this study can facilitate comparisons between monitoring programs. This is important because most zooplankton studies are limited to certain depth zones and changes in zooplankton parameters may not occur uniformly across zones. The high variability in nearshore zooplankton parameters suggests that additional research may be needed to effectively track changes there.     

Prediction of Hydraulic Stability of Francis Turbines of Three Gorges Hydropower Station

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Analysis of Hydrologic Property of Poyang Lake

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State of the “dam-foundation” system during operation of the outlet of the chirkey hydroelectric station

Conclusions  

Analysis of Micro Organic Compound Pollution in Major City River Reaches of the Main Stem of the Changjiang River

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