Eastern Lake Research Articles

The Main Nile Valley at the End of the Pleistocene (28–15 ka): Dispersal Corridor or Environmental Refugium?

Under present environmental conditions, the Nile Valley acts as a ‘natural’ route between Africa and Eurasia, and is often considered as a corridor for dispersals out of and back into Africa in the past. This review aims to address the role played by the Nile Valley at the end of the Pleistocene (28-15 ka) in the context of post-‘Out of Africa’ modern human dispersals. Genetic studies based on both modern and ancient DNA suggest pre-Holocene dispersals ‘back into Africa’ as well as genetic interactions between modern humans across Africa and the Levant. During the Last Glacial, the lowering, or even complete desiccation of major eastern African lakes, including Lake Victoria, reduced the White Nile to a highly seasonal river, depriving the main Nile from its most important tributary in the dry season. This had major consequences, the specifics of which are still debated, on the behavior of the main Nile and the landscape around the Nile Delta. Despite this shift to more arid conditions, there is abundant evidence for human occupation in the main Nile Valley. Combining available geological, palaeoenvironmental, anthropological, genetic and archaeological data, this article discusses problems encountered when trying to reconcile results from different fields, the current limitations of the available data and research perspectives to further address the role of the Nile Valley as a dispersal corridor or an environmental refugium at the end of the Pleistocene.

Urmia Lake dust storms occurrences: investigating the relationships with changes in water zone and land cover in the eastern part using remote sensing and GIS

Urmia Lake is the largest lake in the Middle East which has greatly decreased in recent years. It has had a great impact on the environmental properties of areas around the lake. This study aimed to identify the relationship among dust storms in the eastern part of Urmia Lake and the surrounding vegetation due to the annual and long-term variability of this water zone during the statistical period 1999-2019. Normalized difference water index (NDWI), normalized difference vegetation index (NDVI), Aerosol Optical Depth (AOD), and Dust Storm Index (DSI) were used due to trend and correlation analysis models and T-student analysis. The study results found that, first, the decreasing trend of Urmia Lake, directly and significantly, has led to an increase in dust concentration (AOD) in the lake's eastern part. On the other hand, changes in the water level of Lake Urmia have led to a general decreasing trend in vegetation in the region which led to an increase in the frequency of DSI in the region. The model developed showed that changes in the water zone of Urmia Lake as a very powerful driver leads to an increase in the intensity and frequency of dust storms in the eastern part of the lake and intensifies the dust conditions in the region. The synergistic resultant of these two drivers was maximized in years when both lake area and vegetation were at a minimum at the same time (2011-2016). The estimated scenario of this model is that if the decreasing trend of Urmia Lake intensifies in the study area, more frequent and severe dust storms will occur in the region.

Spatial distribution, historical trend, and ecological risk assessment of phthalate esters in sediment from Taihu Lake, China.

In this study, the distribution of phthalate esters (PAEs) in twenty surface sediment and five core sediment samples in Taihu Lake, China, was investigated, and their ecological risks were assessed. Of the 10 PAE congeners, five PAEs including diethyl phthalate (DEP), dimethyl phthalate (DMP), di-n-butyl phthalate (DBP), di-iso-butyl phthalate (DIBP), and bis(2-ethylhexyl) phthalate (DEHP) were identified and quantified, and the rest 5 PAEs were below the limits of quantification. The concentrations of the total PAEs (ΣPAEs) in surface sediments and core sediments varied from 1.12 × 103 to 18.71 × 103 ng/g and 0.23 × 103 to 5.22 × 103 ng/g, respectively. The dominant PAEs were DBP and DIBP, contributing 85.90% to the ΣPAEs. Overall, the highest concentrations of ΣPAEs occurred in northern lake, followed by eastern lake and western lake, and southern lake was the least polluted area. The spatial distribution of ΣPAEs in sediments showed that the PAE distribution pattern was influenced by the riverside environment. The historical trend of the past 100 years was reconstructed in the core sediment via a 210Pb dating technique. The vertical profile of the PAE congeners indicated that concentrations of PAEs started to increase since the 1990s in northern core sediments. It was estimated that the inventories of ΣPAEs in Taihu Lake was 4868.01 t. The potential ecological risk assessment by hazard quotient (HQ) method revealed that DBP posed a moderate risk due to its relatively high concentrations, with DIBP posed a low risk, while DEP, DMP, and DEHP exhibited no risk to the aquatic system.

Spatial-temporal variations of the <i>in-situ</i> growth rate of bloom-forming cyanobacteria and their environmental factors in Lake Chaohu, China

原位生长率是研究藻类生长、衰亡、种群演变、生产力估算，以及藻类对环境变化响应的重要指标，针对水华蓝藻原位生长率的测定，目前还缺乏成熟可靠的手段.本研究利用改进的原位培养法，根据培养前后藻蓝素浓度的变化，对巢湖东、中、西3个湖区水华蓝藻的原位生长率进行周年调查.结果表明，巢湖水华蓝藻的原位生长率变化范围在-1.16~0.69 d^-1之间，表层的原位生长率最高，中层次之，底层大部分月份都为负值；原位生长率在空间分布上由高到低依次为西部湖区>中部湖区>东部湖区；在季节变化上，原位生长率春季（4—6月）相对较高，冬季（1—2月）相对较低.与环境因子进行相关分析后发现，原位生长率与溶解性总磷和温度正相关，这表明溶解性总磷和温度可能是影响巢湖水华蓝藻原位生长率的重要环境因子.;In-situ growth rate is an important parameter for algae to study their growth, death, population variation, productivity and response to environmental changes. Currently, there is a lack of mature and accurate method to determine the in-situ growth rate of bloom-forming cyanobacteria. In this study, an improved in-situ incubation method base on the change of phycocyanin were used to investigate the annual net in-situ growth rate of bloom-forming cyanobacteria in the eastern, central and western lake areas of Lake Chaohu. The results showed that the net in-situ growth rate of bloom-forming cyanobacteria ranged from -1.16 to 0.69 d^-1. The growth rates in the surface layer were higher than those in the middle layer, and those in the bottom layer were the lowest and negative in most months. In terms of spatial distribution, the growth rates from high to low were the eastern, central and western lake areas. The growth rates were the highest in spring (April to June) and the lowest in winter (January to February). Spearman correlation analysis showed that growth rate was positively correlated with dissolved total phosphorus (DTP) and temperature, which indicates that DTP and temperature are the key environmental factors affecting the in-situ growth rate of bloom-forming cyanobacteria in Lake Chaohu.

Spatiotemporal distribution of carbon dioxide partial pressure and its diffusion flux in surface water of Karst wetland

为揭示岩溶湿地表层水体二氧化碳分压（pCO₂）的时空分布规律及其扩散通量，以我国最大的岩溶湿地贵州威宁草海为研究对象，分别于2019年7月（丰水期）和12月（枯水期）通过网格布点法，系统采集草海表层湿地水体，测定水样理化指标和离子组成，利用PHREEQCI软件计算水体pCO₂，并基于Cole提出的气体扩散模型估算水-气界面二氧化碳（CO₂）的扩散通量.结果表明：草海湿地表层水体丰水期pCO₂的变化范围为0.44~645.65 μatm，平均值为（55.94±124.73）μatm；枯水期变化范围为35.48~707.95 μatm，平均值为（310.46±173.54）μatm；丰水期水体整体pCO₂低于枯水期，空间上两期水体均呈现东部区域及河流入湖口处pCO₂较高，而中西部区域pCO₂欠饱和的特征.水-气界面CO₂的扩散通量在丰水期变化范围为-43.27~27.16 mmol/（m²·d），平均值（-34.49±12.93） mmol/（m²·d），枯水期变化范围为-33.36~28.15 mmol/（m²·d），平均值（-8.02±15.85） mmol/（m²·d），与其他岩溶湖库相比，水生植物丰富的草海在两个极端水文期CO₂扩散通量相对较低，总体表现为大气CO₂的汇.;In order to explore the temporal and spatial distribution of the partial pressure of carbon dioxide (pCO₂) and its diffusion flux in the surface water of karst wetland, the largest karst wetlands in China, Weining Chaohai, Guizhou Province, was selected as the research object. The surface wetland water of Lake Caohai was systematically collected through the method of grid placement in July (wet season) and December (dry season), respectively, in 2019. The physicochemical parameters and ion composition of the water samples were measured, the pCO₂ of the water was calculated by PHREEQCI, and the diffusion flux of carbon dioxide (CO₂) at the water-air interface was estimated base on the gas diffusion model proposed by Cole. The results show that the variation of pCO₂ in the surface water of Lake Caohai wetland ranges from 0.44 μatm to 645.65 μatm in the wet season, with an average value of (55.94±124.73) μatm, while 35.48 μatm to 707.95 μatm in the dry season, with an average value of (310.46±173.54) μatm. In general, the distribution of pCO₂ was higher in dry season than in wet season, and higher in the eastern lake area and the entrance of river to the lake but undersaturated in the midwest area of the study region, spatially. The diffusion flux of CO₂ in Lake Caohai wetland water ranges from -43.27 mmol/(m²·d) to 27.16 mmol/(m²·d), with an average value of (-34.49±12.93) mmol/(m²·d) in the wet season, while ranges from -33.36 mmol/(m²·d) to 28.15 mmol/(m²·d), with an average value of (-8.02±15.85) mmol/(m²·d) in the dry season. Compared with other karst lakes and reservoirs, Lake Caohai, which is rich in aquatic plants, has relatively low CO₂ diffusion flux during the two extreme hydrological periods, and is generally a sink of atmospheric CO₂.

Spatial distribution of lake trout (Salvelinus namaycush) across seasonal thermal cycles in a large lake

Abstract Animal movements are influenced by the environment they inhabit and the need to maximise fitness and minimise cost. As such, seasonal thermal cycles in temperate lakes play an important role in the selection of habitat by species. Lake trout (Salvelinus namaycush) is a native top predator in the Laurentian Great Lakes and currently under rehabilitation in Lake Ontario. This cold, deep‐water species is known to migrate to shallower depths in the autumn to spawn, but their spatial and seasonal distribution have not been examined in detail. We quantified the residency and home ranges of 24 lake trout in eastern Lake Ontario across a full year (1 May 2017 to 30 April 2018) using acoustic telemetry to assess the influence of seasonal thermal cycles. Specifically, we used three thermal logging stations in the eastern basin, 164 acoustic receivers, and a total of over 1,000,000 detections to describe seasonal distribution. We also documented occurrences of long‐distance movements (via 130 acoustic receivers located in the western basin of Lake Ontario), and thus the potential spatial overlap of populations from the eastern and western basins. During stratification (1 July–1 November), lake trout (n = 24) showed a horizontally restricted distribution in regions of deeper water in eastern Lake Ontario. A variable and broad distribution was observed around the shallower Kingston Basin shoals during isothermal (1 January–30 April), spring warming (1 May–30 June; spring mix), and autumn cooling (2 November–31 December) periods. Home range sizes ranged from 0.1 to 3,966 km2 among all thermal cycles, with the largest observed during cooling autumn mix conditions driven by four individuals. Large variation in home range area was observed among individuals, and, thus, means were not statistically different between seasons. Three individuals occupied shallower shoals even during stratified conditions, and another individual crossed the entire lake from the east to the west end of Lake Ontario, travelling over 200 linear km in 17 days. Our results confirm that thermal regimes and spawning needs affect the spatial use of lake trout in Lake Ontario, but demonstrate that there are broad distributions during isothermal conditions, highly individualistic spatial utilisation, and inter‐individual variation in spatial distribution and exploratory behaviour. All of these behaviours are consistent with other top predator species. Defining the spatial utilisation and distribution of individuals are important steps toward a better understanding of reintroduced species ecology in freshwater ecosystems. The variation of individual lake trout distribution across seasons implies that individuals may have different influences on the overall ecosystem function and potentially different responses to increasing water temperatures. These results suggest that an adaptive management approach is required when rehabilitating populations of this native fish where populating multiple habitats in an ecosystem is an objective in the face of a changing environment.

Nutrient footprints on the Toronto-Mississauga waterfront of Lake Ontario

The extent of nutrient enrichment over the urbanized shoreline of western Lake Ontario bordering the Cities of Toronto and Mississauga was investigated in 2018. Concentrations of total phosphorus were higher and more wide-ranging compared with nearshore reference areas in eastern Lake Ontario. Area-weighted chlorophyll a was higher over the shoreline from the mouth of the Credit River to Humber Bay west of Toronto Harbour compared with that to the east from the Toronto Beaches to the Rouge River, a pattern also seen broadly in concentrations of phosphorus fractions and nitrates. Concentrations of phosphate measured by mass spectrometry, and using an internal standard to minimize sampling losses, were higher in Toronto Inner Harbour, near wastewater outfalls, river mouths, and to varying extent over the mixing areas of these discharges. Chlorophyll asuggested broadly oligotrophic to oligo-mesotrophic conditions despite areas with nutrient fractions suggestive of more productive conditions. Toronto Inner Harbour was mesotrophic, with wide-ranging levels of phosphorus fractions strongly influenced by the variable loading from the Don River into the harbour. Phosphorus fractions in the harbour quays which also receive CSOs discharges were elevated at times. Blooms or scums of planktonic algae were not observed. Elevated concentrations of phosphate were found at shallow depths suitable for growth of the green algae Cladophora. As these urban areas continue to grow, the potential for additional nutrient loading to exacerbate growth of algae should be watched given the present conditions that indicate variable but pervasive nutrient enrichment.

The impacts of waterbird-mediated elemental enrichment on chironomid assemblages from island ponds in Lake Ontario

Ring-billed gulls (Larus delawarensis) and double-crested cormorants (Phalacrocorax auritus) have nested in dense colonies across the Laurentian Great Lakes since their rapid population expansions during the early- and mid-20 th century, respectively. Dated sediment cores from ponds located near nesting sites have been used to track the history of these large colonies on islands in eastern Lake Ontario. However, less is known about avian-mediated biotransport of contaminants to these nesting sites and its effects on aquatic biota at mid-trophic levels, such as chironomids. Here, we used a paleolimnological approach to determine the extent of possible avian- mediated metal(loid) contamination of ponds in nesting sites compared to reference sites. Water from avian-im- pacted ponds had higher concentrations of Al, Cd, Cu, Fe, Pb, and Se than the reference ponds, and exceeded the Canadian Council of Ministers of the Environment (CCME) guidelines for the protection of aquatic life at some sites. Down-core geochemical analysis of elements in sediments showed that concentrations of Cd, Se, and Zn were significantly higher in impacted ponds than in reference sites and correlated significantly with stable nitrogen isotopes, a marker of avian-derived nitrogen. In sites impacted by ring-billed gulls, Cd and Zn concentrations in sediments exceeded or approached those at which frequent adverse biotic effects are expected. Metal contamination was linked to altered chironomid assemblages, with subfossil remains in the avian-impacted sites including more taxa tolerant of heavy metal contamination than reference sites. Notably, chironomids were largely absent from the sites with the highest metal concentrations. These findings have implications for understanding and managing contaminant cycling in the Great Lakes, as waterbirds that nest in dense colonies can act as biovectors that transport metals to new and unexpected locations.

Evidence for a late glacial advance near the beginning of the Younger Dryas in western New York State: An event postdating the record for local Laurentide ice sheet recession

Abstract Widespread evidence of an unrecognized late glacial advance across preexisting moraines in western New York is confirmed by 40 14C ages and six new optically stimulated luminescence analyses between the Genesee Valley and the Cattaraugus Creek basin of eastern Lake Erie. The Late Wisconsin chronology is relatively unconstrained by local dating of moraines between Pennsylvania and Lake Ontario. Few published 14C ages record discrete events, unlike evidence in the upper Great Lakes and New England. The new 14C ages from wood in glacial tills along Buttermilk Creek south of Springville, New York, and reevaluation of numerous 14C ages from miscellaneous investigations in the Genesee Valley document a significant glacial advance into Cattaraugus and Livingston Counties between 13,000 and 13,300 cal yr B.P., near the Greenland Interstadial 1b (GI-1b) cooling leading into the transition from the Bölling-Alleröd to the Younger Dryas. The chronology from four widely distributed sites indicates that a Late Wisconsin advance spread till discontinuously over the surface, without significantly modifying the preexisting glacial topography. A short-lived advance by a partially grounded ice shelf best explains the evidence. The advance, ending 43 km south of Rochester and a similar distance south of Buffalo, overlaps the revised chronology for glacial Lake Iroquois, now considered to extend from ca. 14,800–13,000 cal yr B.P. The spread of the radiocarbon ages is similar to the well-known Two Creeks Forest Bed, which equates the event with the Two Rivers advance in Wisconsin.

Estimating Release of Trace Elements from an Area with Historical Open Pit Mining of Alum Shale Using Mass Transport and Element/Sulfate Ratios Calculations

Alum shale was mined for oil and uranium production in Kvarntorp, Sweden, 1942–1966. Remnants such as pit lakes, exposed shale and a 100-meter-high waste deposit with a hot interior affect the surrounding environment, with elevated concentrations of, e.g., Mo, Ni and U in the recipient. Today most pit lakes are circumneutral while one of the lakes is still acidic. All pit lakes show signs of sulfide weathering with elevated sulfate concentrations. Mass transport calculations show that for elements such as uranium and molybdenum the western lake system (lake Söderhavet in particular) contributes the largest part. For sulfate, the two western lakes contribute with a quarter each, the eastern lake Norrtorpssjön about a third and a serpentine pond system receiving water from the waste deposit contributes around 17%. Except for a few elements (e.g., nickel 35%), the Serpentine system (including the waste deposit area) is not a very pronounced point source for metal release compared to the pit lakes. Estimates about future water runoff when the deposit has cooled down suggest only a slight increase in downstream water flow. There could possibly be first flush effects when previous hot areas have been reached by water.

Co-variability of the summer NDVIs on the eastern Tibetan Plateau and in the Lake Baikal region: Associated climate factors and atmospheric circulation.

The Tibetan Plateau and Siberia are both crucial regions in which the vegetation dynamics are sensitive to climate change. The variabilities in the normalized difference vegetation index (NDVI) over the two regions have been explored previously, but there have been few studies on the relationship of the NDVI in the two regions. Using the GIMMS-NDVI, GHCN-CAMS and NCEP reanalysis datasets and statistical and physical diagnostic methods, we show that the summer (June, July and August) NDVI over the eastern Tibetan Plateau and Lake Baikal and its adjacent eastern region of Siberia have an in-phase co-variability, especially on an interannual timescale (with a correlation coefficient of 0.69 during the time period 1982-2014). Further analyses show that precipitation and the related cloud cover and solar radiation are responsible for the variability in the NDVI over the eastern Tibetan Plateau, whereas temperature has the more important role in modulating the variability in the NDVI over the Lake Baikal region. A dipole pattern prevails over the Tibetan Plateau-Lake Baikal region and reflects the anomalies in the intensity and location of the South Asian high and the northeast Asian blocking high. This dipole pattern simultaneously modulates precipitation over the eastern Tibetan Plateau and the temperature over the Lake Baikal region and leads to the co-variability of the NDVI between the two regions. A synergistic sea surface temperature index, which reflects sea surface temperature anomalies in the eastern tropical Pacific Ocean, the northwest Pacific Ocean, the northern Indian Ocean and the subtropical north Atlantic Ocean, appears to adjust this Tibetan Plateau-Lake Baikal dipole pattern and is therefore closely related to the co-variability of the NDVI between the eastern Tibetan Plateau and the Lake Baikal region. Our results suggest that vegetation dynamics may not be only a local phenomenon in some areas, but are also likely to remotely link with variations in vegetation over other regions.

Identifying the critical watershed regions creating lake nutrient enrichment (SLRs) based on a watershed-lake integrated perspective – A case study of Chaohu Lake Basin, China

Identifying critical watershed source regions is essential for lake environments protection. However, related studies are mainly focused on assessing watershed Total Nitrogen (TN) and Total Phosphorus (TP) loads, while the impact of watershed on lake nutrients is rarely considered. To fill this gap, the amounts of watershed nutrient loss over the last ten years were assessed, and the corresponding lake TN and TP concentrations were acquired. Finally, the critical watershed regions creating lake nutrient enrichment (SLRs) were identified by analyzing the relationships from the integrated watershed-lake perspective. The results indicated that: i) The watershed TN and TP output amounts showed a rising trend in the last 10 years (mostly between 2012 and 2016); ii) The lake TP and TN in the western lake were much higher than those in the eastern lake; and iii) SLRs were located in the western Chaohu watershed. Specific findings were obtained from the statistical analysis in sub-watershed and intra-annual scales. First, the SLRs for TN were concentrated in the Nanfei (NF), which covered only 32 sub-watersheds and were mainly located in urban construction areas. In contrast, the SLRs for TP were more widely distributed and located contiguously across the major influent streams belonging to the Hangbu (HB) and NF. Second, the intra-annual variance is obvious. For TP, the spring season can be considered the most ideal period for SLRs identification, while the summer season is ideal for TN. These differences are driven by different loss processes, discharge capacities, and occurrence forms for TN and TP. In general, the integrated perspective of lake-watershed is helpful for identifying SLRs, and the temporal analysis at the seasonal scale and spatial analysis at the sub-watershed scale facilitate a deeper understanding of SLRs.

Improving the robustness of beach water quality modeling using an ensemble machine learning approach

Microbial pollution of beach water can expose swimmers to harmful pathogens. Predictive modeling provides an alternative method for beach management that addresses several limitations associated with traditional culture-based methods of assessing water quality. Widely-used machine learning methods often suffer from high variability in performance from one year or beach to another. Therefore, the best machine learning method varies between beaches and years, making method selection difficult. This study proposes an ensemble machine learning approach referred to as model stacking that has a two-layered learning structure, where the outputs of five widely-used individual machine learning models (multiple linear regression, partial least square, sparse partial least square, random forest, and Bayesian network) are taken as input features for another model that produces the final prediction. Applying this approach to three beaches along eastern Lake Erie, New York, USA, we show that generally the model stacking approach was able to generate reliably good predictions compared to all of the five base models. The accuracy rankings of the stacking model consistently stayed 1st or 2nd every year, with yearly-average accuracy of 78%, 81%, and 82.3% at the three studied beaches, respectively. This study highlights the value of the model stacking approach in predicting beach water quality and solving other pressing environmental problems.

Lateglacial and Holocene environmental history of the central Kola region, northwestern Russia revealed by a sediment succession from Lake Imandra

Bolshaya Imandra, the northern sub‐basin of Lake Imandra, was investigated by a hydro‐acoustic survey followed by sediment coring down to the acoustic basement. The sediment record was analysed by a combined physical, biogeochemical, sedimentological, granulometrical and micropalaeontological approach to reconstruct the regional climatic and environmental history. Chronological control was obtained by 14C dating, 137Cs, and Hg markers as well as pollen stratigraphy and revealed that the sediment succession offers the first continuous record spanning the Lateglacial and Holocene for this lake. Following the deglaciation prior to c. 13 200 cal. a BP, the lake's sub‐basin initially was occupied by a glacifluvial river system, before a proglacial lake with glaciolacustrine sedimentation established. Rather mild climate, a sparse vegetation cover and successive retreat of the Scandinavian Ice Sheet (SIS) from the lake catchment characterized the Bølling/Allerød interstadial, lasting until 12 710 cal. a BP. During the subsequent Younger Dryas chronozone, until 11 550 cal. a BP, climate cooling led to a decrease in vegetation cover and a re‐advance of the SIS. The SIS disappeared from the catchment at the Holocene transition, but small glaciers persisted in the mountains at the eastern lake shore. During the Early Holocene, until 8400 cal. a BP, sedimentation changed from glaciolacustrine to lacustrine and rising temperatures caused the spread of thermophilous vegetation. The Middle Holocene, until 3700 cal. a BP, comprises the regional Holocene Thermal Maximum (8000–4600 cal. a BP) with relatively stable temperatures, denser vegetation cover and absence of mountain glaciers. Reoccurrence of mountain glaciers during the Late Holocene, until 30 cal. a BP, presumably results from a slight cooling and increased humidity. Since c. 30 cal. a BP Lake Imandra has been strongly influenced by human impact, originating in industrial and mining activities. Our results are in overall agreement with vegetation and climate reconstructions in the Kola region.

Composition and assembly of bacterial communities in surface and deeper sediments from aquaculture-influenced sites in Eastern Lake Taihu, China

Although aquaculture provides a stable and high-quality source of food, the environmental effects related to large-scale industrial aquacultural activities have raised concern. To identify the influence of aquacultural activities on sedimentary bacterial communities, we collected surface and deeper sediments from a series of sites subjected to varying intensities of aquacultural activities within Eastern Lake Taihu, China. The associated physicochemical properties were measured, and 16S rRNA gene sequencing was applied to determine the related bacterial communities in sediment. The diversity and composition of bacterial communities within the surface sediments differed significantly from those of the deeper sediment samples. Marked differences were also found between the surface sediments of the aquaculture-influenced and non-aquaculturally influenced sites. More importantly, phylogenetic structure analysis indicated that stochastic processes dominated the assembly of the bacterial communities; yet, the relative contribution of deterministic processes to bacterial community assembly was greater in the aquacultural zones than in the non-aquacultural zones. Furthermore, we identified total phosphorus (TP) as the most important factor driving the assembly of bacterial communities influenced by aquaculture in sediment. These findings provide useful information for ecological assessments and remediation strategies for aquaculture-influenced ecosystems.

Prioritizing coastal wetlands for marsh bird conservation in the U.S. Great Lakes

Human activity surrounding the Laurentian Great Lakes basin has significantly degraded coastal wetland habitats, resulting in severe marsh bird population declines and reduced coastal resilience to changing environmental conditions. Given the need to conserve remaining coastal wetlands for wildlife and people, we developed a spatial prioritization to identify the most important U.S. Great Lakes coastal wetlands for 14 marsh bird species. We modeled occurrence and relative abundance of each species using boosted regression trees, a machine learning algorithm, to relate standardized monitoring data to ten remotely-sensed environmental covariates. We then used Zonation conservation planning software to rank every wetland cell based on its importance for the suite of marsh bird species. Evaluation of the drivers of marsh bird occurrence and abundance revealed that open water, herbaceous wetland, latitude, longitude, and impervious surface were the most important predictors across focal species. The high-priority wetlands for marsh birds (defined as grid cells ranked in the top 20%) occurred along the shores of eastern Lake Ontario, western Lake Erie/St. Clair, Saginaw Bay, Green Bay, northern lakes Michigan and Huron, and western Lake Superior. Overall, less than half (42%) of high-priority coastal wetlands across the Great Lakes basin are currently under some level of protection, with Lake Ontario priority wetlands being the least protected (25%). Our findings represent an opportunity to improve coastal wetland conservation in a region where wetland loss and degradation continue to threaten marsh bird populations and the integrity of one of the world's largest freshwater ecosystems.

Particle Dynamics in the Nearshore of Lake Michigan Revealed by an Observation‐Modeling System

AbstractGiven that few drifter experiments combined with a wave‐current coupled model system had been conducted in the complex nearshore area, this work was motivated to reveal the nearshore dynamics by applying an observation‐modeling system to Lake Michigan. Analysis of 11 surface drifters, wind, and current observations along the lake's eastern coast indicates that their trajectories are synergistically controlled by winds and initial releasing sites. Additionally, strong winds significantly impact nearshore dynamics, and the highly sensitive nearshore and offshore drifters are stranded in distinct regions. Simulations indicate that the model reproduces drifter trajectories and endpoints reasonably and that particle fates are mainly dominated by winds, while effects from heat flux and waves are also important. Further analysis of wave effects on particle dynamics indicates that both the wave‐induced sea surface roughness and Stokes drift advection are crucial to the simulated particle trajectories during wind events. Finally, virtual experiments confirm that particle dynamics are evidently susceptible to winds and initial locations. Overall, both the inclusion of physics effects (e.g., adding winds, heat fluxes, and waves) and diminishing the model uncertainties (e.g., from various wind data sources, wind drag coefficient formulations, model grids, and vertical turbulent mixing parameterizations) are important methods to improve the particle simulations. The successful application of this nearshore observation‐modeling system to Lake Michigan can be beneficial to the understanding of nearshore‐offshore transports and larval and fisheries recruitment success in similar freshwater and estuarine environments.

Changes in the Frequency of Cool Season Lake Effects within the North American Great Lakes Region

The North American Great Lakes influence surface weather downwind, distinctly in winter when southward migrating cold air passes over relatively warm lakes. Study of the synoptic atmospheric patterns favorable for lake effects has focused on lake-effect snowfall, the most impactful effect of the lakes. Although the patterns are conducive to lake effects, they might not actually yield discernible modification of downwind surface weather. This study uses historical daily data (1964–1965 through 2017–2018) of weather types to detect cool season (November–April) modification of cold, dry air upwind of the Great Lakes to cool, moist air downwind of the eastern (Erie, Ontario) and western (Michigan, Superior) lakes. A spatial arrangement of weather types across the region is shown to identify individual days characterized by a lake effect. The frequency of lake effects increased through the first one third of the record, but it has since decreased, most profoundly since a change point in the late 1990s and more prominently for the eastern lakes. At stations immediately downwind of the lakes, the result is a changed cool season hydroclimate, with fifty-four-year declines in lake-effect precipitation amount and frequency and in the percentages of seasonal precipitation amount and frequency attributed to lake effects.

Organic carbon accumulation and productivity over the past 130 years in Lake Kawaguchi (central Japan) reconstructed using organic geochemical proxies

Organic matter in lake sediments contains information that can be used to reconstruct lake environmental histories over decades or centuries. In this study, we used organic geochemical proxies (i.e., total organic carbon [TOC], TOC/total nitrogen [TN] atomic ratios [C/N], stable carbon isotope ratios of TOC [δ13CTOC] and palmitic acid [δ13CC16:0], and nitrogen isotope ratios of bulk sediment [δ15Nbulk]) in sediments from Lake Kawaguchi, Japan, to reconstruct detailed histories of the organic matter accumulation and lake productivity over the past 130 years. Vertical profiles of the mass accumulation rate (MAR) of TOC in the eastern lake basin (core KAW14-7A) showed parallel increases with the C/N ratio from the 1960s to the 1980s, indicating an accelerated delivery of terrestrial organic matter via anthropogenic land-use change. In contrast, the C/N ratios in the western and central basins (cores KAW14-1A and KAW14-4B, respectively) were almost constant prior to the 1980s, suggesting that the increasing trends in the TOC MAR values in these cores are most likely attributable to the onset of eutrophication associated with rapid economic growth after the mid-1950s. On the other hand, the δ15Nbulk showed a gradual increase from the late 1870s, providing evidence for anthropogenic nitrogen input to the lake prior to the apparent eutrophication. After the 1960s–1970s, the δ15Nbulk values rapidly increased, demonstrating water deterioration associated with the direct nutrient discharge into the lake from domestic wastewater. The δ13CC16:0 profiles displayed similar increasing trends to δ15Nbulk from the mid-1960s, demonstrating a close relationship between lake productivity and anthropogenic nitrogen input in Lake Kawaguchi. Our geochemical records as a whole clearly show high algal productivity and enhanced deposition of organic matter in recent decades, suggesting that the amelioration of the lake water is a likely consequence of the transfer of nutrients to the sediment by enhanced productivity, rather than a decrease in the amount of nutrient inflow into the lake.

Differential habitat use patterns of yellow perch Perca flavescens in eastern Lake Michigan and connected drowned river mouth lakes

Understanding stock structure and habitat use is important for sustainable fisheries management and conservation of genetic and phenotypic diversity. In eastern Lake Michigan, yellow perch Perca flavescens is found in both the nearshore region of Lake Michigan proper and drowned river mouth (DRM) lakes, small estuary-like systems directly connected to Lake Michigan. Recent genetic analyses suggest complex stock structure between these habitats and the potential migration of Lake Michigan yellow perch into the profundal zone of DRM lakes. We quantified carbon (δ13C) and oxygen (δ18O) stable isotope ratios of yellow perch otolith cores to index natal origins, and measured muscle δ13C, nitrogen (δ15N), δ18O, and hydrogen (δ2H) isotope ratios to reflect recent diet and habitat use. Stable isotope ratios of otolith cores and muscle samples support the existence of resident populations in nearshore Lake Michigan and DRM lakes, as well as Lake Michigan migrants using DRM lakes. Most fish caught in DRM lakes that had natal and recent stable isotope values similar to Lake Michigan fish were collected during fall in DRM lake profundal zones. Comparison of otolith core and muscle stable isotope ratios of individual yellow perch suggest that individuals that recently migrated to DRM lakes also spent early life in Lake Michigan. Differential habitat use patterns of yellow perch in eastern Lake Michigan may have important implications for harvest estimates and fishing regulations. Migration by Lake Michigan fish into DRM lakes does not appear to be related to reproduction, and the underlying benefits of these migrations remain unclear.