Rip currents near coastal structures in Lake Michigan: Characterization and assessment for warnings

Rip currents near coastal structures commonly occur in Lake Michigan in the Great Lakes region of the United States. Lack of timely warning due to undocumented characteristics of rip currents and no assessment tool can contribute to tragic drownings incidents. In this paper, we characterized rip current occurrences near breakwater structures and developed an assessment tool for providing timely rip current warnings to beachgoers at the study site, City of Port Washington, WI. Characteristics of rip currents near the structure were observed from field measurements or visual images. Deflection rip currents had speeds of ～ 0.2 m/s and lasted for several hours. The rip current occurrences were associated with environmental proxies. It was found that rip currents can occur even when the water appears calm near the structure. A Structure Rip Checklist and Assessment Matrix (SRiCAM) with a four-tiered risk was developed and validated using observations. Furthermore, the SRiCAM was integrated into cyberinfrastructure with a data contingency plan to provide real-time warnings to the public. The applicability of the SRiCAM to other locations across Lake Michigan was further tested and results are promising. Overall, the SRiCAM has the potential to be widely extended to foster recreational water safety and resilience to rip current hazards in the Great Lakes.     

Diet composition and overlap for adult walleye,lake whitefish,and yellow perch in Green Bay,Lake Michigan

Interspecific interactions among walleye Sander vitreus, lake whitefish Coregonus clupeaformis, and yellow perch Perca flavescens in Green Bay could influence the population status of each species, but potential trophic interactions are poorly understood. Our objectives were to determine if diet assemblages for each species and diet overlap among species varied spatially and temporally within Green Bay. Adult walleye (≥381 mm total length (TL); N = 981), lake whitefish (≥432 mm TL; N = 1507), and yellow perch (≥150 mm TL; N = 1174) were collected during May-October of 2018 and 2019 from multiple locations in southern and northern Green Bay. Diet assemblages of each species varied between northern and southern Green Bay, but walleye diets were more temporally variable (among months within zones and between years) than diets of lake whitefish or yellow perch. Lake whitefish represented a seasonally important prey item for walleye in southern Green Bay, composing 10 % and 41 % of walleye diets by weight in May and June, respectively. Yellow perch generally composed <15 % of walleye diets by weight but were consumed at a broader spatiotemporal scale than lake whitefish. Diet overlap between walleye and both lake whitefish and yellow perch was generally weak or moderate, whereas diet overlap between whitefish and perch was generally strong. Our assessment of adult trophic interactions suggests that changes in the population status of one species could influence fisheries for all three, and we identify additional research questions to address potential population-level effects of these trophic interactions.     

Opportunities for combining data of Estonian and Russian monitoring to reflect on water quality in large transboundary Lake Peipsi

Lake Peipsi, one of the world’s largest lakes, is shared between Estonia and Russia. The water quality in different parts of the lake has so far been assessed independently. Here we explore opportunities for combining data of Estonian and Russian monitoring. For that, we 1) analysed the compatibility of data for some water quality variables; 2) estimated the potential effects of the differences in sampling frequency; 3) provided a few regression models to calculate the missing data for months not sampled by the Russian side. Data of the concurrent Estonian and Russian sampling indicated a good compatibility. Estonian data analysis suggested that water quality assessment results are sensitive to sampling frequency. For example, total phosphorus (TP) in the largest basin showed a long-term decreasing trend in three month data that disappeared when data for other months were added. Disregarding some months may lead to under- or overestimation of certain factors with no consistency in the response of different basins. Hence, data of the whole ice-free period are recommended for an adequate water quality assessment. Furthermore, we demonstrated that monthly values of the water quality variables of the same year are autocorrelated. Based on this, we filled the gaps in the long-term data and compiled a dataset for the whole lake that enables its most comprehensive use in water quality assessment and management. Long-term data revealed no water quality improvement of Lake Peipsi. Further reduction of the external nutrient load is needed. Eutrophication is sustained by high internal phosphorus load.     

引江济巢工程对改善巢湖水质的数值模拟分析

巢湖受周围城市工业化及农业生产迅速发展的影响,湖区及流域的生态环境发生了巨大变化,尤其是近几年巢湖水质达到重富营养化水平。引江济巢工程是改善巢湖水质的重要工程措施,采用EFDC生态动力学模型模拟了巢湖不同调水流量、调水线路、调水时间对水环境的影响。结果表明,引江济巢工程在一定程度、时间上使巢湖湖区水质发生一定程度的改善,但若入湖水质不达标,调水也增加了巢湖的富营养化风险。     

Vertical oscillations of the thermocline caused by internal waves modify coldwater pelagic fish distribution: Results from a large stratified lake

Fishes typically occupy a species-specific temperature range, with their occupied depth being related to the lake’s temperature profile. When a fish’s preferred temperature range coincides with the thermocline, the location of their preferred thermal habitat is influenced by the rise and fall of internal waves, leading to possible changes in fish depth. These internal waves are common in large, stratified lakes, yet we do not know how they affect the spatial distribution and behavior of freshwater fishes. We conducted nighttime hydroacoustic surveys in a large, deep embayment of a large thermally stratified lake to observe whether pelagic fish respond to vertical oscillations of the thermocline caused by internal waves. The coldwater pelagic fish in our study (primarily cisco, Coregonus artedi) typically occupied a narrow vertical band approximately 5–8 m thick and temperatures between 10.8 ± 0.8–13.6 ± 1.6 °C (fishes sized 106–500 mm), just below the thermocline (centered around 15–17 °C). Importantly, the upper bound of fish depth varied in response to vertical thermocline movements associated with internal waves, suggesting fish respond to changes in their physical environment on timescales commensurate with basin-scale internal wave periods (hours to days), to remain within their preferred thermal habitat. Dissolved-oxygen levels were typically above avoidance thresholds of these fish, thus not likely exerting a strong influence on fish location. Our findings emphasize the need to account for internal waves when designing hydroacoustic and netting surveys, as thermocline movements can influence where fish are located.     

Association of aerobic anoxygenic phototrophs and zebra mussels,Dreissena polymorpha,within the littoral zone of Lake Winnipeg

While nutrient loading has affected all levels of Lake Winnipeg’s ecology, its greatest influence has likely been on the microbial community. In addition to eutrophication, zebra mussels (Dreissena polymorpha) have recently invaded the ecosystem and threaten food web dynamics. Their filter-feeding predation and association with bacteria, specifically phototrophs, was investigated. A sampling trip to Lake Winnipeg in October 2017, focused on the isolation, enumeration, and identification of aerobic anoxygenic phototrophs in littoral water, sediment, and tissues of mussels. Gimli, Patricia, and Grand beaches, separated by >15 km across the South Basin, had similar bacterial counts when cultivated on rich organic, BG-11, purple non-sulphur, and K₂TeO₃-supplemented media. Culture-based enumeration on rich organic medium revealed 1.74% of heterotrophs from littoral waters were aerobic anoxygenic phototrophs, and represented 13.98% within sediments. In contrast, 0.48, 1.15, and 0.16% of cultured heterotrophs were aerobic anoxygenic phototrophs within zebra mussel gill, gut, and gonadal tissues, respectively. High-throughput sequencing of bacterial 16S V4 rDNA maintained similar trends in respective bivalve organs, where 0.22, 1.13, and 0.20% of total 16S genes belonged to these phototrophs. Several Sphingomonadaceae isolates were recovered from gut tissues, all with filamentous morphology large enough for predation. Bioaccumulation of metals was also studied in D. polymorpha. All tested associated aerobic anoxygenic phototrophs were capable of resisting the metalloid oxide tellurite. The consistent distribution of aerobic anoxygenic phototrophs within microbial communities across Lake Winnipeg, and their predominance in the gut tissues of zebra mussels suggested bacterial consumption by this invasive species.     

The perceived risk of the Line 5 Pipeline and spills under ice

Using the psychometric paradigm of risk in conjunction with surveys of the Michigan public (n = 638) and a regional planning organization (n = 65), we examine the perceived risk and concerns associated with underwater oil pipelines, the Enbridge Line 5 pipeline in particular, and oil spills under ice. The fate of Line 5 is heavily debated in Michigan, specifically the portion that traverses the Straits of Mackinac, which can be ice-covered for months. Scant literature examines how individuals perceive the risk associated with Line 5, its alternatives, or potential spills in open water or under ice. Here we identify considerable concern regarding both the pipeline and the potential for spills under ice on behalf of the public, and increased concern about spills under ice on behalf of the planning organization. Organization members' concerns are significantly predicted by beliefs about the difficulty in remediating spills, however not by beliefs about spills' likelihood, difficulty in detection, noticeability, or consequences. Our results identify the need to better examine and communicate the risks associated with underwater pipelines and spills, both in open water and under ice, as well as options for remediating oil captured under ice. Furthermore, we recommend the adoption of decision-making and risk governance processes that explicitly expand analysis of the social, economic and environmental tradeoffs of underwater pipelines such as Line 5.     

Development and application of a real-time water environment cyberinfrastructure for kayaker safety in the Apostle Islands,Lake Superior

Assessing all pertinent environmental variables to categorize a skill level to safely navigate the water environment can be difficult for inexperienced kayakers, especially at a remote site where internet access is limited. A real-time kayaker safety assessment of water environmental conditions at the Mainland Sea Caves of the Apostle Islands National Lakeshore, Lake Superior is achieved. We present a new cyberinfrastructure that provides kayakers with real-time data access and a Safety Index (SI) with consideration of multiple environmental factors to characterize the degree of navigational difficulty for classifying kayaker skill levels. Specifically, radar reflectivity is added to improve forecasts of dangerous conditions caused by convective storms using state-of-the-art weather and wave modeling. Spectral characteristics of surface waves are employed to correlate the occurrences of extreme and freak waves. In addition, unexpectedly dangerous conditions like coastal upwelling and freak wave occurrence due to changing wind directions are considered. A contingency plan is implemented to handle the issue of possibly missing required environmental data. Display of the SI and visualization of other real-time environmental data are communicated by a power-efficient kiosk. Web analytics demonstrates a public interest in real-time water conditions and the need for the on-site kiosk to provide the latest information before kayakers enter the water. The new real-time water environment cyberinfrastructure for kayaker safety in the Apostle Islands, Lake Superior has been successfully operated since 2014.     

Anaerobic methane oxidation and aerobic methane production in an east African great lake (Lake Kivu)

We investigated CH₄ oxidation in the water column of Lake Kivu, a deep meromictic tropical lake with CH₄-rich anoxic deep waters. Depth profiles of dissolved gases (CH₄ and N₂O) and a diversity of potential electron acceptors for anaerobic CH₄ oxidation (NO₃^?, SO₄^2?, Fe and Mn oxides) were determined during six field campaigns between June 2011 and August 2014. Denitrification measurements based on stable isotope labelling experiments were performed twice. In addition, we quantified aerobic and anaerobic CH₄ oxidation, NO₃^? and SO₄^2? consumption rates, with and without the presence of an inhibitor of SO₄^2?-reducing bacteria activity. Aerobic CH₄ production was also measured in parallel incubations with the addition of an inhibitor of aerobic CH₄ oxidation. The maximum aerobic and anaerobic CH₄ oxidation rates were estimated to be 27?±?2 and 16?±?8?μmol/L/d, respectively. We observed a difference in the relative importance of aerobic and anaerobic CH₄ oxidation during the rainy and the dry season, with a greater role for aerobic oxidation during the dry season. Lower anaerobic CH₄ oxidation rates were measured in presence of molybdate in half of the measurements, suggesting the occurrence of linkage between SO₄^2? reduction and anaerobic CH₄ oxidation. NO₃^? consumption and dissolved Mn production rates were never high enough to sustain the measured anaerobic CH₄ oxidation, reinforcing the idea of a coupling between SO₄^2? reduction and CH₄ oxidation in the anoxic waters of Lake Kivu. Finally, significant rates (up to 0.37?μmol/L/d) of pelagic CH₄ production were also measured in oxygenated waters.     

水动力水质模拟在黑臭湖体治理中的应用

为分析琵琶湖黑臭水体治理效果,应用水动力水质模拟方法,根据琵琶湖水体流动及污染物运移扩散规律等,构建水动力及水质数学模型,通过模拟现状、经工程治理后湖体的流场和污染物浓度场及湖体水质达标时间,对比分析工程治理前后的效果。结果表明,水体治理工程实施后,湖体流场变得均匀;湖体大部分水域COD浓度达到Ⅳ类水质标准;但因湖体现状TN浓度较高,水体治理工程实施后短时间内TN浓度仍严重超标;TP浓度经工程治理后降低明显,基本达到Ⅳ类水质标准。此外,根据湖体水质达标时间模拟结果,在保证工程实施后湖体补水入湖水质维持达标的情况下,至少需50d才可使湖体超标最为严重的TN达到Ⅳ类水质标准。