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Over the last few decades, there has been an increasing recognition for seagrasses' contribution to the functioning of nearshore ecosystems and climate change mitigation. Nevertheless, seagrass ecosystems have been deteriorating globally at an accelerating rate during recent decades. In 2017, research into the condition of eelgrass (Zostera marina) along the eastern coast of James Bay, Canada, was initiated in response to reports of eelgrass decline by the Cree First Nations of Eeyou Istchee. As part of this research, we compiled and analyzed two decades of eelgrass cover data and three decades of eelgrass monitoring data (biomass and density) to detect changes and assess possible environmental drivers. We detected a major decline in eelgrass condition between 1995 and 1999, which encompassed the entire east coast of James Bay. Surveys conducted in 2019 and 2020 indicated limited changes post‐decline, for example, low eelgrass cover (<25%), low aboveground biomass, smaller shoots than before 1995, and marginally low densities persisted at most sites. Overall, the synthesized datasets show a 40% loss of eelgrass meadows with >50% cover in eastern James Bay since 1995, representing the largest scale eelgrass decline documented in eastern Canada since the massive die‐off event that occurred in the 1930s along the North Atlantic coast. Using biomass data collected since 1982, but geographically limited to the sector of the coast near the regulated La Grande River, generalized additive modeling revealed eelgrass meadows are affected by local sea surface temperature, early ice breakup, and higher summer freshwater discharge. Our results caution against assuming subarctic seagrass ecosystems have avoided recent global declines or will benefit from ongoing climate warming. [ABSTRACT FROM AUTHOR]

A large under‐ice plume forms because of the regulated winter discharge from the La Grande River hydroelectric complex (NE James Bay, Canada), which is among the largest winter discharges in the circumpolar north. In 2016–2017, field campaigns were completed to characterize the under‐ice plume's structure, extent, and short‐term dynamics related to tides, weather, and discharge. Amid concerns of the freshwater's impact on eelgrass, the lateral spreading of the under‐ice plume into inshore areas was also assessed. When discharges averaged 4,800 m3 s−1 throughout the January–March periods, the freshwater influence of La Grande River extended more than 100 km north along the James Bay coast, with the brackish (salinity <25) under‐ice plume more than three times larger than for a natural winter discharge of ∼460 m3 s−1. The core area of the under‐ice plume, defined as the area with a highly stratified water column and surface layer of salinity <5, extended 30–35 km north and >20 km south. It was stable throughout the January–March 2016–2017 periods and, despite 30% higher winter discharge, was not significantly larger compared to survey periods in 1984–1987. This stability appears to be due to coastal geometry and width of the landfast ice cover, under which the plume can spread with limited mixing. Inshore salinity was about 5–10 units lower in winter versus the open‐water period. The seasonal duration of reduced salinity at eelgrass habitats will depend on landfast ice duration as well as river discharge magnitude. Plain Language Summary: A major environmental change to affect the east James Bay coast is hydroelectric development of the La Grande River, which increased winter flows ten‐fold. When the river enters coastal waters covered by landfast ice, it forms a freshwater surface layer under the ice and spreads out over the underlying salty water forming an "under‐ice river plume." We describe the results of studies performed with the Cree Nation of Chisasibi during 2016–2017 on the under‐ice plume of the La Grande River. We found that the area of the plume almost completely composed of river water (salinity 0–5) north of the river mouth was of similar size to that in the 1980s/early 1990s but had faster currents and higher turnover rates of freshwater. A similarly fresh area extended southward. The overall region of freshwater influence in northeast James Bay was also larger under the high flows of 2016–2017 than in the 1980s/early 1990s. The results provide new information about how the hydroelectric development has affected the James Bay coast, which contains eelgrass habitats and is a migration staging area for waterfowl. They also show that the downstream impacts of dams may extend beyond enclosed estuaries and well into downstream coastal marine environments. Key Points: Despite higher discharge, and a much larger overall region of freshwater influence, the core area of the plume (salinity <5) was not significantly larger when compared to studies in the 1980sThe plume's northward extent is determined mainly by coastal geometry and the landfast ice narrowing at 35 km from the river mouthThe plume's influence on eelgrass habitats depends upon discharge, proximity to the river mouth and the degree of protection offered by islands [ABSTRACT FROM AUTHOR]

210Pb and 137Cs were measured in 25 sediment cores collected during the International Polar Year from a transect spanning the North American Arctic margin, from the North Bering Sea to Baffin Bay/Davis Strait. Profiles and inventories of the radioisotopes were used to determine sediment mixing and accumulation at each site and to assess the intensity of scavenging and burial. Sediment accumulation rates derived from 210Pb and validated using 137Cs are between ≤0.04 and 0.23 g cm−2 yr−1. 210Pb cannot be used to derive sedimentation rates for vigorously biomixed sediments from the North Bering-Chukchi shelf. Elevated 137Cs activities and inventories in recently deposited sediments imply delayed inputs of particle-associated 137Cs to the sediments, likely transported from the watershed to the coast and subsequently redistributed to shelf/slope sediments. Inventories of 210Pbex in all cores meet or exceed the estimated supply of 210Pbex from atmospheric deposition and decay of 226Ra in the water column. This implies that in contrast to the deep Arctic Ocean basin, there is a sufficient supply of suspended particulates along the North American Arctic margin to scavenge the supply of 210Pbex. 210Pbex inventories in sediments are up to 21-fold greater than the in situ supply at some sites. Large inventories of 210Pbex in sediments along the North Bering-Chukchi shelf result primarily from focusing, while those along the north Chukchi slope (Barrow Canyon) and in Baffin Bay/Davis Strait reflect strong boundary scavenging, likely supported by lateral exchanges with deep/interior Atlantic-origin waters. [ABSTRACT FROM AUTHOR]

Although the presence and distribution of polychlorinated biphenyls (PCBs) in Arctic marine environments has been well documented, the implications for the health of biota are poorly understood. In the present study, multiple lines of evidence, including site-specific effects data, were used to assess PCB-related risks to marine biota at a contaminated military site in Saglek Bay, Labrador, Canada, from 1997 to 1999. Risks were evaluated for three components of the ecosystem: benthic invertebrates, a bottom-feeding fish (shorthorn sculpin, Myoxocephalus scorpius), and a diving seabird (black guillemot, Cepphus grylle). Average sediment PCB concentrations exceeded the Canadian interim sediment quality guideline level by 41-fold. However, sediment toxicity testing and a benthic community survey showed no evidence of adverse effects. In contrast, shorthorn sculpin and black guillemot PCB exposures (measured as sum of 55 congeners) were elevated enough to pose risks to survival or reproduction. Based on the collective evidence, the authors estimated that risks were posed by sediment PCB concentrations greater than 77 ng/g dry weight for black guillemots and 750 ng/g dry weight for shorthorn sculpins. The present study, along with two parallel studies, provided information to support the management decisions concerning potential remedial action on the contaminated sediments. This ecological risk assessment describes the steps and rationale taken to evaluate the risk posed by an area of PCB-contaminated marine sediments in an otherwise relatively pristine northern coastal environment. Environ. Toxicol. Chem. 2013;32:453-467. © 2012 SETAC [ABSTRACT FROM AUTHOR]