Assessing long‐term diatom changes in sub‐Arctic ponds receiving high fluxes of seabird nutrients

Abstract Algal bioindicators, such as diatoms, often show subdued responses to eutrophication in Arctic lakes because climate‐related changes (e.g., ice cover) tend to be the overriding factors influencing assemblage composition. Here, we examined how sub‐Arctic ponds historically receiving high nutrient inputs from nesting seabirds have responded to recent climate change. We present diatom data obtained from 12 sediment cores in seaduck‐affected ponds located on islands through Hudson Strait, Canada. All study cores show consistently elevated values of sedimentary ẟ15N, an established proxy for tracking marine‐derived nutrients, indicating seabirds have been present on these islands for at least the duration of the sediment records (~100 to 400 years). We document diverse epiphytic diatom assemblages to the base of all sediment cores, which is in marked contrast to seabird‐free Arctic ponds—these oligotrophic sites typically record epilithic diatom flora prior to recent warming. Diatoms are likely responding indirectly to seabird nutrients via habitat as nutrients promote the growth of mosses supporting epiphytic diatom communities. This masks the typical diatom response to increased warming in the Arctic, which also results in habitat changes and the growth of mosses around the pond edges. Changes in sedimentary chlorophyll a were not consistently synchronous with large changes in ẟ15N values, suggesting that primary production in ponds is not responding linearly to changes in seabird‐derived nitrogen. Across all ponds, we recorded shifts in diatom epiphytic assemblages (e.g., increases in % relative abundance of many Nitzschia species) that often align with increases in chlorophyll a. The changes in diatoms and chlorophyll a, although variable, are most likely driven by climate change as they are generally consistent with longer ice‐free conditions and growing seasons. Together, our results show that to effectively use diatoms in animal population reconstructions across the sub‐Arctic and Arctic, a strong understanding of eutrophication and climate change, based on supplementary proxies, is also required

A Paleoenvironmental Study Tracking Eutrophication, Mining Pollution, and Climate Change in Niven Lake, the First Sewage Lagoon of Yellowknife (Northwest Territories)

Niven Lake was the first wastewater disposal site for the City of Yellowknife (Northwest Territories, Canada), receiving domestic sewage for more than 30 years. Here, we used a high-resolution sediment core to track past sewage inputs to Niven Lake by comparing changes in sedimentary sterols and three diagnostic ratios for human fecal contamination, as well as biological assemblages and overall lake production, with the known history of sewage inputs to the lake from 1948 to 1981. Coprostanol, often considered the best indicator of human fecal contamination, increased by ~8% between depths of 7.5 cm and 5 cm (~1950 to 1981) and was more reliable in tracking sewage contamination than diagnostic sterol ratios. Muted responses in subfossil diatom and chironomid assemblages were noted during the time of sewage inputs, and similar responses have been reported in other eutrophic Arctic sites, as well as in many macrophyte-dominated shallow lakes in general. More marked shifts in diatoms and chironomids occurred a decade after the end of sewage inputs, in the 1990s, a time that closely aligned with the warmest years on record for Yellowknife. This post–sewage era response was indicative of anoxia and possibly of positive feedback from internal phosphorus loading. The response may have been facilitated by recent climate warming, resulting in a lagging recovery from eutrophication. Changes in the diatoms and chironomids of Niven Lake were also indicative of metal pollution, suggesting that the lake has experienced the compounding effects of arsenic contamination from nearby gold mining.Le lac Niven était le premier site d’évacuation des eaux usées de la ville de Yellowknife (Territoires du Nord-Ouest, Canada) et il a reçu des eaux domestiques pendant plus de 30 ans. Ici, nous avons utilisé une carotte de sédiments à haute résolution pour analyser les anciens apports en eaux usées du lac Niven en comparant les changements dans les stérols sédimentaires et trois rapports diagnostiques pour la contamination fécale humaine, ainsi que les assemblages biologiques et la production générale du lac, selon les antécédents connus d’apports en eaux usées du lac de 1948 à 1981. Le coprostanol, souvent considéré comme le meilleur indicateur de contamination fécale humaine, augmentait d’environ 8 % à des profondeurs se situant entre 7,5 cm et 5 cm (~1950 à 1981) et était plus fiable pour évaluer la contamination par les eaux usées que les rapports diagnostiques des stérols. Des réponses atténuées dans les diatomées subfossiles et les assemblages chironomidés ont été notées dans les apports en eaux usées, et des réponses semblables ont été signalées dans d’autres sites eutrophiques de l’Arctique ainsi que dans de nombreux lacs peu profonds dominés par les macrophytes en général. Des changements plus marqués dans les diatomées et les chironomidés ont eu lieu une décennie après la fin des apports en eaux usées, dans les années 1990, une période étroitement liée aux années les plus chaudes à Yellowknife. La réponse après la fin de l’évacuation des eaux usées révélait une anoxie et possiblement une réaction positive à partir de la charge de phosphore interne. Cette réponse a peut-être été facilitée par le réchauffement récent du climat, provoquant ainsi un retard dans le rétablissement après l’eutrophisation. Les changements touchant les diatomées et les chironomidés du lac Niven témoignaient également de la pollution par les métaux, ce qui suggère que le lac a connu les effets conjugués de la contamination à l’arsenic provenant de l’exploitation minière à proximité

Multi-trophic level response to extreme metal contamination from gold mining in a subarctic lake

112 hlm.; ilus.; 21 c

Sterol and stanol % abundances from Sterols and stanols as novel tracers of waterbird population dynamics in freshwater ponds

Data used in figures 2 and

Extended study site descriptions and methods; dating profiles from Sterols and stanols as novel tracers of waterbird population dynamics in freshwater ponds

Sterol and stanol methods, sediment core dating, total Pb profiles, and personal correspondenc

Multicentury perspective assessing the sustainability of the historical harvest of seaducks

Where available, census data on seabirds often do not extend beyond a few years or decades, challenging our ability to identify drivers of population change and to develop conservation policies. Here, we reconstruct long-term population dynamics of northern common eiders (Somateria mollissima borealis). We analyzed sterols together with stable nitrogen isotopes in dated pond sediment cores to show that eiders underwent broadscale population declines over the 20th century at Canadian subarctic breeding sites. Likely, a rapidly growing Greenland population, combined with relocation of Inuit to larger Arctic communities and associated increases in the availability of firearms and motors during the early to mid-20th century, generated more efficient hunting practices, which in turn reduced the number of adult eiders breeding at Canadian nesting islands. Our paleolimnological approach highlights that current and local monitoring windows for many sensitive seabird species may be inadequate for making key conservation decisions