Arctic Aquatic Ecosystems Research Articles

The mechanisms of effects of oil-derived polyaromatic hydrocarbons on cardiac electrical activity in navaga cod (Eleginus nawaga)

The intensive development of oil and gas industries in the Arctic threatens Arctic aquatic ecosystems. The toxic and primarily lethal cardiotoxic effects of oil in living organisms are believed to be associated with polyaromatic hydrocarbons (PAHs), and previous works revealed the electrophysiological mechanisms of action of individual oil-derived PAHs. However, the physiological effects of a complex PAHs mixture in oil water-soluble fraction (WSF) have not been previously studied. This study is focused on the effects of oil WSF on electrical activity and major ionic currents in the working myocardium of navaga (Eleginus nawaga), which is one of the most important commercial fish species in the Arctic. We found that 1% and 10% solutions of oil WSF cause a marked increase in the duration of action potentials (APs) in navaga cardiomyocytes. This effect appears to be due to the suppression of rapid delayed rectifying current IKr (IC50 about 3% in ventricular and atrial myocardium). At higher concentrations, oil WSF also suppressed calcium current ICaL (IC50 = 10.6%), which led to a decrease in the contractile activity in isolated myocardial preparations. Unlike individual tricyclic PAHs, oil WSF did not affect fast sodium current INa and AP upstroke velocity. An assessment of the content of tricyclic PAHs in 10% solution of oil WSF showed that their total concentration is relatively low and does not exceed 100 nM. Thus, oil WSF also has a powerful cardiotoxic effect in fish myocardium, but its effects differ from the previously studied effects of tricyclic PAHs and suggest the presence of yet unexplored oil compounds that have a more powerful toxic potential against ERG channels.

Temporal patterns in multiple stressors shape the vulnerability of overwintering Arctic zooplankton.

The Arctic polar nights bring extreme environmental conditions characterised by cold and darkness, which challenge the survival of organisms in the Arctic. Additionally, multiple anthropogenic stressors can amplify the pressure on the fragile Arctic ecosystems during this period. Determining how multiple anthropogenic stressors may affect the survival of Arctic life is crucial for ecological risk assessments and management, but this topic is understudied. For the first time, our study investigates the complex interactions of multiple stressors, exploring stressor temporal dynamics and exposure duration on a key Arctic copepod Calanus glacialis during the polar nights. We conducted experiments with pulse (intermittent) and press (continuous) exposure scenarios, involving microplastics, pyrene and warming in a fully factorial design. We observed significant effects on copepod survival, with pronounced impacts during later stressor phases. We also detected two-way interactions between microplastics and pyrene, as well as pyrene and warming, further intensified with the presence of a third stressor. Continuous stressor exposure for 9 days (press-temporal scenario) led to greater reductions in copepod survival compared to the pulse-temporal scenario, characterised by two 3-day stressor exposure phases. Notably, the inclusion of recovery phases, free from stressor exposure, positively influenced copepod survival, highlighting the importance of temporal exposure dynamics. We did not find behaviour to be affected by the different treatments. Our findings underscore the intricate interactions amongst multiple stressors and their temporal patterns in shaping the vulnerability of overwintering Arctic copepods with crucial implications for managing Arctic aquatic ecosystems under the fastest rate of ongoing climate change on earth.

Linking extreme seasonality and gene expression in Arctic marine protists

At high latitudes, strong seasonal differences in light availability affect marine organisms and regulate the timing of ecosystem processes. Marine protists are key players in Arctic aquatic ecosystems, yet little is known about their ecological roles over yearly cycles. This is especially true for the dark polar night period, which up until recently was assumed to be devoid of biological activity. A 12 million transcripts catalogue was built from 0.45 to 10 μm protist assemblages sampled over 13 months in a time series station in an Arctic fjord in Svalbard. Community gene expression was correlated with seasonality, with light as the main driving factor. Transcript diversity and evenness were higher during polar night compared to polar day. Light-dependent functions had higher relative expression during polar day, except phototransduction. 64% of the most expressed genes could not be functionally annotated, yet up to 78% were identified in Arctic samples from Tara Oceans, suggesting that Arctic marine assemblages are distinct from those from other oceans. Our study increases understanding of the links between extreme seasonality and biological processes in pico- and nanoplanktonic protists. Our results set the ground for future monitoring studies investigating the seasonal impact of climate change on the communities of microbial eukaryotes in the High Arctic.

Insights from the remote co‐creation of an Indigenous knowledge questionnaire about aquatic ecosystems in Kinngait, Nunavut

Abstract There is growing interest in co‐developing research projects that more fully address the priorities of Indigenous communities throughout the Canadian Arctic and beyond. However, details regarding collaborative methods are often not adequately described in the literature. Here, we describe a process to remotely co‐create a questionnaire compiling Indigenous knowledge about local aquatic species and their habitats with the community of Kinngait, Nunavut. This project was undertaken in response to interest expressed by the Aiviq Hunters and Trappers Association in understanding and assessing the impacts of climate change on coastal ecosystems. Researchers from Fisheries and Oceans Canada and academic partners drafted an initial questionnaire that was revised through a series of collaborative sessions with community‐based technicians. We detail the stages of this process and discuss elements that enabled co‐creation including: adaptable and frequent communication, community technician roles, and a pre‐existing partnership. This paper emphasizes that project co‐development and the co‐creation of research tools can be a mutually beneficial process that can broaden our collective understanding of the impacts of climate change on Arctic aquatic ecosystems.

Dissolved organic matter characterization in soils and streams in a small coastal low-Arctic catchment

Abstract. Ongoing climate warming in the western Canadian Arctic is leading to thawing of permafrost soils and subsequent mobilization of its organic matter pool. Part of this mobilized terrestrial organic matter enters the aquatic system as dissolved organic matter (DOM) and is laterally transported from land to sea. Mobilized organic matter is an important source of nutrients for ecosystems, as it is available for microbial breakdown, and thus a source of greenhouse gases. We are beginning to understand spatial controls on the release of DOM as well as the quantities and fate of this material in large Arctic rivers. Yet, these processes remain systematically understudied in small, high-Arctic watersheds, despite the fact that these watersheds experience the strongest warming rates in comparison. Here, we sampled soil (active layer and permafrost) and water (porewater and stream water) from a small ice wedge polygon (IWP) catchment along the Yukon coast, Canada, during the summer of 2018. We assessed the organic carbon (OC) quantity (using dissolved (DOC) and particulate OC (POC) concentrations and soil OC content), quality (δ13C DOC, optical properties and source apportionment) and bioavailability (incubations; optical indices such as slope ratio, Sr; and humification index, HIX) along with stream water properties (temperature, T; pH; electrical conductivity, EC; and water isotopes). We classify and compare different landscape units and their soil horizons that differ in microtopography and hydrological connectivity, giving rise to differences in drainage capacity. Our results show that porewater DOC concentrations and yield reflect drainage patterns and waterlogged conditions in the watershed. DOC yield (in mg DOC g−1 soil OC) generally increases with depth but shows a large variability near the transition zone (around the permafrost table). Active-layer porewater DOC generally is more labile than permafrost DOC, due to various reasons (heterogeneity, presence of a paleo-active-layer and sampling strategies). Despite these differences, the very long transport times of porewater DOC indicate that substantial processing occurs in soils prior to release into streams. Within the stream, DOC strongly dominates over POC, illustrated by DOC/POC ratios around 50, yet storm events decrease that ratio to around 5. Source apportionment of stream DOC suggests a contribution of around 50 % from permafrost/deep-active-layer OC, which contrasts with patterns observed in large Arctic rivers (12 ± 8 %; Wild et al., 2019). Our 10 d monitoring period demonstrated temporal DOC patterns on multiple scales (i.e., diurnal patterns, storm events and longer-term trends), underlining the need for high-resolution long-term monitoring. First estimates of Black Creek annual DOC (8.2 ± 6.4 t DOC yr−1) and POC (0.21 ± 0.20 t yr−1) export allowed us to make a rough upscaling towards the entire Yukon Coastal Plain (34.51 ± 2.7 kt DOC yr−1 and 8.93 ± 8.5 kt POC yr−1). Rising Arctic temperatures, increases in runoff, soil organic matter (OM) leaching, permafrost thawing and primary production are likely to increase the net lateral OC flux. Consequently, altered lateral fluxes may have strong impacts on Arctic aquatic ecosystems and Arctic carbon cycling.

What is the impact of urban development and thermokarsting on arctic tundra pond zooplankton communities?

Human development and warming in the Arctic are increasingly putting new pressures on the abundant freshwater ecosystems in the region. In particular, recent and rapid expansion of thermokarst ponds in permafrost regions has been associated with these stresses. Our goal was to examine the relative impacts of pond enrichment by urban encroachment and thermokarsting, compared to relatively unimpacted regions, on the environmental conditions and zooplankton communities of tundra ponds near Utqiaġvik, AK, USA. Both urban ponds and thermokarst ponds were found to have substantially different environmental conditions, as well as distinctive zooplankton communities relative to reference sites. Thermokarst ponds presented an environment rich in DOC and nutrients (N, P, and Si) and phytoplankton biomass. Enrichment by nutrients and DOC in thermokarst ponds led to significantly greater zooplankton abundance composed largely of Daphnia middendorffiana (66 individuals L−1) and cyclopoid copepods (65 individuals L−1). Urban ponds had moderate nutrient levels, with elevated benthic algal biomass. These ponds had intermediate numbers of D. middendorffianna (14 individuals L−1), as well as significantly higher numbers of diaptomid copepods (8 individuals L−1) and chydorids (11 individuals L−1), as compared to one or both reference regions. The two reference regions [Barrow Environmental Observatory (BEO) and International Biological Program (IBP)] had consistently lower nutrient concentrations, algal levels, and zooplankton abundances (less than 3 individuals L−1). Finally, harpacticoid copepods and Bosmina longirostris were new records for the zooplankton in the region. Further collections are required to determine the drivers for these new observations. These results identify the large potential relative contributions of urban inputs and thermokarsting to enrichment of Arctic aquatic ecosystems and point to thermokarsting, which will likely increase with warming, as a major contributor to change in these systems.

Emission of Greenhouse Gases From Water Tracks Draining Arctic Hillslopes

AbstractExperimental and ambient warming of Arctic tundra results in emissions of greenhouse gases to the atmosphere, contributing to a positive feedback to climate warming. Estimates of gas emissions from lakes and terrestrial tundra confirm the significance of aquatic fluxes in greenhouse gas budgets, whereas few estimates describe emissions from fluvial networks. We measured dissolved gas concentrations and estimated emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from water tracks, vegetated depressions that hydrologically connect hillslope soils to lakes and streams. Concentrations of trace gases generally increased as ground thaw deepened through the growing season, indicating active production of greenhouse gases in thawed soils. Wet antecedent conditions were correlated with a decline in CO2 and CH4 concentrations. Dissolved N2O in excess of atmospheric equilibrium occurred in drier water tracks, but on average water tracks took up N2O from the atmosphere at low rates. Estimated CO2 emission rates for water tracks were among the highest observed for Arctic aquatic ecosystems, whereas CH4 emissions were of similar magnitude to streams. Despite occupying less than 1% of total catchment area, surface waters within water tracks were an estimated source of up to 53–85% of total CH4 emissions from their catchments and offset the terrestrial C sink by 5–9% during the growing season. Water tracks are abundant features of tundra landscapes that contain warmer soils and incur deeper thaw than adjacent terrestrial ecosystems and as such might contribute to ongoing and accelerating release of greenhouse gases from permafrost soils to the atmosphere.

Message from the Executive Director Interview with Dave Hambright, Editor‐in‐Chief, Limnology and Oceanography

Message from the Executive Director Interview with Dave Hambright, Editor‐in‐Chief, <i>Limnology and Oceanography</i>

Glacial Melt Inputs of Organophosphate Ester Flame Retardants to the Largest High Arctic Lake.

Organophosphate esters (OPEs) have been detected in the Arctic environment, but the influence of glacial melt on the environmental behavior of OPEs in recipient Arctic aquatic ecosystems is still unknown. In this study, water samples were collected from Lake Hazen (LH) and its tributaries to investigate the distribution of 14 OPEs in LH and to explore the input of OPEs from glacial rivers to LH and the output of OPEs from LH in 2015 and 2018. Σ14OPE concentrations in water of LH were lower than glacial rivers and its outflow, the Ruggles River. In 2015, a high melt year, we estimated that glacial rivers contributed 7.0 ± 3.2 kg OPEs to LH, compared to a 16.5 ± 0.3 kg OPEs output by the Ruggles River, suggesting that residence time and/or additional inputs via direct wet and dry deposition and permafrost melt likely result in OPE retention in the LH watershed. In 2018, a lower melt year, Σ14OPE concentrations in glacial rivers were much lower, indicating that the rate of glacier melt may govern, in part, the concentrations of OPEs in the tributaries of LH. This study highlights long-range transport of OPEs, their deposition in Arctic glaciers, landscapes, and lakes.

Fundamental drivers of dissolved organic matter composition across an Arctic effective precipitation gradient

AbstractThe standard model for aquatic ecosystems is to link hydrologic connectivity to dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition and, ultimately, reactivity. Studies across effective precipitation gradients have been suggested as models for predicting how carbon cycling will change in Arctic aquatic ecosystems with projected drying (i.e., reduced hydrologic connectivity). To evaluate links between DOM dynamics and hydrologic connectivity, 41 stream samples from Greenland were analyzed across an effective precipitation gradient for DOM optical properties and elemental composition using ultrahigh‐resolution mass spectrometry. Sites with negative effective precipitation and decreased hydrologic connectivity exhibited elevated specific conductivity (SpC) and DOC concentrations as well as DOM composition indicative of decreased hydrologic connectivity, for example, lower aromaticity, assessed using carbon‐specific UV absorbance at 254 nm, decreased relative abundances of polyphenolic and condensed aromatic compounds, and increased relative abundances of highly unsaturated and phenolic compounds. Allochthonous inputs decreased as the summer progressed as exhibited by decreases in aromatic compounds. A decrease in molecular richness and N‐containing compounds coincided with the decrease in allochthonous inputs. DOC concentrations increased over the summer but more slowly than SpC, suggesting degradation processes outweighed combined evapoconcentration and production. The patterns in DOM composition suggest evapoconcentration and photodegradation are dominant controls. However, when hydrologic connectivity was high, regardless of effective precipitation, DOM reflected allochthonous sources such as snowmelt‐fed wetlands. These results highlight the challenges of modeling carbon cycling in aquatic ecosystems across effective precipitation gradients, particularly those with strong seasonality and regional variability in hydrologic inputs.

Quantifying Dissolved Organic Carbon Dynamics Using a Three‐Dimensional Terrestrial Ecosystem Model at High Spatial‐Temporal Resolutions

AbstractArctic terrestrial ecosystems are very sensitive to the global climate change due to the large storage of soil organic carbon and the presence of snow, glacier, and permafrost, which respond directly to near surface air temperature that has warmed in the Arctic by almost twice as much as the global average. These ecosystems play a significant role in affecting regional and global carbon cycling, which have been traditionally quantified using biogeochemical models that have not explicitly considered the loss of carbon due to lateral flow of water from land to aquatic ecosystems. Building upon an extant spatially distributed hydrological model and a process‐based biogeochemical model, we have developed a three‐dimensional terrestrial ecosystem model to elucidate how lateral water flow has impacted the regional dissolved organic carbon (DOC) dynamics in the Tanana Flats Basin in central Alaska. The model explicitly simulates the production, consumption, and transport of DOC. Both in situ observational data and remote sensing‐based products were used to calibrate and validate the model. Our simulations show that (1) plant litter DOC leaching exerts significant controls on soil DOC concentration during precipitation and snowmelt events, (2) lateral transport plays an important role in affecting regional DOC dynamics, and (3) DOC export to the Tanana River is approximately 9.6 × 106 kg C year−1. This study provides a modeling framework to adequately quantify the Arctic land ecosystem carbon budget by considering the lateral transport of carbon affected by permafrost degradation. The quantification of the lateral carbon fluxes will also improve future carbon cycle modeling for Arctic aquatic ecosystems.

Multiyear variations in High Arctic river temperatures in response to climate variability

Water temperature measurements (2004–2016) from two small rivers in the High Arctic were analyzed to determine the effects of climate variability on thermal regime and the sensitivity to climate change. The East and West rivers (unofficial names) drain similar watersheds (11.6 and 8.0 km2, respectively) and are located at the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Canada (74°55′N, 109°35′W). Differences in seasonal timing of river temperatures were evident when comparing the coldest and warmest years of the study period, and across different discharge conditions. Snowmelt runoff is characterized by uniformly cold water (∼0–1 °C) over a wide range of discharge conditions, followed by warming water temperatures during flow recession. The rivers showed varying sensitivity to mid-summer air temperature conditions in a given year, with warmer years indicating high correlation (r2 = 0.794–0.929), whereas colder years showed reduced correlation (r2 = 0.368–0.778). River temperatures reached levels which are reported to negatively affect fish and other cold-water aquatic species (&gt;18 °C) with greater frequency and duration during the warmest years. These results provide a basis to further enhance prediction of river thermal conditions to assess ecosystem health in a river system and to refine insights into the effects of climate change on High Arctic aquatic ecosystems.

Mosaic structure of the fungal community in the Kislo-Sladkoe Lake that is detaching from the White Sea

The major part of the north polar region is intensely rising by postglacial crustal movement. This process gives rise to the separation of different basins from seas and oceans, which affects a combination of freshwater and marine organisms. Gradually losing contact with the seas, many near-shore lakes of the Arctic are mostly desalted and form bogs. Fungi as decomposers play an important role in all ecosystems. However, the diversity and role of fungi in Arctic aquatic ecosystems is largely unknown. It is also not clear how the taxonomic structure of the fungal community is affected by the process of gradual desalinization and waterlogging. We investigated the diversity of filamentous culturable fungi in different parts of the brackish Kislo-Sladkoe Lake (White Sea, Russia). Annually, 42 samples of the bottom and coastal soils have been collected at the lake from which fungi were recovered on standard and selective media. Based on morphological and molecular markers, a total of 127 taxa have been identified. The fungal community appeared to be influenced by its sea origin and comprised both marine (Paradendryphiella salina, Acremonium spp.) and terrestrial soil species of Penicillium, Talaromyces, Mucor, Umbelopsis, Cladosporium, Cadophora, Sistotrema, Helotiales, Pleosporales, sphagnum moss destructors (Oidiodendron spp.) and insect-associated species of Tolypocladium. The results indicate that the composition of the fungal community in the rising polar White Sea region reflects the dynamics of global changes in physical–chemical parameters and animal and plant associations because of separation from the sea.

Increasing chloride concentration causes retention of mercury in melted Arctic snow due to changes in photoreduction kinetics

Mercury (Hg) in the Arctic is a significant concern due to its bioaccumulative and neurotoxic properties, and the sensitivity of Arctic environments. Previous research has found high levels of Hg in snowpacks with high chloride (Cl−) concentrations. We hypothesised that Cl− would increase Hg retention by decreasing Hg photoreduction to Hg(0) in melted Arctic snow. To test this, changes in Hg photoreduction kinetics in melted Alert, NU snow were quantified with changing Cl− concentration and UV intensity. Snow was collected and melted in Teflon bottles in May 2014, spiked with 0–10μg/g Cl−, and irradiated with 3.52–5.78W·m−2 UV (280–400nm) radiation in a LuzChem photoreactor. Photoreduction rate constants (k) (0.14–0.59hr−1) had positive linear relationships with [Cl−], while photoreduced Hg amounts (Hg(II)red) had negative linear relationships with [Cl−] (1287–64pg in 200g melted snow). Varying UV and [Cl−] both altered Hg(II)red amounts, with more efficient Hg stabilisation by Cl− at higher UV intensity, while k can be predicted by Cl− concentration and/or UV intensity, depending on experimental parameters. Overall, with future projections for greater snowpack Cl− loading, our experimental results suggest that more Hg could be delivered to Arctic aquatic ecosystems by melted snow (smaller Hg(II)red expected), but the Hg in the melted snow that is photoreduced may do so more quickly (larger k expected).

Long-term changes in pigmentation of arctic Daphnia provide potential for reconstructing aquatic UV exposure

Despite the biologically damaging impacts of solar ultraviolet radiation (UV) in nature, little is known about its natural variability, forcing mechanisms, and long-term effects on ecosystems and organisms. Arctic zooplankton, for example the aquatic keystone genus Daphnia (Crustacea, Cladocera) responds to biologically damaging UV by utilizing photoprotective strategies, including pigmentation. We examined the preservation and content of UV-screening pigments in fossil Daphnia remains (ephippia) in two arctic lake sediment cores from Cornwallis Island (Lake R1), Canada, and Spitsbergen (Lake Fugledammen), Svalbard. The aims were to document changes in the degree of UV-protective pigmentation throughout the past centuries, elucidate the adaptive responses of zooplankton to long-term variations in UV exposure, and estimate the potential of fossil zooplankton pigments in reconstructing aquatic UV regimes. The spectroscopic absorbance measurements of fossil Daphnia ephippia under UV (280–400 nm) and visible light (400–700 nm) spectral ranges indicated that melanin (absorbance maxima at UV wavebands 280–350 nm) and carotenoids (absorbance maxima at 400–450 nm) pigments were preserved in the ephippia in both sediment cores. Downcore measurements of the most important UV-protective pigment melanin (absorbance measured at 305 and 340 nm) showed marked long-term variations in the degree of melanisation. These variations likely represented long-term trends in aquatic UV exposure and were positively related with solar radiation intensity. The corresponding trends in melanisation and solar activity were disrupted at the turn of the 20th century in R1, but remained as strong in Fugledammen. The reversed trends in the R1 core were simultaneous with a significant aquatic community reorganization taking place in the lake, suggesting that recent environmental changes, likely related to climate warming had a local effect on pigmentation strategies. This time horizon is also concurrent with previously recorded major ecological shifts in circumpolar lakes when human induced changes in ecological processes of sensitive arctic ecosystems started to occur. The current centennial record of UV-induced melanisation of sedimentary Daphnia ephippia presents unique reference material for assessing UV impacts in arctic aquatic ecosystems before human influence and during the 20th century climate change and provides potential for assessing past aquatic UV regimes.

Methane turnover and methanotrophic communities in arctic aquatic ecosystems of the Lena Delta, Northeast Siberia.

Large amounts of organic carbon are stored in Arctic permafrost environments, and microbial activity can potentially mineralize this carbon into methane, a potent greenhouse gas. In this study, we assessed the methane budget, the bacterial methane oxidation (MOX) and the underlying environmental controls of arctic lake systems, which represent substantial sources of methane. Five lake systems located on Samoylov Island (Lena Delta, Siberia) and the connected river sites were analyzed using radiotracers to estimate the MOX rates, and molecular biology methods to characterize the abundance and the community composition of methane-oxidizing bacteria (MOB). In contrast to the river, the lake systems had high variation in the methane concentrations, the abundance and composition of the MOB communities, and consequently, the MOX rates. The highest methane concentrations and the highest MOX rates were detected in the lake outlets and in a lake complex in a flood plain area. Though, in all aquatic systems, we detected both, Type I and II MOB, in lake systems, we observed a higher diversity including MOB, typical of the soil environments. The inoculation of soil MOB into the aquatic systems, resulting from permafrost thawing, might be an additional factor controlling the MOB community composition and potentially methanotrophic capacity.

Early summer near-shore fish assemblage and environmental correlates in an Arctic estuary

Abstract Knowledge of reference conditions and species–environment associations is required to ascertain ongoing aquatic biodiversity changes in Arctic regions. The objective of this study was to establish a baseline of fish community structure (species composition, incidence and relative abundance) in relation to salinity, pH and temperature gradients in an Arctic estuary, the Husky Lakes, Canada. Sampling involved an early-summer, standardized, experimental netting survey around the entire perimeter of all estuary basins and peninsulas. Detrended canonical correspondence analysis (DCCA) was used to evaluate species–environment associations. The ecosystem sustains an abundant and diverse fish community, characterized by co-dominance of coregonids and a marine schooling fish, Clupea pallasii , and high abundance of freshwater/freshwater-amphidromous species in the innermost basins. Highest richness and total abundance were related to mixing conditions, warmest temperatures, connectivity to nearby ecosystems, and diversity in species life histories. Salinity determined spatial patterns of fish species abundance and distribution. The incidence of freshwater fish was limited by the availability of low salinity habitat and potential community interactions. These fish, particularly Salvelinus namaycush and Thymallus arcticus , are considered as the most vulnerable to changes in freshwater habitat availability. The fish assemblage reflects environmental information from surrounding fluvial, freshwater, coastal marine and catchment ecosystems, and is thus a prime candidate for monitoring environmental change in the region. The results provide a benchmark against which future studies of fish communities can be compared to evaluate potential effects of climate change and anthropogenic development on fish populations from Husky Lakes and similar Arctic aquatic ecosystems.

Rapid Nutrient Release from Permafrost Thaw in Arctic Aquatic Ecosystems

Few studies provide experimental data to support the role of permafrost thaw on changes in arctic freshwater chemistry. We designed an incubation experiment to look at rapid nutrient release from permafrost soils and active layer soils under different warming scenarios, changes in redox environment, and microbial activity. Permafrost soil tended to immediately release more nutrients than active layer soils, especially under warmer conditions; suggesting the active layer is depleted in nutrients and the water column may be resupplied with these ions from thawing permafrost. The release of micronutrients (Ca, Fe, Mg, S, Si) from incubated permafrost soils responded strongly to increased temperature; however, temperature alone was not necessarily the primary driver of macronutrient (N, P) release from permafrost. Other physicochemical parameters influenced by temperature, such as oxidation-reduction potential (ORP), microbial activity, dissolved organic carbon (DOC), and Fe played an additional role in nutrient release from permafrost. These experiments suggest nutrient release via thaw of permafrost soils is able to contribute ample essential nutrients to arctic aquatic ecosystems, even within one day of warming. Further warming of the Arctic is likely to result in substantial changes to nutrient availability and cycling in these dominant habitats.

Methylmercury biogeochemistry: a review with special reference to Arctic aquatic ecosystems

There has been increasing concern about mercury (Hg) levels in marine and freshwater organisms in the Arctic, due to the importance of traditional country foods such as fish and marine mammals to the diet of Northern Peoples. Due to its toxicity and ability to bioaccumulate and biomagnify in food webs, methylmercury (MeHg) is the form of Hg that is of greatest concern. The main sources of MeHg to Arctic aquatic ecosystems, the processes responsible for MeHg formation and degradation in the environment, MeHg bioaccumulation in Arctic biota and the human health implications for Northern Peoples are reviewed here. In Arctic marine ecosystems, Hg(II) methylation in the water column, rather than bottom sediments, is the primary source of MeHg, although a more quantitative understanding of the role of dimethylmercury (DMHg) as a MeHg source is needed. Because MeHg production in marine waters is limited by the availability of Hg(II), predicted increases in Hg(II) concentrations in oceans are likely to result in higher MeHg concentrations and increased exposure to Hg in humans and wildlife. In Arctic freshwaters, MeHg concentrations are a function of two antagonistic processes, net Hg(II) methylation in bottom sediments of ponds and lakes and MeHg photodemethylation in the water column. Hg(II) methylation is controlled by microbial activity and Hg(II) bioavailability, which in turn depend on interacting environmental factors (temperature, redox conditions, organic carbon, and sulfate) that induce nonlinear responses in MeHg production. Methylmercury bioaccumulation–biomagnification in Arctic aquatic food webs is a function of the MeHg reservoir in abiotic compartments, as well as ecological considerations such as food-chain length, growth rates, life-history characteristics, feeding behavior, and trophic interactions. Methylmercury concentrations in Arctic biota have increased significantly since the onset of the industrial age, and in some populations of fish, seabirds, and marine mammals toxicological thresholds are being exceeded. Due to the complex connection between Hg exposure and human health in Northern Peoples—arising from the dual role of country foods as both a potential Hg source and a nutritious, affordable food source with many physical and social health benefits—-reductions in anthropogenic Hg emissions are seen as the only viable long-term solution.

Evidence for key enzymatic controls on metabolism of Arctic river organic matter

Permafrost thaw in the Arctic driven by climate change is mobilizing ancient terrigenous organic carbon (OC) into fluvial networks. Understanding the controls on metabolism of this OC is imperative for assessing its role with respect to climate feedbacks. In this study, we examined the effect of inorganic nutrient supply and dissolved organic matter (DOM) composition on aquatic extracellular enzyme activities (EEAs) in waters draining the Kolyma River Basin (Siberia), including permafrost-derived OC. Reducing the phenolic content of the DOM pool resulted in dramatic increases in hydrolase EEAs (e.g., phosphatase activity increased >28-fold) supporting the idea that high concentrations of polyphenolic compounds in DOM (e.g., plant structural tissues) inhibit enzyme synthesis or activity, limiting OC degradation. EEAs were significantly more responsive to inorganic nutrient additions only after phenolic inhibition was experimentally removed. In controlled mixtures of modern OC and thawed permafrost endmember OC sources, respiration rates per unit dissolved OC were 1.3-1.6 times higher in waters containing ancient carbon, suggesting that permafrost-derived OC was more available for microbial mineralization. In addition, waters containing ancient permafrost-derived OC supported elevated phosphatase and glucosidase activities. Based on these combined results, we propose that both composition and nutrient availability regulate DOM metabolism in Arctic aquatic ecosystems. Our empirical findings are incorporated into a mechanistic conceptual model highlighting two key enzymatic processes in the mineralization of riverine OM: (i) the role of phenol oxidase activity in reducing inhibitory phenolic compounds and (ii) the role of phosphatase in mobilizing organic P. Permafrost-derived DOM degradation was less constrained by this initial 'phenolic-OM' inhibition; thus, informing reports of high biological availability of ancient, permafrost-derived DOM with clear ramifications for its metabolism in fluvial networks and feedbacks to climate.