Arctic Streams Research Articles

Metal mobilization from thawing permafrost to aquatic ecosystems is driving rusting of Arctic streams

Climate change in the Arctic is altering watershed hydrologic processes and biogeochemistry. Here, we present an emergent threat to Arctic watersheds based on observations from 75 streams in Alaska’s Brooks Range that recently turned orange, reflecting increased loading of iron and toxic metals. Using remote sensing, we constrain the timing of stream discoloration to the last 10 years, a period of rapid warming and snowfall, suggesting impairment is likely due to permafrost thaw. Thawing permafrost can foster chemical weathering of minerals, microbial reduction of soil iron, and groundwater transport of metals to streams. Compared to clear reference streams, orange streams have lower pH, higher turbidity, and higher sulfate, iron, and trace metal concentrations, supporting sulfide mineral weathering as a primary mobilization process. Stream discoloration was associated with dramatic declines in macroinvertebrate diversity and fish abundance. These findings have considerable implications for drinking water supplies and subsistence fisheries in rural Alaska.

Stream Nitrogen Concentrations Across Arctic Vegetation Gradients

AbstractThe Arctic is experiencing dramatic climate‐induced changes, which could have substantial consequences for nutrient export from land to streams and, thus, in‐stream nutrient availability and composition. Arctic freshwater ecosystems are low‐productive systems often limited by nitrogen (N) availability. Studying small streams is important due to their high abundance across the landscape, intimate connection to their catchments, high biogeochemical activity and high sensitivity to climate change. However, little information is available, especially in terms of N availability and composition (i.e., nitrate, ammonium, and dissolved organic nitrogen [DON]). We aimed to quantify N concentrations across small Arctic streams and explore the link between terrestrial vegetation and stream water N concentration. We conducted a literature study and extracted data from published articles, online databases, and unpublished field data. Out of 215 preselected articles, 20 met our criteria and contained 2,381 observations on stream water N concentrations in the Arctic. Data on DON was scarce: only 161 of the 2,381 observations contained DON data. We found that nitrate (NO3−), ammonium (NH4+) and DON ranged undetectable to 1,155, 547 and 1,587 μg N L−1, respectively. We found that sparsely vegetated areas had higher stream water N‐concentrations, while barren areas and higher vegetated areas had lower stream water N‐concentrations. This study provides fundamental knowledge on N availability in small streams across the Arctic, highlights data gaps and contributes to the basic knowledge needed for understanding and predicting future changes in N dynamics.

Macroinvertebrate traits in Arctic streams reveal latitudinal patterns in physiology and habits that are strongly linked to climate

IntroductionArctic freshwater ecosystems are undergoing rapid environmental transformation because of climate change, which is predicted to produce fundamental alterations in river community structure and function.MethodsWe explored how climate change affects benthic invertebrate communities of Arctic streams by examining patterns of their biological traits along latitudinal and climatic gradients in eastern North America (Canada) and northwestern Europe (Sweden, Norway).ResultsDespite differences in taxonomic composition between continents, we identified similarities in the functional trait niche (FTN) of predominant macroinvertebrate taxonomic groups. Trait composition differed by latitude in eastern Canada, with a predominance of cold-tolerant taxa, tubular body shape, and cased and attached habits at the highest latitudes. Differences in trait composition were evident among ecoregions in Europe, with trait dominance at the highest latitudes that was comparable to North America. There was a similar increase in the relative abundance of cold tolerance and tubular body shape and a decrease in obligate shredders and trait richness with decreasing temperatures across both continents.DiscussionThese patterns are indicative of FTNs that include physiological traits and habits that are advantageous for the low temperatures, short ice-free period, and low riparian vegetation cover at the highest latitudes. We predict that climate change will lead to an increase in functional diversity at high latitudes, as organisms with trait modalities that are currently only found at lower latitudes move northward. However, this change in trait composition will be mediated by the effect of spatial connectivity on dispersal ability, with slower change occurring on Arctic islands. These findings can support modelling of future change in Arctic freshwater assemblages in response to ongoing climate change.

Spatial and temporal patterns of stream nutrient limitation in an Arctic catchment

Arctic stream biofilm responses to ongoing climate-related changes in physical and chemical conditions have major implications for stream food webs and biogeochemical cycles. Yet, such effects have rarely been studied outside summer months or at sub-catchment scales in the Arctic. We used deployments of nutrient diffusing substrates (NDS) to assess the spatial (20 deployments) and seasonal patterns (10 deployments) and physical and chemical drivers of nutrient limitation within an Arctic stream catchment. Results show that nutrient limitation of autotrophic processes was common during summer, but that light inhibited biomass accrual under the ice in winter. Alongside single N, P and C responses, co-limitation dominated the overall pattern of limitation over time and across the catchment. However, the primary limiting nutrient to autotrophs changed from N to P in parts of the catchment with higher N concentrations. As Arctic studies are often conducted at individual sites during summer, these may miss shifts in the drivers of stream productivity that arise from variable nutrient, temperature, and light regimes. Our results caution against focusing on one single most important limiting nutrient, as we found that this can shift seasonally and over small spatial scales in this Arctic catchment.

Effects of Reversal of Water Flow in an Arctic Floodplain River on Fluvial Emissions of CO2 and CH4

AbstractWhen organic matter from thawed permafrost is released, the sources and sinks of greenhouse gases (GHGs), like carbon dioxide (CO2) and methane (CH4) in Arctic rivers will be influenced in the future. However, the temporal variation, environmental controls, and magnitude of the Arctic riverine GHGs are largely unknown. We measured in situ high temporal resolution concentrations of CO2, CH4, and oxygen (O2) in the Ambolikha River in northeast Siberia between late June and early August 2019. During this period, the largely supersaturated riverine CO2 and CH4 concentrations decreased steadily by 90% and 78%, respectively, while the O2 concentrations increased by 22% and were driven by the decreasing water temperature. Estimated gas fluxes indicate that during late June 2019, significant emissions of CO2 and CH4 were sustained, possibly by external terrestrial sources during flooding, or due to lateral exchange with gas‐rich downstream‐flowing water. In July and early August, the river reversed its flow constantly and limited the water exchange at the site. The composition of dissolved organic matter and microbial communities analyzed in discrete samples also revealed a temporal shift. Furthermore, the cumulative total riverine CO2 emissions (36.8 gC‐CO2 m−2) were nearly five times lower than the CO2 uptake at the adjacent floodplain. Emissions of riverine CH4 (0.21 gC‐CH4 m−2) were 16 times lower than the floodplain CH4 emissions. Our study revealed that the hydraulic connectivity with the land in the late freshet, and reversing flow directions in Arctic streams in summer, regulate riverine carbon replenishment and emissions.

Diverging life cycle patterns of two Diamesa species (Diptera, Chironomidae) in High Arctic streams, Svalbard

The fauna of streams in the High Arctic, dominated by chironomids, is shaped by extreme environmental conditions that represent the physiological limits for benthic invertebrates. Despite their ecological importance, little is known of chironomid life histories, development strategies and the key abiotic drivers limiting larval growth in High Arctic streams. We investigated the larval development and growth in three High Arctic rivers with contrasting water sources, thermal regimes and nutrient characteristics. Populations of the larvae of Diamesa bohemani (Goetghebuer 1932) and Diamesa aberrata (Lundbeck 1898) from two sampling occasions in July and August 2016 were morphometrically analysed to determine life history patterns and instream productivity. Water temperature differences lead to diverging development patterns on local spatial scales. The lowest larval growth was in a groundwater/snowmelt fed stream with low food concentration and quality, suggesting that stream productivity is not primarily water source dependant, but is dependent on the nutrient supply. Glacially influenced streams are clearly more productive than previously assumed, resulting in comparable secondary production to groundwater/snowmelt-fed streams.

Temperature-induced changes in biofilm organic matter utilization in arctic streams (Disko Island, Greenland)

Temperature-induced changes in biofilm organic matter utilization in arctic streams (Disko Island, Greenland)

Assessment of ecological impairment of Arctic streams: Challenges and future directions.

As increased growth and development put pressure on freshwater systems in Arctic environments, there is a need to maintain a meaningful and feasible framework for monitoring water quality. A useful tool for monitoring the ecological health of aquatic systems is by means of the analysis and inferences made from benthic invertebrates in a biomonitoring approach. Biomonitoring of rivers and streams within the Arctic has been under‐represented in research efforts. Here, we investigate an approach for monitoring biological impairment in Arctic streams from anthropogenic land use at two streams with different exposure to urban development in Iqaluit, Nunavut, Arctic Canada. Sites upstream of development, at midpoint locations, and at the mouth of each waterbody were sampled during 6 campaigns (2008, 2009, 2014, 2015, 2018, and 2019) to address spatial and temporal variability of the macroinvertebrate community. The influence of taxonomic resolution scaling was also examined in order to understand the sensitivity of macroinvertebrates as indicators in Arctic aquatic systems. We demonstrate that standard biological metrics were effective in indicating biological impairment downstream of sources of point‐source pollutants. A mixed‐design ANOVA for repeated measures also found strong interannual variability; however, we did not detect intra‐annual variation from seasonal factors. When examining metrics at the highest taxonomic resolution possible, the sensitivity of metrics increased. Likewise, when trait‐based metrics (α functional diversity) were applied to indicators identified at high taxonomic resolution, a significant difference was found between reference and impacted sites. Our results show that even though Arctic systems have lower diversity and constrained life‐history characteristics compared to temperate ecosystems, biomonitoring is not only possible, but also equally effective in detecting trends from anthropogenic activities. Thus, biomonitoring approaches in Arctic environments are likely a useful means for providing rapid and cost‐effective means of assessing future environmental impact.

Nitrogen supply and physical disturbance shapes Arctic stream nitrogen uptake through effects on metabolic activity

Abstract Climate change in the Arctic is altering the delivery of nutrients from terrestrial to aquatic ecosystems. The impact of these changes on downstream lakes and rivers is influenced by the capacity of small streams to retain such inputs. Given the potential for nutrient limitation in oligotrophic Arctic streams, biotic demand should be high, unless harsh environmental conditions maintain low biomass standing stocks that limit nutrient uptake capacity. We assessed the drivers of nutrient uptake in two contrasting headwater environments in Arctic Sweden: one stream draining upland tundra and the other draining an alluvial valley with birch forest. At both sites, we measured nitrate (NO3−) uptake biweekly using short‐term slug releases and estimated rates of gross primary production (GPP) and ecosystem respiration from continuous dissolved oxygen measurements. Catchment characteristics were associated with distinct stream chemical and biological properties. For example, the tundra stream maintained relatively low NO3− concentrations (average: 46 µg N/L) and rates of GPP (0.2 g O2 m−2 day−1). By comparison, the birch forest stream was more NO3− rich (88 µg N/L) and productive (GPP: 1.7 g O2 m−2 day−1). These differences corresponded to greater areal NO3− uptake rate and increased NO3− use efficiency (as uptake velocity) in the birch forest stream (max 192 µg N m−2 min−1 and 96 mm/hr) compared to its tundra counterpart (max 52 µg N m−2 min−1 and 49 mm/hr) during 2017. Further, different sets of environmental drivers predicted temporal patterns of nutrient uptake at these sites: abiotic factors (e.g. NO3− concentration and discharge) were associated with changes in uptake in the tundra stream, while metabolic activity was more important in the birch forest stream. Between sites, variation in uptake metrics suggests that the ability to retain pulses of nutrients is linked to nutrient supply regimes controlled at larger spatial and temporal scales and habitat properties that promote biomass accrual and thus biotic demand. Overall, constraints on biotic potential imposed by the habitat template determined the capacity of these high latitude streams to respond to future changes in nutrient inputs arising from climate warming or human land use. ​

Long‐term hydrological, biogeochemical, and ecological data for the Kuparuk River, North Slope, Alaska

AbstractThe Kuparuk River, located on Alaska's North Slope, is one of the most studied rivers in the Arctic. For nearly 40 seasons, physical, chemical, and biological parameters have been monitored continuously in a 5 km, 4th‐order reach of the river during the short summer season when there is flow in this river. Flow decreases as the tundra begins to refreeze in the late autumn and these streams normally remain frozen until the spring freshet. The monitoring program has supported a 34‐year phosphorus enrichment experiment conducted by the Arctic Long Term Ecological Research (LTER) program. Enrichment with phosphorus dramatically changed the structure and function of the primary producer community in the fertilized reach, with cascading effects in higher trophic levels. The datasets generated by this experiment have revealed significant increases in flow‐weighted mean concentrations of nitrate and significant decreases in flow‐weighted mean concentrations of dissolved organic N and P over time. In this paper, we present an overview of the nutrient concentration, discharge, macroinvertebrate, and Arctic grayling population datasets we have collected. The purposes of these datasets are to track changes resulting from the enrichment experiment, support ancillary research on responses of an Arctic stream to climate warming and permafrost thaw, and to provide input and validation data for models to predict future changes in Arctic streams.

Biogeochemical responses over 37 years to manipulation of phosphorus concentrations in an Arctic river: The Upper Kuparuk River Experiment

AbstractThe climate of the Arctic region is changing rapidly, with important implications for permafrost, vegetation communities, and transport of solutes by streams and rivers to the Arctic Ocean. While research on Arctic streams and rivers has accelerated in recent years, long‐term records are relatively rare compared to temperate and tropical regions. We began monitoring the upper Kuparuk River in 1983 as part of a long‐term, low‐level, whole‐season phosphorus enrichment of a 4–6 km experimental reach, which was subsequently incorporated into the Arctic Long‐Term Ecological Research (Arctic LTER) programme. The phosphorus enrichment phase of the Upper Kuparuk River Experiment (UKRE) ran continuously for 34 seasons, fundamentally altering the community structure and function of the Fertilized reach. The objectives of this paper are to (a) update observations of the environmental conditions in the Kuparuk River region as revealed by long‐term, catchment‐level monitoring, (b) compare long‐term trends in biogeochemical characteristics of phosphorus‐enriched and reference reaches of the Kuparuk River, and (c) report results from a new ‘ReFertilization’ experiment. During the UKRE, temperature and discharge did not change significantly, though precipitation increased slightly. However, the UKRE revealed unexpected community state changes attributable to phosphorus enrichment (e.g., appearance of colonizing bryophytes) and long‐term legacy effects of these state changes after cessation of the phosphorus enrichment. The UKRE also revealed important biogeochemical trends (e.g., increased nitrate flux and benthic C:N, decreased DOP flux). The decrease in DOP is particularly notable in that this may be a pan‐Arctic trend related to permafrost thaw and exposure to new sources of iron that reduce phosphorus mobility to streams and rivers. The trends revealed by the UKRE would have been difficult or impossible to identify without long‐term, catchment level research and may have important influences on connections between Arctic headwater catchments and downstream receiving waters, including the Arctic Ocean.

Stream diatom assemblages in an Arctic catchment: diversity and relationship to ecosystem-scale primary production

We quantified benthic diatom diversity in streams in the Miellajokka catchment, about 200 km north of the Arctic circle in Sweden. Beta diversity among sites was related to local-scale environmental heterogeneity (occurring on the order of 1 km or less), and its magnitude was equal (Sørensen Index = 0.62) to levels previously reported for rivers on regional environmental gradients across hundreds of kilometres of Arctic Fennoscandia. Species turnover was the dominant (77%) component of beta diversity in the Miellajokka catchment. Small, stress-tolerant taxa dominated the assemblages, and there were no clear patterns of functional class among sites. Site ordinates from non-metric dimensional scaling were most strongly correlated with flood frequency (r = 0.83) and water temperature (r = 0.89), which was higher in harsh tundra sites than below treeline. Additionally, site ordinates were correlated (r = 0.83) with ecosystem-scale gross primary production — indicative of a link between diatom diversity and ecosystem function. Our results advance understanding of patterns diatom diversity in Arctic streams by quantifying local-scale variation that is understudied in this region, and by identifying the consequences of this local-scale diversity for an ecosystem-scale process.

Arctic concentration–discharge relationships for dissolved organic carbon and nitrate vary with landscape and season

AbstractClimate change is intensifying the Arctic hydrologic cycle, potentially accelerating the release of carbon and nutrients from permafrost landscapes to rivers. However, there are limited riverine flow and solute data of adequate frequency and duration to test how seasonality and catchment landscape characteristics influence production and transport of carbon and nutrients in Arctic river networks. We measured high frequency hydrochemical dynamics at the outlets of three headwater catchments in Arctic Alaska over 3 years. The catchments represent common Arctic landscapes: low‐gradient tundra, low‐gradient and lake‐influenced tundra, and high‐gradient alpine tundra. Using in‐situ spectrophotometers, we measured dissolved organic carbon (DOC) and nitrate (NO3−) concentrations at 15‐min intervals through the flow seasons of 2017, 2018, and 2019. These high‐frequency data allowed us to quantify concentration–discharge (C‐Q) responses during individual storm events across the flow season. Differences in C‐Q responses among catchments indicated strong landscape and seasonal controls on lateral DOC and NO3− flux. For the two low‐gradient tundra catchments, we observed consistent DOC enrichment (transport‐limitation) and NO3− dilution (source‐limitation) during flow events. Conversely, we found consistent NO3− enrichment and DOC dilution in the high‐gradient alpine catchment. Our analysis revealed how high flow events may contribute disproportionately to downstream export in these Arctic streams. Because the duration of the flow season is expected to lengthen and the intensity of Arctic storms are expected to increase, understanding how discharge and solute concentration are coupled is crucial to understanding carbon and nutrient dynamics in rapidly changing permafrost ecosystems.

Effects of prolonged sedimentation from permafrost degradation on macroinvertebrate drift in Arctic streams

AbstractRetrogressive thaw slumps are areas of unstable degraded permafrost that often drain into nearby watersheds, leading to increased sediment loads and changes in water quality. Thaw slumps are prevalent across the Arctic, including western Canada, Alaska, and Russia, and high‐altitude areas of western China. Over the past several decades, increased temperatures and precipitation in the Arctic have led to increases in the size and frequency of thaw slumps. Our study explored the effects of prolonged sedimentation from thaw slumps in the Peel Plateau, NWT, Canada on benthic macroinvertebrate drift, an important biological function of stream ecosystems. Though sedimentation is known to initiate a catastrophic drift response, studies have generally not considered the drift response to ongoing, long‐term perturbation. Drift densities and sediment loads were measured using drift nets and sediment traps at paired sites upstream and downstream of thaw slumps. We compared drift densities and sediment loads between sites and examined how drift differed over a fine‐sediment gradient. The amount of suspended and settling fine sediments increased significantly at downstream sites. Drift densities decreased at downstream sites; however, when drift was corrected for benthic abundance at each site, there was an increase in proportional drift density associated with increased fine sediments. These results indicate that prolonged impacts from thaw slumps result in lower macroinvertebrate abundance and higher proportional drift relative to undisturbed sites. Ultimately, increased sediment loads from thaw slumps represent a chronic stressor that will continue to prevent recovery of macroinvertebrate communities at impacted sites until these features stabilize.

Changes in hydrology affects stream nutrient uptake and primary production in a high-Arctic stream

Global change is predicted to have a marked impact on freshwater ecosystems in the High Arctic, including temperature increase, enhanced precipitation, permafrost degradation and increased vegetation cover. These changes in river catchments can alter flow regime, solute transport to streams and substantially affect stream ecosystem functioning. The objective of this study was to evaluate changes in stream functioning in a high-Arctic stream in relation to changes in discharge, and runoff flow path. We measured environmental factors, biofilm structure, nutrient uptake rates and metabolism. We studied three reaches in a headwater stream in NE Greenland with different catchment characteristics in early and late summer (during two different years) to evaluate the potential influence of environmental change on Arctic stream ecosystem functioning. Highest nutrient uptake, primary production and ecosystem respiration was found in late summer showing that streams are more efficient at retaining nutrients and have higher autotrophic production, likely due to less impact of snowmelt, and lower discharge increasing the surface to volume ratio between streambed and water column. Nutrient uptake rates in late summer from high-Arctic tundra streams were comparable to uptake rates in temperate pristine streams, likely due to no shading by bank vegetation and longer days in the high-Arctic summer compared to temperate streams. Overall, the results of this study aids in the endeavor of predicting how climate-derived changes will affect in-stream nutrient uptake and metabolism in high-Arctic streams. The results suggest that their capacity to transport, cycle and retain carbon and nutrient may increase if the importance of soil water flow paths for streams also increase, thus with effect to stream trophic relations and solute export to coastal areas.

Nutrients influence seasonal metabolic patterns and total productivity of Arctic streams

AbstractThe seasonality of gross primary production (GPP) in streams is driven by multiple physical and chemical factors, yet incident light is often thought to be most important. In Arctic tundra streams, however, light is available in saturating amounts throughout the summer, but sharp declines in nutrient supply during the terrestrial growing season may constrain aquatic productivity. Given the opposing seasonality of these drivers, we hypothesized that “shoulder seasons”—spring and autumn—represent critical time windows when light and nutrients align to optimize rates of stream productivity in the Arctic. To test this, we measured annual patterns of GPP and biofilm accumulation in eight streams in Arctic Sweden. We found that the aquatic growing season length differed by 4 months across streams and was determined largely by the timing of ice‐off in spring. During the growing season, temporal variability in GPP for nitrogen (N) poor streams was correlated with inorganic N concentration, while in more N‐rich streams GPP was instead linked to changes in phosphorus and light. Annual GPP varied ninefold among streams and was enhanced by N availability, the length of ice‐free period, and low flood frequency. Finally, network scale estimates of GPP highlight the overall significance of the shoulder seasons, which accounted for 48% of annual productivity. We suggest that the timing of ice off and nutrient supply from land interact to regulate the annual metabolic regimes of nutrient poor, Arctic streams, leading to unexpected peaks in productivity that are offset from the terrestrial growing season.

Metabolism overrides photo‐oxidation in CO2 dynamics of Arctic permafrost streams

AbstractGlobal warming is enhancing the mobilization of organic carbon (C) from Arctic soils into streams, where it can be mineralized to CO2 and released to the atmosphere. Abiotic photo‐oxidation might drive C mineralization, but this process has not been quantitatively integrated with biological processes that also influence CO2 dynamics in aquatic ecosystems. We measured CO2 concentrations and the isotopic composition of dissolved inorganic C (δ13CDIC) at diel resolution in two Arctic streams, and coupled this with whole‐system metabolism estimates to assess the effect of biotic and abiotic processes on stream C dynamics. CO2 concentrations consistently decreased from night to day, a pattern counter to the hypothesis that photo‐oxidation is the dominant source of CO2. Instead, the observed decrease in CO2 during daytime was explained by photosynthetic rates, which were strongly correlated with diurnal changes in δ13CDIC values. However, on days when modeled photosynthetic rates were near zero, there was still a significant diel change in δ13CDIC values, suggesting that metabolic estimates are partly masked by O2 consumption from photo‐oxidation. Our results suggest that 6–12 mmol CO2‐C m−2 d−1 may be generated from photo‐oxidation, a range that corresponds well to previous laboratory measurements. Moreover, ecosystem respiration rates were 10 times greater than published photo‐oxidation rates for these Arctic streams, and accounted for 33–80% of total CO2 evasion. Our results suggest that metabolic activity is the dominant process for CO2 production in Arctic streams. Thus, future aquatic CO2 emissions may depend on how biotic processes respond to the ongoing environmental change.

冰雪覆盖、气温和地下水流动对水迹排水的北极山坡融冻层热状态的影响

Permafrost in Arctic watersheds limits soil biological activity to a thin, seasonally thawed active layer that contributes water to streams. In many hillslopes, relatively wet drainage features called water tracks have distinct freeze-thaw patterns that affect groundwater flow and storage, and thus the export of heat and solutes to Arctic streams. This study uses groundwater flow and energy transport models to examine potential controls on the timing and duration of freeze–thaw conditions and the magnitude of temperature fluctuations within water tracks and their adjacent hillslopes. The simulated length of the active-layer thaw season varies by 1 month over the range of snow-cover and mean annual air-temperature scenarios simulated. The timing and duration of freezing is particularly sensitive to depth and duration of snow cover. Thus, the deeper snowpack covers that can accumulate in water tracks contribute to their more persistent thaw conditions and their ability to conduct groundwater downslope. A three-dimensional simulation shows that during the summer thaw season, the water track captures groundwater laterally from half way across the hillslope. The models presented here elucidate key mechanisms driving small-scale variation in the active-layer thermal regime of tundra hillslopes, which may be responsible for changes in drainage-network geometry and Arctic biogeochemical fluxes under a warming climate.

Wildfires lead to decreased carbon and increased nitrogen concentrations in upland arctic streams

The Central Siberian Plateau is undergoing rapid climate change that has resulted in increased frequency of forest fires and subsequent alteration of watershed carbon and nutrient dynamics. Across a watershed chronosequence (3 to >100 years since wildfire) we quantified the effects of fire on quantity and composition of dissolved organic matter (DOM), stream water nutrient concentrations, as well as in-stream nutrient uptake. Wildfires increased concentrations of nitrate for a decade, while decreasing concentrations of dissolved organic carbon and nitrogen (DOC and DON) and aliphatic DOM contribution for five decades. These post-wildfire changes in stream DOM result in lower uptake efficiency of in-stream nitrate in recently burned watersheds. Nitrate uptake (as uptake velocity) is strongly dependent on DOM composition (e.g. polyphenolics), ambient dissolved inorganic nitrogen (DIN), and DOC to DIN ratios. Our observations and experiments suggest that a decade-long pulse of inorganic nitrogen and a reduction of DOC export occur following wildfires in streams draining the Central Siberian Plateau. Increased fire frequency in the region is thus likely to both decrease DOM and increase nitrate delivery to the main stem Yenisei River, and ultimately the Arctic Ocean, in the coming decades.

How Will Climate Change Affect Arctic Stream Slime?

Rising temperatures and thawing permafrost will change nutrient concentrations in Arctic waterways, which will influence the growth of biogeochemically important biofilms.