Biofilm Growth in Two Streams Draining Mountainous Permafrost Catchments in NE Greenland

Abstract

The objective of this study was to evaluate how stream water nutrient concentrations influence biofilm accrual in streams draining mountainous permafrost headwaters. We selected six stream locations in the Zackenberg area (NE Greenland, 74°N) subjected to a gradient in the areal contribution of different geomorphological units in the watersheds and channel stability. We used nutrient diffusing substrates to evaluate biofilm growth (autotrophic and total biomass). We found elevated stream nitrate concentrations in samples from upstream reaches draining larger areas of solifluction sheets and bare rock and with higher channel instability. Nitrate had the highest standardized effect on autotrophic biofilm growth on control disks. However, stream biofilm growth was not nutrient limited as shown by the absence of an increase in biofilm biomass as a response to the experimental nutrient additions. The response to nutrient additions via diffusing substrates depended on the altitude gradient. Overall, our results showed stream nitrogen availability to be one of the main drivers of algal biofilm accrual in high‐Arctic streams, suggesting that the predicted changes in nutrient exports induced by climate change will have strong impacts on the biogeochemistry and ecological functioning of high‐Arctic streams.

Nutrients influence seasonal metabolic patterns and total productivity of Arctic streams

“…S4 and S5), suggesting that this seasonality is, in part, related to upregulated terrestrial nutrient demand during the growing season (Weintraub and Schimel 2005 b ). This pattern creates persistent nutrient limitation of algal growth during summer (Peterson et al 1983; Pastor et al 2020), which appeared to suppress summer GPP in all but the two most nutrient rich streams (> 90 μ g DIN L −1 ) and led to positive correlations between the temporal variability in GPP and DIN concentrations at the more N poor sites (20–30 μ g L −1 ). Notably, based on the relative area of different streams, DIN‐driven metabolic patterns during the open water season appear to operate across ca.…”

“…Superimposed on this light regime is a strongly seasonal pattern of stream nutrient concentrations, with relatively high levels in winter, and lowest during summer (e.g., Holmes et al 2000;Mann et al 2012), potentially due to catchment nutrient retention during the terrestrial growing season (Weintraub and Schimel 2005b;Ohte 2012). As a result, tundra streams are often strongly nutrient limited when incident light is greatest, as evidenced from studies in Alaska (Peterson et al 1983), Northern Sweden (Myrstener et al 2018), Iceland (Friberg et al 2009), and Greenland (Pastor et al 2020). At the same time, elevated nutrient concentrations in spring and autumn may create time windows that support elevated GPP.…”

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

“…By comparison, streams with strong groundwater connections or in close proximity to solifluction tend to be nutrient enriched and more hydrologically stable, and typically support higher rates of metabolism and biomass accrual (Huryn et al, 2005;Myrstener et al, 2021;Pastor et al, 2020). At the extreme end of this habitat gradient are 5.…”

“…Such conditions are typical for upland tundra streams, which lie near the nutrient‐poor and low‐productivity end of the habitat gradient in Artic landscapes. By comparison, streams with strong groundwater connections or in close proximity to solifluction tend to be nutrient enriched and more hydrologically stable, and typically support higher rates of metabolism and biomass accrual (Huryn et al., 2005; Myrstener et al., 2021; Pastor et al., 2020). At the extreme end of this habitat gradient are spring‐fed streams, which sustain flow throughout the year, are comparatively rich in nutrients, and are home to notably productive biological communities (Huryn et al., 2014).…”