Nutrient uptake controls and limitation dynamics in north-east Greenland streams

Abstract

Permafrost thaw induced by climate change will cause increased release of nutrients and organic matter from the active layer to Arctic streams and, with increased water temperature, will potentially enhance algal biomass and nutrient uptake. Although essential for accurately predicting the response of Arctic streams to environmental change, knowledge of nutrient release on current Arctic in-stream processing is limited. Addressing this research gap, we quantified nutrient uptake of short-term releases of NO 3 − , PO 4 3-and NH 4 + during peak snowmelt season in five streams of contrasting physiochemical characteristics (from unstable, highly turbid to highly stable, clear-water systems) in north-east Greenland to elucidate the major controls driving nutrient dynamics. Releases were plus or minus acetate to evaluate uptake dynamics with and without a dissolved organic carbon source. To substantiate limiting nutrients to algal biomass, nutrient-diffusing substrates were installed in the five streams for 16 days with NH 4 + , PO 4 3-or NH 4 + + PO 4 3-on organic and inorganic substrates. Observed low uptake rates were due to a combination of low nutrient and DOC concentrations, combined with low water temperature and primary producer biomass, and substantial variation occurred between streams. N was found to be the primary limiting nutrient for biofilm, whilst streams displayed widespread PO 4 3-limitation. This research has important implications for future changes in nutrient processing and export in Arctic streams, which are predicted to include increased nutrient uptake rates due to increased nutrient availability, warmer water temperatures and increased concentration of labile carbon. These changes could have ecosystem and landscape-wide impacts.

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

“…In general, in our study a negative response to single nutrient amendments was found for both autotrophic and total biofilm biomass, which contrasts the results of early summer investigations conducted in the same streams where increased chl a with N addition was recorded (Docherty, Riis, Hannah, et al, 2018). Nutrient inhibition of growth has previously been observed in NDS research worldwide (Beck et al, 2017; Francoeur, 2001) and for Arctic studies (Figure S5), but the mechanisms behind remain equivocal.…”

“…Thus, high biomass values were recorded at the upstream sites, especially for the autotrophic fraction with the highest chl a values occurring at the Kærelv A site (1.6–4.1 μg chl a /cm 2 on control disks). The values are conspicuously high compared with those recorded for unamended inorganic substrates in other NDS studies in the Arctic region (Table S3), including the same downstream reaches (C sites) sampled during early summer (0.33 and 0.79 μg chl a /cm 2 ; Docherty, Riis, Hannah, et al, 2018). Concurrently with the large variability in biofilm biomass, we found large variation in water N concentrations among the six sampled stream reaches.…”

“…For chl a , unfrozen disks were directly extracted with 6‐ml 96% ethanol and measured for absorbance after 12 hr on ultraviolet (UV) 1700 spectrophotometer (Shimadzu, Japan). Chl a was calculated as (Docherty, Riis, Hannah, et al, 2018): where E is volume of ethanol (ml), 83.4 is the absorption of chl a in ethanol, and A is the sample area (cm 2 ).…”

“…Most of the available data on nutrient limitation are for low‐Arctic ecosystems, although high‐Arctic region (located above 70°N on the east coast of Greenland) is distinct in various environmental, geomorphological, and biological characteristics (Olson et al, 2001). The combination of N and P additions has been shown to have the highest effects on biofilm productivity in worldwide freshwaters (Beck et al, 2017; Elser et al, 2007) and across the Arctic (Docherty, Riis, Hannah, et al, 2018; Myrstener et al, 2018; Peterson et al, 1983; Tank & Dodds, 2003). These studies have also usually found a higher effect of N than P when added alone (but see Peterson et al, 1983; Tank & Dodds, 2003).…”

Spatio‐temporal dynamics of macroinvertebrate communities in northeast Greenlandic snowmelt streams

“…The high variability in conductivity and solute load between sites is representative of the different levels of fluvial erosion and nivation processes taking place at each site (Hasholt & Hagedorn, 2000), leading to high suspended sediment concentrations in streams, which are then weathered in-stream by turbulent flow, releasing ions and nutrients (Chin et al, 2016). Previous research has shown all streams in this study to have low nutrient and dissolved organic carbon concentrations and low primary producer biomass, with nutrient uptake being low as a result (Docherty, Riis, Hannah, Rosenhøj Leth, & Milner, 2018).…”