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

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