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.