Montana Creek Alaska hydrology and biogeochemistry

Temperate rainforest ecosystems of coastal western North America are experiencing major changes including higher air temperature, more precipitation, and glacier shrinkage. These changes can impact river discharge patterns such as timing and quantity, which can influence the concentrations and yields of ecologically relevant elements such as carbon and nitrogen. However, changes in atmospheric precipitation sources and seasonality, as well as pathways linking the magnitude and variability in rainfall events to watershed biogeochemical exports, remain poorly constrained. This study reveals that greater fall and early winter evaporation in the Arctic Ocean and GOA is influencing seasonally disproportionate precipitation increases across these months. These increased fall rains, which have distinct water isotope signatures, fuel greater stream discharge, but have different impacts on riverine dissolved organic carbon (DOC) concentrations than total dissolved nitrogen (TDN). Preferential winter warming will lead to more rain (less snow) and could drive changes to the riverine concentration-discharge relationships for DOC, while TDN production and export appear more influenced by reach-scale processes (e.g., spawning salmon) that are less sensitive to increases in precipitation. Taken together, the continued influence of reducing Arctic sea ice extent and a warming GOA could drive greater precipitation in Southeast Alaska, but also progressively increase the magnitude and seasonal distribution (e.g., more in winter) of freshwater and DOC yields to coastal ecosystems.