Riverine organic matter and nutrients in southeast Alaska affected by glacial coverage

Abstract

Dissolved organic matter and nutrients from high-latitude coastal watersheds stimulate microbial activity and primary productivity in near-shore ecosystems. A survey of southeast Alaskan watersheds suggests that the extent of glacial coverage may control the release of these nutrients to rivers and ultimately the oceans. The delivery of fresh water, carbon, nitrogen and phosphorous from high-latitude regional watersheds is important to the ecology and nutrient balance of coastal marine ecosystems in the Northern1 and Southern2 hemispheres. Bioavailable dissolved organic matter from rivers can support microbes in near-shore environments, and may also stimulate primary production3,4. Recent studies suggest that impacts of climate change, such as thawing permafrost, may affect nutrient yields in large northern rivers5. Here we analyse riverine dissolved organic matter and nutrient loads in three adjacent coastal watersheds along the Gulf of Alaska. We find that different levels of glacial coverage can alter the timing and magnitude of fresh water, dissolved organic matter and nutrient yields. Our results suggest that a lower extent of glacial coverage within a watershed can lead to higher amounts of dissolved organic matter, but decreased phosphorous yields. Moreover, an abundance of early successional plant species following deglaciation can increase riverine nitrogen levels. We conclude that changes in riverine yields of dissolved organic matter and nutrients due to reductions in glacier extent in coastal watersheds may affect the productivity and function of near-shore coastal ecosystems.