Regional Variation in Nitrate Content of Rock Glacier Outflow

Abstract

&nbsp; As alpine ecosystems undergo widespread deglaciation, rock glaciers and periglacial features are becoming an increasingly critical water reservoir in headwater ecosystems. Thus, rock glacier outlet water chemistry has critical implications for ecosystem resiliency and downstream water quality under accelerating global change. These waters have been observed to contain extremely high nitrate concentrations, among the highest ever recorded in high elevation ecosystems. This has the potential to influence biogeochemical cycling in headwater systems. Despite these potentially significant impacts, sources of reactive nitrogen species in rock glacier outflow remain unknown. We compare concentrations and stable isotopes of nitrate in rock glacier outflow to surface water, groundwater, and snow samples. We examine variations in nitrate loading between the San Juan Mountains and the Front Range, as well as variation across regions globally. Nitrate concentrations in rock glacier outflow are highest in the Front Range but are consistent across regions once normalized to reference stream concentrations. We suggest phase change concentration as a possible mechanism behind elevated [NO3-] in rock glacier outflows. Potential nitrate sources include nitrification and atmospheric deposition of nitrates. </p