Å·ÃÀ¿Ú±¬ÊÓƵ

Burns, Margaret ¹ ; McKnight, Diane ² ; Gabor, Rachel ³ ; Barnard, Holly ⁴

¹ Institute of Arctic and Alpine Research, Å·ÃÀ¿Ú±¬ÊÓƵ Boulder
² Institute of Arctic and Alpine Research, Å·ÃÀ¿Ú±¬ÊÓƵ Boulder
³ Institute of Arctic and Alpine Research, Å·ÃÀ¿Ú±¬ÊÓƵ Boulder
⁴ Institute of Arctic and Alpine Research, Å·ÃÀ¿Ú±¬ÊÓƵ Boulder

Dissolved organic matter (DOM) is a ubiquitous mixture of compounds formed from the degradation of both terrestrial and microbial materials. Current research has begun to explore the spatial and temporal variability of DOM chemistry in hillslope systems during discrete storm events (Inamdar et al. 2013). However, the fine-scale temporal feedbacks of hillslope hydrology and DOM chemistry during snowmelt are poorly understood. In this study, we explore the role of soil water on DOM transport and transformation from the hillslope to the stream in a montane catchment within the Boulder Creek Critical Zone Observatory in Å·ÃÀ¿Ú±¬ÊÓƵ. We installed a suite of tension lysimeters located within the rooting zone across representative north- and south-facing slopes. Soil water and stream samples were collected daily for approximately seven weeks during the 2013 spring snow melt period and analyzed for DOM composition using fluorescence spectroscopy. Results indicate temporal changes in stream DOM chemistry, with no concurrent changes in hillslope DOM chemistry. A high degree of separation between the chemical composition of deep groundwater and soil water suggest that the changes in stream water chemistry can be partially explained by a transition to shallow water flowpaths during snowmelt. Specifically, a significant increase in the humification index (HIX) in the stream concurrent with a significant decrease in both the freshness index (BIX) and the percent protein (p<0.01) indicate a transition in the stream to humic-like compounds, most likely derived from terrestrial sources. Changes in the abundance of compounds identified using parallel factor analysis (PARAFAC) suggest the non-fluorescent fraction of DOM, such as carbohydrates, as the driver behind stream dissolved organic carbon (DOC) increases during snowmelt. Such shifts in chemical properties provide an understanding of the DOM hydrologically connected to the stream and its implications on stream DOM bioavailability and reactivity.

Inamdar, S., Dhillon, G., Singh, S., Dutta, S., Levia, D., Scott, D., … McHale, P., 2013, Temporal variation in end-member chemistry and its influence on runoff mixing patterns in a forested, Piedmont catchment: Water Resources Research, v. 49, p. 1828–1844.