Abstract

Dissolved organic matter (DOM) is a ubiquitous mixture of compounds formed from the degradation of both terrestrial and microbial material. The abundance and composition of the DOM present in stream water is important to stream processes such as UV light attenuation, nutrient supply and metal sorption. However, an excess of DOM can cause reactions with chlorination compounds at drinking water treatment plants, creating potentially harmful disinfection byproducts. Currently, little is known regarding the influence of soil interstitial water on stream DOM composition. In this study, we explore the role of interstitial water on DOM transport and transformation from the hillslope to the stream in a montane catchment within the Boulder Creek Critical Zone Observatory in Colorado. We installed a suite of tension lysimeters located within the rooting zone across representative north- and south-facing slopes. Interstitial 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. To date, we have used fluorescence index (FI) to evaluate differences between microbial and terrestrial DOM inputs and humification index (HIX) to assess degree of humification undergone by the DOM. Preliminary results indicate that FI was significantly correlated with hillslope aspect (p<.01), with higher FI on north-facing slopes, suggesting more microbial precursor material. Stream samples reveal greater humification throughout the snowmelt period (p<.01). This increase could suggest a transition from deeper groundwater sources to shallow soil interstitial water inputs into the stream during snowmelt. These preliminary results suggest that changes in DOM composition through the catchment during snowmelt can be linked to hydrologic transport. Further site specific model development will reveal explicit changes in the DOM chemistry and will increase our understanding of fundamental nutrient cycling processes at the hillslope to catchment scale.

Citation

Burns M.A., McKnight M.D., Gabor R.S., Brooks P.D., Barnard H.R. (2013): Transport and Transformation of Dissolved Organic Matter in Soil Interstitial Water Across Forested, Montane Hillslopes. Abstract H23F-1340 presented at 2013 Fall Meeting, AGU, San Francisco, CA, 9-13 Dec..

This Paper/Book acknowledges NSF CZO grant support.