Colorado mountains
From Long-Term Data to Understanding: Toward a Predictive Ecology
2015 LTER ASM Estes Park, CO - August 30 - September 2, 2015

Scaling properties of rainfall-runoff generation processes and nutrient flushing in the Oregon Cascade Mountains. Part 2: Relation between rainfall runoff and nutrient flushing in the Oregon Cascade Mountains

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Lydia Nickolas
Catalina Segura

Understanding how much water moves through a given catchment following a storm event and its relation to the flux of nutrients, solutes, and contaminants is of fundamental importance to water resource managers. The primary purpose of this research is to investigate the relationship between rainfall runoff generation and dissolved nitrogen export through the incorporation of hydrometric information, measurements of stable water isotopes as natural tracers, and concentrations of total nitrogen (TN), ammonia (NH3), and nitrate (NO3) within a nested framework at the HJ Andrews Experimental Forest, OR. Isotopic and nutrient analyses were conducted for baseflow (before & after storm response), precipitation, and stream samples collected automatically over the duration of 2 storm events (54mm and 145mm in magnitude) from 4 gauging sites (WS1, Mack, McRae, & Lookout). Preliminary analyses indicate that the event transit time is correlated to storm magnitude and drainage area after a certain moisture threshold. In-stream NO3- concentrations during storm response are highest within the smaller catchments (Mack & WS1) and tend to remain elevated throughout the response period. The larger catchments (McRae & Lookout) demonstrate smaller increases in the concentration of NO3-, the response time lags behind that of the smaller catchments, and the concentration returns rapidly to baseflow conditions rather than remaining elevated. In contrast, in-stream concentrations of NH3 show a higher degree of similarity between sites in terms of magnitude and timing of increases in concentration over the duration of the response period. Ultimately we found that fractions of inorganic nitrogen correlate with transit time and drainage area, opening the possibility of a catchment wide model of nutrient export prediction.

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