VARIATION IN STREAMFLOW SOURCES AND COMPOSITION IN RESPONSE TO WOODY ENCROACHMENT IN GRASSLAND WATERSHEDS

Woody encroachment--the expansion of woody plant species into grasslands--has been observed worldwide, imploring us to explore the potential effects this phenomenon is having on their environments. Studies have proven that woody encroachment can alter runoff generation mechanisms, infiltration rates, and the proportions of deep and shallow water sources to streamflow. However, little is understood about the consequences these hydrologic impacts have on surface water quality. To help fill this knowledge gap, we used high intensity sampling during multiple storm events to examine variations in stream water composition located at three watersheds, each experiencing different extents of woody encroachment. We simultaneously collected stream water and precipitation samples every hour during the events and then used isotope hydrograph separation to calculate variations in streamflow sources. Furthermore, we examine concentration-discharge (C-Q) relationships to better understand sources and temporal dynamics of stream water solutes. Ultimately, we expect that woody encroachment is increasing the proportion of deep-water sources in the streamflow and thus increasing concentrations of the solutes generated by bedrock weathering while simultaneously decreasing the proportions of nutrients and other solutes typically found at higher elevations in soil pore water.