Quantifying Stream Flux of Carbon Nitrogen and Phosphorus in a Tropical Watershed, Mae Sa Thailand

Nutrient loading to rivers and, ultimately, oceans is of global concern with implications for both immediate aquatic health and as a longer term feedback system for global elemental cycling and climate change. Southeast Asia has been identified as a global hotspot for high yields of C, N, and P. We present initial results from a nutrient flux study from the Mae Sa watershed in northern Thailand. The Mae Sa is a 74 ha basin at the headwaters of the Chao Praya River and is characterized by diverse land use extending from forest reserves to intensive agriculture. The watershed receives the majority of its annual 1300-2000 mm of precipitation during the monsoonal season with runoff characterized by high intensity, short-duration flooding, typically produced by localized, sub-watershed, precipitation events. Dissolved (<0.7 microns), particulate (0.7 microns to 1 mm) and suspended (>1 mm) fractions were sampled across a series of storm hydrograph events and each fraction was analyzed for total organic C, N, and P contents. Initial results indicate that a significant fraction of the nutrient flux during these events is found in the >1 mm size fraction.