M6 AM Suspended and Bedded Sediments and Nutrients: Exposure-response Relationships
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 324-326

(LEH-1117-657348) Site specific reference conditions determined as functions of watershed attributes: implications for criteria development.

Lehrter, J¹, ¹ EPA -- Gulf Ecology Division, Gulf Breeze, Florida, USA

ABSTRACT- In-stream nitrogen (N), phosphorus (P), organic carbon (OC), and total suspended sediment (TSS) concentrations were measured over two annual cycles to assess how land-use/land-cover (LULC) and geomorphology regulate non-point source inputs of these water quality variables in southeastern coastal plain watersheds. LULC and geomorphology are shown to be important watershed attributes dictating not only the magnitude of constituent concentrations but also the chemical form of the constituents. Watershed LULC, geomorphology attributes, and the water quality data were used in stepwise multiple regression analyses to develop statistical models. Results from these models indicate that N and P concentrations were greatest in streams draining watersheds where the percentage of LULC as row-crop agriculture land-uses was large. Watershed geomorphology attributes such as area and slope were also strongly correlated to some water quality constituent concentrations. For example, the slope of the sub-basin was the best predictor for dissolved organic N, while for dissolved organic P the sub-basin slope, stream-reach slope, and watershed area were the best predictors. At the inter-annual scale, constituent concentrations varied significantly with higher concentrations of N, P, OC, and TSS occurring in a wetter year. Higher concentrations in the wetter year were primarily driven by greater export of nutrients in organic forms such as dissolved organic nitrogen. For management purposes, the stepwise regression models offer a site-specific alternative to the broad scale eco-regional approaches being used for determining reference conditions and criteria for these constituents.

Key words: watershed, land-use/land-cover, geomorphology, nutrient criteria