Process-Based Modeling of the Dairy- McKay Watershed to Inform Monitoring for Agricultural Best Management Practices

Abstract

The project described in this paper specifically looks at the influence of land management practices on water quality, specifically total phosphorus (TP) loads in the Dairy McKay Watershed (DMW). The project is being used to inform a water quality monitoring plan for the Oregon DEQ via outputs from a SWAT model. The DMW is known to have high TP levels that are linked to low dissolved oxygen levels in the Tualatin River. There is a total maximum daily load (TMDL) for the Tualatin River that specifies target TP levels coming out of the DMW, if met these targets are met, the DO levels should remain acceptable for aquatic life in the Tualatin River. As there is little current water quality data within the DMW, it is difficult to identify where the high levels of TP are located and where they can be reduced. The DMW-SWAT model outputs were analyzed, via Linear Regression analysis, to gain a better understanding of which stream segments are most sensitive to TP loading, based on their land use and management. These sensitive stream segments are recommended as future monitoring locations for continuous water quality data in the DMW.