Spatial Analysis and Modeling of Land-Use and Land Cover Change Effects on Water Quality: Boeuf River Watershed

Maryam Roostaee, Department of Civil & Environmental Engineering, Louisiana State University, Baton Rouge, LA 70803: mroost2@lsu.edu; and Zhi-Qiang Deng, Department of Civil & Environmental Engineering, Louisiana State University, Baton Rouge, LA 70803: zdeng@lsu.edu.

Excessive amount of nutrients in surface waters in Mississippi River Basin has led to undesirable growth of aquatic vegetation in Gulf of Mexico that consumes oxygen and causes hypoxic zone. Nationwide studies have shown that agricultural practices and croplands are the major source of nitrogen and phosphorus input to rivers that drain the Mississippi River basin. Boeuf River watershed (HUC 08050001) which lies within the Lower Mississippi/Atchafalaya River Basin is one of the watersheds that is considered critical in recent studies either in case of nutrients flux and percentage of in-stream delivery to Gulf of Mexico. This watershed is, also, listed as impaired in 303d list in Louisiana Water Quality Inventory with increasing Inorganic Nitrogen. Mentioned characteristics of Boeuf River watershed reveal major motivation of this study which is assessing the relationship between land-use/land-cover and nutrients concentration within Boeuf River watershed.

Agriculturally classified spatial data was achieved from U.S Department of Agriculture (USDA) for 1999-2014. Also, all available water quality data for stations within the study area was retrieved via USGS and Louisiana Department of Environmental Quality (LDEQ). These station-based data was used to analyze the correlation between land-use and nutrient concentrations. Since observed water quality data shortage is an obstacle to testing the accuracy of findings of station-based analysis (especially in southern half of the study area), Hydrological Simulation Program-Fortran (HSPF) model is used to provide complementary water quality data for the entire watershed. HSPF model is calibrated and validated for streamflow and water quality parameters such as nitrogen, phosphorus and dissolved oxygen, using ground-based measured data. This model is employed to investigate effects of watershed-scale Land-use and land cover change on water quality parameters.

Results showed that there is a strong correlation between corn acreage in drainage basin of stations and annual average inorganic nitrogen concentration measured at those stations. Wetland acreage with dissolved oxygen concentration and pasture acreage with total nitrogen concentration are, also, correlated. Results from HSPF model, although cannot reveal crops’ impact on water quality, shows the same pattern between agricultural area and nutrients concentration. The results provide new insights into the effects of watershed-scale land use and land cover change on nutrient inputs into streams and rivers.