Water Resources Research Act Program

Details for Project ID 2014LA95B

Identification of Critical Nitrogen Source Areas in Lower Boeuf River Watershed

Institute: Louisiana
Year Established: 2014 Start Date: 2014-03-01 End Date: 2015-02-28
Total Federal Funds: $15,000 Total Non-Federal Funds: $37,467

Principal Investigators: Zhi-Qiang Deng

Abstract: Nitrogen is identified in the latest (2012) Louisiana Water Quality Inventory - Integrated Report (305(b)/303(d)) as one of the most cited suspected causes of water quality impairment. Introduction of excess river-borne nitrogen can exacerbate surface water eutrophication, favor harmful algal blooms, and aggravate oxygen depletion. This is why Dissolved Oxygen (DO) and nutrients (primarily nitrogen and phosphorus) are commonly listed together as the most frequently cited suspected cause of water body impairment in Louisiana. While DO and nitrogen are the most suspected cause of impairment in Louisiana, their sources are mostly unknown. In fact, the top-ranked impairment source is unknown source according to the latest Louisiana Water Quality Integrated Report. A total of 169 water body subsegments, including 128 river subsegments, are impaired due to unknown sources, making it challenging to restore the impaired water bodies. This is particularly true in agricultural watersheds, such as the Boeuf River watershed. As a result, the latest Louisiana Water Quality Integrated Report listed the determination of critical source areas as one of the priorities for the development and implementation of Total Maximum Daily Load (TMDL) and the restoration of water quality. It means that the identification of unknown critical source areas is essential to the restoration of water quality and thereby to meeting designated uses of water bodies. This is a critical regional and state water quality problem needing to be addressed. The overall goal of this project is to develop an efficient and effective modeling approach to identification of critical source areas (CSAs) for contaminants (including nitrogen) and thereby to address the critical regional and state water quality problem. The proposed strategy is to test and demonstrate the new modeling approach by identifying CSAs for nitrogen in the Lower Boeuf River watershed. The Lower Boeuf River (LA080901_00) is impaired due to excess nutrients and primarily nitrogen from unknown sources. The primary objective of the project is to develop a three-tiered new approach to the determination of field-scale CSAs for contaminants. The three-tiered approach involves (1) SPARROW modeling for identification of the critical tributaries controlling nitrogen loading at the watershed scale (8-digit HUC), (2) a VART model-based inverse modeling for identification of the critical subwatersheds controlling nitrogen loading at the subwatershed scale (12-digit HUC), and (3) SWAT model-based watershed modeling for identification of CSAs at the field scale. The three components will be implemented in three separate tasks by combining PI’s proven VART model for solute transport in rivers, watershed modeling systems SPARROW and SWAT, and high resolution distributed data (including but not limited to NEXRAD radar rainfall data). The proposed project has broader implications for environmental restoration and sustainability in Louisiana and in the nation as well. This project will provide an efficient and cost effective tool for environmental and water resources management agencies (such as Louisiana Department of Environmental Quality) to identify critical source areas of nitrogen pollution and restore designated uses of impaired water bodies. While this study focuses on the Lower Boeuf River watershed, the three-tiered approach can be easily extended to other watersheds in Louisiana and in the nation. In addition, the project provides potential research and educational training opportunities for graduate and undergraduate students. This proposal is intended to address the first priority research need: Watershed Education and Research Activities, identified by the Louisiana Water Resources Research Institute (LWRRI) in LWRRI’s Research Priorities for 2014.