Citation:

Rackley, J., R. Devereux, Johne Rogers, M. Machavaram, AND M. Mills. Watershed delineation and nitrogen source analysis for Bayou Chico, an urban watershed in northwest Florida. 2016 American Water Resources Association Annual Conference, Orlando, FL, November 13 - 17, 2016.

Impact/Purpose:

The work compares models used for delineating storm water drainage basins and combining that with chemical and stable isotope techniques to measure nitrogen loadings and identify sources of nitrogen in an urban watershed. Storm water controls in urban settings generally have focused on controlling the flows and quantities of the water and less on the quality of the water. This research will help resource managers evaluate nutrient loads in urban watersheds and where they may be mitigated to improve the water quality in rivers, bayous, bays and estuaries that receive non-point source nitrogen loadings.

Description:

Nutrient pollution in stormwater runoff from urbanized areas contributes to water quality degradation in streams and receiving waterbodies. Agriculture, population growth, and industrial activities are significant sources of nitrogen inputs for surface waters. Increased nitrogen loading stimulates eutrophication through algal blooms, which leads to an overall decrease in drinking water and aquatic habitat quality. Bayou Chico, a highly urbanized watershed in the Pensacola Bay system in northwest Florida, is a nutrient-impaired waterbody under management to reduce bacteria and nutrient loadings, in accordance with the Florida Department of Environmental Protection’s (FDEP) Basin Management Action Plan. Best management practices and green infrastructure (GI) throughout Bayou Chico help reduce nitrogen inputs by retaining and filtering water. GI can function as a nitrogen sink by sorption or infiltration into soils, sequestration into plant material, and denitrification through microbial processes. However, a better understanding of the efficiency of these systems is needed to better inform management practices on future nitrogen reduction. This project will address two issues relating to the presence of nitrogen in the Bayou Chico watershed: 1) the identification of specific nitrogen sources within urbanized areas, and 2) the potential rates of nitrogen removal and sequestration from GI and nitrogen transport throughout the bayou. To accomplish these goals, nitrogen sources and cycling will be investigated in Jones Creek and Jackson Creek, Bayou Chico’s two primary contributing streams. Water analysis results for H and O stable isotopes (and other water attributes, such as pH and salinity) differed notably depending on their source and location within the bayou. Major sources of water inputs into Bayou Chico include urbanized streams (Jackson Creek), more natural streams (Jones Creek), surface water, and bay water. Accurate definition of the bayou’s watershed size and shape is important for conservation, management, and cleanup efforts, such as the distribution of nutrient pollution control substances. Bayou Chico’s watershed and sub-basins were investigated to better distinguish tributaries and tidal influence within the bayou. Sub-basins were delineated in ArcMap using 5-meter LiDAR elevation data from the University of Florida, and compared to watershed boundaries from FDEP and the USGS National Hydrography Dataset (NHD) for general agreement. The EPA’s Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) model was used to calculate another sub-basin delineation of Bayou Chico using 30-meter USGS National Elevation Dataset (NED) data. The ArcMap and BASINS delineation products were compared for accuracy to determine the bayou’s watershed size and shape. These new delineations of Bayou Chico’s watershed, as well as the Jackson and Jones creeks sub-basins, more accurately define the study area and affected sub-basins. This research will provide regional support for conservation and nutrient management efforts, as well as provide a general model for future projects addressing nutrient pollution management and GI implementation within the Bayou Chico watershed.

Record Details: