Nutrient Discharges from Mayagüez Bay Watershed
September 1, 2001 - August 30, 2004
Project Summary Narrative
Water resources in Puerto Rico are subject to tremendous pressure from urban, industrial, and agricultural activities. As a result, most surface waters exhibit some kind of impact from anthropogenic activities. High P concentrations in surface waters of Puerto Rico suggest this to be the single most important nutrient that must be controlled to reduce the accelerated eutrophication of fresh waters. Although local data is not available, agricultural non-point sources are believed to be the leading cause of nutrient (primarily N and P) and sediment contamination of surface waters. Still, diverse point- and non-point sources such as unsewered communities in urban, suburban, and rural areas, landfills, agricultural activities, and wastewaster treatment facilities have been identified as major contributors of nutrient loads to surface waters in the island. A systematic approach to water quality and watershed restoration must first identify specific contaminant sources as well as characterize their pollution pattern (i.e., relative contribution, seasonal variability, etc).
We propose an intensive research study to identify and quantify nutrient discharges along the main channel and major tributaries of the Rio Grande de Añasco in the Mayagüez Bay Watershed (MBW). We will examine seasonal and spatial trends in sediment and nutrient (nitrogen and phosphorus) concentrations in areas of contrasting land use characteristics. Trends in total P concentrations in water will be related to land use, soil test P information, hydrologic discharge, and known point inputs to assess the relative contribution of different sources to the watershed. This information in combination with land use characterization will serve to better delineate the various nutrient contributing sources and establish a targeted nutrient management program for the watershed.
Year Report and Activities:
- Farm delineation on digital orthoquad photographs (in cooperation with USDA-NRCS personnel)
- Prepare database which includes
- Farm identification
- Aerial extent of farms
- Crops planted
- Crop management practices
- Nutrient management practices
- Identification of animal waste management operations (with and without permits)
- Adjust watershed delineation based on ground-truthing
- Visit the sub-watersheds with a GPS to provide ground information on landuse for the five sub-watersheds selected.
- Identification of major nutrient point sources within the sub-watersheds.
- Hydrographs and rating curves at USGS site and at all points of interest corresponding to the five sub-watersheds.
- Assemble the HEC-1 model for each sub-watersheds
- Topography and cross-sections of all sampling sites
- Develop rating curves for the USGS site and the five sub-watersheds
- Calibrate HEC-1 model for the USGS site and correct the model for the other five indicator sites based on calibration results
- Continue bi-weekly sampling and water quality (nutrient, sediment and bacterial) characterization through 15 June 2002
- Perform synoptic sampling (grab sampling) based on historical discharge data.
- Analysis and interpretation of water quality data (relate trends in water-quality parameters to land use, hydrologic discharge, point and non-point sources)
- Apply a model of an indicator of actual P transport (the P index developed by USDA-NRCS) to selected farms within the subwatersheds
- Storm-event sampling (perform systematic and detailed evaluations of water quality by sampling during storm events using automated storm water samplers)