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1995 Annual Research and Extension Report

Hydrology and Water Quality at Buck Island

Donald A. Graetz and Keneth L. Campbell

Department of Soil and Water Science
and
Department of Agricultural and Biological Engineering

1. Establish water quality monitoring stations on different land-uses.

2. Determine baseline water quality parameters from selected land-uses.

3. Develop tools for extending results to similar land-uses in the area.

Although numerous agro-ecological issues are being addressed at Buck Island Ranch, water quality emerges as a central theme. This issue is being fueled by concerns that cattle ranches and citrus groves may be contributing to the deterioration of both surficial and ground water supplies. The program at Buck Island Ranch provides a unique opportunity to study this issue and to provide recommendations for remedial actions, if necessary.

Baseline water quality monitoring stations were designed and installed on the following sites: 1) the existing citrus grove discharge, 2) the planned new citrus grove discharge, 3) a discharge which represents improved, intensively-used pastures, 4) a discharge which comes from native pastures, and 5) a discharge from a wetland area. Grab samples were obtained from the sites prior to installation of the automated stations.

All flow measurement structures and related monitoring and sampling instrumentation are currently installed and operational except the citrus grove site. Due to difficulties in determining the pump rating curve, that site does not yet measure flow data. These installations have just recently been completed due to the excellent work of the new field engineer, Lisa Collins, hired by Archbold Biological Station. We have worked with her to develop the data logger control programs for flow measurement and sampler control, which she now has operational at East Marsh (wetland), West Marsh (native pasture), Griffith Park (improved pasture), and the citrus grove. We will now be able to determine water discharge rates and mass nutrient loads leaving each of these locations on a continuous basis instead of only nutrient concentrations from grab samples which we have been limited to until now.

Nitrogen and phosphorus concentrations in runoff from the various land-use areas, averaged for the period of January 1994 to March 1995, are shown in Table 1. Although all concentrations continue to be relatively low, the improved pasture area continues to have the highest nitrogen and phosphorus concentrations. Total nitrogen concentrations ranged from 3.5 to 4.3 mg/L. Most of this nitrogen was in the organic form as indicated by the very low concentrations of ammonium and nitrate forms of nitrogen. Total phosphorus concentrations were less than 1 mg/L - 0.13 to 0.63 mg/L. In contrast to nitrogen, about 50% of the phosphorus was in the readily-available inorganic form, i.e., soluble reactive phosphorus (SRP). Total phosphorus concentrations for the improved pasture, native range, and citrus grove runoff were slightly above the SFWMD regulatory limit of 0.35 mg/L. Relationships between nutrient concentrations, land-use activity, and rainfall are still being evaluated. There appear to be small seasonal variations in runoff nutrient concentration which may be more related to rainfall amounts than any particular land-use activity.

1. The water sampling protocol will switch from grab sampling during flow events to auto sampling and flow recording. This will allow quantitation of nutrient losses (water and nutrient discharge and mass loading) from the various land-uses for further evaluation of the significance of nutrient losses. Data from specific flow events will be characterized in detail to determine the relative movement of particulate and soluble forms of nutrients from the monitored areas.

2. A GIS framework will be used to link together the FHANTM water quality model being used for the beef decision support system with an existing bahiagrass crop growth model. This will enhance the functionality of the beef decision support system being developed under contract with SFWMD.

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