Quantifying the Effects of Land Use and Management on Receiving Water Quantity, Quality, and Ecosystem Health in a Karst Watershed

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The Upper Floridan Aquifer (UFA), one of the most productive aquifers in the world, supports productive agricultural and silvicultural industries, and provides drinking water to more than 10 million people. A significant portion of the UFA is unconfined and thus is rapidly recharged by rainfall and easily polluted by a variety of land uses. As a result, the aquifer and the springs and rivers it feeds face significant threats to water quality, water quantity and ecosystem health. In Florida, minimum flows and levels (MFLs) and numeric nutrient criteria (NNC) for nitrate-nitrogen (NO3-N) have been set to protect the ecological integrity springs and rivers fed by the UFA, but these standards are not currently being met throughout much of the state.
This study focuses on the Santa Fe River Basin, where it is estimated that a 11.3 % reduction in water withdrawals and 35% reduction in NO3-N leaching to the UFA are needed to meet the mandated MFL and NNC. Land use in the basin is dominated by production forestry and agriculture (primarily corn, peanut, hay, pasture). The objective of this study was to quantify NO3-N loads and net groundwater recharge across the range of production practices currently being implemented for these land uses and to understand changes needed to achieve environmental standards. Results showed that, for current practices, corn-peanut rotations yield average net recharge of -170 mm/year and average NO3-N leaching of 200 kg/ha/yr. For grazed pastures, hay, and production forestry, average net recharge was 504, 476, and 316 mm/yr, and average NO3-N leaching was 110, 3.4, 4, kg/ha, respectively. We found that required reductions in irrigation pumping and NO3-N leaching can be achieved by conversion from more intensive (corn, peanut, pasture) to less intensive (hay, forest) land uses, or by strict adoption of advanced irrigation and nutrient management strategies such as soil moisture sensor triggered irrigation, reduced rates and improved timing of fertilizer application, reduced stocking densities, and rotational grazing. Current work is investigating the regional economic impact of required changes and assessing both the public’s willingness to pay and producers’ willingness to accept incentives to bring about these changes.

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Presented at the AGU Fall Meeting on December 11, 2019 in San Francisco, CA