A water budget and hydrology model of a basin mangrove forest in Rookery Bay, Florida

Abstract

Water budgets of two basin mangrove forests in Rookery Bay were determined by measuring during a 2-year period the inputs of precipitation and tides, together with losses through seepage, runoff and evapotranspiration. Precipitation inputs to the forest floor were 75.1% from throughfall and 19% from stemflow for a total of 1097 mm year-1, or 91% of annual rainfall. Runoff was estimated at 896 mm year-1, or nearly 77% of the combined input of throughfall and stemflow. Loss from evapotranspiration was linear with saturation deficit of the atmosphere and was 967 mm year-1 (0.7–4.5 mm day-1). Loss from horizontal flow of groundwater in shallow mangrove soils was ~285 mm year-1. Frequency of tidal inundation was seasonal, ranging from <5 tides month-1 in February to 30 tides month-1 in September. Tides recharged soil saturation deficits, the cumulative tidal input being 12 276 mm year-1 and efflux being 11767 mm year-1. The relative significance of tides and rainfall deficits (rainfall – evapotranspiration) on the seasonal patterns of soil saturation (water levels) and soil salinity were simulated with a finite-difference hydrology model (HYMAN). Model simulations demonstrate that soil salinity at higher elevations in the intertidal zone, where tidal inundation frequency is reduced, is more sensitive to changes in rainfall deficit.