Abstract
<p>Benthic functioning was monitored in the East River (ER), in the Ten-Thousand Islands region of southwestern Florida, from June 1981 to October 1982. The purpose of the study was to determine the effects of seasonal salinity transitions on benthic functioning in mangrove estuaries, which seasonally change from oligohaline or freshwater conditions to marine or hypersaline conditions. Sediment oxygen demand (SOD) and nutrient fluxes were measured using a linear, constant-flow respirometer system. SOD (sampling period mean (SPM)) ranged from 21.5 to 120 (time-weighted mean = 71.3) ml m('-2) hr('-1). SOD (SPM) was not correlated with DO (0.36-4.32 ml l('-1)) (SPM). SOD (SPM) was not correlated with salinity (SPM) but was correlated with salinity change (relative to previous SPM). SOD and nutrient fluxes fell precipitously after acute salinity declines in September 1981 and July 1982.Benthic NH(,4)('+) flux (SPM) ranged from 1.2 to 432 (mean = 174) umol m('-2) hr('-1). PO(,4)('3-) flux ranged from 0.62 to 65.7 (mean = 22.8) umol m('-2) hr('-1). The N:P flux ratio was about 8:1 (atoms), based on regression of individual measurements. Pore water concentrations of NH(,4)('+) (<270 uM) and PO(,4)('3-) (<28 uM) were low, and fluxes calculated from pore water gradients were only 5-6% and <1%, respectively, of the mean measured fluxes. These results and those from periodic measurements of other parameters, including sediment pH, sediment E(,h), pore water and sediment sulfide, pore water salinity, and fractionated SOD, were consistent with a conclusion that ER benthic metabolism and nutrient remineralization is quantitatively dominated by processes occurring in shallow (<2 cm) and superficial (<0.5 cm) sediments.The O:N:P flux ratio (based on time-weighted SPM SOD and grand mean SPM NH(,4)('+) and PO(,4)('3-) fluxes) was about 212:5.8:0.8 (atoms) and probably reflected the stoichiometry of mangrove detritus (C:N around 106:0.7 to 106:7.6), which is the primary form of ER organic input. The high ER SOD and nutrient fluxes indicate that subtidal benthic communities metabolize a large portion of the organic material tansported from intertidal mangroves and remineralize a large fraction of the nutrients required to sustain mangrove productivity.</p>