Patterns of nutrient exchange in a riverine mangrove forest in the Shark River Estuary, Florida, USA

Abstract

This study aimed to evaluate tidal and seasonal variations in concentrations and fluxes of nitrogen (NH4 +, NO2+NO3, total nitrogen) and phosphorus (soluble reactive phosphorus, total phosphorus) in a riverine mangrove forest using the flume technique during the dry (May, December 2003) and rainy (October 2003) seasons in the Shark River Estuary, Florida. Tidal water temperatures during the sampling period were on average 29.4 (± 0.4) oC in May and October declining to 20 o C (± 4) in December. Salinity values remained constant in May (28 ± 0.12 PSU), whereas salinity in October and December ranged from 6?21 PSU and 9?25 PSU, respectively. Nitrate + nitrite (N+N) and NH4 + concentrations ranged from 0.0 to 3.5 µM and from 0 to 4.8 µM throughout the study period, respectively. Mean TN concentrations in October and December were 39 (±0.8) µM and 37 (±1.5) µM, respectively. SRP and N+N concentrations in the flume increased with higher frequency in flooding tides. TP concentrations ranged between 0.2?2.9 µM with higher concentrations in the dry season than in the rainy season. Mean concentrations were <1. 5 µM during the sampling period in October (0.75 ± 0.02) and December (0.76 ± 0.01), and were relatively constant in both upstream and downstream locations of the flume. Water residence time in the flume (25 m2 ) was relatively short for any nutrient exchange to occur between the water column and the forest floor. However, the distinct seasonality in nutrient concentrations in the flume and adjacent tidal creek indicate that the Gulf of Mexico is the main source of SRP and N+N into the mangrove forest.