Patterns of mangrove forest structure and soil nutrient dynamics along theShark River estuary, Florida

The basal area and productivity of mangrove wetlands are described in relat ion to selected soil properties to understand the general pattern of optimu m forest stature at the mouth of estuaries in the Everglades, such as the S hark River Slough, Florida (U.S.). The basal area of mangroves decreases fr om 40.4 m(2) ha(-1) and 39.7 m(2) ha(-1) at two stations 1.8 km and 4.1 km from the estuary mouth to 20.7 m(2) ha(-1) and 19.6 m(2) ha(-1) at two site s 9.9 km and 18.2 km from the mouth, respectively The gradient,in basal are a at these four sites is mostly the result of approximately 34 yr of growth since Hurricane Donna. Wood productivity is higher in the lower estuary (1 0.7 Mg ha(-1) yr(-1) and 12.0 Mg ha(-1) yr(-1))than in the upper estuary (3 .2 Mg ha(-1) yr(-1) and 4.2 Mg ha(-1) yr(-1)). Porewater salinity among the se four mangrove sites during seasonal sampling in 1994 and 1995 ranged fro m 1.6 g kg(-1) to 33.5 g kg(-1), while sulfide was generally < 0.15 mM at a ll sites. These soil values indicate that abiotic stress cannot explain the decrease in forest structure along this estuarine gradient. Concentrations of nitrogen (N) and phosphorus (P) are more closely related to patterns of forest development, with higher soil fertility at the mouth of the estuary as indicated by higher concentrations of extractable ammonium, total soil P, and available P, along with higher ammonium production rates. The more f ertile sites of the lower estuary are dominated by Laguncularia racemosa, w hereas the less fertile sites in the intermediate and upper estuary are dom inated by Rhizophora mangle. Relative N mineralization per unit of total N is higher in the lower estuary and is related positively to concentrations of available P, indicating the importance of turnover rates and nutrient in teractions to soil fertility. Concentrations of Ca-bound P per volume soil in the fewer estuary is 40-fold higher than in the upper estuary, and along with an increase in residual P in the upper estuary, indicate a shift from mineral to organic P along the estuarine gradient. Mineral inputs to the m outh of Shark River estuary from the Gulf of Mexico (rather than upland inp uts) apparently control the patterns of mangrove structure and productivity .