A simulation model of organic matter and nutrient accumulation in mangrovewetland soils

The distribution and accumulation of organic matter, nitrogen (N) and phosp horus (P) in mangrove soils at four sites along the Shark River estuary of south Florida were investigated with empirical measures and a process-based model. The mangrove nutrient model (NUMAN) was developed from the SEMIDEC marsh organic matter model and parameterized with data from mangrove wetlan ds. The soil characteristics in the four mangrove sites varied greatly in b oth concentrations and profiles of soil carbon, N and P. Organic matter dec reased from 82% in the upstream locations to 30% in the marine sites. Compa risons of simulated and observed results demonstrated that landscape gradie nts of soil characteristics along the estuary can be adequately modeled by accounting for plant production, liner decomposition and export, and alloch thonous input of mineral sediments. Model sensitivity analyses suggest that root production has a more significant effect on soil composition than lit ter fall. Model simulations showed that the greatest change in organic matt er, N, and P occurred from the soil surface to 5 cm depth. The rapid decomp osition of labile organic matter was responsible for this decrease in organ ic matter. Simulated N mineralization rates decreased quickly with depth, w hich corresponded with the decrease of labile organic matter. The increase in organic matter content and decrease in soil bulk density from mangrove s ites at downstream locations compared to those at upstream locations was co ntrolled mainly by variation in allochthonous inputs of mineral matter at t he mouth of the estuary, along with gradients in mangrove root production. Research on allochthonouns sediment input and in situ root production of ma ngroves is limited compared to their significance to understanding nutrient biogeochemistry of these wetlands. More accurate simulations of temporal p atterns of nutrient characteristics with depth will depend on including the effects of disturbance such as hurricanes on sediment redistribution and b iomass production.