Net Aerial Primary Production and Dynamics of Soil Organic Matter Formation in a Tidal Marsh Ecosystem

Relationships between net aerial primary production (NAPP) and soil organic matter formation in a tidal marsh environment were analyzed using a dynamic model. Four basic parameters were considered in the model: NAPP, disappearance rate of dead standing crop, and rates of plant decomposition in soil and air. The model was tested in a sawgrass (Cladium jamaicense) tidal marsh of north Florida. Net aerial primary production was estimated to be 2643 g m−2y−1using a paired‐plot method. The mean annual disappearance rate of dead standing crop was estimated to be 1.965 g g−1y−1. The disappearance rate of sawgrass in soil was estimated to be 4.308 g g−1y−1for the labile portion and 0.105 g g−1y−1for the resistant portion. The sawgrass consists of 34% labile and 66% resistant portions. The soil organic matter due to NAPP was estimated to be 12.5 kg m−2. The actual soil organic matter under the marsh was found to be about 100 kg m−2. Most of the soil organic matter was preserved by constant submergence in water and, therefore, did not actively participate in the carbon cycle. Only about 20 kg m−2of the soil organic matter that had an average thickness of 30 cm was considered to be actively participating in the carbon cycle. The dynamic model predicted 30 y is needed for soil organic matter to be stabilized, and < 2 years is needed for dead standing crop to be stabilized under the environment. Ninety‐eight percent of the soil organic matter was from the resistant pool of sawgrass. The mean fraction remaining (MFR) of the soil organic matter was 0.36. Two carbon cycles were defined in the marsh soil: the short one (mean retention time = 0.73 y) is probably important to the food and energy supply of the ecosystem; the long one (mean retention time = 10 y) comprises the major portion of the soil organic matter.