Decomposition of Coarse Woody Debris and Microbial Biomass in Tidal Freshwater Forested Wetlands along a River to Estuary Gradient on the Apalachicola River in Florida

Abstract

Decomposition dynamics of mass, carbon (C), nitrogen (N), and phosphorous (P) as well as downed woody debris biomass and microbial biomass were assayed along a river to estuary gradient in wetlands alongside the Apalachicola River in Florida. Decay rates (unitless) ranged from 0.007 to 0.030 for coarse woody debris (CWD) and 0.006 to 0.009 for control wood among plots and was significantly different among plots (P<0.05). Differences in decay rates are likely due to hydrological factors. All other parameters measured, such as distance to coast, soil salinity, soil nutrients, and microbial biomass C and N either were not significantly related to decay rates (P<0.05) or had very low R2 values (<0.02). Although C decomposition followed closely with mass loss, N and P did not follow such easily distinguishable trends. Nitrogen and P mineralization/-immobilization patterns varied greatly among plots and collection periods. Average downed woody debris biomass ranged from 1.54 Mg/ha to 5.84 Mg/ha among plots. Downed woody debris biomass in the size class >7.62 cm was significantly related to the parameter, distance to coast, because the three plots farthest from the coast had the highest amounts of downed woody debris biomass. The smaller size class of <7.62cm was statistically related to the parameters of soil C, soil N, and soil P concentrations (P<0.05) and showed no real pattern among plots. Microbial biomass C ranged from 0.37 to 0.79 g C/ kg while microbial biomass N ranged from 13.92 to 73.74 mg N/kg among plots. Both microbial biomass C and N were significantly different among plots, although there was no clear pattern in terms of distance to coast. Microbial C and N increased consistently from May - August.