Comparison of Detritus Dynamics in Two Tidal Freshwater Wetlands

Abstract

We have examined the generation and persistence of detritus in two contrasting tidal freshwater wetlands on the Hudson River. These wetlands offer a difference in vegetation, with Tivoli South Bay dominated by a floating—leafed macrophyte (water—chestnut, Trapa natans) and North Bay a typical Typha marsh. In South Bay, there was a large amount of water—chestnut dry biomass (400 g/m 2 ) available to enter the detritus pool, but there was no increase in the standing stock of benthic organic matter following senescence of water—chestnut. Our estimates show that mineralization plus leaching of dissolved material are sufficient to remove much of this detritus. In the Typha marsh, there is a large amount of detritus generated (°25% of annual primary production) and this material persists as a thick layer. Decomposition of this litter is very slow (0.3/yr). A portion of the litter may be exported because decomposition alone cannot account for the observed rate of disappearance from the marsh surface. Microbial abundance was used to estimate the amount of heterotrophic biomass supported by these different types of detritus. Bacterial growth on water—chestnut detritus is relatively slow (10 6 cells°mg — 1 °d — 1 ), resulting in a turnover of bacterial biomass in 10—36 d. Bacterial and fungal biomass associated with Typha were low, and could not account for the observed increase in nitrogen content.