Effects of Microtopography on Hydrology, Physicochemistry, and Vegetation in a Tidal Swamp of the Hudson River

Hudson River freshwater tidal swamps have dynamic flooding and oxygenation regimes due to daily tidal flushing. Microtopography, small scale differences in elevation, adds even more complexity to inundation patterns and may have important implications for nutrient flow and wetland plant communities. The objective of this study was to determine if differences in inundation between microtopographic features were sufficient to alter physical, chemical, and biological attributes. Microtopography significantly affected flooding duration and redox conditions. Hummocks had lower concentrations of soluble phosphate in their porewater probably due to differing depths of iron oxidation. Hummocks also had lower porewater ammonium concentrations which could be explained by higher plant uptake of nitrogen on hummocks or less ammonium being nitrified and subsequently denitrified in hollows due to lack of oxygen. Decomposition rates were slower in hollows perhaps due to lack of oxygen due to flooding or differing decomposer communities. Fewer herbaceous plant species were found in hollows compared to hummocks perhaps because of hollow's anoxic soils. Microtopography affects freshwater tidal swamp ecosystem function by affecting oxygen penetration, nutrient availability, rates of decomposition, and herbaceous plant species distributions.