Print PageTidal freshwater wetlands have a demonstrated capability to alter water quality by adding/removing solutes and particles to tidal waters that exchange with these wetlands. Understanding the direct and indirect links between macrophytes and ecological processes has implications for both current management and restoration practices. These often target certain plant communities as desirable without an appreciation for which ecological functions may be associated with these communities. Additionally, plans for future climate change generally concentrate on maintaining the areal extent of wetlands without necessarily considering how an altered physicochemical regime might affect wetland function. Since tidal freshwater wetlands tend to occur on large rivers that are also susceptible to human disturbance and probably subject to high pressure from invasive species.
Results/Conclusions
In the tidal freshwater portion of the Hudson River there are approximately 200 wetlands and sampling over flood and ebb tide cycles shows significant changes in organic carbon, nutrients and dissolved oxygen. We see consistent net export of dissolved organic carbon and removal of nitrate from these wetlands. There is however considerable variability among these wetlands in the degree of alteration in various constituents and we are examining whether vegetation attributes can account for differences in performance among wetlands. At the largest scale we look for associations between simply the proportional cover by different classes of vegetation and the degree of change in water quality between flood and ebb tide water. For some solutes we find statistically significant relationships between plant cover and change in solute concentration yet these have only modest predictive reliability (r2 ~ 50% or lower). At a finer scale we anticipate that there may be spatial contingencies for wetland effects on some of the solutes, dissolved gases in particular, such that the actual location of vegetation patches becomes an important predictor variable. We can further separate direct effects of vegetation such as assimilation of nitrogen for macrophyte growth from indirect effects such as supply of carbon that drives demand for nitrogen by heterotrophic microbes. The broad classes of macrophytes present in these wetlands (grasses, reeds, broad-leafed, submerged) have very different growth rates, peak standing crops and rates of decomposition so the direct incorporation and release of nutrients or carbon varies dramatically across vegetation type. Intentional or other types of change in macrophyte relative abundance will lead to alterations in wetland function.
