| Although the influence of hydrology is manifest to some degree in nearly every component of wetland ecosystems, little work has been done to quantify the exact nature of this relationship. Four experimental, created wetlands receiving two levels of water inflow (15 or 35 cm wk{dollar}sp{lcub}-1{rcub}{dollar}) were studied at the Des Plaines River Wetlands Demonstration Project in northwestern Illinois. The effect that two different hydrologic regimes might have on the development of aquatic plant communities, rates and patterns of sediment deposition, and temporal changes in the availability and spatial distribution of soil nutrients was investigated. A divergence in primary productivity of the macrophyte communities of the four wetlands as a function of water inflow was not seen, and may take longer than a few growing seasons to appear. Tissue nutrient concentrations at the Des Plaines River site were low (averaging 2.1 mg g-1 P and 21 mg g-1 N), reflecting low concentrations of nutrients in the influent and in the soil. Temporal comparisons (examining Typha angustifolia, Phalaris arundinacea, and Alisma plantago-aqauatica) showed tissue nitrogen levels increased and phosphorus concentrations decreased during the first year of pumping. Sediment deposition was very high in the wetlands; rates were not significantly higher under high flow conditions in part because resuspension and autochthonous production was high in all wetlands. Sedimentation was negatively correlated with stem density and distance from the point of water inflow in each wetland. The patchy distribution of macrophytes resulted in channelized flow and thus heterogeneous sedimentation rates. The spatial distribution of nutrients in the wetland soils was determined both before flooding (1988) and 14 months after flooding (1990). Mean concentrations of extractable phosphorus decreased and organic carbon levels increased significantly in all four wetlands. The influence of the rate and direction of water flow is evident in the temporal changes seen in the spatial patterns of nutrients (including extractable P, exchangeable K, Ca and Mg, and percent organic carbon) over this time period. The mechanisms driving these changes appear to be both biological (e.g. primary production) and physical (redox changes due to flooding). |
