Abstract
Sedimentation rates in constructed wetlands in northeastern Illinois, USA, ranged from 5.9 to 12.8 kg m
−2 y
−1 in 1989–1990, higher than expected based on concentrations of suspended sediment in influent waters of the wetlands. This predicted an accumulation of 0.5 to 1.0 cm/y. Rates were significantly lower in 1991 growing season, ranging from 1.2 to 4.2 kg m
−2 y
−1. Factors contributing to the high sedimentation included internal autochthonous production of organic matter and resuspension. Low- and high-flow hydrologic conditions had little effect on sedimentation from 1989–1990 but sedimentation was higher in the high-flow wetlands in the 1991 growing season. Deposition was a function of hydrologic loading near the water inflows; no differences were evident further downstream in the basins. Deposition rates and organic and phoshporus concentrations of the sediments increased through the growing season in conjunction with higher sediment concentrations in the inflow water. The patchy nature of vegetation density within the experimental wetlands created channelized flow, resulting in spatial variability in sediment deposition.