Effects of construction site sedimentation basins on receiving stream ecosystems

The effects of sedimentation basin discharges on receiving stream ecosystems were investigated for three construction sites in Lancaster County, Pennsylvania. Samples were collected in the receiving stream at two locations upstream and downstream from the basin outlet pipe and directly from the outlet pipe while the basin was discharging following rainfall events. Suspended sediment concentration, particle size distribution, benthic macroinvertebrates, and temperature were evaluated at each location. Stream temperature increased slightly (+0.3°C) on the discharge side of the streams immediately below the sedimentation basins, but the elevated temperatures did not extend farther downstream. Stream sediment concentrations increased significantly (p < 0.05), and the high concentrations persisted to the downstream sampling site located 100 m below the basin discharge. During storm events, the basin effluent contributed a larger proportion of finer suspended sediments, as measured by particle size distribution, than the stream, and the smaller particle sizes persisted downstream. There was no significant change in number of macroinvertebrate individuals as a result of the sedimentation basin discharge, but there was a significant decrease in the number of taxa observed in the receiving stream directly below the basin outlet. However, this observed reduction in species richness was not significant 100 meters downstream from the basin discharge pipe.