Assessing effectiveness of pond sediment removal for phosphorus management in stormwater ponds

Project summary:

Sediment removal by dredging is a pond maintenance measure typically performed to increase pond volume and restore stormwater detention capacity. Removal of accumulated sediments--which tend to be highly organic and phosphorus-rich--and exposure of buried sediments will affect the phosphorus sediment-water interactions, i.e., flux from sediments to the overlying water. However, it is not clear if and how much the sediment phosphorus release (internal phosphorus loading) will decrease or be impacted by sediment removal in ponds treating stormwater. The objectives of this project are to determine the impacts that sediment dredging will have on the release of sediment phosphorus and on the water quality in six ponds treating stormwater. The ponds will have variable attributes relevant to phosphorus input and related processes, such as watershed characteristics, tree cover, impervious area/pond area ratio, pond age, etc. Indications from past pond sediment cores taken by St. Anthony Falls Laboratory are that sediment release of phosphorus will decrease after dredging, although the extent of this reduction is unknown, and resuspension of sediment may complicate the answer to that question. This project is designed to answer, in definitive terms, the following research questions:

1. Is sediment removal an effective pond maintenance measure to reduce the release of sediment-bound phosphorus, and thus improve water quality in stormwater ponds and reduce phosphorus exported to receiving water bodies from stormwater ponds?

2. Should sediment treatment be considered to further reduce sediment release of phosphorus in stormwater ponds at the time of dredging?