TITLE:
Effect of Sand Capping on Phosphorus Release from Phosphorus-Enriched Coastal Wetland Sediments: A Laboratory Study
AUTHORS:
Alan D. Steinman, Katie Tyrrell, Michael C. Hassett
KEYWORDS:
Sand Capping, Coastal Wetlands, Restoration, Water Quality, Phosphorus
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.17 No.8,
August
22,
2025
ABSTRACT: Restoration of coastal wetland habitat in the Laurentian Great Lakes often includes addressing excess soil nutrient levels because of prior land use. A wetland restoration project is underway in former celery fields located at the mouth of Mona Lake (MI), a drowned rivermouth system that drains directly into Lake Michigan. One approach proposed to address high phosphorus (P) levels in the sediment is sand capping. This study examined the effectiveness of two sand sources (within-pond and quarry) and two sand cap thicknesses (15 and 30 cm) in inhibiting P release from the native sediment using sediment cores incubated in the laboratory. Our results indicated that there was not a strong difference in sand type or capping depth on P release. Both sand sources resulted in an approximate total phosphorus (TP) reduction of 60% - 70% over time, although this still left TP concentrations well above desirable levels. The quarry sand did better than pond sand in reducing TP, whereas pond sand did better with respect to soluble reactive phosphorus (SRP). Given the relatively small differences in P reduction performance, pond sand is recommended because it is already present on site and therefore is less expensive and easier to move. In addition, pond sand had higher amounts of apatite than quarry sand, suggesting more of the attached P will remain in a stable form. Sand capping is a relatively inexpensive approach for reducing P levels in coastal wetlands, although it may need to be paired with other approaches to reduce nutrient concentrations to desired levels.