Date of Award
Global reductions in biodiversity and water quality are having major consequences for ecosystem health and societal well-being. The restoration of riverine floodplains and wetlands provides an ideal opportunity to increase biodiversity and water quality because their hydrologic connectivity to adjacent streams and rivers promotes the formation of heterogeneous habitat while also facilitating their functioning as a nutrient sink, in general. However, many historic floodplains and riverine wetlands have been drained for the creation of agricultural land, resulting in an accumulation of nutrients in the soils. Therefore, restoration practices that hydrologically reconnect former agricultural land to an adjacent stream or river can stimulate the release of nutrients into downstream waters, at least in the short-term, which can result in the restoration of wildlife habitat at the expense of downstream water quality.
To avoid the high risk of a wetland habitat restoration project in the Muskegon Lake Area of Concern resulting in phosphorus (P) release to downstream waters, the former agricultural land was dredged prior to hydrologic reconnection. I evaluated restoration success by measuring sediment P release in the wetland after dredging and comparing those results to studies that measured P release before dredging. My results showed that maximum P release rates were reduced by 95-99 % after dredging, regardless of temperature or dissolved oxygen treatment. In turn, this avoided between ~25-250 kg of total phosphorus (TP) from entering a eutrophic lake downstream per year (depending on transport scenarios). While internal P loading was drastically reduced, P adsorption isotherm experiments suggested that the deep dredging depth (~1 m on average) exposed sediments with significantly reduced binding capacities, resulting in the wetland acting as a phosphate sink only when water column soluble reactive phosphorus concentrations exceed 40 μg L-1. This study showed that the ability of sediment dredging to reduce sediment P release largely depends on the underlying sediment characteristics. If prerestoration monitoring indicates that deeper sediments have low TP and labile P concentrations, sediment dredging can be a useful technique for balancing the goals of both habitat restoration and water quality improvements in wetlands restored on former agricultural lands.
Oldenborg, Kimberly, "Impacts of Sediment Dredging on Phosphorus Dynamics in a Restored Riparian Wetland" (2018). Masters Theses. 887.