Beneficial Use of Dredged Material to Enhance Salt Marsh Habitat in New Jersey : Monitoring and Project Assessment
Date
2023-01
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Trenton, N.J. : Department of Environmental Protection and Energy, Division of Science and Research
Abstract
This report summarizes monitoring conducted at three pilot beneficial use of dredged material to enhance salt marsh projects in New Jersey. Constructed between August 2014 and April 2017, these projects tested sediment addition techniques that included thin-layer placement (TLP) of dredged material on the platform of vegetated, stressed marshes (Ring Island, Avalon, and Fortescue) and the filling of degraded and expanding pool-panne complexes with dredged material on the surrounding stressed marsh platform (Avalon). The objectives for the three marsh pilot projects were (1) to increase and maintain the optimal tidal elevation (hydroperiod) for native salt marsh species, (2) to increase the cover and health of native salt marsh vegetation, and (3) to return all other metrics to baseline (i.e., pre-implementation) conditions (unless they were expected to change due to habitat conversion). Topographic surveys indicated that 1) on average sites reached target elevations, but the placement was uneven, 2) all sites initially gained elevation, but it was challenging to measure small elevation changes, 3) the higher the final elevation, the slower vegetation grew back, and 4) sites gained resilience against 10- to 27-years’ worth of sea-level rise. As of 2021, none of the salt marsh sites had increased plant cover from baseline conditions or established the targeted Spartina patens habitat. However, several sites matched control site conditions, and much was learned about how to increase the rate of plant recovery. Soil makeup, benthic infauna communities, and epifaunal macroinvertebrates did not return to baseline conditions by 2021, but water chemistry returned to control conditions. Nekton and avian use were variable and results were dependent on changes to vegetation and elevation. These findings suggest that both thin- and thick-layers of sediment addition to existing tidal marshes led to large initial changes in the habitat, from which the ecosystems rebounded/are rebounding at different rates.
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Keywords
New Jersey, Salt marshes - New Jersey, Dredging spoil - Environmental aspects