Restoring a degraded marsh using thin layer sediment placement: Short term effects on soil physical and biogeochemical properties

Abstract

Recent interest has focused on wetland restoration techniques that introduce a thin layer of sediment onto degrading marsh surfaces. A restoration project in Avalon, New Jersey, received 5–19 cm of dredged sediment onto vegetated marsh areas and 32–82 cm of sediment into degraded open water panne features interspersed within the degraded marsh plain. There were significant differences in soil physical properties between the placed dredged sediments and the buried native marsh and panne soils. For example, six months after project implementation, application of dredged sediment increased surface panne bulk density from 0.22 ± 0.02 g cm−3 to 0.83 ± 0.09 g cm−3, surpassing the threshold required for Spartina alterniflora Loisel. establishment. Soil nutrient and microbial properties also differed between placed sediments and buried marsh/panne soils. Notably, buried marsh soils remained microbially active demonstrating the capacity for buried soils to provide labile nutrient sources, such as ammonium, during vegetation recruitment. Results suggest that thin layer sediment placement techniques may jump-start marsh recovery by maintaining native vegetation seed sources, rhizomes, and microbes in near-surface soils compared to other restoration approaches. Examining short term changes in soil microbial activity may provide early indicators of restoration outcome, although, additional research is required to more accurately predict changes in soil properties over time.