Evaluating soil properties and potential nitrate removal in wetlands created using an Engineering With Nature based dredged material placement technique

Abstract

Many waterways around the globe, including those in southern Louisiana, require periodic dredging to maintain navigability in channels, rivers, and at ports. Traditionally, dredged materials are deposited in confined disposal facilities, relegated to deep open water disposal, or used as fill material to build wetlands. Over the past 15+ years, dredge material from the Atchafalaya River was strategically placed up-river of a small, natural shoal, located mid-channel, resulting in the creation of a wetland exhibiting many structural characteristics of the naturally occurring riverine wetlands within the basin. This construction practice adheres to Engineering With Nature (EWN) concepts which utilize natural processes to produce maximum benefit for navigation, while lowering economic costs and improving habitat features. The current study determined soil physical, nutrient, and biogeochemical properties at the EWN wetland and compares these characteristics to values observed at a traditional dredge shoreline material placement wetland (TDMP), essentially examining the effect of construction technique on soil biogeochemical properties. Soil total carbon and nitrogen at EWN continued to accumulate with time; however, TDMP exhibited a significantly higher degree of soil formation as indicated by lower bulk density, and higher soil organic matter, carbon, and nitrogen. Despite the observed differences, rates of potential nitrate removal and microbial biomass nitrogen did not differ between wetlands, suggesting that the nature based construction technique resulted in nutrient cycling and nitrate removal capacities equivalent to traditionally constructed dredged material wetlands in the region.