No abstract

Summary Tested was the hypothesis that juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) would exhibit no response in short‐term survival or swimming performance when exposed to varying concentrations of suspended sediment simulating dredge plumes in waterways where this species may be impacted by dredging operations. Sediment collected from Savannah Harbor, South Carolina, USA was used to simulate a worst‐case scenario. Juvenile sturgeon were contained for a 3‐day period in flow‐through aquaria, with limited opportunity for movement, in sediment of varying concentrations (100, 250 and 500 mg L−1 total suspended solids [TSS]) mimicking prolonged exposure to suspended sediment plumes near an operating dredge. Of the 90 fish exposed, 86 (96%) survived the test. Of the four fish that died, one was exposed to 250 TSS and three to 500 TSS. Swimming performance results indicated that nearly all fish were positively rheotactic. Critical swim speeds (Ucrits) were moderate, whether measured as absolute values (21–31 cm s−1) or as relative values (1.4–2.1 body lengths s−1), with no significant differences among treatments (F < 0.83, P ≥ 0.4874). Behavior was dominated by contact‐based locomotion and station‐holding. Absence of substantial or significant immediate effects on survival and swimming performance suggest that impacts of sediment plumes in nature, where fish have freedom of movement and the power to escape rapidly, are minimal.

Given the reported extent of microplastics in the aquatic environment, environmentally relevant exposure information for sediments dredged by the US Army Corps of Engineers will lend context to the risks posed by this contaminant during dredging. We measured the occurrence, abundance, and polymer composition of microplastics in sediments collected from nine dredged waterways and two non-dredged reference areas. The number of particles in sediment samples ranged from 162 to 6110 particles/kg dry wt., with a mean of 1636 particles/kg dry wt. Fragments were the most prevalent shape observed among the 11 study sites (100% frequency of occurrence), followed by fibers (81%), spheres (75%), foams (38%) and films (34%). Based on analyses of chemical composition of the particles using Fourier transform infrared spectroscopy, polyethylene:propylene was the most common polymer type observed. Consistent with results presented by other investigators, microplastic concentrations and polymer types in bottom sediments in this study were also aligned with the most widely used plastics worldwide.

Coastal Louisiana (USA) continues to sustain immense land and habitat losses due to subsidence, sea‐level rise, and storm events. Approximately 65 million m3 (85 million cubic yards) of sediment is dredged annually from Gulf Coast federal navigation channels to maintain safe waterway passage. The beneficial use of these sediments continues to increase, and now this sediment is recognized as a critical resource in large‐scale (estimated multibillion dollar) ecosystem restoration efforts to mitigate land and habitat losses along the US Gulf Coast. However, the documentation of restoration benefits where dredged sediments are the primary resource is lacking, which limits the potential for future applications. Therefore, this study documents the progress to restore marsh habitat and the resultant benefits in West Bay, Louisiana, and investigates how the restoration practices align with principles of the US Army Corps of Engineers (USACE) Engineering with Nature® (EWN®) and UN Sustainable Development Goals (UN SDGs). West Bay, a 4964‐ha subdelta adjacent to the Mississippi River, typifies risks of coastal land loss that also threatens the integrity of the adjacent federal navigation channel. To help restore coastal marsh habitat on a large spatial and temporal scale, the USACE constructed an uncontrolled diversionary channel from the Mississippi River and with subsequent direct and strategic placement of dredged sediment. Restoration performance was assessed through remotely sensed methods using data spanning approximately 70 years. To date, placement of dredged sediment in the bay has facilitated the creation of over 800 ha of new land in the formerly open waters of West Bay. The West Bay restoration project aligns with the principles of the EWN initiative, which supports more sustainable practices to deliver economic, environmental, and social benefits through collaborative processes and meaningfully integrates 10 of the UN SDGs designed to achieve a better and more sustainable future. Integr Environ Assess Manag 2022;18:1162–1173. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.