The impact of recently excavated dredge pits on coastal hypoxia in the northern Gulf of Mexico shelf.

Laura Thompson, Kanchan Maiti, John R White, Christopher M DuFore, Haoran Liu

Marine environmental research 2021 Jan

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Large volumes of sand are needed in order to combat coastal land loss due to global sea-level rise for restoration of barrier island systems and beaches undergoing rapid erosion and submergence. The sediment required for such projects often originates from dredging of sand deposits on the adjacent shelf. Two dredge pits, with contrasting geology and located at varying distances from the Mississippi River Delta in the northern Gulf of Mexico shelf were sampled during spring and summer. Samples were also collected concurrently from surrounding continental shelf stations that are subject to seasonal hypoxia every summer. The bottom water dissolved O2 inside the dredge pits were found to be consistently hypoxic or near hypoxic throughout both seasons, with high sediment O2 consumption (SOC) rates of 23.7 to 51.8 mmol m-2 d-1 in spring and 34.3 to 51.3 mmol m-2 d-1 in summer. In contrast, control stations immediately outside the dredge pits showed lower SOC rates ranging between 6.3 and 35.9 mmol m-2 d-1. The SOC rates of the surrounding continental shelf subjected to annual seasonal hypoxia ranged between 25.7 and 59.6 mmol m-2 d-1 indicating that the dredge pits experienced similar high rates of SOC. Our results suggest that sluggish water circulation inside these topographic depressions coupled with higher SOC rates does result in persistent low bottom O2 conditions inside these dredge pits well beyond the duration of the seasonal hypoxia period in this region. This is the first study to provide insight on the impacts of dredge pits to surrounding hypoxia in this region which is critical as future dredging operations are expected to increase worldwide with projected sea-level rise. Copyright © 2020 Elsevier Ltd. All rights reserved.

Citation

Laura Thompson, Kanchan Maiti, John R White, Christopher M DuFore, Haoran Liu. The impact of recently excavated dredge pits on coastal hypoxia in the northern Gulf of Mexico shelf. Marine environmental research. 2021 Jan;163:105199