Department of Oceanography and Coastal Sciences, Louisiana State University, Energy Coast & Environment Building, Baton Rouge, LA, 70803, USA.
Department of Oceanography and Coastal Sciences, Louisiana State University, Energy Coast & Environment Building, Baton Rouge, LA, 70803, USA.
Mar Environ Res. 2021 Jan;163:105199. doi: 10.1016/j.marenvres.2020.105199. Epub 2020 Nov 6.
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 O inside the dredge pits were found to be consistently hypoxic or near hypoxic throughout both seasons, with high sediment O consumption (SOC) rates of 23.7 to 51.8 mmol m d in spring and 34.3 to 51.3 mmol m d in summer. In contrast, control stations immediately outside the dredge pits showed lower SOC rates ranging between 6.3 and 35.9 mmol m d. The SOC rates of the surrounding continental shelf subjected to annual seasonal hypoxia ranged between 25.7 and 59.6 mmol m d 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 O 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.
为了应对全球海平面上升导致的海岸土地损失，需要大量的沙子来恢复屏障岛系统和遭受快速侵蚀和淹没的海滩。此类项目所需的沉积物通常来自毗邻大陆架上的砂矿床的疏浚。在墨西哥湾北部大陆架上，两个地质条件截然不同的疏浚坑，位于密西西比河三角洲不同的距离处，在春季和夏季进行了采样。同时还从周围的大陆架站采集了样本，这些站每年夏季都会经历季节性缺氧。结果发现，疏浚坑内的底层水溶解氧一直处于缺氧或接近缺氧状态，春季沉积物耗氧率（SOC）高达 23.7 至 51.8 mmol m d，夏季高达 34.3 至 51.3 mmol m d。相比之下，疏浚坑外的对照站 SOC 速率较低，范围在 6.3 至 35.9 mmol m d 之间。每年都会经历季节性缺氧的周围大陆架的 SOC 速率在 25.7 至 59.6 mmol m d 之间，表明疏浚坑经历了类似的高 SOC 速率。我们的研究结果表明，这些地形洼地内部水流缓慢，加上 SOC 速率较高，导致这些疏浚坑内的底层氧气条件持续较低，远远超过该地区季节性缺氧期的持续时间。这是首次研究疏浚坑对该地区周围缺氧的影响，随着预计的海平面上升，未来全球的疏浚作业预计将会增加，这一研究至关重要。
