| Abstrakt: |
Barataria (LA, USA) is an interdistributary deltaic basin that has experienced extensive marsh loss. The fate of these marshes is strongly controlled by the concentration of total suspended sediments (TSS) in the adjacent open bay water. This parameter, however, is poorly constrained, thus limiting the ability to predict the future marsh evolution. Here we investigate the open bay water sediment dynamics using three complementary approaches: monthly field surveys at 37 locations along the bay axis over 22 years, remote sensing over 20 years, and turbidity time series at 5 locations over 4 years. Monthly field sampling and remote sensing reveal that the TSS is highly seasonal and spatially variable. In particular, the sediment delivered through the Gulf Intracoastal Waterway (GIWW) during the flood season (January–April) dominates the TSS signal in mid-Barataria. This sediment originates mainly from the Atchafalaya River and is advected for more than 100 km before reaching Barataria. Because of a hysteresis in sediment transport, the TSS in the river water, and hence in the GIWW, is not uniquely related to the river discharge. As such, late flood season discharges do not contribute much sediment to Barataria. We estimate that the GIWW delivers on average 0.21 Tg of sediment per year to mid-Barataria. A different sediment input is instead present in lower Barataria, where river-borne sediment exiting the "birdfoot" of the Mississippi Delta is advected by easterly winds, especially during spring. At all five stations within Barataria, turbidity time series reveal that the daily sediment dynamics is mainly associated with local wind wave resuspension. River inputs and wave resuspension contribute nearly equally to the yearly averaged TSS, of about 80 mg/l on average. The GIWW, built in the 1920s, is an important but overlooked source of sediments for Barataria that can serve as a present-day analogue for the proposed Mississippi River sediment diversions. [ABSTRACT FROM AUTHOR] |
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