Abstract Large freshwater pulses to coastal ecosystems change local hydrologic regimes and alter biogeochemical processes. The Mississippi Bight coastal ecosystem, located in the northern Gulf of Mexico shelf, is influenced by extensive freshwater inputs: the Mississippi River (MSR) and several smaller rivers to the east. Under river flood conditions, MSR waters flow through the Bonnet Carre Spillway (BCS) to relieve pressure on levees in New Orleans, Louisiana. In 2015, mild wintertime temperatures and heavy rainfall throughout the MSR watershed led to extreme flooding and prompted an unusually early BCS opening on January 10, 2016 for 23 days. This study examines the effects of such intermittent freshwater diversions on local shelf circulation, planktonic distributions, and potential contaminant transport pathways. Physical, chemical, and remote sensing data collected one month after the BCS opening suggested the region was comprised of three water masses: shelf saltwater, MSR waters, and local river waters. Observations and circulation model results showed the BCS waters remained within the estuarine lakes and sounds, where winter wind patterns mixed the waters and prevented BCS waters from flowing onto the shelf. Freshwater within the Mississippi Bight was primarily from concurrent flooding of local rivers. Two distinct clusters of microplankton (offshore versus nearshore stations) and zooplankton (Chandeleur Sound versus other stations) community compositions were detected. No algal blooms were observed during this BCS opening. The 2016 wintertime BCS opening resulted in muted effects on the sounds and shelf because of its short duration and uncharacteristically early release.

中文翻译：

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密西西比湾的 Bonnet Carré 溢洪道淡水运输和相应的生化特性

摘要 沿海生态系统的大量淡水脉冲改变了当地的水文状况并改变了生物地球化学过程。位于墨西哥湾北部陆架的密西西比湾沿海生态系统受到大量淡水输入的影响：密西西比河 (MSR) 和东部的几条较小的河流。在河流洪水条件下，MSR 的水流过 Bonnet Carre 溢洪道 (BCS)，以减轻路易斯安那州新奥尔良的堤坝压力。2015 年，整个 MSR 流域温和的冬季气温和强降雨导致极端洪水，并促使 BCS 于 2016 年 1 月 10 日异常提前开放 23 天。本研究考察了这种间歇性淡水改道对当地陆架循环、浮游生物分布和潜在污染物运输途径的影响。物理、化学、BCS 开放一个月后收集的遥感数据表明该地区由三个水团组成：陆架咸水、MSR 水域和当地河流水域。观测和环流模型结果表明，BCS 水域仍留在河口湖泊和声音中，冬季风模式将水域混合并阻止 BCS 水域流入陆架。密西西比湾内的淡水主要来自当地河流的并发洪水。检测到两个不同的微型浮游生物群（离岸站与近岸站）和浮游动物（Chandeleur Sound 与其他站）群落组成。在此 BCS 开放期间没有观察到藻华。