California Department of Water Resources, Sacramento, California, United States of America.
Delta Science Program, Sacramento, California, United States of America.
PLoS One. 2020 Oct 1;15(10):e0234673. doi: 10.1371/journal.pone.0234673. eCollection 2020.
While flow is known to be a major driver of estuarine ecosystems, targeted flow manipulations are rare because tidal systems are extremely variable in space and time, and because the necessary infrastructure is rarely available. In summer 2018 we used a unique water control structure in the San Francisco Estuary (SFE) to direct a managed flow pulse into Suisun Marsh, one of the largest contiguous tidal marshes on the west coast of the United States. The action was designed to increase habitat suitability for the endangered Delta Smelt Hypomesus transpacificus, a small osmerid fish endemic to the upper SFE. The approach was to operate the Suisun Marsh Salinity Control Gates (SMSCG) in conjunction with increased Sacramento River tributary inflow to direct an estimated 160 x 106 m3 pulse of low salinity water into Suisun Marsh during August, a critical time period for juvenile Delta Smelt rearing. Three-dimensional modeling showed that directing additional low salinity water into Suisun Marsh ("Flow Action") substantially increased the area of low salinity habitat for Delta Smelt that persisted beyond the period of SMSCG operations. Field monitoring showed that turbidity and chlorophyll were at higher levels in Suisun Marsh, representing better habitat conditions, than the upstream Sacramento River region throughout the study period. The Flow Action had no substantial effects on zooplankton abundance, nor did Suisun Marsh show enhanced levels of these prey species in comparison to the Sacramento River. Fish monitoring data suggested that small numbers of Delta Smelt colonized Suisun Marsh from the Sacramento River during the 2018 Flow Action. Comparison of the salinity effects of the Flow Action to historical catch data for Suisun Marsh further supported our hypothesis that the Flow Action would have some benefit for this rare species. Our study provides insight into both the potential use of targeted flow manipulations to support endangered fishes such as Delta Smelt, and into the general response of estuarine habitat to flow management.
虽然水流已知是河口生态系统的主要驱动力，但由于潮汐系统在空间和时间上极具变异性，而且很少有必要的基础设施，因此针对水流的人为干预措施非常少见。2018 年夏，我们利用旧金山湾（SFE）独特的水控结构，将人为管理的水流脉冲引入苏西恩沼泽，这是美国西海岸最大的连续潮间沼泽之一。此举旨在增加濒危的三角洲西鲱（Hypomesus transpacificus）的栖息地适宜性，这种小鱼是 SFE 上游的特有物种。具体做法是，与萨克拉门托河支流的增加流入量相结合，共同操作苏西恩沼泽盐度控制门（SMSCG），以在 8 月向苏西恩沼泽输送估计 160×106m3 的低盐度水脉冲，这是幼鱼成长的关键时期。三维模型表明，将额外的低盐度水输送到苏西恩沼泽（“水流行动”）极大地增加了幼鱼的低盐水域面积，且这种效果持续到 SMSCG 操作结束之后。实地监测表明，在整个研究期间，苏西恩沼泽的浊度和叶绿素水平均高于上游的萨克拉门托河地区，表明其栖息地条件更好。“水流行动”对浮游动物的丰度没有显著影响，苏西恩沼泽也没有显示出比萨克拉门托河更高水平的这些猎物。鱼类监测数据表明，在 2018 年的水流行动期间，少量的三角洲西鲱从萨克拉门托河进入苏西恩沼泽。将水流行动的盐度效应与苏西恩沼泽的历史捕捞数据进行比较，进一步支持了我们的假设，即该行动将对这一珍稀物种产生一定的益处。我们的研究为有针对性的水流干预措施提供了支持濒危鱼类（如三角洲西鲱）的见解，同时也为河口栖息地对水流管理的一般反应提供了见解。
