RECOVER MAP 3.3.3.4 SAV Monitoring for Caloosahatchee Estuary 2004-2007 CP040627

The Caloosahatchee River and Estuary are located on the southwest coast of Florida (Figure 1). The Caloosahatchee River runs from Lake Okeechobee to the Franklin Lock and Dam (S-79) where it empties into the estuary which is some 40 kilometers long and terminates at Shell Point. The Calooshatchee River is the major source of freshwater to the estuary. Enough water enters the estuary at S-79 to fill its volume over 8 times per year. The hydrology of the Caloosahatchee system has been altered over time. The river has been permanently connected to Lake Okeechobee and about 20% of the water entering the estuary now comes from the Lake mainly as regulatory releases to maintain the Lake at a prescribed water level. The river has also been straightened, deepened and three water control structures have been added. The last, Structure S-79, was completed in 1966 to act, in part, as a salinity barrier. The result is that freshwater delivery to the estuary has been altered and shows characteristics consistent with a watershed that has lost storage capacity. Storm water is not retained but runs off quickly and at higher peak flows. Because there is no retention base flows are low or nil during the dry season. The combination of over-draining and the addition of S-79 as a salinity barrier results in a truncated and highly variable salinity gradient in the estuary. During periods of low freshwater discharge typically during the dry season, salt water regularly intrudes all the way to the structure, often exceeding 10 psu. By contrast, high freshwater discharge can cause salinity to drop below 5 psu at the mouth. The transition between the two states can be rapid, sometimes requiring less than a week. The fluctuations observed at the head and mouth of the estuary exceed the salinity tolerances of oligohaline and marine species. The South Florida Water Management District and the U.S. Army Corps of Engineers are trying to fix these problems through regulation and the construction of additional infrastructure. The South Florida Water Management District has recently established a minimum flow and level for the Caloosahatchee River and Estuary to partially address the lack of freshwater inflow during a typical dry season. As part of the Comprehensive Everglades Restoration Plan (CERP), the C-43 Basin project will construct a reservoir and a number of aquifer storage and retrieval wells (ASR). These storage facilities will allow water to be retained during high flow periods, with subsequent release to the estuary during drier times. The infrastructure will thus reduce high discharges during the wet season and provide a base flow during the dry season. The Southwest Florida Feasibility Study will examine the water requirements of Southwest Florida in more detail and suggest additional possibilities for water storage and management. All these programs, CERP (through RECOVER), C-43 Basin Project, the Southwest Florida Feasibility Study, and the Caloosahatchee MFL require monitoring of biological resources in the Caloosahatchee Estuary. The implementation of this project is in response to the Monitoring Assessment Plan (MAP) created to determine how well the Comprehensive Everglades Restoration Plan (CERP) is meeting its goals and objectives. The premise of CERP is that restoring hydrology in Caloosahatchee estuary will improve the spatial and structural characteristics of submerged plant communities. The objective of this monitoring is to determine if the restoration of beneficial patterns of freshwater inflow, salinity and water quality to the Caloosahatchee Estuary will achieve the expected distribution, community structure and viability of submerged aquatic vegetation (SAV) beds. This monitoring will provide the scientific basis for quantifying the success of these projects.卡洛萨哈奇河与河口湾（Caloosahatchee River and Estuary）坐落于佛罗里达州西南海岸（图1）。卡洛萨哈奇河发源于奥基乔比湖（Lake Okeechobee），流经富兰克林船闸大坝（S-79）后注入河口湾；该河口湾全长约40公里，终点为谢尔波因特（Shell Point）。卡洛萨哈奇河是该河口湾的主要淡水补给来源，每年经S-79闸坝注入河口湾的水量可达其容积的8倍以上。 卡洛萨哈奇水系的水文状况随时间推移已发生改变。该河已与奥基乔比湖永久连通，如今约20%注入河口湾的淡水来自该湖，主要为维持奥基乔比湖水位在规定阈值而进行的调控性放水。此外，河道已被拉直、加深，并新增了三座水控构筑物。其中最后一座S-79闸坝于1966年建成，其部分功能为充当盐度屏障。此举改变了河口湾的淡水补给模式，使得该水系呈现出储水能力丧失的流域特征：雨水无法被留存，而是以更高的峰值流量快速径流。由于缺乏储水能力，旱季的基流极低甚至近乎为零。 过度排水与S-79盐度屏障的共同作用，导致河口湾内的盐度梯度被截断且变化剧烈。通常在旱季淡水补给量较低时，海水会持续上溯至闸坝处，盐度常超过10实用盐度单位（psu）。与之相反，当淡水补给量较高时，河口湾入口处的盐度可降至5实用盐度单位以下。两种状态间的转换极为迅速，有时仅需不到一周时间。河口湾头部与入口处的盐度波动幅度，超出了寡盐（oligohaline）物种与海洋物种的盐度耐受范围。 南佛罗里达水资源管理区（South Florida Water Management District）与美国陆军工程兵团正通过调控政策与新增基础设施建设来解决上述问题。近期，南佛罗里达水资源管理区为卡洛萨哈奇河与河口湾设定了最低流量与水位标准，以部分缓解典型旱季淡水补给不足的问题。作为大沼泽地综合修复计划（CERP）的子项目，C-43流域项目将修建一座水库与多座含水层储回井（ASR）。这类储水设施可在高流量时段留存水体，在旱季向河口湾补水，从而降低雨季的峰值泄水量，并为旱季提供基流支持。西南佛罗里达可行性研究将更细致地评估西南佛罗里达的用水需求，并提出更多水资源存储与管理方案。上述所有项目——包括通过RECOVER推进的CERP、C-43流域项目、西南佛罗里达可行性研究以及卡洛萨哈奇河最低流量水位（MFL）计划——均需对卡洛萨哈奇河口湾的生物资源开展监测。 本项目的实施是为响应《监测评估计划》（MAP），该计划旨在评估大沼泽地综合修复计划（CERP）的目标达成情况。CERP的核心前提是：修复卡洛萨哈奇河口湾的水文状况，可改善沉水植物群落的空间分布与结构特征。本次监测的目标为：验证向卡洛萨哈奇河口湾恢复有益的淡水补给、盐度与水质模式，能否实现沉水水生植被（SAV）群落的预期分布、群落结构与生存活力。本监测将为量化上述项目的实施成效提供科学依据。