In an effort to assess the effects of surface water withdrawal, FWRI's Fisheries-Independent Monitoring Program, Southwest Florida Water Management District, and Tampa Bay Water are working together to monitor several rivers along the west coast.
As Florida's population increases, demands for surface water withdrawals to meet potable water demands also increase. Freshwater must often be extracted from various water bodies in the state to meet this demand, and tidal rivers are often selected as suitable locations. However, the same freshwater that is being harvested is a key ingredient for the state's estuaries.
Each day, millions of gallons of freshwater enter into Florida's bays and estuaries. This water quickly mixes with the saltwater, creating within the estuary a salinity gradient that ranges from freshwater to full-strength saltwater. This range between freshwater and saltwater is necessary for the estuary's inhabitants to flourish. In fact, the majority of marine fish caught by recreational anglers (i.e. red drum) depend upon this influx of freshwater for at least the early stage in their lives.
Several rivers flowing into Florida's estuaries have become sites for freshwater withdraw to satisfy the demands of Florida's growing population. Scientists have worked for years to define the point at which withdraws begin to disrupt the ecosystem. Water resource managers call this limit the Minimum Flows and Levels (MFL) for the water body. Florida statutes (Section 373.042) require that water management districts across the state establish MFL for all water bodies. Several of the water management districts have funded short-term monitoring programs to develop baseline data that can be used to establish more meaningful MFL.
In addition to Minimum Flows and Levels, the water management districts oversee water resource permitting. In the late 1990s, Tampa Bay Water, a government agency that provides wholesale water to Hillsborough, Pasco, and Pinellas counties, was granted a permit by the Southwest Florida Water Management District to withdraw additional surface waters from the Hillsborough, Alafia, and Palm rivers during periods of high water flow. In granting this permit, the Southwest Florida Water Management District (SWFWMD) required that Tampa Bay Water initiate the comprehensive Hydro-Biological Monitoring Program (HBMP). The HBMP is designed to ensure that water flows do not deviate from the normal rate to the extent that water quality, vegetation, and animal populations are adversely affected, that salinity distributions in tidal streams and estuaries are not significantly altered, and that recreational use and aesthetic qualities of the resource are not adversely affected.
The multi-disciplined HBMP established by Tampa Bay Water surveys hydrology, water quality, benthic fauna, zooplankton and ichthyoplankton, fish and macro-invertebrates, emergent and shoreline vegetation, and birds. Most of the surveys employ a stratified-random sampling design, so the data collected can be used to describe the entire study site. The Fisheries-Independent Monitoring Program at the Fish and Wildlife Research Institute has been contracted to conduct the fish and macro-invertebrate survey portion of the study.
During each of these studies, the Fisheries-Independent Monitoring (FIM) program collects fish and macro-invertebrate samples at randomly selected sites within each river. In each study area, shallow water samples (<1.8 m) are collected with 21.3 m seines, and deeper water samples (>1.8 m) are collected with 6.1 m otter trawls. All fish and select macro-invertebrates (blue crabs, stone crabs, pink shrimp, and grass shrimp) are identified to species and counted.
Fish lengths are also recorded prior to releasing the animals. Specimens are visually inspected for external abnormalities, such as parasites, ulcers, and tumors. Animals determined to have abnormalities are returned to the lab for further analysis. Additional data recorded at each sample site include the following:
- Habitat-bottom vegetation, bottom type, and shore type
- Site-latitude, longitude, and depth
- Weather-wind, cloud cover
- Water-salinity, temperature, pH, dissolved oxygen, clarity, tide
Also, monitoring is taking place on the Myakka river and Venice inlet for 18 months to support establishing MFL. A similar twelve-month study is taking place on the Weeki Wachee river.