Estuaries in Danger

Background

    The St. Lucie River and the Indian River Lagoon are estuaries. An estuary is a shallow, protected, coastal body of water where fresh and salt water mix. This mixture of fresh and salt water is called brackish water. The open ocean averages 35 parts per thousand (ppt.) salt. That’s 35 parts of salt per 1000 parts of water. The Indian River Lagoon ranges from 25 to 35 ppt. The St. Lucie River ranges from 5 to 35 ppt.

    Estuaries are very productive places. They are important for the survival of life on the land and in the ocean. The shallow water of the estuary is perfect for the growth of seagrass beds. These plants clean the water, trap sediment, and provide important breeding and nursery grounds for many species of fish and invertebrates. Oyster beds grow in the areas where the bottom is too hard for the seagrasses. Almost all ecologically and economically important species of marine fish and invertebrates spend some portion of their life cycle in estuaries. When the salinity drops below 20 ppt the seagrass and oyster beds start to die off. If there is too much sediment floating in the water the seagrass beds die from lack of light and the oysters die from being choked with dirt.

History

    Since 1881 People have worked to drain the wetlands, especially the Everglades. In 1905 the Board of Drainage Commissioners was created and put in charge of draining South Florida. Between 1916 and 1928 the St. Lucie Canal (C-44) was constructed as part of the Everglades Drainage District Works. (see map) Before this time there was no flow of water between lake Okeechobee and the St. Lucie River. Discharging water to the St. Lucie Canal and the Caloosahatchee River became the main flood control method for Lake Okeechobee. This water does not stay in the system long so it tends to be filled with nutrients and sediment. This water damages the coastal estuaries while the Everglades and Florida Bay could use fresh water.

Recent Problem

    The El Niño event of 1997-98 dumped lots of rain on Florida during its "dry" season. The entire system from Kissimmee to Lake Okeechobee was swollen to bursting with water. Because of this and the coming "wet" season discharges of water into the St. Lucie River Estuary were heavy.

    It is understood that discharges greater than or equal to 2500 ft3/sec. (18700 gal./sec) causes damage to the estuary. Discharges exceeded 2500 ft3/sec. for 115 straight days, from January 7, 1998 through April 21, 1998. In that time over 315 billion gallons of fresh water have been dumped into the St. Lucie River Estuary from the St. Lucie Canal draining Lake Okeechobee. This is more than 40 times the volume of the estuary. All of this fresh water is caused several different problems.

    The salinity regime in the estuary should range from 5 ppt (parts per thousand) inland to 35 ppt near the inlet. The range was between 0 ppt and 20 ppt during the discharges. Under 20 ppt, seagrasses and benthic (bottom dwelling) invertebrates begin to die off.

    The water is not the only problem. The water is filled with sand, silt and vegetative matter. On March 26, 1998 it was estimated that 598 yd.3/day of sediment was entering the estuary from the St. Lucie Canal. That is the same as a truckload of dirt being dumped into the estuary every 45 minutes, 24 hours a day. This sediment reduced the visibility in the estuary to around 6 inches. The seagrasses die from lack of sunlight. The benthic invertebrates are choked out. Hundreds of dead or malnourished coastal birds were found. They could not find anything to eat in the murky water. As the vegetative matter begins to break down it is going to create a heavy biological oxygen demand (BOD) which can lead to anoxic conditions and fish kills.

    Ten species of fish were confirmed to have lesions. These lesions are caused by a toxic dinoflagellate called Cryptoperidiniopsis. Crypto is a relative of the dinoflagellates that cause red tides. The appearance of Crypto is not directly correlational to the discharges into the estuary; however, the low salinity and high nutrient content of the water are ideal for Crypto to bloom. Once the discharges stopped and the salinity returned to the estuary the cases of crypto began to diminish.     

Help make sure this is the last time the St. Lucie River Estuary and the Indian River Lagoon are damaged like this.


  • St. Lucie River Estuary Water Quality Monitoring Network Data
  • Central & Southern Florida Restudy
  • The Governor's Commission for a Sustainable South Florida
  • South Florida Water Management District
  • U.S. Army Corps. of Engineers - Jacksonville District
  • St. Lucie Lock and Dam (S-80) Discharge
  • Port Mayaca Lock and Dam (S-308) Discharge
  • Kissimmee River Report
  • South Florida Restoration Electronic Library
  • Everglades Digital Library
  • Florida Internet Center for Understanding Sustainability
  • The Everglades Home Page
  • Everglades Factsheet
  • Lake Okeechobee and Surrounding Areas
  • Newspaper articles on the St. Lucie River
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