The Lagoon Monitor
Water Clarity: No Sunlight = No Seagrass, No seagrass = Very Few Fish
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Plants that live under the water, such as sea grasses, produce oxygen for fish and other aquatic life, as well as provide food, shelter, nurseries and habitat. Like any plant, seagrasses need sunlight to produce energy in a process called photosynthesis. When the lagoon becomes murky, light is not able to penetrate the water very far and if the seagrass are unable to photosynthesize for long enough they die. Each time the lagoon loses some seagrass it loses all the fish and shellfish that would have thrived there. Since the 1940s the Indian River Lagoon has lost over 10,000 acres of sea grasses with an economic value of over 14 million dollars a year. The economic loss since the 40s, totals $880 million due to reduced water quality.
Secchi depth is a method for measuring the penetration of light below the surface of the water. The method uses a Secchi disk with a checkerboard pattern of four alternating black and white painted quarters with a pre-measured line attached. The disk is lowered into the water until it can no longer be seen from the surface or the black can be no longer distinguished from white areas. This depth is known as the Secchi depth. Low Secchi depths usually are caused by large amounts of suspended materials or natural or man-made chemicals dyeing the water a dark color. The higher the Secchi depth, the deeper the seagrass can survive.
The goal for water clarity in the Indian River Lagoon is one and a half meters (almost five feet). If this goal could be reached then large areas of the lagoon would grow seagrasses where currently there is little or none. Unfortunately this goal is usually not reached even during a drought period. The series of maps on the right show average Secchi depths observed by Lagoonwatch volunteers during the past year. The readings proved consistent enough within sections of the lagoon to allow for generalizations to be made. 2003 started out with heavy runoff from December rains. Heavy rainfall in the winter months have a particularly high impact because the cooler temperatures result in less evaporation. In the St. Lucie River region, the storm water runoff included deliberate discharges from Lake Okeechobee which were highly colored and also carried heavy sediment loads from farm run-off. The result was a brown
mass of water with poor water clarity. From Vero Beach north, most of the lagoon was similarly impacted by run-off water that, as usual, carried a lot of fine sediment into the lagoon. Even normally clear Mosquito Lagoon in the far north was adversely impacted. In January, sediment tends to stay in suspension longer as the lagoon is churned up by strong winter winds from the north. By March, moderate rainfall, caused water clarity to improve with areas of water clarity greater than 1 meter expanding to include almost the entire lagoon by April
By June the rainy season had begun. The full effect of the rainy season is most evident in the map of August. In addition to the clouding of the water by sediments, stormwater brought large quantities of fertilizers estimated by the EPA to be over 3 million pounds of nitrogen and over 400 thousand pounds of phosphorus per year. This fertilizer feeds green and red-brown algal blooms which further reduce water clarity. Once again the large rainfalls triggered more Lake Okeechobee discharges hitting the St. Lucie River hard, with exceptionally poor clarity recorded there. Sebastian River discharges were impacting that area in a similar way.
Rainfall in September and October declined, so the really poor readings in the south and around Sebastian moderated, but the algae were still ever-present, resulting in secchi depths of less than 1 meter in most of Brevard and Martin County. Areas adjacent to the inlet faired better since ocean water tends to be clearer and have lower concentrations of nutrients and algae.
So 2003 proved once again to be a "fair" to "poor" year both from the standpoint of water clarity and, inevitably, also of seagrass growth. Grass beds were again deprived of vital light during the major portion of the summer growing season.
What can you do to help the lagoon?
Using ground covers such as composted leaves and wood chips on areas with exposed soil keeps the soil from washing into the lagoon. Don't blow grass clippings into the street or dump them down storm drains. Once clippings and leaves reach the lagoon, they can cause algae blooms.
Use environmentally friendly alternatives to pesticides, herbicides and fertilizers as noted in the Florida Yardstick Workbook. Call the Univ.of Fl. Extension Service to obtain your free copy. Use slow-release fertilizers, use as little as possible and never apply within 50 ft. of a water body or when rain is expected.
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Next Article: Lagoon History
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