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Spring 2004 - V.19 N.1 Table of Content |
Algae and the Lagoon | ||||||||
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The Lagoon Monitor
Is Removing Lagoon Causeways Good or Bad? Algae and the Lagoon |
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| © 2003 Marine Resources Council of East Florida |
Algae grows rapidly in warm water, particularly because we contribute fertilizers and septic tank seepage into the stormwater that flows into the lagoon. Fertilizers cause algae to bloom rapidly and can cause the entire lagoon to appear green or brown. At night some algae will glow when disturbed, giving the water an eerie glow when agitated. In areas where the causeways cut down on lagoon circulation, the effect of algae is to rob the water of oxygen overnight causing morning fishkills. On the maps to the left, areas with low Dissolved Oxygen (DO) are marked by Xs and cross hatching. When oxygen levels drop below 2 milligrams per liter of water (2 parts per million) it usually results in fish kills. As you can see on the maps, low oxygen levels and fish kills occur in small natural coves and in the stagnant areas created by causeways.
So would removing the causeways be good for the lagoon? Lagoonwatch data supports that it would be very helpful in reducing fishkills and increasing oxygen levels in the Lagoon. Would removing the causeways reduce water clarity? Lagoonwatch data suggest that in the summer months when seagrass need the sunlight most, it is likely algae and not sediment that is causing the greater harm. Removing the causeways would not exaggerate the algae problem and in fact would remove much of the algae's impact on oxygen levels in the water. If we are serious about improving water clarity in the lagoon we need to address the sources of nutrients like fertilizers and septic tanks that feed the algae. Until we better educate the public on the negative impacts of over fertilizing lawns, expect to see a green lagoon to match the green lawns.