The problems with run-off

With all the rain and the ensuing run-off these past few months, the RMP received many questions about the effects of sedimentation on the reef. The earliest coral reef researchers recognized that coral growth was strongly inhibited wherever muddy freshwater enters the sea. Negative impacts of rivers include the introduction of freshwater and sediments such as mud, silt, and clay. While freshwater can cause bleaching, excessive sediment smothers and kills coral. Corals differ greatly in their ability to resist sedimentation, however most species are highly intolerant of even small amounts.

Unfortunately for the coral of Roatan, increases in development often worsen sedimentation. One of the main culprits is coastal dredging, like that which has occurred in Mahogany Bay and French Cay. Dredging generates huge muddy plumes which smother reefs in areas that previously had clear water. These plumes continue to cause damage long after the dredging has ceased as the mud is re-stirred by every storm, causing clouds of sediment to slowly work their way down coastlines, damaging reefs many times more before they are washed away.

The other main cause of sedimentation is soil erosion caused by increased deforestation and development. Depending on rainfall, topography, soil types, and land management, deforestation and development can result in up to thousand-fold increases in sedimentation in near shore waters. As a result sedimentation is taking a severe toll on almost all coastal reefs worldwide. In healthy coastal watersheds, sediments are naturally removed from fresh water before it enters the sea. Plants such as grass, trees, and mangroves act as buffers between the land and the sea by trapping sediment. If the natural buffer zones are damaged, sediment runs straight out onto the reef.

Roatan’s soil is composed mainly of red clay, which is easily soluble. After a heavy rain, it’s easy to see the threat to the reef as huge muddy plumes of water fill our lagoons. Our island’s reefs are under great threat of sedimentation. Unregulated deforestation and development, illegal road building (especially during rainy season), and the rampant destruction of huge swathes of mangroves, the list of threats is endless. Only through more conscientious development will Roatan’s reefs have a fighting chance.

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