People Asked: Q & A
03. Muck Removal & Dredging
- Sources: University of Florida, IFAS Sea Grant, Water Resources
Muck is the result of human impact on the Indian River Lagoon. As human population and development has grown, freshwater runoff into the lagoon has also increased, carrying with it land-based sources of nutrients and pollutants. This runoff includes soil from erosion and organic debris from sod, grass clippings, leaves and other vegetation. Decomposing algae blooms also accumulate in muck. All of these sources over time contribute to muck which now covers an estimated 15,900 acres of the lagoon bottom in Brevard County.
Muck removal is the only project in the Save Our Lagoon Project Plan that is designed to remove many decades of accumulated pollutants from the lagoon. The plan focuses on dredging large deposits of muck in big, open water sites within the lagoon. The goal of removing the muck is to reduce the amount of nitrogen and phosphorus that would be released from the muck if it were to stay in the lagoon. Muck removal is expensive so projects are prioritized based on the potential for water quality improvement versus estimated removal cost.
When muck is dredged from the bottom of the waterways, it is deposited in a temporary holding site where it can be de-watered. The water may be treated further to remove additional nitrogen and phosphorus before it is returned to the lagoon. Once the muck dries out, it is hauled to be safely repurposed, such as addition to agricultural areas or it may be disposed of at the landfill. At this time, there are few uses for the muck once it is removed.
Muck is fine-grained organic rich sediment with a high water content. It is made up primarily of clay, sand and organic matter (decaying plant material). Because of its high water and clay content, muck looks like black ooze. Muck is not the natural bottom of the lagoon. It is found throughout the lagoon though it tends to accumulate in deeper waters, sometimes in layers more than 6 feet thick.
Muck covers the natural sandy bottom, destroys habitats such as seagrasses by inhibiting growth, and impacts bottom-dwelling organisms by depleting oxygen in the sediments and surroundings waters. Muck accumulates potential pollutants and stores and releases nutrients into the water, which can then feed algal blooms.
Every time the muck is disturbed, by water movement caused by wave action from weather, boats or other activity, it “fluxes, or re-releases the harmful nitrogen and phosphorus back into the Lagoon. The only way to prevent this continual release of these pollutants is to remove the muck by dredging.
Removing muck is only one necessary tool for restoring the Lagoon. Reducing the inflow of material that makes up the muck is essential as well; otherwise in time the same problem will return. The muck deposits formed over a period of the past 50 years by silt, utility and septic system sewage, grass clippings, stormwater runoff, etc. entering the Lagoon.
Until about 1996, our wastewater treatment plants dumped their partially treated sewage directly into the Lagoon. This largely ended due to the federal Clean Water Act and the IRL System and Basin Act of 1990, reducing contributors to muck formation. Under the Save Our Indian River Lagoon Plan other controls are also being installed, including retention ponds, baffle boxes, and other solutions, which slow the formation of new muck.