Formatted Title:

Making Strides Towards Restoration: Environmental Dredging to Remove Fine-Grained, Organic-Rich Sediment (Muck) in the Indian River Lagoon, Brevard County, Florida

Background/Objectives:

The Indian River Lagoon (IRL) in Brevard County, Florida, is an incredibly unique and diverse estuary. However, anthropogenic alterations to the natural hydrology and increased nutrient loading over decades have led to the accumulation of fine-grained, organic-rich sediment known as “muck.” Muck is characterized by having >60% silt + clay, >75% water by weight, and >10% organic matter. These sediments contribute to the degradation of water quality in the IRL by releasing dissolved nitrogen and phosphorus into the water column fueling harmful algae blooms. The characteristics of muck make it prone to accumulate other pollutants like metals. Muck creates an anoxic environment with high sediment oxygen demand. This can lead to the accumulation of hydrogen sulfide, which is toxic to seagrasses and benthic infauna and epifauna. Additionally, muck can smother seagrass and can be easily resuspended which increases turbidity and blocks sunlight from reaching submerged aquatic vegetation.

Addressing the accumulation of decaying muck is a complex but important step toward restoring the IRL. Both the IRL Comprehensive Conservation and Management Plan (CCMP) and the IRL Surface Water Improvement and Management Plan (SWIM) commend the removal of muck as an effective way to improve water quality. Additionally, the Florida Department of Environmental Protection (FDEP) approves muck removal under the Basin Management Action Plan (BMAP) program to reverse impaired water quality. Following persistent and prolonged harmful algae blooms that started to plague the IRL in 2011, the citizens of Brevard County voted to implement a half-cent sales tax (Save Our Indian River Lagoon - SOIRL) to fund pollution reduction and removal efforts. Removal of muck through environmental dredging along with treatment of the interstitial water is funded by this sales tax.

Approach/Activities:

Currently, there are 21 muck removal projects approved and funded in the sales tax project plan. One project is currently under way (Grand Canal), and two to three additional projects will be going out for bid in 2024/2025 (Eau Gallie Northeast, Sykes Creek Phase 2, Canaveral South). Research has shown that the interstitial water, or the water being “squeezed” out of the muck, has high concentrations of nitrogen and phosphorus. Although not required by the permits, Brevard County saw this as an opportunity to challenge the dredging industry by offering Pay for Performance financial incentives to develop a process to remove nutrients from the interstitial water to meet or exceed advanced wastewater treatment standards (3,000 ppb or 3 mg/L for nitrogen and 75 ppb or 0.075 mg/L for phosphorus).

Results/Lessons Learned:

Monthly sampling of the IRL shows water quality improvements extend miles around our environmental dredging projects. Notably, the removal of fine-grained, organic-rich sediments has led to increased oxygen concentrations and saturation in both overlying and adjacent waters. Researchers at Florida Tech observed higher dissolved oxygen levels in recently dredged canals compared to those not yet dredged. Ongoing monitoring continues to assess post-dredging nutrient fluxes and impacts on infauna communities. Furthermore, our unchartered endeavor to treat interstitial water has vaulted up a steep learning curve and is now achieving desired target levels and continuously enhancing the process, resulting in the removal of thousands of additional pounds of nitrogen and phosphorus before the interstitial water is reintroduced to the lagoon.

The SOIRL Plan allocated over $170,000,000 to environmental dredging and treatment of interstitial water. These projects are projected to remove over 870,000 lbs of nitrogen and 65,000 lbs of phosphorus from the IRL.

Beb Sebastian

Affiliation

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Making Strides Towards Restoration: Environmental Dredging to Remove Fine-Grained, Organic-Rich Sediment (Muck) in the Indian River Lagoon, Brevard County, Florida