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Coral reef recovery, bioerosion and wastewater injection wells

December 21, 2017
BY RUSSELL SPARKS • Hawaii Department of Land and Natural Resources, Division of Aquatic Resources , Lahaina News

Recently, a scientific publication titled "Vulnerability of Coral Reefs to Bioerosion From Land-Based Sources of Pollution" was reported on by several local news outlets. Bioerosion describes the erosion (gradual destruction or disintegration) of hard ocean substrates such as coral reefs by living organisms, and this research effort led by the U.S. Geological Survey (USGS) is part of numerous scientific peer-reviewed publications consistently demonstrating concerns with the disposal of treated wastewater into coastal injection wells.

The Kaanapali area in West Maui is one of the U.S. Coral Reef Task Force's designated priority watersheds. With this designation, many agencies have partnered with the Department of Land and Natural Resources (DLNR) to study threats to the area's coral reefs and identify management approaches to help corals survive. The work recently reported on by the USGS is part of this partnership.

A key finding of this study was that bioerosion rates on corals next to seafloor groundwater vents off Kahekili Beach Park are up to eight times greater than expected for corals growing away from pollution. In another independent study, Kahekili had the highest average coral bioerosion rates when compared to other sites in the state. The groundwater vent sites at Kahekili are composed primarily of wastewater effluent from the injection wells at the treatment plant. Water quality studies and dye tracer work has demonstrated that the groundwater discharging at Kahekili is contaminated by injected, treated wastewater with nitrate concentrations 50 times higher than background seawater concentrations. This fact has been conclusively shown and is currently undergoing legal litigation.

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In a recent article in the Lahaina News (Oct. 12, 2017), I reported on some early signs of parrotfish and surgeon fish recovery and concurrent improvements in coral health offshore of the Kahekili Beach Park. The changes in the reef ecosystem health appear to be the result of herbivore fisheries management actions taken by the state in 2009 (administrative rules prohibiting the harvest of important seaweed-grazing fishes). Results are encouraging with changes towards a reef ecosystem better suited for new coral recruitment and growth.

Coral reefs may rise up many feet above the ocean bottom, but the actual live coral tissue is only the outermost skin of this structure. It is, therefore, important to understand that although we are seeing improvements in the living layer of the corals at Kahekili, the accelerated bioerosion rates reported on by the USGS can result in the collapse of the underlying reef structure. As a result, this reef may lose its ability to continue to support fish populations and to serve as a natural barrier protecting the shoreline from coastal hazards such as storms and waves.

The best available science suggests that the accelerated bioerosion of the coral reef structure at Kahekili is the direct result of the constant exposure to contaminated waters from the Lahaina wastewater injection wells. While we await the final judgment of the courts and hope for an increased prioritization of wastewater recycling within the county, we must take other proactive resource management actions to reduce the loss of coral structure and the overall collapse of the coral reefs. The herbivore management actions taken by DLNR at Kahekili were designed to help buy us some time. However, for the long-term survival of this reef, we must find other alternatives to the injection of treated wastewater, and we must all work together to reduce other land based impacts to our coastal waters.

For more information on the scientific research from this area, and for suggestions on how we can all help reduce land-based pollution impacts, please go to



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