Water quality experts say lagoon forewarnings evident
Nutrient loading has occurred in the Indian River Lagoon (IRL) for decades and has adversely impacted its water quality and ecology. The limiting nutrient nitrogen triggers suspended algae and sessile (attached) macro algae growth in the IRL. Reducing nitrogen loading must be the primary goal if cleanup efforts are to be successful.
The commonly acknowledged first step for remediation of any contaminated water is control and elimination of sources. Nitrogen fertilizers and human waste are the two major sources of nitrogen loading to the IRL in Brevard County that can be reduced or eliminated through improved management. Nitrogen from both sources has increased as population has increased. While some lawn fertilizer nitrogen enters the IRL in runoff, groundwater is the primary mode of entry for both fertilizer and human waste nitrogen. Irrigation water and precipitation leach fertilizer nitrogen through sandy soils to groundwater.
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The wet season nitrogen-fertilizer ban reduces nitrogen-loading during periods of heavy rains when nitrate is easily leached through the sandy soils to shallow groundwater where it can be transported down-gradient to the IRL and its tributaries. Human waste nitrogen enters groundwater primarily from septic tank leach fields. This major source has singularly been ignored by policy makers and sorely needs attention. Policy makers and the citizenry need to recognize that high density septic tank distribution, sandy soils, and a high groundwater table near surface water bodies (IRL) is a recipe for disaster.
Independent peer-reviewed research by Brian LaPointe and colleagues at Harbor Branch Oceanographic Institute concludes that nitrogen from the approximately 300,000 septic tanks lining the 156-mile IRL is a major source of its nitrogen pollution. Elimination of septic tanks in both Tampa Bay and Sarasota Bay, two estuaries that have successfully confronted nutrient pollution similar to that in our own IRL, has improved water quality and sea grass is again proliferating.
So the question you may have is why not promote muck removal and bio-filtration via bivalves (mussels and oysters)? The simple answer is neither are sources of nitrogen loading to the IRL. Muck is clearly an anaerobic (devoid of oxygen) sink for nitrogen and phosphorous-containing organic compounds and as such has trapped these nutrients. While muck removal has already been adopted and supported by the state as a solution for improving water quality, its value has yet to be shown. Our concern is that muck removal likely will re-suspend particulate matter and nutrients will re-solubilize into the water and could actually increase nutrient levels. It is our understanding that FIT was to investigate these concerns before additional muck removal occurred. Bio-filtration removes suspended solids (algae) and does not impact source loading. It is a case of the cart leading the horse. Firstly, control nutrient loading and then bivalves will proliferate and increase water clarity.
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Technology exists to convey septic tank effluent to main lines with minimal disruption to property and streets. This is a less expensive approach than elimination of septic tanks and sewering and has already been implemented in Vero Beach. Treatment plants also require upgrades to tertiary treatment which converts nitrate and ammonium, nitrogen forms used by algae, to innocuous nitrogen gas.
Commissioner Barfield’s recognition of the need for a special property tax to ensure a reliable source of funds for lagoon-related projects is gratifying. Eliminating a major nitrogen source to the IRL through improved management of individual septic systems and upgrading wastewater treatment plants should be a major goal of the Save Our Lagoon Special Taxing District action plan. The brown tide and massive March 2016 fish-kill are clear forewarnings that it’s time to act and pay the piper.
Roy and Mary Spalding reside on Merritt Island. University of Nebraska professors emeriti, they each have 40 years’ experience in research and teaching water quality.