Sewage Spills and Algal Blooms

With recent heavy rains in the Northeast causing wastewater treatment plants to reach and exceed capacity, there have been overflows and sewage spills directly into lakes and rivers. This has included both raw sewage and graywater. Outdated and inadequate infrastructure are lending to the potential increase in toxic algal blooms and pathogens within the waters we drink from and recreate in.

When wastewater spills or is dumped into a body of water, it contains pharmaceuticals, synthetic hormones, pollutants and nutrients that can feed algal growth. There is an impact to the aquatic ecosystem from raw sewage or partially treated effluent that makes their way into our freshwater resources.

Raw sewage is untreated septic from toilets. Graywater comes from showers, sinks and washers. Both contain nutrients that will feed algal growth. Raw sewage contains more nitrogen, while graywater contains more phosphorus. Depending on the limited nutrient in a body of water, the sewage spill has the potential of causing a cyanobacteria harmful algal bloom.

Any algal bloom can alter water quality and have an impact to a body of water. As organic pollutant tolerant forms of algae dominate, they force out typical nutritional forms of algae that zooplankton and fish populations prefer. These same forms of algae can reduce sunlight that is needed for healthy macroalgae and macrophytes to grow. During the day an algal bloom will alter the pH of a water body and elevate the oxygen levels. At night the oxygen levels can plummet causing fish kills. Within the littoral zone, the excessive algal growth can smother fish feeding and breeding habitats. Following an algal bloom, when the algae die and decompose, the bacteria that feed on them will deplete the oxygen causing hypoxic conditions. This can kill fish and other aquatic organisms.