By Bill Willis
January 5, 2017
Discovery Lake’s appearance changed noticeably this past summer. Dark green mats of Lyngbya wollei, flourished along the shoreline, along with several green algal and blue-green cyanobacteria blooms occurring. The lake was responding to nutrient overload a phenomenon known as eutrophication. Eutrophication is the process of enrichment of lakes with nutrients, and the associated biological and physical changes. Human activities can influence the rate and severity of the response. Introducing fifty new grass carp couldn’t keep pace with the various algal growths. Also NIEHS increased the number of grass carp in the lake, in an attempt to slow algal growth, but this was not enough to keep the algae at bay.
Enrichment is usually related to excess nitrogen and phosphorous from storm water runoff. In other urban settings, it might be from a sewage spill, but that’s not the case here. Confidence is high that the primary nitrogen source was urea used for snow/ice melt on Institute roads and sidewalks. Changes in weather conditions across the southeast have also increased the frequency of algal blooms across North Carolina.
Other possibilities include:
This summer, the North Carolina Division of Water Resources confirmed the presence of cyanobacteria and stated that the blooms didn’t constitute a toxic algal bloom condition. However, reduction in the nutrient load of the lake will help reduce the blooms and improve the overall appearance of the lake.