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Algal Blooms and Nutrient Enrichment

By Bill Willis

January 5, 2017

Discovery Lake Seems to Keep Changing. What’s Going On?

Algae bloom covering Lake
With an algae bloom covering Discovery Lake in May 2016, a little green heron continues to look for fish.
Photo courtesy of Bill Willis

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.

What could cause the nutrient enrichment?

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:

  • Phosphate rocks breakdown from soil erosion
  • High nitrogen urea fertilizer
  • Nitrogen rich grass clipping discharged into the lake
  • Nitrogen rich goose and duck feces deposited in or near the water
  • Atmospheric nitrogen and lightening produced nitrogen compounds in the lake
  • Polluted rain water containing nitrogen and phosphates runs into the lake
  • Disturbance of the bottom sediments releasing bound nutrients.

What are the biological and physical changes of lake eutrophication?

  • Water turns green or turquoise from floating algae
  • Algal mats form along the shoreline
  • Decaying vegetation creates odor, color, and taste changes (don’t drink the water!)
  • Scum, foam, and oily slicks appear on the surface, moved by the wind
  • Dissolved oxygen levels fall, causing some fish die
  • In significant quantities, large blooms can be toxic to animals and humans

Where does the algae come from?

  • Inflow from upstream sources.
  • On the feet of migrating and local fowl.
  • On the shells of turtles
  • From humans on boats, fishing tackle, recreational items
  • Storms with heavy rains and winds drop organisms.

What can be done to prevent?

  • Remove or moderate the source if it is a point emission
  • Maintain our population of various aged grass carp
  • Insure that riparian zones are intact and stable
  • Use alternatives to nitrogen as a deicer on campus

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.

Snake peering out of water
With the coming of spring, both wildlife and algae began to appear in Discovery Lake in March 2016.
Photo courtesy of Bill Willis
Filamentous cyanobacteria covering Discovery Lake
Filamentous cyanobacteria, a blue-green bacteria grew from sediments in the water, survived the winter freeze, and reached the water surface.
Photo courtesy of Bill Willis
Gas bubbles
Gas bubbles buoyed the mat of algae and bacteria to the surface where it trapped surface debris.
Photo courtesy of Bill Willis
Bacteria growing in clusters
The bacteria grew together and became so dense that small turtles walked on the surface.
Photo courtesy of Bill Willis
Fats and oils over Discovery Lake
Over the summer, a slide of fats and oils developed as the bloom started to decay, a normal part of decomposition. Fortunately, the fish, turtles and birds didn't appear to be affected by the soup of dying plant material.
Photo courtesy of Bill Willis
Surface film on lake
The surface film became very large and gelatinous as more organisms decayed, floating back and forth across the lake during the day.
Photo courtesy of Bill Willis
Cyanobacteria film over lake
The lake had one more surprise with another cyanobacteria bloom in October after Hurricane Matthew, leaving the lake looking like a spinach smoothie.
Photo courtesy of Bill Willis
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