This is the 5th in a series of posts on the water quality of Missouri’s surface waters. This post focuses on impairment to Missouri’s lakes in 2014, and its causes (I’m using the word “impaired” for what the Missouri Department of Natural Resources calls “non-support”).

Impairment might mean that the water is unsafe, or it might not. For instance, too much bacteria or lead in the water would make the water unsafe. On the other hand, too much weedy material in the water can make water unpleasant to swim in, or it can give it an unpleasant taste, but it doesn’t necessarily make it unsafe.

Table 1. Source data: Missouri Department of Natural Resources 2015.

As noted in the first post of the series, Missouri’s lakes were used for a variety of purposes. Those that were impaired may not have been impaired for all uses, but for only some. Table 1, shows the number of classified lake acres in each use category, the number of acres assessed, and the number of miles impaired. In the table, Whole Body Contact Rec. – A (WBC-A) indicates designated or known swimming areas, Whole Body Contact Rec. – B (WBC-B) indicates areas other areas where recreational whole body contact with the water occurs.

The number of lake acres used varied from purpose to purpose. The most widespread uses were Aquatic Life & Fish Consumption and Livestock Watering. Relatively few miles were used for Industrial purposes or WBC-B. For some uses, only a very small fraction of miles were assessed: none of the lake acres used for Industrial or Livestock and Wildlife Watering were assessed, and only 18% of those used for Drinking Water Supply (public drinking water systems have to make their own, separate assessments of their water quality).

You have to use caution in using the data in the last two columns of the table. While only one use category shows any impairment at all, several of the use categories had no acres assessed. You can’t assess lake water as impaired if you don’t assess it at all. On the other hand, 82% of the lake acres used for WBC-A (swimming) were assessed, and none of them were impaired. I would tend to believe that if water is not impaired for WBC-A, then most likely it is not impaired for WBC-B, Industrial, or Livestock and Wildlife Watering.

Table 2. Source data: Missouri Department of Natural Resources 2015.

Table 2 shows the problem causing the impairments. They are quite different from the causes of stream impairment. Five out of 7 are related to eutrophication. This is a fancy word that means the ability of the lake to support plant life – seaweed and especially algae. Too little, and the lake can’t support a population of fish and other marine life. Too much and the lake becomes choked with weeds or there is an algal bloom. Algal blooms use up all the oxygen, kill the fish, are sometimes toxic, and can turn a lake into a stinking mess. Lake Erie has had notorious algal blooms in the last 5 years that closed the lake to swimming and fishing, and made the water unsafe to drink.

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Table 3. Source data: Missouri Department of Natural Resources 2015.

Table 3 shows the source of the problems causing the impairments. Of the sources of impairment that are known, Municipal Point Source was the largest, followed by Atmospheric Deposition. Municipal Point Source probably refers mostly to sewage treatment facilities that discharge incompletely treated sewage into lakes, while Atmospheric Deposition probably refers to mercury, which ultimately derives from coal burned in power plants.

There appears to be a disconnect between Tables 2 and 3, however. Of the causes of impairment, 3 are signs of eutrophication, not causes of it, and one is a heavy metal deposited from the atmosphere. The other 3, Total Nitrogen, Total Phosphorous, and Pesticides (Atrazine) are all chemicals primarily used in agriculture. Total Nitrogen alone was the cause of impairment in 25,180 acres. However, Agriculture was listed as the source of impairment for only 133 acres, less than 1%. How chemicals primarily used in agriculture can be the cause of so much impairment, but agriculture the source of so little is beyond me.

In summary, the largest causes of impairment of Missouri lakes seem to be mercury originating in coal-burning power plants and then deposited by the atmosphere, and chemicals primarily used on farms. The source of most impairment either has not been studied or is unknown.

Sources:

Missouri Department of Natural Resources. 2015. Missouri Integrated Water Quality Report and Section 303(d) List, 2014. Downloaded 4/20/2016 from http://dnr.mo.gov/env/wpp/waterquality/303d/303d.htm.

(A word about the availability of the Missouri Water Quality Reports. As of 5/1/2016, reports for 2002, 2004, 2006, 2008, 2010, 2012, and 2014 are available on the Department of Natural Resources, Water Protection Website. Though the 2014 report is dated April 24, 2014, it was not available on the website until much later. The report for 2016 is not yet available, and may not be for many months.)

Wikipedia. 2016. Algal Bloom. Viewed online at https://en.wikipedia.org/wiki/Algal_bloom.