Stream pollution makes mosquitoes happy

This week the Ecological Society of America is having their annual meeting, and several papers of entomological interest have been presented. One found that increased pollution in urban streams leads to increased mosquito populations:

“Luis Fernando Chaves, a post-doctoral researcher at Emory University, and his team discovered mosquitoes in abundance in a sewage-contaminated stream in Atlanta, but rarely in a nearby clean stream. They also found that mosquitoes were largest in streams with high levels of organic minerals – in this case, nitrogen and phosphorous – that originated from the sewage treatment plants.”

The issue of sewage runoff is a major one here in Michiganclosed beach sign

Many of our cities use the same pipes for sewer water and storm runoff.  This means that in a heavy storm, excess water–with all that sewage too–goes right into the watershed.  This usually means the Great Lakes or other bodies of water.

Signs posted warning against swimming because of high fecal bacterial counts are a pretty common sight here.  Sadly, because of Michigan’s state budget woes, the annual required report of wastewater release has been suspended, effective April 2009.  Right now, there is simply not enough staff to monitor our water safety.

Chaves’ work suggests a double whammy–all those bacteria are wonderful food supplies for the bacteria that feed mosquitoes. And the mosquitoes are bigger, which means they can live longer–and have a better shot at transmitting a mosquito-borne disease, of which there are many.

You can read some research about storm runoff closer to home in the Journal of Great Lakes Research–here’s a couple of representative papers:

McLellan, S., Hollis, E., Depas, M., Van Dyke, M., Harris, J., & Scopel, C. (2007). Distribution and Fate of Escherichia coli in Lake Michigan Following Contamination with Urban Stormwater and Combined Sewer Overflows Journal of Great Lakes Research, 33 (3) DOI: 10.3394/0380-1330(2007)33[566:DAFOEC]2.0.CO;2

Tracie M. Jenkins, Troy M. Scott, Mechelle R. Morgan and Joan B. Rose (2005). Occurrence of Alternative Fecal Indicators and Enteric Viruses in Michigan Rivers Journal of Great Lakes Research, 31 (1), 22-31 : doi:10.1016/S0380-1330(05)70235-5

Link to Chaves’ home page

Great Lakes Assessment of Urban development and Water Quality

One thought on “Stream pollution makes mosquitoes happy

  1. Yeah, the whole issue of sewage water running off into places like the Great Lakes and other bodies of water during storms is a big problem… and, suite frankly, a disgusting one. I’m a little surprised it would have much effect on mosquitoes, though, because the waste water tends to at least be dumped into very large bodies of water, oceans, rivers and large lakes, as opposed to the stagnant ponds and marshes that mosquitoes like. Although I suppose some of it can back-flow into marshy lands. Ug.. that’s even more bothersome. If it were out in a big body of water at least it would tend to disperse and become very dilute and quickly break down.

    Poo festering in inlet waters and marshes… not a pleasant thought.

    The reason this happens is the design of older sewage systems that have been in place for often more than a century. You can’t really replace the entire sewage system of a place like Chicago where there is so much dense development and it has been built over so many years.

    When these systems were put in place, there was little or no sewage treatment. The waste was mostly dumped far out from shore, but that isn’t sufficient with the growth of cities. Since all the water was just discharged, these systems combined sewers and storm drains. The drains on the side of the road that carry away rain water and snow melt go into the same system that has carries away sewage from sinks and toilets. There are now sewage treatment plants and so the sewage all gets treated before being released. By the time it is released it is free sediment and has been sanitized and had most ammonia and phosphorus removed.

    The problem is that a heavy rain can easily increase the volume of water these sewer systems are handling by many times and the treatment plants just can’t accommodate that. The only thing it can do is go out overflow pipes. The alternative would be to have it come out into everyone basements (which it occasionally does anyway).

    Of course the better way to do it is to have seperate storm drains that drain directly to waterways. As long as nobody is dripping too much motor oil that works fine. That reserves sewers for sanitary waste. In some cities they are trying to at least do this in areas of new development, but replacing them all with a new system just won’t work. In Chicago they are digging a huge tunnel to act as a holding tank so the sewage can be stored until the plant can process it all.

    I don’t mean to get this off track, but this is a major enviornmental and human health issue that is not getting a lot of attention and mosquito are just one of the problems with it.

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