EUTROPHICATION

   Eutrophication is, in the simplest terms, too much of a good thing. It occurs when too many nutrients are deposited into a body of water, throwing off the established balance of production and consumption of organic matter. Eutrophication can take place in ponds, lakes, rivers, and oceans. At first, the overload of nutrients in the body of water encourages plant growth. However, soon this excess of organic material uses up most of the available oxygen in the water, taking it away from the other plants and animals. These other organisms can no longer survive with such depleted oxygen levels and die off, creating what is referred to sometimes as a "dead zone", devoid of life.
    Below is a table of the different trophic states, or levels of organic matter in relation to available oxygen, that a body of water traverses on its way to becoming a "dead zone".
 
 
 

TROPHIC STATES

       Eutrophication of bodies of water is a naturally occurring phenomenon. However, the process has been aggravated by the human population. Such man-made eutrophication is caused by excessive discharge of nutrients, especially phosphorous (P) in the form PO4, nitrogen (N) in the form NO3, and silicate. Pictured is a diagram of how nutrients, such as phosphorous, in runoff lead to plant and animal die offs.
    In this diagram, phosphorous in the surface runoff fertilizes small floating aquatic plants. As these aquatic plants proliferate, sunlight penetration is reduced. Submerged aquatic vegetation can no longer survive, and as they die and decompose, oxygen levels in the water are also depleted. Eventually, animals die too, due to lack of oxygen.
    Some probable causes of this excessive nutrient runoff include sewage treatment plant leakage, septic tank leakage, urban runoff, agricultural runoff, channel dredging, and loss of wetlands.

    As mentioned earlier, the initial effect of eutrophication- increased productivity- is deceptively good. However, the first indications of eutrophication's ill effects are such visual changes as muddled and discolored water, coupled with a noxious odor. This change in water clarity is a result of the primary effect of eutrophication, which is algal blooms. To the left is an example of such an algal bloom. For more examples of what algal blooms look like, click on the image.
    Algal blooms occur when excess nutrients cause a proliferation of algae. These algae blooms, known as Harmful Algal Blooms (HABs) because of their effects, are deceptive as well. Because they photosynthesize, one would think they actually add oxygen to the water, helping it. While algal blooms do increase oxygen levels during the day, they respire during the night, using all of this oxygen up. This oxygen usage, combined with the oxygen usage of decomposing organic matter, accounts for an overall lowering of oxygen levels in eutrophic bodies of water.
    Aside from using up all of the available oxygen in a body of water, algal blooms also cloud the water, blocking the sunlight from underwater grasses which need it for photosynthesis. These grasses, in turn, die off, destroying the habitats and food necessary for other organisms to survive. These organisms, therefore, die off as well, the most sensitive and more conservationally valuable species going first, followed by more tolerant species such as gar and shad.
    In rivers in particular, the excessive initial growth of plants can cause a reduction in the river's flow capacity, which results in an increased chance of flooding, as well as changes in animal behaviors like salmon spawning.
    These results can have an almost immediate effect on the human population surrounding the body of water. For example, they can lead to reduced recreational and commercial value of beaches, wetlands, and estuaries, while also decreasing the wildlife population with sport and commercial value.
    As for the long term effects, the organic remains of plant and animal life are deposited over time on the floor of the body of water. These deposits build up over centuries, making the water shallower and warmer. Marsh plants, more conducive to these conditions, begin to grow. Lakes, for example, eventually become bogs. In the end, the body may actually disappear into land, having drastic ecological consequences.
    Below is a diagram of how these processes lead up to one another.

    As an individual citizen, you can help to stop man made eutrophication by:
 

• limiting your fertilizer use
• controlling runoff and soil erosion in your own yard
• starting a compost pile and recycling yard waste
• conserving water and energy
• planting trees
• maintaining your septic system
• driving less
• and being a responsible boater by pumping out wastes.

1. Environmental Agency, http://www.environment-agency.gov.uk/
s-enviro/viewpoints/4health/3eutroph/4-3.html

2. Eutrophication, http://www.btnep.org/pages/eutrophication1.html

4. Harmful Algal Bloom Photo Gallery, http://habserv1.whoi.edu/hab/
rtphotos/rtphotos.html

5. Impact of Phosphorus on Aquatic Life: Eutrophication, http://www.
agnr.umd.edu/users/agron/nutrient/Factshee/Phosphorus/Eutrop.html

6. Marine Research on Eutrophication, http://www.mare.su.se/english/
index.html

7. Midatlantic Integrated Assessment, http://www.epa.gov/emfjulte/
tpmcmaia/html/eutroph.html

8. United Nations Environment Programme, http://www.grida.no