Pomme de Terre Watershed Project
Did anyone see the episode of "Man Vs Wild" where the host Bear Grylls squeezed drinking water out of a pile of fresh elephant dung? I think the water that dribbled into his mouth would be what most would consider "not high quality". Because we usually think of water quality in terms of drinking water, we tend to think of high-quality water as being clear and cold. Although that is a narrow measure of good water for human consumption, it is insufficient for measuring the overall quality of water in a stream.
Water quality in a stream can be assessed using biological indicators - what kind and numbers of different organisms are present in a stream reach. Water quality is also determined by measuring a variety of physical and chemical properties like temperature, dissolved oxygen, nutrients, sediments and pathogens. Natural streams exhibit and maintain a characteristic range of water quality measures depending on things like flow, precipitation and stream geology. Human activities change water quality by upsetting the natural condition of the stream system. These changes are often harmful from the standpoint of stream life and system balance.
Good water quality is maintained by natural channel shape and flows, naturally vegetated riparian zones, a healthy biological community, and proper land stewardship. The most common pollution sources in Minnesota are sediment, herbicides, insecticides, industrial chemicals, sewage outflow, and fertilizers.
Excessive erosion of topsoil commonly degrades water quality, primarily by decreasing water clarity. Of all pollutants in streams, the most expensive to deal with and the most damaging to stream life is sediment. It plugs the spaces between gravel and rocks in the streambed, preventing their use as living spaces for life forms that live on the stream bottom. Sediment can smother eggs of fish whose eggs rest in the spaces of well-oxygenated gravel beds. An excess of sediment in streams means the end of natural reproduction for many fish species.
Field and lawn fertilizer and manure inputs add excess nutrients, principally nitrogen and phosphorus to streams, causing extreme plant and algal growth. At night, the excessive algae no longer produce, but only consume oxygen. Dissolved oxygen levels can dip during the night below life sustaining levels. Once this alga dies, the decomposing of this growth can also rob a stream of dissolved oxygen. The breakdown of ammonia into nitrates also takes oxygen out of the water, and may reduce dissolved oxygen to lethal levels.
Pesticides, herbicides, and insecticides have been found at dangerous levels in some streams. Research indicates that these chemicals kill aquatic organisms, inhibit reproduction, and upset hormones in animals in addition to a multitude of other adverse affects.
Some sources such as industrial and sewage effluent are point sources, which are identifiable sources that are easy to monitor and regulate. Others are non-point sources such as fertilizer and sediment. These sources are more diffuse, and are harder to assess and regulate. These factors along with financial disincentives and a lack of regulatory authority make solving the problem of non-point pollution a big challenge. The framework for controlling the discharge of pollutants into streams was set by the federal Clean Water Act, passed in 1972. In the early days of the Clean Water Act, efforts focused on regulating discharges from traditional point source facilities, with little attention paid to runoff from fields, streets and other "wet-weather" sources. Starting in the late 80s, efforts to address polluted runoff have increased significantly. For non-point runoff, voluntary programs including cost-sharing with landowners are the key tool to remediate the non-point problem.
Shaun McNally is the Pomme de Terre Watershed Project Coordinator. He is located in the Stevens SWCD office in Morris and can be reached at 320-589-4886 ext. 109.
The Pomme de Terre River Association maintains a website: www.pdtriver.org.