Eutrhophication Study

Eutrophication is caused by the increase of chemical nutrients, typically compounds containing nitrogen or phosphorus, in an ecosystem. It may occur on land or in water. Eutrophication is frequently a result of nutrient pollution such as fertilizer runoff or the release of sewage effluent into natural waters, although it may also occur naturally in situations where nutrients accumulate. Eutrophication generally promotes excessive plant growth and decay, favors certain weedy species over others, and is likely to cause severe reductions in water quality. In aquatic environments, enhanced growth of choking aquatic vegetation or phytoplankton (that is, an algal bloom) disrupts normal functioning of the ecosystem, causing a variety of problems. Human society is impacted as well: eutrophication decreases the resource value of rivers, lakes, and estuaries such that recreation (highly eutrophic waters feel 'slimy'), fishing, and purely aesthetic enjoyment are hindered. In severe cases it can be harmful to fish, and to the animals or humans that eat them.

The major nutrients which affect lake productivity are phosphorus and nitrogen. For the majority of lakes in Pennsylvania, phosphorus is the limiting nutrient - that is, the nutrient which is in least supply and thus serves to limit productivity. The limiting nutrient can be determined by calculating the nitrogen phosphorus ratios. A nitrogen/phosphorus ratio of greater than 15:1 indicates a phosphorus limitation; less than 7:1 indicates nitrogen limitation. Ratios between 7:1 and 15:1 indicate co-nutrient limitation.

Phosphorus discharges to lakes, ponds, and impoundments are controlled through 25 Pa. Code Section 95.6. Phosphorus is chosen as the primary nutrient to control because, based on a comprehensive analysis of water quality data, phosphorus is the limiting nutrient in 53 percent of all lakes in the state, and in an additional 33 percent of the State, control of phosphorus could make it the limiting nutrient. (A limiting nutrient is that nutrient which is in least supply relative to the needs of the organism in question and thus serves to restrict or limit productivity). The extracts below are from the DEP procedures for performing the study.

Water Transparency - The transparency of the water column can, with the exception of naturally turbid lakes, be used as an indicator of lake productivity. The more productive a lake, the more algae in the water column, and the lower the transparency. A secchi disc is a common method of evaluating such transparency. The disc should be lowered through the water column until it is no longer visible and then raised until it reappears. This depth should be recorded in tenths of a meter.

Chlorophyll-a - Chlorophyll-a is an indicator of primary productivity. The higher the values, the more productive the ecosystem. Water for measurement of chlorophyll-a pigments should be collected from mid-secchi depth and filtered through a 47 mm diameter glass fiber filter (Gelman type A/E). The filters should then be placed in individual vials, packed in ice (dry ice if available) and held in the dark until delivery to the lab. They should then be frozen until extraction and quantitative measurements are performed.

Near Surface Phosphorus - Measured 1 meter below the surface in target area.