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Chemical Monitoring of a Primary Water Supply: Lake Pelham in Culpeper, Virginia
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Over the last decade there has been an increase in public and government concern over water quality in the United States, especially water bodies that are sources of drinking water. A study conducted by the United States Geologic Survey (USGS) and the National Water-Quality Assessment (NAQWA), has indicated that nutrient concentrations in streams and groundwater in basins with significant agricultural or urban development are substantially greater than naturally occurring or “background” levels (Dubrovsky, 2010). Various academic studies throughout the United States have demonstrated that many water sources are in danger of being severely polluted, with accelerated eutrophication occurring in many lakes. Specifically, the EPA, who has the task of monitoring these water bodies along with the USGS, has tightened the regulations about point and non-point sources of pollution, in an attempt to reduce the amount of eutrophication in sensitive water bodies. Lake Pelham, located in Culpeper, Virginia has experienced an increase in water quality problems; specifically an increase in nutrients in the lake, causing significant algae blooms. Increasing concern over the amount of nutrients found in lakes, rivers, streams and other water ways (i.e. the Chesapeake Bay) have yielded an increase in the amount of money spent on studies, both at the Federal (EPA) and state level (DEQ). Furthermore, several counties and towns have taken it upon themselves to conduct monitoring programs on their local water sources, to ensure the health of potable water as well as the health of their constituents. The objectives of this research program for Lake Pelham were to: 1.) conduct a literature review of similar surface water systems to highlight current trends in nutrient concentrations 2.) measure and monitor the total phosphorus and nitrogen levels in the lake and examine relationships between nutrient concentrations, water temperature, dissolved oxygen content, and pH and 3.) outline future actions for monitoring Lake Pelham and possible preventive actions for nutrient control. In 2010, the interaction between pH, temperature, nitrogen and phosphorous was investigated. The total nitrogen concentration of Lake Pelham is highly dependent on the leachate entering the lake. Large increases in nitrogen occur during even the smallest rainfall events, suggesting nitrogen is entering the lake from the surrounding environment. The current study indicates that the mean annual average total nitrogen concentration of the lake is approximately 10 mg/l. This value provides a baseline which can be used while the total nitrogen is being monitored over the next several years. In previous years, an increase in pH values (< 1.0 between test dates) was associated with algal blooms in the lake and necessitated the treatment with copper sulfate. Between 1992 and 2010, the nitrogen concentration doubled and the phosphorus concentration increased 7 fold. Algae concentrations and pH fluctuation decrease as the water temperature decreases. Similar to nitrogen, phosphorus concentrations in the lake increase with rainfall events suggesting a relationship to runoff and/or leeching entering from the surrounding watershed. Even during lower water levels, similar to what occurred in August of 2010, when the lake was 15 inches below peak level, a small rainstorm had a large impact on the amount of phosphorus entering the lake requiring the addition of copper sulfate. The trophic state for Lake Pelham was calculated from the average values of the total phosphorus measured in the lake over 2010 and the Secchi disk readings from the same time period. The Tropic State Index (TSI) was calculated to be 59.75 when using the total concentration of phosphorus in Lake Pelham. The TSI calculated from the Sechhi Disk values was 54.5. This gives a average TSI value of 57.1, which indicates that the lake is in a eutrophic state. This was the first attempt at determining the trophic state of Lake Pelham. The study is an important first step for understanding nutrient loading in Lake Pelham and applying protective measures to preserve water quality. Similar to a study conducted in King County, Washington, long term data (decade or more) and in depth statistical analysis will be needed to explain the seasonal variability of Lake Pelham.