Procedure to Quantify Environmental Risk of Nutrient Loadings to Surface Waters
Nordberg, Tone Merete
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Agricultural production and human activities in a watershed can expose the watershed to environmental degradation, pollution problems, and a decrease in water quality if resources and activities within a watershed are not managed carefully. In order to best utilize limited resources and maximize the results with respect to time and money spent on nonpoint source (NPS) pollution control and prevention, the environmental risk must be identified so that areas with a higher quantified environmental risk can be targeted. The objectives of the research presented in this master thesis were to develop a procedure to quantify environmental risk of nutrient loadings to surface waters and to demonstrate the procedure on a watershed. A procedure to quantify environmental risk of nutrient loadings to surface waters was developed. The risk is identified as the probability of occurrence of a nonpoint source (NPS) pollution event caused by a runoff event multiplied by the consequences to a biological or chemical endpoint. The procedure utilizes the NPS pollution model ANSWERS-2000 to generate upland pollutant loadings to receiving waters. The pollutant loading impact on stream water quality is estimated using the stream module of Hydrologic Simulation Program FORTRAN (HSPF). The risk is calculated as the product of probability of occurrence of a NPS event and consequences of that event. The risk quantification procedure was applied to a watershed in Virginia. Total phosphorus (TP) loadings were evaluated with respect to resultant in-stream dissolved oxygen (DO) concentration. The TP loadings were estimated in ANSWERS-2000 then the consequences were estimated in HSPF. The results indicated that risk was higher for the smaller, more frequent storms indicating that these smaller, more frequent loading events represent a greater risk to the in-stream water quality and ecosystem than larger events. While the probability of occurrence of lower TP loading was higher because they were caused by smaller, more frequent storms, the consequences were less for the same events. The developed procedure can provide watershed stakeholders and managers with a useful tool to quantify the environmental risk a watershed is exposed to as a result of different land management and development scenarios. The scenarios can then be compared to identify a risk level that is considered acceptable. The procedure can also be used by policymakers to set a cap on the risk a certain activity can expose a watershed to.
- Masters Theses