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THE COMPARISON OF TWO WATERSHEDS USING A WATERSHED NUTRIENT LOADING MODEL
Citation:
FRICK, W. E., A. C. SIGLEO, AND L. M. PRIETO. THE COMPARISON OF TWO WATERSHEDS USING A WATERSHED NUTRIENT LOADING MODEL. Presented at Second Interagency Conference on Research in the Watersheds, Otto, NC, May 16 - 18, 2006.
Impact/Purpose:
A main objective of this task is to combine empirical and physical mechanisms in a model, known as Visual Beach, that
â— is user-friendly
â— includes point and non-point sources of contamination
â— includes the latest bacterial decay mechanisms
â— incorporates real-time and web-based ambient and atmospheric and aquatic conditions
â— and has a predictive capability of up to three days to help avert potential beach closures.
The suite of predictive capabilities for this software application can enhance the utility of new methodology for analysis of indicator pathogens by identifying times that represent the highest probability of bacterial contamination. Successful use of this model will provide a means to direct timely collection of monitoring samples, strengthening the value of the short turnaround time for sampling. Additionally, in some cases of known point sources of bacteria, such as waste water treatment plant discharges, the model can be applied to help guide operational controls to help prevent resulting beach closures.
Description:
Monitoring data, collected from the Yaquina River, Oregon, from 1999 through 2002 were used as the basis for developing the nutrient flux model as part of a larger agency program for quantifying nutrient processes. The PNWL nitrate loading model indicates that the nitrate load is generally a direct function of water discharge normalized to drainage area. The relationship is least accurate during the first major storm event of the water year in the fall. The dissolved nitrate concentrations during the first fall storm event tend to exceed those of the predicted nitrate values possibly due to the washout of nutrients during the first storm. The nitrate source in the freshwater reaches of Oregon coastal rivers is due primarily to nitrogen leaching from litter fall in alder stands in the surrounding watershed. The highest concentrations occurred during winter periods of higher runoff, whereas the lowest concentrations occurred during late summer and low river flow. To test the predictive ability of the model for other Oregon coastal rivers, empirical data from the nearby Alsea River were compared with the nitrate concentrations predicted by the model. The results indicated that the model provides a reasonable first estimate of nitrate concentrations from water discharge data, which may then be used to calculate nutrient loads. However, the model appears to predict slightly higher values than expected for the Alsea. Differences between predicted and observed concentrations may be reduced by adjusting the model coefficients. However, they may reflect watershed differences, not just statistical variations. For example proximate source areas may be more important than distal ones in determining nitrate concentrations.