NITRATE AND PHOSPHORUS RETENTION IN THE APPLE CREEK WATERSHED

The Apple Creek retention pond was designed by the City of Appleton engineers to retain nutrients contributed to the natural ecosystem from the watershed via urban run-off. In theory, through nutrient retention, the downstream ecosystem is more natural and pristine as a result of decreased nutrient loads. Nitrate and phosphorus are two plant nutrients found in fertilizers, detergents, and other man-made substances that run-off into urban streams, changing the diversity of both the plant and animal life of the watershed.

The effectiveness of nitrate and phosphorus retention during both base and storm flow was studied to determine the success of the pond at limiting ecological changes further downstream. The water flowing in and exiting, as well as the water within the pond was sampled weekly and following storm events to determine the effectiveness of the pond. The cadmium-reduction method was used to determine nitrate levels, while the phosphorus levels were found using a calibration curve made from standard solutions.

The research indicated that nitrate was mitigated during all flow events. The incoming nitrate levels were drastically reduced within the pond. The outflow had nitrate levels well below the drinking water standard set by the Environmental Protection Agency. In terms of phosphorus levels, the pond did not mitigate the nutrient during the base flow. However, the pond did mitigate the phosphorus pulse following the storm event. The levels of phosphorus in the outflow during both events were near the phosphorus concentrations of natural waters.

Phosphorus concentrations during storm events were increased suggesting urban run-off has a contribution to phosphorus levels. Nitrate levels during storm events, however, were decreased, which implies that nitrate was diluted by the increased volume of water. The research was conducted in October and November. A follow-up study in the spring, when fertilizer-use and storm frequency increase would support the findings from the fall months.