Segment Analysis of the Mill Creek Watershed, Monroe County, New York

Mill Creek is a small watershed of the Lake Ontario coastal plain in Monroe County, New York. The watershed, covering approximately 16 square kilometers, has a variety of land uses ranging from dense urban within the Village of Webster to small agricultural plots. With the observation of persistently poor water quality, Mill Creek is indicated as having some level of impairment. To address this issue, and assist local agencies in the implementation of best management practices, a segment analysis study is underway. Segment analysis is an effective tool for evaluating the impact of non-point source pollution (NPSP) to streams. The segment analysis approach uses target analyte concentration increases to suggest segments of concern for NPSP within a watershed. Preliminary studies have shown that total phosphorus concentrations are seen to increase in at least three segments. Concentrations of TP are typically found to range from less than 90 ug/L in low impact segments to over 320 ug/L in segments of concern with TP increases within a segment moving downstream approaching 90 ug/L. As is often found, the segments of concern are linked to land uses within the segment. In this case, and as shown in similar regional watersheds, a correlation of r2 > 0.9 is seen when comparing the increase in TP within a segment to the land use change over a 5-year period within the same segment. Ongoing studies are evaluating the source areas within the segments of concern using a segment analysis approach within the stormwater collection systems.