Relating Land Use Factors to Phosphorus Runoff Concentrations within the Northrup Creek Watershed using GIS

Abstract

Efficiently and accurately measuring storm event non-point source pollution contributing to streams and lakes from various land uses is one of the more difficult tasks in watershed management. Many physical variables go into the input and export of nutrients, making it difficult to identify source contamination areas that may lead to reduced stream quality and increased eutropication of water bodies. A major drawback to rehabilitating these impacted streams is being able to easily identify the specific land use types or source areas. Designing a simple method with adequate precision and consistent outcomes to help identify sources of nutrient export would increase efforts to remediate these locations as well increase efficiency. This study evaluates (1) the use of geographical information system (GIS) and stream segmentation to identify the correlation between land use variables and total phosphorus concentrations in storm events, (2) the ability of land use variables in predicting storm event runoff phosphorus concentrations, and (3) identifies specific high and low risk areas of phosphorus contribution throughout Northrup Creek, a small watershed in Rochester, NY. Correlation and modeling results show that an increase in vegetative lands, including forested, shrub, and grasslands, that are in close proximity to the creek have a tendency to decrease the amount of total phosphorus (TP) in runoff stormwater. Increases in low residential lands, including barren and open lands uses, have a tendency to decrease the amount of TP in runoff stormwater as well. Two variable groupings, individual land uses and individual land uses 90 meters from the creek, have the strongest correlations with total phosphorus runoff concentrations during storm events. Segmental risk ranking results suggest Segments 3 and 8 of the Northrup Creek Watershed study have the highest average storm event TP runoff concentrations and thus pose the greatest risk to phosphorus contribution to the creek. Noted specific land uses identified in Segment 3 and 8 include a public golf course, barren developmental lands, and inputs from the Erie Canal. Additional physical processes not analyzed were have found to influence the runoff concentrations calculated within the study. Non-uniform storm rainfall duration and rates coupled with antecedent soil moisture content throughout the segments are very probable influences on the amount of phosphorus entering the creek at the various segments. A lower runoff residence time created by ponds and the low sloping areas is suggested to have aided in the settling of particulate phosphorus to the creek bed between segments, influencing a decrease of runoff concentrations during storm events. Lastly, the introduction of artifact phosphorus back into the stream system, created by the former STP, through turbid creek conditions is suggested to increase of TP concentrations downstream.