SMALL SCALE WATER QUALITY MONITORING IN AN URBAN WATERSHED

Several small scale water quality studies were conducted in a stressed urban watershed, the Pennypack Creek, near Philadelphia. The first study examined water quality changes from a storm pipe to a second point in the buffer zone. Buffer zones are areas of restricted development next to a stream. Buffer zones can improve bank stability and increase infiltration. However, the importance of buffer zones for improving water quality has not been documented. The second study evaluated the effects of upstream ponds on temperature in tributaries and Pennypack Creek. Warm temperature is a commonly cited habitat threat in urban streams. The third project was a comparison of urban and natural spring discharge at the same location. In each of the studies, continuous monitoring was conducted so that the water quality response to storm events was measured over time.

One theme that emerged from these small scale studies is that overland flow is as important as point discharge at the stormpipe in affecting stream water quality. Both concentrations and arrival times of conductive water and nutrients were similar at the storm pipe and in drainages located 100-300 m along the buffer zone. Although temperatures were 1-4 degrees C warmer in upstream ponds, the higher temperatures rapidly dissipated downstream in the tributary before the water reached Pennypack Creek. Finally, water level increased at the onset of storm events, showing the importance of overland flow. Thus, overland flow homogenizes the water quality, such that the impact doesn't just begin at the point of stormpipe discharge. However, urban discharge generally had higher conductivity and more variability than natural spring discharge measured at the same location.

An implication of this work is that effective Best Management Practices include those that increase infiltration and reduce overland flow, such as infiltration galleries and wetlands, would have more effect on water quality. More detailed monitoring – continuous data on smaller scale – improved understanding of how urbanization affects the watershed.