Human waste contains phosphorus, as do many of the products that we introduce into the wastewater system such as detergent and food waste. This wastewater is ultimately transported to a wastewater treatment plant (WWTP), where it is treated to meet target nutrient levels. The water is then reintroduced into the watershed. Not all of the nutrients can be removed, however, so the body of water into which the WWTP discharges may receive more nutrients than it would otherwise. These nutrients may be suspended in the water column or bound to sediment on the streambed.
Nutrients can also be introduced into urban streams via overland flow, when the water that does not infiltrate the soil flows downslope into a body of water and carries with it fertilizers and waste. Overland flow is especially likely to transport nutrients in urban watersheds, as there are contaminants from local roads and lawns.
A surplus of in-stream nutrients resulting in excess algae growth is known as eutrophication. This abundance of algae causes the stream to become depleted in oxygen and leads to the death of organisms within the ecosystem. Whereas most studies have focused on dissolved nutrients, this study examines the potential for sediment-bound nutrients contribute to eutrophication.
The Wissahickon Creek is a tributary of the Schuylkill River; its watershed includes parts of Philadelphia and Montgomery counties and the Abington WWTP is located along one of its branches. To determine identify the impact of the WWTP on the Wissahickon Creek, bed sediment sampling was conducted at several points upstream and downstream of the WWTP as well as on a stream that is not fed by any WWTP, Jenkintown Creek. Bioavailable phosphorus was extracted from all sediment samples with a calcium chloride solution, and was then quantified with inductively coupled plasma optical emission spectrometry (ICP-OES).
In doing so, we can achieve an improved understanding of the relative contributions of WWTPs and overland flow. This can help us identify high-risk areas along urban streams and better implement preventative measures.