Many older cities on the east coast of the U.S., including Lancaster PA, have a combined sewer system. This type of sewer system funnels wastewater from residential and commercial urban areas to a treatment facility where the water can be filtered and cleaned before being returned to the watershed. Rainwater also enters the same system. During large rain events, rainwater can overwhelm the sewer system, which leads to untreated rainwater and raw sewage entering the watershed. This is a particularly large problem for Lancaster and other cities in the area because we are a part of the Chesapeake Bay Watershed, which is known for its ecological uniqueness and economic importance.
The city of Lancaster has taken a number of initiatives to reduce the amount of stormwater runoff that enters the sewer system. Over the last few years, urban parks have been renovated to include features that increase infiltration of stormwater such as rain gardens and permeable basketball courts and a number of alleys and parking lots have been renovated with permeable pavement. One of the important initiatives of the City of Lancaster is to increase the urban tree canopy since trees are known to facilitate the infiltration and absorption of rainwater.
Many factors are taken into consideration when deciding which trees to plant in the urban environment. Arborists are well aware of which trees to grow in confined spaces and which ones can be left for decades. We also know which trees lift sidewalks, provide deeper shade, tolerate pollution and are preferred by the public for their esthetic beauty. While these are all important factors to consider when choosing a street tree, there are additional physiological and hydrological parameters to consider to maximize the mitigation of stormwater runoff by trees.
This research addresses the two following questions:
1)Which of the commonly planted street trees intercept the greatest amount of rainwater? 2)Which of these species transpire the most rainwater following a storm?
The Gotsch lab has recently started a long-term project in collaboration with the City of Lancaster. The aforementioned questions will provide an important base of information that we can then use to expand our understanding of the ecohydrological benefits of different street trees to mitigating stormwater runoff. Results of this research will be beneficial to urban planners as they work to try to mitigate the effects of larger and more frequent rain events, which are projected for our region.
This research program began in the classroom. Students in Bio 371: Applied Research in Ecophysiology built the sap flow sensors (to measure transpiration), through fall gauges and stem flow gauges (to measure interception) in the lab and they installed them in the field at the end of the semester. We are currently seeking funding for wireless transpiration sensors that can be deployed in tight spaces throughout the city.