Urban growth boundaries are created by governments in an effort to concentrate urban development — buildings, roads and the utilities that support them — within a defined area. These boundaries are intended to decrease negative impacts on people and the environment. However, according to a Penn State researcher, policies that aim to reduce urban sprawl may be increasing water pollution.
“What we were interested in was whether the combination of sprawl— or lack of sprawl — along with simultaneous agriculture development in suburban and rural areas could lead to increased water-quality damages,” said Douglas Wrenn, a co-funded faculty member in the Institutes of Energy and the Environment.
These water quality damages were due to pollution from nitrogen, phosphorus and sediment, three ingredients that in high quantities can cause numerous environmental problems in streams, rivers and bays. As a part of the EPA’s Clean Water Act (CWA), total maximum daily loads (TMDL) govern how much of these pollutants are allowed in a body of water while still meeting water-quality standards.
According to Wrenn, an associate professor in Penn State’s College of Agricultural Sciences, one of the reasons anti-sprawl policies can lead to more water pollution is because higher-density development has more impervious surfaces, such as concrete. These surfaces don’t absorb water but cause runoff. The water then flows into bodies of water, bringing sediment, nitrogen and phosphorus with it.
Secondly, agriculture creates considerably more water pollution than low-density residential areas. And when development outside of the boundaries that could replace agriculture is prevented, the amount of pollution that could be reduced is lost.
“If you concentrate development inside an urban growth boundary and allow agriculture to continue business as usual,” Wrenn said, “then you could actually end with anti-sprawl policies that lead to an increase in overall water quality damages.”
Wrenn said it is important for land-use planners in urban areas and especially in urbanizing and urban-fringe counties to understand this.
The EPA’s water quality regulation is divided between point source and nonpoint source polluters. Point source polluters include wastewater treatment facilities, big factories, consolidated animal feeding operations and stormwater management systems. Nonpoint sources are essentially everything else. And the CWA does not regulate nonpoint sources, which includes agriculture.
“When it comes to meeting TMDL regulations, point source polluters will always end up being responsible,” he said. “They are legally bound to basically do it all.”
Wrenn said point source polluters are very interested in getting nonpoint source polluters, specifically agriculture, involved in reducing pollution because their cost of reduction is usually far less expensive and often times more achievable.
“What our research has shown is that land-use regulation where land-use planners have some ability to manage where and when land-use development takes place, this gives some indication that land-use policy can be a helper or a hindrance to meeting these TMDL regulations,” Wrenn said.
Wrenn et al. (2019) Price based policies for managing residential development: Impacts on water quality. Resource and Energy Economics. DOI: https://doi.org/10.1126/sciadv.aax5343
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