Constructed Climates

We know that even very small amounts of impervious surface in a watershed harms water quality, changes the fundamental nature of urban streams, kills aquatic organisms, reduces the pollution-sequestering abilities of these streams, and impairs our drinking water sources. We’ve seen that impervious surfaces connected directly to stormwater systems, which flow directly into streams, are the biggest water quality problem. Yes, farmers use fertilizers and produce concentrated animal wastes that sometimes run off into streams. They pay for fertilizers, and their economic constraints and task of feeding the immense human population demand that they use it. But suburban residents nurture lawns, fertilizing them simply out of habit with little functional purpose other than a ritualized, nonmarket pleasure. Along with atmospheric nitrogen falling on impervious surfaces, lawn fertilizers get washed away with stormwater into nearby streams. Construction sites cause problems, too, when grading and digging remove vegetation and living soils, exposing easily eroded dirt that washes into streams, burying bottom-dwelling organisms and ecosystems with sediment.

Improving water quality means filtering out molecules and sediments from every gallon of rainwater, an important job that forests perform naturally in rural areas, and open space can perform in urban areas. An important goal for cities could be to make certain that every stormwater drains empties into buffers and constructed wetlands without overwhelming their biological limitations. Relatively intact urban forests, soils, and constructed wetland ecosystems may be the most maintenance-free approach to handle the large water volumes involved in stormwater flows.

An interesting complication surrounding Durham’s stormwater situation, certainly repeated across the country in many jurisdictions, concerns the issue of scale. Durham’s water comes from reservoirs in the northern parts of the county, filled by more rural and forested areas, lacking many sediment and pollution problems. Some critical watershed lands have been purchased with county and state taxpayer money for that express purpose. However, the City of Durham’s stormwater drains into the Falls Lake and Jordan Lake reservoirs, with that water destined for drinking by citizens of other municipalities. Wake County is one of those municipalities, and it has a much higher household income. One can legitimately argue whether cash-strapped Durham citizens ought to spend money on constructed wetlands and urban open space to improve Wake County’s water quality, taking on changes in land use that might even reduce Durham’s tax base at a time when Durham County schools need more resources.