Friday, June 9, 2023

Estimating the benefits of stream water quality improvements in urbanizing watersheds: An ecological production function approach

Streams are under significant ecological stress in rapidly urbanizing watersheds around the world. However, estimates of the combined use and nonuse benefits of improving urban stream water quality, which are critical for guiding policy, are generally lacking. To address this gap, Roger H. von Haefen, George Van Houtven, Alexandra Naumenko, Daniel R. Obenour, Jonathan W. Miller, Melissa A. Kenney, Michael D. Gerst and Hillary Waters develop an ecological production framework that is tailored to urban stream stressors, conditions, human uses, and preferences in the Piedmont ecoregion of the United States and that allows analysts to translate changes in measurable water quality indicators into monetary benefit estimates. An application of the framework to illustrative policy scenarios in an urban county of North Carolina indicates that these benefits can be substantial, and it provides a template for expanding the methods and findings geographically.

Streams in urbanizing watersheds are threatened by economic development that can lead to excessive sediment erosion and surface runoff. These anthropogenic stressors diminish valuable ecosystem services and result in pervasive degradation commonly referred to as “urban stream syndrome.” Understanding how the public perceives and values improvements in stream conditions is necessary to support efforts to quantify the economic benefits of water quality improvements. The authors develop an ecological production framework that translates measurable indicators of stream water quality into ecological endpoints. Their interdisciplinary approach integrates a predictive hierarchical water quality model that is well suited for sparse data environments, an expert elicitation that translates measurable water quality indicators into ecological endpoints that focus group participants identified as most relevant, and a stated preference survey that elicits the public’s willingness to pay for changes in these endpoints. To illustrate our methods, we develop an application to the Upper Neuse River Watershed located in the rapidly developing Triangle region of North Carolina (the United States). Their results suggest, for example, that residents are willing to pay roughly $127 per household and $54 million per year in aggregate (2021 US$) for water quality improvements resulting from a stylized intervention that increases stream bank canopy cover by 25% and decreases runoff from impervious surfaces, leading to improvements in water quality and ecological endpoints for local streams. Although the three components of our analysis are conducted with data from North Carolina, we discuss how their findings are generalizable to urban and urbanizing areas across the larger Piedmont ecoregion of the Eastern United States.

by Roger H. von Haefen (, George Van Houtven, Alexandra Naumenko, Daniel R. Obenour, Jonathan W. Miller, Melissa A. Kenney, Michael D. Gerst and Hillary Waters 
Proceedings of the National Academy of Sciences
Volume 120, Number 18; accepted January 20, 2023; published by April 24, 2023

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