Abstract
We developed a cost-based methodology to assess the value of forested watersheds to improve water quality in public water supplies. The developed methodology is applicable to other source watersheds to determine ecosystem services for water quality. We assess the value of forest land for source water mitigation of total organic carbon (TOC) through the use of linked watershed and reservoir simulation models and cost-based valuation economics. Watershed modeling results indicated that expected urbanization will increase TOC loads to Converse Reservoir (Mobile, AL). Reservoir model results indicated that future median TOC concentrations increased by 1.1 mg·L−1 between 1992 and 2020 at the source water intake. Depending upon dynamic reservoir TOC concentrations, additional drinking water treatment with powdered activated carbon (PAC) often is necessary between May and October to comply with Safe Drinking Water Act regulations. The cost for additional treatment was calculated using minimum and maximum volume treated with simulated TOC concentrations at the source water intake. Daily simulated TOC concentrations for the base scenario using 1992 land cover (3% urban) were compared with simulated TOC concentrations following forest to urban land conversion predicted in the watershed by 2020 (22% urban). The daily cost for additional drinking water treatment with PAC was calculated if simulated TOC concentrations exceeded 2.7 mg·L −1 . The mean increase in daily treatment costs between base and future scenarios ranged from $91 to $95 per km 2 per day for forest land water purification ecosystem services.
Highlights
Protecting watersheds that are a source for public water supply can generate large benefits
While our economic analysis focuses on total organic carbon (TOC), analysis of total N (TN) and total P (TP) were necessary since these nutrients support algae growth, simulated during reservoir modeling, which is a form of C important to the overall TOC budget
TOC concentrations between May and October are important since additional drinking water treatment is positively related to elevated water temperatures
Summary
Protecting watersheds that are a source for public water supply can generate large benefits. Many municipalities, such as New York, NY, Boston, MA, and Portland, OR, actively purchase land in their source water catchments to minimize potential water quality problems and avoid costly drinking water treatment plant upgrades [1]. Water related ecosystem services provided by forested landscapes support many beneficial uses and public goods, including improved water quality. While the water quality services from minimally impacted ecosystems are generally appreciated, the actual economic value has been rarely quantified within an existing cost structure related to drinking water quality. This research estimates an economic value ($ per km2) for the ecosystem services provided by a forested landscape for mitigation of total organic carbon, a contaminant to drinking water treatment. In addition to the specific value we estimate for a watershed in south Alabama, we present a cost-based methodology that is usable within the United States or, for that matter, globally
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