Potomac Watershed Priority Lands Strategy: Conserving lands to benefit drinking water quality

by Weidner, Emily

Rapid development in the Potomac watershed – the conversion of forests to agricultural, suburban, and urban land — threatens water quality. Similarly, strategic land conservation can protect water quality. Inspired by examples of water purification through land conservation, the EPA Region 3 and the Potomac River Basin Source Water Protection Partnership (PRBSWPP) aim to prioritize areas of the Potomac watershed for conservation. To work toward this goal, I analyzed two questions: (1) How do land areas in the Potomac Watershed support stream water quality?; and (2) In a larger context, how should land conservation be prioritized to protect water quality?

To assess the relationship between land use and water quality, I created a regression model to correlate land characteristics including land use composition, land use pattern, and hydrological connectivity, with water quality. The final regression shows that buffer capacity (i.e. the average percentage of downstream forest area) has the largest impact on water quality, followed by urban saturation (i.e. average percentage of downstream urban area), and two estimates of soil loss and erodibility. I mapped the output of this regression analysis.

To identify priority lands for conservation, I developed a multi-object decision analysis (MODA) tool. I used the weighted averaging approach to combine a land parcel’s water quality protection value, water intake protection value, and ecological value, along with its vulnerability to future development. This resulted in a map showing areas of higher and lower conservation priority, which can be used to allocate funds for conservation, update local zoning to designate strategically located natural areas, assist developers in minimizing their environmental impact, and strengthen coalitions in developing a common understanding of the multiple benefits of land conservation.