Impacts of land-use change on groundwater supply: Ecosystem services assessment in Kona, Hawaii

Payments for watershed management link upstream inhabitants whose actions affect water resources with downstream water users. This paper evaluates the effect of plausible shifts in watershed land use on hydrologic services on the Kona coast of Hawai'i Island by measuring vegetation effects on hydrologic fluxes, modeling land-use change impact on the water-supply aquifer, and evaluating the local water department's associated pumping expenses. Transitions between native and plantation forest will have a 25-40% greater impact on the aquifer than the transition from pasture to either forest type. However, for all transitions, the value to the water department is just 2-5% of the opportunity cost to landowners. To provide context for these findings, the effects of these land transitions on carbon storage, provision of native bird habitat, and land stewardship are assessed. Estimates show that delivery of other services does not always increase when water services increase and suggest that the value of impacts to these other services are greater than effects on water. In Kona, as in any watershed payment project, the particular physical and social context determines which services are valuable.