How do we measure water quality regulation services?


We defined water quality regulation (WQR) as the capacity of a forested ecosystem to maintain the concentration of pollutants within legal drinking water standards. In this case, standards are seen as indicators of collective social demand for a given level of water quality. At HBEF, concentration thresholds for two pollutants were based on New Hampshire drinking water standards (nitrate, chloride). Additional thresholds for sulfate and pH were taken from U.S. Environmental Protection Agency (EPA) secondary standards. Standards at other sites were selected from equivalent state, provincial and national standards. Water quality data were available on a periodic (monthly to semi-weekly) time step. We were therefore able to quantify the percentage of measurement days in each year that concentrations remained within each of the legal thresholds for drinking water (see Figure 1, nitrate at Hubbard Brook). In addition to analysis of individual pollutants, data pertaining to concentrations of several nutrients (nitrate, ammonium, phosphate) were translated to a standard measure of eutrophication potential (kg N-eq) using weightings derived from the U.S. EPA Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts or TRACI (Bare et al. 2003). The ratio of the eutrophication potential of stream water to the eutrophication potential of precipitation was then calculated as measure of the forest’s capacity to absorb and remediate nutrient pollution (see Figure 2, Hubbard Brook).

FEST case studies involving this service include quantification of WQR at Hubbard Brook and Turkey Lakes, as well as the inclusion of WQR metrics in a tradeoff analysis.

Figure 1

Figure 2