Groundwater Provides and Receives Hydrologic System Services.

The concept of Environmental or Ecologic System Services (ESS) is well established in the technical, social science, and policy literatures, and is useful for assessing economic and/or social values of natural resources, and identifying potential impacts of planned or proposed management decisions. The ESS concept has been applied widely to water resources and aquatic habitats, for example, valuing coastal wetlands for mitigating hurricane damage, widening or raising river levees to reduce flood risk, and managing catchments to maximize water delivery. I propose that the concept of Hydrologic System Services (HSS) be considered when assessing the influence and value of hydrologic systems, including groundwater resources. HSS include benefits that apply to human populations and activities (much like ESS), but HSS also include hydrologic functions, associated with flows and/or storage, that are beneficial to other hydrologic systems and/or nearby habitats. Here are a few examples that illustrate the HSS concept, applied first to surface water, and then to groundwater. Recent surface water management projects were designed to increase the variability of controlled river and stream flows. For example, high-discharge floods were created on the Colorado River, downstream of the Glen Canyon Dam, with the goal of delivering gravel and sand trapped in tributaries into the main channel, restoring bars that had been lost after years of relatively steady flows, thereby improving recreational opportunities and riparian habitat. Dam removal is a more extreme case of restoring the range and complexity of natural flows, thereby improving HSS. Enhancing coastal and riparian wetlands can help to reduce nutrient and sediment export from basins, benefitting adjacent aquatic habitats,