Groundwater-dependent ecosystems (GDEs) include wetlands, lakes, rivers, springs, estuaries and off-shore marine environments, subterranean ecosystems, and some areas of specific terrestrial vegetation such as phreatophytes, as well as the many species that rely on groundwater to meet part or all of their water requirements (Brown et al. 2010; Eamus and Froend 2006; Sinclair Knight Merz 2011). At the same time, groundwater discharging to GDEs often is tapped or altered to meet human needs, including municipal, agricultural, domestic, and industrial water supply.
A key to protecting GDEs is to determine the amount, timing, and quality of discharging groundwater that they need, and to set limits to what is available for other uses (Aldous and Bach 2014). This requires a robust methodology for determining the groundwater needs of ecosystems that is straightforward to implement, monitor, and adapt to a variety of management situations. The Nature Conservancy and the U.S. Forest Service are developing such a method to make management decisions related to groundwater development that are protective of GDEs and seek to meet societal needs. This method is termed Environmental Flows and Levels (EFL), and is defined as follows (eFlowNet 2007):
“Environmental flows and levels describe the quantity, quality, timing and range of variability of water flows and levels required to sustain or restore freshwater and estuarine ecosystems and the functions and services they provide. Environmental flows and levels include instream flows, geomorphic and flood flows, groundwater levels, and lake and wetland levels established for environmental purposes”.
This method was developed and tested in three groundwater-dependent wetlands (fens) in a grazing allotment on the Fremont-Winema National Forest, Oregon. Each of these steps is summarized below in the context of those field sites. Much of the data collection, modeling, and analyses are conducted simultaneously so that hydrogeologic results inform ecological analyses, and vice versa. The method allows an EFL to be determined using differing levels of hydrogeologic analysis, depending on site complexity, significance of the management action, and level of uncertainty.
Photo credit: Allison Aldous/TNC