Effects of groundwater pumping on the sustainability of a mountain wetland complex, Yosemite National Park, California

•Fens are perennially saturated, peat-accumulating, groundwater dependent ecosystems.•We quantified/modeled the effects of groundwater pumping on fens.•Pumping had the greatest effect on the water table in years with low snowpack.•Vegetation has changed to species in tolerant of saturated soils.•Our model predicts water level changes from pumping and assists water managers.

Study RegionWe analyzed the effects of groundwater pumping on a mountain wetland complex, Yosemite National Park, California, USA.Study FocusGroundwater pumping from mountain meadows is common in many regions of the world. However, few quantitative analyses exist of the hydrologic or ecological effects of pumping.New Hydrological Insights for the RegionDaily hydraulic head and water table variations at sampling locations within 100 m of the pumping well were strongly correlated with the timing and duration of pumping. The effect of pumping varied by distance from the pumping well, depth of the water table when the pumping started, and that water year's snow water equivalent (SWE). Pumping in years with below average SWE and/or early melting snow pack, resulted in a water table decline to the base of the fen peat body by mid summer. Pumping in years with higher SWE and later melting snowpack, resulted in much less water level drawdown from the same pumping schedule. Predictive modeling scenarios showed that, even in a dry water year like 2004, distinct increases in fen water table elevation can be achieved with reductions in pumping. A high water table during summers following low snowpack water years had a more significant influence on vegetation composition than depth of water table in wet years or peat thickness, highlighting the impact of water level drawdown on vegetation.