Source water contributions and hydrologic responses to simulated emerald ash borer infestations in depressional black ash wetlands

Forested wetlands dominated by black ash ( Fraxinus nigra ) are currently threatened by the rapid expansion of the exotic emerald ash borer (EAB; Agrilus planipennis , Coleoptera: Buprestidae) in North America, and very little is known about the hydrology and ecology of black ash wetlands. The ecohydrological response of forested wetlands following a canopy disturbance has the potential to affect critical ecosystem services, and the degree of this effect may largely depend on the wetland's hydrogeological setting. The main objectives of this study were to characterize the hydrologic connectivity of uninfested black ash wetlands and evaluate the water table response to a simulated EAB disturbance. We hypothesized that black ash wetlands in northern Michigan were (a) seasonally connected to, and derived the majority of their water from groundwater, and (b) wetland water tables would be elevated following a simulated EAB infestation due to decreased transpiration with the loss of black ash. The results indicate that the black ash wetland sites received most of their water from groundwater discharge. Significantly smaller site transpiration fluxes and significantly slower rates of drawdown were detected during the growing season in the girdled and ash‐cut treatment sites, and these responses collectively produced significantly elevated wetland water tables when compared to control sites in the latter portions of the growing season. However, the wetlands' strong connection with groundwater sources likely buffered the magnitude of hydrological responses associated with the loss of black ash from the landscape.