Agricultural and forested land use impacts on floodplain shallow groundwater temperature regime

Given the importance of groundwater temperature to the biogeochemical health of aquatic ecosystems, a floodplain study was implemented to improve understanding of rural land use impacts on shallow groundwater (SGW) temperature. Study sites included a historic agricultural field (Ag) and bottomland hardwood forest (BHF), each with nine piezometers in an 80x80m grid. Piezometers were equipped with pressure transducers to monitor SGW temperature and level at 30min intervals during the 2011, 2012, 2013, and 2014 water years. The study is one of the first to utilize long-term, continuous, automated, in situ monitoring to investigate rural land use impacts on shallow groundwater temperatures. Average SGW temperature during the study period was 11.1 and 11.2 degrees C at the Ag and BHF sites, respectively. However, temperature range at the Ag site was 72% greater than at the BHF site. Results indicate a greater responsiveness to seasonal climate fluctuations in Ag site SGW temperature related to absence of forest canopy. Patterns of intra-site groundwater temperature differences at both study sites illustrate the influence of stream-aquifer thermal conduction and occasional baseflow reversals. Considering similar surface soil temperature amplitudes and low average groundwater flow values at both sites, results suggest that contrasting rates of plant water use, groundwater recharge, and subsurface hydraulic conductivity are likely mechanistic causes for the observed SGW temperature differences. Results highlight the long-term impact of forest removal on subsurface hydrology and groundwater temperature regime. Copyright (c) 2015 John Wiley & Sons, Ltd.