Rural Land Use Impacts on Floodplain Shallow Groundwater Temperature

Abstract:

The temperature of shallow groundwater is tightly coupled to aquatic ecosystem health and rates of subsurface geochemical processes. Shallow groundwater temperatures are understood to respond to soil surface temperatures, which in turn depend on climate and land use. To address gaps in knowledge concerning land use impacts on shallow groundwater quality, a bookended floodplain study was implemented in Hinkson Creek Watershed, central Missouri, USA to better understand rural land use impacts on shallow groundwater temperature (SGW). Study sites included a historic agricultural field (Ag) and remnant bottomland hardwood forest (BHF). Each site included nine piezometers equally spaced in an 80 x 80 m grid. Piezometers were equipped with pressure transducers to monitor SGW temperature and water level at 30 minute intervals during the 2011, 2012, and 2013 water years. Average SGW temperature during the three water years was 11.3 °C at both the Ag and BHF sites. However, the temperature range at the Ag site was 63% greater than the BHF. Results indicate a greater responsiveness to seasonal climate fluctuations in the SGW temperature of the Ag site where there was an absence of forest canopy. Average SGW temperatures at the Ag site were 11.8, 11.1, and 10.9 °C, for piezometer rows located 10, 50, and 90 m from the stream, respectively. Average shallow groundwater temperatures at the BHF site were 11.0, 11.8, and 11.2 °C, for piezometers located 10, 50, and 90 m from the stream, respectively. The range of SGW temperatures at the Ag site also decreased with increasing distance from stream, suggesting a distinct stream influence on Ag site SGW temperature. The 63% greater SGW temperature range indicates the Ag site may contribute warmer water to the stream, relative to the BHF. Results hold broad implications for land managers seeking to mitigate the impact of land use on floodplain processes and groundwater quality.