Surface water-groundwater interaction affects soil temperature distributions and variations in salt marshes

Abstract

Soil temperature is an important environmental factor affecting biogeochemical processes in salt marshes and further wetland ecological functions. This study conducted field investigation and numerical simulations to examine temperature distributions and variations in a creek-marsh section subjected to estuarine and meteorological forcing conditions. The results showed that periodic tidal inundation induced water and heat exchange across sediment-water interfaces and thus modified diurnal temperature variations in shallow soil layers caused by meteorological fluctuations. The combination of periodic tidal inundation and sediment-atmosphere heat exchange led to the formation of three characteristic soil temperature zones along the creek-marsh section: a high-elevation marsh zone with diurnal temperature variations influenced by meteorological fluctuations, a near-creek zone where tide-induced porewater circulations regulated soil temperatures, and a low-elevation and sloping zone where sediment-atmosphere heat exchange decreased with the reduced marsh elevation. Sensitivity analyses demonstrated that a larger hydraulic conductivity facilitated the porewater circulation and heat transport in the near-creek zone, enhancing temperature fluctuations. An increased soil thermal conductivity intensified vertical heat exchange across sediment-water-atmosphere interfaces and increased the effect of estuarine and meteorological conditions on soil temperature. This study highlights the importance of surface water-groundwater interaction on temperature variations and helps to understand thermodynamics-dependent biogeochemical processes in salt marshes.