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Keywords:

  • hedgerows;
  • water flux;
  • saturated and unsaturated zone;
  • shallow groundwater;
  • reverse hydraulic gradient

Abstract

Linear vegetation structures such as hedge tree networks (hedgerows), shelterbelts, and isolated trees play a major role on soil water transfer. Our objective is to evaluate the influence of a bottomland hedgerow on water flux in the saturated and unsaturated zones. Soil water movement was investigated in a hillslope crossed by a hedgerow using total water-potential gradients and shallow groundwater dynamics. Results of a dry year were presented by Ghazavi et al. (2008). In this study, we analyse a wet year and then compare the two contrasting years (dry and wet). During the 2 years, the soil located at the vicinity of the hedgerow developed a drier status than the surrounding soils. Water flux in the unsaturated zone was directed towards the hedgerow for a longer period during the dry year than the wet year. The duration of delayed rewetting of the soil decreased from 3 months for the dry year to 1 month for the wet year. Variation in water storage calculated over the study period was highest near the hedgerow and lowest far from the hedgerow.

In the hillslope studied, hedgerow and stream proximity controlled water transfer. It is clear that the hedgerow controlled water transfer in the unsaturated zone throughout the year, except for the period when the soil profile was fully saturated. First, hedgerows control water transfer by increasing lateral transfer, which is related to high soil water potential gradients in its vicinity. These processes may increase capillary rise and decrease groundwater recharge near the hedgerow. Second, reverse hydraulic gradient (upward flux of water) occurred during the period of lowest groundwater level, mainly because of groundwater and stream connectivity. Processes related to hedgerow presence, such as delayed soil rewetting and flow towards the hedgerow need to be considered to quantify the impact of linear vegetation structures on water flux. Copyright © 2010 John Wiley & Sons, Ltd.