Effects of Deforestation on Water Flow in the Vadose Zone

Heye Reemt Bogena,Inge Wiekenkamp,Harry Vereecken,Johan Alexander Huisman

doi:10.3390/w12010035

Abstract

The effects of land use change on the occurrence and frequency of preferential flow (fast water flow through a small fraction of the pore space) and piston flow (slower water flow through a large fraction of the pore space) are still not fully understood. In this study, we used a five year high resolution soil moisture monitoring dataset in combination with a response time analysis to identify factors that control preferential and piston flow before and after partial deforestation in a small headwater catchment. The sensor response times at 5, 20 and 50 cm depths were classified into one of four classes: (1) non-sequential preferential flow, (2) velocity based preferential flow, (3) sequential (piston) flow, and (4) no response. The results of this analysis showed that partial deforestation increased sequential flow occurrence and decreased the occurrence of no flow in the deforested area. Similar precipitation conditions (total precipitation) after deforestation caused more sequential flow in the deforested area, which was attributed to higher antecedent moisture conditions and the lack of interception. At the same time, an increase in preferential flow occurrence was also observed for events with identical total precipitation. However, as the events in the treatment period (after deforestation) generally had lower total, maximum, and mean precipitation, this effect was not observed in the overall occurrence of preferential flow. The results of this analysis demonstrate that the combination of a sensor response time analysis and a soil moisture dataset that includes pre- and post-deforestation conditions can offer new insights in preferential and sequential flow conditions after land use change.

Highlights

Forests play a crucial role in the partitioning of water into surface flow, subsurface flow, and evapotranspiration
The soil moisture in the treatment area deviated more from the soil moisture fewer events per month during the control period than after partial deforestation. This was related in the reference area after the partial deforestation
The differences in soil moisture dynamics were to the fact that 72 events were omitted during the control period, whereas only one event was not larger in the dryer period

Summary

Introduction

Forests play a crucial role in the partitioning of water into surface flow, subsurface flow, and evapotranspiration Forest related processes, such as plant transpiration, root water uptake, and infiltration, affect the water fluxes aboveground and beneath the subsurface. A large database with paired and single catchment studies that analyze changes in hydrological functioning in response to deforestation has been created [4,5,6]. Highly relevant, such paired catchment studies often focus on discharge and do not look in detail at the effects of vegetation change on soil moisture patterns and subsurface water flow. Soil moisture storage and water flow in the vadose zone (i.e., the unsaturated zone of the subsurface) are of crucial importance to understand energy and water exchange between the surface and the atmosphere (e.g., [7,8,9,10,11,12,13]), and infiltration and subsurface stormflow (i.e., fast lateral subsurface flow of water) play a crucial role in discharge generation (e.g., [14,15])

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