Microenvironmental and seasonal variations in soil water content of the unsaturated zone of a sand dune system at Pinery Provincial Park, Ontario, Canada

Variations in soil water content have been determined for a soil chronosequence in a sand dune system at Pinery Provincial Park, southwestern Ontario, Canada. Samples were obtained from seven soil profiles along a 250 m succession from unvegetated dunes to dunes partially stabilized by C3 or C4 grasses to stable dunes supporting an oak-savannah ecosystem. This location provided the opportunity to determine the relative influences of topography, vegetation and seasonality on the volumetric soil–water content under temperate-humid conditions.Despite frequent and abundant precipitation, the soils were well drained at all times. Nevertheless, the sands typically retained a fraction of older soil water even following large rain events. The presence and type of vegetation had the greatest influence on soil moisture contents, both within a given profile and along the transition from unvegetated to forested dunes. Relative to unvegetated soils, grass roots facilitated more rapid infiltration of precipitation into deeper soil layers. During the growing season, however, soils in both forested and grassy areas became depleted of moisture in the rooting zone. The greater moisture retention of the organic-rich A-horizon and shading resulted in higher water contents of the uppermost soil layer in forested areas despite interception of some precipitation by the oak canopy. During warm summer months, the competing effects of increased evapotranspiration and periodic wetting accentuated differences in soil moisture content among sites.