Infiltration and moisture movement in coastal sand dunes, Studland, Dorset, UK: Preliminary results

This paper reports the initial findings from a study of soil moisture withi n a series of three unlithified dune ridges at Studland, Dorset, on the sou thern coast of England. The infiltration and movement of moisture was monit ored at each dune crest, slack and mid position on windward and leeward fla nks, using capacitance probe technology. The mean moisture level in the dun es (excluding the troughs) was close to 7% and ranged between 1 and 18%. Th e rapidity and sensitivity of response of the dune sands to wetting and dra ining decreased markedly with depth over a distance of 1.3 m, and the behav iour patterns fell into three clear zones: 0-45 cm; 60-90 cm 110-150 cm. Th e uppermost was the most sensitive and experienced the greatest number of w etting and drying cycles. Differences in moisture regime also varied accord ing to the density of vegetation cover and position over the dune. On well vegetated sands the moisture was concentrated in the upper levels of the du ne, corresponding to the thin soil and the rhizosphere, and in unvegetated dunes moisture was retained at depth. Spatially, crests are the driest posi tions and small but persistent differences in moisture were recorded betwee n windward and leeward flanks which may reflect the movement of subsurface moisture along bedding planes. These observed patterns correspond well with existing knowledge of susceptibility to early diagenetic change within the vadose zone of dune sands.