Impact of land use and soil type on the contribution of sulphate to total sulphur in drainage waters from upland soils

Up to 50% of sulphur in soil solution leachate from a range of northern temperate soils is present in a non-sulphate organic form. This component must be accounted for in measurements of soil profile or catchment S budgets and the calculation of critical loads as S losses may be significantly underestimated. The effects of land use on the distribution and amounts of S in both solid and solution phases are complex. No single soil factor or simple combination of soil factors alone can explain the observed results. Thus C:S ratios and relative amounts of S leached in organic form probably depend not only upon soil chemical parameters, but also upon vegetation type, variations in atmospheric S deposition and soil management history. Understanding the significance of S leaching to longer-term soil and water change, especially for upland catchments, is further complicated by the need to take into account hydrological pathways. Biological transformations and selective sorption properties of topsoil compared with subsoil with regards to Si and So are important considerations as water drains through the soil profile.