IMPACT OF LAND-USE AND SOIL TYPE ON THE CONTRIBUTION OF SULFATE TO TOTAL SULFUR IN DRAINAGE WATERS FROM UPLAND SOILS

Up to 50% of sulphur in soil solution leachate from a range of norther n temperate soils is present in a non-sulphate organic form. This comp onent must be accounted for in measurements of soil profile or catchme nt S budgets and the calculation of critical loads as S losses may be significantly underestimated. The effects of land use on the distribut ion and amounts of S in both solid and solution phases are complex. No single soil factor or simple combination of soil factors alone can ex plain the observed results. Thus C:S ratios and relative amounts of S leached in organic form probably depend not only upon soil chemical pa rameters, but also upon vegetation type, variations in atmospheric S d eposition and soil management history. Understanding the significance of S leaching to longer-term soil and water change, especially for upl and catchments, is further complicated by the need to take into accoun t hydrological pathways. Biological transformations and selective sorp tion properties of topsoil compared with subsoil with regards to S-i a nd S-o are important considerations as water drains through the soil p rofile.