Sulphate leaching from diffuse agricultural and forest sources in a large central European catchment during 1900–2010

Abstract

Using dynamic, mass budget, and empirical models, we quantified sulphate–sulphur (SO4–S) leaching from soils in a large central European catchment (upper Vltava river, Czech Republic) over a 110-year period (1900–2010). SO4–S inputs to soils with synthetic fertilisers and atmospheric deposition increased in the 1950s–1980s, then rapidly decreased (~80%), and remained low since the middle 1990s. The proportion of drained agricultural land rapidly increased from 4 to 43% between the 1950s and 1990s; then the draining ability of the system slowly decreased due to its ageing. Sulphate concentrations in the Vltava exhibited similar trends as the external SO4–S inputs, suggesting that they could be explained by changes in atmospheric and fertiliser S inputs. The available data and modelling, however, showed that (i) internal SO4–S sources (mineralization of soil organic S in the drained agricultural land), (ii) a hysteresis in SO4–S leaching from forest soils (a net S retention at the high S inputs and then a net release at the lowered inputs), and (iii) hydrology must be taken into account. An empirical model was then employed, based on parameters representing hydrology (discharge), external SO4–S sources (inputs by synthetic fertilisers and atmospheric deposition), and internal SO4–S sources (mineralization related to soil drainage). The model explained 84% of the observed variability in annual SO4–S concentrations in the Vltava river during 1900–2010 and showed that forest soils were a net sink (105kgha−1) while agricultural land was a net source (55kgha−1) of SO4–S during 1960–2010. In the late 1980s, forest soils changed from a sink to a source of S, and the present release of SO4–S accumulated in forest soils thus delays recovery of surface waters from acidification, while S losses from agricultural soils increase the risk of future S deficiency in S-demanding crops.