Input–output analysis of macroelements in ICP-IM catchment area, Estonia

Using bulk deposition, throughfall, stemflow, soil infiltration, runoff water, litterfall data, ion mass budgets were calculated for a catchment area and for mature spruce and pine stands on it. The ions considered in mass balances were Na+, K+, Ca2+, Mg2+, SO42−, NO3−, NH4+, HCO3−, and H+. Corresponding fluxes for the budgets were calculated as an average for 6 years of studies (1995–2000). Annual input–output balances of all nutrients were positive at the plot-scale, so that leaching into soil water was less than the corresponding deposition load. Deposition of Ca, Mg, Na and S into soil by precipitation exceeded input through litterfall. A proton budget approach shows that the main soil buffering process is retention of sulphate, which clearly exceeds weathering. At the catchment-scale, input–output analysis shows essential output of cations due to weathering from the soil. A distinct change in input–output balance of sulphate during study period was evident. The retention of sulphur has been replaced by its release from the catchment area.