Interactions of atmospheric deposition with coniferous canopies in Estonia.

Throughfall and open field bulk precipitation were measured at three coniferous sites during 1995-2002 in the framework of ICP Integrated Monitoring and at five coniferous sites during 1996-2002 in the framework of ICP Forests (Level II). The coniferous canopies acted as a sink for nitrate and ammonium and as a source for base cations: Ca(2+), Mg(2+) and K(+). The estimated share of SO(4)-S dry deposition from total deposition was 1.5-4 times higher for dormant period compared to growing period. During the study period average annual throughfall and bulk deposition of SO(4)-S decreased significantly, 2.8 and 2.3 times, respectively. Throughfall enrichment with base cations increased in the order Mg < Na < Ca < K. Using Na as a tracer ion, average dry deposition and canopy leaching were calculated. Leaching was the dominant process for TF enrichment by potassium. Leaching of base cations occurred during growing as well as dormant period. The calculated internal flux of Ca(2+) and Mg(2+) varied in the range of 0.6-2.0 and 0.6-1.2 kg ha(-1) per year in spruce and pine stands, respectively. The internal circulation of K(+) was significantly higher (8.9-10.9 kg ha(-1) per year) in spruce stands than in pine stands (2.7-4.4 kg ha(-1) per year).