Estimating the total deposition of base cations from throughfall measurements

The relationships between the deposition of ions in bulk precipitation and throughfall have been examined in order to assess the validity of the simple ratio technique proposed by Sverdrup et al. (1990) for determining total base cation deposition to forest canopies. The results of the analysis are consistent with the hypothesis that there is negligible canopy leaching of sodium and chloride, at least for Sitka spruce. The enrichment in throughfall compared to precipitation for sodium is very similar to that for chloride but differs from that of the other base cations. The relationship between the deposition of sodium and chloride in throughfall and bulk precipitation can be described using a simple linear regression model which could provide a basic tool for estimating total base cation deposition to UK Sitka spruce forests at a regional scale. Independent verification of the model is required to ascertain whether it is appropriate for base cations such as calcium, which have a significant non-seasalt deposition component.