Partitioning the variation within the acid neutralizing capacity of surface waters in Scotland in relation to land cover, soil and atmospheric depositional factors

A method of decomposing the variation in the acid neutralizing capacity (AN C) of surface waters in Scotland is described. Using national datasets, a s eries of variables relating to 703 catchments across Scotland is divided in to three components representing (i) land cover, (ii) soil and (iii) atmosp heric deposition/altitude. Redundancy analysis (RDA) and (partial) redundan cy analysis are used to quantify the amount of variation in ANC uniquely at tributable to each of these components, independent of the effects of the o thers. The variation accounted for by covarying combinations of these compo nents is also determined. Approximately 55% of the total variation in ANC a cross the 703 sites is explained by the variables representing catchment ch aracteristics and atmospheric deposition. Of this, 8.5%, 2.4% and 6.9% are uniquely attributable to the land cover, soil and deposition/altitude compo nents, respectively. A further 38% of ANC variation is associated with the covariation between components, with 18% accounted for by the combination o f all three. Approximately 45% of the variation in ANC remains unexplained. The results reflect the integrated nature of catchment processes and demon strate, for these data, that it is a combination of land cover. soil and de position and altitude factors which most explain variation in freshwater AN C level. The approach offers a tool with which to assess the sensitivity of surface waters to acid deposition at a regional scale and provides a way o f identifying regional differences in catchment response to acid loading. ( C) 2001 Elsevier Science B.V. All rights reserved.