Spatial variations in throughfall chemistry at the small plot scale

Abstract

The results of a study of spatial variations in throughfall chemistry are presented for a small plot located within a beech forest in southern England. Throughfall data were collected from three late-autumn storms using an array of 48 fixed-position collectors. For each of these storms, there were large variations in collection volume and in major and minor chemical determinands. Most chemical determinands had a strong positive correlation with one another and a slight negative correlation with volume. Strong correlations were observed even for chemicals which are associated with different processes; e.g. K and Mn derive from leaching, but were correlated with marine-derived Na and Cl inputs. In other words, locations with high occult or dry deposition inputs had a correspondingly high contribution from leaching. This means that great care is required in field experimentation if canopy processes are to be described accurately: high correlation between chemicals indicates that the different supply mechanisms are not independent. The spatial distribution of throughfall volume and chemistry showed consistent storm-to-storm patterns: there was a localized systematic location effect. Ratios between different chemical species in throughfall were consistent from point to point, whereas concentrations and fluxes were very variable. The practices of random relocation, of collecting multiple samples and of bulking before chemical analysis are strongly recommended.