Effects of forest cover and topographic factors on TOC and associated metals at various scales in western Scotland.

Studies at the stream catchment scale have yielded inconclusive evidence of the effects of forest land use on the concentrations of organic carbon in drainage waters. The aim of this paper is to examine the effects of forests on carbon in drainage waters at the plot scale by comparing concentrations of total organic carbon (TOC) and associated metals in soil solutions from sites under forest and moorland vegetation. At an upland site in south-west Scotland soil solution TOC, aluminium and iron concentrations varied with land cover. Mean concentrations of all three determinands were at least 1.5 times greater under forest than under moorland, despite considerable spatial and temporal (seasonal) variability. TOC in soil solutions was also found to vary significantly with both relief and altitude. The altitude effect was particularly marked, with an increase of 26 mg x l(-1) x 100 m(-1) increase in altitude found at an upland site in west-central Scotland. There were no differences in chloride, sulphate or base cation concentrations between forest and moorland sites. Differences in aluminium concentrations could not be linked to atmospheric scavenging at the forest sites, but were closely linked to differences in TOC.