Water chemistry of throughfall and soil water under four tree species at Gisburn, northwest England, before and after felling

The chemistry of throughfall, from intact canopies and felling debris, and soil waters beneath four tree species, alder (Alnus glutinosa), Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and oak (Quercus petraea), and an unplanted control plot, was monitored before and after felling at a site on humic gley soils in the north of England. The results show clear differences in solute concentrations below the four species both before and after felling. Before felling the concentrations of the mainly atmospherically derived ions (Na+, Mg2+, SO42-, Cl-) were larger in both throughfall and soil waters below the conifers than the hardwoods. There were smaller inter species differences in the concentrations of solutes mainly controlled by within system processes (K+, NO3-, PO4-, DOC); NO3- concentrations were largest below the alder. Following felling, concentrations of the mainly atmospherically derived solutes declined below all four species and the inter-species differences reduced sharply so that in the second year after felling there was little difference between species. Concentrations of the solutes controlled by within system processes mainly increased after felling. The largest increase in K+ concentrations was below the conifers, which had foliage at the time of felling; most of the K was retained in the upper soil except below spruce. Nitrate concentrations declined below alder after felling while increasing below the other species. The largest increase was below spruce and the increased concentrations were seen in the lower horizons below both conifer species, suggesting that there would probably be leakage to ground- or surface waters. The factors leading to the reduction in nitrate concentrations below alder merit further research. PO43- released from the felling debris and litter layer was retained in the upper soil. (C) 2000 Elsevier Science B.V. All rights reserved.