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 di fferences in solute concentrations below the four species both before and a fter felling. Before felling the concentrations of the mainly atmospherical ly derived ions (Na+, Mg2+, SO42-, Cl-) were larger in both throughfall and soil waters below the conifers than the hardwoods. There were smaller inte r species differences in the concentrations of solutes mainly controlled by within system processes (K+, NO3-, PO4-, DOC); NO3- concentrations were la rgest below the alder. Following felling, concentrations of the mainly atmo spherically derived solutes declined below all four species and the inter-s pecies 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 fol iage at the time of felling; most of the K was retained in the upper soil e xcept below spruce. Nitrate concentrations declined below alder after felli ng while increasing below the other species. The largest increase was below spruce and the increased concentrations were seen in the lower horizons be low both conifer species, suggesting that there would probably be leakage t o ground- or surface waters. The factors leading to the reduction in nitrat e concentrations below alder merit further research. PO43- released from th e felling debris and litter layer was retained in the upper soil. (C) 2000 Elsevier Science B.V. All rights reserved.