EFFECTS OF FOREST AGE ON SURFACE DRAINAGE WATER AND SOIL SOLUTION ALUMINUM CHEMISTRY IN STAGNOPODZOLS IN WALES

The influence of forest development on soil solution and surface drain age water aluminium chemistry was investigated in Sitka spruce (Picea sitchensis) plantations in Wales. Comparisons with semi-natural grassl and and moorland sites are described. A highly significant positive re lationship was shown between increasing forest age and soilwater alumi nium concentrations in the B horizons. Short-term/episodic peaks in Al concentrations were strongly related to incidences of high concentrat ions of neutral, marine-derived, salts in the soilwater. Nitrification may be an important factor in soil acidification and the mobilization of Al in soilwaters beneath the older mature-forest plantations in Wa les. Labile monomeric Al concentrations were largest in surface waters draining the oldest forestry plantations compared with younger forest catchments and moorland, although response to discharge of soilwater acidity to the surface waters at individual sites was dependent on the acid neutralizing capacity of the groundwater component of the surfac e waters.