| At Vyrnwy, in mid-Wales, a study of the hydrogeochemistry of two small spruce
forested catchments, one a control and one felled midway through the study, shows a classic
picture of rainfall inputs damped by the catchment and stream waters the chemistry of which
varies as functions of flow and particularly of the supply of more acidic and aluminium-bearing
soil water and of more basic and calcic ground waters from the zone where weathering
reactions with the bedrock are high. The ground waters are most alkaline although pH may be
depressed due to high dissolved carbon dioxide pressures. Nitrate concentrations increase in
the first year after felling and decrease thereafter below those of the control. Water
quality changes due to the dominant hydrogeochemical processes show that harvesting raises
no significant water quality management issues.
Keywords: Gran alkalinity, aluminium, spruce, harvesting, forestry, nutrients, trace
elements, Vyrnwy, water quality |