CHEMICAL AND MINERALOGICAL WEATHERING RATES AND PROCESSES IN AN UPLAND GRANITIC TILL CATCHMENT IN SCOTLAND

Weathering in an upland granitic till catchment receiving an intermedi ate level of acidic deposition has been studied by chemical and minera logical analyses of soil profiles and chemical analysis of precipitati on and streamwater. Long-term weathering rates for base cations calcul ated from analyses of soil profile horizons using Zr as an internal, i mmobile, index element are similar for alpine podzols and peaty podzol s and are 2-3 meq.m-2.a-1 for Ca and Mg, and 10-11 meq.m-2.a-1 for K a nd Na. The high loss of Na is associated with the weathering of oligoc lase, particularly in the coarse sand fraction. Loss of K is related t o weathering of K-feldspar and micas. Current weathering rates for bas e cations calculated from input-output budgets are higher than long-te rm rates by factors of 12, 8 and 3 for Ca, Mg and Na, but lower by a f actor of 7 for K probably due to biomass uptake. The higher current ov erall loss of base cations may be due to increased rates of weathering in recent times but this is not conclusive as there are large uncerta inties inherent in both methods of estimation.