INORGANIC NUTRIENT INPUTS FROM MINERAL WEATHERING IN 2 SCOTTISH UPLAND ECOSYSTEMS

Uptake of K, Ca, Mg and Na by vegetation in two upland ecosystems, one situated in andesitic parent material and the other on mica-schists, has been studied in relation to the mineralogy of the soils and the ra tes of weathering of base cations. Rates of weathering were calculated by two methods: (1) long-term rates were calculated from losses of th e elements in soil horizons using Zr as an internal index; (2) current rates were calculated from input-output budgets using rain-water and stream chemistry over a 3 a period. Vegetation uptake can be related i n a general way to mineralogy and weathering trends. Most of the K rel eased from the soil appears to be taken up by the vegetation and the c ontent of K in grass-dominated plant communities is related mainly to the availability of K from the weathering of mica. High levels of Ca i n the streams indicate an overabundance of Ca which is being released mainly by weathering of plagioclase feldspar. Amounts of Mg in the veg etation are related to variations in the content of chlorite which is easily weathered at both sites.