QUANTIFICATION OF THE EFFECT OF PLANTS ON WEATHERING - STUDIES IN ICELAND

The weathering of calcium and magnesium silicate minerals on the conti nents has exerted a major control on atmospheric CO2 over geologic tim e, and vascular plants may have played an important role in this proce ss. In western Iceland, we have examined the role of plants in weather ing by measuring the chemistry of waters draining adjacent areas of ba saltic rocks that are either barren (having a partial cover of mosses and lichens) or populated by trees. The study area was chosen to maxim ize vegetational differences and to minimize differences in microclima te, slope, and lithology, while avoiding hydrothermal waters and anthr opogenic acid rain, Results, including data on cation uptake by growin g trees, indicate that the rate of weathering release of Ca and Mg to streams and vegetation is two to five times higher in vegetated areas than the release of Ca and Mg to streams in barren areas. This finding suggests a major role for vascular plants in accelerating weathering and thereby lowering atmospheric CO2 as they invaded upland areas of t he continents between 380 and 350 Ma.