Mineral weathering rates in glacial drift soils (SW Michigan, USA): New constraints from seasonal sampling of waters and gases at soil monoliths

Based on water chemistry and discharge, bulk reaction rates of calcite, dolomite (Ca0.5Mg0.5CO3), K-feldspar and plagioclase are calculated to be at 3400, 3100, 220, and 320 mol ha− 1 yr− 1, respectively. Based on mass balance of soil composition, long-term plagioclase-weathering rates (over the past 12,500 years) are calculated at about 2400 mol ha− 1 yr− 1, much higher than the current rates. This agrees with previous conclusions that weathering rates decrease with time, due to loss of reactive mineral surfaces. Furthermore, both long-term and short-term plagioclase dissolution rates in Michigan are relatively high compared to those in other watersheds with similar age, possibly due to fresh surfaces produced by glaciation, in combination with the high discharge and high plagioclase abundances.