Alkalinity buildup during silicate weathering under a snow cover

Results from the study of experimental plots at Hubbard Brook, New Hampshire for the years 1987, 1988, 1993, 1994, 1995, and 1996 show that the water draining from under a plot planted with pine trees exhibits its highest alkalinity during the year at about the time of spring snowmelt. This high alkalinity is believed to be due to buildup during the winter under a snow cover. The soil solutions are protected from acidic precipitation by the snow, and the natural process of the reaction of organic acids and carbonic acid with minerals and exchange complexes to form dissolved HCO₃ ^– (and organic anions) proceeds with an increase in alkalinity through the winter. When the snow melts the acidic meltwater mixes with, neutralizes and displaces the water previously occupying the soil interstices. This leads to a decided drop in alkalinity of the drainage water. The alkalinity buildup under the pine plot was found to be two to ten times greater than under a similar plot containing no higher plants. This strongly emphasizes the important role of plants, in their ability to produce organic acids and high levels of CO₂, in accelerating the weathering of silicate minerals.