Weathering rates of fine pebbles at the soil surface in Kärkevagge, Swedish Lapland

In 1994, nylon mesh bags containing 6.2-mm diameter fragments of either freshly crushed dolomite or granite were placed on meadow, solifluction meadow, birch, heath and alpine tundra vegetation that cover surfaces within Kärkevagge, a glaciated arctic–alpine valley in Swedish Lapland. Each vegetation category contained three replicate sites comprising one bag of each rock type. In 1995, the study was extended to Dryas heath and willow (two sites only) surfaces. Percentage annual weight loss was used as a metric of chemical weathering rates. One site in each of the 1994 categories was measured in 1995. All sites were measured in 1999. Two dolomite and granite standards stored in the laboratory and subjected to identical cleaning and weighing regimes to the field samples, exhibited no more than a 0.24% total weight loss after 5 years. The percentage weight loss in the subgroup examined after 1 year (dolomite 0.54%/year; granite 0.41%/year) significantly exceeded the average annual loss for the subsequent 4 years in all cases (dolomite 0.40%/year; granite 0.07%/year). Ten sites with a 5-year record had a mean annual loss of 0.326±0.115%/year (two standard errors) for dolomite and 0.121±0.020%/year for granite. Assuming an exponential decay model, a 0.326%/year rate of loss produces a ‘half-life’ of approximately 212 years and a 0.121%/year loss rate, a half-life of approximately 570 years. Kruskal–Wallis one-way ANOVA on rank-ordered data determined significant differences in dolomite pebble mass loss between the Dryas heath and willow plus meadow microenvironments, as well as between the birch forest and the willow plus meadow microenvironments. The underpinning factor behind these differences appears to be moisture differences. A similar test failed to determine statistically significant differences for the granite pebbles. Dolomite appears to be a viable medium for determining mass loss rates over quite modest time periods providing that the number of samples is sufficiently large.