Acidification of till in Northern Finland: experimental study

The acid neutralizing capacity of till and some effects promoted by increasing acidity, were studied in a number of tills in northern Finland. pH profiles were measured in the field and acid neutralizing capacity (ANC mmol/100 g sample) in the laboratory as a function of the varying acidity in solution. The concentrations of Al, Ca, Mg, Fe, K, Mn, Zn, Cu and Sr in solutions were also analyzed. The results are presented in the form of graphs of ANC versus final pH of the solution and element concentration versus final pH. The total concentrations of the major elements were analyzed by XRF and those of trace elements by AAS. The pH measured in the test pits was lowest just below the ground surface, and rose rapidly to a value of 6 at a depth of about 1 m and then it remained more or less constant with depth. The laboratory analyses clearly suggest that the acid neutralizing capacity of till correlates well with sample depth. The ANC values, which represent the fast-working part of the capacity, are higher in the surficial parts owing to the easily soluble aluminium and iron hydroxides which have their origin in the weathering processes. The experiments resemble acid rain conditions, where the higher pH-level buffers are unable to neutralize the increase in acidity immediately, so that lower pH-level buffering processes such as Al and Fe hydroxide buffers come into play. The situation can be hazardous for both forests and surface water