Abstract
The RAIN project (Reversing Acidification In Norway) entails catchment-scale experimental manipulations to investigate the effect on water and soil chemistry of drastic changes in precipitation chemistry. At Risdalsheia in southernmost Norway wet deposition of acid is excluded from a 860-m2 headwater catchment by means of a roof and “clean” precipitation is added beneath. Four years of acid exclusion (through June 1988) have resulted in lower concentrations of the strong acid anions NO3 (from 35 to 7 ueq L-1) and SO4 (from 110 to 53 ueq L-1) in runoff. The decline in strong acid anion concentrations has been compensated partially by a decrease in concentrations of base cations (55%) and partially by an increase in alkalinity (45%). pH has increased only slightly from 4.0 to 4.1. Organic acids have become increasingly important for the pH of runoff. Runoff from the shallow organic soils contains 10 to 20 mg C L-1 total organic carbon (TOC). The concentration of organic anions (estimated from the ionic balance) has increased from about 22 ueq L-1 in 1984 to 49 ueq L-1 in 1987. This increase is due to increased dissociation of organic acids and not to change in TOC concentrations. The organic C in these acid samples apparently has a maximum charge density of about 4.5 ueq mg C-1 and pK of about 4.
Published Version
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