CONTROLLING MECHANISMS FOR STREAM WATER CHEMISTRY AT THE PRISTINE INGABEKKEN SITE IN MID-NORWAY - SOME IMPLICATIONS FOR ACIDIFICATION MODELS

Stream water at the 18.7 ha pristine Ingabekken catchment, on granitic bedrock, in mid‐Norway has been studied for 2 years, including intensive episode studies in the spring and autumn. The pH varied from over 7 at base flow to 5 or slightly below at high flow, while inorganic monomeric Al was <1 μM for all flow conditions. The lowest pH (4.8) was observed in the early snowmelt during release of meltwater highly enriched in sea salts. The cation exchange capacity and base saturation of organic soils were comparable to those found at the acidified Birkenes site in southern Norway, but the ratio of exchangeable Al to exchangeable H+ was much lower at Ingabekken. This suggests that soils could undergo a transition during acidification whereby exchangeable H+ is replaced by aluminium. Such a transition may well be important in understanding long‐term trends in acidification but is not a feature of most models. Copyright 1990 by the American Geophysical Union.