Geological Survey of Norway, P.O. Box 3006-Lade, N-7002, Trondheim, Norway

Owing to its proximity to the sea, the Birkenes catchment receives seasalt-influenced precipitation, which results in episodic, natural acidification of the groundwater via cation exchange of marine Na⁺ with soil-bound H⁺ and/or Al³⁺. However, it is uncertain whether all of the recent groundwater acidification can be attributed to intensifying seasalt deposition alone: the steep slopes on the (Ca^* + Mg^*) vs. alkalinity plot and the increase in groundwater SO₄^* suggest that strong acids, of possible anthropogenic origin, may be involved. Additionally, seasalt deposition appears not to have increased during the 1990s: Cl^? content in precipitation has not increased significantly and river water pH has not decreased significantly over the period 1990–1993. The suggestion is made that the observed intensification in groundwater acidification at Birkenes partly results from the exhaustion or weakening of an acid buffering system caused by soil acidification, under persisting, even if abating, anthropogenic acid loading.