SEASALT EFFECTS ON THE ACID NEUTRALIZING CAPACITY OF STREAMWATERS IN SOUTHERN NORWAY

Input of neutral salt, primarily NaCl, from sea spray is an important factor for shortterm acidification of surface water, primarily in alre ady acidified areas, because Na may substitute for Ht and cationic alu minium by cation-exchange reactions in the soil. By evaluating the var iation of non-marine sodium (Na) separately it is possible to estimat e the major effect of seasalt episodes on the neutralizing capacity (A NC) of stream water. At four long-term monitored Norwegian catchments, the Na in stream water on average explained 28 +/- 4% of the monthly variations of ANC in stream water at Birkenes, and 27 +/- 3%, 20 +/- 2% and 56 +/- 5% of the correspondent variations at Storgama, Langtjer n and Kaarvatn, during the respective monitoring periods. The remainin g variations in acid neutralizing capacity are explained by the differ ence between non-marine base cations (Sigma Ca,Mg*,K*) and non-marine sulphate (SO4) and NO3. This paper also indicates that seasalt episo des are probably of greater importance for the periodic variations in ANC of stream water than commonly recognized. During the last years, e xtreme seasalt episodes have occurred in southern Norway, and more fre quently at winter-time, which means that seasalt inputs have played a more important role for the short-term variations of ANC in stream wat er the last years. This tendency is also strengthened by the fact that there has been a significant decline in the input of acidic sulphur c ompounds and non-marine base cations in stream water during the last 1 0-15 years. Because the decline in soil-derived base cations in stream water is somewhat lower than the correspondent decline of sulphate, a slowly improving ANC of stream water should be expected on long-term basis. Seasalt episodes of the same magnitude as those present during the last years, will therefore most likely cause less extreme water-ch emical conditions in the years to come. Because the seasalt effect see ms to be a short-term effect, there is no reason to claim that these e ffects may cause longterm acidification, a conclusion earlier drawn fr om several correspondent studies.