Effects of cold and warm years on the water chemistry at the Birkenes catchment,Norway

During the last years, several scientists have been concerned with the consequences of global warming. In the Birkenes catchment, situated in southernmost Norway, several warm years have occurred during the last decade. In this climatic region, warm years primarily mean warmer winters with mean air temperatures close to or higher than 0 °C. Small temperature changes are therefore decisive for the quality of precipitation, i.e. whether the precipitation enters the catchments as snow or rain, which accordingly has large consequences for the residence time of water and its pathways through the catchment. Another important effect of higher winter-temperatures at Birkenes, is that stronger and more frequent seasalt episodes seem to occur. This may enhance the negative effects to aquatic organisms, because the most extreme concentrations of acute toxic Al-forms in streamwater are related to seasalt episodes during warm winters, when the precipitation comes as rain and thus leaves the catchment relatively fast through the uppermost soil layers. When seasalt-enriched water enters into the uppermost soil horizons, a large amount of sodium will be temporarily retained due to cation exchange processes, where sodium may substitute for H⁺ and cationic Al. At Birkenes, but also in similar acidified areas with high seasalt input, seasalt episodes are probably of greater importance for the periodic variations in streamwater H⁺ and Alⁿ⁺ than commonly recognized. Higher winter-temperatures may also change the timing of the highest streamwater fluxes of nitrate. This may have local consequences for the primary-production in the fjords, both quantitatively and qualitatively. Thus, global warming may have negative consequences for the surface water chemistry in near-coastal areas that also receive high amounts of acidifying atmospheric compounds, and may change the eutrophication status of many fjords.