SOIL AND STREAM WATER CHEMISTRY IN A PRISTINE AND BOGGY SITE IN MID-NORWAY

Stream-and soilwater at the 18.7 ha pristine Ingabekken catchment, on gneiss bedrock at Hoylandet, have been studied for three years, includ ing intensive episode studies in spring and autumn. The site mainly co nsists of blanket bogs which are typical for these marine west coast c limates. Water drains through the blanket peats by means of two major flowpaths. Each flowpath contributes to the stream with a distinct che mical fingerprint rendered by the soil/soil water interactions along t he flowpath, i.e. they may be regarded as end-members. The soil water from the upper peat layers is the end-member representative of stormfl ow discharge whereas baseflow originates mainly from seepage of the ot her end-member, which is the mineral soil water from beneath the peat. The pH(BaCl2) of the soils that control the runoff chemistry during h ighflow conditions was as low as 2.6, allowing for a substantial pH dr op in streamwater in the case of a seasalt episode. pH in the stream v aried from more than 7 at baseflow to 5 or slightly below at stormflow . The lowest pH (4.8) was observed during early snowmelt due to releas e of meltwater highly enriched in seasalts. The fraction of exchangeab le aluminum (AIS) was much higher in the surface layers of the lower r eaches of the catchment than close to the water divide. This suggests a transport of Al, much like podzolisation, though downslope by a late ral flowpath. A Principal Component Analysis on the stream water chemi cal data shows the importance of water flowpaths in addition to diluti on or ionic strength and antecedent conditions as a factor in determin ing the water quality. On the plane of the two major principal compone nts the base cations (Ca2+, Mg2+, Na+, K+) were negatively related to [H+], and the total organic carbon (TOC) was negatively related to str ong acid anions (Cl-, SO42-, NO3-). These relationships between the pa rameter loadings along the two main principal components remained indi fferent to the effects of both dilution and flowpaths. Under the prese nt conditions of low acid deposition, this sensitive system is effecti vely buffered by its weak acids and all released Al is complexed by na tural organic acids. Similar boggy areas located in regions with heavy anthropogenic acid deposition may not be able to neutralize the miner al acids. A shallow water flowpath and a high H+ saturation of the ion exchanger in the soils controlling the highflow chemistry may lead to discharge episodes where strong mineral acids are allowed to pass thr ough the system releasing elevated levels of toxic aluminum in the str eam.