Soil and stream water chemistry in a pristine and boggy site in mid-Norway

Abstract

Stream- and soilwater at the 18.7 ha pristineIngabekken catchment, on gneiss bedrock at Hoylandet,have been studied for three years, including intensiveepisode studies in spring and autumn. The site mainlyconsists of blanket bogs which are typical for thesemarine west coast climates. Water drains through theblanket peats by means of two major flowpaths. Eachflowpath contributes to the stream with a distinctchemical fingerprint rendered by the soil/soil waterinteractions along the flowpath, i.e. they may beregarded as end-members. The soil water from the upperpeat layers is the end-member representative ofstormflow discharge whereas baseflow originates mainlyfrom seepage of the other end-member, which is themineral soil water from beneath the peat. ThepHBaCl2 of the soils that control the runoffchemistry during highflow conditions was as low as2.6, allowing for a substantial pH drop in streamwaterin the case of a seasalt episode. pH in the streamvaried from more than 7 at baseflow to 5 or slightlybelow at stormflow. The lowest pH (4.8) was observedduring early snowmelt due to release of meltwaterhighly enriched in seasalts. The fraction ofexchangeable aluminum (AlS) was much higher in thesurface layers of the lower reaches of the catchmentthan close to the water divide. This suggests atransport of Al, much like podzolisation, thoughdownslope by a lateral flowpath. A Principal ComponentAnalysis on the stream water chemical data shows theimportance of water flowpaths in addition to dilutionor ionic strength and antecedent conditions as afactor in determining the water quality. On the planeof the two major principal components the base cations(Ca2+, Mg2+, Na+, K+) werenegatively related to [H+], and the total organiccarbon (TOC) was negatively related to strong acidanions (Cl-, SO42-, NO3-).These relationships between the parameter loadingsalong the two main principal components remainedindifferent to the effects of both dilution andflowpaths.Under the present conditions of low acid deposition,this sensitive system is effectively buffered by itsweak acids and all released Al is complexed by naturalorganic acids. Similar boggy areas located in regionswith heavy anthropogenic acid deposition may not beable to neutralize the mineral acids. A shallow waterflowpath and a high H+ saturation of the ionexchanger in the soils controlling the highflowchemistry may lead to discharge episodes where strongmineral acids are allowed to pass through the systemreleasing elevated levels of toxic aluminum in thestream.