Den bäcknära zonen vid små skogliga vattendrag i Värmland
generell beskrivning, förekomst av traktorspår samt kvicksilverhalter i körpåverkat ytvatten
Forest streams and the associated riparian zones are sensitive to disturbances and changes that occur within these riparian areas. Particularly sensitive are small streams of low order, which will have large impacts down-stream. The disturbances that occur in the riparian zones are reflected quickly in the stream. Driving with forestry machines in the riparian zone will have detrimental effects to the soil and water. Driving the machines will lead to changes in the mineral soil composition, resulting in the reduction of porosity, less infiltration, compaction, and an increased bulk density. Driving can also increase consequences for the biological life in the stream. Machine tracks that enter the stream can increase the amounts of organic and inorganic material transported to the stream.
The aim of this thesis was to collect the general characteristics of the riparian zones along small forest streams of first order in Värmland and to determine the frequency of machines entering these zones. Furthermore, the aim was to determine concentrations of methylmercury and total mercury in the surface water, which has been affected by machine tracks. To determine the characteristics of the riparian zones and the frequency of machine traffic, data from the project called "Skog & Vatten" was used. The "Skog & and Vatten" project began in 1997 at Skogssvårds-styrelsen Värmland/örebro. The purpose of the project was to describe the riparian zones, their history, and docu-ment the biological qualities of the streams.
Generally the most common riparian zone along streams of first order in Värmland can be summarized as having a fresh soil moisture class and productive soil with uniseriate coniferous forests and a grass-herb type vegetation class. Dead wood was not common occurring in the study area. Machine tracks were found in 12 % of all the compart-ments and half of these lead to a stream. The machine tracks were evenly distributed in the different soil moisture classes, with an exception for the wet soil moisture class. Of all of the riparian zones (0-10m) on productive soils that contained machine tracks, 71 % of the tracks were related to some kind of forestry. Concentrations of total mercury and methylmercury between 7,2 and 13 ng/l respectively, 0,07 and 4,8 ng/l were measured in machine tracks that affected surface water. The total mercury consisted between 0,54 and 66 % of methyl mercury. The results indicate that terrain driving can release and transport mercury.