Surhetstillståndet i bäckar uppströmskalkdoserare i Dalarnas län
The acid deposition of sulphur- and nitrogenoxides from combustion of coal and oil cause acidification that lowers pH and gives increased contents of metals and altered aquatic biodiversity in the stream. The liming of lakes and streams, which was introduced to resist the acidification, demand large economic resourses despite of the decreased deposition of the acidifyng substances. Some of the streams are influenced by the acid deposition, while others are naturally acidic. It is therefore importaint to separate the anthropogenically acidified waters from the naturally acidic, in order to optimize the use of governmental fundings for liming. This thesis aims to estimate the acidity status and impact of acidification on 24 catchments upstream liming dispensers, which is part of the liming activities at the County of Dalarna.The acidity status of the streams was classified according to the Swedish Environmental Protection Agency old classification system (Naturvårdsverket 1999) as very acid to acid, with small ability to withstand a pH-change (alkalinity) due to acid deposition. The new acidification classification system (Naturvårdsverket, 2007c) could not be utilized, since the data on water chemistry from the liming effect assessment are too scarce for the calculations of ANC and use of the BDM-model or/and the MAGIC-library. These models require a complete analysis of base cations (Ca2+, Mg2+, Na+, K+) and anions (SO42-, Cl-, NO3-). Instead, the buffer capacity was calculated from CBALK, which means that the alkalnity at pH=5,6 and TOC were used to estimate the buffer capacity. Streams with organic anions as the main buffering system were primarily considered as naturally acidic. The results show that in most streams, high concentrations of humic matter contribute more to low values of pH, compared with sulfate (SO42-). Wetlands within the drainage area can act as sink for the sulphate ions and have an impact on the sulphate concentrations in the streams.The County of Dalarna is recommended to extend the liming effect assessment with analysis of a larger numbers of parameters. For a limited cost, the necessary measurements for classification of acidification status and for separating natural acidic from acidified streams, will be obtained. This could lead to termination of liming of naturally acidic waters, reducing the costs.