Sensitivity analyses of MAGIC modelled predictions of future impacts of whole-tree harvest on soil calclum supply and stream acid neutralizing capacity

Stephan Köhler1, Therese Zetterberg2, Stefan Löfgren3
1 aquatic sciences and assessment, University of agricultural sciences
2 IVL Swedish Environmental Research Institute Ltd., P.O. Box 53021, SE-400 14 Gothenburg, Sweden
3 Swedish University of Agricultural Sciences, SLU, Department of Aquatic Sciences and Assessment, P.O. Box 7050, SE-750 07 Uppsala, Sweden

O 1.4 in Long term trends in the functioning of ecosystems

14.07.2014, 12:15-12:35, H18

Forest biofuel is a main provider of energy in Sweden and the market is expected to grow even further in the future. Removal of logging residues via harvest can lead to short-term acidification effects but the long-term effects are largely unknown. The objectives of this study were to 1) model the long-term effect of whole-tree harvest (WTH) on soil and stream water acidity and 2) perform sensitivity analyses by varying the removal amounts of logging residues, calcium (Ca2+) concentrations in tree biomass and site productivity in nine alternate scenarios. Data from three small forested catchments and the Model of Acidification of Groundwater in Catchments (MAGIC) was used to simulate changes in forest soil exchangeable Ca2+ content and stream water acid neutralizing capacity (ANC). Large depletions in soil Ca2+ supply and a reversal of the positive trend in stream ANC was predicted at all three sites after WTH. However, the magnitude of impact on stream ANC varied depending on site and the concentration of mobile strong acid anions. Contrary to common beliefs, the largest decrease in ANC was observed at the well-buffered northern catchment. The effects at the central and southern sites were much more limited and not large enough to offset the general recovery from acidification. Varying tree biomass Ca2+ concentrations had the largest impact on modelled outcome. Site productivity was the second most important variable whereas changing the amounts of biomass left on site only marginally affected the results. The outcome from the sensitivity analyses pointed generally in the same direction of change as in the base scenario, except for Kindla where soil Ca2+ pools was predicted to be replenished under a given set of input data. The reliability of modelled outcome would increase by using site-specific Ca2+concentrations in tree biomass and proper identification of catchment site productivity.

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last modified 2014-06-19