Influence of canopy budget model approaches on atmospheric deposition estimates to forests |
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Authors: | Sandy Adriaenssens Jeroen Staelens Lander Baeten Arne Verstraeten Pascal Boeckx Roeland Samson Kris Verheyen |
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Institution: | 1. Forest and Nature Laboratory, Ghent University, Geraardsbergsesteenweg 267, 9090, Gontrode (Melle), Belgium 6. Belgian Interregional Environment Agency, Kunstlaan 10-11, 1000, Brussels, Belgium 2. Isotope Bioscience Laboratory – ISOFYS, Ghent University, Coupure Links 653, 9000, Ghent, Belgium 7. Flemish Environment Agency, Kronenburgstraat 45, 2000, Antwerp, Belgium 3. Terrestrial Ecology Unit, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000, Ghent, Belgium 4. Research Institute for Nature and Forest, Kliniekstraat 25, 1070, Brussels, Belgium 5. Department of Bioscience Engineering, University of Antwerp, Groenenborgerlaan 171, 2020, Antwerpen, Belgium
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Abstract: | Accurate quantification of total nitrogen and acidifying deposition is a major source of uncertainty in determining the exceedance of critical loads in forest ecosystems. Monitoring of atmospheric deposition is frequently based on throughfall measurements in combination with the canopy budget model to calculate ion-exchange fluxes between the forest canopy and incident rainfall water. Various approaches for each step in the canopy budget model have been reported and compared, but combinations of different approaches were not yet assessed. Therefore, the present study quantified the range of estimated dry deposition and total deposition resulting from all possible combinations of canopy budget model approaches for three typical case studies: (i) total nitrogen and potentially acidifying deposition onto a forest canopy, (ii) the ratio of these deposition variables between adjacent coniferous and deciduous stands and (iii) the parameters of a deposition time trend analysis. The time step, type of precipitation data and tracer ion used in the model had a significant effect on the findings in the three case studies. In addition, including or excluding canopy leaching of weak acids and canopy uptake of nitrogen during the leafless season largely affected the results, while including or excluding canopy uptake of nitrate generally showed no effect. In general, the use of wet-only precipitation data can be recommended, along with sodium as a tracer ion and the inclusion of weak acids. We conclude that further research should focus on the assumptions of inertness of the tracer ion and the equal deposition efficiency of base cations and the tracer ion and on the quantification of weak acids in rainfall and throughfall water. Since local or tree-species specific effects might influence the results obtained in this study, a similar analysis is recommended for other tree species and regions when using the canopy budget model. |
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