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Seasonality in Na/Cl ratios in precipitation and throughfall samples

Seasonality in Na/Cl ratios in precipitation and throughfall samples. Karin Hansen, Anne Thimonier, Peter Waldner , Maria Schmitt, Flurin Sutter, Ülle Napa, Lars Vesterdal, Arne Verstraeten, Sue Benham. ……..an on-going project with preliminary results. Background for this study.

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Seasonality in Na/Cl ratios in precipitation and throughfall samples

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  1. Seasonality in Na/Cl ratios in precipitation and throughfall samples Karin Hansen, Anne Thimonier, Peter Waldner, Maria Schmitt, Flurin Sutter, Ülle Napa, Lars Vesterdal, Arne Verstraeten, Sue Benham ……..an on-going projectwithpreliminaryresults

  2. Background for this study • Thimonier, A., Schmitt, M., Waldner, P., Schleppi, P. (2008). Seasonality of the Na/Cl ratio in precipitation and implications of canopy leaching in validating chemical analyses of throughfall samples. Atmospheric Environment 42: 9106-9117.

  3. Hypotheses • A portion of Na/Cl ratios in throughfall in Europe fall outside the recommended range of 0.5-1.5; • Leaching of Na and Cl from forest canopies do occur in the autumn or spring; • Leaching is highest from deciduous tree species; • The seasonality in leaching is connected to the distance from the nearest sea.

  4. Research questions • Is there a seasonal pattern to the leaching of Na and Cl? • Can Na and Cl be said to be inert in forest canopies? • Do certain tree species leach more Na or Cl than others? • Is the seasonal pattern in any relation to how far away from the sea the forest stand is situated?

  5. Data used in the study • ICP Forests database • Bulk precipitation (BP) • Throughfall (TF) • Tree species • Criteria implemented on an annual basis • sampling during at least 300 days • gaps between sampling periods < 50 days • Na and Cl values for at least 300 days • Calculated distance to the nearest sea

  6. Statistics The seasonalitywithin the data was analysed by introducingharmonic terms (sine and cosine) in a stepwise regression of the dependent variable x versus time: x = c1 + c2 sin t + c3 cos t + c4 sin 2t + c5 cos 2t + c6 sin 3t + c7 cos 3t + c8 sin 4t + c9 cos 4t + c10 sin 5t + c11 cos 5t Where t=2π/365 * (day of the year) and c1–c11 are regression coefficients.

  7. Determination of distance to the sea • The longitude and latitude as submittedto the ICP Forests Database in the format DDMMSS translatedinto decimal degrees • The Europeancountriesavailable from the EDIT geoplatform (http://edit.csic.es/AdministrativeUnits.html)weremergedto a continentand transformed from polygon to a polyline • Plotcoordinates and country boundaryswere imported into ESRI ArcGIS 10.1 using the WGS1984 coordinatereferencesystem and the distancewascalculatedwith the Analyses Tool'near’.

  8. Countries and plots included

  9. Data included

  10. Some preliminary results – Na/Cl in BP GermanyPlot 1601, R2=0.46 (P<0.0001)

  11. Some preliminary results – Na/Cl in TF FrancePlot 16, R2=0.68 (P<0.0001)

  12. Some preliminary results - TF United KingdomPlot 516, R2=0.64 (P<0.0001)

  13. Somepreliminaryresults and conclusions (1) • For bulk precipitation (BP) • 81 plots (outof 438 plots) hadsignificant (p<0.0001) seasonalpatterns for the Na/Clratio • Explaining from 0-46% of the variation (R2) • For throughfall (TF) • 188 plots(outof 438 plots) hadsignificant (p<0.0001) seasonalpatterns for the Na/Clratio • Explaining from 0-68% of the variation (R2) • Significant seasonality was observed in both bulk precipitation and throughfall Na/Cl ratios • Throughfall showed significant seasonality more often and the explanation of it was stronger than for bulk precipitation

  14. Somepreliminaryresults and conclusions (2) • 63 deciduous ( R2=0.14-0.68) showedsignificant (p<0.0001) seasonalpatterns. • 119 coniferousstands (R2=0-0.55) showedsignificant (p<0.0001) seasonalpatterns. • No straight forward relationship wasobservedbetweentree species groups (deciduous and coniferous) and the seasonalpattern.

  15. Work to be done still (1) • Analysing data will continue during the coming months. • Which plots have and which do not have clear seasonal patterns? • The seasonal patterns are in part hampered by quality problems in data • Weneedtoclearout data withquality problems

  16. Work to be done still (2) • We are looking into the possibilities to calculate a 'direction weighted distance to the sea. • The difficulties are to get information on how to weight the directions to different seas and how to model and include the wind directions as a weight. • Areal data of the wind direction would be needed.

  17. Work to be done still (2) • We will look further into the possibility for different tree species to affect the seasonal pattern in throughfall. • Communication to and feedback from people in charge of deposition measurements in the countries that are included in this study. • Aiming at a publication in the beginning of 2014 (Atmospheric Environment)

  18. Thanks for listening!

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