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ECN publication
Throughfall monitoring during one year at 14 ICP forest level 2 sites in The Netherlands
Published by: Publication date:
ECN 1997
ECN report number: Document type:
ECN-C--97-090 ECN publication
Number of pages: Full text:
45 Download PDF  

During one year throughfall composition was monitored at 14 ICP ForestLevel II sites in the Netherlands. The aim of this research was to estimate the atmospheric deposition at the sites and to compare the results with measurements made by the University of Nijmegen in Nijmegen, Netherlands, nine years ago to determine the influence of abatement strategies so far. In order to estimate atmospheric deposition a canopy budget model was applied. Wet deposition measurements were obtained from the national monitoring network run by RIVM. The average total nitrogen deposition to the 14 stands was 3080 mol/ha/a, whereas the average potential acid deposition amounted to 4600 mol/ha/a. Dry deposition made up about 75% of the total deposition. Model estimates agreed reasonably well with measurements, except for three locations. At Smilde, Netherlands, the throughfall flux was much higher, probably due to the soil conditions. At Ulvenhout, Nethrlands, the measured flux was lower than the model results. This is mainly due because of the poor quality of the measurements at this site as the result of vandalism, forest management and recreation. At the third Dutch location (Zeist) measurements were also lower than model results, which could not be explained. The measurements show that the pollution gradient has changed during the past years. There used to be a clear gradient from south to the north of the country, with decreasing fluxes of nitrogen and potential acid. No such strong gradient could be obtained from our measurements. It is impossible to derive conclusions about the abatement strategies by comparing the throughfall data made nine years ago and those presented here. The uncertainty in the data is too large and the difference in meteorological conditions between the years dominate the observed changes in deposition. In 1986 the precipitation was about a factor two higher than that in the period October 1995 - October 1996. The throughfall fluxes were therefore also a factor two higher. Time-series of throughfall measurements and micro meteorological measurements made at Speulder forest, Netherlands, between 1987 and 1996 show that the sulphur deposition decreased, but that the nitrogen deposition remained about the same. It is useful to repeat the measurements annually to monitor the effect of abatement strategies, because it is the only method which provides deposition estimates against relatively low costs. However, several conditions have to be fulfilled. The samplers must remain in the same position for several years, the method should be the most accurate, the method should be tested continuously against micro meteorological measurements such as those conducted at Speulder forest and the interpretation should be done together with a deposition model. The deposition model is tested with the measurements to see if the model parameters have been changed. The number of sites can be limited and should represent the gradient over the country and some tree species. 6 figs., 8 tabs., 19 refs., 1 appendix

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