IVL Swedish Environmental Research Institute

Introduction: Nitrogen (N) gradient studies in some cases use N deposition inthroughfall as measure of N deposition to forests.

For evaluating critical loadsof N, however, information on total N deposition is required, i.e., the sum ofestimates of dry, wet and occult deposition.Methods: The present paper collects a number of studies in Europe wherethroughfall and total N deposition were compared in different forest types

.From this dataset a function was derived which allows to estimate total Ndeposition from throughfall N deposition.Results: At low throughfall N deposition values, the proportion of canopyuptake is high and thus the underestimation of total deposition by throughfallN needs to be corrected.

At throughfall N deposition values > 20 kg Nha􀀀1 yr􀀀1 canopy uptake is getting less important.Conclusion: This work shows that throughfall clearly underestimates totaldeposition of nitrogen. With the present data set covering large parts of Europe it is possible to derive a critical load estimate from gradient studiesusing throughfall data.