MEASUREMENTS OF ATMOSPHERIC DEPOSITION AND INTERNAL CIRCULATION OF BASE CATIONS TO A FORESTED CATCHMENT-AREA

The dry deposition of base cations to a Norway spruce stand was estima ted by multiplying the ratio of the ion deposition to the sodium depos ition on a surrogate surface with the dry deposition of sodium on the forest stand. The method can in principle only be applied to species t hat are present only in particles, but the method gives reasonable res ults when tested on ions that are also dry deposited in other forms (S O42-, NO3- and NH4+). The atmospheric input and especially the dry dep osition of base cations is an important replacement for tho loss of ba se cations from the soil by run-off. The calculated internal circulati on of K+ and Ca2+ showed maxims synchronously with rainfall maxims and constitute 71% and 53%, respectively, of the net throughfall depositi on. The internal circulation of Ca2+ was almost equal to the SO2 uptak e.