F. Hagedorn et al., Contrasting dynamics of dissolved inorganic and organic nitrogen in soil and surface waters of forested catchments with Gleysols, GEODERMA, 100(1-2), 2001, pp. 173-192
In this study, we investigated the dynamics of dissolved inorganic and orga
nic nitrogen (N) in throughfall, in sail solutions of Gleysols, and in outf
lows from experimental sub-catchments as well as from a headwater catchment
in Switzerland. Additionally, we studied the effect of increased N deposit
ion on dissolved N by applying 3 g NH4NO3-N m(-2) year(-1) to soil plots an
d to one of the sub-catchments. Dissolved organic N (DON) was the dominant
form of total dissolved N (TDN) in the soil and surface waters. The proport
ion of DON in TDN increased from the throughfall down to the subsoil, which
indicates that the retention of DON was lower than that of inorganic N. Co
ncentrations of DON in the subsoil were higher under reducing than under ox
idising conditions. In the soil solution and in the runoff from all catchme
nts, nitrate and DON displayed inverse seasonal patterns with concentration
s of NO3- being highest in late winter and those of DON being maximal in su
mmer and fall. This difference shows that during periods of increased biolo
gical activity, NO3- was retained in the forest ecosystem while the product
ion of DON was stimulated. Concentrations of both NO3- and DON were negativ
ely correlated with the amount of throughfall. In the outflow of the headwa
ter catchment, however, the concentration-discharge relationship was negati
ve for NO3-, but positive for DON. The reason for this difference appeared
to be the larger contribution of topsoil water at high now, which was poor
in NO3- and rich in DON. Experimentally increasing the N deposition increas
ed NO3- leaching significantly, but had no effects on DON leaching and on D
ON export from the catchments. In conclusion, our results show that the dyn
amics of dissolved organic and inorganic N are controlled by different fact
ors. (C) 2001 Elsevier Science B.V, All rights reserved.