Runoff changes have a land cover specific effect on the seasonal fluxes of terminal electron acceptors in the boreal catchments

Abstract Climate change influences the volume and seasonal distribution of runoff in the northern regions. Here, we study how the seasonal variation in the runoff affects the concentrations and exportof terminal electron acceptors (i.e. TEAs: NO 3 , Mn, Fe and SO 4 ) in different borealland-cover classes. Also, we make a prediction how the anticipated climate change induced increase in runoff will alter the exportof TEAs in borealcatchments. Our results show that there is a strong positive relationship between runoff and the concentration of NO 3 -N, Mn and Fe in agricultural catchments. In peaty catchments, the relationship is poorer and the concentrations of TEAs tend to decrease with increasing runoff. In forested catchments, the correlation between runoff and TEA concentrations was weak. In most catchments, the concentrations of SO 4 decrease with an increase in runoff regardless of the land cover or season. The wet years exportmuch higher amounts of TEAs than the dry years. In southern agricultural catchments, the wet years increased the TEA exportfor both spring (January–May) and autumn (September–December) periods, while in the peaty and forested catchments in eastern and northern Finland the exportonly increased in the autumn. Our predictions for the year 2099 indicate that the exportof TEAs will increase especially from agricultural but also from forested catchments. Additionally, the predictions show an increase in the exportof Fe and SO 4 for all the catchments for the autumn. Thus, the climate induced change in the runoff regime is likely to alter the exportedamount of TEAs and the timing of the exportdownstream. The changes in the amounts and timing in the exportof TEAs have a potential to modify the mineralization pathways in the receiving water bodies, with feedbacks in the cycling of C, nutrients and metals in aquatic ecosystems.