Temporal trends of bulk precipitation and stream water chemistry (1977-1997) in a small forested area, Krusne hory, northern Bohemia, Czech Republic

The Krusne hory (Erzgebirge or Ore Mountains) has been: heavily; affected b y high atmospheric pollutant deposition caused by fossil fuel combustion in an adjacent Tertiary coal basin. Long-term routine sampling of bulk precip itation (1977-1996) and stream water (1977-1998) in a forested area on the south-eastern slope of the mountains were used to evaluate trends and patte rns in solute concentration and flux with respect to controlling processes. From 1977 to 1996, the annual volume-weighted Ca2+ and SO42- concentration s decreased in bulk precipitation. However, after 1989, when a pronounced a nd continuous decrease occurred in coal production, annual volume-weighted concentrations decreased for most solutes, except H+. The concentration dec reases were marked, with 1996 levels at or below 50% of those in 1989. The lack of a trend in H+ is attributed to similar decreases in both acid anion s and neutralizing base cations. Stream water concentrations of most solute s, i.e. H+, Ca2+, Mg2+, SO42- and NO3-, were highest at the onset of sampli ng in 1977, decreased markedly from 1977 to 1983 and decreased more gradual ly from 1983 to 1998. The spruce forest die-back and removal reduced dry de position of these solutes by reducing the:filtering action, which was provi ded by the forest canopy. A notable decrease in stream water Ca2+ concentra tions occurred after 1995 and may be due to the depletion of Ca2+, which wa s provided by catchment liming in 1986, 1988 and 1989. Solute flux trends i n bulk atmospheric deposition and stream water generally were not significa nt and the lack of trend is attributed to the large interannual variability in precipitation quantity and-runoff, respectively. All solutes except Na varied seasonally. The average seasonal concentrations varied between the solutes, but for most solutes were highest in winter and spring and lowest in summer, correlating with the seasonal trend in runoff. For Ca2+, Mg2+ an d SO42-, the concentration minimum occurs in September and the maximum occu rs in February or March, correlating with the seasonal baseflow. These solu tes;are primarily controlled by the contribution of soil water and groundwa ter to stream flow. During snowmelt, the meltwater generally causes concent rations to decrease as soil water and groundwater are diluted. For NO3, ave rage minimum concentrations occur in August at the end of the growing seaso n concurrent with the lowest stream flow, and the maximum occurs in Februar y and March with high stream flow during snowmelt. Seasonal: stream water N O3- concentration variations are large compared with the long-term decrease . Copyright (C) 1999 John Wiley & Sons, Ltd.