Water chemistry and runoff in forest streams at Kloten

Abstract: Natural variability of stream water composition and discharge was studied in the Kloten area, Central Sweden, by means of statistical methods and simulation technique. The effects of Urea (155 kgN ha-1) and ammonium nitrate (AN, 160 kgN ha-1) fertilization and clear-cutting were studied by comparing treated and reference streams before and after management.The concentrations of the chemical constituents and runoff were mostly inhomogeneous in space and time and the coefficients of variation were considerable.Urea fertilization had a more prolonged nitrogen leaching and a total of 750 kgN km-2 compared with AN treated areas (500 kgN km-2). The difference was due to higher nitrate leaching. Base cation leaching was larger and pH increased after Urea fertilization. pH decreased after AN fertilization.Runoff increased 180 mm year-1 after clear-cutting, while no significant change was found after fertilization. The immediate effect of clear-cutting on stream water chemistry was an increase in dissolved organic matter, followed by increased leaching of ammonia (10x), nitrate (9x) and potassium (4.8x). The total excess leaching of nitrogen was 1 040 kgN km-2 during the first three years after clear-cutting.A Norwegian hydrochemical model, that explained stream water composition, was modified and parameterized (40 parameters) for two catchments to analyse differences between them.The differences in parameters between the catchments were interpreted as differences in slopes close to the drainage net, dilution due to different evaporation, differences in standing biomass and current annual increment and slightly different mineral composition of the soils. pH at high flows could be deduced from stand characteristics.