Based on the experience from runoff and groundwater recharge simulation a model system has been developed for terrestrial, hydrochemical, and hydrological simulations. The system emphasizes the role of temporary or long term storage in the aquifers of a basin and, separately, accounts for each rainfall or snowmelt event from its entrance into the ground until mixing in the river system. The model is primarily intended for simulation of natural short term variations in alkalinity and pH in running waters. The hydrochemical processes are modelled in a semi-empirical way without assumption of complete hydrochemichal mass-balance. In the paper a brief hydrochemical background is given, and a model with two alternative hydrochemical sub-structures is described. Examples of daily simulations of runoff alkalinity and pH from three different basins are given.

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The chemistry of groundwater has been altered to a large degree through the influence of human activities. Addition of acids through precipitation and dry deposition, nitrogen from agriculture and sewage systems, and chloride from deicing are quantitatively the most important sources. In this paper the chemical characteristics of groundwater are discussed for a crystalline bedrock area located above the highest marine shoreline in southern Sweden. The aim of the study is to establish the background levels for the main chemical constituents in these waters. Focusing on sulphate and chloride, contributions from deposition are evaluated and a comparison with surface water chemistry is performed. Approximately 50% of the base cations in the lakes with extremely low alkalinity originate directly from deposition, while the corresponding figure for lakes with higher, though still low alkalinity, is approximately 39%, and for shallow wells the figure is 36%. There is evidence that the lakes receive water from a shallower depth than the shallow wells, but both groups receive the base cations mostly from the exchange store, or from weathering where the alkalinity produced is consumed by acid inputs. Deposition levels of sulphate and chloride are better approximated by lake water than by groundwater.

The heavy use of manure and fertilizers has in some parts of Sweden resulted in unacceptable concentrations of nitrate in ground water used for private and municipal water supply. In Halland for example, several of the municipal water supplies have nitrate concentrations close to 50 mg/I. Either anionic exchange or mixing with water with less nitrate are used to reduce the nitrate content in the distributed water. However, some wells have been abandoned because of high nitrate concentrations. In this study an attempt is made to reduce the nitrogen contamination of the ground water at the source. In well recharge areas the agricultural practices are investigated and, if necessary, alterations are proposed to the farmer in order to decrease the nitrogen leaching from the soil profile. The effect of these improvements is continuously studied in soil and ground water. An action plan is proposed for water supplies with dominating arable land in the recharge area.