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Recovery from anthropogenic acidification in streams and lakes is well documented across the northern hemisphere. In this study, we use 1996–2009 data from the four Swedish Integrated Monitoring catchments to evaluate how the declining sulfur deposition has affected sulfate, pH, acid neutralizing capacity, ionic strength, aluminum, and dissolved organic carbon in soil water, groundwater and runoff. Differences in recovery rates between catchments, between recharge and discharge areas and between soil water and groundwater are assessed. At the IM sites, atmospheric deposition is the main human impact. The chemical trends were weakly correlated to the sulfur deposition decline. Other factors, such as marine influence and catchment features, seem to be as important. Except for pH and DOC, soil water and groundwater showed similar trends. Discharge areas acted as buffers, dampening the trends in streamwater. Further monitoring and modeling of these hydraulically active sites should be encouraged.

Sampling of groundwater in theQuaternary deposits was carried out at 70 sitesin Stockholm for, among other things, metalanalyses. The objectives were to get a notion of the metal content and to get a basis for anestimation of the order of magnitude of thegroundwater transported metal contribution to themain surface water bodies in comparison to otherroutes. Thus, in three watershed areaswithin the Stockholm Town, groundwater flow andmetal concentration propagation were simulatedand metal fluxes were calculated. Theconcentrations of heavy metals were in generalfound to be very high in comparison withgroundwater in forested areas. This was mostpronounced for mercury (Hg) and copper (Cu). Themost remarkable result was a Hg concentration of4.57 μg L-1 in the vicinity of a closed downhospital. The annual contribution of heavy metals(kg) by groundwater to the main surface waterbodies was estimated to: As (2.2), Cd (0.20), Co(4.9), Cr (3.1), Cu (34), Hg (0.06), Ni (28), Pb(2.2) Zn (118). These fluxes are much smallerthan those in forest ecosystems, due to lowergroundwater recharge in urban areas, where agreat part of the runoff is diverted bylandsealing, drainage, tunnels etc. The modelingresults emphasize the importance of the sorptionprocesses indicating that the modeled areas arein a non-steady state condition. It also showsthat the sources generating elevatedconcentrations of the high adsorptive metals Pband Hg are likely to be nearby.

An inexpensive and easy-to-handle setup for freeze-thaw experiments was developed. The system mimics field conditions, with a relatively deep monolith of undisturbed soil and a soil-air interface as an upper boundary condition. The setup includes a freezing device for vertical freezing of a soil monolith and transducers at several depths in the soil monolith for continuous measurement of unfrozen water content (TDR), temperature and radial temperature differences. The setup makes rudimentary control of boundary conditions and sophisticated monitoring of soil water and heat conditions possible. To study the performance of the system, soil temperatures and water contents in a clay soil monolith were measured during two freeze-thaw cycles. The setup was shown to be useful in terms of simulating freeze-thaw cycles in a lysimeter placed in the laboratory. One-dimensional heat flows could be simulated, with a thermal error (horizontal vs vertical heat flows) during freezing of about 5%. The setup was used to test the hypothesis that the similitude between freezing/thawing and drying/wetting holds for unsaturated clay soils. The results indicated a good agreement between water retention curves calculated from freezing-point depression data and from measurements, using pressure plates.

Long-term integrated catchment monitoring within the Swedish Environmental Monitoring Programme (PMK) aims primarely at the fate and effects of pollutants in mature ecosystems, mainly protected boreal forests. The measurements that were conducted since the early eighties, with some variation, included deposition, throughfall, litterfall and the chemistry of soil water, groundwater and runoff water.Together with, or perhaps partly due to acidification, accumulation and transport of heavy metals are a serious threat to the ecosystem and in the end to the health of human beings. This paper discuss the behaviour of Hg, Pb, Cd, Zn and Cu based on the experiece gained from the studies in the small catchment areas. The importance of present deposition, soil storage and biogeochemical condition for metal mobility to the transport of metals is discussed The storages of Hg and Pb have been built up during a long time span and are very large in comparison with the flux. The present atmospheric deposition have probably little impact on the flux, which rather is governed by the biogeochemical conditions. There is still a small accumulation of Cd, but its great mobility under acidic conditions makes input and output almost in balance. A reduction in deposition will probably have an immediate effect on flux, which also is the case for Zn. Cu generally accumulates in soil. The mobility and hence the flux are certainly regulated by the biogeochemical conditions, but more detailed studies are required to reveal the general mecanisms for Cu transport within the catchment.

Numerical modelling of soil processes in the field can be based on soil surface temperature or soil surface heat flow as the thermal upper boundary condition. In this study the soil surface temperature and the heat flow were estimated from the air temperature and the soil surface energy balance, respectively, using a physically based numerical model. Simulated values of soil temperature, snow depth and frost depth for a lawn in northern Sweden were compared with measured data over a 22-year period. The air temperature boundary condition gave overestimates of soil temperature during summer and underestimates during autumn. These discrepancies were reduced to negligible levels when an additional resistance to soil heat flow, corresponding to a 4-cm-thick humus layer, was introduced. The heat flow boundary condition based on the soil surface energy balance underestimated soil temperature during autumn. Sensitivity tests indicated that this underestimation was related to the use of a constant crop extinction factor for net radiation. The results of both methods pointed to between-year differences in development of the grass cover. Simulated values of snow depth agreed with measured values. However, the predicted frost depth was an overestimate, probably because the thermal conductivity of snow was overestimated. The temperature boundary condition may be used for prediction purposes, whereas the heat flow boundary condition should be used for physically based studies of soil boundary processes.

The infiltration of snow melt water on arable land influences both the water storage and the nutrient budget. The infiltration rate during thawing was assumed to depend on the ice content of the soil. Field measurements of soil temperature, water content and infiltration rate were made and used to test a numerical model. Efforts were made to create different ice contents in three plots by adding different amounts of water before freezing as well as during winter. The total water content in spring was not influenced by the pre-freezing addition of water, but slightly increased by water added during the winter. The simulated total water content was constant throughout the winter. The measured infiltration rates were high, at maximum 8 mm/min, and the differences between the plots were small, although lower infiltration rates were found in plots with higher amounts of added water. Simulated infiltration rates never exceeded 0.1 mm/min. The discrepancy was probably due to water flow in the partially unfrozen crack system, which the model was not capable to simulate, and to a time lag in the simulated soil temperature during thawing. Low infiltration rates were probably caused by high ice content in the cracks, originating from the added water. It should be possible to predict the infiltration capacity during thawing using a simple model which treats the crack system, the water content before freezing, and the number and intensity of warm spells during the winter.