Modelling the impact of climate change and atmospheric N deposition on French forests biodiversity.

A dynamic coupled biogeochemical-ecological model was used to simulate the effects of nitrogen deposition and climate change on plant communities at three forest sites in France. The three sites had different forest covers (sessile oak, Norway spruce and silver fir), three nitrogen loads ranging from relatively low to high, different climatic regions and different soil types. Both the availability of vegetation time series and the environmental niches of the understory species allowed to evaluate the model for predicting the composition of the three plant communities. The calibration of the environmental niches was successful, with a model performance consistently reasonably high throughout the three sites. The model simulations of two climatic and two deposition scenarios showed that climate change may entirely compromise the eventual recovery from eutrophication of the simulated plant communities in response to the reductions in nitrogen deposition. The interplay between climate and deposition was strongly governed by site characteristics and histories in the long term, while forest management remained the main driver of change in the short term.

A dynamic modelling approach for estimating critical loads of nitrogen based on plant community changes under a changing climate.

A dynamic model of forest ecosystems was used to investigate the effects of climate change, atmospheric deposition and harvest intensity on 48 forest sites in Sweden (n = 16) and Switzerland (n = 32). The model was used to investigate the feasibility of deriving critical loads for nitrogen (N) deposition based on changes in plant community composition. The simulations show that climate and atmospheric deposition have comparably important effects on N mobilization in the soil, as climate triggers the release of organically bound nitrogen stored in the soil during the elevated deposition period. Climate has the most important effect on plant community composition, underlining the fact that this cannot be ignored in future simulations of vegetation dynamics. Harvest intensity has comparatively little effect on the plant community in the long term, while it may be detrimental in the short term following cutting. This study shows: that critical loads of N deposition can be estimated using the plant community as an indicator; that future climatic changes must be taken into account; and that the definition of the reference deposition is critical for the outcome of this estimate.

Modelling changes in forest soil chemistry at 16 Swedish coniferous forest sites following deposition reduction.

The dynamic forest ecosystem model ForSAFE was applied at 16 coniferous forest sites in Sweden to investigate past and future changes in soil chemistry following changes in atmospheric deposition. The simulation shows a considerable historical soil acidification. Acidification in the southwest, where deposition has been greatest, was more expressed in the deepest soil layers, while it was more evenly distributed through the soil profile in central Sweden, and was greater in the upper soil layers in the north. The simulation also shows that a slight recovery took place after the reduction in emissions, but was counteracted by the effect of harvesting. The simulation predicts an increase in the number of acidified sites in the future. The results also suggest that future acidification will be mainly due to the enhanced tree growth resulting from the chronic high deposition of nitrogen and the removal of soil base cations through harvesting.

A systems approach to assess farm-scale nutrient and trace element dynamics: a case study at the Ojebyn dairy farm.

A systems analysis approach was used to assess farmscale nutrient and trace element sustainability by combining full-scale field experiments with specific studies of nutrient release from mineral weathering and trace-element cycling. At the Ojebyn dairy farm in northern Sweden, a farm-scale case study including phosphorus (P), potassium (K), and zinc (Zn) was run to compare organic and conventional agricultural management practices. By combining different element-balance approaches (at farmgate, barn, and field scales) and further adapting these to the FARMFLOW model, we were able to combine mass flows and pools within the subsystems and establish links between subsystems in order to make farm-scale predictions. It was found that internal element flows on the farm are large and that there are farm internal sources (Zn) and loss terms (K). The approaches developed and tested at the Ojebyn farm are promising and considered generally adaptable to any farm.

Modelling future soil chemistry at a highly polluted forest site at Istebna in Southern Poland using the "SAFE" model.

The multi-layer dynamic model SAFE was applied to the forested catchment Istebna (Southern Poland), to study recovery from acidification. Environmental pollution in the area has been historically high. The model uses data from an intensive monitoring plot established in 1999 in a spruce stand, which was planted in 1880. Observations showed that the soil was depleted of base cations. The measured base saturation in 1999 was between 5 and 8% in the different soil layers. Model predictions assuming full implementation of the UNECE 1999 Gothenburg Protocol and present day base cation deposition show that the base saturation will slowly increase to 20% by 2100. Despite large emission reductions, Istebna still suffers from the very high loads of acidifying input during the past decades. Soil recovery depends on future emissions especially on base cation deposition. The recovery will be even slower if the base cation deposition decreases further.

Modeling recovery of Swedish ecosystems from acidification.

Dynamic models complement existing time series of observations and static critical load calculations by simulating past and future development of chemistry in forest and lake ecosystems. They are used for dynamic assessment of the acidification and to produce target load functions, that describe what combinations of nitrogen and sulfur emission reductions are needed to achieve a chemical or biological criterion in a given target year. The Swedish approach has been to apply the dynamic acidification models MAGIC, to 133 lakes unaffected by agriculture and SAFE, to 645 productive forest sites. While the long-term goal is to protect 95% of the area, implementation of the Gothenburg protocol will protect approximately 75% of forest soils in the long term. After 2030, recovery will be very slow and involve only a limited geographical area. If there had been no emission reductions after 1980, 87% of the forest area would have unwanted soil status in the long term. In 1990, approximately 17% of all Swedish lakes unaffected by agriculture received an acidifying deposition above critical load. This fraction will decrease to 10% in 2010 after implementation of the Gothenburg protocol. The acidified lakes of Sweden will recover faster than the soils. According to the MAGIC model the median pre-industrial ANC of 107 microeq L(-1) in acid sensitive lakes decreased to about 60 microeq L(-1) at the peak of the acidification (1975-1990) and increases to 80 microeq L(-1) by 2010. Further increases were small, only 2 microeq L(-1) between 2010 and 2040. Protecting 95% of the lakes will require further emission reductions below the Gothenburg protocol levels. More than 7000 lakes are limed regularly in Sweden and it is unlikely that this practice can be discontinued in the near future without adverse effects on lake chemistry and biology.

Critical loads of acidity for forest soils and relationship to forest decline in the northern Czech Republic.

Critical load calculations in the Czech part of 'the Black Triangle' show exceedance of critical load in 75% of the forest area. A comparison with forest damage data shows an insignificant tendency toward more forest damage in areas with high exceedance. We conclude that high exceedance of critical load is a probable contributing factor to forest damage in the area.

Critical levels of atmospheric pollution: criteria and concepts for operational modelling of mercury in forest and lake ecosystems.

Mercury (Hg) is regarded as a major environmental concern in many regions, traditionally because of high concentrations in freshwater fish, and now also because of potential toxic effects on soil microflora. The predominant source of Hg in most watersheds is atmospheric deposition, which has increased 2- to >20-fold over the past centuries. A promising approach for supporting current European efforts to limit transboundary air pollution is the development of emission-exposure-effect relationships, with the aim of determining the critical level of atmospheric pollution (CLAP, cf. critical load) causing harm or concern in sensitive elements of the environment. This requires a quantification of slow ecosystem dynamics from short-term collections of data. Aiming at an operational tool for assessing the past and future metal contamination of terrestrial and aquatic ecosystems, we present a simple and flexible modelling concept, including ways of minimizing requirements for computation and data collection, focusing on the exposure of biota in forest soils and lakes to Hg. Issues related to the complexity of Hg biogeochemistry are addressed by (1) a model design that allows independent validation of each model unit with readily available data, (2) a process- and scale-independent model formulation based on concentration ratios and transfer factors without requiring loads and mass balance, and (3) an equilibration concept that accounts for relevant dynamics in ecosystems without long-term data collection or advanced calculations. Based on data accumulated in Sweden over the past decades, we present a model to determine the CLAP-Hg from standardized values of region- or site-specific synoptic concentrations in four key matrices of boreal watersheds: precipitation (atmospheric source), large lacustrine fish (aquatic receptor and vector), organic soil layers (terrestrial receptor proxy and temporary reservoir), as well as new and old lake sediments (archives of response dynamics). Key dynamics in watersheds are accounted for by quantifying current states of equilibration in both soils and lakes based on comparison of contamination factors in sediment cores. Future steady-state concentrations in soils and fish in single watersheds or entire regions are then determined by corresponding projection of survey data. A regional-scale application to southern Sweden suggests that the response of environmental Hg levels to changes in atmospheric Hg pollution is delayed by centuries and initially not proportional among receptors (atmosphere >> soils not equal sediments>fish; clearwater lakes >> humic lakes). This has implications for the interpretation of common survey data as well as for the implementation of pollution control strategies. Near Hg emission sources, the pollution of organic soils and clearwater lakes deserves attention. Critical receptors, however, even in remote areas, are humic waters, in which biotic Hg levels are naturally high, most likely to increase further, and at high long-term risk of exceeding the current levels of concern: