Assessment of critical loads and their exceedance on European forests using a one-layer steady-state model

Critical loads for N, S and total acidity, and amounts by which they are exceeded by present atmospheric loads, were derived for coniferous and deciduous forests in Europe using the one-layer steady-state model START. Results indicated that present acid loads exceed critical values in approximately 45% of the forested area i.e. 52% of all coniferous forests and 33% of all deciduous forests. The area exceeding critical loads was nearly equal for N (50%) and S (52%). However, the maximum exceedances were much higher for S (up to 12000 mol_c ha^?1 yr^?1 in Czechoslovakia, Poland and Germany) than for N (up to 3500 mol_c ha^?1 yr^?1 in the Netherlands, Belgium and Germany). Furthermore, the critical N loads derived refer to the risk of increased vegetation changes. Higher values, i.e. lower exceedances, were found for N when it was related to an increased risk in forest vitality decrease. The uncertainty in the area exceeding critical loads was estimated to be about ±50% of the given value. This is mainly due to uncertainties in the chemical criteria that have been used. However, despite the uncertainties involved it is clear that large exceedances in critical N and S loads occur in Western and Central Europe. This coincides with the area where a decrease in forest vitality has been reported.     

Assessment of critical loads in liuzhou,China using static and dynamic models

The project Comprehensive Control and Demonstration for Acid Deposition in Liuzbou area is a national key project in the 8th Five-year-plan, and the study on critical loads will provide scientific and quantitative accordance for formulating control strategy. In this paper, critical loads of acid deposition to soil in Lirzhou area, China, were calculated using the Steady State Mass Balance method (SMB and PROFILE) and dynamic modeling methods(MAGIC), based on data obtained from field investigations and physiochemical properties measured through experiments such as the organic content, cation exchange capacity, base saturation, sulfate adsorption capacity, gibbsite coefficient, biomass base cation uptake and selectivity coefficient for cations. Weathering rates necessary to calculate soil chemistry in applying SMB and MAGIC model were determined by computation with PROFILE using independent geophysical properties such as soil texture and mineralogy as the input data, or by the total soil base cation content correlation. The results have shown that the critical loads of acidity in this area are in the range of 0.7–6.0 keq ha^–1 yr^–1, indicating sulfur deposition should be cut down by 50–90 percent of the present level. The upper soil layer is the most sensitive. The maximum allowable deposition loading of this area is also presented in the paper.     

Assessment of land management practices on soil erosion using SWAT model in a Tunisian semi-arid catchment

Journal of Soils and Sediments - Soil erosion is a widespread problem that has threatened the majority of Mediterranean countries. Land management practices are widely used to minimize runoff and...     

Predicting freshwater critical loads from national data on geology,soils and land use

Using information on geology, soils and land use, a map has been generated for Great Britain which indicates five classes of sensitivity of surface waters to acidification. This map has been used for designing sampling strategies for mapping critical loads of acidity for freshwaters. This paper evaluates the freshwater sensitivity map using a data set of water chemistry collected as part of the UK critical loads programme. Discriminant analysis was used to predict five critical load classes from information on geology and soil sensitivity for freshwater sites. This showed geology and soil information can correctly predict approximately 50% of all critical loads classes. In addition, 77% of sites fall within one critical loads class of that predicted. Predictions may be improved by including other variables eg altitude and geographical location. Differences between lake, stream and reservoir sites are also examined. Ranges of critical loads values were determined for each of the five classes of surface water sensitivity. While a trend in critical load values was evident between classes, there was significant overlap. A simplified sensitivity map with only three classes related more closely to critical loads values. The paper demonstrates the usefulness of the surface water sensitivity map for assessing acidification at a national scale, but highlights the difficulties of predicting critical loads for individual sensitive catchments using national data.     

Validation of the UK critical loads for freshwaters: Site selection and sensitivity

Critical loads maps for UK freshwaters have been produced on a 10×10 km grid square basis, and used to map critical load exceedances under various deposition scenarios. A single lake or stream site was selected to represent the most sensitive water body in each grid square using predefined criteria. In the UK a major programme of data screening and validation has been undertaken in order to address issues of accuracy and validity. A major part of this validation exercise, the within-square variability study, is designed to test the extent to which the site chosen for mapping represents the most sensitive water body within each grid square or mapping unit. Sampling of all lake sites in thirty-two randomly chosen 10 × 10 km grid squares has shown that in two thirds of cases, the selection exercise has identified a site in the lowest critical load class within a square. However, up to a third of all sites selected to represent grid squares could be replaced by more sensitive sites with a critical load smaller by at least one Skokloster class. The mean overestimate of diatom model critical loads for sulphur in the within-square variability study is 0.188 keq ha^–1 yr^–1. This means that current critical load maps show overestimates for some grid squares. In order to determine where the most sensitive site has not been identified, further work on catchment scale classification of freshwater sensitivity is being carried out.     

Assessment of the resilience and resistance of remediated soils using denitrification as model process

Purpose

Soil contamination by pollutants is increasing, urging for remediation strategies but little is known about the functional sustainability of these strategies.

Materials and methods

We assessed the resistance and resistance of a microbial respiratory process, denitrification, to two different levels of heat-drought disturbances among (1) thermally treated industrial soil, (2) constructed Technosol made of thermally treated soil, compost, and paper by products, and (3) an arable soil.

Results and discussion

We showed that thermal remediation lead to low resistance and resilience after disturbances. However, addition of compost and paper mill sludge improved the stability.

Conclusions

This work underlines the relevance of resistance and resilience ecological concepts for assessing remediation strategies.     

The effects of scale and resolution in developing percentile maps of critical loads for the UK

Critical loads are estimated in the UK by the Department of Environment's Critical Loads Advisory Group and sub-groups. The Mapping and Data Centre at ITE Monks Wood acts as the National Focal Centre for the UNECE programme for mapping critical loads. The centre is responsible for the generation of UK data sets and their application for national and European purposes. To make effective use of these data, it is necessary to draw upon other environmental data and examine the issues of scale, uncertainty and the way that data are presented. This paper outlines the methodologies which have been employed to derive national maps. Early critical load maps were not vegetation specific, but now critical loads for acidity and for nutrient nitrogen for soils, critical levels maps for ozone and sulphur dioxide, and sulphur deposition maps, have been generated on a vegetation or ecosystem specific basis. These have been used to derive a number of different types of critical load and exceedance maps. The results show the importance of the method selected and the data used for the interpretation. The visualisation of critical loads and the corresponding exceedance data is an important aspect in producing information for pollution abatement strategies.     

Evaluation of estimation methods and base data uncertainties for critical loads of acid deposition in Japan

Simplified steady state mass balance model for critical load (CL) estimation was applied to a test area in Japan to evaluate applicability of the model. Three different criteria for acidification limits (1: [Al³⁺]<0.2 eq.=">^–3, 2: Al/BC<1.0 mol=">^–1, 3:Al depletion criterion) were used. Mean values and spatial distribution patterns of CL values calculated by these criteria were extremely different from each other. The first criterion produced much higher CL than the second criterion in the Japanese condition with high annual precipitation. Improvements including definition of the criterion were considered necessary. As quantitative data of the base cation weathering rate (BC_w) was lacking, the rate was specified based on surface geology and the soil type of each site. To evaluate uncertainty of BC_w used for CL calculation, ion content and particle-size distribution were measured for the soils collected from the test area, and BC_w was estimated with PROFILE model based on these measurements. It appeared that BC_w estimates by surface geology were adequate as a mean value, but they had uncertainty of about 50% of the average values due to variability of ion contents within the same surface geology group.     

Mapping of critical loads and levels for pollution damage to building materials in the United Kingdom

The United Kingdom National Materials Exposure Programme was initiated in 1986 to study the effects of acid deposition on building materials. The output data in the form of empirical dose-response equations (described elsewhere) have been incorporated into a geographical information system (GIS). In addition, data for the stock at risk of building materials has also been used. The dose-response relations indicate a dominance of dry deposition of sulphur dioxide in the decay process. Critical level/load maps have been determined for a number of materials. General pollution and meteorological data sets are also included in the mapping process. Maps give ‘exceedence squares’ on a 20 km square grid basis, indicating the unprotected areas or those still at risk for a given scenario for SO₂ reduction in the context of the UNECE protocol for sulphur. In order to derive maps of areas sensitive to pollutants in the future a model, HARM 7.2, is used for the prediction of distribution of emissions of pollutants in the UK. A series of maps has now been produced for different materials at 70% and 80% scenarios for the reduction of SO₂. Studies of the sensitivity of the exceedence maps to the accuracy or variation of the components in the dose-response equations have been undertaken. Results from the mapping programme and the sensitivity analysis are presented together with discussion of the concept of critical loads of materials.     

Impacts of conservation buffers and grasslands on total phosphorus loads using hydrological modeling and remote sensing techniques

To better assess the impacts of conservation buffers and grasslands on water quality at large spatial scales, development and integration of novel approaches are crucial to ensure that these land management practices are functioning properly and meeting their original goals. Recent developments in remote sensing technology have greatly enriched the availability of geospatial data that can be used in hydrological modeling to assess the potential hydrological response of conservation practices over larger areas. A methodology was developed using the object-based image analysis approach with Landsat-5 TM imagery of the year 2005 and thematic layers of streams to quantify conservation buffers and grasslands (OBIA-2005). The OBIA-2005 land cover data was used in the Soil and Water Assessment Tool hydrologic model to assess the impacts of vegetative conservation practices on total phosphorus (TP) loads. The model was calibrated and validated for discharge and TP loads in the Cedar Creek Watershed (CCW) in northeast Indiana. In general model efficiency for streamflow values was within acceptable statistical ranges. While calibration of TP loads was satisfactory for the total contributing area of two nested catchments within the upper CCW. Vegetative buffers of 30.5 m and 61 m combined with conservation grasslands generated from the OBIA-2005 resulted in a large reduction of TP loads as compared to no practices. The results also showed that including conservation grassland alone reduced TP loads by less than 2%. However, the combination of these practices with the width of edge-of-field buffer strips module of the SWAT model achieved the largest TP loads reduction. These findings demonstrate that improved representation of vegetative conservation practices in geospatial land cover data sets are more effective in assessing the impacts of conservation buffers and grasslands on water quality through hydrologic modeling.     

Correlation between the morphogenetic types of litter and their properties in bog birch forests

A formalized arrangement of morphogenetic types of litter according to the physicochemical parameters provided their significant grouping in three genetic associations. The litter group (highly decomposed + moderately decomposed) is confined to the tall-grass group of bog birch forests. The rhizomatous (roughly decomposed) litter is formed in the sedge-reed grass bog birch forests. The litter group (peaty + peatified + peat) is associated with the bog-herbaceous-moss group of forest types. The genetic associations of the litters (a) reliably characterize the edaphic conditions of bog birch forests and (b)correspond to formation of the peat of certain ecological groups. We found highly informative the acid-base parameters, the exchangeable cations (Ca²⁺ + Mg²⁺) and the total potential acidity, which differentiated the genetic associations of litter practically with 100% probability. The expediency of studying litters under groups of forest types rather than under separate types of bog birch forests was demonstrated.     

Assessment of carotenoid bioavailability of whole foods using a Caco-2 cell culture model coupled with an in vitro digestion

Epidemiological studies have shown that consumption of carotenoid-rich fruits and vegetables is associated with a reduced risk of developing chronic diseases. beta-Carotene, alpha-carotene, and beta-cryptoxanthin are precursors of vitamin A, a nutrient essential for human health. However, little is known about the bioavailability of carotenoids from whole foods. This study characterized the intestinal uptake performance of carotenoids using monolayers of differentiated Caco-2 human intestinal cells and mimicked human digestion to assess carotenoid absorption from carrots and corn. Results showed that Caco-2 cellular uptake of beta-carotene and zeaxanthin was higher than that of lutein. Uptake performances of pure carotenoids and carotenoids from whole foods by Caco-2 cells were both curvilinear, reaching saturated levels after 4 h of incubation. The time kinetics and dose response of carotenoid uptake presented a similar pattern in Caco-2 cells after plating for 2 and 14 days. Furthermore, the applicability of this new model was verified with whole grain corn, showing that cooked corn grain significantly enhanced carotenoid bioavailability. These results support the feasibility of the in vitro digestion cell model for assessing carotenoid absorption from whole foods as a suitable and cost-effective physiological alternative to current methodologies.     

Mercury in swedish forest soils and waters — Assessment of critical load

As a result of air pollution, the content of Hg in fish has significantly increased in a large part of Scandinavia and North America. In this paper, the occurence and fluxes of Hg in Swedish forest soils and waters are reviewed and synthesized. The main objective is to describe and evaluate the present transport of anthropogenic Hg from atmospheric deposition, through the terrestrial compartment and running waters to lake basins and also to comprehend the main factors influencing these fluxes. The transportation and distribution. of Hg in forest soils and waters is closely related to the flow of organic matter. The content of Hg in humic matter is higher in southern and central areas compared to the north of the country. Compared to background concentrations, the Hg content has increased in the southern and central part by about a factor of 4–7, while the overall increase in the north is by about a factor of 2 to 3. The increased content of Hg in forest soils may have an effect on organisms and biological processes in the soil. Regarding budget calculations for whole catchment areas and for the mor layer of the soil, a reduction of about 80% from present atmospheric wet deposition must be obtained to reach “critical load” with respect to conditions in Scandinavia.     

Potential effects of climatic change on some western Canadian forests,based on phenological enhancements to a patch model of forest succession

We enhanced the forest patch model, Zelig, to explore the implications of 2×CO₂ climate change scenarios on several forest regions in British Columbia and Alberta, Canada. In addition to the processes and phenomena commonly represented in individual-based models of forest stand dynamics, we added some species-specific phenology and site-specific frost events. The consideration of bud-break heat sum requirements, growing season limits, and chilling requirements for the induction of dormancy and cold hardiness slightly improved the ability of Zelig to predict the present composition of B.C. forests. Simulations of the predicted effects of future climatic regimes (based on the averaged predictions of four general circulation models) include some major shifts in equilibrial forest composition and productivity. Lowland temperate coastal forests are predicted to be severely stressed because indigenous species will no longer have their winter chilling requirements met. High-elevation coastal forests are expected to increase in productivity, while interior subalpine forests are expected to remain stable in productivity but will gradually be replaced by species currently characteristic of lower elevations. Dry, interior low-elevation forests in southern B.C. are likely to persist relatively unchanged, while wet interior forests are expected to support dramatic increases in yield, primarily by western hemlock. Northern interior sub-boreal forests are likewise expected to increase in productivity through enhanced growth of lodgepole pine. Conversely, the precipitous collapse of spruce stands in the true boreal forests of northeastern B.C. is expected to be associated with reduced productivity as they are replaced by pine species. Boreal-Cordilleran and Moist Boreal Mixedwood forests in Alberta are less likely to undergo compositional change, while becoming somewhat more productive. We believe these model enhancements to be a significant improvement over existing formulations, but the resulting predictions must still be viewed with caution. Model limitations include: (1) the current inability of climate models to predict future variation in monthly temperature and precipitation; (2) sparse information on the phenological behaviour of several important tree species; and (3) a poor understanding of the degree to which growth is constrained by different suboptimal climatic events.     

The larger mammals and their endangered habitats in the silent valley forests of South India

A study has been made of the population ecology of large mammals of Silent Valley and contiguous forests of South India. The vegetation of Silent Valley and Attapadi forests are mostly west coast tropical evergreen and semi-evergreen types. In the adjoining forests Nilambur and Nilgiris, the vegetation is southern secondary moist mixed deciduous and southern montane wet temperature, respectively. Silent Valley and its contiguous forests harbour 25 species of large and medium-sized mammals, including two endangered endemic species and many others that are endangered and protected. The lion-tailed macaque, Nilgiri tahr and tiger were sighted in and around the submergence area of the proposed Silent Valley hydroelectric project. If constructed, the impact of this dam on the populations of larger mammals in the area would be severe.     

a critical evaluation of the use of the PROFILE model in calculating mineral weathering rates

The PROFILE model is used extensively in the European Critical Loads programme as an aid to international negotiations on SO₂ emission abatement. PROFILE calculates the rates of cation release by mineral weathering and it then uses these data to calculate soil solution and runoff chemistry. No independent assessment of the underlying assumptions and data in the model has been published and this paper reports such an assessment. The rate equations, which are the key to the PROFILE model require rate coefficients and constants. These have been derived from the literature but more work is required to produce a consistent set of constants. Manipulation of these rates to take into account the exposed reactive surface area of the minerals is fraught with problems. Calculation of exposed mineral surface area from soil textural data results in under-estimates and the requirement to determine the surface area fraction of the different minerals in the soil to be known is extremely difficult if not impossible. Further uncertainty is introduced by adjustment of the rates to take into account temperature differences and by the use of a default mineralogy which is compositionally unrealistic. Despite its flaws PROFILE usually predicts similar weathering rates to other methods of calculation. It is argued that the unrealistic constraints imposed by the use of the surface area equation may be responsible for limiting calculated weathering rate to a fixed range which coincides with characteristically determined values for weathering rates.     

Vertical distribution of Collembola (Hexapoda) and their food resources in organic horizons of beech forests

 Micro-samples of the surface organic horizons of 13 beech forests in Belgium were fixed immediately after collection in ethanol. Collembola (6255 animals) were sorted directly from micro-samples in the laboratory using a dissecting microscope, while the litter/soil matrix was analysed semi-quantitatively. The vertical distribution of Collembolan species was studied by correspondence analysis. Gut contents of animals were examined under a light microscope and their composition was compared with that of the matrix. A consistent association was found between the vertical distribution of gut contents and that of food resources in the immediate proximity of animals. Species differed in their feeding habits but most of them ingested a wide spectrum of food items. Plasticity in the food regime according to depth could be demonstrated in members of the Onychiuridae family. Received: 11 January 1999