MODERN BIOGEOCHEMISTRY: SECOND EDITION Phần 3

BIOGEOCHEMICAL APPROACHES TO ECOSYSTEM ENDPOINTS 79 – weakness of available data due to sampling and/or measurement problems, insuf-ficient time-series of data, lack of replication; – datagapssuchasnomeasurementsonbaselineenvironmentalconditionsatastudy site; – toxicological data that are extrapolated from high dose experiments to relatively low exposure; – natural variations in environmental parameters due to weather, climate, stochastic events. Consequently,riskassessmentprocessistheobligatorycontinuationoftheprocess ofquantitativecalculationandmappingofcriticalloadsofsulfur,nitrogenandacidity at various natural and agricultural ecosystems. This is connected with numerous uncertainties a priori included in the computer algorithm for CL calculations: – at the receptor selection step the uncertainty is related to the determination of the mostsensitivereceptor,whichprotectionwilldefinitelyprotectother,lesssensitive, ecosystems; – at the select environmental quality criteria step the uncertainty is connected with an assessment of biogeochemical structure of ecosystems and quantitative charac-terization of biogeochemical cycles of individual elements; – at the select computer method (model) step the uncertainty is related to the appli-cability of steady-state models to dynamic systems requiring the definite simplifi-cation of these systems; – at the calculate critical loads step the uncertainty is usually minimum and related mainly to the possibilities of modern computer pools; – at the compare with actual load step the uncertainty is connected with an assess-ment of modern deposition and their spatial and temporal conjugation with definite ecosystems at the selected resolution scale. 1.2. Comparative Analysis of CL and ERA Calculations of Acidification Loading at Ecosystems The existing uncertainty at all steps of an algorithm for critical load calculation and mapping influences the probabilistic character of these values and arise the necessary tocombinebothapproaches.ThisisillustratedinFigure2.Inthemaximumdegreethe given conjugation is required at the risk management step in the ERA flowchart. The probabilistic approach to the critical loads of acid forming compounds allows us to apply the set of emission reduction scenarios to minimizing the financial investments for ecosystem protection (see Figure 3). Within the defined areas, critical loads are calculated for all major combinations of tree species and soil types (receptors) in the case of terrestrial ecosystems, or water biota (including fish species) and water types in case of freshwater ecosystems. 80 CHAPTER 4 These combinations include the great variety of different ecosystems, the sensitivity of which to both acidification and eutrophication inputs by atmospheric pollutants differs greatly, determining the necessary reduction needs when CLs are exceeded by modern deposition levels. This information on ecosystem sensitivity can be compared with a pollutant de-position map, to determine, which areas currently receive deposition levels, which exceed the area’s CL. The areas of “exceedance” indicate where present levels of pollutant deposition increase the risk of damage to ecosystems. 2. BIOGEOCHEMICAL ENDPOINT IN CRITICAL LOADS CALCULATIONS FOR HEAVY METALS At present, the calculation and mapping of critical loads for heavy metals is only at the beginning and in Europe there are only a few examples of application of methods described in Section 3.2. We will refer to case studies from Germany and Russia as the most characteristic research in this direction. The typical endpoints in these calculations refer to critical concentrations of different heavy metals in the ecosystems. The determination of the given critical concentrations is still uncertain and the relevant risk assessment calculated as an exceedance of critical loads should be based on selecting values of critical concentrations (see 3.2.2). 2.1. Calculation and Mapping of Critical Loads for HM in Germany We have seen that heavy metals can cause toxic effects to living organisms when critical limits are exceeded. Present deposition rates may cause the long-term accu-mulation of heavy metals in the soil, especially in the forest humus layers and bottom sediments. Calculations based on comprehensive models show the long-range trans-port of various heavy metals in regional and continental scale. In addition to atmo-sphericdeposition,inagroecosystemstheinputofHMsisconnectedwithphosphorus fertilizers and application of wastewater effluents. Under increasing acidification of theforestecosystems,manyheavymetalsaccelerateaqueousmigrationinthebiogeo-chemical food web. The known example is related to Cd and Cu. The accumulation of pollutants in various terrestrial and aquatic ecosystems of Germany is almost non-reversible. That is why we will consider the precautionary measures based on critical load calculations of HM. The case study in Germany may give the best example of such an approach (Schutze, 2004). Methods of Critical Load Calculations for Heavy Metals The approach, similar to that described in Section 3.2 was applied for the calculation of critical loads of HM s for German soils. Critical concentrations as ecosystems endpoints According to the heavy metals’ effects, the soil microbes, crops and ground waters as a source of drinking water, are the most important receptors. During migration in the food web, the heavy metals, especially Cd and Hg, can affect also higher organisms, BIOGEOCHEMICAL APPROACHES TO ECOSYSTEM ENDPOINTS 81 including people. After consideration of different pathways, the most sensitive links of food webs should be chosen for establishing the critical concentration in the soil’s solution (critical limit) to protect all other pathways at this concentration. TheCriticalconcentrationswithrespecttothesoilorganismsshouldberelatedtoa loweffectlevelonthemostsensitivespecies.Theeffectsontheprocessofmetabolism and other processes within the organisms should be considered and also the diversity ofthespecies,whichismostsensitivetotheheavymetals,hastobeaccounted.Critical limits must refer to the chronic or accumulated effects. For assessment of the critical concentrations in crops and in drinking water, human-toxicological information is required.Ingeneral,forestablishingcriticalloadsweshouldalsoaccounttheadditive effects of the different metals and combination effect between the acidification and biogeochemical mobilization of the heavy metals in soils and bottom sediments. The environmental standards based on total heavy metal concentration in the soil solution seem the most important criterion for the exposition of further compart-mentsoftheenvironment.Theadditionaleffectsconnectedwithmetalspeciationand complexations were not considered in the study. A Monte Carlo simulation is proposed to appreciate the uncertainty in the process of establishing the critical concentrations of heavy metals in the soil solution. Models In this case study, steady-state mass balance models are applied for critical loads calculation for the heavy metals. SMV +SMDep +SMD +SMAbf = SME +SMAw +SMEr +SMG +1SMVorr. where SMV is release by weathering; SMDep is input by the atmospheric deposition; SMD is input by “usual” fertilising; SMAbf is input by the use of waste; SME is output by harvest; SMAw is output by leaching; SMEr is output by erosion of the soil’s parts; SMG is output by degassing; 1SMVorr is changes of the heavy metal pool in soil. This mass balance presents the possible links in the biogeochemical food web for variousheavymetals.Someitemsmaybeneglected,likedegassingofPb,Cd,Cuand Zn metals. However, this process is of crucial importance for mercury (see Section 3.2). The output of the heavy metals with soil erosion may also be neglected. After elimination of these processes, the simplified following equation is workable. The sum of inputs by deposition, fertilizing, and waste and rubbish as fertilizer stands as the term Critical Load’. Thus, critical loads of any heavy metals may be calculated as follows: CLSM = SME +SMAw −SMV +1SMVorr. Themassbalancemodelforcalculationofcriticalloadsforheavymetalsincludes the weathering process, the net removal through the crop biomass harvest, leaching, and also leaf uptake and litterfall. Using the simple dynamic way, the distribution between adsorbed and dissolved phases was accounted. 82 CHAPTER 4 Figure 4. Database for initial information for calculation of HM critical loads in Germany (Bashkin and Gregor, 1999). The uncertainties in the model inputs were elaborated using the statistic distribu-tion functions for the initial parameters and also the Monte Carlo simulation. The available information for calculation of critical loads of HMs in Germany is shown in Figure 4. This figure shows also the schematic algorithms for CL calcula-tions. The application of CL model and initial information allowed the researchers to map the critical loads of various heavy metals for different ecosystems. 2.2. Calculation and Mapping of Critical Loads for Cd and Pb in the European part of Russia Biogeochemistry of heavy metals has been extensively studied in the former Soviet Unionduetoawidespreadenvironmentalpollution.Thenumerousresultsonecosys-tem sustainability or sensitivity to metal inputs have been accumulated. The assessment of ecosystem sustainability to the heavy metal loading includes primarily the estimation of soil compartment (Solntseva, 1982; Elpatievsky, 1994; Glazovskaya, 1997). These researches as well as literature data from other countries showedthattheprocessesofmetalaccumulationandtransformationinsoilandfurther migration in biogeochemical food webs, like metal uptake by plants and metal leach-ing from the soils, are mainly dependent on geochemical properties of the soils. The followingsoilparameterswereshownasthemostimportant:pH,organicmattercom-position(mainlythehumicandfulvicacidsratio),redoxreaction,andsoilgranulomet-ric composition (Davies, 1980; Sanders, 1982; Kabata-Pendias, Pendias, 1984, 1992; Adriano, 1986; Balsberg-Pahlsson, 1989; Bowen, 1989; Temminghof et al., 1997). BIOGEOCHEMICAL APPROACHES TO ECOSYSTEM ENDPOINTS 83 Glazovskaya (1997) applied an analysis of geochemical conditions in different soilsanddevelopedprinciplesforassessingquantitativelythesustainabilityofecosys-tems under the technogenic impact of heavy metals. The soils of the main natural zones distinguished on the East European plain area were combined into 6 groups ac-cordingtotheirecological-geochemicalsustainabilityunderHMloading(from“very sensitive” to “insensitive”). As shown in this research, most of the soils of the East European plain area have medium or weak sustainability under metal exposure. But quantitative parameters of HM impacts on the soil (including the permissible levels of metal depositions) were not considered in this classification. The quantitative assessment of biogeochemical mass–balances of the metals in various natural, urban and agricultural ecosystems were carried out in the different regions of the Russian Federation (Bashkin et al., 1992; Elpatievsky, 1994; Kasimov et al., 1995; Priputina et al., 1999, 2002, 2004a, 2004b). Methodologically, these researches are similar to the general approach used for calculations of HM critical loads in Europe (de Vries et al., 1998a, 1998b). However, the results of these local researchescouldnotbedirectlyusedforcalculationsofHMcriticalloadsforthewhole area of the East European plain due to scarcity of the data needed for computation according to the steady-state mass balance equation (see Section 3.2). Nevertheless, thesedatawereusedforestimatingandmappingofHMcriticalloadsfortheEuropean Russia area (Priputina et al., 1999; Bashkin, 2002). Preliminary calculating and mapping of critical loads for heavy metals (Pb and Cd) in the forest ecosystems of European Russia have been accomplished using a simplified version of the steady-state mass balance model (Priputina et al., 2002). For present study effect-based critical loads evaluated in accordance to the Guid-ance (de Vries et al., 2002) have been derived using critical limits of heavy metals concentration in the soil solution (0.6–1.0 mg m−3 and 6–10 mg m−3 for Cd and Pb, respectively). Input data applied for preliminary estimations of ERA endpoints includedtheparametersrequiredforcomputingrootuptake,leachingandweathering of heavy metals in different soil types (Priputina et al., 2003). The calculations of critical loads for lead and cadmium have been accomplished for the forest ecosys-tems of several key plots located in various natural conditions of the European part of Russia; background areas from north taiga to deciduous forests zone have been taken for these evaluations (Figure 5). Calculation Methods and Critical Limits Inthisstudytwodifferentendpointshavebeenselected:humanhealthaspects(critical limits based on drinking water quality) and ecotoxicological effects on biota (critical limits based on free metal ions concentration) (Priputina et al., 2004b). Two metal fluxes (net uptake in harvestable parts of plant biomass and leaching from the considered soil layer) are included in the mass balance equation (M&M Manual, 2004): CL(M) = Mu + Mle(crit). (1) ... - tailieumienphi.vn