With the rapid development of computer technology, numerous simulation models have been developed for agricultural systems and farms. Nevertheless, most of them are rather appropriate for developed countries as they have considerable data requirements and often aim at optimizing farm resources, excluding the farmer's household from the system. Yet, the latter is crucial for the understanding of semi-subsistence systems such as those found in developing countries.We present a dynamic model of an agricultural system in the Central Highlands of Nicaragua. It aims at giving a deeper insight into the functioning of the system and the constraints the latter is subject to. Such an approach helps to explain why farmers make certain choices. Although for the study area few data are available, a robust model with a one-day resolution could be designed.For simulation two groups of scenarios were chosen:(a) Minimum farm sizes for the production of a certain food supply (e.g. basic staples) were assessed and the impact of increased fertilizer use was estimated. (b) Monoculture farms were simulated with the main crops of the region. The production of calories, protein and added value were chosen as indicators. We determined the labour requirements for both groups of scenarios. Simulation results show that the latter is a limiting factor. This is true even for farming systems aiming at covering minimum needs (food, elemental health care and schooling) only. We can show that farmers' strategies (e.g. crop mix, fertilizer application) are crucial for the system. Last but not least, we produce some evidence for the advantage of the current crop mix in the study region. (c) 2004 Elsevier B.V. All rights reserved.

The temperature, redox conditions, and residence times of the solid waste on the grate and of the raw gas in the secondary combustion zone determine the mineralization processes of organics in municipal solid waste incinerators. An improved knowledge of the influence of these factors on the incineration process might help to optimize incinerators with regard to mineralization efficiency of organics. This paper presents a method for investigating the influence of process parameters on mineralization of organics to CO2 by using the elemental carbon (EC) and organic carbon (OC) concentrations in the solid residues as indicators. The results obtained by experiments in full-scale incinerators show that the EC concentration in these residues is a good indicator of oxygen supply, whereas the OC/EC ratio is a good indicator of temperature in and above the furnace bed. Very effective burnout of the bottom ash up to 0.95 g of TOC (EC + OC) per kilogram of dry matter (DM) and of the electrostatic precipitator (ESP) ash up to 0.24 g of TOC per kilogram of DM was achieved in a full-scale incinerator.

In this paper, dynamic models for managing durables are applied for the first time to an urban region in developing countries, i.e., Tunja in Colombia. The focus lies on the analysis of the material balance of furniture, as an example, in private households. One of the major problems in calculating the material balances in regions in developing countries is the low availability of reliable data. The investigations lead to the following conclusions: (1) In developing countries, regional stocks and fluxes of durables can be described using a dynamic model based on a stratified approach. This allows forunderstanding the relevance of different social strata, i.e., the use of goods in form of cascades;identifying the parameters relevant for the system behavior;estimating a plausible development pattern.(2) The three behavioral parameters: (i) stock saturation and residence time of the goods; (ii) ratio of reused to new durables; and (iii) ratio of deposited to recycled material drive the development of the regional furniture balance. (3) To anticipate changes and problems in the management of durables in the region the potential changes of these behavioral parameters in each stratum have to be included in the analysis. (C) 2001 Elsevier Science B.V. All rights reserved.

A sustainable management of non-renewable metals calls for scientific-ecological understanding of the regional material household. The copper household in the USA between 1900 and 2100 was chosen to illustrate mathematical modelling of such systems. Relatively limited and inaccurate sets of data already allow a first approximation of the metal management system. The copper fluxes of the 20th century have contributed to the formation of two new ore deposits of the same order of magnitude as the currently still available reservoir (90 million tons), i.e. copper stock in consumption products (approx. 70 million tons) and in land fills (approx. 40 million tons). The "land fill", therefore, contains copper whose potential use is lost due to dilution. The long-term copper consumption stock is greater than the short-term stock. Scenarios show that the current economically mineable Cu-stocks will be exhausted in 30 to 50 years if a change in the existing management system does not occur. In case of a reorientation, the use of copper as a "new resource" in the consumption stocks appears to be the most promising strategy. The future waste management processes will have to increase their copper recycling rates.

The method of material flux analysis is applied as an instrument for the early recognition of environmental problems in an urban region of developing countries. It is shown that, even with poor data quality and quantity, it is possible to apply the method in Tunja, an urban region in Colombia. With sensitivity analysis monitoring points are developed to attain 'early recognition' concerning changes in water quality and quantity in this region. Using the scenario technique it is shown that, owing to the low dilution capacity for sewage in the region, surface water cannot reach the quality of water at a natural state even if technical measures used in industrialized countries are taken.

Summary and Conclusions Efforts to achieve development in densely populated regions have to focus on the settlement areas with their stocks in buildings and transportation networks. In chemical kinetics, the “slowest step” within a series of connected steps of transformation determines the time of the entire transformation. Analogously, the rate of transformation to sustainability of urban systems such as the one we have described in this paper, would be determined by its “slowest step"—the transformation of the stock of buildings and transportation networks. Because of economic and technical factors, that transformation would take two generations, or approximately 60 years. The capital invested in the stock of the buildings and transportation networks (See “Buildings and Underground” in Figure 5.) of the KSM region amounts to $US300,000 per capita. The annual expenditure for the stock's metabolism is $US 10,000 per capita. This amount is within the same order of magnitude as the annual net income per cap...

In developing countries problems concerning water quality have agravated during the last decade. While in industrialized countries the traditional and modern types of water pollution (e.g. domestic, industrial, nutrients) occured in over a 100- year period, in developing countries however they have occured within one generation [WHO, 1989]. Short time technical measures have important immediate effects, but for achieving sustainability it is critical to develop tools for long term planning which allow a better understanding of how different strategies affect outcomes and how strategies are sensitive to different levels and types of financing [Bower, 1989]. In industrialized countries the method of Material Flux Analysis (MFA), has been shown to be a suitable instrument for early recognition of environmental problems and evaluation of environmental measures [Baccini and Brunner, 1991]. It has been shown that it is possible to combine data from market research on one hand with data from urban waste management on the other hand to observe the metabolic dynamics of a region [Baccini et al. 1993]. However, this method has not been applied yet in Developing Countries due to the low data availability and the poor data quality. The aim of this paper is to show how the method of MFA was applied to a region in a Developing Country with regard to water resource management.

Environmental protection aims to prevent damage by early recognition of possible hazards. The potential of accounting techniques for materials (similar to financial accounting) to forewarn of critical loadings on water, air and soil is assessed. The increase of the annual mean concentration of the various substances introduced by man are very small and directly measurable only after many years. However, analysis of material flux can quantify such changes. This is illustrated for zinc.

A method is presented to predict the short-term (months to years) and long-term (> 30 years) chemical behaviour of bottom ash from municipal solid waste incinerators in monofills. It is based on bottom ash composition and laboratory kinetic studies of bottom ash with water. Bottom ash after the quench tank is a reactive mixture in which slow and fast acid/base reactions occur. These intrinsic acid/base reactions continue for at least several months, and the end point is not yet known. The heavy metal concentrations observed in the aqueous extracts reflect primarily the advance of these reactions. Consequently leaching tests based solely on short-term (hours to months) extraction procedures cannot predict the chemical behaviour of bottom ash in monofills. However, laboratory experiments with samples of bottom ash, in which the intrinsic acid/base reactions have proceeded differently, provide useful information on the nature of chemical reactions significant in the short- and long-term.

The goal of environmental protection is to prevent damage by early recognition of possible hazards. In the present paper, the potential of materials accounting techniques to forewarn of critical loadings on water, air and soil is assessed. For this purpose, the anthropogenic and natural contributions to the metabolism of a region are measured and estimated respectively. The control of man-made material fluxes to the environment is discussed with regard to a waste management concept based on sustainable fluxes of emissions and final storage quality of landfill materials. According to the results, regional material balances are powerful tools for integrated waste management: they allow the setting of priorities in waste management by identifying important material quantities and qualities, they are the base for the design and evaluation of waste treatment technologies, they are necessary for environmental impact statements, and they allow the recognition and minimization of the overall flux of materials from the anthroposphere to the environment.

A method is presented to predict the long-term behavior of element concentrations (non-metals and metals) in the leachate of a municipal solid waste (MSW) landfill. It is based on water flux and concentration measurements in leachates over one year, analysis of drilled cores from MSW landfills and leaching experiments with these samples. A mathematical model is developed to predict the further evolution of annual flux-weighted mean element concentrations in leachates after the "intensive reactor phase", i.e. after the gas production has dropped to a very low level. The results show that the organic components are the most important substances to control until the leachate is compatible with the environment. This state of low emissions, the so-called "final storage quality", will take many centuries to be achieved in a moderate climate.

A major problem of sanitary landfills is the assessment of element transfers from inputs to outputs as a function of time. The prediction of gas and leachate generation is necessary for this purpose. Water and element balances for the non-metals carbon, nitrogen, fluorine, phosphorus, sulfur and chlorine and the metals iron, copper, zinc, cadmium, mercury and lead were investigated in four municipal solid waste landfills of various ages. Data from these mass balances were then used to develop a method that permits elucidation of the behaviour of landfill in its most active phase, i.e. that in which relatively high gas generation occurs.

Group discussions were limited to metals and certain metalloids, except that N, P, and S were considered in the broader topic of biogeochemical cycles. In many instances, the statements concerning metals are also applicable to many, or even most, other elements. However, our discussions were focused on the metals and metalloids because of their major importance as environmental pollutants.

The influence of organic matter in the translocation of metals between soil and soil solution of an acid forest soil Water extracts were prepared from soil samples which were collected from a soil profile showing very little variation in the texture down to a depth of 120 cm and thus only little translocation of clay in the soil profile. The aim of the study was to describe the distribution between soil and soil solution of several metals like Cu, Pb, Cd, Zn, Al and Mn as a function of humic substances, electrolyte concentration and pH. From the experimental results the following hypothesis on the reaction mechanisms involving metals and humus derived substances has been deduced. The metals Cu, Fe, Al and Pb are mobilized through complexation by soluble humus substances in addition to the usual pH dependent desorption and dissolution of hydroxides. This mobilization determines the solution concentration of Cu and Fe at pH > 3.7 and Al and Pb at pH > 4.2. Al, Fe and Pb are complexed selectively by high molecular weight humus derived substances which undergo adsorption on soil mineral surfaces. Cu interacts with low molecular weight humus derived substances which are not easily adsorbed by the mineral surfaces. Zn, Cd and Mn primarily undergo sorption and are thus controlled by pH and electrolyte concentration of solutions because their complexation with humus derived substances seems to be weak or nonexistant. It is further postulated that the humus derived substances mobilize Al 3+ and Fe 3+ ions. By this, other metals like Cd, Zn, Mn, Ca and Mg can occupy the free exchange sites.

The master variable in the transport of copper and zinc in lakes is the particle flux. The autochthonous contribution to this particle flux stems primarily from the primary producers. The bioavailability of copper and zinc is strongly influenced by the proton activity in the lake water. Since this property is also a function of primary production a negative feed‐back mechanism can be postulated for the biota/metal interaction. If the two metals exceed a certain threshold value, the biota adapts itself primarily on the level of the primary producers. This adaption results in a phytoplankton community having a reduced capacity to assimilate trace metals.