Constitución de la República del Ecuador – Presupuesto General del Estado

bookkeeping practised by farmers in the Netherlands to obtain insight into the mineral losses resulting from their agricultural operations. In the future, this bookkeeping overview may be linked to a mineral surplus tax et 1993). Another example is the Substance Deposit system (Huppes et 1992), which is rather like the surplus tax but would be operated on a national or supra-national level.

The third step of the framework, the interpretation of the results, will not be treated further in this article. In Chapter 4, the interpretation of the SFA is treated in more detail.

2.3 SFA System definition

As mentioned in Section 2.2, the choices regarding both system definition and the most suitable type of modelling depend on the aim of the study. The general aim of the conducted studies, for which the method presented here has been developed, can be specified as: to provide the relevant information for a management strategy regarding pollutants. This leads to two basic choices, substantiated by the starting point of the pollution problems as they present themselves within the region:

- the choice for the regional approach;

- the choice for one substance or a limited group of substances to be analysed at a time. Space, time and materials

The first demarcation to be made is a geographical one: the choice of a region. Such a choice often follows naturally from the of the study. In general, there are no real requirements for the region's size: any size from purely local (e.g. 1 hectare) to global is possible. A choice for an administrative region such as a country or a group of countries has definite advantages, especially with regard to data availability (production and trade statistics). It also facilitates a linkage with a country's environmental policy. Other choices are possible, from the point of view of environ- mental analysis (river basins, coastal seas), or otherwise (counties, polders, agricultural units). The inclusion of various scale levels within one study may also yield relevant information. The choice for the materials to be investigated has been inspired, in the SFA studies conducted in the past, by established environmental problems within the region. Another possibility is a choice for economic bulk flows such as iron and steel, aluminium or (fossil) carbon.

For the remainder, the SFA system definition is derived from three basic notions regarding the relationship between the economy and the environment:

- the economy/environment distinction - the economy/environment analogy - the economy/environment integration.

Figure represents the SFA system in its most general terms.

The distinction

useful for interpreting the results in terms of the economic-environmental interaction. Two subsystems are acknowledged:

- the societal subsystem, also referred to as the economy, or (also used) the technosphere or the This subsystem contains the stocks and flows mainly controlled or caused by humans;

- the environmental subsystem, also referred to as the biosphere. This subsystem contains the stocks and flows in the environment that can be described as biologically available.

The immobile stocks, encompassing the geological stocks in the or lithosphère, could be defined as a third, separate subsystem, with its own flows and processes (be it on a geological time scale) and its own exchanges with the other two subsystems. Isolation from the economic or environmental surroundings is then the key criterion for characterizing stocks as immobile. Another possibility is to define the immobile stocks as a category of stocks within the other two subsystems, since scrutinizing the actual geological processes will hardly ever be relevant in SFA practice. The geological stocks, as well as some environmentally inert bulk stocks such as atmospheric nitrogen gas and in the sea, or specific forms of long-term storage in the economy could then be encompassed. In Figure 2.1 these are pictured on the border between the economy and environment, because both certain economic and certain environmental stocks could theoretically be described as immobile stocks.

It is, of course, also possible to divide both subsystems into further subsystems. Husar (1994) for example distinguishes the biosphere, atmosphere and hydrosphere as subsystems of the environ- ment. Within the economy, a distinction can be made between the various stages of a substance's life cycle, for example, or between the intentional and the unintentional flows of a substance. The usefulness of such subdivisions once again depends on the goal of the conducted study.

Figure 2.1 The Substance Diagram

Actually drawing the borderline between the economy and environment inevitably leads to practical problems. Arguments can be found, for example, for viewing "landfill" as an emission to the environment, but also for keeping the landfill facility itself within the economy and counting only the losses from this landfill as emissions. Agricultural soil may be considered a part of the production system and therefore part of the economy, but may also be looked upon as an environmental compartment. In the latter case, application of fertilizer counts as an emission, while in the first case only the losses from agricultural soil to the atmosphere or groundwater qua- lify as emissions. It may depend on the aim of the study how exactly the demarcation is specified, as long as the specification is clear and is followed through in all its consequences.

In specific cases, it may be sufficient just to take one subsystem into account. Modelling the economic flows, for example, will be adequate when the goal of the study is to establish whether certain emissions may be expected to be reduced to a specific level. In the case of overall substance management, however, it is useful to consider both subsystems: relevant information can be obtained on the magnitude of the economic flows relative to the environmental flows, and a relation may be established between environmentally problematical flows and the economic flows that cause them.

The economy/environment analogy

The economy/environment analogy as a criterion for the system definition originates directly from the concept of industrial metabolism. The Substance Flow Diagram (SFD) shows this analogy by specifying the subsystems inflows as well as outflows in corresponding terms:

- import/inflow and export/outflow: flows entering the region from, or leaving the region to, neighboring regions. In the economy, this concerns the import and export of the substance in raw materials, goods and waste products; in the environment, this is the in- and outflow via air or surface waters;

- formation and degradation: the coming into existence, and ceasing to exist, of substances by chemical formation and degradation in economic or environmental processes;

- recovery/erosion and immobilization: the becoming available, and becoming unavailable, of substances because of extraction from or addition to the immobile stocks;

- accumulation: the addition to the available stocks of the system. Accumulation occurs in products that are produced but not discarded in the same year. Negative accumulation, or stock decrease, also may occur. In the environment, accumulation mostly occurs in soils and sediments, in the groundwater, and in standing stocks of biota.

The economy/environment integration

Another demarcation concerns the specific flows and stocks to be taken into account. The SFA method encompasses economic and environmental flows in a single system, so that the substance's fate can be followed from its (mostly economic) cradle to its (usually environmental) grave. In many cases, mostly owing to a lack of data, stocks are ignored and only flows (including accumulations, i.e. changes of stocks) are taken into account. If the life span of the applications of the substance is not too long, the error in outcome will not be too large.

SFA also aims at obtaining an overview of all the region's economic and environmental flows (and stocks), inspired by the approach. Not only the intended effects, but also the unintended changes in substance flows resulting from certain societal developments then become apparent. As stated above, other goals may lead to different choices: a sectoral analysis is also with virtually the same investigative instrumentarium, as is the scrutinizing of a specific production/consumption chain.

The processes: the life cycle

The system's flows are directed by the system's economic and environmental processes. These processes in fact determine the substance's pathways into, out of and through the region, and are

therefore the main object for modelling. Each process, economic or environmental, is described in terms of a redistribution of flows. Together, these processes and the flows that connect them provide a network of nodes, describing the substance's life cycle from cradle to grave.

A great deal of modelling has been performed on the environmental processes: atmospheric dispersal, evaporation, leaching, bio-accumulation, etc. This has even led to some very generalized models of the total environment, describing the exchange between the environmental compartments, such as the multimedia Mackay models & Clark, 1991). In fact, such a multimedia type model could very conveniently be incorporated in a general SFA model for the