The elements redistributed by industrial metabolism of fossil fuels are carbon, sulfur, nitrogen, as well as crustal and trace metals. In fact, these are the main chemicals of which living matter is composed of. As such, they are the key nutrients for the plants on earth. However, these substances may be either beneficial or harmful to the receiving ecosystem depending on their quantity, rate, and their chemical form.
In order to asses the possible harm and/or benefit of fossil fuel residues and the possible remedying actions, it is helpful to construct a complete material flow scheme that describes the end-to-end transfer of these materials as pass from one long-term geo-chemical reservoir to another. In order to construct such a flow model, it is helpful to utilize the ecosystem analogue for the human induced material flow, consisting of producers, consumers and receptors (recyclers) as the key players. A general description and mathematical formulation of the ecological analogue is given elsewhere. (Husar 1986, Husar 1992).
The purpose of this setion is to illustrate the application of the producer, consumer, receptor method to the construction of a sulfur and nitrogen flow scheme for the U.S. The essence of the approach is that one follows the path of the fuel or nitrogen from "production", i.e. mining through the consumers to the environmental receptors. More details on the methodology can be found in (Husar 1986). In constructing the materials flow model emphasis was placed on obtaining the relevant data from the measurement records of various U.S. agencies. Also, data were sought for the term trends in order to illuminate the dynamics of the producer-consumer system.
The presentation of the fuel production and consumption data sets are accompanied by a discussion of the technological trends for different industrial consumer sectors. The changes in technology were taken mostly from Darmstadter and al., 1987.
Energy Consumption by Fuel Type
Combustion of coal and oil products, along with the smelting of metals, produces the bulk of the anthropogenic sulfur and nitrogen emissions to the atmosphere. The driving force for fuel production is the consumption of energy by different sectors.
From the turn of the century to the 1970s, U.S. energy consumption has been characterized by a steady increase in total consumption and shifts from one fuel to another (Figure 1). From 1850 to about 1880 wood was the primary energy source. By 1900, and during the first quarter of this century, rising energy demand was matched by the increasing use of coal. The depression years of the early 1930s are reflected in the sharp drop of coal consumption, which increased again during the war years in the early to mid-1940s. Coal consumption declined to another minimum in 1960, because the increasing energy demands were supplied by cleaner fuels, natural gas and petroleum. Accelerated oil and gas consumption began in the late 1930s and 1940s, such that by 1950 the energy supplied by oil exceeded that of coal and maintained its rise up to the early 1970s. By 1960 natural gas surpassed coal as an energy source.
Figure 1. Trend for U.S. fossil fuel consumption since 1850. (a) Consumption by fuel type; (b) fraction of total energy by fuel type (Husar 1986).