Dr. WOODWELL. It is important to understand what net primary production is. Net primary production is the dry organic matter or energy that is left over after needs of the plants for metabolism have been filled; it is the energy available to support man, other animals and the decay organisms. More than 60 percent of the Earth's net primary production is terrestrial, most of that in forests. Cultivated land provides for only 43 × 1012 kWh of this total.

Probably somewhere between 5 and 10 percent of the world total is used directly now in support of man as food, fuel or fiber. The fraction of the net production of the sea used as food may be higher than that for land because we harvest only fish and may be harvesting fish now at close to the maximum rate that the oceans can sustain.

The most difficult question for us is how much of this flux is used indirectly in support of man through maintenance of essential service? How big can human activities get with respect to the rest of life before all aspects of life in the broadest context of the meaning of "life" are progressively degraded? It seems very doubtful that we will be able to substitute energy-based technologies for all of the functions of forests, for the functions of the biota of the oceans, or for the biota of the coastal wetlands. These are simple systems in the limited sense that they run themselves. They do not require man-controlled energy to sustain them; they do their job in support of man without any tinkering from us. How can we measure the total function of these systems in support of man? Keeping in mind the age-old principle of ecology that no single-factor analysis is ever adequate, we may use as one criterion a comparison of the flux of energy through natural systems with that through man-dominated systems to establish an estimate of the equivalence between the constructive forces of ecological succession and the biotically destructive forces of fossil-fueled man. Table 4 offers such a comparison (Woodwell, 1972).

"Man's Impact on the Global Environment (SCEP)," MIT Press, 1970, p. 294. Estimated on basis of per capita use of energy in United States.

Dr. WOODWELL. Less than 0.1 percent of the solar energy impingent on the top of the atmosphere is fixed in photosynthesis and made available as net production. This does not mean that photosynthesis is inefficient, it simply means that the rest of the solar energy is used in other ways. Photosynthesis provides an average world-wide density of net production of 1.4 kWh/m2/year of the surface of the Earth. The nonbiotic energy flux controlled by man when averaged over all of the land, is very much lower, about 0.3 kWh/m2/year; the average flux

in the United States is about 1.67 kWh/m2/year, appreciably less than the 5 to 15 kWh/m2 characteristic of forests and agriculture in the temperate zone.

In areas such as Manhattan and Brooklyn the flux of nonbiotic energy probably rises to 1,000 kWh/m2/year to 3,000 kWh/m2/year (table 4), nearly as high as the mean solar flux at the top of the atmosphere.

These areas are clearly dependent on other regions for food, fiber, and essential services. The significance of the worldwide fluxes and the U.S. flux require further analysis. What can we say about the effects on the biosphere of the growth of human activities to the point of using an average of 1.67 kWh of energy annually per square meter over the entire United States? The answer is sufficiently complex to be easily ignored.

I shall offer an answer in two segments. First, a general segment showing the pattern of change in the biota caused by disturbance; second, an examination of certain specific effects that are more or less directly caused by energy production.

There is a popular assumption that the Earth's biota is a more or less random array of species, capable of adjusting by evolution or short-term successional rearrangements to virtually any disturbance. The assumption is misleading.

A hundred years of post-Darwinian experience has shown that there are clear, quantitative relationships between species by whatever criterion we choose for measurement. If we choose energy, we can show that there is in any mature natural community a transfer of 10 percent to 20 percent of the energy fixed by the plants to animals that eat plants. Consumers of these animals commonly take 10 percent to 20 percent of this energy. And so on through two or three levels of carnivores. No matter how large the plant population and its net production, carnivores will be rare because there is simply not enough energy transferred to them to support them in abundance.

This does not mean that they are unimportant: they exert controls over the sizes of populations below them in the trophic structure that keep the flow of energy within the 10 percent to 20 percent limits. This simplification emphasizes that there are quantitative relationships between populations in nature. Natural systems have powerful interactive mechanisms to maintain these relationships and to preserve the integrity of biotic structure. There is overwhelming evidence that man is now overriding these interactive mechanisms by changing the basic chemistry, physics and therefore the biology of the Earth, locally, regionally, and worldwide. What are the changes, how important are they, and what should be done?

The changes, no matter how complex they may appear and potentially advantageous in one or more respects, are reductions in biotic structure that can only be considered unstabilizing and retrogressive. The pattern is consistent throughout all of the plant and animal communities of the earth. First, the highly specialized carnivores, perched high in the food web, are reduced or eliminated either by the accumulation of toxins such as the chlorinated hydrocarbons or by changes in the food web below them that leave them without an essential ingredient of their environment. Second, the entire array of plants and

animals is changed from one in which large-bodied, long-lived species occur to one in which small-bodied, short-lived, rapidly reproducing plant or detritus-eating organisms predominate. We see this pattern now in the reduction of forests in the Los Angeles Basin by toxins in the air. The forest is replaced by low growing shrubs and annual herbs. It can be illustrated dramatically in agriculture where use of broadly toxic compounds as insecticides has eliminated predators and competitors not only of the target species but also of other previously benign inhabitants of the crop, releasing insect and mite populations as new "pests", all of which are herbivorous, plant-eating, competitors with man for the crop.

It can be seen in carefully designed experiments such as those at Brookhaven National Laboratory where ionizing radiation has been used to reduce the structure of a forest systematically to offer an opportunity to study specifically such questions. It can be seen in the biotic impoverishment of the lands around the Mediterranean and in eutrophic and polluted streams, lakes, and estuaries.

Data from Lake Pontchartrain obtained by R. Darnell (1961) illustrate these points for a disturbed estuarine lake. The lake was receiving significant quantities of organic matter at the time of the study and was turbid with Mississippi River silt. It contained a surprising diversity of consumers, most of which showed a dependence on two or more sources of food. (Fig. 2) Most, but not all, were dependent on organic detritus in some degree. It is clear that with further disturbance such as elimination of bottom-dwelling animals by siltation, by dredging, or by an oil spill, the fish populations would shift still more heavily toward plant and detritus-eating forms low in the list insofar as the fish survived at all.

[Figure 2 follows:]

FIG. 2 Trophic relationships of the biota of Lake Pontchartrain,

Lousiana. (Adapted from Darnell, 1961).

Dr. WOODWELL. It is important that here few species of fish were dependent directly on the plants; most fed only indirectly through detritus, zooplankton, or other fish. Disruption of one of these populations has implications throughout the system, although the changes are often difficult to measure. The pattern, however, is clear; a reduction of complexity favoring fewer forms that are detritus-feeders.

We guess that this would mean a reduction in total production of fish; it would certainly mean a reduction in the variety of fish and in the opportunity for harvest of food that would otherwise be totally unavailable to man, who does not eat phytoplankton, most small zooplankton or detritus.

These are gross disturbances: minor disturbances such as small changes in the chemistry of environment must be assumed to bring increments of change in the same direction, although individual increments may be unmeasured and unmeasurable. We are learning now that fish and various other animals communicate by chemical signals at incredibly low concentrations. With the experience of DDT and radioactivity behind us we would be naive to assume that small concentrations of other substances cannot be returned to man in toxic quantities.

Indeed, we must assume that they do have biotic effects and manage our affairs to assure that on those systems, such as the oceans, lakes, streams, and terrestrial communities, where biotic integrity is important to us, there is no accumulation of minor chemical insults that can become significant in total. This conclusion bears directly on the recent legislation on air and water pollution as we shall see in a

moment.

There are abundant signs that growth in human influences has already progressed to the point where these individually small insults are worldwide. Clear worldwide effects seem to be limited to an increase in the CO2 content of air, the worldwide distribution of DDT residues and PCB's to the point where virtually every organism contains detectable residues, to fallout radioactivity, to dust in the atmosphere, and to a worldwide reduction in biotic diversity through a combination of direct exploitation and changes in habitat. While each of these has potentially great significance for man, I use them only to emphasize that we are changing the physics, chemistry and biology of the earth worldwide, a clear sign that growth in the aggregate effect of man has already exceeded the point where we can rely longer on the classical assumptions of an Adam Smithbased economics, in which free enterprise organizes itself through the self-interest of the entrepreneur and the economy grows unbridled into a limitless world.

The magnitude and seriousness of the ecological problems associated with the current scale of human activities is shown most lucidly by a consideration of the acidity of rainfall in the Northeastern United States. I have chosen to use as an example the acidity of rainfall.

2

Normally rain has acidity that is determined by the CO2 in the atmosphere. On the pH scale rain usually has a value of 5.6 to 6.0, indicating slight acidity. Increasing acidity is indicated by lower numbers, each whole unit representing a 10-fold increase. During