♦ Living matter ♦

Living matter is made out of three major elements: hydrogen, oxygen, and carbon. These constitute about 98% by weight of living matter. Three other elements: nitrogen, phosphorous, and sulphur, are regarded as leading nutrients, due to their existence in comparatively large quantities compared to other nutrients. The remaining nutrients are sodium, calcium, potassium, magnesium, iron, zinc, boron, chloride, chromium, cobalt, copper, fluoride, manganese, molybdenum, and selenium.

♦ The biosphere ♦

The architecture of the biosphere requires specific quantities of these nutrients. The quantities vary with the type of organism. Plants obtain their carbon and oxygen from the air, and their hydrogen from water in the surrounding environment. The surplus oxygen molecule in water is released to the air. Thus, in order to go about their livelihood, plants produce oxygen as a byproduct. Plants get the nutrients they need from the surrounding soil and, increasingly in subsidized societies, by artificial fertilization. Thus, plants require solar energy, carbon dioxide, water, and nutrients.

♦ Limiting factors ♦

The supply of solar energy varies primarily with latitude. Plants in tropical and temperate regions are able to get their energy needs during the day or, significantly, during the growing season. Carbon dioxide exists in the air in concentrations that are sufficient for plants to avail themselves of as much carbon and oxygen as needed. Therefore, the limiting factors are always water and nutrients.

The Sahara Desert

Water is limited in regions with little or no rain; conversely, nutrients are limited in regions with too much rain. Throughout geologic time, in humid regions, enough rainfall has percolated through the soil to wash the nutrients out into neighboring streams and rivers. This process is referred to as the leaching of the nutrients. In arid regions, the soils are relatively unspoiled and typically rich in nutrients, because leaching has not had a chance to take place.

So, therein is the dichotomy:  In arid regions, there is plenty of nutrients, but not enough water; in humid regions, there is plenty of water, but not enough nutrients. At the extremes of the climatic spectrum, regions where mean annual precipitation is less than 100 mm are referred to as superarid; regions with mean annual precipitation greater then 6400 mm are referred to as superhumid.¹ In superarid regions, life is hard because there is very little water. In superhumid regions, life is hard, particularly for humans, because there is too much water.

The Amazon Rainforest

♦ Water and anthropogenia ♦

Over the past century, humans have endeavored to counter Nature's design by irrigating arid lands, that is, moving water great distances to irrigate the deserts, thereby making them productive. Since deserts have a store of nutrients, all that is required to start using those nutrients is to add imported water to the soil. Superhumid regions, though, remain largely unused by humans, because most people are uncomfortable in the high humidity that prevails in these regions.

♦ The quandary of civilization ♦

How to cope with the natural balance of water and nutrients across the climatic spectrum? By all accounts, the import of water into arid regions solves the problem of water supply, but necessarily at the cost of creating a problem of salt disposal. In effect, the two major salts, sodium and calcium, are produced from soils in greater quantities than needed by the artificial ecosystems, and end up polluting neighboring watercourses, in the case of open drainage systems; or inland lakes, in the case of closed drainage systems. For instance, the Salton Sea, in California, is a closed system which has been receiving agricultural drainage for the past 80 years, with no end in sight.

Too little precipitation leads to too little water and too many nutrients; conversely, too much precipitation leads to too much water and too little nutrients. It follows that there must be a happy medium where the supply of water and nutrients are optimal, that is, just enough water for life's needs, and not enough nutrients to require disposal.

♦ The 800-mm isohyet ♦

The preceding considerations lead to the concept of mean annual global terrestrial precipitation, and to the recognition of its unique role in fostering sustainability. Mean annual global terrestrial precipitation is the amount of rain that falls globally, on the average, in the continental regions of the Earth. Climatological studies indicate that this number is around 800 mm.² Thus, a region with about 800 mm of mean annual precipitation ought to be in natural balance, with theoretically no need for extra water or nutrients. If subsidies means extra energy expenditures, and if energy expenditures translate into an additional carbon footprint, it is readily seen that the 800-mm isohyet region adheres to the principle of sustainability. We conclude that the 800-mm isohyet is a region where life, particularly human life, would find itself in its most comfortable, and secure, position.

To reiterate, if humid regions leach soils excessively and arid regions conserve nutrients due to lack of use, then the 800-mm region must be at an optimum balance between water and nutrients:  Enough water and nutrients, in quantity and type, to satisfy the needs of the ecosystem.

The type of nutrients in pristine soils depends on the local geology and geomorphology. In practice, this amounts to the proverbial luck of the draw: Either we have the nutrients, or we don't. Nevertheless, given a supply of nutrients predetermined by a region's geology, the amount of soil leaching, that is, the amount of mean annual precipitation, must determine, in the broad mean, the balance of available nutrients. In other words, other things being equal, the 800-mm isohyet must be at or close to the optimal region from the standpoint of livability and survivability. At this annual rainfall amount, the nutrients would be in ample supply, in quantity and type, and the nutrient waste, namely, the unwanted salts, would be minimized.

♦ Outlook ♦

A good supply of diverse nutrients enhances biotic potential; so, the 800-mm isohyet is where life, particularly for humans, is likely to be optimal. Thus, there is where health and hope, essential to body and soul, ought to be most naturally at their peak.