Environmental Engineering Reference
In-Depth Information
2 Sustainability and the Environment
INTRODUCTION
Life on Earth is supported by the planet systems working in a complex interdependent
coordination. The ultimate source of energy, the sun, provides the power to produce food we
eat through plant conversion into biomass. Even when the amount of solar energy that reaches
the planet is significant, its capture and conversion by plants has a low efficiency that is limited
by the photosynthesis process itself, by seasons in temperate climates, by lack of moisture in
the tropics, and by limited nutrients (e.g., nitrogen, phosphorus, potassium, and so on). So
before the introduction of fossil fuels, life and the economic system were, to a large extent,
controlled by the production of biomass through photosynthesis.
At a basic level, the Earth's ecosystems work through energy flow and nutrients cycling.
Solar energy captured by plants (primary producers) is fixed throughout the conversion of
carbon dioxide into carbohydrates with the use of water and nutrients from the ground. Plants
are then eaten by herbivores (primary consumers), which are subsequently eaten by tertiary
consumers. Once tertiary consumers expire, nutrients are recycled into the soil and the
atmosphere by decomposers, which close the loop. The opposite effect of carbon fixation is
respiration, which takes place at all levels of the energy cycle or food supply chain.
At the same time the energy cycle takes place, essential chemical compounds are moved
around the global ecosystem through what is called the nutrients cycles or biogeochemical
cycles, the most important being the carbon, nitrogen, oxygen, phosphorus, sulfur, and water
cycles. When left to their own devices, most of the biogeochemical cycles move at rates much
lower than is known today. By the input of energy from fossil fuels, humans have been able to
accelerate the nutrient cycles by producing plant-assimilable nitrogen and mineral fertilizers
that are limiting factors in nonintervened ecosystems and by providing water in places where
moisture is another limiting factor for agriculture.
The acceleration of biogeochemical cycles has allowed the production of more food. This
additional food promoted human population growth at the expense of ecosystems because
more land was needed for agriculture; mineral and water resources were depleted; and carbon,
which may have been out of the system for millions of years, was released into the atmosphere.
The explosive population expansion in the last century has been the foundation of escalating
consumption that has produced constant economic growth, which is the main predicament of
the current economic system in the developed world and the aspiration of many underdeveloped
