Biogeochemical cycles, as the name implies, are perfect examples of the fusion of concepts from various science disciplines. Principles of biology, geology, and chemistry are combined in these cycles. Each has important implications to all living inhabitants of earth.
The hydrologic cycle, also known as the water cycle, is the simplest of the cycles I will discuss here. The water cycle consists of three phases; evaporation, condensation, and precipitation. All are examples of physical changes. Heat from the sun constantly evaporates water from the earth’s surface. This includes sources as small as mud puddles to as large as oceans. As the water vapor rises into the upper atmosphere it cools and condenses. This condensation, also called cloud formation, requires microscopic dust particles that serve as nuclei which are necessary for raindrop formation. Under the right conditions, precipitation in the form or rain, sleet, hail, freezing rain, or snow will return the water to the earth to begin the process again. Since most of our weather in this part of the world originates far to our west, I often told my students that the rain we got last night might have come from as far away as Hawaii several days ago. The fact that our weather originates over vast quantities of ocean has far reaching consequences when we consider the effects that warmer ocean temperatures resulting from global warming and other phenomena have on weather patterns. I also made a special effort to point out that the amount of water that we have today is the same as what we have always had and presumably always will have. The basis for this lies in the Law of Conservation of Matter which essentially says that matter is neither created nor destroyed (with some exceptions like Einstein’s theories of relativity) but simply changed in form (chemical or physical). So why are we so concerned about having enough water if the amount never changes. I will answer that questing at the end of the essay. The following diagrams taken from the internet illustrates the water cycle, carbon cycle, and nitrogen cycle
Credit to: nj.gov
The carbon cycle is of great interest and concern since one of its principle components, carbon dioxide (CO2) has been identified as a major greenhouse gas and a contributor to global warming. All living organisms contain carbon atoms and, therefore, when they die and decay or are burned (after being converted to fossils fuels), CO2 is released as the carbon atoms combine chemically with oxygen atoms. Even waste products release CO2 as does cellular respiration. I will discuss the photosynthesis/cellular respiration cycle in a later essay but let me just say that plants remove CO2 from the air. The transfer rate of carbon from the atmosphere by photosynthesis just about equals the rate at which respiration and decay return carbon to the atmosphere. However, when fossil fuel burning is added to the equation, the rate of CO2 returned to the atmosphere is greatly favored. That is bad. In 1850, atmospheric CO2 was about 280 parts per million (ppm) and today it is about 350 ppm and climbing. Destruction of vegetation for any reason reduces the amount of CO2 sequestration from the atmosphere. Just think for a moment about the many ways that we remove vegetation from the earth’s surface. We can’t blame all of it on rainforest destruction
Credit to: slideshare.org
Most of us know that nitrogen makes up about 80% of the atmosphere and that nitrogen is necessary for plant growth. But plants can’t just take nitrogen out of the air in its elemental form. It has to be “fixed” or changed into a form that they can use. That’s similar to us changing our food into forms our bodies can use. Certain kinds of bacteria in water and soil can fix nitrogen into ammonium (NH3+) or nitrate (NO3-) compounds so that plants can make amino acids, DNA, and RNA. Nitrogen fixation also occurs when organic matter decomposes. This includes animal waste. It should be noted that fertilizer use results in the release of nitrogen oxide (NO2), a greenhouse gas. Fossil fuel burning also pumps sulfur dioxide (SO2) into the atmosphere. Both nitrogen oxides and sulfur dioxide are converted to acids which eventually return to earth. Carbon dioxide combines with water vapor in the atmosphere to form carbonic acid, another form of pollution. Normally rain has a pH of about 5.6(slightly acidic). In many parts of the heavily industrialized northeastern United States, the pH of the rain is between 5.0 and 4.0 which is more acidic. In fact, a pH of 4 is ten times more acidic as rain with a pH of 5. Has anyone ever heard of acid rain?
Credit to: data.allenai.org
Now let’s answer the question I posed above. The real water concern is twofold. Will we have enough useable (unpolluted) water and will that water be distributed adequately on a global basis? There have always been arid regions and high precipitation zones but human activities are now exaggerating those extremes.