Ecology: biology of interaction. II-04. Biogeochemical cycles

II-4. Biogeochemical Cycles. I am a collection of water, Calcium, and organic molecules, called Carl Sagan. You are almost the same system of molecules with a different collective name. And that's all? Do we have nothing but molecules? Some find this demeaning to human dignity. Personally, I find it inspiring that our world allows for the development of such subtle and complex molecular machines as we are. Carl Sagan. Earthly life is built on a rather complex chemical foundation. Many chemical elements are necessary for its existence (Fig. II-4.1). Although the main compound in organisms is water, organic substances, consisting of various atoms, are extremely necessary for life. Among the elements that are important resources for the biosphere, the most important are the so-called biogenic elements or biogens. About half of the 54 elements found in the Earth's crust are biogenic. Macronutrients are especially important - C, H, N, O, P, S, Ca, K, and Mg, and some trace elements - Fe, Cl, Na, Zn, V, Mo, B, Co, Cu, Si, Se, Cr, Ni, I, F, Sn, and As. Fig. II-4.1. Elements important for living organisms in the periodic table. The roles played by biogens are diverse. Four of them (the so-called organogens: Carbon, Hydrogen, Nitrogen, and Oxygen) form the structural basis of organic molecules. Phosphorus is always included in nucleic acids, and Sulfur is included in some amino acids (and thus in proteins). Calcium, Potassium, Sodium, and Chlorine ions are important for the life of living cells. Many metals are part of the most important organic molecules. For example, Magnesium is part of the chlorophyll molecule, and an iron ion is part of heme (a component of hemoglobin - the protein in the blood that carries oxygen, as well as some other proteins). For organisms to incorporate these elements into their composition, they must be in an accessible form in the environment inhabited by organisms. Once incorporated into living organisms, the same atom can pass from one molecule to another, from one creature to another. However, over time, any atom of any biogen will leave the composition of living matter and return to the environment. For organisms to be able to fill the deficiency of the biogens they need, biogeochemical cycles must operate in the environment. The study of BGC cycles probably began with the Scottish geologist James Hutton (in the more common transliteration - Hutton, 1726-1797). Before Hutton, Neptunism dominated geology, which considered the features of the Earth's geological structure as a consequence of the biblical flood. Hutton contrasted this with Plutonism - the idea that Earth's substance is destroyed by erosion, forms new rocks on the seabed, passes through the Earth's interior, transforms, and rises again to the surface, where it is again subjected to erosion. Hutton contrasted catastrophism, which prevailed in geology, with actualism - the idea of a long geological history during which the same processes that are currently operating have been active. For the thinking of the 18th century, Hutton's views can be considered a real revolution. He can also be considered a precursor to Vernadsky's ideas about the biosphere, and even a precursor to the Gaia hypothesis. The fact is that Hutton compared the Earth's activity to the life processes of an organism. A biogeochemical cycle (BGC cycle) is defined as a set of relatively closed pathways for the transformation and movement of substances through living organisms and their environment. Biogeochemical cycles are called so because both biological and geochemical processes are involved in their provision. Of course, it is not necessary for elements to move in a circle as they move along a BGC cycle. However, as they transition from one molecule to another within organisms and the environment, the same atom can repeatedly return to a certain state. This is how the cyclical nature of biogeochemical processes manifests itself. Examining the following diagrams, which show BGC cycles, one can see that funds and flows are distinguished within them. Funds are collections of substances containing the element in question in a certain form. Flows are pathways of element transformation that transfer it from one fund to another. Within different funds, elements change at different rates. Consider the hydrological cycle (Fig. II-5.1). The amount of water vapor in the atmosphere at any given moment passes through it several times a year. At the same time, only a small amount of water bound in the lithosphere changes over millions of years. This is why reserve and exchange funds are distinguished in BGC cycles. Several types of cycles are distinguished, the main ones being the cycles of gaseous substances with reserve funds in the atmosphere and hydrosphere, as well as sedimentary cycles with reserve funds in the lithosphere. Biogeochemical cycles that have funds in the atmosphere (cycles of Carbon, Nitrogen, water, as well as Oxygen and Hydrogen separately) can be regulated by organisms much better than cycles whose funds are all located in the lithosphere. BGC cycles differ in the degree of regulation by living organisms. It should be noted that the regulation of sedimentary cycles is worse. If the descent of an element into the crust is faster than its ascent from it, a deficiency arises that limits the circulation but slows down the descent. The element that is lacking for circulation will be retained more strongly by living matter and will be released from circulation more slowly. The role of living organisms in retaining biogens was clearly demonstrated in an experiment conducted at the American biological station in Hubbard Brook (Fig. II-4.2). A small area of territory (a gorge) bounded by a watershed was chosen. Measuring equipment was installed on the stream flowing from this area. After all vegetation on the experimental plot was destroyed, the experimenters registered not only a twofold increase in the amount of water (before the experiment, it was retained by the soil and plants and returned to the atmosphere through transpiration), but also an increase in the content of biogens in this water. Fig. II-4.2. One of the consequences of deforestation at the American Hubbard Brook Experimental Station was a multifold (more than an order of magnitude) increase in nitrate runoff from the territory where all vegetation was destroyed (note the break in the y-axis scale!). For example, although metals such as Ca, K, Na, Mg are not usually part of organic molecules, they are extremely necessary for cell life. They are very mobile in ecosystems. The influx of cations into an ecosystem is associated with the geological and biological weathering of parent rocks, and their transport by dust and precipitation. The outflow of cations occurs due to their removal by surface and groundwater. The biological community actively retains the outflow, increasing the amount of cations in exchange funds. After the destruction of the forest plot in Hubbard Brook, the export of biogens increased many times (calcium - by three, nitrogen - by 15). In tropical forests, the predominant part of biogens is in the plant biomass; in temperate forests, it is in the litter. Humans are a powerful geological factor. Humanity uses almost all elements in its activities, including those used only for the needs of the technosphere (Uranium, Plutonium, Mercury, and others). We are intensively interfering with the biogen cycle due to the production of fertilizers, which has caused biogenic pollution of a significant part of the biosphere. Conservation efforts should be aimed at transforming acyclic processes into cyclic ones. In the Philippines, there are areas where rice has been grown for over 1000 years on fields separated by sacred forests. Unfortunately, there are very few such examples among artificial ecosystems. One method of studying BGC cycles is related to radiation ecology. For example, by adding a certain amount of labeled Phosphorus (i.e., a substance containing a radioactive isotope of Phosphorus) to a body of water, one can study the pathways and dynamics of its fixation by living matter and litter. Deuterium (an isotope of Hydrogen), released into the atmosphere as a result of hydrogen bomb tests, has proven very useful for studying groundwater. The amount of Deuterium in modern precipitation is known; by how much it is found in groundwater, one can determine the rate at which it is replenished by water from the surface. It is clear that elements are distributed very unevenly across the Earth's surface. Their deficiency can cause a number of anomalies. The best example for analyzing such anomalies is the deficiency of Iodine. The main reserves of Iodine available to organisms are in the World Ocean. Algae and marine animals are a rich source of it. Some land areas remote from the seas are iodine-deficient. The Alps, for example, are such a region. Humans need 0.15-0.2 mg of Iodine per day; its main role is participation in the synthesis of triiodothyronine and thyroxine (which is converted to triiodothyronine in peripheral tissues). As is known, these hormones play an important role in maintaining metabolism, heat production, and nervous system function. A deficiency of these hormones (which can be caused by a lack of Iodine) leads to weakness, apathy, and in severe cases, to cretinism and dwarfism. About 1 billion people suffer from iodine deficiency to varying degrees. Iodine deficiency in the Alps was the cause of the widespread endemic goiter - a compensatory hyperplasia (enlargement) of the thyroid gland, which is a response to insufficient iodine intake. This enlargement causes increased secretion of thyrotropic hormone (thyrotropin) by the pituitary gland - a protein that enhances the binding of iodine by thyroid tissues. As a result of these factors, the population of Switzerland has always suffered from endemic goiter, which was considered one of the medical mysteries. The first attempts to determine the effect of iodine on human health ended in failure: excessive, toxic doses of iodine were used, causing poisoning. In the early 20th century in Switzerland, it was proven that salt iodization protects against goiter. Table salt is a suitable component for iodization in everyday food; the reason is that a person consumes approximately a constant amount of salt. For iodization, 20-40 grams of KIO3 are added per ton of table salt. The introduction of salt iodization, which was the merit of several Swiss doctors, became a vivid example of the benefits of science: a large number of patients were cured, and the quality of life in the entire country improved. A number of such examples (as well as the spread of vaccines, medical technologies, etc.) have led to an increase in the authority of science. Over time, this trend reversed; an uneducated population living in a safe world becomes vulnerable to anti-scientific propaganda and falls for the deceptive advertising of "organic," "natural," "traditional" food, etc.