2. Concept of biosphere life-component and its biogeochemical functions.
Life-component - all living organisms presented as mass, energy and chemicals.
Biogeochemical functions of living component:
Formation of gas composition of the Earth atmosphere: only due to the living component the free oxygen released into the atmosphere and the amount of carbon dioxide restricted.
Concentration: organisms can accumulate some chemical elements in their bodies (sedimentary rocks, carbonates deposits)
Redox reactions: oxidation of organic compounds to CO2 and H2O and their reduction to organic compounds.
• Biogeochemical activity of humans: people affect biosphere in different ways (anthropogenic factor, mostly industrial).
The food supply still depends on productivity of ecosystems. In theory, the total annual production of biosphere (dry weight) is about 141010 tons, and the production of all fields and pastures is about 2,8×1010 tons. All humans at present consume directly and indirectly about 2×109 tons of grain per year (wet weight).
At present, all agricultural areas of humankind occupy 37% of all land, with fields and pastures occupying 28%. This area covers 4,1×109 hectares. The proportion of woods is nor more than 31% of all land and the remaining land (about 32%) is mainly of low productivity.
Bearing this in mind, the warnings of the ecologists regarding continuing demolition of woods become clear. However, human population should double in size in the next 50 years. Would it be possible to supply everyone with food? This question is not trivial, if one considers that at present at least 1 billion of people are constantly underfed. It can be expected, that more and more poor countries will have the opportunity to modernize their agriculture and approach the productivity of land areas found in developed countries. However, these optimistic expectations will not solve the problem of food supply for population of more than 10 billions. Thus, the gap in food content of rich and poor countries will also be retained in the future. The food is obtained in abundance in rich countries, which partially export it to other regions, donate its small part as a humanitarian aid and sometimes, just destroy the food excess, as happening in Europe due to cattle epidemics. Poor countries are able to feed their people mainly with vegetative food – rice, maize, potato.
Biogeochemical Cycles: Water cycle. Nitrogen cycle. Oxygen-Carbon cycle.
Biogeochemical cycle - the process by which inorganic materials move from the atmosphere or soil into living organisms and back again.
Water Cycle: Of the nearly 1.5 billion km3 of water on the earth, less than 1% is available to land organisms.
Nitrogen Cycle: Includes 4 major processes: Nitrogen fixation - Ammonification - Nitrification - Denitrification
Carbon Cycle: Two main processes: Photosynthesis and Cellular Respiration
Terrestrial and Aquatic Biomes.
Terrestrial, or Land biomes:
Biome - is a large area identified by presence of characteristic (dominant) plants and animals, broadly defined life zones, environments with similar climates, topographies, soil conditions, and biological communities. Distribution mainly dependent on temperature and precipitation.
Polar - biomes found at the earth's coldest extremes.
Tundra - a treeless biome blanketed by snow in the winter.
Permafrost - a permanently frozen layer of ground over 500 m thick.
Coniferous Forest - is a biome that is dominated by conifers, cone-bearing evergreen trees such as pines, firs, spruces, and cedars (Taiga).
Deciduous forest - is a biome characterised by the presence of trees that lose their leaves in the fall.
Grassland - is a biome dominated by grasses. Grasslands are known by various names in different regions of the world:
Prairie in North America
Steppes in Asia Pampas in South America
Veldt in South Africa
Savannas - is grassland with scattered trees found in tropical and subtropical areas.
Desert - is an area where rainfall averages less than 25 cm per year. Water -is the limiting factor.
Rain forests
Tropical rain forest biome - is found near the equator where rainfall and sunlight abound.
Temperate rain forest extends along the west coast of North America.
The major factors determining the characteristics of biomes include temperature and precipitation. Life is affected either by a lack or an abundance of either. For instance, where there is very little moisture, there will be deserts, whether they are in warm or extremely cold areas (like the north slopes of Alaska). Where there are extremely low or very high temperatures, life is also affected. Some of the most productive and diverse ecosystems are the wettest and warmest, including the tropical rain forests.
Aquatic, or Water biomes: Marine and Freshwater
Marine biome:
Ocean (3.5% salt)
Oceanic (Pelagic) zone - the deep water of the open sea, is less populated (animals of this zone feed on sinking plankton and dead organisms).
Coastal waters (neritic zone) - extends over the continental shelf (light penetration, minerals from the ocean bottom support the greatest amount of marine life).
Intertidal zons - area of ocean shores where tides produce a rhythmic rise and fall of water (animals are adapted to periodic exposure to air, to the force of waves crashing onto the shore).
Estuaries - is a biome found throughout the world where freshwater rivers and streams flow into the sea (great variation in temperature and salinity, exposure to the air during low tide).
Freshwater Biome:
Low levels of dissolved salts characterise the Freshwater Biome (0.005% salt content)
Lakes and Ponds
Eutrophic lakes are rich in organic matter and vegetation, making the waters relatively murky.
Oligotrophic lakes contain little organic matter.
River and Streams
A river is a body of water that flows down a gradient, or slope, towards its mouth. Gradient (current) is a key abiotic factor in a river.
Questions for review:
1. What is biosphere? What are components and limits of biosphere?
2. Define the functions of living component. Give examples.
3. What mechanisms maintain stability of biosphere?
4. What is biogeochemical cycle? Give some examples.
5. Name the two major processes involved in the oxygen-carbon cycle?
6. Describe three ways in which nitrates become available to an ecosystem.
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Critical Thinking (Writing an essay):
1 How has the increased consumption of fossil fuels and deforestation affected the oxygen-carbon cycle?
2. What abiotic factors might affect the rate of nitrogen cycling?
3. Explain why farmers often grow up soybeans or other legume crops in the field after they have grown corn.
4. Give evidence that species diversity affects ecosystem stability. Is there any evidence to contradict this idea? What is it?