ENVIRONMENTAL BIOLOGY – I Unit I (USLSC504) INTRODUCTION TO FUNDAMENTALS OF ENVIRONMENTAL SCIENCE Asst.Prof :Yogita Walke Department of LifeSciences Jai Hind College,Mumbai SUCCESSION Theories of Succession Stages of Succession 1) NUDATION 2) INVASION 3) COMPETITION & COACTION 4) REACTION 5) STABILIZATION Floating pH= 3.7 pH= 7.3 Biogeochemical Cycles What Sustains Life on Earth? Biogeochemical or Nutrient cycle These cyclic movements of chemical elements of the biosphere between the organisms and environment are referred as biogeochemical or nutrient cycle (Bio = living, geo = rock, chemical = element). MATTER CYCLING IN ECOSYSTEMS Nutrient Cycles: Global Recycling Global Cycles recycle nutrients through the earth’s air, land, water, and living organisms. Nutrients are the elements and compounds that organisms need to live, grow, and reproduce. Biogeochemical cycles move these substances through air, water, soil, rock and living organisms. Types of a biogeochemical cycle 1. Gaseous cycle: the reservoir for gaseous type of nutrient cycle (e.g., nitrogen, carbon cycle) exists in the atmosphere. Gaseous cycles include those of Carbon, Nitrogen, Oxygen and Water. 2. Sedimentary cycle: the sedimentary cycle (e.g., sulphur and phosphorus cycle), the reservoir is located in Earth’s crust. Sedimentary cycles include those of iron, calcium, phosphorus, and other more earth bound elements Components of a biogeochemical cycle 1. Reservoir pool - atmosphere or rock, which stores large amounts of nutrients.The function of the reservoir is to meet with the deficit which occurs due to imbalance in the rate of influx and efflux 2. Cycling pool or compartments of cycle- which are the living organisms (producers, consumers and decomposers), soil, water and air in which Nutrients stays temporarily. Nitrogen cycle Nitrogen is an essential component of protein and required by all living organisms including human beings. Our atmosphere contains nearly 78% of nitrogen but it can not be used directly by the majority of living organisms. Broadly like corbondioxide, nitrogen also cycles from gaseous phase to solid phase then back to gaseous phase through the activity of a wide variety of organisms. Cycling of nitrogen is vitally important for all living organisms. There are five main processes which are essential for nitrogen cycle (a) Nitrogen fixation:(Conversion of N2 → NH3 )This process involves conversion of gaseous nitrogen into Ammonia, a form in which it can be used by plants. Atmospheric nitrogen can be fixed by the following three methods:- (i) Atmospheric fixation: Lightening, combustion and volcanic activity help in the fixation of nitrogen. (ii) Industrial fixation: At high temperature (400oC) and high pressure (200 atm.), molecular nitrogen is broken into atomic nitrogen which then combines with hydrogen to form ammonia. 2 NO2 + O ----------> N2O5 (iii) Bacterial fixation: There are two types of bacteria: • Symbiotic bacteria e.g. Rhizobium in the root nodules of leguminous plants. • Free living or assymbiotic e.g. 1. Nostoc 2. Azobacter 3. Cyanobacteria can combine atmospheric or dissolved nitrogen with hydrogen to form ammonia. (c) Assimilation: (Roots absorb NH3, NH4, or NO3 and incorporate them into nucleic acids and protein )In this process nitrogen fixed by plants is converted into organic molecules such as proteins, DNA, RNA etc. These molecules make the plant and animal tissue. (d) Ammonification : (Amino acids and nucleotides are broken down into waste products NH3 or NH4 )Living organisms produce nitrogenous waste products such as urea and uric acid. These waste products as well as dead remains of organisms are converted back into inorganic ammonia by the bacteria. This process is called ammonification.eg Actinomycetes and Bacilli (b) Nitrification: (Conversion of NH3 →NO3 )It is a process by which ammonia is converted into nitrites by Nitrococcus and Nitrosomonas bacteria. Another soil bacteria Nitrobacter can covert nitrite into nitrate NO3. In the first step, bacteria such as Nitrosomonas convert the ammonia (or ammonium ions) to nitrites NO2. Nitrites are very toxic to plants, so a second conversion is necessary. This is accomplished by bacteria, such as Nitrobacter, that convert the nitrites to nitrates NO3 . Since flowering plants use nitrates more readily than ammonia as a nitrogen source, nitrification is important to the maintenance of the earth’s flora. (e) Denitrification: (The reduction of NO3 to N2 ) Conversion of nitrates back into gaseous nitrogen is called denitrification. Denitrifying bacteria live deep in soil near the water table as they like to live in oxygen free medium. Denitrification is reverse of nitrogen fixation.eg Pseudomonas 2 NO3 ----------> 2 NO2 ----------------> 2 NO ----------->N2 F) Sedimentation Nitrogen Fixation CARBON CYCLE Carbon cycle The atmosphere only contains about 0.04 per cent of total global carbon. Total quantity of global carbon found dissolved in oceans is 71 per cent. This oceanic reservoir regulates the amount of carbon dioxide in the atmosphere. Carbon constitutes 49 percent of dry weight of organisms Fossil fuel also represent a reservoir of carbon. Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. According to one estimate 4 × 1013 kg of carbon is fixed in the biosphere through photosynthesis annually. A considerable amount of carbon returns to the atmosphere as CO2 through respiratory activities of the producers and consumers. Decomposers also contribute substantially to CO2 pool by their processing of waste materials and dead organic matter of land or oceans. Some amount of the fixed carbon is lost to sediments and removed from circulation. Burning of wood, forest fire and combustion of organic matter, fossil fuel, volcanic activity are additional sources for releasing CO2 in the atmosphere. Human activities have significantly influenced the carbon cycle. Rapid deforestation and massive burning of fossil fuel for energy and transport have significantly increased the rate of release of carbon dioxide into the atmosphere and caused global warming. The global carbon cycle consists of following steps1. Photosynthesis 2. Respiration 3. Decomposition 4. Combustion 5. Impact of human activities Water Cycle or Hydrologic Cycle Water is essential for life. No organism can survive without water. Precipitation (rain, snow, slush dew etc.) is the only source of water on the earth. Water received from the atmosphere on the earth returns back to the atmosphere as water vapour resulting from direct evaporation and through evapotranspiration the continuous movement of water in the biosphere is called water cycle (hydrological cycle). Earth is a watery planet of the solar system, about 2/3rd of earth surface is covered with water. However a very small fraction of this is available to animals and plants. Water is not evenly distributed throughout the surface of the earth. Almost 95 % of the total water on the earth is chemically bound to rocks and does not cycle. Out of the remaining 5%, nearly 97.3% is in the oceans and 2.1% exists as polar ice caps. Thus only 0.6% is present as fresh water in the form of atmospheric water vapours, ground and soil water. The driving forces for water cycle are 1) solar radiation 2) gravity . Evaporation and precipitation are two main processes involved in water cycle. These two processes alternate with each other Water from oceans, lakes, ponds, rivers and streams evaporates by sun’s heat energy. Plants also transpire huge amounts of water. Water remains in the vapour state in air and forms clouds which drift with wind. Clouds meet with the cold air in the mountainous regions above the forests and condense to form rain precipitate which comes down due to gravity. Sulphur cycle Sulphur has its reservoir both in atmosphere (as oxides of sulphur, hydrogen sulphide) and in rocks and sediments (as mineral pyrites). Atmospheric sulphur plays an important role, as the oxides of sulphur react with rain water producing sulphuric acid, which comes down as ‘acid rain’. Oxides of sulphur (SOx) are released into the atmosphere due to burning of fossil fuels. Thus human beings play a significant role in the material cycling of sulphur. In the soil or water, there are different groups of microorganisms which carry out oxidation and reduction of various sulphur compounds. A special role is played by Thiobacillus bacterium, which converts sulphides into sulphuric acid. These bacteria help in bio-leaching of metals from ores containing pyrites (S) as impurities. Effects of Human Activities on the Sulfur Cycle We add sulfur dioxide to the atmosphere by: – Burning coal and oil – Refining sulfur containing petroleum. – Convert sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment. Phosphorous cycle Phosphorus is a major constituent of biological membranes, nucleic acids and cellular energy transfer systems. Many animals also need large quantities of this element to make shells, bones and teeth. The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates PO43- . When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants and incorporated into nucleic acids, phospholipids and ATP . Herbivores and other animals obtain this element from plants. PO43- is released to the soil again by decomposers. Dissolved PO43- gets absorbed by algae and aquatic plants. The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria releasing phosphorus.Decomposers break down waste and returns PO43- to sediments on the seabed. mining excretion Fertilizer Guano agriculture uptake by uptake by weathering autotrophs autotrophs leaching, runoff Dissolved Land Marine Dissolved in Soil Water, Food Food in Ocean Lakes, Rivers Webs Webs Water death, death, decomposition decomposition weathering sedimentation settling out uplifting over geologic time Rocks Marine Sediments Effects of Human Activities on the Phosphorous Cycle We remove large amounts of phosphate from the earth to make fertilizer. We reduce phosphorous in tropical soils by clearing forests. We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers.