Biogeochemical cycles

Transcription

1 Lecture -2: Biogeochemical cycles ENV 107: Introduction to Environmental Science Dr. A.K.M. Saiful Islam

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3 Case Study: Lake Washington The city of Seattle, USA lies between two major bodies of water- saltwater Puget Sound to west and fresh water Lake Washington to the east. In 1930, fresh water lake was used for disposal of sewage. By 1954, ten sewage treatment plants added. 1959, additional effluent plant added with capacity of 76,000 cubic meter per day

4 The Lake s response A major bloom of undesirable algae and photosynthetic bacteria. Affect fishing and general aesthetics of the lake. Lake turned a dark, turbid green; Fish and algae died. Once clear, the lake had become dark and dying.

5 Public response Public concerns increased immediately. Seattle s mayor appointed an advisory committee to determine what might be done. Scientific research showed that it was phosphorus in sewage effluent that stimulated the growth of the algae and bacteria. With many freshwater lakes, this chemical element has been the factor limiting algae and bacteria.

6 Lesson learned Studies at experimental lakes in Canada showed that phosphorus and no other chemical element caused the kind of changes that took place in Lake Washington. This research showed that specific chemical elements can have great effects on life within an ecosystem, and that the study of chemical cycles could provide the basis for the solution to some kinds of environmental problems. The story of Lake Washington illustrates the importance of knowledge about biogeochemical cycles, which is the subject of today s lecture.

7 Introduction Earth is a peculiarly fit planet for life especially from chemical point of view. There is plenty of oxygen in the atmosphere. There is plenty of water. Soils are fertile, containing chemical elements necessary for plants to grow. But. The whole surface of the earth is not perfect for life. Therefore, it s essential to know the biogeochemical cycle of the earth.

8 Biogeochemical Cycle It s the pathway that a chemical element follows through the Earth system- from the atmosphere, waters, rock, or soils, to living organisms and back to the atmosphere, ocean, soils, or to other organisms. It s chemical cycle because chemical elements are the form that we consider. It s bio because these are the cycles that involve life. It s geo because these cycles include atmosphere, water, rocks, and soils.

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10 Biogeochemical Cycles and Life All living things made up of chemical elements. But about 103 known chemical elements, only 24 are required by organisms. They are divided into Macro-nutrients elements in large amounts by all life. Micro-nutrients elements required either small amounts by life or moderate amounts for some forms of life and not others. Big-six are macro-elements that form the fundamental building blocks of life: Carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.

11 ENV 107:Introduction to Environmental Science Dr. Akm Saiful Islam

12 Geological Cycle The processes responsible for formation and change of Earth materials are referred to as the geological cycle. Three sub-cycles are: 1. Tectonic cycle. 2. Hydro geological cycle. 3. Rock cycle.

13 1. Tectonic Cycle Creation and destruction of the solid outer layer of Earth, known as the lithosphere. Lithosphere about 100 km, is broken into several large segments called plates which are moving relative to one another.

14 Plate tectonic Plate tectonics -> the slow movement of large segments of Earth s outermost rock shell. Move 2 to 15 cm/year. Three types of plate boundaries: (i) Divergent plate boundary -> occurs at a spreading ocean ridge where plates are moving away from one another and new lithosphere is produced, a process known as seafloor spreading which produces ocean basins.

15 Geological Cycle

16 Plate boundaries (ii) Convergent plate boundary -> occurs when plates colloids. If one plate (composed of relatively heavy ocean basin rocks) dives or subducts beneath the leading edge of another (composed of lighter continental rocks), a subduction zone is present and convergence may produced linear mountain ranges, such as the Andes in South America.

17 Plate boundaries (Cont..) (iii) Transform fault boundary -> occurs when one plate slide to others. For example, the San Andreas Fault in California, a boundary between North America and Pacific Plates. The pacific plate is moving north relative to the North American plate at about 5 cm/year. Los Angeles, about 500 km south of San Francisco, is moving slowly toward that city. If this motion continues in about 10 million years San Francisco will be a suburb of Los Angeles.

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19 2. Hydrologic Cycle Movement of water from oceans to atmosphere by evaporation, from atmosphere to oceans and land by precipitation, from land to oceans by runoff from streams and rivers and subsurface groundwater flow, and from land to atmosphere by evaporation. Water on earth = 97% is ocean + 2% ice +1% fresh water.

20 Hydrologic Cycle

21 3. Rock Cycle Consists of several processes that produce rocks and soils. Three classifications of rock 1. Igneous 2. Sedimentary 3. Metamorphic Igneous Rock: Internal heat from tectonic cycle produces igneous rocks from molten material near the surface such as lava from volcanoes.

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23 Sedimentary rocks These new rocks weathered when exposed. Freezing and Thawing of water in cracks in the rocks breaks the material apart due to unusual property of water becoming less dense and expanding as a solid. Weak acids that form in water, including carbonic acid formed when carbon dioxide in the atmosphere dissolved in water, dissolve some chemical elements and compounds from the rocks. The process of weathering produces sediments, including boulders, pebbles, sand, silt and clay as well as dissolved chemical elements. The sediments are transported by wind, water, or the movements of glaciers.

24 ENV 107:Introduction ENV 107:Environemental to Environmental Science Science Dr. Akm Dr. Saiful Akm Islam Saiful Islam Metamorphic rock The weathered materials accumulated in depositional basin. These can be in the ocean, whether the sediments are compacted by material deposited above them, and then converted to sedimentary rocks. After sedimentary rocks are buried to sufficient depth (usually ten ~ 1000 km), they may be altered by heat, pressure, or chemically active fluid. They are transferred again, to metamorphic rocks.