Environmental Sciences Course Biogeochemical Cycles Dr.-Eng. Hasan Hamouda Eng. Osama Othman

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman2 Outline  Definitions  Carbon Cycle  Nitrogen Cycle

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman3 Biogeochemical Cycles The Earth is a closed system for matter, except for small amounts of cosmic debris that enter the Earth's atmosphere. This means that all the elements needed for the structure and chemical processes of life come from the elements that were present in the Earth's crust when it was formed billions of years ago. This matter, the building blocks of life, continually cycle through Earth's systems, the atmosphere, hydrosphere, biosphere, and lithosphere, on time scales that range from a few days to millions of years. Definitions

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman4 Biogeochemical Cycles These cycles are called biogeochemical cycles, because they include a variety of biological, geological, and chemical processes. Many elements cycle through ecosystems, organisms, air, water, and soil. Many of these are trace elements. Other elements, including carbon, nitrogen, oxygen, hydrogen, sulfur, and phosphorous are critical components of all biological life. Together, oxygen and carbon account for 80 percent of the weight of human beings. Because these elements are key components of life, they must be available for biological processes.

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman5 Carbon, however, is relatively rare in the Earth's crust, and nitrogen, though abundant in the atmosphere, is in a form that is not useable by living organisms. The biogeochemical cycles transport and store these important elements so that they can be used by living organisms. Each cycle takes many different pathways and has various reservoirs, or storage places, where elements may reside for short or long periods of time. Each of the chemical, biological, and geological processes varies in their rates of cycling. Some molecules may cycle very quickly depending on the pathway. Biogeochemical Cycles

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman6 Carbon atoms in deep ocean sediments may take hundreds to millions of years to cycle completely through the system. An average water molecule resides in the atmosphere for about ten days, although it may be transported many miles before it falls back to the Earth as rain. How fast substances cycle depends on its chemical reactivity and whether or not it can be found in a gaseous state. A gaseous phase allows molecules to be transported quickly. Phosphorous has no gaseous phase and is relatively unreactive, so it moves very slowly through its cycle. Biogeochemical Cycles

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman7 Phosphorous is stored in large amounts in sediment in the oceans or in the Earth's crust and is recycled back to the surface only over very long periods of time through upwelling of ocean waters or weathering of rocks. Biogeochemical cycles are subject to disturbance by human activities. Humans accelerate natural biogeochemical cycles when elements are extracted from their reservoirs, or sources, and deposited back into the environment (sinks). For example, humans have significantly altered the carbon cycle by extracting and combusting billions of tons of hydrocarbons in fossil that were buried deep in the Earth's crust, in addition to clearing vegetation that stores carbon. Biogeochemical Cycles

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman8 Biogeochemical Cycles Global release of carbon through human activities has increased from 1 billion tons per year in 1940 to 6.5 billion tons per year in About half of this extra carbon is taken up by plants and the oceans, while the other half remains in the atmosphere. In addition to carbon cycle, humans have altered the nitrogen and phosphorous cycles by adding these elements to croplands as fertilizers, which has contributed to over- fertilization of aquatic ecosystems when excess amounts are carried by runoff into local waterways.

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman9 Carbon is one of the fundamental building blocks of life; we are carbon-based life forms. Carbon cycles through the oceans, atmosphere, the lithosphere, and the biosphere over both short and long term time scales. The geological Carbon cycle takes place over hundreds of millions of years and involves the cycling of carbon through the layers of the Earth. The biological/physical carbon cycle occurs over days, weeks, months and years and involves the absorption, conversion, and respiration of carbon by living organisms. Carbon Cycle

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman10 Carbon Cycle

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman11 Nitrogen is both the most abundant element in the atmosphere and, as a building block of proteins and nucleic acids such as DNA, a crucially important component of all biological life. The nitrogen cycle is a complex biogeochemical cycle in which nitrogen is converted from its inert atmospheric molecular form (N 2 ) into a form that is useful in biological processes. The nitrogen cycle contains several different stages. Nitrogen Cycle

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman12 Nitrogen Cycle

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman13 Nitrogen Cycle

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman14 Nitrogen fixation Atmospheric nitrogen occurs primarily in an inert form (N 2 ) that few organisms can use. (It takes a great deal of energy to split the N 2 molecule.) Therefore, it must be converted to an organic form, or fixed, in a process called nitrogen fixation. A small amount of nitrogen is fixed through high energy fixation, primarily lighting strikes that convert atmospheric nitrogen into ammonia (NH 4 + ) and nitrates (NO 3 - ). But most atmospheric nitrogen is fixed through biological processes. First, the nitrogen is deposited from the atmosphere into soils and surface waters.

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman15 This is done by certain microorganisms, which fall under three broad categories: bacteria living in symbiotic relationships with certain plants, free anaerobic bacteria, and algae. Crops such as alfalfa and beans are often planted in order to remedy nitrogen-depletion in soils. Nitrogen fixing bacteria employ an enzyme, known as nitrogenase, to do the energy-intensive work of splitting the atmospheric nitrogen molecule into individual atoms for combination into other compounds. Nitrogen is also fixed by man-made processes, primarily industrial process that create ammonia and nitrogen-rich fertilizers Nitrogen fixation

University Of Palestine UNI 3316 Dr. Hasan Hamouda - Eng. Osama Othman16 Nitrification: While ammonia can be used by some plants, most nitrogen taken up by plants is converted by bacteria from ammonia, which is highly toxic to many organism, first into nitrite (NO 2- ), and then into nitrate (NO 3- ). This process is called nitrification, and these bacteria are known as nitrifying bacteria. Assimilation: compounds such as nitrate, nitrite, ammonia, and ammonium are taken up from soils by plants. The nitrogen in these compounds is used in the formation of plant and animal proteins. Nitrification & Assimilation