University of Palestine Faculty of Engineering Environmental Sciences Course

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 2 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 International ENVI005 Dr.-Eng. Hasan Hamouda 3 Nitrogen Cycle

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 4 Nitrogen Cycle

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 5 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 International ENVI005 Dr.-Eng. Hasan Hamouda 6 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 International ENVI005 Dr.-Eng. Hasan Hamouda 7 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

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 8 When animals emit wastes, and when plants and animals die, the nitrogen in this organic matter reenters the soil, where it is broken down by other microorganisms, known as decomposers. Decomposition of this organic matter produces ammonia. Just as the ammonia created through nitrogen fixation becomes available for other biological processes, so does the ammonia created in the process of decomposing animal waste and dead plants and animals. Ammonification

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 9 Nitrogen makes it way back into the atmosphere in a process called denitrification, in which it is converted from nitrate (NO 3- ) to gaseous nitrogen (N 2 ). Denitrification occurs in wet soils where the water makes it difficult for microorganisms to get oxygen. In these conditions, certain organisms, known as denitrifiying bacteria, will process nitrate for their oxygen, leaving free nitrogen gas as a byproduct. Denitrification

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 10 Phosphorus is one of the most biologically important elements. Phosphorus helps hold the DNA and RNA molecules together. Phosphorus plays an important role in the transfer of energy to the key energy-storing molecules ATP and ADP. Like calcium, it is an important element in the bones of vertebrate animals (although too much phosphorus can lead to calcium loss). It is also widely used in agricultural fertilizers. The phosphorus cycle is unique among the major biogeochemical cycles in that it does not include a gas phase, Phosphorous Cycle

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 11 although small amounts of phosphoric acid (H 3 PO 4 ) may make their way into the atmosphere, contributing in some cases to acidic precipitation. The water, carbon, and sulfur cycles all include at least one phase in which the element is in its gaseous state. The largest reservoir of phosphorus is in sedimentary rock. The phosphorus cycle originates with the introduction of phosphate (PO 4 ) into soils from the weathering of rocks. Phosphate enters living ecosystems when plants take up phosphate ions from the soil. Phosphorous Cycle

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 12 Phosphorous Cycle

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 13 Phosphate moves from plants to animals when herbivores eat plants, and when carnivores eat herbivores. The phosphate that has been taken up into the tissue of animals is returned to the soil through the excretion of urine and feces, as well as through decomposition of dead animals. Phosphate in plants also returns to the soil through decomposition. These same processes occur in aquatic systems as well. Plants take up waterborne phosphate, which then travels up through successive stages of the aquatic food chain. Phosphate Cycle

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 14 Phosphate that is not taken up into the food chain, as well as that in dead and decomposing organisms, settles on the ocean floor or on lake bottoms. When these sediments are stirred up, this phosphate may re-enter the biological phosphorus cycle, but much more of it is buried in the sedimentary rock.  Like nitrogen, phosphorus is considered a pollutant when it occurs in excess concentrations in surface waters. Phosphorus can contribute to over-fertilizing, or eutrophication, of these waters. Phosphate Cycle

University Of Palestine International ENVI005 Dr.-Eng. Hasan Hamouda 15  Unlike nitrogen, phosphorus is not highly soluble. It binds tightly to molecules in the soil and so can build up to harmful levels. It reaches surface waters not by dissolving but by traveling with soil particles in runoff to which it has bonded. Phosphates were once commonly used in laundry detergents, which contributed to excessive concentrations in rivers, lakes, and streams. Most detergents no longer contain phosphorous. The predominant sources of phosphorous in bodies of water are agricultural and lawn fertilizers and improperly disposed animal wastes. Phosphate Cycle