Nitrogen+Cycle

=Nitrogen Cycle = 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 (N2) into a form that is useful in biological processes.  The nitrogen cycle contains several stages: **Nitrogen fixation**

Atmospheric nitrogen occurs primarily in an inert form (N2) that few organisms can use; therefore it must be converted to an organic - or fixed - form in a process called nitrogen fixation. Most atmospheric nitrogen is 'fixed' through biological processes. First, nitrogen is deposited from the atmosphere into soils and surface waters, mainly through precipitation. Once in the soils and surface waters, nitrogen undergoes a set of changes: its two nitrogen atoms separate and combine with hydrogen to form ammonia (NH4+). This is done by microorganisms that fall into 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 the nitrogen-depletion in soils, and nitrogen-fixing bacteria employ an enzyme, known as nitrogenase, to split atmospheric nitrogen molecules into individual atoms for combination into other compounds. A small amount of nitrogen is 'fixed' through a process of high energy fixation that occurs primarily as lighting strikes converting atmospheric nitrogen into ammonia (NH4+) and nitrates (NO3-). Nitrogen can also be fixed through man-made processes, primarily industrial processes that create ammonia and nitrogen-rich fertilizers. **Nitrification**

While ammonia can be used by some plants, most of the nitrogen taken up by plants is converted by bacteria from ammonia - which is highly toxic to many organisms - into nitrite (NO2-), and then into nitrate (NO3-). This process is called nitrification, and these bacteria are known as nitrifying bacteria. **Assimilation**

Nitrogen compounds in various forms, such as nitrate, nitrite, ammonia, and ammonium are taken up from soils by plants which are then used in the formation of plant and animal proteins. **Ammonification**

When plants and animals die, or when animals emit wastes, the nitrogen in the organic matter reenters the soil where it is broken down by other microorganisms, known as decomposers. This decomposition produces ammonia which is then available for other biological processes. **Denitrification**

Nitrogen makes its way back into the atmosphere through a process called denitrification, in which nitrate (NO3-) is converted back to gaseous nitrogen (N2). Denitrification occurs primarily in wet soils where the water makes it difficult for microorganisms to get oxygen. Under these conditions, certain organisms - known as denitrifiying bacteria - will process nitrate to gain oxygen, leaving free nitrogen gas as a byproduct.  <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> The Nitrogen Cycle This page from NASA's Soil Science Education section contains a summary of the process as well as a detailed diagram of the nitrogen cycle. Also included is an extensive glossary of terms relating to nitrogen and the nitrogen cycle. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Nitrogen Cycles Project The Illinois Department of Natural Resources' State Water Survey, in affiliation with the University of Illinois, compiled this page on the nitrogen cycle. The material covered includes biogeochemical cycles, properties of nitrogen, an illustration of the nitrogen cycle, and the effect of human activity on the cycle. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Nitrogen Cycle Dr. Terry Cooper from the University of Minnesota provides a good basic overview of the nitrogen cycle. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Nutrient Overload: Unbalancing the Global Nitrogen Cycle This article by the World Resource Institute discusses potential impacts of the overabundance of usable forms of nitrogen which can affect both terrestrial and aquatic ecosystems. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Human Alteration of the Global Nitrogen Cycle: Cause and Consequences One of the Ecological Society of America's "Issues in Ecology," this 1997 report has been peer reviewed and is written to be "understandable by non-scientists."

<span style="background-color: #ffffff; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 16px;">FOR THE CLASSROOM
<span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> There's Something Fishy The Nitrogen Cycle This lesson from //<span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px; line-height: 18px;">Science in the Real World: Microbes in Action Program //has students measure the nitrogen levels in a classroom aquarium over the period of a few weeks. The experiment explains the nitrogen cycle, and contains detailed worksheets for students and instructions for the teacher. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Traveling Nitrogen Middle school students can get involved in this UCAR Windows to the Universe interactive classroom exercise by playing the role of nitrogen atoms as they move to different stations around the room, representing the various stages in the nitrogen cycle.

=<span style="background-color: #ffffff; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 20px;">Unbalancing the Nitrogen Cycle = <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;">Because it takes a great deal of energy to convert atmospheric nitrogen into biologically useful forms, ecosystems have evolved to get by on fairly modest amounts of organic nitrogen. From forest fires to farming to burning fossil fuels, human activities have been altering the natural nitrogen cycle for centuries. Human practices that add reactive nitrogen (nitrogen that has been fixed) to ecosystems can change ecological balances. Farming, for example, is a relatively nitrogen intensive activity. Crops deplete nitrogen in the soil; therefore many farmers use man-made fertilizers in order to augment nitrogen levels. Unfortunately, in its nitrate form, nitrogen is extremely soluble and is readily leached from the soils into ground water reservoirs which feed into lakes and streams. In heavily agricultural areas, fertilizers are the primary source of nitrogen pollution. Where livestock is raised, animal wastes that are rich in nitrogen - if not properly managed - can also be carried by rainwater into nearby bodies of water. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;">In areas with large human populations, most of the reactive nitrogen that is introduced into the environment by human activity comes from food and food processing. As with other animals, human wastes are nitrogen rich. This is especially the case with the large amounts of food protein that most Americans consume. Waste treatment facilities permit significant quantities of reactive nitrogen from human wastes to reenter the water cycle. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;">There are a variety of consequences of nitrogen pollution. A major source of reactive nitrogen is atmospheric deposition which comes largely from transportation emissions, as nitrogen oxides (NO x ) are released through the exhaust. These emissions are a key ingredient in the formation of ground level ozone (smog). Another form of reactive nitrogen - nitric acid (HNO 3 ) - is an important ingredient in the creation of acid rain. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;">One of the most serious consequences of nitrogen pollution is over-nutrition, or eutrophication, of aquatic ecosystems. Nitrogen leaches into the soil, and eventually into standing bodies of water, causing an unnaturally high level of nitrogen in the water. This eutrophication harms aquatic ecosystems by fueling excessive algae growth, which overshadows the water surface and deprives other aquatic organisms of necessary sunlight. When the algae dies, the oxygen consumed in the decomposition process can further deprive other aquatic organisms of needed oxygen. In extreme cases, eutrophication can result in the total die-off of fish in lakes and ponds. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Nutrient Overload: Unbalancing the Global Nitrogen Cycle This article by the World Resource Institute discusses potential impacts of the overabundance of usable forms of nitrogen which can affect both terrestrial and aquatic ecosystems. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Human Alteration of the Global Nitrogen Cycle: Cause and Consequences One of the Ecological Society of America's "Issues in Ecology," this 1997 report (.pdf) has been peer reviewed and is written to be "understandable by non-scientists." <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Human Health Impacts of Nitrogen Cycle Manipulation A University of Colorado at Boulder study found that excess nitrogen production and human use has contributed to human health afflictions such as respiratory ailments, heart disease, and several cancers. <span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Nitrogen in the Earth System The National Center for Atmospheric Research and the University Corporation for Atmospheric Research explain the nitrogen cycle and human impacts on its functioning.

<span style="background-color: #ffffff; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 16px;">FOR THE CLASSROOM
<span style="background-color: #ffffff; color: #333333; font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px;"> Classroom Aquaponics: Exploring Nitrogen Cycling in a Closed System - Teacher's Guide This high school classroom experiment provides background on the nitrogen cycle and aquaponics, an explanation of the activity, related science education standards, and tips for tailoring the experiment. []