The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmosphere and marine ecosystems. The conversion of nitrogen can be carried out through both physical processes. Important processes in the nitrogen cycle include fixation, ammonification and denitrification; the majority of Earth's atmosphere is atmosphere nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems; the nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, release of nitrogen in wastewater have altered the global nitrogen cycle. Human modification of the global nitrogen cycle can negatively affect the natural environment system and human health.

Nitrogen is present in the environment in a wide variety of chemical forms including organic nitrogen, nitrite, nitrous oxide, nitric oxide or inorganic nitrogen gas. Organic nitrogen may be in the form of a living organism, humus or in the intermediate products of organic matter decomposition; the processes in the nitrogen cycle is to transform nitrogen from one form to another. Many of those processes are carried out by microbes, either in their effort to harvest energy or to accumulate nitrogen in a form needed for their growth. For example, the nitrogenous wastes in animal urine are broken down by nitrifying bacteria in the soil to be used by plants; the diagram alongside shows. The conversion of nitrogen gas into nitrates and nitrites through atmospheric and biological processes is called nitrogen fixation. Atmospheric nitrogen must be "fixed", into a usable form to be taken up by plants. Between 5 and 10 billion kg per year are fixed by lightning strikes, but most fixation is done by free-living or symbiotic bacteria known as diazotrophs.

These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia, converted by the bacteria into other organic compounds. Most biological nitrogen fixation occurs by the activity of Mo-nitrogenase, found in a wide variety of bacteria and some Archaea. Mo-nitrogenase is a complex two-component enzyme that has multiple metal-containing prosthetic groups. An example of free-living bacteria is Azotobacter. Symbiotic nitrogen-fixing bacteria such as Rhizobium live in the root nodules of legumes. Here they form a mutualistic relationship with the plant, producing ammonia in exchange for carbohydrates; because of this relationship, legumes will increase the nitrogen content of nitrogen-poor soils. A few non-legumes can form such symbioses. Today, about 30% of the total fixed nitrogen is produced industrially using the Haber-Bosch process, which uses high temperatures and pressures to convert nitrogen gas and a hydrogen source into ammonia. Plants can absorb ammonium from the soil by their root hairs.

If nitrate is absorbed, it is first reduced to nitrite ions and ammonium ions for incorporation into amino acids, nucleic acids, chlorophyll. In plants that have a symbiotic relationship with rhizobia, some nitrogen is assimilated in the form of ammonium ions directly from the nodules, it is now known that there is a more complex cycling of amino acids between Rhizobia bacteroids and plants. The plant provides amino acids to the bacteroids so ammonia assimilation is not required and the bacteroids pass amino acids back to the plant, thus forming an interdependent relationship. While many animals and other heterotrophic organisms obtain nitrogen by ingestion of amino acids and other small organic molecules, other heterotrophs are able to utilize inorganic compounds, such as ammonium as sole N sources. Utilization of various N sources is regulated in all organisms; when a plant or animal dies or an animal expels waste, the initial form of nitrogen is organic. Bacteria or fungi convert the organic nitrogen within the remains back into ammonium, a process called ammonification or mineralization.

Enzymes involved are: GS: Gln Synthetase GOGAT: Glu 2-oxoglutarate aminotransferase GDH: Glu Dehydrogenase: Minor Role in ammonium assimilation. Important in amino acid catabolism; the conversion of ammonium to nitrate is performed by soil-living bacteria and other nitrifying bacteria. In the primary stage of nitrification, the oxidation of ammonium is performed by bacteria such as the Nitrosomonas species, which converts ammonia to nitrites. Other bacterial species such as Nitrobacter, are responsible for the oxidation of the nitrites into nitrates, it is important for the ammonia to be converted to nitrates or nitrites because ammonia gas is toxic to plants. Due to their high solubility and because soils are unable to retain anions, nitrates can enter groundwater. Elevated nitrate in groundwater is a concern for drinking water use because nitrate can interfere with blood-oxygen levels in infants and cause methemoglobinemia or blue-baby syndrome. Where groundwater recharges stream flow, nitrate-enriched groundwater can contribute to eutrophication, a process that leads to high algal population and growth blue-green algal populations.

While not directly

Ruth Isabelle Skinner was an American businesswoman and philanthropist. She was a daughter of silk manufacturer William Skinner and his second wife, the former Sarah Elizabeth Allen. Belle Skinner was a humanitarian and music-lover whose life her brother William memorialized in the construction of the Skinner Hall of Music at Vassar College in 1932, she lived most of her life at the family home, Wistariahurst, in Holyoke, now an historic site. She renovated and expanded this house to reflect her interests, including adding the music room, where she housed her musical instrument collection, now housed at Yale University. In 1902 she and her sister Katherine established the Skinner Coffee House in honor of their late father, the coffee house hosted women working in the Skinner mills for social and educational activities but became a meeting place for dozens of men's and women's clubs, the 4-H Club, neighborhood organizations, children's groups, dancing clubs. After the first world war, Belle Skinner helped rebuild the small town of Hattonchâtel and Château de Hattonchâtel.

In return for her efforts following the war, Ms. Skinner was presented the Médaille de la Reconnaissance française by future French president and then-commissioner general of Alsace-Lorraine, Alexandre Millerand, in January 1919, at the ministry of foreign affairs in Paris, she led the effort to rally American cities to adopt French villages during the postwar reconstruction, establishing the American Committee of Villages Libérés in New York City that year. Holyoke would be the first city to take part in the program, providing a water supply to the village of Apremont-la-Forêt. Two years on January 26, 1921, she was decorated with the rank of Chevalier in the Légion d'honneur for her continued aid to the French people. While her acts of charity to the French village received general praise and influenced other towns and cities to follow suit, they drew the ire of nativists and anti-Catholicists, the Klan publication The Fiery Cross lambasted Skinner's efforts "to throw away one million excellent American dollars on two hundred French peasants when a few thousands of that sum would have built them good comfortable homes...is little less than a crime against one's country".

Skinner would contribute to her alma mater, providing Vassar College with the first fellowship for foreign studies in 1926, $10,000 for graduates to study history in France, as she had spent time in Paris as a young girl herself soon after her own graduation. While travelling to France to oversee the completion of the Hattonchâtel restoration, Ms. Skinner contracted pneumonia and died on April 9, 1928, her death being reported by papers all across France and the United States. In her memory, her brother William would contribute funds to raise her fellowship to $25,000, as well as fund construction of Skinner Hall for the college's department of music. Belle Skinner's body was brought back to New York City, where a funeral service was held, after which a second was held days at the Skinner Memorial Chapel of the Holyoke United Congregational Church, she was interred in the family's plot at Forestdale Cemetery. Posthumously, she has been described by the American Musical Instrument Society as a "pioneer American instrument collector".

"The Christening of the Bell". The Atlantic Monthly. July 1921. Pp. 62–66. "Christmas at Hattonchatel. The Outlook. December 20, 1922. Pp. 707–709. "The Month of Mary". The North American Review. Vol. CCXIX no. 822. May 1924. Pp. 673–678 – via JSTOR. Skinner, William; the Belle Skinner collection of old musical instruments, Massachusetts. Philadelphia: Beck Engraving Company. OCLC 64299108. Wistariahurst Museum - Belle Skinner's primary residence Château de Hattonchâtel - Restored by Belle Skinner Belle Skinner and Skinner Hall at Vassar

Jennifer Ash Rudick is an American journalist, best-selling author and Emmy-nominated documentary filmmaker. She is the producer of the documentary Iris by Albert Maysles starring Iris Apfel, it premiered at the New York Film Festival in October 2014, was subsequently acquired by Magnolia Pictures for US theatrical distribution in 2015. Following this, Iris ran on PBS's POV, she directed and produced the short documentary Diner en Blanc, which competed in national festivals and is now on iTunes. Rudick is the author of four books: Palm Beach Chic, her next design book, City of Angeles, will be published in fall 2018 by Vendome Press. As a journalist, she has written for national publications, including The Washington Post and Forbes magazine, she was an editor at WWD/W and Town & Country magazine and is a contributor to Veranda magazine. Born in Miami and raised in Palm Beach, Rudick's father was Clarke Ash, the editor for The Miami News. Under his direction, the paper won three Pulitzer Prizes.

Ash was editor of the editorial page for the Palm Beach Post. He received an award for leadership and support from President Lyndon Johnson for his support of the passage of the 1964 Civil Rights Act. Florida Governor, Claude Kirk cited Ash for his campaign to protect the Everglades and for the creation of the Biscayne National Monument, her mother, Agnes Ash, was the publisher of the Palm Beach Daily News. She won 12 newspaper awards, including the New York Women's award as editor of The New York Times, she was a reporter for The Atlanta Journal-Constitution and was the first business editor for The Washington Post. Rudick received a BA from an MFA from the New School for Social Research, she lives in New York City with her husband, Joe Rudick, their two children and Amelia