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In freshwater or estuarine systems close to land, nitrate can reach concentrations that are lethal to fish. While nitrate is much less toxic than ammonia, [26] levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species. [27] Nitrate toxicity remains a subject of debate. [28]
For his 1934 paper, Alfred Redfield analyzed nitrate and phosphate data for the Atlantic, Indian, Pacific oceans and Barents Sea. [1] As a Harvard physiologist, Redfield participated in several voyages on board the research vessel Atlantis, analyzing data for C, N, and P content in marine plankton, and referenced data collected by other researchers as early as 1898.
Freshwater environmental quality parameters are those chemical, physical and biological parameters that can be used to characterise a freshwater body. Because almost all water bodies are dynamic in their composition, the relevant quality parameters are typically expressed as a range of expected concentrations.
In contrast, freshwater invertebrates are more tolerant (~90+mg/l), and adult freshwater fish can tolerate very high levels (800 mg+/l). [51] Nitrate levels also contribute to eutrophication , a process in which large algal blooms reduce oxygen levels in bodies of water and lead to death in oxygen-consuming creatures due to anoxia.
Nitrates in drinking water can cause blue baby syndrome in infants and can react with chemicals used to treat water to create disinfection by-products in drinking water. [51] Getting direct contact with toxic algae through swimming or drinking can cause rashes, stomach or liver illness, and respiratory or neurological problems .
A common nitrate test, known as the brown ring test [2] can be performed by adding iron(II) sulfate to a solution of a nitrate, then slowly adding concentrated sulfuric acid such that the acid forms a layer below the aqueous solution. A brown ring will form at the junction of the two layers, indicating the presence of the nitrate ion. [3]
The reaction above is the overall half reaction of the process of denitrification. The reaction can be further divided into different half reactions each requiring a specific enzyme. The transformation from nitrate to nitrite is performed by nitrate reductase (Nar) NO 3 − + 2 H + + 2 e − → NO 2 − + H 2 O
Diagram depicting the sources and cycles of acid rain precipitation. Freshwater acidification occurs when acidic inputs enter a body of fresh water through the weathering of rocks, invasion of acidifying gas (e.g. carbon dioxide), or by the reduction of acid anions, like sulfate and nitrate within a lake, pond, or reservoir. [1]
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