Thursday, October 10, 2019
Impact of nitrogen and phosphorous inputs on water quality Essay
Both Nitrogen and Phosphorous are necessary in agriculture for a farmer to achieve optimum yields in most crops, they have to use fertilizer which often contains either nitrogen or phosphorous. Despite their importance, these elements in excess can affect the environment adversely. Eutrophication is enhanced when nitrogen and phosphorous are in excess in surface waters and where nitrogen is in excess in ground water. (www. soil. ncsu. edu/) Nitrogen makes up about 78 percent of the gases in the atmosphere. A major constituent of proteins it is abundant in most living things. Nitrogen gas (N2), nitrate (NO3), nitrite (NO2) and ammonia NH3 are the common forms in which in organic nitrogen exists. Organic nitrogen exists in proteins. (http://kywater. org/). Compounds that contain nitrogen are found in water bodies such as reservoirs, streams and rivers. There are various routes by which nitrogen enters water bodies. These include wastewater (municipal and industrial), animal wastes such as bird wastes and wastes of fish, septic tanks and runoff from fields and lawns that have been fertilized. In certain parts of the United States, especially the northeast, some forms of nitrogen are deposited through acid rain (Baird, 1990). Nitrites are then converted to nitrates by bacteria, a process that uses up oxygen. (http://kywater. org). Surface and subsurface drainage are some of the ways through which nitrogen from fertilizers enter streams. When there is heavy rainfall following surface application of nitrogen fertilizers, most of the nitrogen is lost and even more is lost if the area is sloppy. When the fertilizer is mixed with soil the runoff is decreased. However, the loss of nitrogen becomes substantial when heavy rainfall causes soil erosion and movement of debris. The highly soluble nature of nitrogen makes it be absorbed easily into the soil when it rains heavily. Findings from research studies show that leaching does contribute to the presence of nitrates in groundwater. This however does not cause much contamination since the concentrations of nitrogen do not reach high enough levels. The crop uses up to 50 percent of the applied nitrogen leaving about 30 percent to 50 percent available for leaching. This, from a study done on North Carolina soils leads to leaching to a level of only two feet where there was 3 inches of percolated water (Baird, 1990). Eutrophication is a slow process whereby streams and lakes are enriched with natural nutrients. This process leads to the accelerated Ã¢â¬ËagingÃ¢â¬â¢ of lakes and reservoirs. Eutrophication generally means excess growth of algae. The growth and decomposition of algae causes depletion of oxygen available in water. Nitrogen has a fertilizing effect in algae and other plankton which are food to other organisms in water such as fish and invertebrates. Overproduction and decomposition of these plankton uses up oxygen, meaning that other oxygen-dependent animals have inadequate oxygen which leads to their death. (http://kywater. org/). In addition to using up oxygen excessively, the overgrowth of algae and other plankton can lead to clogging up of water systems such that water flow is inhibited. This is especially common at points of water intakes. A lot of sea plants also block light from reaching the deeper waters (http://ga. water. usgs. gov/). This has the effect of compromising respiration for aquatic invertebrates and fish, making the death of animals and plant inevitable. High concentrations of nitrites produce a condition called brown blood disease which is fatal to fish. (http://kywater. org/). Eventually diversity of animal and plant life is lost. The death of fish results in offensive odours, and affects the water such that it cannot be used for recreative purposes like swimming, boating and fishing. Mueller and Helsel conducted a study of 12,000 ground water samples and approximately 22,000 samples of surface water at over 300 sites. The samples were collected within NAWQA study units. They report that the concentrations of nutrients in water have a close relationship to how land is used upstream or in the area that overlies a ground water aquifer. According to the analysis there were higher concentrations of nitrates in groundwater than surface water bodies. The regions with the highest concentration were the Northeast, the Great Plains and areas along the West Coast (Mueller and Helsel, 1996). Agricultural areas have a higher likelihood of having water with increased concentrations of nitrates. Research shows that public-supply wells and domestic supply wells outside areas where land is used for agriculture generally have lower concentrations of nitrates compared to wells in agricultural areas. On the other hand, urban areas have higher concentrations of Ammonia and phosphorous in surface water (Mueller and Helsel, 196). For water to be considered safe for domestic water supply, nitrates or nitrite level should be below 10mg/L. (United States Public Health Service). Nitrites undergo a direct reaction with haemoglobin in humans and warm-blooded animals leading to the formation of methemoglobin. This compound leads to decreased ability of red cells to transport oxygen. The most affected by this inability are infants less than three months because the babies develop methemoglobinaemia (blue baby disease. (http://kywater. org/ww/ramp/rmnox. htm). Due to this reason, when nitrates levels exceed 1. 0mg/L, the water should not be used to feed babies. In older people high nitrate levels cause disturbances in the digestion system. (http://kywater. org/). Phosphorous is a naturally occurring element that can be found in rocks and mineral deposits. Phosphate ions are soluble in water and are released when rock undergoes the weathering process. Phosphates have three forms of existence, metaphosphate, orthophosphate and organic phosphate. Orthophosphate is mainly produced by natural processed but there are man-made sources that produce orthophosphate. These include untreated sewage and partially treated sewage, use of certain fertilizers and runoff from sites where the main land use is agriculture. Metaphosphate or polyphosphate are used in treatment of detergents and boiler waters. When in water metaphosphate changes to orthophosphate and it can be used up by plants in this form. Organic phosphate occurs tied to organic material like plant tissue or waste solids. When decomposition occurs organic phosphate is converted to orthophosphate (www. water-research. net/phosphate. htm). Phosphorous is necessary for animal and plant growth and acts as a growth limiting nutrient in lake ecosystems. Well-oxygenated waters have low amounts of phosphates. Phosphate undergoes a complex process of uptake and mineralization to be retained in the soil, unlike the nitrogen cycle which is simpler. Soluble phosphate is incorporated by plants and animals in their biological systems to form compounds like ATP, DNA and RNA. ATP is necessary for energy production via the KrebÃ¢â¬â¢s cycle while DNA and RNA have genetic importance. Phosphorous is therefore necessary for photosynthesis to occur (www. water-research. net/) Phosphates enhance growth of aquatic plants which are the food source for other organisms. Increased production of plankton result in an initial increase in population of fish and the entire biological system of the water body. This however has an adverse effect because as the phosphate levels build-up the process by which the water ecosystem is aging is speeded up leading to an imbalance of nutrients where production begins to exceed consumption. Phosphates like nitrates also cause eutrophication resulting in more plants than can be consumed by the system. The result is anoxic waters, presence of algal blooms that are toxic and a reduction in biodiversity as well as destruction of food supply and habitat. (www. water-research. net) Eutrophication is an issue that compromises water quality and has received much attention since 1980 when there was extensive occurrence of blue-green algae in fresh water systems. These blue-green algae (cyanobacteria) sometimes produce toxins that cause harm to human beings and farm animals. Poor conditions resulting from eutrophication have been noted in eastern North Carolina in the Chowan, Neuse and Pamlico River systems (Baird, 1990). Water that has very high levels of phosphates causes digestive problems to people. The negative effect of high levels of phosphate then is more indirect to humans but has a bigger impact because by altering the environment and destroying habitats the destruction caused is much harder to reverse. A compound like nitrates dissolves in water and moves in water in surface streams and ground water. Most forms of phosphorous, however, are transported together with soil that has undergone erosion especially when runoff is high flowing precipitation and irrigation. This is because instead of dissolving they attach themselves to soil particles. As such phosphorous is more likely to contaminate surface water rather than ground water (USGS, Circular1225, 2007). Findings from a USGS report indicate that phosphorous has a greater effect in causing eutrophication with 0.1mg/L of phosphorous being sufficient to cause excessive growth of aquatic plants (USGS, Circular 1225, 2007). In urban areas, the most significant point sources are urban streams which have discharged from wastewater treatment plants. A report of the US Geological service indicates that the streams in the semiarid western and south-western cities coupled with those in urban areas on the East had high levels of phosphorous (USGS, Circular1225). Recent research shows that phosphorous can travel with ground-water flows. The study was conducted in Cape Cod, Massachusetts where there has been contamination of the groundwater with phosphorous, an unlikely thing since most scientists generally believe that phosphorous is not transferable via groundwater (McCob et al, 2003; Stollenwerk, 1996). The main factors influencing vulnerability to contamination are the type of soils and slope of land. These two factors determine how fast and how much runoff there will be. Areas with steep slopes, poorly drained clay soils and little vegetation have higher likelihood of contamination of their surface waters. In urban centres, pavements and drains made of tile cause acceleration of flow of streams. Ground water on the other hand has a high chance of contamination if the soils drain well and the subsurface material is highly permeable. Some practices of crop-management designed to decrease sediment flow may increase infiltration leading to greater contamination of groundwater (USGS, Circular, 1225). To reduce the impact of phosphorous and nitrogen in water quality, strategies need to be employed that reduce the use of chemicals and alter transportation of the hydrologic system (USGS). In planning these strategies consideration of watersheds, patterns of land use and the differences in vulnerability to contamination in various areas should be foremost to ensure that whatever interventions are put in place are effective. References Baird J (1990) Nitrogen management and water quality retrieved from www. soil. ncsu. edu/publications/soilfacts/AG-439-02 Harvard, Olson and Cooke, 1999, Impact of soil phosphorous loading on Water Quality in Alberta, Alberta Agriculture, Food and Rural Development. McCob T D, Leblanc DR, Watter DA, Hess KN Kent DB and Smith RL 2003, Phosphorous in a Ground-water contaminant Plume Discharging to Ashumet Pond, Cape Cod, Massachusetts, 1999: US Geological Survey Water-Resources Investigations Report 02-4306, 70p Mueller D K and Helser D R, Nutrients in the NationÃ¢â¬â¢s water-Too much of a Good Thing? National Water-Quality Assessment Program USGS, retrieved from http://water. usgs. gov/nawqa/CIRC-1136. html National findings and their implications for water policies and strategies, USGS, Circular 1225, retrieved from http://pubs.usgs. gov/circ/circ1225/html/nawqafind. htm/. Nitrogen and water quality retrieved from http://kywater. org/ww/ramp/rmnox-htm Stollenwerk K-G 1996, Simulation of phosphate transport in sewage-contaminated groundwater, Cape Cod, Massachusetts, Applied Geochemistry, V. 11. no 1-2 pp 317-324 The effects of urbanization and agriculture on water quality: Nitrogen retrieved from http://ga. water. usgs. gov/edu/urbannitrogen. html Total phosphorous and Phosphate impact in surface waters Wilkes University, Environmental. Engineering and Earth Science retrieved from www.water. research. net/phosphate. htm Water-quality patterns in agricultural areas, USGS, Circular 1225 retrieved from http://pubs. usgs. gov/circ/circ1225/html/wq-agri. htm/ Water-quality patterns in urban areas, United States Geological Society, retrieved from http://pubs. usgs. gov/circ/circ1225/html/wq-urban. htm/ Water-quality patterns in areas with mixed hand use and a range of hydrologic and environmental settings, USGS, Circular 1225 retrieved from http://pubs. usgs. gov/circ/circ1225/html/wq-hydro. htm/.