effectively demonstrated that narrow-spaced lateral drainage lines have a greater capacity to promote nitrate removal. Drainage control strategies essentially manage soil water to promote anoxic soil conditions resulting in denitrification. #Subler chapter equivalent for pcs install#reviewed the literature and noted that agricultural investigations aimed at reducing N losses from tile-drained soils include (1) properly adjust timing and rate of nitrogen fertilization, (2) quantify soil organic matter mineralization to reduce overapplication of nitrogen fertilizers, (3) using appropriate yield goals when making fertilizer recommendations, (4) encourage prescription fertilization practices, (5) employ nitrification and urease inhibitors, (6) employ remote sensing technologies to monitor crop nutrient status, (7) diversify crop rotations and cover crops, (8) manage plant residues, and (9) install riparian buffers and drainage control strategies. Phosphorus concentrations emanating from surface- or subsurface-drained landscapes are markedly most severe if the soils have a low P sorption capacity or have been heavily amended with phosphate manure/fertilizers. Nitrate concentrations emanating from subsurface drainage systems frequently exceed the USEPA maximum contamination levels. Surface water runoff from intensively fertilized agricultural fields or urban landscapes, soil erosion, livestock and poultry operations, and effluent discharge from subsurface drainage technologies are important nutrient sources for freshwater contamination. Watersheds having N-fertilized row crop and metropolitan/suburban areas are known to contribute N runoff to tributaries, supporting hypoxia in the Gulf of Mexico. The United States Environmental Protection Agency (USEPA) maximum contamination level for nitrate-N is 10 mg NO 3-N/L and the scientific literature is replete with manuscripts addressing nitrate levels in groundwater and surface water exceeding this concentration. Hypoxia typically persists until weather patterns and storms remix the water column.ġ.2.1. Disruption of commercial fishing is common. Organisms that are more predatory and higher in the food chain vacate the region, while other less mobile species perish. Water column stratification isolates the reduced oxygen-bearing deep water layers. The increased growth of phytoplankton exceeds the food web’s capacity to consume the phytoplankton, permitting a portion of the phytoplankton to sink to the ocean bottom, supporting bacterial growth. The current concentrations of nitrogen and phosphorus in the Mississippi River and other rivers has been attributed to increased use of nitrogen and phosphorous fertilizers, the potential for nitrogen and phosphorus to become transported from crop fields to tributaries of the Mississippi River, and atmospheric deposition of oxidized nitrogen gases arising from the combustion of fossil fuels.Įutrophication follows when aquatic systems receive these nutrients and increase primary production, including algae. Mississippi River nutrient concentrations have increased in the twentieth century and continue to increase to the present time. One large hypoxia zone exists in the northern Gulf of Mexico, adjacent or superimposed on the Louisiana/Texas continental shelf.įactors believed to be influencing the areal extent and the degree of oxygen depletion in the northern Gulf of Mexico include (i) nutrient concentrations flowing from the Mississippi River, (ii) eutrophication, (iii) microbial biomass respiration at the ocean floor, and (iv) water column stratification and attendant oxygen depletion. Hypoxia may be a naturally occurring phenomenon in selected marine environments (fjords, deep ocean basins, etc.) however, human activities are increasingly associated with the expanding of existing hypoxia zones. Hypoxia in the northern Gulf of Mexico is defined as a dissolved oxygen concentration smaller than 2 mg/L. Hypoxia is considered as oxygen depletion in a water column to the point that living aquatic organisms may no long survive. Impact of nutrient migration from cropland to fresh water
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