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Anthropogenic Nutrient Sources Fertilizers Human & Animal Wastes Fossil Fuel Combustion Leguminous Crops Potential Ecosystem Effects Algae Blooms Hypoxia Anoxia Food Web & Production Disruption Reduced Biodiversity

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Hypoxia is most severe in JUNE, JULY and AUGUST What cause this?

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Nutrient sources: Water shed and land-use change First, flood control and navigational channelization are clearly important watershed alterations. Second, significant landscape alterations (e.g., deforestation, conversion of wetlands to cropland, loss of riparian zones, expansion of artificial agricultural drainage) e Third, there was a dramatic increase in nitrogen input into the Mississippi River, primarily from fertilizer application, between the 1950s and the 1980s flux of nitrogen to the Gulf tripled between 1955 and 1970 and between 1980 to 1996 to the present average of 1.6 million metric tons per year, with 61% of that flux in the form of nitrate.

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Schematic of agricultural landscape with wetlands intercepting drainage tiles and riparian buffers along all streams and rivers (Mitsch and Gosselink 2000, reprinted with permission).

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Other factor that can contribute are: Flux of poorly oxygenated water from offshore (Turner and Allen 1992) invasion of water from poorly Oxygenated layer Organic carbon load Sediment load in river has decreased by half and stable Carbon isotope from hypoxic zone are very high Climate change Influence from both nitrogen level and intensity of Salinity stratification on the shelf Cause river discharge

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How excess nutrients alters the flow of sediments through the system? Excess nutrients stimulates phytoplankton bloom (algae bloom). Phytoplankton bloom increases the flux of organic material from surface waters fueling microbial decomposition causing oxygen depletion. Low oxygen level in the bottom water leads to increased mortality among organisms sensitive to hypoxic condition.

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What can be done to remediate this problem? Preventative measures include: -Applying less fertilizers on farms upstream -Injecting fertilizers below the soil surface and by using controlled-release fertilizers -Using no-till cultivation on farms which would help to reduce soil erosion -Farmers or conservation agencies could plant strips of forests and grasslands along waterways to soak up excess nitrogen in order to restore and create wetlands between crop fields and streams emptying into the Mississippi River Other measures: -Improving flood control and upgrading sewage treatment systems -lower emissions of nitrogen oxides from motor vehicles and phasing in forms of renewable energy to replace the burning of fossil fuels

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Hypoxia Oxygen Depletion Dissolved Oxygen less than 2mg/L Gulf of Mexico 2 nd Largest Hypoxic Zone Worldwide Largest hypoxic zone 2002 about size of Massachusetts Average Size about the size of Lake Ontario

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References Boesch, Donald F. Challenges and Opportunities for Science in Reducing Nutrient Over-Enrichment of Coastal Ecosystems, Estuaries, Vol. 25, No. 4, Part B: Dedicated Issue: Nutrient Over-Enrichment in Coastal Waters: Global Patterns of Cause and Effect (Aug., 2002), pp. 886-900 Article Stable URL: http://www.jstor.org/stable/1353041http://www.jstor.org/stable/1353041 Dodds, Walter K. "Nutrients and the dead Zone: The Link between Nutrient Ratios and Dissolved Oxygen in the Northern Gulf of Mexico." Frontiers in Ecology and the Environment 4.4 (2006): 211-17. Print. Kim, Il-Nam, and Dong-Ha Min. "Temporal Variation of Summertime Denitrification Rates in the Texas Louisiana Inner Shelf Region in the Gulf of Mexico: A Modeling Approach Using the Extended OMP Analysis." Continental Shelf Research 66 (2013): 49-57. Print. Miller, G. T., & Spoolman, S. (2012). Living in the environment: Principles, connections, and solutions. Belmont, CA: Brooks/Cole. Rabalis Nancy N., Turner, R. Eugene, and Scavi, Donald A, Beyond Science into Policy: Gulf of Mexico Hypoxia and the Mississippi River, BioScience, Vol. 52, No. 2 (February 2002), pp. 129-142 Article DOI: 10.1641/0006-3568(2002)052[0129:BSIPGO]2.0.CO;2 Article Stable URL: http://www.jstor.org/stable/10.1641/0006- 3568%282002%29052%5B0129%3ABSIPGO%5D2.0.CO %3B2

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