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
Slide 3
Hypoxia is most severe in JUNE, JULY and AUGUST What cause
this?
Slide 4
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.
Slide 5
Slide 6
Schematic of agricultural landscape with wetlands intercepting
drainage tiles and riparian buffers along all streams and rivers
(Mitsch and Gosselink 2000, reprinted with permission).
Slide 7
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
Slide 8
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.
Slide 9
Slide 10
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
Slide 11
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
Slide 12
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