What is a Dead Zone? What does Hypoxia mean? What does it mean to be Anoxic?
All of these terms refer to an environment in which the oxygen in a water body decreases so much that aquatic life can no longer live there. One such place is in the Gulf of Mexico (shown below on the toe of Louisiana), which is the second largest hypoxic zone in the world. |
| https://upload.wikimedia.org/wikipedia/commons/2/2a/Sediment_in_the_Gulf_of_Mexico.jpg |
What Causes Hypoxia?
Major events leading to the formation of hypoxia in the Gulf of Mexico include:
- Freshwater discharge and nutrient loading of the Mississippi River
- Nutrient-enhanced primary production, or eutrophication
- Decomposition of biomass by bacteria on the ocean floor
- Depletion of oxygen due to stratification
How Exactly Does It Work?
#1. Too much nutrients added to a field or urban area will not be absorbed, as plants can only absorb so much until they are full (nutrients such as Nitrogen & Phosphorus).
#2. When it rains this excess is carried off by runoff into the nearest body of water and then eventually ends up in the ocean.
#3. Once it reaches this "dead end", this huge amount of nutrients fertilize microscopic plants (phytoplankton) in a process called eutrophication.
#4. Once these micro plants eat it all up, they die and sink to the bottom and are then eaten by bacteria, which greatly increases the oxygen consumption by the bacteria, which depletes the total oxygen available.
So, Who Is The Main Culprit Behind Hypoxia?
Well, actually we all play a role whenever we toss trash on the side of the road and do not think about the consequences of our actions and the harm they may have on the environment and those that rely on those ecosystems (i.e. fishermen who earn their living fishing in the Gulf of Mexico). Of the major causes of hypoxia forming (listed above), much of this nutrient loading comes from Agriculture. |
| https://www.populationeducation.org/sites/default/files/gulf_of_mexico_hypoxia_zone.jpg |
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| http://www.cbf.org/about-the-bay/issues/dead-zones/nitrogen-phosphorus |
Model of Residence Time and Analysis of Nitrogen Removal for Two Constructed Wetlands at the Franklin Demonstration Farm in Lexington, Illinois
Emma Baghel, Illinois State University
Abstract
Pollution from nonpoint agricultural runoff has become a major problem facing our streams and rivers today. Not only are fish and aquatic life affected, but so is the quality of our drinking and recreational water resources. Studies have shown that wetlands have proven to be the most cost-effective and low maintenance method of removing nonpoint or diffused contaminate inputs. The biological processes and removal of nutrients in wetlands depend on the total surface area available for microbial activity in the soil and a certain period of water retention time. Since chemical processes take time, the measure of residence time is an important factor of the degree to which wetlands can change water chemistry. Knowing that nitrogen concentrations decrease as water residence time increases, a model of residence time will help interpret the mechanisms determining groundwater flow paths within and around the constructed wetlands. The main objectives of this research are to model water's residence time, compare the size and gradient of two experimental wetlands, and determine the water flow paths within the site and how they relate to the areas of high denitrification rates. The two constructed wetlands chosen are the West and Gully located in Lexington, Illinois. Of the two, Gully is about half as small and has a higher gradient. Using MODFLOW to create a local-scale model that includes both wetlands and the tile drainage will help to determine how groundwater influences the fate of nitrogen and the effectiveness of wetland construction parameters. Since the outflows from groundwater to the wetlands are significantly greater than the inflows from the surface water, it can be assumed that the wetlands have zones where they are being recharged from groundwater. Franklin West had an average residence time of about 1.41 days (121,580 sec) which is much slower than Gully's 0.011 day (918 sec). With a lower overall groundwater discharge into Franklin West, this may help to explain why the wetland system removes less N than Gully even though it has a longer surface water residence time. As the nutrients can also travel within the groundwater, they have the potential of contaminating the water supply, but with a long enough distance, denitrification and the process of diffusion within the subsurface can also remove excess N. With the 10 years of travel time from Franklin West to the Mackinaw River and the six years it takes water to travel from Gully to Turkey Creek, any nutrients from Franklin West will have more time, both within the wetland system itself and the groundwater, to denitrify and more effectively remove nutrients before the water reaches surface features. The results of this research will be beneficial when considering effective wetland design, monitoring procedures, and wetland management.
The solutions to this problem include:
- preventing animals from walking around and pooping in streams (lowers amount of Phosphorus added to the water),
- planting cover crops and/or only adding as much fertilizer as needed (there are ways to figure out just how much is enough),
- and maintain grassed or forested buffer strips along farm fields or install wetlands to filter and trap the extra nutrients before the water continues its trip to the ocean.
