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Gulf Of Mexico Dead Zone
Que. 1 Dead zones
Dead zones are environments in the ocean that are characterized by low concentration of oxygen, to the extent that no animal life can survive in them (National Oceanic and Atmospheric Administration, 2009). Dead zones usually affect the enclosed water bodies such as estuaries, lakes, seas, and bays. In these water bodies, the local conditions such as inflow from rivers, wind and wave patterns, and bottom topographies, promotes water stratification (the separation of water such that layers which are highly rich in dissolved oxygen are at the top, while those which are less dissolved with oxygen are at the bottom). In non-hypoxic waters, nutrients and sunlight usually penetrates through the water, promoting the growth of phytoplanktons, which are fed by fish and aquatic creatures (Joyce, 2000).
Moreover, some of these phytoplanktons usually fall and settle at the bottom of oceans or lakes, and become food for the aquatic population in these environments, such as worms, bottom-feeding fish, crabs, and shrimp. In hypoxic waters, many phytoplanktons settle at the bottom of the ocean, and because they are in excess of what the aquatic creatures in these environments require, they usually start decomposing. The decomposition process depletes the available oxygen, which cannot be renewed by the surface water due to stratification of salt and fresh water (Joyce, 2000).
Most dead zones occur in black seas, Baltic Sea, in the Chesapeake Bay, coast of Oregon and some lakes such as Lake Erie. However, however, it is established that the world`s largest dead zone is located at the gulf of Mexico, at the mouth of river Mississippi. This dead zone is less than two parts per million (ppm) of dissolved oxygen, and the area covers approximately 6,000 to 7,000 square miles (Bruckner, 2012). The zone occurs at the beginning of river Mississippi delta and extending to the west side of Texas coast.
Que.2 Causes of dead zones
Most dead zones occur due to anthropogenic activities such poor agriculture mechanisms which increase the concentration of some nutrients such as nitrates and phosphates. For example, most studies depict that most hypoxia started to be noticed in 1950s when agriculture became intensive in most regions (National Oceanic and Atmospheric Administration, 2009). Other human activities that threaten water quality include land transformation, atmospheric emissions such as burning of fossil fuels, poor treatment of sewage, urban storm water run-offs among others. The worsening of Chesapeake hypoxia since 1960s is good evident that this problem is contributed by human activities. Moreover, the occurrence of dead zones is also contributed by natural causes such as tides and waves, which sometimes concentrate nutrients at one point, favoring the growth of algae, which depletes the limited oxygen.
Que.3 Specific causes of river Mississippi dead zone
The dead zone at river Mississippi is caused by the enrichment of nitrates and phosphates, which arise from various anthropogenic activities carried out along this river. For example, most of these nutrients come from States that practice intensive farming, such as Mississippi, Missouri, Louisiana, Minnesota, Arkansas, Illinois, Tennessee, Iowa, and Wisconsin. These nutrients enter river Mississippi through upstream runoff of agricultural fertilizers, sewage, and animal wastes. A high concentration of these nutrients stimulates the growth of algae, creating algal blooms, which depletes the oxygen in that area. However, the size of this dead zone is not constant as it depends with the farming practices (National Oceanic and Atmospheric Administration, 2013).
In addition, natural factors such as seasonal stratification of water cause the existence of hypoxic conditions in the Gulf of Mexico. In this Gulf, saline gradient (point where fresh and saline water meet) makes the fresh water at the top to be warmer than the deeper water in the ocean, and this heightens the level of stratification. This stratification limits oxygen-laden fresh water from mixing with poor oxygenated saline water, making hypoxic atmosphere to persist at this region (Hypoxia 101, 2014).
Que. 4 Monitoring of dead zones
The approaches of monitoring dead zones help in minimizing the concentration of nitrates and phosphates in the water bodies (Committee on Environment and Natural Resources, 2010). However, the ultimate approach of monitoring dead zones involves using real-time monitoring devices such as the optical nutrient sensors. These sensors are located at the mouth of the river and in areas where tributaries drain into the main river, giving data concerning the flow and concentration of nitrate and phosphate nutrients. These sensors give data within little duration that range from 15 minutes to three hours. Consecutively, the real-time information that is provided by these nutrient sensors enables researchers to track the source of excessive nutrients, and then taking necessary measures in order to reduce the high nutrient concentration. For example, the researchers can determine when to when turn on nitrate-removal systems, and when to mix water with various sources that have a lower concentration of nutrients. Along river Mississippi, there are approximately 56 real-time nitrate sensors, out of which 36 are along this river while the rest are at the draining points of its tributaries (U.S. Geological Survey, 2013).
Que. 5 effects of dead zones
Dead zones have numerous vital negative effects to the aquatic creatures living in the bottom parts of oceans or lakes. Dead zones reduce the biomass and diversity of benthic fauna (the bottom-living aquatic communities). However, the biological effects of dead zones to these organisms changes depending on the magnitude and frequency of the dead zone and the tolerance of these species. For example, short-term dead zones cause the mass mortality of aquatic species that cannot manage to escape from the affected region. As the dead zone becomes long lasting, it reduces both the number of benthic communities and their diversity. Consecutively, hypoxia alters the normal process of sediment geochemistry, making the latter to release nitrates and phosphates, which further increase the rate of organic production (National Science Foundation, 2014).
Dead zones also lead to production of toxic hydrogen sulfate nutrients from the sediments, which increase the amount of dissolved carbon dioxide and change of PH levels, which in the long run increases the mortality rates of benthic species. Dead zones can also contribute to the extinction of some fish species. For example, hypoxia in Baltic Sea made Norwegian lobster become extinct. Consecutively, hypoxia can cause some fish species migrate to other regions that are favorable for their survival (Joyce, 2000). Alternatively, some aquatic species may migrate after the species of fish that they feed on become extinct, or minimal for their survival. Moreover, some fish stocks may become less stable because of the young ones lacks the necessary habitats or food that enables them to mature into adulthood. For example, the current fish that are being caught at black sea are small and less valuable sprat, horse mackerel and anchovy fish.
The dead zone at river Mississippi has led to massive death of numerous types of fish such as shrimp and oysters. The increased deaths of these fish have negatively affected the rate of fish production in the Gulf of Mexico (Joyce, 2000). This in the long run affects the economy of this region. Consecutively, hypoxia has also reduced the production of big and matured shellfish since this atmosphere has reduced the habits and food that young shellfish requires in order complete their life cycle.
Que.6 Economic impacts of dead zones
The mass mortality of numerous types of fish due to dead zones reduces the level of fish production, which in the long run reduces the amount of returns an area realizes. For example, the Gulf of Mississippi experience a decline of shellfish and shrimp during periods of hypoxia since most of them die or migrate to other regions (Joyce, 2000).
Que. 7 Actions that can reduce the impacts of dead zones
In order to reduce the adverse impacts that are associated with dead zones, numerous measures can be adopted. First, farmers should be sensitized and educated on quantity and time of applying fertilizers in the agricultural lands (Kenyon, 2014). For example, farmers can be advised to use fewer amounts of fertilizers, and not to apply them during rainy days, in order to reduce surface runoffs containing that are rich in nitrates and phosphates. In addition, farmers can be encouraged to plant and maintain vegetation between agricultural fields and the tidal creeks. This vegetation acts as a buffer that filters agricultural nutrients before they reach the nearby water bodies. Consecutively, farming communities can be sensitized to build wetlands that temporarily hold and filter water from runoffs, before being allowed to enter rivers or lakes (National Science and Technology Council, 2000).
Secondly, governments should sensitize citizens and industries to treat raw sewage before directing it to the water bodies. Wastewater treatment plants should be constructed in order to enhance treatment of sewage both at the source and non-point sources. Moreover, legislative policies should be formulated and implemented in controlling the discharge of water pollutants from industrial plants, and residential areas. The necessary measures should be undertaken to any individual or industry that directs sewers and effluents in the water bodies. However, this measure can be achieved through the collaboration of various stakeholders such as water and environmental protection agencies, local governments, national governments, and citizens (Joyce, 2000).
Thirdly, all stakeholders who are involved in regulating the concentration of nutrients in the water bodies should be meeting periodically in order to assess their progress. In the process, barriers that limit them in realizing the goal of reducing nutrient loads should be outlined, and the necessary solutions should be made (Reassessment, 2013).
Fourth, national governments need to develop and implement nutrient monitoring devices in order to regulate the in-flow of nitrates and phosphates in the ocean or lakes. For example, real-time nutrient sensors are installed at both along river Mississippi and its tributaries (U.S. Geological Survey, 2013).
U.S. Geological Survey, (2013). Real‐time Monitoring Pays Off for Tracking Nitrate Pulse in Mississippi River Basin to the Gulf of Mexico. Retrieved from, http://www.sciencedaily.com/releases/2013/08/130822164326.htm
Reassessment 2013: Assessing Progress Made Since 2008, Mississippi River Gulf of Mexico Watershed Nutrient Task Force. Retrieved from, http://water.epa.gov/type/watersheds/named/msbasin/upload/hypoxia_reassessment_508.pdf
Joyce Stephanie, (2000).The Dead Zone: Oxygen‐Starved Coastal waters, Environmental health perspectives, Vol. 108. Retrieved from, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1637951/pdf/envhper00304‐0022‐color.pdf
National Oceanic and Atmospheric Administration,(2009). Dead Zones: A Common Symptom of Nutrient Pollution, NOAA. Retrieved from,http://stateofthecoast.noaa.gov/hypoxia/dead_zone.html
Bruckner M., (2012). The Gulf of Mexico Dead Zone. Retrieved from,http://serc.carleton.edu/microbelife/topics/deadzone/index.html
Hypoxia 101, (2014). Mississippi River Gulf of Mexico Watershed Nutrient Task Force. Retrieved from, http://water.epa.gov/type/watersheds/named/msbasin/hypoxia101.cfm
National Science and Technology Council, (2000). An Integrated Assessment: Hypoxia in the Northern Gulf of Mexico. Retrieved from, http://oceanservice.noaa.gov/products/hypox_final.pdf
National Oceanic and Atmospheric Administration, (2013). Large Gulf Dead Zone, but Smaller than Predicted, Science Daily. Retrieved from, http://www.sciencedaily.com/releases/2013/07/130729133436.htm
Kenyon C.,(2014). Agricultural Impacts in the Gulf of Mexico. Retrieved from, http://www2.kenyon.edu/projects/Agri/eintro.html
National Science Foundation, (2014). Dead Zones: Mysteries of Ocean Die‐offs Revealed, NSF. Retrieved from, http://www.nsf.gov/news/special_reports/deadzones/
National Oceanic and Atmospheric Administration, (2009). The Dead Zone, NOAA. Retrieved from, http://www.nnvl.noaa.gov/MediaDetail2.php?MediaID=1062&MediaTypeID=3&ResourceID=104616
Committee on Environment and Natural Resources, (2010). Scientific Assessment of Hypoxia in U.S. Coastal Waters, Committee on Environmental and Natural Resources. Washington, DC. Retrieved from,http://www2.coastalscience.noaa.gov/publications/detail.aspx?resource=d596/N/PZ790pPMbl3+Me3eaMWtPPGzVXDW7CdGobGM=