Baltic Sea in the Atlantic Ocean has world’s largest dead zones. It has been a victim of anthropological activities such as over fishing and excess use of fertilizers in agricultural lands (Baltic Nest Institute, 2014). Dead zones similar to that of Baltic Sea are also seen in US territorial waters including Chesapeake Bay, Great Lakes, northern Gulf of Mexico, Long Island Sound and coastal Oregon. The Chesapeake Bay is a major nutrient sink that receives the storm water run-off from the 88, 000 farms in the surrounding states as well as effluents from 5 major effluent treatment plants. Hypoxic conditions in the bay vary annually depending on the rainfall and the load of nutrients in the storm water runoff (Reader, 2013). Dead zones in Great Lakes are mainly due to wastewater discharge from the surrounding cities. The enclosed condition of these shallow lakes further promotes stratification and minimizes oxygen mixing, which leads to eutrophication. Additionally, in Long Island Sound and Coastal Oregon, the spread of hypoxic conditions is attributed to changing weather and wind patterns (Reader, 2013).
There was an explosion on April 20, 2010, in one of BP’s major oil wells in the northern Gulf of Mexico. It resulted in a spill of about 206 million gallons of crude oil that began to spread in an unprecedented manner, affecting the ecosystem of Mississippi delta. The Mississippi shelf was already hypoxic due to land use changes and nutrient run-off, and the spill further triggered the formation of dead zones, algal blooms and fish kills (Rabalais, 2011).
Dead zones can be revived by geo-engineering strategies such as pumping oxygen-saturated surface water into the deep hypoxic region. But, care should be taken when handling under water sediments that may be disturbed during the pumping, and this technique is energy intensive. Sweden is trying to employ deep-water oxygenation to revive dead zones in the Baltic Sea (Stigebrandt, 2012). Upgrading effluent treatment plants with nutrient removal systems as well as by legislations that restrict nutrient run-off into water bodies can also help revive dead zones. US Environmental Protection Agency is trying to set a maximum daily load limit for farms, industries and waste treatment plants in states surrounding the Chesapeake Bay and the Maryland local Government has imposed storm water fee to restrict nutrient loads to the Bay (Reader, 2013). These measures could reduce dead zone incidences to considerable extent.
Baltic Nest Institute. (2014). Dead Zones have increased by more than 10-fold in the last century. Retrieved Jul. 4, 2015, from http://www. balticnest. org/balticnest/activities/
Rabalais, N. N. (2011). Troubled Waters of the Gulf of Mexico. Oceanography, 24, 200-211. Retrieved Jul. 4, 2015, http://www. tos. org/oceanography/archive/24-2_rabalais. pdf
Reader, R (2013). The Biggest Dead Zones in America’s Waterways. Retrieved Jul. 4, 2015, from http://motherboard. vice. com/blog/the-biggest-dead-zones
Stigebrandt, A. (2012). Evaluating Geoengineering as a Method to Revive Baltic Sea Dead Zones. Retrieved Jul. 4, 2015, from http://box-win. se/wp-content/uploads/2013/01/Soapbox