Lake Erie
Lake Erie had become victim to the seasonal and interannual effects of hypoxia that seem to be targeting its fish habitat quality. The dead zone had appeared around 1993, where it was speculated as a naturally occurring phenomenon. According to reports, the hypoxic zone's loss of oxygen were most likely influenced by climate change and that it become more amplified during the summer months. The areas that were depleted of oxygen the most were the bottom waters in the central basin of Lake Erie. This location was very broad and shallow and these typical locations were most likely targeted by hypoxia, because of the low supply of oxygen and the larger risk of algal blooms since it was shallow. Statistics have shown that levels of phosphorus has doubled over the last twenty years. The main factors which contribute to the formation of the Lake Erie dead zone are most likely to be excess of phosphorus and nitrogen from human activity and climatic influences.
Hannah Osborne. (2014). Lake Erie on Verge of Death as Climate Change Effects to Serve Double Blow. http://www.ibtimes.co.uk/climate-change-crisis-lake-erie-north-america-verge-death-1438220. Last accessed 18th March 2014.
Hannah Osborne. (2014). Lake Erie on Verge of Death as Climate Change Effects to Serve Double Blow. http://www.ibtimes.co.uk/climate-change-crisis-lake-erie-north-america-verge-death-1438220. Last accessed 18th March 2014.
The Causes
The main cause of the hypoxic zone is the input of a special type of phosphorus called dissolved reactive phosphorus which is extremely effective to promoting explosive algae growth. Human activity have become largely responsible for this issue. The source of excess phosphorus mainly comes from sewage treatment plants, agriculture, pollution and climate change. Most of these generally trigger algal blooms, when algae die and sink to the lake bottom and oxygen consuming bacteria feed on them, creating hypoxic zones in the process. Compared to other factors which cause hypoxia in the lake, climate change becomes only a minor cause. Usually it is the spring rains which predict how serious the algal blooms in the summer time would be. When downpours and become heavy and frequent, it could enhance nutrient enrichment and amplify algal blooms.
Agriculture in areas around Lake Area create a significant contribution to the input of phosphorus. This is due to the nutrient of phosphorus being used in crop fertilizers. The farmland around Lake Erie are positioned near rivers, so during rainstorms, any excess of phosphorus would be washed downstream into the rivers. Many of these rivers are tributaries that connected to Lake Erie. One example, is the Maumee River, which is the single largest source of phosphorus loading to Lake Erie in the present day from agriculture and is also the largest tributary connecting to Lake Erie. Once the phosphorus travels to the central basin of Lake Erie, it acquires conditions where it is able to trigger algal blooms and ultimately deplete the oxygen in the area, creating a hypoxic zone.
Sewage treatment plants were also a major factor for the input of phosphorus. Lake Erie had been suffering from the sewage that was constantly being pumped into it. The sewage wastewater discharge occurs at the southern end of the Detroit River where it enters into Lake Erie. Sewage wastewater contain large amounts of phosphorus and having 30 billion of raw and partially treated sewage dumped into the lake, The Detroit Wastewater Treatment Plant was the single largest contributor of phosphorus to Lake Erie in the 1970's. Even though it emits less phosphorus today, it still has a significant effect. The Maumee River had also contributed phosphorus to the Lake in terms of sewage, but its majority of phosphorus came from agriculture. The large amounts of phosphorus had greatly accelerated nutrient enrichment and algal blooms, making the area anoxic.
Hannah Osborne. (2014). Lake Erie on Verge of Death as Climate Change Effects to Serve Double Blow. http://www.ibtimes.co.uk/climate-change-crisis-lake-erie-north-america-verge-death-1438220. Last accessed 18th March 2014.
Dave Spangler. (2014). Detroit Wastewater Plant. Available: http://www.lakeeriewaterkeeper.org/detroit-wastewater-plant/. Last accessed 20th March 2014.
Agriculture in areas around Lake Area create a significant contribution to the input of phosphorus. This is due to the nutrient of phosphorus being used in crop fertilizers. The farmland around Lake Erie are positioned near rivers, so during rainstorms, any excess of phosphorus would be washed downstream into the rivers. Many of these rivers are tributaries that connected to Lake Erie. One example, is the Maumee River, which is the single largest source of phosphorus loading to Lake Erie in the present day from agriculture and is also the largest tributary connecting to Lake Erie. Once the phosphorus travels to the central basin of Lake Erie, it acquires conditions where it is able to trigger algal blooms and ultimately deplete the oxygen in the area, creating a hypoxic zone.
Sewage treatment plants were also a major factor for the input of phosphorus. Lake Erie had been suffering from the sewage that was constantly being pumped into it. The sewage wastewater discharge occurs at the southern end of the Detroit River where it enters into Lake Erie. Sewage wastewater contain large amounts of phosphorus and having 30 billion of raw and partially treated sewage dumped into the lake, The Detroit Wastewater Treatment Plant was the single largest contributor of phosphorus to Lake Erie in the 1970's. Even though it emits less phosphorus today, it still has a significant effect. The Maumee River had also contributed phosphorus to the Lake in terms of sewage, but its majority of phosphorus came from agriculture. The large amounts of phosphorus had greatly accelerated nutrient enrichment and algal blooms, making the area anoxic.
Hannah Osborne. (2014). Lake Erie on Verge of Death as Climate Change Effects to Serve Double Blow. http://www.ibtimes.co.uk/climate-change-crisis-lake-erie-north-america-verge-death-1438220. Last accessed 18th March 2014.
Dave Spangler. (2014). Detroit Wastewater Plant. Available: http://www.lakeeriewaterkeeper.org/detroit-wastewater-plant/. Last accessed 20th March 2014.
Figure 9:
Figure 9 is a diagram of Lake Erie and its surroundings. It shows the major tributaries to the Lake and the amount of phosphorus flowing from them recorded in 2011 by the University of Michigan. As seen in the map, the Detroit River and the Maumee River are the largest contributors of phosphorus to the Lake measured in 2,000 (tonnes P). There are also several smaller tributaries that contribute to the input of phosphorus and connect to Lake Erie. Although it seems like the Western Basin is affected the most by the phosphorus, more hypoxic regions are formed in the Central Basin due to its broad and shallow structure, making it more vulnerable to algal blooms. The pie graph displayed in the diagram shows the Point Source, Non-Point Source and Lake Huron which are loading sources for the Western Basin. The central basin and Eastern basin pie graphs are similar, with non-point sources being the majority of the phosphorus loading sources in those areas. The non-point sources refers to the water pollution from diffuse sources, which may include runoff from agricultural land, while the point sources refer to the single identifiable source of the water pollution, such as sewage wastewater.
University Of Michigan . (2014). Ambitious new pollution targets needed to protect Lake Erie from massive 'dead zone'. Available: http://phys.org/news/2014-02-ambitious-pollution-lake-erie-massive.html. Last accessed 20th March 2014.
Figure 9 is a diagram of Lake Erie and its surroundings. It shows the major tributaries to the Lake and the amount of phosphorus flowing from them recorded in 2011 by the University of Michigan. As seen in the map, the Detroit River and the Maumee River are the largest contributors of phosphorus to the Lake measured in 2,000 (tonnes P). There are also several smaller tributaries that contribute to the input of phosphorus and connect to Lake Erie. Although it seems like the Western Basin is affected the most by the phosphorus, more hypoxic regions are formed in the Central Basin due to its broad and shallow structure, making it more vulnerable to algal blooms. The pie graph displayed in the diagram shows the Point Source, Non-Point Source and Lake Huron which are loading sources for the Western Basin. The central basin and Eastern basin pie graphs are similar, with non-point sources being the majority of the phosphorus loading sources in those areas. The non-point sources refers to the water pollution from diffuse sources, which may include runoff from agricultural land, while the point sources refer to the single identifiable source of the water pollution, such as sewage wastewater.
University Of Michigan . (2014). Ambitious new pollution targets needed to protect Lake Erie from massive 'dead zone'. Available: http://phys.org/news/2014-02-ambitious-pollution-lake-erie-massive.html. Last accessed 20th March 2014.
Figure 10:
Figure 10 is a diagram explaining why the Central Basin of Lake Erie becomes the most affected by hypoxia. It depicts a cross-section of Lake Erie in summer showing the West, Central and East basin. The elevation of the central basin is situated between the top layer and bottom layer of water, which are conditions unique to the other basins. The text on the bottom of the diagram shows how the oxygen becomes depleted in the Central Basin:
Figure 10 is a diagram explaining why the Central Basin of Lake Erie becomes the most affected by hypoxia. It depicts a cross-section of Lake Erie in summer showing the West, Central and East basin. The elevation of the central basin is situated between the top layer and bottom layer of water, which are conditions unique to the other basins. The text on the bottom of the diagram shows how the oxygen becomes depleted in the Central Basin:
- Phosphorus fertilizes algae,
- Which Grows in top layer,
- But which sink to the bottom when they die.
- Bacteria and fungi decompose the algae near the bottom,
- Using up the oxygen which is dissolved in the water
Figure 11:
Figure 3 is an image depicting the bottom water oxygen concentration in Lake Erie during September, 2005. In this figure, the oxygen saturation of Lake Erie is measured in miligrams per litre(mg/l). The optimal level of dissolved oxygen is usually 5mg/l - 7mg/l, but from this figure, we can see that the amount of dissolved oxygen at the centre
of Lake Erie is extremely low, approximately 1mg/l - 2mg/l. This is considerably lower than the oxygen level required to thrive, and lower than the amount required to survive(2mg/l).
Brian Wallheimer. (2011). Lake Erie hypoxic zone doesn't affect all fish the same, study finds. Available: http://www.purdue.edu/newsroom/research/2011/110110HookHypoxia.html. Last accessed 15 March 2014.
Figure 3 is an image depicting the bottom water oxygen concentration in Lake Erie during September, 2005. In this figure, the oxygen saturation of Lake Erie is measured in miligrams per litre(mg/l). The optimal level of dissolved oxygen is usually 5mg/l - 7mg/l, but from this figure, we can see that the amount of dissolved oxygen at the centre
of Lake Erie is extremely low, approximately 1mg/l - 2mg/l. This is considerably lower than the oxygen level required to thrive, and lower than the amount required to survive(2mg/l).
Brian Wallheimer. (2011). Lake Erie hypoxic zone doesn't affect all fish the same, study finds. Available: http://www.purdue.edu/newsroom/research/2011/110110HookHypoxia.html. Last accessed 15 March 2014.
Effects
The Lake Erie dead zone negatively effects the marine life which inhabit the lake's waters. Since dissolved oxygen is essential for the survival of all marine plants and animals, and oxygen is being depleted due to eutrophication and nutrient enrichment, most of the living organisms in the lake eventually suffocate and die. This becomes a concern for people, because it is a large ecosystem which provides the human society with a lot of essential resources and many benefits. Lake Erie has suffered more on the commercial side due to the dead zone, mostly targeting commercial fisheries and tourism industries and crippling its economy as well.
Lake Erie's tourism industry is most essential for surviving economically. Its success includes generating more than $10 billion in revenue annually, but this amount is decreasing at a high rate due to its dead zone. The result of algal blooms creates fouling beaches and a thick, growing coat of algae which appears every summer. This makes the place unattractive, repelling away tourists, because of its toxicity.
Commercial fishing once was a popular recreational activity in Lake Erie. However, due to hypoxia that started to appear in the lake, it is in great decline. Fish populations have plummeted dramatically, with fisheries and sport anglers claiming that they were only able to retrieve only one fifth of their usual annual catch. Fish in the lake's center have either perished due to insufficient oxygen or have moved away to other places seeking food and oxygen. Since sport fish such as yellow perch and walleye have become rarer, putting commercial fishing in peril.
Michael Wines. (2013). Spring Rain, Then Foul Algae in Ailing Lake Erie.Available: http://www.nytimes.com/2013/03/15/science/earth/algae-blooms-threaten-lake-erie.html. Last accessed 22 March 2014.
Lake Erie's tourism industry is most essential for surviving economically. Its success includes generating more than $10 billion in revenue annually, but this amount is decreasing at a high rate due to its dead zone. The result of algal blooms creates fouling beaches and a thick, growing coat of algae which appears every summer. This makes the place unattractive, repelling away tourists, because of its toxicity.
Commercial fishing once was a popular recreational activity in Lake Erie. However, due to hypoxia that started to appear in the lake, it is in great decline. Fish populations have plummeted dramatically, with fisheries and sport anglers claiming that they were only able to retrieve only one fifth of their usual annual catch. Fish in the lake's center have either perished due to insufficient oxygen or have moved away to other places seeking food and oxygen. Since sport fish such as yellow perch and walleye have become rarer, putting commercial fishing in peril.
Michael Wines. (2013). Spring Rain, Then Foul Algae in Ailing Lake Erie.Available: http://www.nytimes.com/2013/03/15/science/earth/algae-blooms-threaten-lake-erie.html. Last accessed 22 March 2014.