Pascal Tuarze
To General Public
ENVS*1020 F10 (01-06)
14/10/2010
Nitrous Oxide formed in the Ohio River
Introduction
In my blog I will be explaining the research being done on the emissions of N2O, or nitrous oxide, of the Ohio River into the atmosphere. It is well known that nitrous oxide is a greenhouse gas and a major contributor to the destruction of the ozone layer. N2O is formed naturally in the oceans and tropical soil but research has shown that a great quantity of N2O is being formed when runoff and sewage inputs nitrogen into river systems. This is then converted biologically into N20 in both the sediment and water column of the river.
What is happening?
A great quantity of waste water is being pumped into the Ohio River by the sewage plants of Cincinnati. The waste water is then being transformed from nitrogen to N2O by nitrifying bacteria found in the waste water. These bacteria are also stimulated by the (NH4)+ found in the waste water which catalyzes the reaction, creating nitrous oxide more quickly.
“The three highest rates co-occurred with high NH4+ concentration (figure 4C) and N2O emission rates (figure 4B) downstream of the WWTP outfall. Nitrous oxide production in WWTP effluent (1.01 μgN2O-NL-1) exceeded the highest rate observed in the river by a factor of 49.” (report 1)
The researchers found that the production of N2O in the water column almost doubles that produced by the sediments. They also found that production of N2O in the Ohio River is strongly correlated to the season or temperature of the water and perhaps even the concentration of CO3-. The highest rates of emissions were observed in the summer months when there was a very high temperature but a very low concentration of NO3-. The lowest rate of emission was during winter when the temperature was very low and had a high concentration of CO3-.
Research:
The researchers conducted experiments over a period of 13 months between the summers of 2008-2009 in the Markland Pool of the Ohio River. The study consisted of four sample types. The first sample type was to find the concentration of N2O and other nutrients in the top 5 centimetres of water. In the second they measured sediment production rates and found which nutrients limited the production of N2O. The third was water chemistry and the last was the measurements of the production of N2O in the water column and emissions from the surface. With all this data they were trying to find the pattern of how much N2O is produced in large rivers such as the Ohio River. This is something that has not really been done before.
Results:
In their research they found that in large rivers such as the Ohio River the water column is responsible for large amount of the production of N2O. This is not the case in smaller rivers because the benthic ratio is much higher. They also discovered that production of N2O can be stimulated by the nitrifying bacteria and (NH4)+ found in wastewater. Their results proved to them that the mechanisms that were set to find the production of N2O in small rivers do not apply to large rivers such as the Ohio River. This is due to the different contributing factors such as the slow water movement, high turbidity (low water transparency) and the low ratio of benthic surface area (sediments and sub surfaces of water compared to the rest of the water).
Why is it important
This is a major concern to life on earth because researchers concluded that emissions are rising almost a quarter of a percent per year. This causes a major problem for us because N2O has a global warming potential 300 times greater than CO2 emissions and it is generally accepted that global warming has detrimental consequences. It is also a problem because it destroys the ozone. Without the ozone life would cease to exist because the sun’s radiation would no longer be filtered before it hits earth.
Conclusion
In conclusion the results of these experiments should help us understand the emission rates of N2O in other large urban rivers that come in contact with waste water, for example the Seine River in France. The amount of waste water we put into the river systems needs to be cut down significantly to limit the amount of N2O emitted into our atmosphere. If we do not come up with a solution there will be great consequences in the future, including the holes in our ozone, which would greatly affect all organisms on earth.
Bibliography
"Nitrous Oxide Emissions from a Large Impounded River: The Ohio River." ACS Publications. Web. 10 Oct. 2010.
http://pubs.acs.org/doi/pdf/10.1021/es1016735
"Nitrous Oxide." Encyclopedia of Earth. Web. 12 Oct. 2010.
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