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In the figure, the 3 years with highest nutrient load are signalized with red arrows: 1993, 2008, and 2013. The 3 years with lowest nutrient loads are signalized with blue arrows: 2000, 2005, and 2012. In Figure 2, the same years are marked with arrows. It can be observed that although 1993, 2008, and 2013 are among the years with largest hypoxic zone areas, they do not represent the 3 largest hypoxic zones. The same is true for the years with low nutrient loads: they correspond with smaller than average hypoxic zone sizes, but they are not the smallest zones observed. These observations indicate that there are other process involved on defining the extent of the hypoxic area.
Figure 1: May Nitrate Flux from the Mississippi River in Metric Tones.
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