What physical forces or conditions affect the dissolved oxygen content of water?
What are the biological processes that can affect dissolved oxygen concentration?
What might cause each identified condition to fluctuate over the seasons?
What is the average temperature of water in the top 5 meters in April? In August? How do those values compare to the average temperatures at 15â20 meters for those months?
Typical seawater has a salinity of 35 psu (practical salinity units). In which month is the diï¬erence in salinity of surface and bottom waters the greatest? Why do you think the diï¬erence is the greatest at this time of year?
Water that contains 2 mg oxygen per liter or less is termed hypoxic, since at that concentration many aquatic aerobic organisms are unable to survive. How does the depth at which hypoxia is observed change over time?
What are the peak months for nitrate-nitrogen discharge from the Mississippi River into the Gulf? Why do you think this is?
How do the peak months for nitrate-nitrogen discharge compare to the peak months for phytoplankton primary production?
Does it seem likely that any of the seasonal changes noted in Part II, Question 3, re-oxygenate the bottom waters of the Dead Zone in the autumn and winter?
What makes the hypoxia disappear in the fall and winter?
Which nitrogen source has added the greatest amount of nitrogen to the land in the Mississippi River basin in the years since 1970? Give a reasoning why this source is on the rise.