: 6. Oxygen demanding wastes

Oxygen demanding wastes:

Waters 'enriched' with wastes or nutrients from human, domestic or wildlife are likely candidates for oxygen depletion.
Rapid microbial growth spurred on by excess nutrient availability requires oxygen - lots of oxygen. The net result of this feeding frenzy is that the oxygen supply once available for all organisms, large and small, is now a limited resource.
Organisms which require lots of oxygen for their high metabolic rates. esepcially fast moving fish, are the hardest hit. Freely mobile organisms which can, will move out of these zones, but sessile life including filter feeders and even higher plants, with little means for transport will likely lose out, forming 'lifeless' zones.

Modified abstract: Gulf zone a deadly pool of distant sources

By Robinson Shaw

The dead zone in the Gulf of Mexico knows many rivers, according to a U.S. Geological Survey study. Most of the nitrogen pollution that reaches the Gulf by way of the Mississippi River originates far upstream in the upper Midwest and Ohio Valley states, and stream size is a major factor in sending the nitrogen on its way.

Dead zones are marine areas that do not have enough oxygen to support life. Fish can swim to safety from dead zones, but other forms of marine life such as starfish and sea anemones rarely escape. The loss of oxygen, known as hypoxia, begins in late spring, reaches a maximum in midsummer and disappears in the fall. Researchers have discovered that areas near rivers in northern states such as Ohio and Minnesota deliver more dead zone-producing nitrogen to the Gulf and at a faster rate than areas near streams only a few hundred miles away.

Animal waste is a major non-point source of nitrogen pollution in waterways. Non-point nitrogen sources such as fertilizer, animal waste, runoff from developed land, deposits from the atmosphere and soil erosion account for 90 percent of the nitrogen pollution in waterways. Point sources such as sewage and industrial discharge contributes 10 percent. The amount of nitrogen removed from water depends on the amount of water in contact with sediment. Because water in streams has more contact with sediment than water in rivers, more nitrogen is removed from the streams. Increased nitrogen in the Mississippi River is the leading cause of eutrophication (excessive algal growth) and chronic hypoxia (low dissolved oxygen) in the Gulf of Mexico over the past 50 years.

These dead zones are found not only in The Gulf of Mexico....our own Chesapeake Bay has it own version: note the black area below indicating still another aquatic mortuary...


The level of available oxygen makes a large difference in terms of what species can survive; low oxygen levels support when we consider 'trashy' fish while high oxygen availability fosters conditions for "desirable" fish.

Return to introduction 1. Go to sediments 2. Go to inorganics: 3. Go to disease vectors 4. Go to plant nutrients: 5. Got to organics 6. Go to Oxygen-demanding wastes 7. Go to radioactive & thermal wastes