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Island, British Columbia), and Gulf of Cariaco (Caribbean). However, 
at certain times of the year, these areas are flushed out with heavier, 
oxygenated water. When flushing occurs rapidly, poisonous sulfide- 
bearing waters impinge on the productive surface layers resulting in 
massive fish kills. Several such catastrophies have occurred in ithe 
Norwegian fjords. 
Man made 
When water circulation is restricted by the construction of man- 
made barriers anoxic conditions may develop. An example of this is the 
Charles River Basin and the Charles River Dam in Boston (see fig. 
2a). As in the example of Lake Nitinat, the horizontal circulation is 
severely restricted. Only the top few meters of the water are sufficiently 
oxygenated to support a fish population. If this stagnant water,is over- 
turned (as in the Norwegian fjords) by displacement with heavier 
waters, large volumes of noxious hydrogen sulfide gas will be released 
into the Boston air. The gas would be immediately oxidized to equally 
noxious sulfur dioxide. The above situation could have been readily 
avoided by construction of ducts in the lower portion of the dam 
ae could be opened periodically to allow mixing to occur (see_fig. 
2b). 
Figure 2 Charles River Basin. Not drawn to scales 
A. Present situation 
Be solution 
Be 
Anoxic conditions can be initiated by excessive dumping of organic 
wastes into the marine environment. Excessive dumping means the 
rate of accumulation of nutrient-rich organic wastes in the sediment is 
so high that a large biological oxygen demand (BOD) results. That is, 
oxygen is consumed through biological activities at a rate higher than 
can be supplied by normal circulation. As in natural anoxid environ- 
ments, the normal marine benthic population dies off and is replaced 
by anaerobic bacteria. Examples of the above situation are common in 
waters of large coastal cities. Many estuaries and bays are extremely 
