offshore Louisiana extending along the 20-m depth contour from the delta 

 westward to Atchafalaya Bay. During the same period, Reitsema (1980) 

 observed hypoxic water as far west as offshore of West Hackberry, 

 Louisiana (latitude 29° 39' 46", longitude 93° 37' 47") in waters in excess 

 of about 6-m depths. Fotheringham and Weissberg (1979) had previously 

 noted oxygen-deficient waters in this region during the same general 

 time period. 



Harper and McKinney (1980) were the first to document hypoxia in 

 bottom waters offshore of the Texas coast. This event was observed 

 during the spring and summer of 1979 for waters from about 10 m deep out 

 to depths of 33 m and beyond. The area affected was estimated to extend 

 north and eastward from Matagorda Bay to Sabine Pass and likely on into 

 Louisiana. Harper and McKinney (1980) attributed the condition to large 

 quantities of fresh water discharge resulting in water column 

 stratification, which was then intensified by lack of mixing during 

 calm, warm weather. The resulting oxygen depletion was believed to have 

 been enhanced by the decomposition of river-borne organic material. 



As in other parts of the United States and the world 

 (Brongersma-Sanders 1957; Garlo et al. 1979), the occurrence of hypoxia 

 results in mortalities of marine organisms. A fish kill was noted at 

 the mouth of Timbalier Bay during 1973 (Brent et al. 1979), and 

 Bedinger et al. (1980) reported extensive areas of dead bottoms (Figure 

 13) in hypoxic areas observed offshore of Louisiana during the summer of 

 1978. These areas were characterized by very poor trawl catches 

 consisting largely of recently dead organisms. Harper and McKinney 

 (1980) made in-situ observations during late June 1978 in the hypoxic 

 waters offshore of Texas, and observed numerous dead benthic organisms 

 including polychaete worms, brachyuran crabs, mantis shrimp, and 

 hemichordates "strewn about the bottom in various states of decay." A 

 rocky structure which had been previously observed to have had a healthy 

 assemblage of sea whips, solitary corals, sea urchins, mollusks, crabs 

 and reef fish was also observed. The reef fish component was absent; 

 all sea urchins and corals were dead, as were many of the crabs. The 

 mollusks observed were sluggish and many sea whips were missing sections 

 of the colony and were characterized by exposed internal axial 

 skeletons. 



Processes controlling dissolved oxygen levels in shelf waters have 

 not been quantitatively investigated. All reports of hypoxia for the 

 northwestern gulf have noted stratification of the water column 

 attributable to fresh water overflow, and have implicated degradation of 

 river-borne organic materials as a major contributor to the phenomenon. 

 The major source of oxygen-demanding materials is the Mississippi River 

 which was estimated by Presley et al. (1980) to discharge some 280 

 Mtonne of sediment per year. Gunter (1952) showed that whereas, 

 historically, sediment contained in Mississippi River runoff was 

 deposited over the broad river plain, marshes, and shallow bays during 

 floods, it is now funneled directly into the gulf in a rapid pulsed 

 fashion attributable to the leveeing and channelization of the river 



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