richest available source of free energy, and de- 

 nitrification ensues. Again, phosphate and am- 

 monium ions can be pictured as being hydrolyt- 

 ically released, and the organic residues are 

 oxidized, by denitrifying bacteria, to carbon 

 dioxide and water, with the concurrent reduc- 

 tion of nitrate and nitrite ions to free nitrogen. 

 [The ammonia released during this process 

 accumulates.] 



Following the disappearance of nitrate and 

 nitrite ions, the next richest source of free 

 energy in seawater is sulfate ions, which then 

 take their place as hydrogen acceptors, being 

 reduced to sulfides in the process. Again, phos- 

 phate and ammonium ions are hydrolytically 

 released and accumulate while the organic resi- 

 dues are oxidized to carbon dioxide and water. 



Brickell and Goering (1972) reported that on 

 29 September 1969, ammonia concentrations 

 near the mouth of Sashin Creek were as high 

 as 7.80 ^g-atoms N/liter. This figure was 10 

 times higher than the concentrations in late 

 August and early September before carcasses 

 had begun to accumulate from the escapement 

 of 30,000 pink salmon, Oiicorhy)ichus gorbiisclia. 

 Dissolved organic nitrogen was at a peak con- 

 centration of 10.3 jUg-atoms N/liter in the Inner 

 Bay surface waters on 28 October — twice the 

 concentration measured by Brickell and Goering 

 in a control area lacking salmon carcasses. 

 They did not report the presence of oxygen or 

 sulfide, but their reported high levels of ammo- 

 nia and dissolved organic nitrogen clearly indi- 

 cate that chemical conditions were leading to 

 sulfide formation at that time. 



We did not measure ammonia and dissolved 

 organic nitrogen in October 1971, but the es- 

 capement of 72,000 pink salmon, over twice 

 that at the time of Brickell and Goering's study 

 in 1969, would make the presence of excess 

 ammonia and dissolved organic nitrogen even 

 more likely in 1971. The detection of the odor 

 of hydrogen sulfide by divers and in water 

 samples implies that the reduction of organic 

 materials had proceeded through oxidation and 

 denitrification stages; i.e., in some parts of 

 the water anoxic conditions were present. 



The milky appearance of the water could 

 have been due to the formation of colloidal 

 sulfer when sulfide-bearing waters formed near 



the bottom mixed with oxygenated waters higher 

 in the water column (Cline and Richards, 1969). 



The sudden disappearance of the anoxic water 

 from the bay was probably associated with ex- 

 treme spring tides that immediately preceded 

 the flushing. The large volume of exchange and 

 relatively greater current velocities during the 

 large tides probably caused a gradual reduction 

 of the pycnocline. When the pycnocline was 

 reduced sufficiently, mixing occurred through- 

 out the water column, and the anoxic water 

 was flushed out of the bay. 



The coincident sudden disappearance of the 

 dead organisms may have resulted from one or 

 a combination of factors: use by scavengers 

 such as amphipods, which moved back into the 

 affected area after the flushing, or physical re- 

 moval of many of the decaying organisms by 

 water movements in the area. 



Applicability of Observations of 

 Anoxic Conditions 



It seems probable that other estuaries in 

 Alaska may also develop temporary anoxic 

 conditions. Likely estuaries could be identified 

 by studying the morphometry of the basin for 

 presence of a shallow entrance sill and by deter- 

 mining the presence of periodically or chroni- 

 cally high biological oxygen demand. A capa- 

 bility for predicting formation of anoxic con- 

 ditions in estuaries would aid in determining 

 the proper management of susceptible bays 

 which might be subjected to artificial introduc- 

 tion of large quantities of organic material. 



Acknowledgments 



Thanks are due to Robert J. Ellis, William 

 R. Heard, and Roy Martin who assisted in the 

 underwater observations and to Melford Bony 

 who collected the water samples and oceano- 

 graphic field data. 



Literature Cited 



Brickell, D. C, and J. J. Goering. 



1972. Chemical effects of salmon decomposition 

 on aquatic ecosystems. //; R. S. Murphy and D. 

 Nyquist (editors). International Symposium on 



899 



