650 Marine Microbiology 



It is significant that only a portion of tlie daily contribution 

 of organic material to the bottom is mineralized and returned to 

 the water column. Some of the remainder enters into tlie food 

 chain of enriched benthic and bottom fish populations. Hartman 

 (6), Gunnerson (3) and Hume et al. (7) have discussed the 

 effects of fertilization by discharges from various outfalls. The 

 latter reported populations of capitellid worms of up to 200,000 

 individuals/m^, equivalent to a biomass of 6 kg/m^, near the 

 Hyperion digested sludge outfall which was placed in operation 

 in 1957. Comparable observations were not made near the one- 

 mile outfall discussed in this study. Since operation of the sludge 

 outfall primarily involves a change in the point of disposal rather 

 than a significant difference in the quantity or nature of the 

 settleable solids, the figures are probably indicative of conditions 

 near the one mile outfall in 1956. While there was some increase 

 in the organic carbon content of the sediments ( 15 ) , there has 

 been no evidence of a progressive buildup of a sludge bank. Ac- 

 cordingly, the unassimilated organics must have been removed 

 periodically by turbulence and wave action, and it follows that 

 essentially aerobic conditions are likely in the sediment. 



It is apparent that the phosphorus mineralization rate of 

 3,500 kg/day computed from the areal distributions does not agree 

 with that derived from the profiles. The possible error introduced 

 by the several simplifying assumptions is not known; however, 

 the larger value could result from the greater extent of the field 

 and from the presence of old effluent in the diluting water. The 

 return of old effluent to the outfall area was demonstrated by a 

 radioactive tracer study of effluent dilution (9). Available data 

 do not permit an adequate evaluation of this phenomenon, but 

 the probabihty of dilution by older, more mineralized effluent 

 is almost certainly proportional to the age and volume of the 

 field. 



The difference may be explained, at least in part, by as- 

 suming that the values represent mineralization which takes 

 place over two diff^erent areas. The first is the surface area derived 

 from the steady-state volumetric relationships where the equiva- 

 lent radius for the water mass after one day is 5.8 km; the cor- 

 responding area is 1.42 x 10' m^. The second area is the 1.38 x 



