Station 



213 

 213 

 219 

 219 



CHAPTER 10 



Table 10-3. — Bacterial carbon measurements at station 213 (anoxic area) and station 21^ (control area) 



Depth 



Bacteria 

 measured 



Mean 



cell 



volume 



Bacterial 



cell 



density 



Bacterial 

 carbon' 



Number 



' Bacterial carbon was estimated by multiplymg mean cell volume by the number of bacterial cells per sample, and assuming a density of 1.1 g C/ 

 m', a dry to wet weight ratio of 0.23 and a carbon to dry weight ratio of 0.344 (Ferguson and Rublee 1976). 

 a. Not done. 



PROBABLE ORGANIC CARBON SOURCES 



Let us consider that the organic carbon contained in 

 Ceratium tripos has already undergone aerobic decay at 

 the time of anoxia (0 ml OJl). If the assumptions in the 

 model by Malone et al. (ch 9, pt. 1) are correct, the C. 

 tripos biomass consumed 71 percent of the oxygen lost 

 below the pycnocline. In the temporally and spatially av- 

 eraged scenario presented here, C. tripos carbon does not 

 account for the excesses of phosphate that we believe 

 originate anaerobically. 



The logical sources of organic carbon that could provide 

 the organic material necessary to generate observed phos- 

 phate concentrations are primary production, the DOC 

 pool, and decaying benthic macrofauna. Decaying benthic 

 macrofaunal biomass could have provided a significant 

 proportion of the organic carbon anaerobically decom- 

 posed. An estimated benthic macrofaunal biomass off 

 Atlantic City near our stations 213 and 217 ranges from 

 25 to 100 g wet weight/m- (Wigley and Theroux 1976). A 

 second estimate for this area is 67 g wet weight/m- of 

 mollusca, annelida, echinodermata, and Crustacea (Boesch 

 et al. 1977). A third estimate, based on the major mol- 

 luscan biomass components (surf clam and ocean quahog), 

 censused between 18.6 and 36.6 m off the New Jersey 

 coast (April 1976) was 75 g shellfish meat/m- (Chang et 

 al. 1976; Chang, personal communication). 



Most of the demersal finfish apparently avoided the low 

 D.O. area (ch. 13) and consequently did not materially 

 add to the carbon pool, which decomposed anaerobically. 

 For discussion, we will use the upper value of 100 g wet 

 weight/m- to represent the potential contribution by the 

 benthos. This does not include the benthic meiofaunal 

 biomass. However, using the upper value of 100 g wet 

 weight/m- may amend this oversimplification. An estimate 

 of total macrofaunal biomass of 5.5 g C/m- results from 

 a conversion factor of 500 cal/g wet weight (F. W. Steimle, 

 NMFS Sandy Hook Laboratory, personal communica- 

 tion), which applies to the surf clam and other affected 

 dominant benthic species and an oxi-caloric equivalent of 



4.9 cal/ml O, (Odum 1971) and an RQ of 1. If all this 

 biomass were actually killed and anaerobically decom- 

 posed, it would represent 47 and 56 percent of the organic 

 carbon anaerobically mineralized at stations 213 and 217, 

 respectively. 



Atwood et al. (ch. 4) suggest that concentrations of 

 DOC in excess of expected "normal" oceanic values (0.8 

 mg. C/1) may represent biologically labile carbon and a 

 potential BOD load. If DOC in subpycnocline-low D.O. 

 water was the sole resource of carbon mineralized ana- 

 erobically to account for the observed phosphate concen- 

 trations, then DOC at the beginning of our 45-day interval 

 might have been double the concentrations observed be- 

 low the pycnocline during our cruise (1.6 mg C/1). Sub- 

 pycnocline DOC concentrations at station 213 are about 

 half those above the pycnocline . This hypothesis is difficult 

 to evaluate in the absence of DOC data before our cruise 

 and poor quantitative understanding of the dynamic in- 

 teractions between phytoplankton and bacteria and the 

 DOC and POC pools in the New York Bight. 



In situ primary production can potentially supply to sub- 

 pycnocline waters the quantity of organic carbon needed 

 over the 45-day period. The photosynthesized carbon ac- 

 tually available is the portion remaining after water col- 

 umn aerobic carbon mineralization is subtracted from the 

 rates of carbon photosynthesis. Total primary productivity 

 and total water column respiration appear to be related, 

 but offset in time. A large portion of the daily nutrient 

 requirement of phytoplankton can be satisfied directly 

 through upper water column respiration and mineraliza- 

 tion of organic matter. Measured rates of daily integral 

 total primary productivity in the oxygen-depleted area and 

 vicinity were about 1 g C/m-/d (fig. 10-8). About 0.22 g 

 C/m-/d would have to be supplied to the subpycnocline 

 waters, which is about 22 percent of the daily photoassi- 

 milated carbon. A production/respiration (P/R) ratio over 

 the water column of 1.28 (assuming primary productivity 

 = 1 g C/m-/d) would be required over the 45-day period 

 to account for the observed phosphate concentrations. We 

 observed P/R ratios between 0.5 and 2.0 (including esti- 



255 



