CHAPTER 10 



spatial heterogeneity and low sampling density. However, 

 rates did appear to be higher around the oxygen-depleted 

 area (12.5 ± s.d. 5.5 ml O^/m-Zh, n = 21. in August- 

 September 1976) than in the same area during the follow- 

 ing summer (6.5 ± s.d. 3.6 ml 0,/m-/h, n = 19, in June 

 1977). The 1977 rates of seabed oxygen consumption in 

 the area of former low D.O. were comparable to rates 

 measured in surrounding areas in 1977. Away from the 

 oxygen-depleted area no differences between summers 

 were readily apparent. These data further suggest that 

 during the 1976 event the seabed received additional or- 

 ganic loading in and adjacent to the low D.O. area. 



The contribution of the seabed to the total oxygen con- 

 sumption (water column plus seabed) ranged from zero 

 in the low D.O. area (because aerobic respiration could 

 not be measured) to 40 percent at station 51 in the Apex 

 and averaged 14 percent over the area sampled (table 

 10-2). Two stations on the periphery of the anoxic area 

 (200, 207), as well as stations in the estuary and Apex, 

 had seabed oxygen consumption rates that accounted for 

 more than 10 percent of the carbon oxidized in the entire 

 water column, including the seabed. At the remaining 



stations, the seabed contributed less than 10 percent to 

 the aerobic mineralization of organic carbon. These data 

 suggest higher than expected contributions for the seabed 

 at stations 200 and 207 and indicate additional organic 

 loading to the seabed in and around the low D.O. area. 

 An August 1975 study in the Apex demonstrated that 

 the seabed contributed only 3 to 7 percent of the total 

 oxygen consumption — water column plus seabed (Thomas 

 etal. 1976b). During June 1977, oxygen consumption rates 

 in the water column and on the seabed were measured 

 concurrently over the same area sampled during the low 

 D.O. episode of 1976. The seabed contribution to the total 

 aerobic oxygen consumption (water plus seabed) ranged 

 from 1 to 11 percent and averaged 6 percent. The highest 

 contributions (89f-119f ) were within 20 km of the New 

 Jersey coast in a band from Sandy Hook to Atlantic City. 

 The remaining stations contributed less than 6 percent 

 including those in the area of depressed D.O. in the pre- 

 vious year. Again, these temporal and spatial comparisons 

 indicate that the seabed at stations adjacent to the anoxic 

 area in 1976 contributed disproportionately to total aero- 

 bic respiration. The relatively greater contribution of the 



Table 10-2. — Conlnbulwn of the seabed and suhpycnocline water to total aerobic oxygen consumption and relationship of total primary production 



to total aerobic decomposition above and below pycnoclme 



' P is the daily production using '"C method; R is the daily respiration using oxygen method (assumed R0= 1) 



", No pycnocline present. 



", May reflect an elevated rate caused by aeration of sediment core prior to rate measurements. 



', Dissolved oxygen concentration was 0. Anaerobic rate could not be measured at ambient DO. concentration. 



", Anaerobic metabolism estimated from phosphate accumulated below pycnocline. (See text.) 



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