The occurrence of anoxia in 1976 resulted from temporal sequence of 

 climatological , physical, and biological processes that were significantly 

 different in 1976 in comparison to 1975, or other years of record. Analysis of 

 the observed and computed components of the midshelf oxygen budget (fig. 5) 

 demonstrates the interaction of physical transport mechanisms and biological/ 

 chemical processes on the cross-shelf and seasonal distribution of dissolved 

 oxygen in 1976. The dominant physical and biological factors influencing the 

 observed spatial and temporal distributions of oxygen included: 



(1) Circulation regime over the New Jersey shelf with upwelling predominant 

 from May-July and downwelling occurring in August. 



(2) Cross-shelf vertical distribution of viable Ceratium populations and 

 the balance between photosynthetic oxygen production and respiratory oxygen 

 demands, i.e., compensation depth, in relation to the anomalously deep pycno- 

 cline during May-August. 



(3) Decline of the Ceratium bloom and decomposition of the additional 

 organic carbon load within the water column and on the seabed resulted in the 

 onset, and progression, of anoxia over the New Jersey shelf during July-September, 



(4) Increased wind mixing, surface cooling, and erosion of the pycnocline 

 resulted in replenishment of oxygen during late September-October above, and 

 below, the pycnocline with the isothermal vertical dispersion coefficient ( 10- 

 15 cm^sec - *) estimated from the observed data and a one-dimensional, vertical 

 calculation for the New Jersey Midshelf. 



Oxidation of particulate organic carbon derived from sewage effluents 

 represented a negligible component (1%) of water column oxygen consumption over 

 the New Jersey midshelf in 1976. Even within the Apex region, where the ocean 

 dump sites are located and sewage carbon concentrations are higher, the oxygen 

 demand from sewage-derived materials represented a minor component (4%) of 

 oxygen consumption below the pycnocline. This suggests that the major impact 

 of carbonaceous waste discharges is limited to the vicinity (30 km) of the 

 discharge location, i.e., a relatively localized process. The results of the 

 oxygen budget analysis demonstrate the necessity of including a kinetic process 

 in the model that accounts for the conversion of phytoplankton biomass to 

 nonliving organic detritus in the water column (O'Connor et al. 1981). 

 Incorporation of such a mechanism would then account for the distribution of 

 particulate organic carbon observed in August-September 1976 with mineralization 

 of the observed biomass accounting for the oxygen depletion rate observed during 

 July-September 1976 over the midshelf area off New Jersey. 



MODEL PROJECTION OF APEX WATER QUALITY 



The validated model was used to evaluate the impact of a ten-fold increase 

 in present urban carbon and nitrogen loading (Mueller et al . 1976) on eutrophi- 

 cation and oxygen depletion in the Apex (Segar and Berberian 1976; Garside et 

 al . 1976). Steady-state August distributions are used to examine the water 

 quality response in the Apex to present and increased anthropogenic loading. 

 Substantial increases in sewage sludge carbon diminished light penetration near 

 the ocean dumpsites and reduced primary productivity. In the outer Apex, 

 increased nitrogen abundance increased primary productivity slightly over an 



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