INTRODUCTION 



The increasing use of the sea for urban waste disposal requires an 

 understanding of the subtle biological impacts of nutrients, organic matter, 

 and other pollutants discharged into coastal waters. Significant water quality 

 problems frequently result from the transient response of natural waters to 

 some perturbation such as changes in circulation patterns, climatic conditions, 

 nutrient enrichment, organic carbon loading, or phytoplankton species composition. 

 In particular, an extensive bloom of the dinof lagellate Ceratium tripos developed 

 throughout the Middle Atlantic Bight continental shelf from January through 

 July 1976. From July through September 1976 bottom water oxygen was also 

 progressively depleted to less than 2 ml 02^"* over a large area (8600 km ) of 

 the New Jersey coastal region from the 20 m to 60 m isobath (fig. 1). Presence 

 of this anoxic region resulted in the formation of hydrogen sulfide and mass 

 mortalities of demersal fishes and shellfish (Swanson and Sindermann 1979). 

 The occurrence of the C. tripos bloom, and the onset of anoxic conditions, 

 suggested that the abundance of C_. tripos had imposed an unusually large oxygen 

 demand on the subpycnocline layer off the New Jersey coast and was causally 

 related to the anoxic episode (Malone et al. 1979; Falkowski and Howe 1976). 



A marine ecosystem model, designed to evaluate the relative significance 

 of natural physical and biological processes and anthropogenic waste inputs on 

 oxygen depletion in the New York Bight, described the continental shelf of the 

 Bight as a two-layer system separated by the pycnocline (Stoddard 1983). The 

 model equations specified the interactions of carbon, oxygen, and nitrogen in 

 an analysis of oxygen depletion, nutrient dynamics, and phytoplankton distribution 

 during the stratified summer season. 



A comparison of a year of high bottom oxygen content (1975) and the large- 

 scale anoxic episode during 1976 is the problem setting for the analysis. 

 Previous studies of the 1976 anoxic episode (Falkowski et al . 1980; Swanson and 

 Sindermann 1979; Falkowski and Howe 1976) examined the influence of urban waste 

 inputs, and climato logical , physical, chemical, and biological forcing on oxygen 

 depletion in the New York Bight. The model quantitatively incorporates the 

 hypotheses presented in these studies coupled with a quasi-time-dependent 

 circulation sub-model (Han et al. 1980) to assess the relative significance of 

 the various forcing terms on the development of anoxia. 



RESULTS 



Verification of the model included a synthesis of physical, chemical, and 

 biological data collected by Brookhaven National Laboratory and other institutions 

 during the MESA New York Bight Project. In general, the model is capable of 

 simulating most of the ecological behavior of the Bight where the calculations 

 are in reasonable agreement with observations during a year of high bottom 

 oxygen (1975) (fig. 2), and during the anoxic episode in 1976 (fig. 3). The 

 significance of transport processes on water quality distributions in the Bight 

 are clearly demonstrated in an analysis of: the component sources and sinks of 

 nitrogen, Ceratium , and dissolved oxygen for the 1976 verification case; and 

 onshore subpycnocline penetration of high nitrate across the shelf during June - 

 October for the 1975 verification case. The model also clearly demonstrates 

 the influence of the flow field reversal on the accumulation of Ceratium and 

 other particulate substances during June - July 1976 (fig. 4). 



225 



