NO A A PROFESSIONAL PAPER 11 



to assess and because interpretations of "excessive" vary 

 (Bascom 1974a, 1974b; Woodweli 1974). In any case, riv- 

 erine nutrient enrichment of certain coastal regions hundreds 

 of square miles in area has been recognized for several 

 years. 



OXYGEN DEPLETION AND THE NEW 

 YORK BIGHT 



The oxygen depletion event of 1976 stimulated a search 

 for answers to two questions. 



1. How much do human activities influence the proc- 

 esses leading to oxygen depletion in the New York 

 Bight? 



2. How large a region off New York is significantly 

 enriched (in carbon and plant nutrients) by human 

 activities? 



Oxygen depletion in the Bight in 1976 and factors re- 

 lating to it are summarized. Despite the widespread nature 

 and severity of bottom oxygen decline in 1976, this was 

 not a unique event. Less widespread oxygen declines were 

 noted in the summer and autumn of 1968, 1971, 1974, and 

 1977 (fig. 15-1). Thus, the 1976 phenomenon was not 

 necessarily caused by some special, or even rare, set of 

 circumstances. The most important factors probably have 

 contributed to other oxygen declines, including those in 

 years when there were no observations of benthic mor- 

 talities or dissolved oxygen concentrations below 2 ml/1. 



The most influential external controls (anomalies) act- 

 ing upon the Bight are understood very well relative to 

 within-Bight processes. An exception was the onwelling 

 of nutrient-rich oceanic water in the spring and summer 

 of 1976. Also anomalous atmospheric conditions in 1976 

 (ch. 3) led to unusually warm surface waters and pro- 

 longed density stratification (ch. 2 and 5; Bowman and 

 Wunderlich 1977). Surface winds exhibited unusually per- 

 sistent northward to northwestward flow from February 

 through June and storm frequency fell to a 25-year min- 

 imum (ch. 3.). 



Other significant external factors are the exceptionally 

 large inputs of plant nutrients and carbon released to the 

 Bight primarily by human activities. Of the plant nutrients, 

 only nitrogen is discussed, because it is important in lim- 

 iting phytoplankton productivity (Ryther and Dunstan 

 1971 ; Malone 1976a). Available estimates of total nitrogen 

 and carbon reaching the Bight proved useful, but were 

 less precise than desirable for assessing the relative im- 

 portance of eutrophication and other factors controlling 

 the concentrations of dissolved oxygen (D.O.). 



The discussion of nutrient and carbon loads and other 

 influences upon oxygen depletion emphasizes conditions 

 over the New Jersey continental shelf to about 9U km 



offshore during the spring and summer. This is the region 

 where substantial oxygen depletion was observed and the 

 season during which short-term controlling factors are 

 most influential. Nutrient and carbon loadings of the Bight 

 during late autumn and winter contribute to oxygen de- 

 pletion largely during the following year via accumulations 

 of chemically reduced substances in sediments (Garside 

 and Malone 1978). Hence, it is important to distinguish 

 between annual and spring/summer (or stratified period) 

 nutrient and carbon loadings. 



Nitrogen Loadings 



Stimulation of phytoplankton productivity by nutrient 

 enrichment from the Hudson-Raritan estuary is consist- 

 ently one of the most striking features of the inner Bight 

 under stratified conditions (Malone 1976a; Yentsch 1977). 

 Nutrient enrichment from the estuarine source is less sig- 

 nificant for the entire Bight, and probably is a relatively 

 minor contribution (ch. 4). 



It is difficult to estimate with much precision or accuracy 

 the net seaward flux of carbon, nutrients, and other ma- 

 terials to the Bight from the Hudson-Raritan estuary. The 

 tendency of estuaries, like New York Harbor, to accu- 

 mulate dissolved as well as particulate contaminants from 

 watersheds and from subsurface seawater contributions 

 has been known for some time (Ketchum 1967; Riley 

 1967). Studies of the net estuary-to-Bight nutrient flux 

 indicate that significant amounts of nitrogen from river 

 runoff and from direct pollutant inputs are found accu- 

 mulated in estuarine sediment (Parker et al. 1976). 



Several investigators have stressed the importance of 

 estuarine-derived nitrogen (and carbon) in stimulating the 

 growth of nuisance algae and the depletion of oxygen in 

 this region (e.g., Torpey 1967; Ryther and Dunstan 1971; 

 Hardy 1972; Carpenter 1973). Unfortunately, these earlier 

 estimates were made without the benefit of later research 

 work on nutrient and carbon loading. Given the more 

 extensive and reliable bases for recent flux estimates, the 

 following newer estimates are almost certainly more ac- 

 curate. 



Nitrogen input to the Bight from the estuary was esti- 

 mated by Garside et al. (1976) from statistics on the pop- 

 ulation of the New York/New Jersey metropolitan area 

 and the per capita nitrogen discharges via sewage treat- 

 ment plants. The amount of inorganic nitrogen discharged 

 in wastewater to the Hudson-Raritan estuary was esti- 

 mated to be about 160 t/d (comparable to that estimated 

 by Howells et al. 1970). A more detailed estimate of all 

 inorganic nitrogen loadings to the Hudson-Raritan estuary 

 (including gaged and nongaged runoff) is 210 t/d. 120 t of 

 which is from municipal and industrial wastewater (Muel- 

 ler et al. 1976b). Garside et al. (1976) concluded that 

 inorganic nitrogen in wastewater alone greatly exceeded 

 (by four times) the amount assimilated by phytoplankton 



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