nitrogen content (<70yg-at NO^.i" ) has also increased over the past 25 

 to 50 years from sewer inputs, agricultural fertilizers, and nitrate 

 release to groundwater after deforestation (Likens et al. 1978). The 

 White's Point Sewage outfall off Los Angeles, for example, has a daily 

 discharge to the Southern California Bight, which is 1 percent of the 

 flow of the Rhine and contains -2500yg-at NH 3 «-~ . Other U.S. rivers 

 which drain areas of low populations in the south and west (e.g., the 

 Columbia (Park et al., 1972), the Yukon (W. Reeburgh, personal communi- 

 cation), and the MacKenzie (Van Dennekom and Salomons, 1981) rivers) 

 contained 10-fold less inorganic nitrogen (<7-10 yg-at IU~ ) before 1970 

 than the rivers discussed in previous sentences. However, the nitrate 

 content of at least the southern region rivers, e.g., the Altamaha 

 (Walsh et al., 1981) and Pamlico (Hobbie et al., 1975), is now >J30 



yg-at NO-, 2 " . Primary production within the Altamaha River plume is as 



2 1 

 high as 550 g C m yr e.g., more than Georges Bank (Table 4-1), while 



those of the Mississippi (Thomas and Simmons, 1960; Fucik, 1974) and Hudson 



-2 -1\ 

 (Malone and Chervin, 1979) river plumes (250-350 g C m yr ) are more 



than the Bering Sea. 



To specify the area! extent and fate of production from anthropogenic 

 and natural sources of nutrients, the MAREX program proposes to assess 

 the increase in phytoplankton biomass per unit area over a specific in- 

 crement of time as one measure of primary productivity , i.e., the rate 

 of change of biomass on these shelves (Table 4-1). This approach 

 assumes that there is no competing process, such as the removal of newly 

 produced phytoplankton biomass by herbivore grazing or the dispersal of 

 a unit or patch of phytoplankton by advective currents. In most parts 

 of the ocean this assumption is rarely met, with perhaps the shelf 

 spring bloom as an exception; hence, additional experimental and 

 modeling techniques will also be used within MAREX to determine and 

 predict regional primary production. 



The experimental approach, of course, entails subsampling a parcel of 

 water from a ship (and, hence, include the errors associated with 

 plankton patchiness previously discussed) and incubating the water 

 sample with 14„ to determine instantaneous rates of photosynthesis per 

 unit phytoplankton biomass. These rates are then extrapolated to give 



4-4 



