Table 23-3. New Nutrient Input Versus Oceanic Advection 

 from the Southeast Sector (+ is in) (thousands of moles/day) 



Process 



low-density plume which flows northwestward from the sewer outfall. 

 Nevertheless, either this simple mixing model underestimates advective losses 

 by two-three fold, or there are additional budgetary terms to be considered. 



The budget can be further amplified. There is uptake of nutrients by 

 planktonic and benthic algae, and subsequent cycling of these particulate 

 materials within the food web. There is fallout of particulate organic material 

 to the lagoon floor and nutrient release from the lagoon floor back into the 

 water column. We have obtained nutrient release rates, gathered over one year 

 by using 1 -meter diameter Plexiglas hemispheres as in situ incubation 

 chambers, and we can solve for fallout by difference between nutrient inputs 

 and outputs (Table 23-4). The advective flux of nutrients from the southeast 

 sector equals 30-50 percent of the nutrient inputs from terrigenous sources. 

 The fallout of particulate nitrogen substantially exceeds terrigenous nitrogen 

 inputs to the southeast sector. The high nitrogen fallout is maintained by rapid 

 nitrogen release from the sediments. Particulate phosphorus fallout is also high, 

 although it does not quite exceed terrigenous inputs. As with nitrogen, the 

 rapid phosphorus fallout is maintained in large part by nutrient release from 

 the sediments. The steps from stream plus sewage input to particulate fallout 

 to release from the sediments show a progressive increase in the N:P ratio 

 (9->14^18). Material advected from the southeast sector is proportionally low 

 in nitrogen (N:P ^ 5), largely reflecting the virtually complete uptake of 

 dissolved inorganic nitrogen from the water. 



355 



