Plant Nutrients 



Plant nutrients, together with 

 sunlight, facilitate organic production, 

 especially that of phytoplankton. This 

 lowers visibility underwater. 



At the tower, the plant nutrient 

 concentrations are determined with an 

 Auto Analyzer. This apparatus mechan- 

 ically mixes the sea water sample with 

 chemical reagents and introduces the 

 mixture into a continuously recording 

 colorimeter. The various plant nutrients 

 such as phosphate, silicate, and nitrate 

 have been continuously recorded with 

 respect to both space and time. Silicon 

 was determined by a modification of a 

 molybdenum blue method, using stannous 

 chloride as a reductant; nitrate was de- 

 termined by reduction to nitrite with a 

 copper- cadmium couple, followed by an 

 adaptation of a standard nitrite deter- 

 mination. 



At the shallow-water tower site, 

 the nitrate and silicate recordings in the 

 vertical water column vary widely. In 

 spring, the nutrient content in the upper 

 layer of the sea is normally low. A 

 strong thermocline separates this layer 

 from the high values in the deeper layer. 



MIXING 



A continuous supply of sea water from the sub 

 ble pump on the north track is automatically 

 with reagents by an Auto Analyzer proport 

 pump and fed into the colorimeter. 



nersi- 

 mixed 



A continuous recording at a constant depth (30 feet) 

 from the bottom shows the changes in temperature 

 and concentration of silicate caused by internal 

 waves as they move the nutrient boundary vertically 

 past the sampling level. 



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