472 



BULLETIN OF THE BUREAU OP FISHERIES 



Analyses of nitrogen (as N>) in sea sediments from the Gulf of Maine and vicinity, performed by the 

 chemical laboratory, United States Geological Survey 



Owing to technically unsatisfactory preservation of the specimens, these deter- 

 minations can be regarded only as approximations of the amounts of nitrogen actually 

 present in the muds; but recognizing this possible source of error, the average is about 

 0.16 per cent of nitrogen (as N 2 ), for the whole series (otherwise expressed, about 3.2 

 pounds per ton of mud or sand). 



As long as this store of nitrogenous detritus remains mingled with the mineral 

 deposits that cover the sea floor, it remains unavailable for the use of the planktonic 

 vegetation, though it supports many mud-eating animals that live on the bottom. 

 It must be constantly going into solution, however, as the breaking down by decom- 

 position proceeds, a process hastened in regions of strong tides where vertical currents 

 keep much of this flocculent material in suspension, as is proved by the considerable 

 amounts of fine organic debris often taken in the tow nets. Its availability for the 

 support of diatoms and of the other planktonic plants thus depends largely on the 

 state of circulation of the water, a question discussed below (p. 479). 



The gradual impoverishment of the animal plankton, which takes place from 

 autumn on, with the dying of the large medusse, copepods, and other groups, has been 

 commented on (pp. 47, 88). Its natural result is to cause a more rapid accumulation of 

 animal debris during the cold half of the year than in summer. Generally the death 

 rate among the animals living on bottom along the littoral zone is also higher in winter 

 than in summer. Everyone who frequents the shores of the gulf knows that this is 

 true of the algae, vast quantities of rockweed and kelp being torn adrift from the rocks 

 by the autumnal gales and piled up along the beaches, where they are soon ground up 



