48 Nature of Aquatic Environment 



position. Of these, methane or marsh gas, is perhaps 

 the most important. This is formed where organic 

 matter decays in absence of oxygen. In lakes such 

 conditions are found mainly on the bottom. In marshes 

 and stagnant shoal waters generally, where there is 

 much accumulation of organic matter on the bottom, 

 this gas is formed in abundance. It bubbles up through 

 the bottom ooze, or often buoys up rafts of agglutinated 

 bottom sediment. 



Nitrogen — The supply of nitrogen for aquatic organ- 

 isms is derived from soluble simple nitrates (KN0 3 , 

 NaN0 3 , etc.) Green plants feed on these, and build 

 proteins out of them. And when the plants die (or 

 when animals have eaten them) their dissolution yields 

 two sorts of products, ammonia and nitrates, that 

 become again available for plant food. Ammonia is 

 produced early in the process of decay and the nitrates 

 are its end products. 



Bacteria play a large role in the decomposition of 

 proteins. At least four groups of bacteria successively 

 participate in their reduction. The first of these are 

 concerned with the liquefaction of the proteins, hydroly- 

 zing the albumins, etc., by successive stages to albu- 

 moses, peptones, etc., and finally to ammonia. A 

 second group of bacteria oxidizes the ammonia to 

 nitrites. A third group oxidizes the nitrites to 

 nitrates. A fourth group, common in drainage waters, 

 reduces nitrates to nitrites. Since these processes are 

 going on side by side, nitrogen is to be found in all 

 these states of combination when any natural water is 

 subjected to chemical analysis. The following table 

 shows some of the results of a large number (415) of 

 analyses of four typical bottomland bodies of water, 

 made for Kofoid's investigation of the plancton of the 

 Illinois River by Professor Palmer. 



