186 DEEVEY 



the intensity of that metabolism has not been appreciated because it is screened 

 from our view by an oxidizing environment. 



As to nitrogen, I can say very little and nothing that is novel, for the 

 limnological chemistry of nitrogen is beset with quantitative uncertainties. The 

 dominant reservoir, as for soil nitrogen, is of course the N 2 of air. Nowadays 

 there is reason to suspect that airborne nitrate from fertilizer and automobile 

 exhaust has much to do with the eutrophication of lakes. Insofar as there is 

 steady-state exchange between biosphere and atmosphere, the closure of each 

 redox cycle depending on reduction steps performed anaerobically, one would 

 expect a quantitative expansion of anaerobic environments resulting from 

 organic overloading to intensify the recycling of nitrogen as of sulfur and 

 phosphorus. But intensified recycling on a regional scale should enhance the 

 rates of emission of reduced substances to oxidized environments, e.g., the 

 emission of ammonia and nitrous oxide to the atmosphere, and these emissions 

 are so hard to detect, when diluted into enormous oxidized reservoirs, that we 

 have exceedingly little reliable information. (More or less identical considera- 

 tions apply, of course, to the emission of CO, CH 4 , NO, H 2 S, S0 2 , and 

 polythionates.) Limnologists have been exclusively concerned with the import of 

 nitrogen and with its internal cycling within the lake, and they have contributed 

 almost nothing to the export side of the equation. Most export is of course as 

 nitrate in surface outflow. 



I have pointed out that the biosphere, quantitatively dominated by woody 

 plant tissue, can be regarded as a chemical compound with the empirical formula 



H2960 O 1480 C ]48 o Nj 6 P 18 S 



This tells us that the N : S ratio by atoms averages 16, the C : N ratio is 92.5, 

 and the C : N : S proportions are 1480 : 16 : 1. If we cannot compare budgets 

 of C, N, and S, we can at least look at relative global mobilities (Table 2). 

 Mobility of these three elements is entirely biogeochemical, a function of their 

 redox properties, and has little to do with relative geochemical abundance or 

 even with the present sizes of their mobile reservoirs. 



TABLE 2 



CARBON, NITROGEN, AND SULFUR: MOBILE 



RESERVOIRS, METABOLISM, AND 



BIOSPHERIC COMPOSITION 



C N S 



Mobile reservoir, g/cm e 

 Metabolism, mg cm e 2 year 1 

 Biospheric composition, g/g S 



