SULFUR, NITROGEN, AND CARBON 

 IN THE BIOSPHERE 



EDWARD S. DEEVEY, JR. 



The Florida State Museum, University of Florida, Gainesville, Florida 



ABSTRACT 



Sulfur, nitrogen, and carbon have closely analogous biogeochemical cycles, closure of which 

 requires a biological reduction step. The cycles are coupled by the occurrence of all three 

 elements in reduced form (as protein) in the biosphere, steady synthesis of which demands 

 the coexistence of reducing environments, such as soil, deep water, and mud, with oxidizing 

 water and air. On a global basis, reduction (fixation, metabolism) of C, N, and S appears to 

 proceed at rates related as 10 : 1 : 1, respectively, although the biospheric proportions, by 

 weight, are 5 54 : 7 : 1. Quantitative budgets are full of uncertainties, many of which center 

 on unevaluated and even unproved emissions from anaerobic to aerobic environments. For 

 example, about half the sulfur that moves through the atmosphere annually is 34 S-depleted 

 and therefore biogenic and must come from the ocean in sulfide form, but emission of H 2 S 

 to the atmosphere has not been detected. Accelerated recycling of the three elements (plus 

 phosphorus), now suspected as a consequence of pollution, can be both cause and effect of 

 eutrophication, which is defined very broadly as organic overloading. In general, 

 eutrophication, by increasing the proportion of anaerobic to aerobic environments, can 

 change the mean redox state of the oceans or of the globe. The sulfur-isotope data of Holser 

 and Kaplan 2 5 give evidence that the redox state has varied remarkably over Phanerozoic 

 time. 



After some hard study of the splendid review of biological cycling of 

 atmospheric trace constituents by Hitchcock and Wechsler, I have to emphasize 

 that the gaps in our understanding of sulfur and nitrogen in nature are wider, if 

 possible, than those related to carbon. The broad outlines of the nitrogen and 

 sulfur cycles have been visible for a long time, but those nagging quantitative 

 details that tell us how to balance budgets are mostly unknown. I shall have to 

 be content, then, with some marginal notes. The limnologist's assumptions that 

 underlie them, however, are not to be blamed on Hitchcock and Wechsler. 



To make my bias explicit, I use as my first model a small lake of the sort 

 represented by Linsley Pond. This suburban ecosystem serves as well as any to 



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