TERRESTRIAL DETRITUS 

 AND THE CARBON CYCLE 



WILLIAM A. REINERS 



Department of Biological Sciences, Dartmouth College, 



Hanover, New Hampshire 



ABSTRACT 



The objectives of this paper are to review methods for estimating carbon turnover in 

 terrestrial detritus and to provide an estimate of turnover. Reviewed are the input method, 

 the direct C0 2 -evolution-measurement method, and the ' 4 C-isotope method. Four 

 approximations of turnover are presented and are based on input data derived from the 

 literature. These approximations range from 37 to 64 x 10 9 tons C/year. Because of human 

 activities, detritus pools are currently not in steady states and it cannot be assumed that 

 inputs equal outputs. In general, man's activities decrease inputs through harvesting and 

 other manipulations and increase outputs by accelerating decay. Thus global carbon output 

 from this pool may exceed current inputs. Since the range of estimates for inputs probably 

 exceeds cultural effects on outputs, it is premature to attempt an estimate of contemporary 

 outputs. A model is presented, however, that may simulate patterns of change and suggest 

 directions for future investigations. 



In most ecosystems a proportion of carbon fixed by plants becomes in- 

 corporated in material that dies and persists for a time as detritus. On land, 

 detritus accumulates on and in the soil, forming a reservoir of carbon and other 

 biogenic elements that are gradually mineralized and recycled by a myriad of 

 decomposition processes. An enormous literature exists on the biological details 

 of this process. 



Terrestrial detritus — termed forest floor, mulch, matting, humus, etc., 

 depending on custom or the ecosystem — represents a significant compartment 

 in an inventory of global carbon. Bolin 1 estimates this compartment to be 

 700 X 10 tons or 1.8% of nonsedimentary global carbon (Table 1). Delwiche 2 

 estimates the nitrogen content of this pool to be 760 X 10 9 tons. If we assume 

 an average carbon to nitrogen ratio 3 of 12, this leads to 9120 X 10 9 tons carbon 

 for terrestrial detritus— over 10 times Bolin's estimate. A 10-fold difference 

 suggests that further estimates are necessary. 



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