Organic carbon input rates

St-Onge, G. and Hillaire-Marcel, C. (2001) Isotopic constraints of sedimentary inputs and organic carbon burial rates in the Saguenay Fjord, Quebec. Marine Geology, 176, 1-22. 

Input rates of organic C into the soil system are hard to quantify, particularly for natural ecosystems and to a lesser extent for agricultural ecosystems. Whereas quantity and quality of carbon inputs via litter fall and plant residues after harvest might be directly measurable, inputs via roots and rhizodeposition are more difficult to assess. 

Even within the subset of boreal lakes there is probably a direct relationship between external inputs of organic matter and their importance to zooplankton (Meili, M. Fry, B. Kling, G. W. unpublished data). In the case of Lake N2 and other upland arctic lakes, thermokarst processes and active erosion of shoreline peat banks are much less important than they are in coastal plain lakes (62, 75, 103). In addition, DOC made up less of the total organic carbon in Lake N2 than it did in the humic lake studied by Hessen (72) the ratio of DIC DOC.POC in Lake N2 was 25 8 1 (Table II), whereas in the humic lake the ratio was 1.6 21 1. The lower loading rates of particulate carbon and the smaller relative amounts of DOM in Lake N2 may explain the observation that pelagic productivity depended mainly on new algal production. 

Total S content cannot indicate whether increased carbon inputs to sediments cause increased diffusion of sulfate into sediments or restrict reoxidation and release of S from sediments, because the net effect is the same. In a survey of 14 lakes, Rudd et al. (80) did not observe a strong correlation between organic matter content per volume and net diffusive flux of sulfate. However, in English lakes the lowest C S ratios occur in the most productive lakes (24) whether this represents enhanced influx or retarded release is not clear. Among 11 Swiss lakes, ratios of C to S sedimentation rates are relatively constant and substantially below C S ratios in seston net S fluxes... 

Although hydrogen sulfide production via putrefaction correlated strongly with numbers of proteolytic bacteria (r=0.94,0.86), none was found for protein (r=0.16) or organic carbon (r=034) in Third Sister Lake. The significance of this is not known due to the many associated uncertainties, but it seems reasonable to assume that protein input would result in enhanced hydrogen sulfide production via putrefaction. Results of experiments to test this in laboratory bioreactor studies indicated that protein (egg albumin) added at the rate of approximately 20 ppm d 1 increased the population of putrefying bacteria by 90 percent and the rate of sulfide production via putrefaction by... 

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