184 DEEVEY 



from deep water, the vertical circulation of phosphorus and nitrate being 

 enhanced by their tendency to accumulate in soluble form under stagnation and 

 then to be redistributed during overturns as a massive injection to the entire 

 lake. As a result of public changes in the basins of lakes like Erie, the importance 

 of this form of nutrient recycling is now generally recognized. What is less 

 obvious, but what may be of greater significance to the biosphere as a whole, is 

 that all products of biological reduction, and not phosphates alone, will recycle 

 at faster rates if stagnation (1) is more prolonged, (2) occurs in more lakes than 

 before, or (3) is biochemically more intense in the eu trophic lakes we already 

 had. I am saying that eutrophication is organic overloading and can expand 

 reducing environments by overloading nature with larger amounts of a powerful 

 reducing agent. Accelerated recycling is then both cause and effect of organic 

 overloading. 



The lake's main sources of carbon and sulfur, like those of phosphorus, are 

 dominated by hydrologic throughflow. Sulfate from an oxidized environment 

 flows through in such quantities as to mask a limnological process — sulfate 

 reduction — that is just as important from the standpoint of this conference as 

 photosynthetic fixation of carbon. We knew that it was important, but the first 

 quantitative demonstration waited for the availability of isotopic tracers. Sulfide 

 sulfur is depleted in 34 S with respect to sulfate, and in 1960—1961 Nakai 

 proved the existence of fractionation, i.e., of an enrichment— depletion cycle, in 

 the deep water of Linsley Pond. 6 From the enrichment of the heavier isotope in 

 the remaining sulfate when ferrous sulfide was precipitated in the mud, and from 

 mass-balance considerations, Nakai and I calculated that about 1 mg of sulfur 

 was annually reduced per square centimeter of lake surface. As the figure is nearly 

 a tenth of the estimated carbon fixation (13 mg C cm -2 year -1 from Riley's old 

 figures), we thought it must be too high. But when Stuiver 7 in 1964 injected 

 radiosulfur, 35 S, into the hypolimnion of Linsley Pond and found that it all 

 went into mud sulfide and stayed there, it turned out that 1 mg S/cm is the 

 figure for 4 months of summer stagnation and that the annual fixation may be 

 two or three times as much. Meanwhile, in 1962 we acquired some data on a 

 more special lake, meromictic Green Lake at Fayetteville, N. Y., that far 

 surpasses Linsley Pond as a microbial sulfur— redox system (Table 1). 



Green Lake 9-13 is permanently stagnant below 20 m. At the top of the 

 r-ionimolimnion, where H 2 S diffuses up from below, is a port-wine-colored 

 bacterial plate, the color belonging to the photosynthetic sulfur bacterium 

 Chromatium vinosum, although the green bacterium Chlorobium phaeo- 

 bacteroides is actually more common. About 83% of the primary carbon 

 fixation in this lake is by these sulfur oxidizers. 14 However, what keeps them in 

 business is free H 2 S, made anaerobically in the depths by sulfate reducers of the 

 Desulfovibrio type. At its maximum, near bottom in 52 m, sulfide sulfur reaches 

 a concentration of nearly 40 mg/liter, diminishing upward to zero at the 

 chemocline (Table 1). None is detectable in the upper lake, of course, but the 

 34 S ratio in surface-water sulfate is depleted below the ratio in the inlet water. 



