Seston primary production

Primary production (trophic state) affects S retention and speciation in several ways. As primary production increases, inputs of organic S to sediments in seston increase. Hence, as the organic carbon content of sediments increases, S content would be expected to increase proportionally. Such a simple relationship is not observed among nearly 80 lakes for which sediment S and C content are available (Figure IB). However, a line defining the minimum S content does increase linearly with increasing carbon content. The slope of this line corresponds to the mean C S ratio measured in seston... 

Paleolimnological Conditions. Because of the interplay between primary production, oxygen content of bottom waters, and the sulfur content and speciation of sediments, sediment profiles of S probably preserve records of paleolimnological conditions. Several studies (23-25, 205) point to increased S content of sediments as a result of eutrophication. Mechanisms involve both rates of S supply to sediments (seston deposition and diffusive gradients) and rates of S reduction and oxidation. The relative S enrichment... 

Seston-S deposition probably is a more important process than dissimilatory reduction in lakes with low [SO42 ]. As lakewater sulfate concentrations increase, seston deposition reaches a plateau limited by the overall primary production rate and the maximum algal S content, but diffusive fluxes continue to increase in direct proportion to [SO42 ]. Thus, in highly acidic lakes (pH 3 5 [SOjt2 J > 100 peq/L), such as McCloud Lake, Florida and Lake 223, Ontario, dissimilatory sulfate reduction probably is the major sulfate sink. Nriagu and Soon (131 concluded that endproducts of dissimilatory reduction and elevated sediment S content would not be observed below S mg/L (240 / eq/L), but we see clear evidence of dissimilatory reduction in Little Rock Lake at concentrations of approximately SO /teq/L. 

In addition to limitations on sulfate reduction, seston deposition of S is limited by algal-S content and primary productivity. The relationship between primary productivity and lake acidification is unclear 1621. but limited evidence suggests that primary productivity is not particularly sensitive to moderate lake acidification. Further, there is little evidence to indicate that the S content of seston changes much with acidification (Table III). Hence, within a given lake, the loss of sulfate from the water column from seston deposition probably changes little during the acidification process. 

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