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Microbial metabolic activity in the hypolimnia and sediments of lakes drives the recycling of organic matter both through mineralization and the production of microbial biomass, which may be utilized by grazers. A correction factor was developed based on the water content of sediment samples that corrects sediment bacteria microscopic counts for masking due to sediment particles. Using this correction factor, it was found that sediment bacterial biomass in 22 lakes was positively related to an indicator of the rate of allochthonous organic matter input to lakes. However, the total hypolimnetic carbon mineralization rate of lakes, which integrates both sediment and hypolimnetic water column mineralization, was found to be driven mainly by phytoplankton carbon and to occur mainly in the hypolimnetic water column. Indeed, various hypolimnetic and sediment catabolic processes were found to show a strong positive relationship with indicators of autochthonous organic matter standing stocks and production. In no cases were the processes significantly positively correlated with allochthonous organic matter standing stocks. Results of this research show that autochthonous primary production drives carbon recycling in the hypolimnetic water column, with the ultimate fate of this production being determined principally by the hypolimnetic thickness. The main fate of allochthonous organic matter in lakes is to become a major component of sediment organic matter where it likely drives a much slower catabolism due to its recalcitrance.

Organic matter mineralization by sediment bacteria was measured by the accumulation of DIC + CH$ sb4$ in the water overlying intact cores taken from littoral and profundal sediments of 9 lakes. The variability in areal carbon mineralization was much greater within lakes than among lakes, with the rate of organic matter mineralization in littoral sediments, on average, 3-fold higher than in the deeper sediments. / Sixty percent of the variation in summer carbon mineralization rates is explained by site depth, a surrogate variable which incorporates the effect of temperature and may also be reflecting organic matter quality and/or supply. Lake-specific variables become useful predictors of carbon mineralization only after the site depth is considered. / A comparison of the mineralization in sediments overlain by epilimnetic water to the whole lake sediment mineralization demonstrates the overwhelming importance of the littoral sediments in organic matter mineralization, with more than half (54-100%) of the mineralization in the sediments occurring in the littoral zone. However, the littoral sediments account for less than 20% of the gross respiration in the epilimnion. (Abstract shortened by UMI.)

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<p>This study examined the relationship between sediment structure and infaunal polychaete communities off the southern coast of Namibia from two separate sets of data, and a total of ninety-two samples. It also examined whether a selected group of organisms (polychaetes) could provide the same level of information regarding community structure, as the entire fauna, at a number of taxonomic resolutions.</p>

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