Sediment-associated Bacteria

Each sample was split for analysis of the whole (unfiltered) water and analysis of sediment-associated bacteria. Samples for whole-water analysis were sonicated to disaggregate microbial masses and detach bacteria fixed to sediment. Samples for analysis of bacteria associated with suspended sediment were gently agitated and filtered through an 8-pm membrane (for this study the bacteria-sediment conglomerate was operationally defined as having a minimum size of 8 pm to preclude retention of any unadhered bacteria). Sterile distilled water was then passed through the membrane to... 

Rainfall at the site sufficient to cause Terrieu Creek to flow resulted in marked temporal changes in TSS and bacterial content in both surface and ground water. Both wells P7 and P8 responded quickly to elevated TSS concentrations and bacteria in Terrieu Creek. Temporal changes in TSS and concentrations of free and sediment-associated bacteria continued over several days. 

A study using resuspended river sediment (Marchesi et al. 1991) illustrated the important interdependence of substrate attachment to particulate matter and its biodegradability. Addition of sodium dodecyl sulfate that is degradable resulted in a relative increase in the number of particle-associated bacteria, whereas this was not observed with the nondegrad-able analogs such as sodium tetradecyl sulfate or sodium dodecane sulfonate. 

Bott, T.L., Standley, L.J. (2000) Transfer of benzo[a]pyrene and 2,2,5,5,-tetrachlorobiphenyl from bacteria and algae to sediment-associated freshwater invertebrates. Environ. Sci. Technol. 34, 4936 -942. 

Field studies point in a similar direction field comparisons of peptide hydrolysis rates and amino acid turnover in coastal sediments showed that amino acid production could exceed uptake by a factor of approximately 8 (Pantoja and Lee, 1999). A comparison of potential enzyme activities and sedimentary amino acid and carbohydrate inventories in sediments from the Ross Sea also showed that potential hydrolysis rates on time scales of hours should in theory rapidly deplete sedimentary amino acid and carbohydrate inventories (Fabiano and Danovaro, 1998). In deep-sea sediments, Poremba (1995) also found that potential enzyme activities in theory could exceed total sedimentary carbon input by a factor of 200. Finally, Smith et al. s (1992) investigation of potential hydrolysis rates and amino acid uptake in marine snow demonstrated that the particle-associated bacteria were potentially producing amino acids far in excess of their own carbon demand. 

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

A major experimental issue to be addressed is the rate and means by which particles are hydrolyzed and solubilized to provide substrates for heterotrophic bacteria, and the role of free enzymes in this process. Burns (1982) reviewed the possible locations and origin of enzyme activities in soils, and particularly underscored the potential importance of enzyme-humic complexes in microbial catalysis of substrates. As Burns (1982) discussed, enzymes associated with soil particles or humic substances are not subject to the same biochemical and physical restraints as are enzymes newly produced by microbial cells. Soil-held (or sediment-held) enzymes may therefore play a catalytic trigger role in substrate degradation, providing critical signals about substrate availability to the local microbial community. The conceptual model presented by Vetter et al. (1998) suggested that release of free enzymes into the environment may in fact represent... 

There is some hope, since certain sediments are thought to be produced only by biological activities. Obviously many of the involved reactions, if not mediated by biocatalysts would require the addition of too much time and heat. In these cases it is plausible to conclude that bacteria had provided the necessary catalysts. Especially, if a specific inorganic formation is found to be associated with organic chemofossils and microfossils, it is very likely a result of biological activities. This is exemplified by stromatolltic formations. When such deposits are found, one can deduce the nature of the biological activities from the characteristics of the mineral formation. 

Table 5. Sediment quality in waters associated with the rivers Saar and Moselle (old arms, harbors, and marinas). The ecotoxicological characterization is based on porewater and elutriate bioassay responses generated with algae, bacteria, and daphnids. Bioassays conducted according to HABAB-WSV (2000), refer to Box 1. For shade code information of toxicity classes, refer to Table 3.

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