Metabolism particulate detritus

Some 90 per cent or more of the total metabolism in aquatic ecosystems is microbial, accomplished by heterotrophic metabolism of bacteria, fungi, and many protists, all of a size less than 100 m [1,31]. Therefore, the material and energy fluxes of aquatic ecosystems is totally dominated by metabolism of particulate detritus (non-living) and especially DOM from autochthonous and allochthonous sources. The pelagic open water is but a portion of the whole lake or river ecosystem. In relation to loading and fluxes of DOM, allochthonous and littoral sources are critical because of their chemical differences from that produced by algal photosynthesis. 

Terrestrial Detritus. Variability in ecosystem response to fertilization may be attributed in part to the interaction of aquatic and terrestrial ecosystems. In contrast to the many aquatic ecosystems in which higher trophic levels are fueled almost entirely by organic matter originating in the water column, other systems are driven by inputs of particulate and dissolved organic matter from land. The importance of this land-water interaction in regulating system metabolism has been obvious to stream ecologists for some... 

Detritus includes nonliving particulate, colloidal, and dissolved organic matter, and metabolically size affects only the rates of hydrolytic attack (Wetzel, 1995). Inland aquatic ecosystems collect organic matter, particularly... 

Detritus includes non-living particulate, colloidal, and dissolved organic matter, and metabolically size only affects rates of hydrolytic attack [31]. Inland aquatic ecosystems collect organic matter, particularly in dissolved forms, from terrestrial, wetland, and littoral sources in quantities that supplement if not exceed those produced autochthonously. Rates of utilization of that organic matter are slowed by a combination of chemical recalcitrance as well as displacement to anoxic environments. As a result, inland aquatic ecosystems are hetero-trophic and functionally detrital bowls, not algal bowls. 

Bacteria only assimilate dissolved substrates solid substrates are first hydrolysed by extracellular enzymes before being assimilated. Degradation of detritus starts with hydrolytic cleavage of the particulate material into small molecules which can be assimilated by the bacteria. The end-products of extracellular hydrolysis are most amino acids, mono- and disaccharides, and long-chain fatty acids. In aerobic environments these are taken up directly by heterotrophic bacteria, and further metabolism is intracellular. A variable fraction of the detritus in marine ecosystems is never completely remineralised, but accumulates mainly within the anoxic environment, and is gradually transformed into organic complexes refractory to microbial attack (Fenchel and Jorgensen, 1977). 

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