Factors Affecting Biological Lability

Biodegradability of DOM is often considered a function of molecular structure, including size, stoichiometry, spatial arrangement of atoms, and molecular constituents that alter electron density (Brezonik, 1990 Pitter and Chudoba, 1990 Boethling et al., 1994). Aliphatic molecules generally are 

FIGURE 4 Uptake of glucose and arabinose in first- to fourth-order SE Pennsylvania woodland streams, (a) Mass transfer coefficients, (b) Ratios of mass transfer coefficients. 

FIGURE 5 Schematic view of DOM cycling in a stream ecosystem, showing spatial scales of spiraling for different lability forms. 

Rates of supply may be controlled, in part, by the activity of hydrolytic enzymes that degrade combined molecules in dissolved or particulate organic matter to monomeric constituents prior to enzymatic transport into bacterial cells (Skoog et al., 1999 see also Chapter 13). At present, in situ rates of such exoenzymes have not been accurately measured, but enzyme potential has been estimated with the addition of artificial substrates in saturating 

Financial support was provided by a grant from the National Science Foundation (DEB 9904047) and the Pennswood Foundation for Environmental Research. 

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