Labile dissolved organic

Weiss, M., and M. Simon. 1999. Consumption of labile dissolved organic matter by limnetic bacterioplankton The relative significance of amino acids and carbohydrates. Aquatic Microbial Ecology 17 1-12. 

Sondergaard, M., and M. Middleboe. 1995. A cross-system analysis of labile dissolved organic carbon. Marine Ecology — Progress Series 118 283-294. 

Sobczak, W. V. 1996. Epilithic bacterial responses to variations in algal biomass and labile dissolved organic carbon during biofilm colonization. Journal of the North American Benthological Society 15 143-154. 

III. Organic Forms of Limiting Element (Labile Dissolved Organic... 

The formula for BCD in Eq. (2) was derived under the assumption that the bacterial growth rate was mineral nutrient limited. If the supply rate of labile organic carbon from allochthonous and autochthonous sources is insufficient to meet this demand, the pool of labile dissolved organic carbon (DOC) will eventually be depleted and the bacteria will become carbon... 

III. ORGANIC FORMS OF LIMITING ELEMENT (LABILE DISSOLVED ORGANIC NITROGEN AND DISSOLVED ORGANIC PHOSPHORUS)... 

Cherrier, J., J. E. Bauer, and E. R. M. Druffel. 1996. Utilization and turnover of labile dissolved organic matter by bacterial heterotrophs in eastern North Pacific surface waters. Marine Ecology Progress Series 139 267-279. 

Zweifel, U. L. 1999. Factors controlling accumulation of labile dissolved organic carbon in the Gulf of Riga. Eastuarine, Coastal and Shelf Science 48 357—370. 

L.J. Tranvik (1993). Microbial transformation of labile dissolved organic matter into humic-like matter in seawater, 12,177-183. 

These ectoenzymes play a significant part in phosphorus cycling in natural waters. In lakes and oceans, phosphorus is partitioned among particulate and dissolved inorganic and organic fractions and is rapidly transformed from one fraction to another. Estimates of the size of the labile dissolved organic phosphorus pool in waters off the coast of Hawaii (0.01-0.2 /rg at P L 1), and its rapid turnover (0.008-0.04 h 1), presumably facilitated by extracellular phosphatases, are comparable with those of PO4- (Smith et al., 1985) and indicate the importance of ectoenzymes in the major nutrient cycles. 

From flux calculations at this Sargasso Sea station, Gagosian and Nigrelli (1979) found that a maximum of 0.05—0.3% of the sterols produced by phytoplankton in surface waters are deposited to the ocean floor. A similar calculation was done for hydrocarbons by Farrington and Tripp (1977) and found to be 0.01—1%. The sterol residence time (the average lifetime of a sterol molecule before it is metabolized) in the euphotic zone was calculated to be approximately one month, whereas the deep-water residence time value was found to be 20—150 years. This monthly turnover of surface water sterols is in contrast with that of more labile dissolved organic compounds such as amino acids whose turnover time has been estimated to be on the order of several days (Lee and Bada, 1977). 

Heterotrophic bacteria are now seen as potentially important links between dissolved resources and higher trophic levels (Vadstein et ah, 1993). This altered view of the role of bacteria has especially important consequences for conceptualizing the significance of bacteria in phosphorus dynamics at the base of the food web, because heterotrophic bacteria differ from phytoplankton in being relatively phosphorus-rich organisms (Vadstein, 2000). Heterotrophic bacterial metabolism of phosphorus is dependent not only on phosphorus availability but also on the availability of labile dissolved organic carbon in the immediate environment. 

Table 9.2. Two physiological states of natural bacterioplankton assemblages. Cellular phosphorus content and phosphate uptake in environments with low or high concentrations of labile dissolved organic carbon. Values are means (standard error in parentheses). Reproduced from Gao (2002) with permission. ND, not determined.

The results of this analysis are usually reported in an operationally defined context because minor quantities of labile dissolved organic P may hydrolyze due to the addition of sulfuric acid and be measured as orthophosphate. For details of this method, see EPA (1990) or APHA (2005). 

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