Limitation inorganic nutrient

Hofmann and Ambler, 1988). The Hofmann and Ambler (1988) model had 10 compartments which included NO3 and NH4, large and small phytoplankton size classes and a copepod submodel (Fig. 33.3). The latter included parameterizations for N assimilation, excretion, egg production, molting and predation. Steele and Frost (1977) incorporated comparable levels of detail more than 10 years earlier. Although not, strictly speaking, an N-based model, it specified N as the limiting inorganic nutrient and assumed a fixed C/N ratio for biota defined in carbon units, so the distinction is to some degree semantic. 

In natural ecosystems, microbial growth and metabolism may be limited by the concentrations of inorganic nutrients such as nitrogen, phosphorus, or even iron. Systematic investigation of these... 

Limitation in the concentrations of these inorganic nutrients does not therefore appear to have had a dramatic effect on the persistence of the relatively few compounds that have been examined systematically. However, it has been suggested that competition between organisms for inorganic phosphorus may account for differences in biodegradability when several carbon sources are present (Steffensen and Alexander 1995). 

BTEX bioremediation projects often focus on overcoming limitations to natural degradative processes associated with the insufficient supply of inorganic nutrients and electron acceptors. However, other limitations associated with the presence and expression of appropriate microbial catabolic capacities may also hinder the effectiveness of bioremediation. Thus, while subsurface addition of oxygen or nitrate has proven sufficient to remove BTEX below detection levels [134,145,292,315,316], it has been only marginally effective at some sites [6]. Sometimes, the concentration of a target BTEX compound fails to decrease below a threshold level even after years of continuous addition of nutrients and electron acceptors [317]. This phenomenon has also been observed for many other xenobiotic and natural substrates under various experimental conditions [327-332]. 

Rivkin, R., and M. Anderson. 1997. Inorganic nutrient limitation of oceanic bacterioplankton. Limnology and Oceanography 42 730-740. 

In the Central North Pacific Ocean (CNPO) it has also been reported that phosphorus availabiHty limits N2 fixation and primary production (Karl et al, 2001 a,b) (but iron availability may also play a role as suggested by Wu et al (2000). Karl et al (2001a,b) contend that since the mid 1970s there has been an enhanced stratification in the CNPO and a decreased inorganic nutrient avadabihty which selects for diazotrophs and shifts from a N-hmited phytoplankton population to one that is either P or Fe Hmited (see Karl et al. Chapter 16, this volume). 

The experimental scheme for anaerobic decomposition is shown in Fig. 5-4. Exactly 1.5 g of each substrate was added to a modified 1 litre Sohngen flask and autoclaved at 120°C and 15 psi to ensure sterility, after which each flask was filled to capacity with a sterile inorganic nutrient medium and pH adjusted. Next 50 ml of a heterogeneous innoculum prepared from muds from a local lake was injected into each flask as "inoculates", while 50 ml. of sterile nutrient medium was used for control samples. Headspace C1-C4 hydrocarbons were measured prior to incubation to provide baseline concentrations. Minimum detection limits were 3 ppb on a volume basis using a high-sensitivity gas chromatograph equipped with a flame ionisation detector. Samples were incubated at 25°C and 36°C over a five week period. 

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