Nutrient addition experiments

Devol, A. H, H. dos Santos, B. R. Forsberg, and T. M. Zaret. 1984b. "Nutrient addition experiments in lago Jacaretinga, Central Amazon, Brazil 2. The effect of humic and fulvic acids." Hydrobiologia 109 97-103. 

Zaret, T. M., A. H. Devol, and A. dos Santos. 1981. "Nutrient addition experiments in Lago Jacaretinga, central Amazon Basin, Brazil." Verhandlungen International Vereinigen Limnologie 21 721-724. 

TyreU (1999) produced a model showing that the proximate limiting nutrient in the ocean is NOs", while the ultimate limiting nutrient is P04 . Mills and colleagues (2004) confirmed that N is the proximate limiting nutrient in the eastern tropical North Atlantic with nutrient addition experiments. N limitation or P limitation is not always constant temporally and spatially. Hence Karl et al. (2001) suggested that when considering nutrient limitation in the oceans, the exact time and spatial scale should be defined. 

It is now evident that marine N2 fixation can be limited by either P or Fe, although the relative importance of these two nutrients is stiU highly debatable. There may be an interaction between iron supply and P limitation of primary production through N2 fixation. Recently, Mills et al. (2004) used a factorial nutrient addition experiment to show that Fe and P can co-limit N2 fixation in the eastern tropical North Atlantic. They used trace-metal clean techniques with the addition of N, P, Fe, or Saharan dust individually or in combination to investigate which nutrient limits N2 fixation. Their experiments demonstrated that at two out of three stations, N2 fixation was enhanced by 2-3 times by the addition of P and Fe together, but the addition of either P or Fe alone had less effect (Fig. 38.14). Added dust also enhanced N2 fixation, which they suggested could be due to mineral dissolution of both Fe and P. 

Aside from adding defined compounds, experimental additions of natural DOM mixtures suspected to vary in lability have helped test ideas about the contribution of various DOM sources to aquatic ecosystems. In a nice example using manipulation of natural DOM sources, Battin et al. (1999) used flowthrough microcosms to measure the relative uptake rates of allochthonous and autochthonous DOM by stream sediments. They documented greater than fivefold differences or more in uptake and respiration, depending on whether the DOM was extracted from soil or periphyton. Moreover, they were able to show, via transplant experiments, several cases where prior exposure to a particular source of DOM increased the ability of that community to metabolize the DOM supplied. There appears to be some preadaptation of microbial catabolic capacity when these stream biofilms were re-exposed to a familiar type of DOM. Similarly, the response of heterotrophic bacteria to carbon or nutrient addition was greatest when the source community was particularly active (Foreman et al., 1998). Kaplan et al. (1996) showed that fixed film bioreactors, colonized on one water source, were unable to rapidly metabolize DOC in water from another source. 

Nutrient Addition Bioassay Experiment, Ti Neuse River, Juiy 2003... 

Kudela, R., and Dugdale, R. (2000). Regulation of phytoplankton new production as determined from enclosure experiments with nutrient additions in Monterey Bay, California. Deep Sea Res. II 47, 1023-1053. 

The three classic oceanic high nutrient, low chlorophyll (HNLC) regimes are now universally recognized by oceanographers as being Fe-limited. A plethora of deck-board and open ocean Fe addition experiments have conclusively demonstrated... 

Flowever, biologists have demonstrated that N is more Hkely to control phytoplankton productivity in the coastal and open oceans through nutrient enrichment experiments and observations of nutrient distributions (Falkowski et al., 1998). Typically, NO3 runs out slightly before P04 when nutrients become depleted in the surface waters (Fig. 38.9, GEOSECS 1996, TyreU and Law, 1998). It has long been known that additions of to natural samples collected from oligotrophic... 

Within this context, it would be interesting to consider potential interactions between nutrient/substrate limitation and UV-B stress. Nutrient additions have been reported to decrease the sensitivity of bacterioplankton production to UVR [91]. As has been demonstrated [106] a large fraction of the bacterioplankton in marine waters is metabolically inactive as a result of substrate limitation. Phytoplankton may also experience nutrient (N, P, Fe) limitation in the open ocean or in a post-bloom situation. Suboptimal metabolic activity in these cells would hamper DNA repair, and would thereby contribute to rapid accumulation of DNA damage in these cells. In turn, damage accumulation would then decrease viability in this fraction of the community. The low repair rates and residual DNA damage levels (morning samples) in combination with low growth estimates in many bacterioplankton field studies seem to support this hypothesis. 

The most detailed studies of warm-core eddies have been carried out by Krom and co-workers on the Cyprus Eddy (aka Shikmona Gyre Krom etal., 1992, 1993 Zohary etal., 1998). It has also been the site of the recent CYCLOPS phosphate addition experiment which was designed to increase understanding of microbiological processes and nutrient cycling in the Eastern Mediterranean (Carbo etal., 2002). The Cyprus Eddy is a quasi-stationary warm-core feature situated south of Cyprus. It has been found both to the east and west of the Eratosthenes Seamount. It seems to remain stationary for several years and then move out probably to the northeast to be replaced with another similar feature from the southwest (Brenner etal., 1990). 

We can combine these generahsations into predicted scenarios, at present for lakes, and eventually for streams as Euro-limpacs data accumulate. We assume in Europe a future of increased temperature and reduced summer rainfall (IPCC, 2007), with nutrient additions to lakes most likely to be maintained as human populations and dietary aspirations increase, despite the best efforts at control under the Water Framework Directive. Experience has shown that many years are likely to elapse before the effects of nutrient control become significant. 

Additional experiments are needed to relate not only the monosaccharide composition of the fibers fed to fecal output but also the structures of those fibers and how they may have been modified In the digestive tract even If not fermented. The effect of fiber particle size and pretreatment should be studied. Free sugar, starch, cellulose and uronlc acid measurements should be made in order to obtain a more complete picture of what survives and what is metabolized. The effect of dietary fibers on the digestion and utilization of other polysaccharides and other food components should be studied. This Information, together with fermentation data. Including gas and VFA production, will provide a better understanding of the role and value of different dietary fibers and their effects on nutrient bloavallablllty. 

Table 19.3 Results of niacin determinations for milk samples. Niacin determinations by liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) are compared to expected values for four milk samples. Expected niacin levels for milk are roughly 1 ppm, according to the USDA Nutrient Database for Standard Reference (US Department of Agriculture 2010) and results obtained for two commercial milk samples (Brands F and G) are a little under 1 ppm. The result for sample NFY0409F6 is about 30% lower, but is consistent with results obtained for other milk samples from the same source. In addition, the niaein level for NFY0409F6 was estimated by a standard additions experiment, the result from which is in agreement with the estimate from the normal LC-IDMS procedure. The level obtained for the reference material (RM) RM 8435 whole milk powder, reported on a dry mass basis, is in agreement with the reference value. Data are from Goldschmidt and Wolf (2007), with permission from the publisher.

Vitamin A acetate is an important nutrient additive and its synthesis is now carried out on a technical scale. The three major routes of preparation used today were developed by HofFmann-La Roche, Rhone Poulenc, and BASF [43]. For the work presented here, we were particularly concerned with the Wittig-Horner reaction between a C15 and a C5 precursor as it occurs in the BASF process [44,45]. This study describes the investigation of important process parameters for a synthesis that involves a thermally unstable ylide intermediate. In the current experiments, this intermediate is generated in situ and immediately converted in order to simulate the conditions in the technical process. However, while in a conventional process the reaction hardly can be performed under isothermal conditions due to the exothermic heat of reaction of about 250kJ/mol, the microreactor setup offers the opportunity to study relevant process parameters such as temperature, concentrations of starting materials, and mixing protocol of the components. 

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