Nutrient concentrations element ratios

The major constituents in seawater are conventionally taken to be those elements present in typical oceanic water of salinity 35 that have a concentration greater than 1 mg kg excluding Si, which is an important nutrient in the marine environment. The concentrations and main species of these elements are presented in Table 1. One of the most significant observations from the Challenger expedition of 1872-1876 was that these major components existed in constant relative amounts. As already explained, this feature was exploited for salinity determinations. Inter-element ratios are generally constant, and often expressed as a ratio to Cl%o as shown in Table 1. This implies conservative behaviour, with concentrations depending solely upon mixing processes, and indeed, salinity itself is a conservative index. 

Of particular interest in relation to Si N interactions and diatoms is the relatively recent finding that iron provides a strong regulating influence on the species composition of phytoplankton assemblages, as well as on the elemental ratios of diatoms. Fe and Si supply appear to be particularly important in several large areas where high concentrations of other macro nutrients (N, P) are present in surface waters. These HNLC areas (Minas et al, 1986) are characterized by low phytoplankton biomass... 

Redfield stoichiometry Redfield and colleagues noted that organisms in the sea consistently removed nutrient elements from the water in a fixed ratio (C N P=106 16 1). Subsequent workers have found that nutrient concentrations in the sea typically are present in those same ratios. 

A TBma,) explicit functions of the available concentrations of the other nutrients. This approach allows for a pronounced interdependence between the fluxes of the different nutrients but it does not ensure that the Redfield ratios are maintained. In the second approach the contents of the nutrients in the biota reservoir are forced to remain close to the Redfield ratios. This method was used by Mackenzie et al. (1993) in their study of the global cycles of C, N, P, and S and their interactions. They were able to demonstrate how a human perturbation in one of these element cycles could influence the cycles of the other elements. 

One measure of the distribution of residence times (ages) of the fluid elements within a reactor is the -function, defined so that E d0 is the fraction of material in the exit stream with age between h and h + dO (Levenspiel, 1972). It can be shown (Levetispiel, 1972) that the C and E functions are identical, and that for an isothermal process the ratio of the final (C) to initial (Co) concentrations of either microorganisms or nutrients can be determined from the expression ... 

Since eroded material frequently differs in composition from the original soil, the loss of plant nutrients in runoff may be expressed in terms of an enrichment ratio (E.R.). This is the ratio of the concentration of that element in the runoff to that in the original soil (Barrows and Kilmer, 1963) ... 

The crucial parameters are the concentration ks at which uptake is half of the maximum rate and the fixed ratio (or yield) q l at which nutrient is converted to biomass. The yield may be the Redfield ratio or some other optimum composition. Tilman etal. (1982) used the model to show how freshwater phytoplankters of different optimum composition or different half-saturation concentrations, might succeed to different extents depending on the ambient ratios of nutrient elements. Although the assumption of constant yield may be appropriate for pelagic heterotrophs, it is now seen to be too simple for accurate prediction of the growth of phytoplankters (Droop, 1983 Sommer, 1991 Ducobu etal., 1998). 

Fig. 9.1 Cell-quota theory for control of photo-autotroph growth by internal nitrogen or phosphorus. Q is the cell quota for the nutrient, in atoms of the element per atom of organic carbon. kfj is the minimum value, or subsistence quota. /////1IU1X gives growth as a proportion of maximum rate. The function 10) multiplies nutrient uptake (which is also a function of ambient concentration) and brings it towards zero as Q tends towards (i llax. The third part of the diagram compares typical ranges of values of cellular N and P content and show how these contribute to variation in the cell N P ratio.

Scavenged type Trace metals such as Al, Co, Ce, and Bi, show surface enrichment and depletion in deep waters, in contrast to the opposite trend in nutrient types. These elements are highly particle-reactive and are rapidly removed from the water column by sinking particulate matter and/or by scavenging at the sediment-water interface. Their mean oceanic residence times are short (<10 -10 years). Interoceanic variations in their concentration can be large (e.g., Atlantic/Pacific concentration ratio 40 for Al) depending on kinetic balance between supply and removal for the specific basins. 

The type of root system developed by a plant depends not only on soil tilth but also on the level of nutrients present. The root system tends to be more branched and more concentrated in a fertile soil than in a poor one. If a poor soil is fertilized with well-rotted manure, for example, each pocket of manure will be filled with a mass of much-branched roots, whereas the remainder of the soil will have few roots other than the larger primary and secondary ones. Undoubtedly this extreme development of fine roots in manure is a response to chelated minor elements as well as to the major nutrients. If a poor soil is not fertilized with either chemical fertilizers of manure the top—root ratio is likely to be unusually narrow, and the roots may extend to deeper depths (Oswalt et al., 1959). We sometimes say that such roots are long because they are searching for nutrients, but the real explanation is that the carbohydrate level in the root increases as the available nutrient supply decreases. When the nutrients are inadequate for a luxuriant top growth there is a bigger excess of carbohydrates that are transported downward and used for root growth. Inadequate soil moisture in the upper part of the soil profile may also result in a deeper root system. 

The total atmospheric fluxes to the southern YS are respectively calculated based on the results as we discussed above. In order to account for the importance of air to sea fluxes in the area, the values are compared with the riverine inputs (Table 3.11, Wan et al., 2003). The Changjiang River flows into the southern YS in a different ratio for each season. Based on the drainage areas and concentrations of nutrients, the riverine inputs of nutrient elements to the YS can be obtained. 

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