Bioavailability phosphorus

The iron-based redox cycle depicted in Figure 18.9 provides an effective preconcentrating step for phosphorus by trapping remineralized phosphate in oxic sediments. The conversion of phosphorus from POM to Fe(lll)OOH to CFA is referred to as sink switching. Overall this process acts to convert phosphorus from unstable particulate phases (POM to Fe(lll)OOH) into a stable particulate phase (CFA) that acts to permanently remove bioavailable phosphorus from the ocean. This is pretty important because most of the particulate phosphate delivered to the seafloor is reminer-alized. Without a trapping mechanism, the remineralized phosphate would diffuse back into the bottom waters of the ocean, greatly reducing the burial efficiency of phosphorus. 

N. Sequi, P. (1994) Interlaboratory comparison of iron oxide-impregnated paper to estimate bioavailable phosphorus. J. Environ. 

In terrestrial soils and in the euphotic zone of lakes and the ocean the concentration of dissolved orthophosphate is typically low. When bioavailable phosphorus is exhausted prior to... 

Major differences in size (filterable, particulate) and chemical reactivity (condensed, organic) of phosphorus forms in samples can be used as the basis for speciation, as shown in Table 1. Of these fractions, total phosphorus (TP) and FRP are perhaps the most commonly measured, although it is arguable that the understanding of the aquatic phosphorus cycle is somewhat lopsided because of that bias. For example, wastewater discharge licenses often specify a maximum permissible concentration of TP, and provide an indication of the maximum potentially bioavailable phosphorus discharged. However, FRP, comprising mostly orthophosphate, is a measure of the amount of most readily bioavailable phosphorus. 

Sharpley AN (1993) An innovative approach to estimate bioavailable phosphorus in agricultural runoff using iron oxide-impregnated paper. Journal of Environmental Quality 22 597-601. 

Ion chromatography is extensively used for the determination of phosphorus species in waste, industrial, drinking, and natural waters, and is accepted as a standard method of analysis, e.g., USEPA Method 300.0 and APHA Standard Methods Method 4110B (Table 8.2) [128]. Ion chromatographic separations for separation of phosphorus species have been extensively reviewed by Ruiz-Calero and Galceran [129]. Use of ion chromatography arguably provides a better estimate of the concentration of bioavailable phosphorus because it avoids the problem of acid hydrolysis of labile phosphates that occurs in those methods that rely on reactions between phosphate and molybdate. 

TP is most frequently used to monitor the compliance of wastewater discharges with license agreements because it provides a measure of the efficiency of phosphorus removal in water treatment processes, whereas FRP is more commonly used as a surrogate measure of readily bioavailable phosphorus. The ability to perform frequent or even online determination of these parameters provides the potential for improved process control. A number of flow injection [156,157] and segmented continuous flow analysis systems for measurement of FRP or TRP have been developed [128]. 

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