Phosphorus particulate forms

In all of the techniques which use artificial barriers to surface run-off of nutrients there is a need to consider the influence of land drains. If these are widespread in a catchment a reduction in nitrogen loading to the watercourses will be unlikely, because the nitrogen is predominantly dissolved and runs through the sub-soil to the drains. Phosphorus control by these barriers will be less affected by land drains because the main input of the phosphorus is in the particulate form which would be prevented from running off the surface to the watercourses. 

The sediment reservoir (1) represents all phosphorus in particulate form on the Earth s crust that is (1) not in the upper 60 cm of the soil and (2) not mineable. This includes unconsolidated marine and fresh water sediments and all sedimentary, metamorphic and volcanic rocks. The reason for this choice of compartmentalization has already been discussed. In particulate form, P is not readily available for utilization by plants. The upper 60 cm of the soil system represents the portion of the particulate P that can be transported relatively quickly to other reservoirs or solubilized by biological uptake. The sediment reservoir, on the other hand, represents the particulate P that is transported primarily on geologic time scales. 

Fig. 3-2. I assume that 95 percent of the phosphorus supplied to the surface sea is incorporated into organic matter and returned to the deep sea in particulate form. One percent of the total survives to be buried in sediments. The rest is restored to the deep sea as dissolved phosphorus. The loss to sediments is balanced for the whole ocean by supply by the rivers. The fluxes here are in relative units.

The problem is to calculate the steady-state concentration of dissolved phosphate in the five oceanic reservoirs, assuming that 95 percent of all the phosphate carried into each surface reservoir is consumed by plankton and carried downward in particulate form into the underlying deep reservoir (Figure 3-2). The remaining 5 percent of the incoming phosphate is carried out of the surface reservoir still in solution. Nearly all of the phosphorus carried into the deep sea in particles is restored to dissolved form by consumer organisms. A small fraction—equal to 1 percent of the original flux of dissolved phosphate into the surface reservoir—escapes dissolution and is removed from the ocean into seafloor sediments. This permanent removal of phosphorus is balanced by a flux of dissolved phosphate in river water, with a concentration of 10 3 mole P/m3. 

For phosphorus, Cdeep/C river = 3 0 and Csurface/Qver = 0.15, SO = 0.95. This means that if enough time has elapsed for the complete exchange of water between the two reservoirs, then 95% of the phosphorus that enters the surface box is removed in particulate form. Detailed studies of nutrient dynamics in the mixed layer indicate that the average atom is recycled 10 times before escaping as a sinking particle into the deep sea. 

The sediment reservoir (1) represents all phosphorus in particulate form on the Earth s crust that is (a) not in the upper 60 cm of the soil and (b) not mineable. This includes unconsolidated marine and freshwater sediments and all sedimentary, meta-morphic, and volcanic rocks. The reason for this... 

Both filterable and particulate forms of organic phosphorus are transferred from soils, but the lack of suitable techniques for determining specific phosphorus compounds in aqueous samples means that there is little information available on the chemical composition of either fraction. Conceptual understanding of organic phosphorus forms and their behaviour in water is also limited by the operational definitions that arise from conventional analysis procedures (see below). For detailed reviews of speciation techniques for organic phosphorus in soil waters see McKelvie (Chapter 1, this volume) and Cooper et al. (Chapter 3, this volume). 

Phosphorus is transported through wetlands in soluble and particulate forms, including dissolved inorganic phosphorus (DIP), particulate inorganic phosphorus (PIP), dissolved organic phosphorus (DOP), and particulate organic phosphorus (POP). 

Although they cannot reject any dissolved salts or other low-molecular-weight soluble matter, UF systems can remove very fine particulate material and high-molecular-weight organic matter from water streams. To remove any low-molecular-weight soluble species with a UF membrane, a process must occur to convert the soluble matter to particulate form. As examples, soluble phosphorus may be precipitated with a metal salt, soluble organics may be adsorbed onto powdered activated carbon, and soluble iron may be oxidized to particulate form. All of these processes and others will allow a UF membrane to remove even soluble matter. 

In aquatic systems, phosphorus occurs in a wide variety of inorganic and organic forms (Figure 8.1) [3]. While these may exist in either the dissolved, colloidal, or particulate forms, the predominant species is orthophosphate in either the mono- or diprotonated forms (HP04, H2P04 ). The dissolved component is operationally defined by filtration, and for this reason, the term filterable is used in preference to either dissolved or soluble, both of which are used extensively and interchangeably in the literature. 

Table 3.1 gives the local elemental composition of three different tubercles from three different systems formed under different chemical treatments. At the floor of each tubercle, the concentration of chlorine and sulfur is higher than in the crust. The concentration of most crust elements, except that of iron, also decreases near the tubercle floor. The crust contains traces of treatment chemicals including zinc, phosphorus, and silicon. Tubercle 1 contains up to 40% silicon in the crust, which strongly suggests accumulation of silt by settling of particulate. 

In a general way, the overall movement of phosphorus on the continents can be considered as the constant water erosion of rock and transport of P in both particulate and dissolved forms with surface runoff to river channels and further to the oceans. The intermediate transformations are connected with uptake of P as a nutrient by... 

Incubation of lake water with 32P or 33P as tracers and subsequent gel chromatography reveals that a major pathway exists between dissolved orthophosphate and the particulate phase (3, 5-7). Low-molecular-weight phosphorus forms in the presence of bacteria and algae. SUP is present in the low-molecular-weight fraction and is classified as individual DOP compounds unassociated with particulate or colloidal material. The HMW fraction found in gel chromatography studies is characterized as a colloid that contains phosphorus compounds or incorporates orthophosphate. The colloidal material then releases orthophosphate, replenishing the dissolved phosphorus cycle. In some eutrophic lakes the HMW SRP fraction can make... 

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