Seawater suspended particle matter

The concentrations of suspended particle matter (SPM) near bottom waters at stations B1 and E3 were 9.6 14.2 and 19.3 24.0 mg/L with averages of 12.2 and 22.2 mg/L, respectively. The reciprocal of the SPM near bottom waters was 0.08 L/g at station B1 and 0.045 L/g at station E3. The annual variation of SPM between the BH98 and BH99 cruises was 25% and 11% at stations B1 and E3, respectively. This implied that the nutrient releases from sediments could be very close to the maximum release. In the experiment, the atom ratios of released nutrients were Si DIN P=40 25 l, which indicated that the phosphorus amount was relatively low compared to the Redfield ratio (Si N P 16 16 l). Fig. 2.45 (Liu et al., 2004) is the plot of time dependent desorption/release of phosphate and silicate from sediments. When surface sediment and seawater were mixed, they were released from sediments (Fig. 

In aquatic environments, radiocerium readily forms chemical complexes in seawater and associates with particles by adsorption (Mauch-line and Templeton, 1963). When radiocerium was added to natural seawater, it became associated with suspended matter, especially that with apparent particle diameters of 0.02 to 0.1 fim (Carpenter and Grant, 1967). When ionic radiocerium was added to filtered seawater at pH > 6.0, it hydrolyzed and formed complexes with hydroxide, chloride, or other anions in seawater and went on to form particles (Hirano et al., 1973). Adsorption of radiocerium onto suspended particles has also been noted after its release to freshwater ecosystems (Beninson et al., 1966). 

Seawater, available at the premises of the Royal Netherlands Navy s Chemical Laboratory, was sub-sampled. This coastal seawater was initially collected at about lOm water depth, in the nearby tidal channel (Marsdiep). The water passed a sand filter directly after collection, in order to remove larger particles and organisms. About lOm seawater was thus collected in a glass-fibre tank and transported to the TNO Laboratory for Applied Marine Research, at Den Helder, where it was contained in a concrete basin, treated with a metal-free paint. In this basin the suspended particulate matter was allowed to settle for 4 weeks. This water served as source material for the candidate CRM, and had a salinity of 28 %o. 

It is difficult to obtain reliable values of plutonium concentration in natural aquatic systems as it is very low, approximately 0.001 dpm per liter sea water. Moreover, the plutonium associated with suspended particles may be more than an order of magnitude greater than that in true solution. In tests of water from the Mediterranean Sea, filtration (0.45 /tm) reduced the concentration of plutonium by a factor of 25. In laboratory tests with filtered seawater to which plutonium was added, after one month the total concentration of Pu was 1.3 X 10 M, but only 40% (5 X10" M) was in solution as ionic species and the other 60% was probably in colloidal form. The mean residence time of Pu in the water column is proportional to the concentration of particulate matter. As a consequence, > 90 % of the Pu is rapidly removed from coastal waters whereas, in mid-ocean waters where the particulate concentrations are lower, the residence time for Pu is much longer. 

In seawater, most TE occur primarily as dissolved including colloidal species (< 0.45 or <0.4 pm see Chapter 2). Therefore, in the analysis of TE filtration is often avoided, to minimize contamination or losses due to adsorption. Exceptions are made, however, when the suspended particulate matter (SPM) itself or selected elements are studied for which the particulate species constitute a significant fraction of the total concentration in seawater (c.g., Fe, Pb). The SPM should also be separated when its concentration increases to 1 mg/L and thus impacts the accuracy and precision of the methods used to determine the dissolved TE fractions. Higher SPM concentrations are often observed in mixing zones of estuaries, in coastal waters, in the euphotic layer during plankton blooms or in intermediate turbidity layers and close to the bottom. Particle fluxes of TE in the ocean are best measured directly" with sediment traps deployed at different water depths (see Chapter 1). 

Some rivers, such as the Yellow River (China) can carry as much as several grams per litre of suspended solids [7]. Lakes and oceans can be considered to be huge colloidal suspensions, typically containing 0.5 -1.5 mg 1 of suspended fine solids. The near-colloidal-sized fraction, particles of up to about 0.1 pm in diameter, may be able to remain in suspension for considerable periods of time, days to weeks, even in quiescent waters. This fraction is called the wash load [6]. Table 9.2 shows the terminal sedimentation velocities of sand, silt and clay particles in seawater [8]. It can be seen that while the sand particles are likely to settle out near then-point of entrance to the ocean, the clay particles could, in principle, be transported almost anywhere in the world before sedimenting out. In addition to being suspensions, oceans can also comprise foam systems where they contain free gas bubbles (which can result from volcanic gases or the decomposition of organic matter). 

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