Large-volume in situ filtration

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Krishnaswami S, Lai D, Somayajulu BLK (1976) Large-volume in-situ filtration of deep Pacific waters Mineralogical and radioisotope studies. Earth Planet Sci Lett 32 420-429 Krishnaswami S, Mangini A, Thomas JH, Sharma P, Cochran JK, Turekian KK, Parker PD (1982) °Be and Th isotopes in manganese nodules and adjacent sediments nodule growth histories and nuclide behavior. Earth Planet Sci Lett 59 217-234... 

A Multiple-Unit Large-Volume In Situ Filtration System for Sampling Oceanic Particulate Matter in Mesoscale Environments... 

The multiple-unit large-volume in situ filtration system consists of 12 pump-filter units, an electromechanical cable, a current monitoring and switching box interfaced to an Apple II control computer, a drum winch, and a level wind (Figure 1). 

Figure 1. Block diagram of the multiple-unit large-volume in situ filtration...

We will present flow-rate, particulate dry weight, and particulate-calcium data from selected MULVFS and LVFS stations to (1) further document the sampling performance of the MULVFS and (2) demonstrate one application of large-volume in situ filtration to understanding the processes governing the distributions of particulate matter in a productive environment. Detailed presentation and interpretation of warm core ring data are outside the scope of this chapter. 

An example of the usefulness of large-volume in situ filtration is illustrated by the particulate Ca data collected in the interdisciplinary Warm Core Rings program. Particulate Ca in the < 53-pm size fraction showed a factor-of-three drop in concentration in the thermostad of WCR 82-B be-... 

A more effective approach to determining the concentration of HCs on suspended sediments is to separate the sediment from the water column and analyze it directly. Although there are several approaches to this, as described by Horowitz (1995), the least expensive and most efficient method for use on low-TSS karst spring water is large-volume filtration (LVF). This involves in situ filtration of the spring water using an apparatus that allows both a sufficient amount of material to be collected for analysis and the material in a form that lends itself to analysis. 

Filtration. Except for the in situ pumps, large-volume filtration has to be performed on board, for which a variety of pressure or suction techniques is available (compare with Chapter 2 and Chapter 12, Section 12.6). In order to prevent the loss of any particulate or dissolved activity, the risk of settling of particles and adsorption/adhesion to walls of the sampling bottles has to be considered. If a water pump is used before the filter, it should be carefully checked, e.g., by microscopy, whether the pump leaves the particles intact. Centrifugal pumps are notoriously harmful to plankton. An elegant filtration method has been described by Dehairs et al. (1997). A 30L calibrated Perspex cylinder with a conical bottom is filled with the sample obtained from a Rosette cast. The outlet is connected to a 142 mm Teflon filtration unit. Controlled (50-100 kPa) air pressure is applied to a series of these units from a simple small compressor. 

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