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Chemical Factors
Published in Michael J. Kennish, Ecology of Estuaries Physical and Chemical Aspects, 2019
Because seawater is an electrolyte and conducts an electric current, salinity can be measured by electrical conductivity. Chlorinity measurements are less accurate (± 0.02% for 32 to 38‰) than conductivity techniques (± 0.003 ‰) of salinity estimation.11 Therefore, salinity is now more frequently measured by a salinometer, which records conductivity, rather than by volumetric titration of chlorinity. Measurements of density (with a hydrometer), the refractive index of seawater (with a refractometer), and freezing-point depression provide alternate methods of estimating salinity.
Assessment of biogrowth assemblages with depth in a seawater intake system of a coastal power station
Published in Biofouling, 2021
T. Subba Rao, P. S. Murthy, P. Veeramani, D. S. Narayanan, R. Ramesh, B. N. Jyothi, D. Muthukumaran, M. Murugesan, A. Vadivelan, G. Dharani, J. Santhanakumar, G. A. Ramadass
The seawater temperature was measured directly using a standard mercury thermometer with an accuracy of ± 0.1°C. Salinity was estimated by salinometer, the principle being based on the measurement of conductivity ratio of a sample of seawater with a standard reference. Using an internal reference, the conductivity signal of the sample and standard are transformed into a ratio, which is twice the conductivity value. The internal reference was standardized regularly using standard seawater (Strickland and Parsons 1969). For dissolved oxygen measurement, seawater from each station was collected in an amber coloured BOD (biological oxygen demand) bottle and dissolved oxygen in the sample was fixed as a precipitate by adding 1ml each of Winklers A and B solutions and transported to the laboratory under dark conditions. Dissolved oxygen was measured by the titration method (Strickland and Parsons 1969). The nitrite and nitrate nitrogen of the samples was determined sequentially as per standard procedure (Strickland and Parsons 1969). Vanadium (III) chloride is used for the quantitative reduction of nitrate to nitrite and when the Griess reagent (sulfanilamide and N-(1-naphthyl)-ethylenediamine) is added to the reduced solution a red precipitate is formed. The absorbance of the coloured solution was measured at 540nm in a spectrophotometer [Shimadzu: Model-UV-2700i]. Concentrations of other inorganic nutrients such as phosphorus and ammonium were analyzed spectro-photometrically. Other parameters such as silica, seston, combustible matter, particulate organic matter and chlorophyll-a were assayed as per standard procedures of seawater analysis (Strickland and Parsons 1969). Diatom counts were made using a haemo-cytometer, while total bacterial counts were made using Zobel marine agar (Strickland and Parsons 1969; Rao et al. 2009).