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Brief description Since 2003, ambient water quality monitoring has been carried out on a monthly basis at up to 28 sites throughout the Derwent estuary by Norske Skog Boyer, Nyrstar Hobart and the State Government (EPA/Derwent Estuary Program-DEP). Monitoring is carried out by three different boat-based sampling parties, but is co-ordinated to occur on the same day each month. At each site, in-situ field measurements are taken using calibrated sensors for temperature, salinity, pH, dissolved oxygen and turbidity. Water clarity is also measured using a secchi disk. Surface and bottom water samples are collected for analysis of true color, total suspended solids(TSS), total and dissolved nutrients, organic carbon and zinc. At most sites, depth integrated samples are also collected for chlorophyll a using a plastic tube. In the middle and outer estuary , surface samples are collected by hand, while bottom samples are collected using a Niskin bottle. Pumps are used in the upper estuary site to fill up the bottles. All water samples are analysed at Analytical Service Tasmania, a National Association of Testing Authorities-accredited laboratory. A complete description of the program is available in the "State of the Derwent Estuary 2009" report as well as on the DEP website (links below).
The DEP monitoring program achieves Quality Assurance (field sampling and laboratory activities are carried out in a way that ensures the generation of accurate and reliable results) through the use of standard operating procedures that are used by the three different sampling operators. The majority of collected water samples are analysed by Analytical Services Tasmania (AST), a NATA-accredited laboratory, to ensure that consistent analytical methods are used. For those parameters measured using field-based equipment(salinity, temperature, dissolved oxygen, pH and chlorophyll-a), regular inter-calibration exercises have been carried out between operators.
Quality Control (activities or techniques to ensure that all quality requirements are being met) is achieved by the use of specific control samples, including the use of an artificial seawater standard for use of 'nutrient field blanks'(treated like a collected sample and filtered in the field) and 'nutrient trip blanks' (sample bottles that are not opened, but are handled and stored in the same manner as other samples). 'Metal field blanks' and 'metal trip blanks' are also used, consisting of deionised water.