Changes in water quality and phytoplankton communities in the Lower River Murray in response to a low flow-high flow sequence

Historical data on river flow, nutrient and dissolved organic carbon (DOC) concentrations and phytoplankton were investigated to evaluate how these parameters change between low flow and high flow periods. Data were provided by SA Water, the Murray-Darling Basin Authority and the South Australian Environment Protection Authority. The databases were combined and data were plotted to identify sites and parameters where sufficient data existed for investigation. Several sites in the South Australian section of the River Murray were included and sites upstream were included in order to identify sources of nutrients and phytoplankton. Not all sites had sufficient data for all parameters, but sites investigated were: • River Murray at Merbein – RM-1 – upstream of junction with Darling River; • Darling River at Burtundy – DR –upstream of junction with River Murray; • River Murray at Lock 9 – RM-2 – downstream of Murray-Darling junction; • Rufus River outlet – RR – outlet of Lake Victoria; • River Murray downstream of Rufus River outlet – RM-3; • River Murray at Lock 5 – RM-4; • River Murray at Lock 3 – RM-5; • River Murray at Waikerie – RM-6; • River Murray at Morgan – RM-7; • River Murray at Murray Bridge – RM-8; and • River Murray at Tailem Bend – RM-9. These data were obtained from surface water grab samples. Samples for dissolved nutrients and DOC were filtered through 0.45 μm membrane filters upon collection and stored frozen. Samples for TP and TKN remained unfiltered and were stored frozen before digestion. All water samples were analysed by the Australian Water Quality Centre, a National Association of Testing Authorities accredited laboratory using standard methods. Parameters measured were DOC, oxidised nitrogen (nitrate plus nitrite; NOX), ammonia (NH4), total Kjeldahl nitrogen (TKN), total nitrogen (TN), filterable reactive phosphorus (FRP), total phosphorus (TP), silica (Si, molybdenum reactive fraction), chlorophyll a (chl-a) and phytoplankton cell counts. On occasions when TN data were not provided concentrations were calculated as the sum of TKN and NOX. Additional relevant water quality parameters were also investigated where appropriate data existed. These parameters included dissolved oxygen and electrical conductivity. Phytoplankton data were not always distinguished to species or genus and so presentation of the data were limited to the available groupings.

Geospatial Location

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