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This indicator is the annual median concentration of chlorophyll in each distinguishable body of marine and estuarine water. The concentration of the photosynthetic pigment chlorophyll a (referred to as chlorophyll) in marine waters is a proven indicator of the biomass of microscopic plants such as unicellular algae. It can be employed to give an estimate of primary production. Increases in the annual median concentrations of chlorophyll in individual water bodies may be related to changes in nutrients, and to increasing eutrophication.
In the Tasmanian Aquaculture and Fisheries Institute (TAFI) study (Murphy et al. 2003), water quality parameters were measured at 22 Tasmanian estuaries between July 1999 and June 2000. The estuaries included in the study were chosen to reflect a range of physical estuarine groups (e.g. barrier, river, inlet, lagoon), estuaries of different conservation significance (Edgar et al. 1999) and location within biogeographic regions. In addition, potential relevance to government agencies and community groups, as well as accessibility, influenced the selection of estuaries. Large, previously studied estuaries such as the Derwent, Tamar and Huon Rivers and Bathurst and Macquarie Harbours were deliberately not included in the study. Due to accessibility, estuaries in the south-west of the State and the King and Furneaux islands were not included in the study. Relatively low rainfall characterised the climate across most of Tasmania during the study period. However, estuary sampling was also conducted following some large floods. Floods occurred on the central north coast (Don and Mersey Rivers, Port Sorell) in early August 1999 and on the north-east coast (Ansons Bay, Grants Lagoon, Douglas River) in mid January 2000. Heavy rainfall also preceded sampling in the south-east (Browns and Catamaran Rivers, Cockle Creek) in mid July 1999. Therefore, for most estuaries, a broad range of conditions were captured in the sampling, something that would normally occur only over longer periods (Murphy et al. 2003). The table shows mean values (each sampling event) and yearly median values for chlorophyll a from surface waters, for each estuary. ANZECC (2000) default trigger levels for estuarine water quality contain no Tasmanian data. Therefore, draft indicator levels, referenced against the baseline values from the TAFI study, are provided for Tasmanian estuaries. Draft indicator levels are based on the likelihood of exceeding these values during a single sampling event, using data from all estuaries. Depending on the scale of future studies, alternative indicator levels could be based on a bioregional or estuary scale. However, given that the data are from surface waters and vertical stratification occurs in most estuaries, indicator levels should be applied with caution to samples taken from other depths. Mean chlorophyll a (µg l-1) concentrations and yearly medians for estuaries, July-August 1999 (JA99) to May-June 2000 (MJ00), by bioregion and sampling event Sample Median Bioregion Estuary JA99 SO99 ND99 JF00 MA00 MJ00 (JA99-MJ00) Boags East Inlet 0.1 0.0 4.4 0.6 0.0 0.2 0.0 Black River 0.2 0.1 0.8 0.9 0.7 0.2 0.4 Mersey River 0.8 0.3 3.1 0.9 0.7 0.2 0.5 Don River 2.5 0.7 25.6 17.6 0.7 0.1 0.8 Port Sorell 1.3 1.2 1.6 0.9 0.5 0.3 0.8 Little Musselroe River 1.6 0.6 0.0 33.2 2.5 2.0 1.1 Boobyalla Inlet 1.7 1.4 0.8 4.1 1.1 0.8 1.2 Duck Bay 2.9 2.0 1.4 1.4 1.5 1.7 1.5 Bruny Cloudy Bay 2.3 0.9 0.3 0.9 0.6 1.0 0.7 Browns River 2.4 0.7 2.5 7.0 9.2 4.7 2.6 Davey Catamaran River 0.0 0.6 0.5 0.1 0.1 0.0 0.0 Cockle Creek 0.7 1.2 0.6 0.1 1.1 0.8 0.4 Franklin Pieman River 0.0 0.0 0.0 0.1 0.2 0.0 0.0 Nelson Bay River 0.0 0.1 0.0 3.4 1.5 0.0 0.0 Arthur River 0.0 0.1 0.0 0.6 0.1 0.0 0.0 Freycinet Douglas River 0.1 1.0 0.7 0.0 0.3 0.0 0.0 Earlham Lagoon 0.9 0.2 0.5 0.8 0.6 0.1 0.4 Great Swanport 0.3 0.4 0.1 0.9 0.6 1.0 0.5 Little Swanport 0.7 0.3 1.2 2.4 6.1 1.1 1.1 Grants Lagoon 1.3 1.0 0.4 3.0 1.2 0.8 1.2 Meredith River 6.0 2.2 8.8 3.2 10.0 0.8 1.9 Ansons Bay 20.3 8.8 5.7 11.2 7.5 2.2 5.3 low medium high very high 0.0 to 2.0 2.1 to 5.0 5.1 to 10.0 >10.0 Source: Murphy et al. 2003
Key indicator for estuaries and the sea E+S3.17 (Ward et. al. 1998) |
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