Gregory River (Drainage basin 137)

DSITIA staff sample Chlorophyll-a, observe Secchi depth and measure physiochemical depth profiles at three Gregory River tidal estuarine sites and sample nutrients at one site.

Period of operation: From 1993 to 2013
Region: Central Coast Queensland
Australian drainage basin: 137
Water body: Tidal estuarine sections of the Gregory River at mid-stream monitoring sites
Water column profile depth: Monitoring starts at a depth of 0.2m near the water surface and the water column profile is monitored at regular 2m intervals plus the last available depth greater than 0.5m above the bottom
Secchi depth: AS 3550.7-1993
Algal biomass Chlorophyll-a : APHA & AWWA (1998) monochromatic method [Ref: Lorenzen, Carl J. (1967) Limnology and Oceanography, Vol12: pp343-346.]
in situ physiochemical profile: Currently the in situ physiochemical depth profiles are measured with YSI model 6-Series Sondes such as the YSI 6920 V2 handheld multi probe sonde connected to a data recorder. The YSI 6920 V2 has been in use since 2011. The YSI 610 – 650 was used from 1998 to 2012. The YSI 3800 was used from 1993 to 2001. Up to 1998 a range of Martek, Hydrolab and TPS instruments as well as some earlier YSI models were used. [Ref YSI Multiparameter Water Quality Sondes User Manuals]
- Dissolved Oxygen concentration (mg/L)
- Dissolved Oxygen % saturation (%)
- pH
- Salinity (PSU)
- Specific Conductance at 25 deg C (mS/cm)
- Temperature (°C)
- Turbidity (NTU)
Surface nutrient samples: APHA (1998) Queensland Health Forensic and Scientific Services photochemical methods using a flow injection analyser (FIA). A laboratory method change in 1997 improved the Kjeldahl digestion of samples resulting in a lower Organic Nitrogen detection limit. In 1999, a change in the laboratory instrument has led to slightly lower and more stable Nitrogen Oxides and Filterable Reactive Phosphorus results. A 1999 change replaced the higher temperature and stronger acid concentration Kjeldahl digestion with Persulphate Oxidation digestion which in some circumstances will extract less P from particulates with the effect of an apparent small reduction in Total Phosphorus results. These changes are mostly apparent at low levels and the differences lie within the precision range of the method.
- Ammonia as N (mg/L)
- Organic Nitrogen as N (mg/L)
- Nitrogen Oxides as N (mg/L)
- Total Nitrogen as N (mg/L)
- Filterable Reactive Phosphorus as P (mg/L)
- Total Phosphorus as P (mg/L)