About the Catchment Area : Issues & Problems

Water quality monitoring in the
Onkaparinga Catchment Water Management Board's Area

The Onkaparinga Catchment Water Management Board (OCWMB) regularly undertakes a program of water quality and biological monitoring. This monitoring covers a total of 32 sites within the main Onkaparinga River Catchment and the coastal catchments within the Board’s area including the Field River, Pedler Creek, Christies Creek, Sellicks Creek, Maslin Creek, Pt Willunga Creek and the Washpool catchment.

The monitoring program consists of:

• Water quality sampling for a range of parameters on a monthly basis, including:
  - Plant nutrients
  - Heavy metals
  - Physical parameters (salinity, turbidity, etc.)
  - Faecal bacteria
• Biological sampling three times per year, mainly involving the macroinvertebrate fauna (insects, molluscs, crustaceans, etc.) as bioindicators of riverine health and general water quality status.

Click here to read more about the things that are measured (parameters) when monitoring the quality of water in our creeks and rivers.

Click here to read about the impact that the various parameters have on the health of our waterways

Program Objectives
Overall, the monitoring programme objectives are defined as:

• Provide a qualitative and quantitative assessment of the water quality status of watercourses.
• Identify any changes or trends with time in key water quality indicators.
• Provide data to assist in the long term ecologically sustainable development of water resources.

Review of the Boards monitoring program
No monitoring programme should continue indefinitely without periodic review. In November 2001, Eco Management Services Pty Ltd was commissioned by the Board to collate and briefly review trends in the monitoring results to date.

The findings

Water quality in relation to the protection of aquatic ecosystems
In the upper and lower catchments there is a degree of nutrient enrichment, which is to be expected in view of its largely agricultural nature. The effects of horticulture and mixed agriculture (orchards, grazing, etc.) are evident in Cox Creek and Lenswood Creek respectively, and the Hahndorf Waste Water Treatment Plant effluent discharge may also account for high ammonia/ Total Kjeldahl Nitrogen/ nitrate levels in Hahndorf Creek.

In general, in the upper and lower catchments heavy metals appear to be low except for zinc which may be due to natural background levels. All locations occasionally have low dissolved oxygen levels.

In the lower Onkaparinga River, below the effect of River Murray water, input is apparent with relatively high turbidities but lower nutrient levels. The concentration of nutrients in catchment runoff is higher. The loads to the reservoir depends on the relative volumes of catchment runoff and River Murray water.

Turbidity levels in the Upper Onkaparinga above Mt Bold Reservoir are relatively high and above objective levels for inputs into the reservoir, again probably due to River Murray input.

Water quality in relation to recreation
The available results indicate that throughout the Board’s area faecal coliform bacteria can occur in large numbers. This would prevent primary recreation activities that involve contact with the water. In many instances even secondary (passive) recreation would be affected. However, because there have been limited sampling in relation to this, in those areas where low numbers of faecal coliform were found, it could not be assumed that this is the case all the time.

The high turbidity in some of the coastal streams and in the Onkaparinga River would also affect contact recreation use.

The guidelines for toxicants (heavy metals) are the same as for domestic supply, and the comments made above also apply.

The coastal catchments appear to have higher concentrations of metals, turbidity and nutrients. This is likely due to urban stormwater runoff and possibly to the short term effects of construction of the new Southern Expressway.

Water quality in relation to domestic water supply
All waters are subject to agricultural and urban stormwater runoff to some degree. Typically numbers of faecal micro-organisms (faecal coliforms) are high but highly variable. Consequently, all waters should be considered unsuitable for direct consumption without disinfection. In the Onkaparinga River, at the nearest sampling site to the inlet to the Mt Bold reservoir, the limited data suggests that numbers of faecal coliforms are generally below the recommended objective level for the reservoir intake.

Concentrations of phosphorus at most sites exceed the recommended objective level for the reservoir.

Heavy metals are generally below those recommended for human consumption except for the Field River and Christie Creek where arsenic levels exceed guidelines.

Water quality in relation to agricultural use
In most areas water is suitable for stock water use with regards nutrient (nitrite, nitrate) and heavy metals. The exception is Willunga Creek which has high nitrate levels. In some areas the range of salinity would restrict its use for some stock.

With respect to faecal coliforms, high numbers would likely occur, particularly in storm events, affecting suitability for this use.

In most areas waters are suitable for irrigation use, but the above comments for salinity and numbers of faecal coliforms for stock also apply.

Biological Monitoring Results
Six surveys at 32 sites have now been undertaken over the last two years. As required in the study brief, a preliminary review of the data indicates:

• During the course of the surveys, there is an apparent increase in species richness at most sites from April 1999 to October 2000. However, this is considered most likely due to differences in flow patterns and the onset of flows in the watercourses most of which are ephemeral in nature.

• The upper catchment (above Mt Bold Reservoir) sites including the main river and tributaries are generally very diverse, except for Cox Creek and on some occasions in Lenswood Creek. The lower catchment freshwater sites including McKreath Creek and Kangarilla Creek are also relatively diverse. The coastal catchment sites and the estuarine sites in comparison have a reduced diversity.

• At many sites there is a high abundance of individuals, particularly of indicator species. These are species that are tolerant of low oxygen conditions that can occur as a result of a high organic load, or can increase in numbers dramatically to take advantage of an increased food supply causes by nutrient enrichment.

• In the upper catchment and lower catchment freshwater sites, the species richness, abundance and indicator species data is consistent with the observed water quality data, where elevated nutrients occur, and where low oxygen levels also occur. The fact that many of these sites still have a diverse community suggests the absence of toxicity. In situations where species richness and abundance is affected by toxicity there would be a loss of species with only the most tolerant remaining.

• In the coastal catchments, the lower species richness observed may be due in part to the nature of these smaller ephemeral watercourses. It may also reflect the effects of urban development in the catchments and recent construction activities. Many of these sites were rated poor because of turbidity and had elevated concentrations of nutrients and heavy metals. However, some of the elevated metals, e.g. zinc, may be due to natural background levels. Because of the water hardness and pH, only a small fraction is likely to be bioavailable and toxic.

• The low diversity in the Onkaparinga Estuary is not considered a reflection on the water quality status of the estuary, but is more likely to be due to sampling methods. Being an estuarine environment with very different characteristics to other watercourses in the Board’s area, other sampling strategies would be more appropriate.

Click here to read more about the things that are measured (parameters) when monitoring the quality of water in our creeks and rivers.

Source: From a report “Review of Ambient Monitoring Data” by ECO Management Services PTY LTD, November 2001