Overview of Trends

The results of the monitoring program from 1981 to 2009 indicate that:

  • The overall environmental health of the Lake is generally good.
  • Turbidity has decreased and now remains in a consistently lower range. Drought conditions have probably been a factor in producing these low levels.
  • Phosphorus concentrations have gradually decreased in the Lake, probably because of improved catchment management including improvements to sewage treatment plant discharge from the Queanbeyan Wastewater facility, and low inflows because of drought since 2002.
  • Nitrogen concentrations have also decreased gradually, but not as markedly as phosphorus. The decrease in both nutrients has probably been due to the same factors.
  • Total algal cell concentrations have remained within the same general range, with cyanobacterial cell concentrations generally below the high alert level for recreational exposure according to the Australian Government (2008) and ACT Government (2010). However, the intensity of late summer cyanobacterial blooms has increased in recent years.
  • Chlorophyll-a values have decreased and all primary water contact areas are now generally below the benchmark values for other ACT waters (ACT Government, 2011).
  • Conductivity had remained relatively consistent prior to 2003. However, since December 2002, there has been an upward trend. This is likely to be due to drought conditions.
  • pH values have remained in the same general range, and within an acceptable limit for this type of water body.
  • Bacterial counts have generally remained within the guideline values but have had some significant exceedences of undetermined cause.
  • The Lake contains high levels of some metals, particularly in the sediments.
  • Averaged dissolved oxygen concentrations were at their maximum during the late winter months, and at their minimum during the late summer months.

Generally, observed values for the above mentioned water quality characteristics were:

  • Turbidity, generally below 40 NTU in East Basin and generally below 20 NTU in West Lake (since 2000).
  • Suspended solids, usually below 50 mg/L in East Basin and below 25 mg/L in West Lake.
  • Total phosphorus concentrations, usually below 0.08 mg/L in East Basin and below 0.06 mg/L in West Lake (although concentrations in the past were generally 2–3 times higher).
  • Total nitrogen concentrations, usually below 1.4 mg/L in East Basin and usually below 1.0 mg/L in West Lake (although concentrations in the past were generally 20–30% higher).
  • Ammonia concentrations, usually below 0.1 mg/L for both East Basin and West Lake.
  • Cell concentrations of cyanobacteria have increased to levels in excess of 10,000 cells/mL since 2005.
  • Chlorophyll-a, usually below 10 μg/L for West Lake (although higher in the past), and usually below 30 µg/L for East Basin.
  • Conductivity in West Lake and East Basin generally below 400 μS/cm.
  • pH in the range of 7.0 to 9.0, with a mean Lake value of 7.8 (±0.4).
  • Bacterial counts, (faecal coliforms) usually below 150 CFU/100mL in West Lake and usually below 1000 CFU/100mL in East Basin.
  • Averaged dissolved oxygen concentrations for Central Basin, West Lake and Scrivener Dam ranging with depth from 1.4-8.5 mg/L in the warmer months and from 6.6-11.1 mg/L in the cooler months.

General

Routine water quality monitoring in Lake Burley Griffin started in December 1981 and with some minor modifications has been continued to the present day by ECOWISE Australia Pty Ltd, trading as ALS Water Resources Group. Public health monitoring is undertaken by ACT Health Protection Service. Intensive monitoring of specific events or at specific locations is undertaken by a wide range of organisations (including government agencies, research organisations and community groups).

The results of various monitoring programs and research projects are summarised in a number of previous reports (ACT Electricity and Water, 1988; ACT Parks and Conservation Service, 1988a and b; Burgess and Olive, 1975; Cullen, Rosich and Bek, 1978; Department of Housing and Construction, 1982 and 1984; EcoChemistry Laboratory, 2003; Ecowise Scientific and Aquatech, 1995; Gutteridge, Haskins and Davey, 1982; Hillman, 1980; Maher et al. 1992; Nagy and Butters, 1987 and 1988; Nazer, 1986; Norris, 1983; Office of ACT Administration, 1987; Scientific Services and Aquatech, 1994). Collectively, these research and monitoring programs contain a considerable amount of valuable information on Lake Burley Griffin water quality.

Most of the monitoring effort has used the following four main sites, and generally a monthly sampling frequency:

  • East Basin (site 529).
  • Central Basin (site 530).
  • West Lake (site 504).
  • Scrivener Dam (site 507).

A fifth site was added in April 2009:

  • West Lake (2) (site 505).

Refer to Appendixes A and B for location of sites.

At each site, both surface and tube samples have been collected. Surface samples (taken at 0.3 m below the surface) were generally used for bacteriological analysis. Tube samples, which consisted of a composite of the top 5 m of the water column, were used for chemical and algal analyses. The only exception to this was East Basin (site 529), where only surface samples were taken, because the site is relatively shallow.

The remainder of this section provides an overall assessment of the results from the past 28 years of monitoring focusing on:

  • Turbidity and suspended material.
  • Phosphorus.
  • Nitrogen.
  • Algae and chlorophyll-a.
  • Conductivity and pH.
  • Bacteria.
  • Metals.
  • Dissolved oxygen.

Also included are water column depth profiles taken in 2009 and 2010 in order to better understand and manage blue-green algal blooms within Lake Burley Griffin.

Turbidity and Suspended Material

Background

Turbidity is used as an indication of the amount of suspended material in the water, and is important for environmental, public health and aesthetic reasons.

Turbidity is important environmentally, as it reduces the clarity of the water and thus the amount of sunlight available for algae and aquatic plants. Also, nutrients such as phosphorus and nitrogen are often attached to the surface of suspended material.

Turbidity is also important in terms of public health, as bacteria and pollutants (such as heavy metals) are often attached to the surface of suspended material.

Furthermore, turbidity is an important aesthetic measure, particularly for recreational areas, as it is an indication of water clarity.

Suspended material and turbidity can come from the surrounding catchment (as part of rainfall runoff during storm events), or it can be resuspended Lake sediment (due to wind mixing in shallow areas).

Like most lakes in south-east Australia, Lake Burley Griffin has always been a relatively turbid lake. The Lake's catchment contains:

  • Large areas of agricultural land (used primarily for grazing).
  • Large areas of urban land (involving residential and light commercial uses).

Such relatively high levels of turbidity can introduce significant amounts of nutrients into a lake, but can also reduce the ability of algae to use such nutrients (due to reduced light penetration into the water column). The relatively high turbidity can also serve to reduce the aesthetic value of the water for recreational activities (such as swimming or boating) and potential for growth of aquatic macrophytes.

The Lake also experiences a considerable amount of wind induced sediment resuspension. This is especially the case in East Basin, which is relatively shallow (less than 3 metres) over large parts of its area, and relatively exposed to strong westerly winds (Scientific Services and Aquatech, 1994).

General Trends

Turbidity is measured in nephelometric turbidity units (NTU), and its monitoring in Lake Burley Griffin commenced in 1981. Information is generally available from four sites (five sites from April 2009) in the Lake and usually at a monthly frequency.

From the collected information (EcoChemistry Laboratory, 2003; Ecowise Scientific and Aquatech, 1995; Office of ACT Administration, 1987) and more recent water quality data, it is possible to indicate the following general trends:

  • Turbidity is higher in the shallower eastern parts of the Lake than in the deeper western parts. This is to be expected, as suspended solids settle out on entering most lakes, and indeed one of the intended functions of the Lake was to serve as a settling basin for catchment runoff.
  • Turbidity is higher just after stormwater inflow into the Lake. Once again, this is to be expected, as stormwater runoff contains higher levels of suspended material, resulting in higher turbidity values.
  • Turbidity is higher just after strong windy periods, especially in the shallower eastern parts of the Lake. This is largely the result of wind resuspension of bottom sediments (Scientific Services and Aquatech, 1994).
  • Turbidity values in East Basin are generally below 40 NTU, whereas in West Lake values are generally below 20 NTU.
  • Suspended solids show very similar patterns to turbidity, with values in East Basin generally below 50 mg/L, whereas in West Lake values are generally below 25 mg/L.

Turbidity values for East Basin (site 529 surface) and West Lake (site 504 tube) are shown in figures 1A and 1B respectively for the period from 1981 to 2009. The figures show that turbidity in East Basin has remained in the same general range over the 28 years of available monitoring data. However, the turbidity in West Lake has decreased since 2000. Turbidity values in East Basin are generally below 40 NTU, whereas in West Lake values are generally below 20 NTU. The turbidity value for undisturbed sites of 20 NTU cited in the ANZECC/ARMCANZ Guidelines (2000) is shown on the graph and has generally been achieved in more recent years. Given the lower comparative turbidity a revised water quality benchmark value for turbidity in East Basin could be 40 NTU, and for West Lake 20 NTU.

The water quality standards in other parts of the ACT for water based recreational swimming areas state that turbidity should not be objectionable. The standard for water based recreational boating areas states the same condition (ACT Government, 2011).

Corresponding values for suspended solids are 40 mg/L in East Basin and 20 mg/L in West Lake. These will be discussed in more detail in Development of Benchmark Levels for Water Quality.

Figure 1: Turbidity (NTU) values in Lake Burley Griffin for 1981–2009.

 

A.	East Basin Turbidity 1981 to 2009, is  graph of turbidity levels in East Basin over this period expressed in nephelometric turbidity units (NTU) in relation to the ANZECC Guideline of 20 NTU (represented by a red line across the graph).  Turbidity values are generally below 40 NTU, with some spikes in the mid 1990s.

A. East Basin (Site 529 surface) Turbidity 1981 - 2009.

West Lake Turbidity 1981 to 2009, is a graph of turbidity levels in West Lake over this period expressed in nephelometric turbidity units (NTU) shown in relation to the ANZECC Guideline of 20 NTU (represented by a red line across the graph).  Turbidity values have been higher than this level in the past, peaking in the mid 1990s, but generally below the ANZECC guideline level from 2000.

B. West Lake (Site 504 tube)Turbidity 1981 - 2009.

Phosphorus

Background

Phosphorus is an essential nutrient in aquatic ecosystems, particularly to photosynthetic organisms such as algae and macrophytes. However, high concentrations of phosphorus increase the amount of biological activity. Consequently, phosphorus promotes algal activity and this in turn can result in serious water quality problems. During algal blooms, the water becomes unsuitable for a number of recreational activities, whereas after a large algal bloom, the decaying material can deplete the oxygen levels in the water column (and thus result in fish deaths).

Phosphorus originates from a number of sources including:

  • soils in the catchment;
  • wastewater discharges;
  • fertilizers applied to agricultural land or suburban gardens;
  • waterbirds defecating into or near the water body; and
  • releases from lake sediments if oxygen becomes depleted in the overlying waters.

In environmental waters, both total phosphorus and filterable phosphorus concentrations are measured. Filterable phosphorus is generally regarded as the fraction that is biologically available in the short term. In Australian lakes and rivers, filterable phosphorus usually represents 30–60% of the total phosphorus in the water column.

General Trends

Total phosphorus and filterable phosphorus concentrations are both measured in terms of mg/L. Generally, both have been monitored in Lake Burley Griffin since 1981, at four sites (five sites from April 2009) and usually at a monthly frequency.

From the collected information (EcoChemistry Laboratory, 2003; Ecowise Scientific and Aquatech, 1995; Office of ACT Administration, 1987) and more recent water quality data, it is possible to indicate the following general trends:

  • Both total phosphorus and filterable phosphorus concentrations have been gradually decreasing since the mid 1980s. The main reason for this decrease has been a reduction in the amount of phosphorus entering the Lake from the Queanbeyan Wastewater Treatment Plant. This plant was upgraded in the mid 1980s and its phosphorus discharges were reduced by over 90%. Other contributing factors have included a range of catchment management and lake management practices (such as the harvesting and removal of aquatic plants from some areas).
  • Total phosphorus and filterable phosphorus concentrations are higher in the shallower eastern parts of the Lake, than in the deeper western parts. This is to be expected, as higher suspended solids concentrations (caused by stormwater runoff and wind resuspension of sediment) generally correlate with higher phosphorus and nitrogen values.
  • Total phosphorus concentrations are higher just after stormwater inflows into the Lake.
  • Total phosphorus concentrations are higher just after strong windy periods, especially in the shallower eastern parts of the Lake.
  • Total phosphorus concentrations in East Basin are generally below 0.08 mg/L, whereas in West Basin values are generally below 0.06 mg/L.

Filterable phosphorus concentrations in East Basin and West Basin are generally below 0.02 mg/L.

Total phosphorus concentrations for East Basin (site 529 surface) and West Lake (site 504 tube) are shown in figures 2A and 2B respectively for the period from 1981 to 2009. The water quality standards in other parts of the ACT for water based recreational activities and for aquatic habitat indicate a value of <0.1 mg/L total phosphorus (ACT Government, 2011). The values observed for Lake Burley Griffin are generally below this level. Total phosphorus concentrations were consistently below 0.06 mg/L but well above the 0.05 mg/L suggested in the ANZECC/ARMCANZ (2000) for undisturbed sites. The benchmark concentration of 0.1 mg/L for total phosphorus should be lowered to 0.06 mg/L. This will be discussed in more detail in Development of Benchmark Levels for Water Quality.

Filterable reactive phosphorus concentrations for East Basin (site 529 surface) and West Lake (site 504 tube) are shown in figures 3A and 3B respectively. Filterable reactive phosphorus concentrations have been generally below 0.01 mg/L in recent years. However, this is biologically available phosphorus and would be expected to decrease when it is taken up into algal biomass.

The figures show that total phosphorus concentrations in both basins have gradually decreased since the mid 1980s. As indicated previously, the main reason for this decrease has been the upgrading of the Queanbeyan Wastewater Treatment Plant (during the mid 1980s). Ongoing reductions since then have probably been due to a range of other catchment management practices.

Figure 2: Total Phosphorus (mg/L) concentrations in Lake Burley Griffin for 1981–2009.

 

A.	East Basin Total Phosphorus 1981 to 2009, is a graph of total phosphorus levels in East Basin over this period expressed in milligrams per litre.  Total phosphorus levels have decreased from the 1980s, with a spike in the mid 1990s and have generally been below 0.08 milligrams per litre since 2000.

A. East Basin (Site 529 surface) Total Phosphorous 1981 - 2009.

B.	West Lake Total Phosphorus 1981-2009, is a graph of total phosphorus levels over this period in West Lake over this period expressed in milligrams per litre.  Total phosphorus levels have decreased from the 1980s, with a spike in the mid 1990s and generally below 0.06 milligrams per litre since 2000.

B. West Lake (Site 504 tube) Total Phosphorus 1981 - 2009.

Figure 3: Filterable Reactive Phosphorus (mg/L) concentrations in Lake Burley Griffin for 1981–2009.

A.	East Basin Filterable Reactive Phosphorus 1981-2009, is a graph of filterable reactive phosphorus levels in East Basin over this period expressed in milligrams per litre.  Filterable reactive phosphorus levels have decreased since the early 1990s, with levels generally below 0.01 milligrams per litre since 2000.

A. East Basin (Site 529 surface) Filtrable Reactive Phosphorus 1981 - 2009.

B.	West Lake Filterable Reactive Phosphorus 1981-2009, is a graph of filterable reactive phosphorus levels in West Lake over this period expressed in milligram per litre.  Filterable reactive phosphorus levels have decreased since the early 1990s, with levels generally below 0.01 milligrams per litre since 2000.

B. West Lake (site 504 tube) Reactive Phosphorus 1981 - 2009.

Nitrogen

Background

Nitrogen is also an essential nutrient in aquatic ecosystems. High nitrogen concentrations can promote nuisance growths of algae and macrophytes, which in turn can result in eutrophication.

Nitrogen originates from the same general sources as phosphorus, including:

  • soils in the catchment;
  • wastewater discharges;
  • fertilizers applied to agricultural land, or suburban gardens;
  • waterbirds defecating into or near the water body; and
  • releases from lake sediments as ammonia, if oxygen becomes depleted in the overlying waters.

In environmental waters, nitrogen is measured in a number of forms, including ammonia, nitrate, nitrite, total kjeldahl nitrogen, and total nitrogen. Of these, total nitrogen and ammonia are particularly important (especially for algal and fish activity). High concentrations of total nitrogen and ammonia can promote algal blooms, whereas high ammonia concentrations can interfere with the ability of fish gills to absorb oxygen (and can thus result in fish deaths).

General Trends

Total nitrogen and ammonia concentrations are both measured in terms of mg/L. Generally, both have been monitored in Lake Burley Griffin since 1981, at four sites (five sites from April 2009) and usually at a monthly frequency.

From the collected information (EcoChemistry Laboratory, 2003; Ecowise Scientific and Aquatech, 1995; Office of ACT Administration, 1987) and more recent water quality data, it is possible to indicate the following general trends:

  • Both total nitrogen and ammonia concentrations have decreased slightly over the past 28 years of monitoring (but not as dramatically as total phosphorus and filterable phosphorus). This decrease has probably been the result of a range of catchment and sewage management practices.
  • Nitrogen concentrations are higher just after stormwater flows into the Lake.
  • Nitrogen concentrations are higher just after strong windy periods, especially in the shallower eastern parts of the Lake.
  • Total nitrogen concentrations in East Basin are generally below 1.4 mg/L, whereas in West Basin values are generally below 1.0 mg/L.
  • Ammonia concentrations are generally below 0.1 mg/L.

Total nitrogen concentrations for East Basin (site 529 surface) and West Lake (site 504 tube) are shown in figures 4A and 4B respectively for the period from 1981 to 2009. The figures show that total nitrogen in both basins has decreased slightly over the three decades of available monitoring data.

There are no total nitrogen water quality standards for other parts of the ACT for recreational waters or for aquatic habitat. Nitrogen is not regarded as a limiting factor for algal growth in regional waters and is non-toxic to other organisms (ACT Government, 2011). Furthermore, the availability of oxidized nitrogen will generally favour the growth of green algae as opposed to blue-green algae (which are less desirable from the recreational, ecological or aesthetic perspective). Consequently, the water quality benchmark proposed for total nitrogen concentrations is 1.4 mg/L in East Basin, and 1.0 mg/L in West Lake. This is discussed in more detail in Development of Benchmark Levels for Water Quality.

Ammonia concentrations for East Basin (site 529 surface) and West Lake (site 504 tube) are shown in figures 5A and 5B respectively for the period from 1981 to 2009. The figures show that ammonia concentrations in both basins have decreased slightly over the 28 years of available monitoring data. However the presence of ammonia or ammonium nitrogen has the potential to select for the presence of blue-green algae, particularly Microcystis.

The water quality standard for ammonia in other parts of the ACT is calculated from ANZECC/ARMCANZ (2000), and is dependent on water pH and temperature at the time of sample collection. However, a concentration of 0.1 mg/L, as recommended in the previous version of this Water Quality Management Plan, has been retained as a benchmark. It is recommended that sampling of hypolimnetic concentrations of ammonium nitrogen is undertaken on all occasions when the water column is stratified. This will be discussed in more detail in Development of Benchmark Levels for Water Quality.

Figure 4: Total Nitrogen (mg/L) concentrations in Lake Burley Griffin for 1981–2009.

 

East Basin Total Nitrogen 1981-2009, is a graph of total nitrogen levels in East Basin over this period expressed in milligrams per litre.  Total nitrogen levels have decreased slightly over this period.

A. East Lake (site 529 surface) Total Nitrogen 1981 - 2009.

West Lake Total Nitrogen 1981-2009, is a graph of total nitrogen levels in West Lake over this period expressed in milligrams per litre.  Total nitrogen levels have decreased slightly over this period.

B. West Lake (Site 504 tube) Total Nitrogen 1981 - 2009.

Figure 5: Ammonia as N (mg/L) concentrations in Lake Burley Griffin for 1981–20090.

 

East Basin Ammonia 1981-2009, is a graph of ammonia as nitrogen levels in East Basin over this period expressed in milligrams per litre.  Ammonia levels have decreased slightly over the period, although there was a spike in the mid-1990s.

A. East Basin (Site 529 surface) Ammoni 1981 - 2009.

West Lake Ammonia 1981-2009, is a graph of ammonia as nitrogen levels in West Lake over this period expressed in milligrams per litre.  Ammonia levels have decreased slightly over the period.

B. West Lake (Site 504 tube) Ammonia 1991 - 2009.

Algae and Chlorophyll-a

Background

Algae are aquatic plants that can range in size from microscopic to several metres long. Water quality problems can occur when some algae rapidly increase in numbers (during a bloom) and make the water unsuitable for a wide range of recreational uses (such as swimming, boating, or even passive recreation, such as sightseeing). Even more significant problems can occur when such blooms die and decompose. The decomposing algae use up the oxygen in the water column, which in turn often results in fish deaths.

General Trends

Algal cell concentration is measured in cells/mL. Classification then divides the algal assemblage into cyanobacteria (blue-green algae), green algae and the like. Further classification of problematic algae may occur to the level of genus and species. Cyanobacterial blooms may produce unsightly green powder like scums on the surface of water bodies, malodorous compounds and in some cases toxins which pose a health risk to humans and animals. Some cyanobacterial species do not produce surface scums but produce cells and toxin at depth. Biovolume may be used as a surrogate for the determination of the biomass of algae in a water body. Chlorophyll-a (µg/L) is also used as a measure of algal biomass.

Both total algal and cyanobacterial cell concentrations, and chlorophyll-a concentrations have been monitored in Lake Burley Griffin since 1981, at four sites (five sites from April 2009), and usually at a monthly frequency. As the monitoring program is time based, as opposed to event based, it is possible that the true peaks in algal activity have been under-reported.

From the collected information (EcoChemistry Laboratory, 2003; Ecowise Scientific and Aquatech, 1995; Office of ACT Administration, 1987) and more recent water quality data, it is possible to indicate the following trends:

  • Both total algal cell concentrations and chlorophyll-a concentrations have remained in the same general range. This is despite the previously mentioned reductions in the amount of phosphorus entering the Lake, and better flow management through the Lake during the key summer months (Nagy and Butters, 1988). However, the intensity of late summer cyanobacterial blooms has generally increased in recent years.

Total algal and cyanobacterial cell concentrations for East Basin (site 529) and West Lake (site 504 tube) are shown in figure 6A and 6B respectively for the period from 1981 to 2009.
Water quality standards for cyanobacterial cell concentrations in other parts of the ACT provide a value of <5,000 cells per mL for water based recreation and for aquatic habitat (Environment Protection Regulation 2005 (ACT)).

As shown in figure 6, cyanobacterial cell concentrations were usually below this level over the last 15 years, except for in late summer when blooms have generally increased in recent years. A cyanobacterial cell concentration of 20,000 cells/mL may be an appropriate water quality benchmark for Lake Burley Griffin. This will be discussed in more detail in Development of Benchmark Levels for Water Quality.

Chlorophyll-a concentrations for East Basin (site 529 surface) and West Lake (site 504 tube) are shown in figures 7A and 7B respectively for the period from 1981 to 2009.

It is possible to indicate the following trends:

  • Chlorophyll-a concentrations are generally the same over the period from 2004 to 2009 but far greater than the ANZECC/ARMCANZ (2000) guideline for undisturbed sites.
  • The cell concentration of cyanobacteria has increased during the period 2004 to 2009.

The water quality standards in other parts of the ACT indicate a chlorophyll-a concentration of <10 μg/L for water based recreation, and between <2-<10 μg/L for aquatic habitat (ACT Government, 2011). As shown in figure 7, chlorophyll-a concentrations have generally decreased at both sites. However East Basin (a secondary contact recreation area) was often above this level over the past 15 years. Consequently, a concentration of 20 μg/L chlorophyll-a may be an appropriate water quality benchmark for Lake Burley Griffin. This will be discussed in more detail in Development of Benchmark Levels for Water Quality.

Figure 6: Total Algae and Cyanobacteria (cells/mL).

 

East Basin Total Algae and Cyanobacteria 1981-2009, is a graph of total algae and cyanobacteria levels in East Basin over this period expressed in cells per millilitre.  The graph shows total algae levels in black, overlayed with the levels of cyanobacteria in blue.  The levels of total algae and cyanobacteria have remained in the same general range, but with the intensity of cyanobacteria blooms increasing during summer in recent years.

A. East Basin (Site 529 surface) Total Algae and Cyanobacteria 1981 - 2009.

West Lake Total Algae and Cyanobacteria1981-2009, is a graph of total algae and cyanobacteria levels in West Lake over this period expressed in cells per millilitre.  The graph shows total algae levels in black, overlayed with the levels of cyanobacteria in blue.  The levels of total algae and cyanobacteria have remained in the same general range, but with the intensity of cyanobacteria blooms increasing during summer in recent years.

B. West Lake (Site 504 tube) Total Algae and Cyanobacteria 1981 - 2009.

Figure 7: Chlorophyll-a concentrations in Lake Burley Griffin for 1981–2009.

East Basin Chlorophyll-a 1981-2009, is a graph of chlorophyll-a levels in East Basin over the period expressed in micrograms per litre.  The ANZECC guideline level for chlorophyll-a at undisturbed sites (5 micrograms per litre) is shown as a red line across that level on the graph.  The level at East Basin has generally decreased in recent years, and are generally below 30 micrograms per litre.

 

A. East Basin (Site 529 surface) Chlorophyll-a 1981 - 2009.

West Lake Chlorophyll-a 1981-2009, is a graph of chlorophyll-a levels in West Lake over the period expressed in micrograms per litre.  The ANZECC guideline level for chlorophyll-a at undisturbed sites (5 micrograms per litre) is shown as a red line across that level on the graph.  Levels in West Lake have decreased in recent years and are generally lower than East Basin, and are mostly below 10 micrograms per litre.

B. West Lake (Site 504 tube) Chlorophyll-a 1981 - 2009.

Conductivity and pH

Background

Conductivity measures the amount of inorganic ions (salts) in the water (in µS/cm). Catchment geology, land use and weather fluctuations (particularly rainfall) significantly impact upon the concentration of salts present. This concentration of dissolved salts subsequently impacts upon ecosystem processes and values.

pH is a measure of the concentration of hydrogen ions in the water. Neutral pH is 7, with waters becoming increasingly acidic as the scale decreases below 7, and increasingly alkaline as the scale increases above 7. Like conductivity, pH influences a wide range of ecological processes and values.

General Trends

Conductivity and pH have been monitored in Lake Burley Griffin since 1981, at four sites (five sites from April 2009), and usually eight times a year.

Conductivity data recorded in East Basin (site 529 surface) and West Lake (site 504 tube) are shown in figures 8A and 8B respectively for the period from 1981 to 2009. East Basin (site 529 surface samples) and West Lake (site 504 tube samples) pH data are shown in figures 9A and 9B respectively for the period 1981 to 2009. From the collected information (EcoChemistry Laboratory, 2003; Ecowise Scientific and Aquatech, 1995; Office of ACT Administration, 1987), and more recent water quality data it is possible to indicate the following general trends:

  • Conductivity recorded in Lake Burley Griffin (and reported in terms of specific conductance) has remained relatively consistent prior to December 2002. However, during the period 2002 and December 2009 there has been an upward trend with values generally in excess of 300 µS/cm.
  • pH values have remained in the same range over the past 28 years of monitoring.

The water quality standard for pH in the ACT for recreational waters is 6.5-8.5 (ACT Government, 2011). This same range may be appropriate as a water quality benchmark for Lake Burley Griffin. Between 1981 and 2009, there were 2% of readings above 8.5 in West Lake and 6% of readings above 8.5 in East Basin. Therefore, the recommended benchmark for pH is between the range 6.5 to 8.5. This will be discussed in more detail in Development of Benchmark Levels for Water Quality.

Figure 8: Conductivity (µS/cm) in Lake Burley Griffin for 1981–2009.

 

East Basin Conductivity 1981-2009, is a graph of conductivity levels in East Basin over the period expressed in microsiemens per centimetre.  Conductivity in East Basin was in the same general range until 2002, and there has been an upward trend since this time likely due to drought conditions.

A. East Basin (Site 529 surface) Conductivity 1981 - 2009.

West Lake Conductivity 1981-2009, is a graph of conductivity levels in West Lake over this period expressed in microsiemens per centimetre.  Conductivity has been in the same general range until 2002, and there has been an upward trend which was likely due to drought conditions.

B. West Lake (Site 504 tube) Conductivity 1981 - 2009.

Figure 9: pH in Lake Burley Griffin for 1981–2009.

East Basin pH 1981-2009, is a graph of pH levels in East Basin over this period.  The graph shows that pH has remained in the same general range between 7.0 and 9.0.

A. East Basin (Site 529 surface) pH 1981 - 2009.

West Lake pH 1981-2009, is a graph of pH levels in West Lake over this period.  The graph shows pH has remained in the same general range between 7.0 and 9.0.

B. West Lake (Site 504 tube) pH 1981 - 2009.

Bacteria

Background

Bacteria are microorganisms which are present in most environments, including aquatic environments such as Lake Burley Griffin. Some bacteria are pathogenic or harmful to humans, and their presence in lake water can make it unsuitable for some recreational uses (especially swimming). Indicator organisms are used to evaluate the human health risk associated with the presence of bacteria in a water body. As it is impossible to regularly monitor for the entire suite of potential pathogens, indicators have been developed which can be monitored and used as an assessment of the risk of human pathogens being present. Historically, faecal coliforms (which include Escherichia coli (E.coli)) were used as the indicator for faecal pollution in Lake Burley Griffin. The limitation of E.coli is that it is a non-specific indicator and it does not identify whether the source of contamination is animals, humans, or from plant decomposition. From 2002 onwards, intestinal enterococci (Enterococci spp.) have also been measured as an indicator of faecal contamination, as they are thought to be better correlated with human pathogens than E.coli. In December 2009, intestinal enterococci replaced faecal coliforms as the indicator used for faecal pollution in Lake Burley Griffin.

The Guidelines for Managing Risks in Recreational Water (Australian Government, 2008) recommend implementing a risk management procedure for managing bacteria in recreational waters, and provide appropriate management and monitoring responses for bacterial hazards (Chapter 5 Guidelines for Managing Risks in Recreational Water (Australian Government, 2008)). The benchmark provided in this Plan is based on these Guidelines. The NCA is now using intestinal enterococci as indicator organisms for bacteria in its risk management programme.

A concentration of <200 CFU/100mL for intestinal enterococci is recommended as a benchmark.

General Trends for the previous testing regime

Faecal coliforms are measured in colony forming units per 100 mL (CFU/100mL) of water. Faecal coliforms have been monitored in Lake Burley Griffin since the late 1980s until late 2009, at a number of swimming locations, particularly in the summer months.

From the collected information (EcoChemistry Laboratory, 2003; Ecowise Scientific and Aquatech, 1995; Lawrence, 2001; Office of ACT Administration, 1987) and more recent water quality data it is possible to indicate the following general trends:

  • Faecal coliforms counts have sometimes been above the guidelines for recreational water. This may be due to a number of reasons, including greater bacterial inputs from the catchment, as well as in-lake regrowth.

Faecal coliform numbers are indicated for East Basin (site 529 surface) and West Lake (site 504 surface) in figures 10A and 10B respectively. Between January 2008 and December 2009 results from faecal coliform testing have indicated concentrations less than 150 CFU/100mL. This number of colony forming units is the water quality standard for other parts of the ACT for primary water based recreational activity (such as swimming) (ACT Government, 2011). The ACT water quality standard for secondary water based recreational activity (such as boating) is 1,000 CFU/100mL (ACT Government, 2011). East Basin is a secondary contact area and coliform numbers have generally been below 1,000 CFU/100mL. West Lake is a primary contact area and coliform numbers have generally been below 150 CFU/100mL.

Although a number of water quality issues in the Lake have improved over the past 23 years of monitoring, faecal coliform numbers may have increased. There are several possible reasons for this, including:

  • Increased urbanisation of the catchments, with urban runoff resulting in greater bacterial levels in the runoff (from such things as food wastes, and animal and pet droppings).
  • The possibility of sewage overflow during heavy rain periods (although this is relatively rare in Canberra, and does not explain the observed relationship between faecal coliform numbers and high water temperatures).
  • In-lake regrowth of coliforms (Lawrence, 2001).
  • Better and more accurate faecal coliform monitoring techniques. The accuracy and sensitivity of faecal coliform enumeration techniques has generally increased over the past 20 years, and this may give the appearance of an increase in faecal coliform levels.
  • Some changes to the monitoring methodology for faecal coliforms.
  • Increased abundance of waterbirds in and around the Lake. Waterbird faeces will contain large numbers of bacteria, including some faecal coliforms.

It is not possible to indicate at this stage which of the above mentioned factors may be the most important in terms of managing bacterial pollution of the Lake. Indeed, it is not even possible to state conclusively if bacterial levels have generally increased in the Lake, even though the issue has been receiving research attention since the early 1970s (Burgess and Olive, 1975).

It is important to note that since December 2009, intestinal enterococci replaced E.coli as the alert measure of faecal contamination. Water bodies remain open when enterococci levels are ≤ 200 CFU/100mL, whereas a closed alert level for primary contact recreation and a series of management protocols apply when intestinal enterococci are > 200 CFU/100mL (ACT Government, 2010). Enterococci data available from the period between 2005 and 2009 are presented for East Basin (site 529 surface) and West Lake (site 504 surface) in figures 11A and 11B respectively.

Figure 10: Faecal coliforms (CFU/100mL) in Lake Burley Griffin for 1981–2009.

 

East Basin Faecal Coliforms 1987-2009, is a graph of faecal coliform levels in East Basin over this period expressed in colony forming units per 100 millilitres.  East Basin levels have generally been below 1000 colony forming units per 100 millilitres, which is the benchmark level for secondary contact recreational areas.

A. East Basin (Site 529 surface) Faecal Coliforms 1987 - 2009.

West Lake Faecal Coliforms 1987-2009, is a graph of faecal coliform levels in West Lake over this period expressed in colony forming units per 100 millilitres.  West Lake levels have generally been below 150 colony forming units per 100 millilitres, which is the benchmark level for primary contact recreation areas.

B. West Lake (Site 504 tube) Faecal Coliforms 1987 - 2009.

Figure 11: Intestinal Enterococci (CFU/100mL) in Lake Burley Griffin for 2005–2009.

East Basin Enterococci 2005-2009, is a graph of available enterococci data from East Basin over the period expressed in colony forming units per 100 millilitres.  There are only a small number of plots on the graph, as the change in testing from faecal coliforms to enterococci formally took place in December 2009.

A. East Basin (Site 529 surface) Enterococci 2005 - 2009.

West Lake Enterococci 2005-2009, is a graph of available enterococci data from West Lake over the period expressed in colony forming units per 100 millilitres.  There are only a small number of plots on the graph, as the change in testing from faecal coliforms to enterococci formally took place in December 2009.

B. West Lake (Site 504 tube) Enterococci 2005 - 2009.

Metals

Background

Trace metal concentrations in Lake Burley Griffin used to be relatively high, due to runoff from abandoned zinc mining areas in the catchment, primarily in the Captains Flat area (Joint Government Technical Committee, 1974 and 1978). However, as a result of major remediation works in the 1970s, the abandoned mining areas were stabilised and metal concentrations in the subsequent runoff were significantly reduced (Hillman, 1980; National Capital Development Commission, 1981).

General Trends

Trace metal concentrations in Lake Burley Griffin waters, sediments and biota have been measured by several research projects (EcoChemistry Laboratory, 2003; Maher et al, 1992; Norris 1983), as well as by some ongoing monitoring programs (Ecowise Scientific and Aquatech, 1995). These research and monitoring programs, together with recent data, indicate that generally:

  • Metal concentrations in the Lake are still elevated, especially in lake sediments.

Dissolved Oxygen

Background

Dissolved oxygen is critical for Lake biodiversity, as many macroinvertebrates and most fish species require concentrations above 5mg/L. Low dissolved oxygen concentrations at the sediment-water interface can result in the anoxic release of bioavailable forms of nutrients and metals into the overlying water column. These nutrient releases may stimulate the growth of cyanobacteria (blue-green algae).

General Trends

Dissolved oxygen values (in mg/L) have been monitored in the Lake since 1981, at four sites (five sites from April 2009), and usually at least eight times a year.

From the collected information (Eco Chemistry Laboratory, 2003; Ecowise Scientific and Aquatech 1995; Office of ACT Administration, 1987) and more recent water quality data it is possible to indicate the following general trends:

  • Dissolved oxygen concentrations in East Basin are generally above 5mg/L, most likely due to wind mixing and its shallow profile.
  • Dissolved oxygen values in Central Basin, West Lake, and Scrivener Dam are at their maximum during the late winter months and at their minimum during the late summer months. This is because during the winter months of the year, water temperatures are relatively homogeneous through the depth profile. However, during the warmer months of the year, the water column becomes stratified (with warmer water at the surface and colder water at the bottom). This layering and lack of mixing of the water column together with greater biological activity in the sediments during the warmer months of the year can deplete dissolved oxygen in the deeper parts of the Lake.

Averaged dissolved oxygen concentrations for Central Basin (site 530), West Lake (site 504), and Scrivener Dam (site 507) are shown in figures 12A, 12B, and 12C respectively for the period from 1981 to 2009.

The figures show dissolved oxygen concentrations through the water column averaged for each quarter of the year (1st quarter – Jan to March; 2nd quarter – April to June; 3rd quarter – July to Sept; and 4th quarter – Oct to Dec).

As shown in the figures, dissolved oxygen concentrations at Central Basin range from about 8–11 mg/L at the water surface, and about 5–11 mg/L at the bottom (near the sediment).

At West Lake, dissolved oxygen concentrations range from about 8-11 mg/L at the water surface and from about 4-10 mg/L at the bottom (near the sediment).

Similarly, dissolved oxygen concentrations recorded at Scrivener Dam, range from about 7–11 mg/L at the water surface and from about 1–10 mg/L at the bottom (near the sediment). This is because West Lake and Scrivener Dam are deeper sites than Central Basin and consequently experience greater temperature and dissolved oxygen stratifications during the summer months.

No particular benchmark value is proposed at this stage for dissolved oxygen concentrations through the water profile at the various Lake Burley Griffin sites. However, as with other water quality characteristics, continuing monitoring will be an important component of the WQMP.

Figure 12: Dissolved Oxygen in Lake Burley Griffin for 1981–2009

Central Basin Dissolved Oxygen 1981-2009 graphs averaged dissolved oxygen concentrations (expressed in milligrams per litre) against depth.  Dissolved oxygen levels are between 8 to 11 milligrams per litre at the surface, and 5 to 11 milligrams per litre at the bottom.  The lower dissolved oxygen concentrations are recorded in the first quarter (January to March).

A. East Basin (Site 529 surface) Dissolved Oxygen 1981 - 2009.

Note: Surface readings taken at 0.1 m and 0.3 m. No 0.1 m readings after 1991; No 0.3 m readings before 1989. Some depth readings have been rounded to the nearest metre. The number of samples (n) taken at each depth, in each quarter over  the 28 year period, ranged in the following way: 1st Quarter, n= 34-86; 2nd Quarter, n=  26-47; 3rd Quarter, n= 19-36 ; 4th Quarter, n= 25-70.

West Lake Dissolved Oxygen 1981-2009 graphs averaged dissolved oxygen (expressed in milligrams per litre) against depth.  Dissolved oxygen levels are between 8 to 11 milligrams per litre at the surface, and 4 to 10 milligrams per litre at the bottom.  The lower dissolved oxygen concentrations are recorded in the first quarter (January to March).

B. West Lake (Site 504 tube) Dissolved Oxygen 1981 - 2009.

Note: Surface readings taken at 0.1 and 0.3 m. No  0.1m readings after 1992; No 0.3 m readings prior to 1989. Some depth readings have been rounded to the nearest metre. The number of samples (n) taken at each depth, in each quarter over  the 28 year period, ranged in the following way: 1st Quarter, n= 31-76;  2nd Quarter, n= 25-47; 3rd Quarter, n= 18-36; 4th Quarter, n= 26-67.

Scrivener Dam Dissolved Oxygen 1981-2009 plots depth against averaged dissolved oxygen (expressed in milligrams per litre).  Dissolved oxygen levels are between 7 to11 milligrams per litre at the surface, and 1 to 10 milligrams per litre at the bottom.  The lower dissolved oxygen concentrations are recorded in the first quarter (January to March).

C. Scrivener Dam (Site 507) Dissolved Oxygen 1981 - 2009.

Note: Surface readings taken at 0.1m and 0.3 m. No 0.1 m readings after 1992; No 0.3 m readings before 1989. Some depth readings have been rounded to the nearest metre. The number of samples (n) taken at each depth, in each quarter over the 28 year period, ranged in the following way: 1st Quarter, n= 30-82; 2nd Quarter, n=  25-40; 3rd Quarter, n= 18-37 ; 4th Quarter, n= 27-70.

Water Column Depth Profiles

In 2009 and 2010, water column depth profiles were taken along a Molonglo River transect and at midstream sites within Lake Burley Griffin in order to better understand and manage blue-green algal blooms within the Lake Burley Griffin.

Water column depth profiles of temperature, dissolved oxygen, specific conductance and pH were compiled for a selected transect upstream in the Molonglo River (Figure 13) between sites 1 and 5 (Figure 14), East Basin (site 529) (Figure 15), West Lake (site 504) (Figure 16) and Scrivener Dam (site 507) (Figure 17). Profiles from upstream in the Molonglo River (site 5) towards the entrance to Lake Burley Griffin at site 1 show a highly thermally and chemically stratified water column with an anoxic, and slightly acidic hypolimnion of lower conductivity. The waters carried by the Molonglo are of lower conductivity than those in the Lake itself. Such an anoxic and slightly acidic hypolimnion would facilitate the release of bound nutrients. Water samples for assessment of the possible presence of cyanobacterial toxins were taken at survey sites 6, 7 and 8 at the same time as the Molonglo transects. The toxicity testing was to determine if the bloom had become uncharacteristically toxic after construction dredging and digging behind the silt curtain of the Kingston harbour.

Cyanobacterial toxins were not detected in these samples.

Quite different mixing and stratification profiles occur in the Lake at sites of distinctly different depths. Profiles show a mixed water column in the comparatively shallow East Basin (site 529) with elevated pH in the summer months. East Basin is the warmest site in summer. Profiles for West Lake (site 504) show mid-summer stratification in temperature, dissolved oxygen, conductivity and pH with decreased oxygen concentrations in the hypolimnion. The profiles from the deeper site near Scrivener Dam (site 507) show a strongly stratified water column between January and April and the presence of an anoxic hypolimnion. Temperature profiles recorded in May 2009 suggest the probability of winter mixing.

Figure 13: Map showing start of transect of sampling sites from Site 1 (Transect Survey 1) to Site 5 (Transect Survey 5) used for the construction of the contour plots in figure 14. Note that data for profiles were not recorded at transect sites 6, 7 and 8 within Lake Burley Griffin.

Figure 14: Vertical water column depth profiles for the series of sites along the Molonglo River transect starting at site 1 at the entrance of Lake Burley Griffin and heading in an upstream direction on 26 February 2010.

 

Temperature against depth.  The graph shows temperature highest at the surface at all five transect sites.  At site 4, there is indication of warmer temperatures between 5 and 6 metres of depth.

A. Temperature

Dissolved oxygen against depth.  The graph shows highest dissolved oxygen levels at the surface of all sites.  Below 4 metres, dissolved oxygen concentrations are below 2 mg/L.  At sites 4, dissolved oxygen levels are slightly higher at the bottom.

B. Dissolved oxygen (mg/L)

Specific conductance against depth.  The graph shows that conductance is highest at the surface of the shallower sites (sites 1 and 2).  Conductance is lower at the surface at site 5, and across all transect sites by depth.

C. Specific Conductance (uS/cm at 25°C)

pH against depth.  The graph shows that pH is in the same general range at the surface of sites 1 to 4.  pH is lower at the surface at site 5, and across all transect sites by depth.

D. pH.

Figure 15: Vertical water column depth profiles for East Basin (site 529) between 20 January and 5 May 2009.

Temperature against depth.  The graph shows that temperature is consistent between the surface and bottom (2 metres from the surface) throughout the five months of sampling.  The site shows warmest temperatures recorded in the summer months, with the water temperature cooling in May.

A. Temperature (°C)

Dissolved oxygen against depth.  This graph shows dissolved oxygen levels lowest at 9 mg/L below the surface in January.  However, levels are consistent at the surface and bottom throughout the other monthly samples.

B. Dissolved oxygen (mg/L)

Conductivity against depth.  This graph shows conductivity in the range of 350 and 380 microsiemens per centimetre.  The conductivity at surface and bottom is the same on all testing occasions, with the lowest conductivity recorded between January and February, and highest in March.

C. Conductivity (uS/cm)

pH against depth.  This graph shows pH levels in the range of 8.0 and 9.0.  Lower pH values were recorded in April and May.

D. pH

Figure 16: Vertical water column depth profiles for West Lake (site 504) between 20 January and 5 May 2009.

Temperature against depth.  The graph shows that temperature is consistent between the surface and bottom throughout the five months (10 metres from the surface).  The graph shows that warmest temperatures recorded in the summer months, with the water temperature cooling in May.

A. Temperature

Dissolved oxygen against depth.  This graph shows very low dissolved oxygen concentrations between 6 and 10 metres in depth in January at between 1 and 2 mg/L.  In February and March, dissolved oxygen concentrations are approximately 5 milligrams per litre at 8 to 10 metres in depth, and 8 mg/L at the surface.  In April and May, the dissolved oxygen concentrations increase and are consistent at all levels of the profile.

B. Dissolved oxygen (mg/L)

Conductivity against depth.  This graph shows conductivity in the range of 350 to 380 microsiemens per centimetre.  Conductivity was highest in March, and lowest at the surface in February.

C. Conductivity (uS/cm)

pH against depth.  This graph shows pH generally consistent across the tests and depth.  pH was higher at the surface in January, but in the same general range of 7.5 to 8.0 from February to May.

D. pH.

Figure 17: Vertical water column depth profiles for Scrivener Dam (site 507) between 20 January and 5 May 2009.

Temperature against depth.  This graph shows that temperature was slightly lower by depth in January to late March, with a consistent temperature at all levels of the profile in April and May.

 

A. Temperature

Dissolved oxygen against depth.  This graph shows very low levels of dissolved oxygen (between 1 and 3 milligrams per litre) for depths less than 8 metres from January to March.  By May, dissolved oxygen concentrations were 5 mg/L at 16 metres of depth.

B. Dissolved oxygen (mg/L)

Conductivity against depth.  This graph shows conductivity in the range of 350 and 380 microsiemens per centimetre.  Conductivity is lowest in January and February, and highest in late March and April.

C. Conductivity (uS/cm)

pH against depth.  This graph shows pH more alkaline at the surface and gradually becoming closer to neutral with depth.  pH is in the range of 7.0 and 8.5.

D. pH