1.1.5.2 Surface water quality


This section discusses available water quality data for surface waters and also reports on whole-of-basin exports of sediment, phosphorus and nitrogen. It should be noted that while there are some long-term water quality monitoring programs for locations in most basins in the Queensland (Natural Resources and Mines) and NSW (NSW Office of Water) sections of the Bioregion, there is no comprehensive monitoring program that covers all key rivers and tributaries. Environmental values and water quality objectives have also been established for riverine, estuarine, coastal waters and groundwater, within the South East Queensland Natural Resource Management area legislated under the Environmental Protection (Water) Policy 2009, and within New South Wales as guidelines in the Protection of the Environment Operations Act 1997 (NSW DEC, 2006a; 2006b). The data on basin export loads are sourced from a modelling analysis which was undertaken for the National Land and Water Resources Audit (NLWRA, 2001). The National Land and Water Audit provides the only consistent Bioregion-wide assessment of water quality. A follow up report for the National Land and Water Resource Audit (NLWRA, 2002a, 2002b) presented broader regional assessments and developed indices to facilitate comparison of basin and river condition. Loads of sediment, nutrient and phosphorus across the basins of the Clarence-Moreton bioregion are summarised in Table 10 and will be discussed in more detail in the sections below. Acid sulfate soils occur throughout the bioregion, especially in the Richmond and Clarence river basins (see Section 1.1.2.1.2). The impacts of acid sulfate drainage are discussed in Section 1.1.5. 2.7.

Table 10 Modelled estimates of total annual sediment, phosphorus and nitrogen export


Basin

Brisbane River

Logan-Albert River

South Coast

Tweed River

Brunswick River

Richmond River

Clarence River

Sediment export to coast (kt/y)

247

189

21

58

2

241

683

Sediment export rate (t/ha/y)

0.18

0.47

0.19

0.55

0.16

0.36

0.31

Sediment ratio (Euro:pre-Euro)

37

35

10

16

5

32

198

Phosphorus export to coast (t/y)

685

265

93

46

3

235

624

Phosphorus export rate (kg/ha/y)

0.5

0.64

0.67

0.42

0.06

0.33

0.28

Phosphorus ratio (Euro:pre-Euro)

5.3

4.7

1.4

1.8

2.1

2.9

3.8

Nitrogen export to coast (t/y)

3162

1251

397

499

35

1941

4799

Nitrogen export rate (kg/ha/y)

2.33

3.01

2.89

4.58

0.64

2.77

2.16

Nitrogen ratio (Euro:pre-Euro)

2.7

3.2

1.5

1.4

1.5

2.3

2

Source data: NLWRA (2001)

1.1.5.2.1 Brisbane river basin

The Brisbane river basin has a sediment export of 247 kt/year – the second highest sediment export of all of the Clarence-Moreton bioregion basins (Table 10). While the total load is high, the areally averaged export rate is one of the lowest in the bioregion. Modelling estimates suggest that sediment export rates have increased by a factor of 37 since pre-European times. Total annual phosphorus export is the highest of any bioregion basin and is 5.3 times greater than that before European settlement. Total annual nitrogen export is around 3162 t which is estimated to be 2.7 times greater than before European settlement.

A water quality report card is prepared for the Brisbane river basin each year by the Ecosystem Health Monitoring Program (EHMP, 2012). For freshwater reaches the following groups of parameters are monitored: physical chemical (pH, electrical conductivity, temperature, dissolved oxygen), nutrient cycling, ecosystem processes, aquatic invertebrates and fish. These factors are combined to produce report card grades that range from A (excellent) to F (fail). The most recent report card (EHMP, 2012) showed that most of the upper Brisbane river basin was in fair (C) to poor (D) condition while the middle basin failed (F) the assessment criteria. The lower reaches received poor (D) ratings. The Queensland Government also undertakes continuous water quality monitoring (electrical conductivity, turbidity, pH and temperature) at many of its stream gauging locations. An ambient water quality monitoring program also exists in which manual measurements of electrical conductivity, temperature, pH, turbidity, dissolved oxygen and total alkalinity are made (see DNRM (2012) for further details). Salinity in the creeks and river of the Lockyer Valley have been investigated by Tien et al. (2004) who showed that mean salinity in Laidley, Lockyer and Tenthill Creeks between 1995 and 2003 was 470, 1700 and 1378 µS/cm. Salinity increased in these streams during the dry season periods. Yu et al. (2013) analysed 10 years’ worth of salinity and turbidity data collected from 16 sites in a transect from the mouth of the Brisbane River to the limit of tidal extent (86.6 km upstream) and they showed that salinity increased by a factor of 30 over this transect. Salinity variation in this same part of the Brisbane River estuary was also reported by Bayly (1965). Modelled pollutant loads (total phosphorus (TP), total nitrogen (TN) and total suspended sediment (TSS)) for the Brisbane river basin have also been given by Chiew et al. (2002).

1.1.5.2.2 Logan-Albert river basin

The Logan-Albert river basin has a modelled annual mean sediment export of 189 kt and the sediment export rate is the second highest of the bioregion basins at 0.47 t/ha/year (Table 10). It is estimated that sediment export rates have increased by a factor of 35 since pre-European times. A study of the sources of sediment within the Logan-Albert river basin was undertaken by Hancock and Roth (2011) who estimated the relative contribution from different land uses. They found that approximately 70% of the sediment delivered to the estuary came from the southern and eastern parts of the basin from soils derived from the Lamington Group rocks. Channel bank erosion was the major sediment source. Total annual phosphorus export averages 265 t and this is 4.7 times greater than those before European settlement. Total annual mean nitrogen export of 1251 t is estimated to be 3 times greater than before European settlement. The nitrogen export rate is the highest per unit area of any of the Clarence-Moreton bioregion basins.

A water quality report card (EHMP, 2012) is also prepared for the Logan-Albert river basin each year. The most recent report card (EHMP, 2012) graded the Logan river basin a D+ while the Albert River was graded a C. The Queensland Government also undertakes continuous water quality monitoring (electrical conductivity, turbidity, pH and temperature) at many of its stream gauging locations in the Logan-Albert river basin. Ambient water quality monitoring is also undertaken with manual measurements of electrical conductivity, temperature, pH, turbidity, dissolved oxygen and total alkalinity (see DNRM (2012) for further details). Modelled pollutant loads (TP, TN and TSS) for the Logan-Albert river basin have also been given by Chiew et al. (2002). Further monitoring of water quality on the Logan-Albert river basin is being undertaken by CSIRO as part of a peri-urban supersite which was set up as part of the Terrestrial Ecosystem Research Network (TERN). The equipment continuously monitors a variety of parameters including water temperature, pH and electrical conductivity, along with river flow, depth, sediment, dissolved organic material and nutrients. While there are no known reports on the surface water salinity in the streams of the upper part of the Logan-Albert river basin, Matveev and Steven (2013) studied the effect of salinity, turbidity and flow on fish biomass in the estuary of this basin and showed that salinity and turbidity were important seasonal drivers of fish abundance. Averaged over the two years of the study the salinity in the Logan River was 13.6 g/L while in the Logan River it was 7.27 g/L. Average pH was similar in the Logan and Albert rivers at 7.56 and 7.19, respectively.

1.1.5.2.3 South Coast basin

The South Coast basin has a modelled annual mean sediment export of 21 kt and the sediment export rate is the second highest of the bioregion basins at 0.19 t/ha/year (Table 10). It is estimated that sediment export rates have increased by a factor of 10 since pre-European times. Phosphorus and nitrogen export rates have increased by about 40% and 50% respectively since European settlement. Annual mean nitrogen and phosphorus export rates are 2.89 t and 0.67 t, respectively (NLWRA, 2001).

As with other basins in south-east Queensland, a water quality report card (EHMP, 2012) is prepared for the South Coast basin each year. The most recent report card (EHMP, 2012) graded the catchments of South Coast basin as being in good condition with grades of B− to B+. The Queensland Government also undertakes continuous water quality monitoring (electrical conductivity, turbidity, pH and temperature) at some of its stream gauging locations in the South Coast basin. Ambient water quality monitoring is also undertaken with manual measurements of electrical conductivity, temperature, pH, turbidity, dissolved oxygen and total alkalinity (see DNRM (2012) for further details). Modelled pollutant loads (TP, TN and TSS) for the South Coast basin have also been given by Chiew et al. (2002). A study of the salinity of the Coomera River estuary was undertaken by Benfer et al. (2007) who showed that parts of the system become hypersaline between wet season flushing events, therefore these systems are adapted to large fluctuations in salinity throughout the year.

1.1.5.2.4 Tweed river basin

The Tweed river basin has a modelled total annual mean sediment export of 58 kt which, when averaged, yields the highest sediment export rate in the bioregion at 0.55 t/ha/year (Table 10). It is estimated that sediment export rates have increased by a factor of 16 since pre-European times. Phosphorus and nitrogen export rates have increased by a factor of 1.8 and 1.4 respectively since European settlement. Total annual mean nitrogen export is 0.42 t and the nitrogen export rate is the highest in the bioregion at 4.58 t/ha/year. Total annual mean phosphorus export is 46 t (NLWRA, 2001).

A water quality report card is also prepared for the Tweed river basin with involvement from the local council. The most recent report card graded the freshwater streams of the Tweed river basin as being in fair to poor condition (C− to D) while the estuarine areas were rated as fair to good (C to B−). The NSW Government also undertakes continuous water quality monitoring (electrical conductivity, turbidity, pH and temperature) at some of its stream gauging locations in the Tweed river basin. Beale et al. (2004) undertook a study of salinity in parts of the Tweed river basin using measurements and modelling approaches. They found that median salinity, as inferred from electrical conductivity, was very low (0 – 200 µS/cm) and that values remained below 400 uS/cm for 80% of the time. A value of 1600 µS/cm is defined as the threshold for ecological damage

1.1.5.2.5 Brunswick river basin

The Brunswick river basin has the lowest sediment export of all of the bioregion basins at 2 kt/year (Table 10). This basin also has the lowest sediment export rate of 0.16 t/ha/year. This produces a sediment load 5 times greater than pre-European levels. Total annual phosphorus export (3 t/year) is also the lowest by far and is a factor of 2.1 greater than pre-European values. Total annual nitrogen export is around 35 t/year which is estimated to be 1.5 times greater than before European settlement (NLWRA, 2001).

The NSW Government also undertakes continuous water quality monitoring (electrical conductivity, turbidity, pH and temperature) at some of its stream gauging locations in this basin. Further water quality sampling has been undertaken by the NSW Government and local councils at various times and much of this data is stored within databases. Data can be accessed by request. In parts of the Brunswick river basin, Beale et al. (2004) undertook a study of salinity using measurements and modelling approaches and found that salinity was very low (0 to 200 µS/cm) and that values remained below this level for 80% of the time.

1.1.5.2.6 Richmond river basin

The Richmond river basin has an annual mean sediment export of 241 kt which represents an increase by a factor of 32 since pre-European times (Table 10). The sediment export rate is 0.36 t/ha/year. The total annual phosphorus export rate (235 t/year) is 2.9 times greater than that before European settlement. The mean annual nitrogen export is estimated to be 1941 t. Nitrogen export rates are 2.3 times greater than before European settlement (NLWRA, 2001).

The NSW Government also undertakes continuous and opportunistic water quality monitoring (electrical conductivity, turbidity, pH and temperature) at many of its stream gauging locations. The Richmond River County Council monitors electrical conductivity, pH, dissolved oxygen, temperature and turbidity at four locations within the estuary. A host of other water quality measurement have been made in basins in northern NSW by councils and NSW Government departments in response to fish kills in areas of these basins. Large numbers of fish have been known to die following dramatic declines in dissolved oxygen following floods. The floods bring increased dissolved organic loads which deplete oxygen levels (Walsh et al., 2004). Beale et al. (2004) undertook a study of salinity in parts of the Richmond river basin using measurements and modelling approaches. They found that in most of the locations they studied median electrical conductivity values were less than 400 µS/cm. However there were streams with median electrical conductivity of between 400 and 800 µS/cm. The differences between locations are attributed to underlying geology.

Eyre and Pont (2003) investigated the loads of nitrogen and phosphorus from diffuse sources during 1996 across the Northern rivers basin in NSW (which includes all the NSW basins included in the Clarence-Moreton bioregion). They found that up to 76% of the total annual nitrogen load and 73% of the total annual phosphorus load was transported in less than 20% of the time. This contrasts with typical temperate systems where it takes 50% or more of the time to deliver 75% of the annual load. They also showed that nitrogen exports were dominated by organic forms with an average of about 80% of the total nitrogen load which consisted of particulate nitrogen and dissolved organic nitrogen. This reflects the high percentage of forest cover in these basins. Phosphorus loads were more evenly distributed between dissolved inorganic, particulate and dissolved organic forms.

1.1.5.2.7 Clarence river basin

The annual mean sediment export from the Clarence river basin is 683 kt which is almost three times larger than for any other basin in the bioregion. The sediment export rate is 0.31 t/ha/year and modelling estimates suggest that sediment export rates have increased by a factor of 198 since pre-European times (NLWRA, 2001). Total annual phosphorus export is the second highest in the bioregion (624 t/year) and is 3.8 times greater than those before European settlement. Total annual nitrogen export is also the highest of all the bioregion at 4799 t/year which estimated to be 2.0 times greater than before European settlement.

The NSW Government undertakes continuous and opportunistic water quality monitoring (electrical conductivity, turbidity, pH and temperature) at many of its stream gauging locations in this basin. Artificial drainage of the floodplain has resulted in increases in acid flux in this basin, which reduce water quality and have detrimental effects on ecosystems. Such processes have been documented and measured in various studies (e.g. Johnston et al., 2004a; Tulau, 1999). Fish kills, as a result of low dissolved oxygen, have also been documented for the Clarence River (Walsh et al., 2004). Beale et al. (2004) undertook a study of salinity in much of the upper parts of the Clarence river basin and reported median salinity levels of less than 200 µS/cm. Local salinity hotspots were attributed to underlying geology.

Serious water quality problems are associated with the drainage of acid sulfate soils, which results in the flow of acidic (low pH) water into the surface water system. It has been estimated that more than 500 km2 of land is affected by drainage works in the Lower Clarence (DLWC, 1998). Tulau (1999) reported that 92% of the 14,700 ha of Clarence wetlands have been affected by drainage. (Johnston et al., 2004a) reported high acid flux rates of up to 5300 mol H+/ha/year from drains located on the lower Clarence River floodplain. Groundwater seepage to ditch drains represents the main hydrological pathway for acid flux with weirs and floodgates affecting the magnitude of acid fluxes (Johnston et al., 2004a, 2004b).

DLWC (1998) identified areas of severely affected acid sulfate soil in the Lower Clarence floodplain for which strategies for rehabilitation should be developed. These areas included (1) Everlasting Swamp – an infilled back lagoon system located on the north-western side of the Clarence River near Lawrence, (2) Shark Creek – a right bank distributary creek which joins the South Arm of the Clarence River approximately 2 km north of Tyndale, (3) the low elevation floodplain and low elevation deltaic island areas downstream of Harwood Island and (4) Alumy Creek – an old flood channel incised into the surrounding floodplain near Grafton. The minimum recorded pH at Sportsmans Creek located in the Everlasting Swamp area is 2.68 (Beveridge, 1998). Corrosion of concrete structures indicating strongly acidic waters were noted in the Everlasting Swamp and Shark Creek areas (Tulau, 1999). The pH in Wooloweyah Lagoon ranged from 6.6 to 8.2 with a much lower pH of 3.5 noted at the Palmers Island drain, both of which are located in the lower estuary floodplain (Maclean Shire Council, 1996). The lowest pH of 2.5 was reported in Alumy Creek with low pH values persisting from December 1994 to February/March 1996 (Tulau, 1999).

Last updated:
23 March 2016
Thumbnail images of the Clarence-Moreton bioregion

Product Finalisation date

28 May 2014