Adelaide Metropolitan Nearshore Marine Biounit
2011 Aquatic Ecosystem Condition Report
- On the map, zoom in and click on the dots to view underwater video at each site.
- Seagrass throughout the biounit was variable with many locations sparse and patchy.
- There are several historical issues that have caused poor water quality over many decades. These have impacted on the ecosystem condition which is particularly evident in the area between Grange and Glenelg.
- The stability of the ecosystem is not known with certainty.
- The biounit is remains under stress due to nutrient enrichment and at times poor water clarity.
- Elevated turbidity is likely to be making waters aesthetically unattractive for swimmers.
About the location
The Adelaide Metropolitan biounit has been created from the original Clinton biounit to more accurately report on the Adelaide metropolitan coastline. The Adelaide Metropolitan boundary extends along the major urbanised areas of the metropolitan coastline from Marino (to the south) up to the Gawler River (in the north). It includes the Port River and Barker Inlet, out to the 5 metre bathymetric contour.
The Adelaide metropolitan coast is a low to moderate wave energy environment where the wave energy generally increases further to the south of the biounit. The biounit is dominated by extensive seagrass habitats which have been impacted over the last 50 years due to terrestrial and industrial inputs, resulting in bare sand where seagrass once proliferated. There are a few small, discrete, rocky reef habitats where rocky substrates allow.
The Port River and Barker Inlet Estuary has large areas of shallow, warm waters with restricted flushing with Gulf waters. They tend to retain poorer quality water, maintain favourable conditions for algal growth have an increased risk of environmental impacts.
The Adelaide Metropolitan biounit receives stormwater runoff from numerous outlets along the Adelaide coastline. There are also two large wastewater treatment plants (at Bolivar and Glenelg) which discharge large volumes of treated wastewater into the Gulf. The Port River is heavily industrialised with the Port of Adelaide managing the shipping traffic for the import and export of goods to and from Adelaide. The Port River is also the site of Penrice Soda Products that has produced soda ash at Osborne for several decades and discharging ammonia into the Port River. These discharges have all contributed to the degradation of the nearshore environment throughout the Adelaide metropolitan biounit with the loss of over 6000 hectares of seagrass and degradation of rocky reefs documented.
The Adelaide metropolitan biounit was expected to be in Poor condition, based on an assessment of threats to the nearshore habitats.
The Adelaide Metropolitan biounit was rated in Good condition during 2011.
There has not been any significant improvement in condition between 2010 and 2011. The biounit was rated in Fair condition during 2010, although in reality both 2010 and 2011 assessments straddled the boundary between Fair condition and Good condition.
The seagrass throughout the biounit was variable, many locations were was sparse in density and very patchy in coverage suggesting that the habitat at these locations was in poor condition. There were two sites sampled where the seagrass was dense and continuous suggesting it was in good condition, these sites were Semaphore Park (inner) and Grange north.
Areas within the Adelaide Metropolitan biounit between Grange and Glenelg had seagrass that was degraded or has been totally lost. The seagrass decline in this biounit has been reported elsewhere (Adelaide Coastal Waters Study Final Report) and it is not likely to have occurred recently; however it is also unlikely that the water quality is suitable for seagrass to regrow in these areas.
There are numerous symptoms of nutrient enrichment throughout the biounit, such as epiphytes growing on seagrass leaves and elevated nutrients in the water. There was also high turbidity throughout the biounit which may have reduced the light passing through the water to the plants and algae. This elevated turbidity can also affect the aesthetic value of the metropolitan beaches making them potentially unattractive for swimmers.
8 sites were monitored during autumn and spring in 2011; 47% of the sites were covered in seagrass, while 46% were covered in unvegetated sand. The remaining habitat was comprised of small algae (< 7%).
The average condition of the seagrass habitat was 51 out of 100 for the entire biounit, the seagrass was variable with many locations where the seagrass was sparse in density and very patchy in coverage. The results showed that there were large areas where seagrass was in very poor condition, and included the sites Grange, Henley Beach South, West Beach Inner, and Glenelg. There were two sites where the seagrass was dense and continuous suggesting that pressures impacting other sites within the biounit have not had had the same magnitude of effect at these sites; Semaphore Park and Grange North. This highlights the patchy nature of seagrass loss along the metropolitan coast and the sampling site locations in respect to the specific discharge locations.
A number of sites throughout the biounit were observed to have elevated epiphyte growth on seagrass leaves suggesting that the seagrass are under stress from an excess of nutrients. The site Black Pole (Inner) near St Kilda showed particularly dense epiphytes in both autumn and spring, while Grange North was particularly dense during spring, suggesting seasonality in epiphyte growth at some locations.
The turbidity in the water throughout the biounit was considerably higher than reference locations suggesting that the water clarity may be contributing to stress on habitats. This elevated turbidity along the metropolitan beaches may also be affecting aesthetic values of water making the nearshore waters potentially unattractive for swimmers.
Aerial photography previously undertaken has highlighted significant areas of seagrass loss along the Adelaide metropolitan coast over time. It is unclear whether seagrass loss is still occurring, however this assessment suggests that the region has an excess of nutrients and at times, may be affected by poor water clarity, which have been shown to be the key drivers in seagrass loss along the metropolitan coast (Adelaide Coastal Waters Study Final Report).
Pressures and management responses
|Nutrient load discharged (over several decades) by 2 wastewater treatment plants along the Adelaide metropolitan coast at Glenelg and Bolivar.||
The Adelaide Coastal Water Quality Improvement Plan (ACWQIP)has targets for reducing nutrient discharges from Glenelg and Bolivar wastewater treatment plants.
SA Water assess and undertake scheduled process improvement actions at wastewater treatment plants, with the aim to reduce environmental risk and ensure operations are compliant with EPA licence conditions.
|Sediment and highly coloured runoff from Adelaide metropolitan stormwater entering the nearshore marine waters||
The Adelaide Coastal Water Quality Improvement Plan (ACWQIP)highlights sediment and coloured dissolved organic matter reduction strategies to reduce the impact of stormwater on the nearshore coastal environment.
The Adelaide and Mount Lofty Ranges NRM Board has a well developed stormwater quality improvement, harvesting and reuse program which has installed (and maintains) gross pollutant (and silt) traps in several watercourses across the region to catch litter, debris and silt in order to minimise impacts and damage to seagrass in the receiving marine environment. Stormwater captured is also treated through artificial wetlands across the region, which act as suspended solid and nutrient filters; these wetlands also provide important habitat for many native species.
|Penrice Soda Products at Osborne contributed high nutrient loads (as ammonia) into the Port River over several decades. This nutrient enriched water has been transported into the nearshore marine waters of the Adelaide Metropolitan Biounit.||Penrice Soda Products at Osborne will close its soda ash plant in June 2013. The ammonia discharge will consequently drop from approximately 670 tonnes per year to almost zero by the end of 2013.|
|Dredging operations discharge turbid water containing high amount of dead seagrass into the nearshore waters||Dredging is a licensed activity under the Environment Protection Act 1993 and is regulated through conditions on licences requiring suitable management of dredge spoil and discharge water and that monitoring programs are in place.|
- Download the 2011 habitat and water quality data
- Download the Methods Report for the nearshore marine ecosystems monitoring, evaluation and reporting program.
- Fox, D., G. Batley, D. Blackburn, Y. Bone, S. Bryars, A. Cheshire, G. Collings, D. Ellis, P. Fairweather and H. Fallowfield, 2007, The Adelaide Coastal Water Study Final Report. Summary of study findings, A report for the Environment Protection Authority. The Adelaide Coastal Waters Study. Adelaide.