Yankalilla Nearshore Marine Biounit
2011 Aquatic Ecosystem Condition Report
Condition overview
Key points:
- On the map, zoom in and click on the dots to view underwater video at each site.
- The seagrass habitats were typically sparse in density and patchy in coverage.
- Reef communities generally had a high cover of large brown canopy algae but also had moderate levels of bare substrate or turfing algae
- Seagrass communities were under stress due to elevated epiphytes loads particularly in the northern part of the biounit.
Area map
About the biounit
The Yankalilla biounit is adjacent to a large portion of the southern Metropolitan Adelaide suburbs as well as a number of small coastal towns dotted along the Fleurieu peninsula including Carrickalinga, Normanville, Second Valley and Rapid Bay.
The Christies Beach wastewater treatment plant discharges large volumes of treated wastewater into nearshore marine waters. The Aldinga wastewater treatment plant discharges much smaller volumes of treated wastewater. Suburbs outside of these facilities treat sewage through either community wastewater treatment systems such as at Sellicks Beach or Second valley or they rely on septic tanks.
Wirrina Marina located at the southern end of the biounit is a potential source of pollutants such as debris and rubbish from vessels as well as oil and fuel leaks and spills. Marinas also provide large roosting areas over water for a number of shore birds; these aggregation points contribute to the nutrients that are flushed out to the near shore marine environment with tidal movements.
The Adelaide Desalination (pilot) plant was established to test the water conditions for the large 100 GL desalination plant while that was under construction. The brine from the pilot plant was remixed with fresh water before being discharged resulting in no net increase in salinity in the discharge. Construction of the 100 GL desalination plant began in December of 2009 and continued into 2010.
The Mobil Adelaide oil refinery ceased operations in 2003 and the plant was ‘mothballed’ in 2009. The site has significant hydrocarbon contamination throughout the site but this is currently being managed and remediated and is unlikely to reach the marine environment. The Port Stanvac Jetty was used for the import of fuel to the Mobil facility and has maintained a 400 meter exclusion zone around the jetty which has acted to preserve both the subtidal and intertidal environments.
The Rapid Bay quarry is located in close proximity to the marine environment and is surrounded by very steep cliff faces. When the quarry was constructed the waste rock was dumped into the bay and has built up the beach to approximately two meters above the natural level, shore currents have made artificial beaches in several coves northward along the coast. Surface water runoff from significant rain events may cause turbidity impacts from the overburden running down the cliff face.
Yankalilla was expected to be in Fair condition based on the threat assessment to the nearshore habitats.
In summary
The condition of habitats in waters between 2 – 15 m deep throughout Yankalilla was assessed based on monitoring data collected during autumn and spring 2011. There are large areas within the biounit that are deeper than 15 m which are not included as a part of this evaluation.
Yankalilla was observed to be in Poor condition and has not changed since the previous assessment in 2010. The monitoring showed that the seagrasses that were present were sparse in density and patchy in coverage. Much of the seagrass communities monitored were under stress due to elevated epiphyte loads particularly in the north of the biounit.
The reef communities monitored were dominated by large brown canopy algae but there were moderate levels of turfing algae or bare substrate which has not largely changed in 2010.
Findings
A total of 8 sites were monitored during autumn and spring in 2011. A number of sites within the biounit have changed since the 2010 survey for logistical reasons. Overall, 56 % of the sites were covered in unvegetated sand, 14 % were covered in seagrass. Rocky reef comprised of 30 % of the area monitored.
The condition of the seagrass throughout Yankalilla was typically sparse to moderate and patchy in coverage with an average condition of 22 out of 100. This is consistent with the 2010 assessment which showed a condition of 20 out of 100.
Seagrass was typically covered in moderate epiphyte loads that were slightly higher during spring compared to autumn. The sites at the northern part of the biounit including Port Stanvac, O’Sullivans Beach as well as Sellicks outer had the highest epiphyte loads. This is again largely consistent with the findings of the 2010 assessment.
Several separate reef communities were sampled during 2011. The average cover of robust brown canopy algae was high at 65 % and the cover of turfing algae or bare substrate was typically in the order of 25 %. Hallett Cove had particularly good coverage with a high proportion of large brown canopy algae (82%) and low cover of turfing or bare substrate with an average of 16 %.
The total nutrient (and dissolved) nutrient concentrations were low and significantly less than typical reference locations. This suggests the uptake of dissolved nutrients by marine biota. The amount of phytoplankton in the water column was also very low compared to what has been observed in reference locations. The turbidity throughout the biounit was similar to reference locations.
Pressures and management responses
Pressures | Management responses |
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Nutrient load discharged (over several decades) by the wastewater treatment plant at Christies Beach |
The Adelaide Coastal Water Quality Improvement Plan (ACWQIP) has targets for reducing nutrient discharges from the Christies Beach wastewater treatment plant (WWTP). In order to accommodate urban growth and improve environmental performance, SA Water has heavily invested in upgrading the Christies Beach WWTP. This upgrade has improved effluent quality and has enabled the development of the Southern Urban Reuse Scheme and large scale irrigation of vineyards. This investment has resulted in a significant reduction in nutrient loads discharges to marine waters from the plant. In addition to these investments, SA Water has commenced a comprehensive marine research program to inform future investments in wastewater treatment and reuse, and continually monitors and reviews treatment plant performance. |
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. |
The Adelaide Desalination Plant was in a commissioning phase discharging variable volumes of brine into nearshore waters | The Adelaide Desalination Plant (ADP) was constructed as a climate independent water source for Adelaide and provides water security for the city for the next 100 years. During the commissioning phase, the ADP was operated in accordance with all conditions specified in its EPA licence including comprehensive water quality and ecological monitoring of the marine environment. Results of these monitoring programs and various ecological studies are available on the EPA website. |
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. In addition the EPA:
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Further information
- 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