Clinton 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 habitats were largely dense and intact
- Initial symptoms of nutrient enrichment with moderate epiphyte loads
About the biounit
The Clinton biounit covers the majority of the upper eastern part of Gulf St Vincent between Ardrossan on the western side through to Marino Rocks just north of Hallett Cove (see map). The Clinton boundaries have been modified in order to separate the Adelaide metropolitan zone.
Clinton, particularly the head of the gulf, is sheltered from large waves experienced further south in the gulf, but the wave energy increases towards the southern section. The biounit is dominated by extensive seagrass meadows and supports the most extensive mangrove and tidal flats within the gulf. Clinton also has large areas of shallow, warm waters which have reduced flushing. This is likely to result in favourable conditions for algal grow that could increase the biological effects of excess nutrients.
There are a number of small coastal towns that border Clinton; the largest being Ardrossan which bridges the Clinton and Orontes biounits. Port Wakefield is the next largest town and both of these centres treat sewage through a community wastewater management system. Other small coastal towns including Port Clinton, Port Parham and Thompson Beach all use onsite wastewater treatment (septic) tanks to treat and dispose of sewage. Septic tanks introduce nutrients into the shallow groundwater, which are likely to flow towards the marine environment where it can contribute to the nutrient load in nearshore marine waters. Clinton is also likely to receive significant nutrient loads from the Bolivar wastewater treatment plant which has been shown to flow to the north from Chapman creek into the Clinton biounit. It is also possible that pollutants will transport into Clinton adjacent the Adelaide Metro biounit.
Clinton was expected to be in Very Good condition, based on an assessment of threats to the nearshore habitats.
The condition of habitats in waters between 2 – 15 m deep throughout Clinton was assessed based on monitoring data collected during autumn and spring 2010. There are large areas within the biounit that are deeper than 15 m which are not included as a part of this evaluation.
Clinton was in Very Good condition during 2011 and has not changed since the previous assessment in 2010.
All sites throughout the biounit had dense and continuous Posidonia spp. seagrass suggesting that the meadows throughout the biounit were largely intact. Throughout the biounit there were sparse to moderate epiphyte loads on the seagrasses suggesting the initial symptoms of nutrient enrichment.
A total of 25 sites were monitored throughout Clinton during autumn and spring in 2011. In total 85% of the sites were covered in seagrass, while 12% were covered in unvegetated sand. There was only a small amount of rocky reef or small algae encountered in the sites assessed (< 3 %).
The average habitat condition for Clinton was 74 out of 100 which is very similar to the result from 2010. Almost all sites throughout the biounit had dense and continuous Posidonia spp. seagrass suggesting that the meadows were largely intact. There were a number of sites that had patchy seagrass that was sparse to moderate in density suggesting poorer condition, these locations were Ardrossan north, Price and near the Black Pole at Outer Harbor, which had an average habitat structure indices of 51, 14 and 39 out of 100 respectively.
Clinton showed some initial symptoms of nutrient enrichment with sparse to moderate epiphyte loads on seagrass. While the epiphyte loads varied only slightly spatially throughout he biounit is appeared that the epiphyte loads were slightly heavier at the head of the Gulf at Port Clinton, Sandy Point, Proof range and Price. It is possible that the head of the Gulf experiences lower currents and less flushing with open waters and as such may exacerbate the affects of nutrients. Other areas with slightly elevated epiphyte loads included the sites Port Gawler, Port Prime and Port Parham. It is possible that the epiphyte loads may be contributing stress on the light availability of the seagrass habitats.
Nutrient concentrations were very low with total nitrogen values equivalent to reference locations. The nutrient concentrations were much lower than observed in 2010. This is most likely due to natural variability which is often found with water chemistry data. The dissolved nutrients were very low suggesting rapid uptake by the large seagrass biomass throughout the biounit. The amount of phytoplankton in the water was lower than seen in reference locations.
Average turbidity values throughout the biounit were 0.30 NTU compared to 0.19 NTU observed in reference locations. Turbidity in spring was slightly higher than in autumn although this was not likely to significantly contribute to the stress on habitats in the biounit.
Pressures and management responses
|Stormwater runoff from the coastal towns discharging to nearshore marine waters adds significant nutrient and sediment loads to these environments.||
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.
|Nutrient load discharged (over several decades) by the wastewater treatment plant at Bolivar.||
The Adelaide Coastal Water Quality Improvement Plan (ACWQIP) has targets for reducing nutrient discharges from Bolivar wastewater treatment plant.
Since the mid 1990’s, SA Water has made a significant investment in reducing nutrient discharge loads from the Bolivar Wastewater Treatment Plant. This included a major upgrade to the Bolivar plant including the development of a large water recycling scheme that delivers treated wastewater for irrigation to market gardens in the Virginia area. This investment has resulted in a significant reduction in nutrient loads from the plant.
|Failing and/or high density of onsite wastewater treatment (septic) systems in some coastal towns. This is probably most significant in the Port Clinton, Port Parham and Thompson Beach areas. Overflowing septic systems contribute nutrients to nearshore marine waters through shallow sub-surface or occasional overland flows.||The District Council of Mallala is not planning to operate community wastewater management schemes in coastal townships. However, the Council does require that onsite wastewater treatment systems are compliant with the wastewater Regulations under the Public and Environmental Health Act. Tighter restrictions are also expected to apply to new applicants for onsite wastewater management systems, in keeping with new legislation (the South Australian Public Health Act 2011)|
|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 Clinton 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.|
- 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.