The blue green algae Anabaena circinalis was first discovered in Lake Trevallyn in bloom proportions in January 2007. The bloom was the catalyst for the establishment of the Lake Trevallyn Algal Bloom Monitoring Program and Working Group. The program is a coordinated partnership approach to monitoring, enabling an increased understanding of the drivers of blue green algal blooms in Lake Trevallyn while allowing for shared resources and information. Partners include: Meander Valley Council, West Tamar Council, TasWater, Hydro Tasmania, Department of Communities and the Institute of Marine and Arctic Studies (IMAS). The group’s aims are to: monitor the occurrence of algal blooms in Lake Trevallyn during the peak summer recreational period; provide early warning mechanisms to water authorities and the public; understand the key drivers influencing the outbreaks and; propose management strategies.
THE BIG PICTURE
At low numbers, algae cause no problems and are, in fact, a natural part of a water body. Occasionally, however, algae can grow very fast or ‘bloom’ and accumulate into dense visible patches at the surface of the water. Algal blooms can be driven by low water flows and high levels of available nutrients, such as phosphorous and nitrogen, which promote its growth. Algal blooms can become a serious public health and environmental problem in many waterways. Contact with an algal bloom may cause a number of human health problems, including skin rashes, eye irritation, earaches, itchiness, swollen lips and other symptoms. Algal blooms can also cause unpleasant taste and odour compounds in drinking water.
WHY THIS ACTIVITY IS IMPORTANT
The Lake Trevallyn Algal Bloom Monitoring Program coordinates water quality monitoring for Lake Trevallyn. Pathogen (enterococci) and Blue Green Algae (Anabaena) assessments are done weekly at the Trevallyn boat ramp and at the Blackstone Park beach. Water quality data (pH, electrical conductivity, turbidity, chlorophyll-a, Phycocyanin and water temperature are collected 24/7 near the dam wall. Water temperature is collected to a depth of 10m at the same location. The data is used to identify early warning signs of Blue Green Algal blooms, while providing a centralised data collection point for all stakeholders. Data collection through monitoring, is increasing our understanding of the bloom processes in Lake Trevallyn for future management of the Lake for recreation and the storage of drinking water.
The monitoring program gives management agencies information to better inform users of the Lake when it is safe for use and better understand why blooms are occurring and what is being done to manage Blue Green Algal blooms.
WHAT WE HAVE ACHIEVED
The first recorded bloom in Lake Trevallyn occurred in the summer of 2007. During 2008/09 summer a smaller bloom occurred over a two week period. Most years, blue green algal numbers increase towards the end of summer however no large visible blooms have been detected in Lake Trevallyn for a number of years.
Key findings from the monitoring program are:
- Water flows are a major controlling factor of blue green algal blooms in Lake Trevallyn. Low residency times (high water flows) during summer may prevent the blooms from becoming established, as seen in the 2009/2010 summer;
- Suitable nutrient concentrations for algal growth always seem to be present;
- Algal blooms persist when stratification of the water temperature occurs under the influence of high summer temperatures, promoting Anabaena cell growth and surface concentration;
- Anabaena circinalis cells detected in the monitoring program have, to date, all been found to be at non-toxic levels.