|
Background
Implications
Regional aspects
Assessing and measuring the current situation
Indicators
Management responses
Future directions
Recommendations
Related issues
|
|
Background 
Algae are aquatic plants that grow either as single cells or as aggregations. They can be so small that they can't be seen with the naked eye or can grow as large as seaweeds such as giant kelps. Algal blooms occur when the growth of algae is excessive. When conditions are suitable, algae multiply rapidly until all the available nutrients are used or conditions once again become unfavourable. Factors such as light entering the water, water temperature, turbulence, nutrient availability and, turbidity determine whether conditions are conducive to algal blooms. Several of these conditions need to be suitable simultaneously for algae before a bloom can occur. Increased nutrient loads from human settlements have resulted in increasing numbers of algal blooms in estuaries and marine environments. Sources of these nutrients include discharge of sewage waters, urban and agricultural run-off, the use of phosphorous containing detergents etc. Increasing nutrient levels in estuaries often results in a change in dominant algal species. Certain species of algae (such as blue-green algae and dinoflagellates) produce toxins, which provide a health hazard to those using the water body for recreation. Swallowing water contaminated with cyanobacterial toxins can cause serious detrimental health effects but even swimming in these waters can cause allergic skin reactions in sensitive people. Another significant source of exotic toxic algae is from ballast water in ports. One of Australia's most hazardous ballast water introductions has been a toxic dinoflagellate, Gymnodinium catenatum, which also probably arrived through ballast at Triabunna in Tasmania. Toxins also provide a source of contamination for food producers within estuaries, such as marine farms. Shellfish themselves are not affected by the toxins, but higher mammals such as seals, birds, whales and humans are. Such contamination results in health risks to ecosystem and human consumers, and creating the potential for serious economic impacts on these industries. During 1986 and for several years after, blooms of Gymnodinium catenatum in Tasmania caused the temporary closure of 15 shellfish farms for periods of up to six months. Other than the significant potential impact of toxic algal blooms on higher mammals, algal blooms also affect natural ecosystems when large amounts of algae die and decompose. This process uses up oxygen in the water at such a great rate that there is not enough to sustain other resident flora and fauna. Large fish kills are typical outcomes of this process. Australian waters are typically low in nutrients and thus this is often the factor limiting algal blooms. The increased frequency of algal blooms is usually considered to be related to land-based anthropogenic sources of nutrients. In Tasmania, the low water temperatures provide an additional factor that limits algal blooms. Implications Clean and safe water for recreation is crucial to the protection of those using it. The same is true for the environment. Healthy waterways are necessary for the variety of aquatic habitats, and the systems that rely on them, to be maintained. Serious economic consequences for tourism and marine farming can also result from algal blooms. Regional aspects This issue is mainly orientated around the settled parts of the State, estuaries with agricultural catchments, or where there is a significant marine farm industry. However, data are also necessary from estuaries with minimal human impact to give context to the former data. Assessing and measuring the current situation - State Water Quality Policy: there is no formal requirement for monitoring within the policy, merely the implication that it is required.
- Tasmanian Shellfish Quality Assurance Program run by the Department of Health and Human Services (DHHS) assesses shellfish growing areas for public health risks.
- Tasmanian Aquaculture and Fisheries Institute (TAFI) assessment of water quality (including chlorophyll a concentrations) in 22 Tasmanian estuaries (Murphy et al. 2003). Major objectives of the study were to provide baseline water quality data and determine water quality indicator levels for Tasmanian estuaries. Chlorophyll a is considered to be an indicator for algal biomass. State of the Environment and ANZECC have both identified a lack of baseline data as severely limiting our ability to set appropriate trigger values for indicators of estuarine health. Determining baseline values is seen as the first step in the detection and possible remediation of environmental problems affecting Tasmanian estuaries.
- The State of the Derwent Report (Coughanowr 1996) compiled existing information on the water quality of the Derwent Estuary including an assessment of nutrients, chlorophyll a concentrations (a measure of phytoplankton biomass and algal growth) and algal blooms. The report indicated the estuary did not experience recurrent nuisance algal blooms, despite relatively elevated concentrations of nutrients in the middle and lower reaches of the estuary. These nutrients were derived predominantly from sewage and from seasonal influxes of nutrient-rich Southern Ocean waters to the estuary.
The report found that chlorophyll a concentrations (a measure of phytoplankton biomass and algal growth) were typically low to moderate, with slightly higher values recorded in the middle reaches of the Derwent estuary, particularly in Prince of Wales Bay. It is unclear why there was a lack of phytoplankton response to available nutrients in the estuary. The Derwent may be physically unsuited to algal blooms (rapidly flushed, cold water, limited light availability), or alternatively, algal growth may be inhibited by some natural or anthropogenic substance or process (e.g. humic/fulvic acids, heavy metals, grazing by zooplankton). The upper estuary, in contrast to the middle and lower reaches, shows extremely low concentrations of orthophosphate at all times (<2 m g/L), and algal growth in this area could potentially be phosphorus-limited (Coughanowr 1996).
In 2000, monitoring conducted as part of the Derwent Estuary Monitoring Agreement (DPIWE 2000) and Derwent Estuary Program found the nutrient and chlorophyll data was more difficult to interpret due to a shorter record (1996-2000) and considerable natural variability. Nutrient levels were somewhat elevated at mid-estuary sites, however, chlorophyll levels were usually moderate to low. There were no clear trends for most of the estuary, with the exception of Prince of Wales Bay, where levels appear to have doubled since 1996.
- The Huon Estuary Study (CSIRO 2000) conducted from 1996-1999 found that two classes of algal blooms typically characterise the Huon Estuary in the spring to autumn period of most years, one of which includes the toxin-producing dinoflagellate, Gymnodinium catenatum. The study determined a close link between physical conditions (e.g. light, temperature, salinity layering) and populations of microalgae. Nitrogen also seemed to be the limiting nutrient for microalgal production in the estuary waters. About half the available nitrogen (for biological production) entering the estuary, under existing conditions, comes from bottom waters at the marine boundary. The other half is split almost evenly between agricultural run-off and from operation of salmon farms (CSIRO 2000).
Indicators
|
|
|
|
|
Management responses - Through the National Land and Water Resources Audit, new information has been obtained on estuaries with some data relating to eutrophication and algal blooms. For example, the recently published report 'Estuarine Health in Tasmania, status and indicators: water quality' (Murphy et al. 2003) by the Tasmanian Aquaculture and Fisheries Institute.
- The Tasmanian Shellfish Quality Assurance Program provides ongoing monitoring for water quality testing in shellfish growing areas. The Program was set up in the mid-1980s to evaluate and classify all commercial shellfish farming areas in the State by way of routine bacteriological, chemical and biotoxin monitoring.
- The State of the Derwent Estuary report (Coughanowr 1996) was produced and is a compilation and synthesis of existing information about the Derwent Estuary from the early 1970s through to 1996 including information on algal blooms.
- Derwent Estuary Program was established in 1999 with the goal of restoring and protecting the environmental resources of the Derwent Estuary.
- The Derwent Estuary Monitoring Agreement was signed in August 2000 by the state government, six local councils and three industrial/commercial partners (Norske Skog Paper Mills, Pasminco Hobart Smelter and Hobart Water). The signatories agreed to coordinate their independent monitoring programs to provide better information on the estuary as a whole, and to report annually on environmental conditions and trends in the Derwent. A 'Report Card' (DPIWE 2000) for the status of the Derwent estuary provided a summary of monitoring data and an update of conditions for the year 2000, including information on nutrients and chlorophyll.
- Huon Estuary Study was conducted from 1996-1999 (CSIRO 2000) providing some environmental research for integrated catchment management and aquaculture. This included an assessment of algal blooms and the links between algal production and catchment and estuary activities.
Future directions - To establish whether fluctuations in algal levels are a function of natural conditions, or indicative of imbalances in ecosystems related to human activities, further monitoring is required to determine natural levels of algae specific to individual sites. This would enable a quantitative definition of algal 'bloom' that is lacking in the current report.
- Alternative indicator definitions may be required in future SoE reporting because the current indicator for algal bloom frequency may lead to data being reported that reflects the monitoring intensity rather than the actual algal blooms relative to other Tasmanian estuaries.
- An extension of sampling to a range of different estuaries is required if algal bloom frequency is to be reported with greater realism in Tasmania. Edgar et. al. (1999) provide a guideline of estuary classification with which to stratify sampling of different estuary types. Estuary selection should have reference especially to the land use of the surrounding catchment. For example, very little monitoring of algal blooms occurs in the north of the State where the impact of agriculture (especially high nutrient run-off which may result from high rates of fertilizer application by the dairy industry) may mean that algal blooms are above natural levels. The measurement of chlorophyll concentration (an indicator for algal biomass) within various estuaries around the State through the Estuarine Health study (Murphy et al. 2003) goes some way to achieving this by providing baseline data for algal biomass in 22 estuaries. However, a formalised monitoring program is required to provide comparison against this baseline data, at a minimum, to be conducted every 5 years. More specific monitoring for different types of algae-particularly toxic algae-is also required.
Tasmania Together and the RMPS Relevant Tasmania Together goals and standards for 'Coastal, Estuarine and Marine' are listed in the linked file. The Tasmania Together Progress Board reported on progress toward targets for benchmarks set (Tasmania Together Progress Board 2003). Indicators, targets and baseline data are available in the latest Progress Report June 2003. Further information, including progress report updates, is available from Tasmania Together. Involvement of the community, and the fair and orderly use of resources are also fundamental principles of the RMPS. The RMPS objectives have been developed to advance the principles of sustainable development. Recommendations
Related issues
|
|
