During the 1990s there was increased demand in the UK for effective methods of monitoring eutrophication. For monitoring tools to have practical application, they must satisfy certain requirements:
• sampling must be quick and easy;
• monitoring must be based on a finite number of easily identified groups; and
• indices for evaluation must be straightforward to calculate.
Within-year variability in nutrient concentrations can be high, particularly for enriched waters. A high sampling frequency may therefore be required to provide representative annual mean data.
In nutrient-enriched lakes, annual means are more likely to provide appropriate estimates of phosphorus than winter-spring means, due to the importance of internal cycling of nutrients in summer. This is an important consideration when designing sampling strategies for use in predictive models of trophic status.
In Britain, water supply companies have tended to regard eutrophication as a serious problem only when it becomes impossible to treat drinking water supplies in an economic way.
Threshold concentrations at which action is taken to reduce nutrient loadings thus depend on economic factors, as well as wildlife conservation objectives.
There are two possible approaches to reducing eutrophication:
1. Reduce the source of nutrients:
• Diversion of effluent
• Phosphate stripping
• Buffer strips
• Domestic campaigns
2. Reduce the availability of nutrients currently in the system (e.g. by removing plant material, removing enriched sediments, chemical treatment of water).
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