Managing multiple stressors in aquatic ecosystems: recommendations from the MARS Project
Managing and restoring aquatic ecosystems affected by multiple stressors is a key contemporary challenge for environmental scientists, managers and policy makers. As we’ve documented on this blog over the last few years, many European water bodies are subject to multiple human pressures such as pollution, climate change, hydrological and morphological alterations.
Such pressures can cause stress to the health and status of aquatic ecosystems. A stressor can represent either the immediate cause of decreasing ecological status (e.g. oxygen depletion caused by high water temperatures), or be part of a chain of factors which cause ecological degradation. In other words, stressors are how human pressures directly affect ecosystems.
The stressor concept allows us to outline both how human pressures can stress ecosystems in numerous ways, and to be specific about why a water body might not reach good ecological status as a result of the presence of different stressors.
Stressors are how human pressures directly affect ecosystems. Image: MARS
Between 2014 and 2018, the EU FP7 MARS project investigated the interactions and impacts of multiple aquatic stressors, resulting in more than 200 scientific publications and an extensive range of online tools for water management.
This week, the project has published a document titled “MARS Recommendations on how to best assess and mitigate impacts of multiple stressors in aquatic ecosystems”. This open-access pdf outlines a framework for how multiple stress conditions might be best mitigated in River Basin Management through the EU Water Framework Directive.
The MARS framework supports environmental decision-making by providing tools and guidance for water managers to identify dominating and interacting stressors. Whilst multi-stressor situations vary between ecosystems, three broad guidelines for their management are identified.
First, where there are dominant individual stressors (e.g. water pollution), these should be the main priority for mitigation. Second, where stressor interactions are antagonistic (i.e. they ‘cancel each other out’ to some extent – e.g. nutrient and water flow increases), then the non-antagonistic stressors present should be targeted for mitigation. Finally, where stressor interactions are synergistic (i.e. they have effects ‘more than the sum of their parts’ – e.g. nutrient and temperature increases), then all present stressors should be targeted simultaneously, as far as possible.
Key questions for tackling multi-stressor conditions in River Basin Management using MARS outputs. Image: MARS
MARS research has demonstrated that there are some general patterns between stressor pairs, particularly in waterbody type specific interactions between nutrient and temperature fluctuations in lakes. However, the new recommendations document emphasises that assessment of stressor interactions and impacts, and planning measures for their mitigation, requires case-specific assessment. In other words, whilst there are some broad guidelines for managers to follow, the stressor conditions in individual waterbodies are key in guiding specific management approaches.
MARS provides a number of open-access online tools to help water managers diagnose and mitigate aquatic stressor conditions. These allow users to explore large spatial datasets on European stressor distributions and effects, and to examine cause-effect relationships between pressures, stressors, ecological status and management measures.
Other tools allow users to select the most suitable computer models to support their River Basin Management, to diagnose the causes of ecological deterioration based on biological metrics, and to visualise current and future multiple-stress conditions and ecological status in European rivers and lakes. Heat maps provide an innovative visual means of identifying how two stressors interact, and how mitigation efforts might shift an ecosystem towards good ecological status.
MARS ‘Heat Maps’ of stressor pairs showing the expected gradient between ‘good’ and ‘moderate’ ecological status achieved by reducing stressor levels in additive (left) and synergistic (right) conditions. Image: MARS
The document also provides examples from seven MARS case studies to show how theory has been applied in practice, and to highlight key questions for River Basin Management.
Broadly, the recommendations from the MARS project show how the large datasets about European aquatic ecosystems (much of which is generated through Water Framework Directive monitoring) can be used to improve River Basin Management Planning. More specifically, it shows how the emerging environmental issue of multiple stressors – arguably a key signal of the Anthropocene in freshwaters – can be addressed by agile and responsive science and management.
MARS has significantly raised the profile of multiple stressor issues in scientific, policy and public realms, and provided an extensive range of information, tools and resources for users to implement in environmental management and restoration. Now is the time for this information to be applied and extended. With the publication of the new MARS recommendations document, there are reasons to be optimistic over the prospects for the health and status of European aquatic ecosystems in the future.
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