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Reporting from MARS: multiple stressor science and management in European aquatic ecosystems

June 20, 2018
Symbolique 2006

MARS has investigated how multiple stressors affect European rivers, lakes and groundwaters over the last four years. Image: Symbolique 2006

After four years of research on multiple stressor interactions and impacts in European aquatic ecosystems, the EU FP7 MARS project has published its final project report (pdf).

The project began in 2014, and investigated how the complex ‘cocktails’ of stressors such as water pollution, habitat loss and climate change affected ecological status and ecosystem services in rivers, lakes and groundwaters across Europe.

The focus of the MARS project was tailored to support water managers and policy makers, in particular through advising the implementation and 2019 update of the Water Framework Directive and the Blueprint to Safeguard Europe’s Water Resources.

The final MARS report gives a breakdown of project activities and results over the last four years. Significantly, it shows that the project has resulted in over 230 scientific publications, numerous policy briefs and factsheets, and a suite of online tools for water management. This blog post gives a brief overview of some of the research highlights, and more detailed information can be found in the project report.

3.Luftbild_Seelabor_© HTW Dresden-Oczipka

The IGB LakeLab in Lake Stechlin, Germany – a ‘floating laboratory’ for MARS experiments. Image: HTW Dresden-Oczipka

Multiple Stressor Research and Management

An initial MARS literature review of 219 existing journal articles on multiple stressors found that nutrient stress was involved in most (71–98%) of multiple stress interactions in rivers, lakes and estuary (or ‘transitional’) waters, and just under half (42%) of those in groundwaters. Their impacts were different depending on habitat type, mostly as a result of different hydromorphological (i.e. the water body banks and bed) characteristics and alterations. As a result, nutrient enrichment and hydromorphological alteration was the most common stressor pair overall, particularly in rivers and transitional waters.

MARS research was carried out at three different scales. At the water body scale, experiments with mesocosms and river flumes were used to investigate stressor interactions, and their impacts on ecological status and ecosystem services. At the catchment scale, modelling and empirical approaches were used to characterise the relationships between multiple stressors and ecological responses, functions and services, across 16 European river basins.

Finally, at the European scale, large-scale spatial analyses were carried out to identify relationships between stressor intensity, ecological status and service provision for large transboundary rivers and lakes. This research produced a series of European multi-pressure maps, with threshold values for four important pressure types, and a Stressor Analysis Tool for water managers.


The HyTEC field station in the Austrian Alps – the site of MARS stream experiments. Image: Christian Feld

Key messages from MARS

Around one-third of the 156 MARS case studies across Europe showed significant multiple-stressor effects. As a result, it can be confidently stated that multiple stressors are an important contemporary topic for aquatic science and management. However, a key message from MARS research is that there are rarely predictable relationships between stressor causes and biological effects, and that the characteristics of the local environment can mask or interfere with observed stressor effects.

As a result, it is necessary to investigate and manage the multiple stressor interactions and impacts for individual water bodies and river basins depending on their local biological and geographical characteristics. These can be assessed, diagnosed and managed using a suite of MARS online tools.

In short, what is required is aquatic science research that investigates the direct causes of deteriorated ecological status in rivers and lakes across Europe, a task which can be aided by advances in multiple stressor data collection and diagnostics. This is a key focus for managing and restoring complex aquatic environments under multiple pressures, both now and in the future.

mars tools

The MARS online tools hosted on the Freshwater Information Platform.

Multiple Stressor Tools

MARS project findings have been integrated into practical and accessible online tools to support water management.

They include:

  • Freshwater Information System – including an information library and factsheets on multiple stressors, ecosystem services, case studies and storylines for future environmental scenarios, alongside a model selection tool and guidelines for river basin management;
  • Diagnostic Tool for Water Bodies – designed to help water managers diagnose and mitigate multiple stress impacts on rivers and lakes;
  • Model Selection Tool – an overview of 21 available computer modelling tools for river basin management;
  • Scenario Analysis Tool – allows users to visualise and map multiple stressor interactions and impacts (both present and projected) at the European scale;
  • Bayesian Belief Models – designed to help predict biological responses to aquatic conservation and restoration measures under projected future environmental scenarios (see approach here).
mars threshold visuals

Visualisation of an additive pair of stressors – riparian vegetation alteration and phosphate levels – and how they might be managed towards good ecological status, as shown by the diagonal threshold line.

One innovative MARS output for water managers is the visualisation of how stressor-pairs can be managed towards good ecological status. Individual stressors are shown on the x and y axes of the ‘heat map’ diagrams, which are generated by computer modelling, and show a threshold line across which multiple stressor levels should be reduced in order to achieve good ecological status.

Summing up

Reflecting on the last four years, MARS project co-ordinator Sebastian Birk says,

“MARS was a fascinating project, joining the forces of highly skilled scientists across Europe towards unraveling the multi-stressor maze. I feel very honoured for this chance of coordinating such a great team. Most project partners knew each other since the early days of the Water Framework Directive, and this long-standing confidence and trust in each other made this project a delight. Daniel and me would like to express our sincere thanks to all MARS colleagues for this memorable experience! With posting the final project report, this will be kind of the last ‘official’ MARS blog entry. However, there is much more on MARS and beyond, so stay tuned to this channel.”

Read the MARS Final Report (pdf)
Read the ‘Messages from MARS’ blog post

Explore the MARS website

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