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Multiple stressor indicators, interactions and impacts at a MARS workshop in Lisbon

January 19, 2016

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In December 2015, a team of MARS scientists responsible for investigating and modelling the effects of multiple stressors on river basins across Europe held a project workshop in Lisbon, Portugal.  The workshop discussions – organised by Teresa Ferreira – are shown here in a series of pictures taken by MARS scientist Christian Feld.

A key topic at the workshop was to analyse ongoing data about how biological indicators, such as fish abundance, are affected by multiple stressors, such as habitat loss or pollution, at the river basin scale.  Here, the team sought to identify most important stressors and, if present, their interactions.

Christian Feld explains how multiple stressors can interact in freshwater ecosystems:

Stressor interactions mean that two stressors – for example, increases in nutrient concentrations and water temperature – act together to create problematic ecological effects.

Here, we have a typical example of ‘synergistic’ stressors, which interact and together increase their individual effects. In other words, the joint effect of nutrient pollution and increased temperatures is more than the sum of individual effects.

The other main type of multiple stressor interaction is antagonistic, which is when one stressor (in part) reduces the effect of another.

Understanding the interactions and impacts of multiple stressors on freshwater ecosystems is one of the key challenges for the MARS project.  In an increasingly human-impacted world, most ecosystems are subject to numerous stresses from many sources.  An awareness how these stressors interact is therefore important for guiding environmental management, policy and conservation.

For example, restoration and conservation efforts on a river which is in poor ecological health as a result of pollution, habitat loss and invasive species need to understand the interactions between these multiple stressors in managing their mitigation.

If there are antagonistic interactions, management of a single stressor could lead to the effects of its interactive pair becoming stronger.  Restoration and conservation efforts which focus on single stressors might therefore have unexpected outcomes for the health and diversity of an ecosystem.

Participants at the Lisbon workshop agreed on a standardised procedure for analysing stressor interactions, which can be applied across all European river basins. The results of these analyses will feed into that of other MARS teams who are synthesising data on multiple stressor impacts and interactions at the European scale.

Christian Feld explains why this work is important:

We wish to see if multiple stressor patterns and results are comparable across Europe; and across streams, rivers, lakes and estuaries.

We want to know which organisms are the best indicators of multiple stressors (fish, invertebrates, plants); and we wish to know which stressors and stressor combinations act at broad (continental) scales, and which act rather regionally or locally.

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