Ecological response of streams, lakes and wetlands

In REFRESH we consider water bodies of all sizes but we focus particularly on the most vulnerable systems which are mainly those with small water mass (where warming will be highest and hydrological impacts most pronounced) in lowland regions (where the risks of eutrophication associated with nutrient loading and oxygen stress are greatest). Such systems are found throughout Europe in all climate zones and represent the most important water masses in the continent in terms of combined number, length and area.

There are three work packages on rivers, lakes and riparian wetlands at the centre of which is a series of carefully designed, co-ordinated field experiments in which river, lake and wetland sites have been selected to represent a gradient of climate conditions across Europe. 

Resources are not available in REFRESH to address rigorously all situations where climate change will affect freshwater ecosystems. We will focus on three principal climate-related and interacting pressures: Increasing temperature, changes in water levels and flow regimes and excess nutrients Similarly, we will restrict our attention to lowland rivers, lakes, reservoirs and riparian wetlands because these often pose the most difficult problems in meeting both the requirements of the WFD and HD, and these waters are heavily used, in great demand for multiple uses, often highly modified and eutrophic and are most amenable to adaptive management.REFRESH Experimental Site

Right: Locations of REFRESH experimental lake, stream and wetland sites across Europe

For rivers the emphasis will be on the impact of changing temperatures and low and variable flows under different nutrient conditions. For riparian wetlands the experiments are designed to study the processes involved in changing temperatures, changing flooding regimes and reducing nutrient loading. River and wetland experiments will be conducted at the same sites situated along a north-south gradient in western Europe where river and wetland impacts are projected to be greatest. For lakes the experimental focus will be on lake-level fluctuations and on ecosystem functioning especially with respect to carbon, nitrogen, phosphorus, oxygen and salinity dynamics. The climatic gradient for lake sites will follow a continental north-south gradient, where lake effects are expected to be greatest.

In REFRESH we will also seek to identify thresholds and reference conditions in particular whether climate change may cause thresholds to be crossed, or may cause thresholds to move. The principal objectives are to identify thresholds in structure, function and biodiversity for the effects of temperature, low flows (rivers), low water levels (lakes, including impacts on salinity), changes in flooding regimes (riparian wetlands) and changes in nutrient and organic matter loads (all). We will then evaluate how the threshold concept and knowledge of specific thresholds can be incorporated into adaptation, mitigation and restoration strategies needed to achieve the objectives of the WFD and HD.

We will build on the results from Euro-limpacs and examine how climate change impacts on  the use of  reference conditions for lakes, rivers and riparian wetlands and how the concept of a dynamic reference state can be built into WFD and HD methodologies.

We will develop an effective system of indicators for freshwaters focussing essentially on ecological indicators sensitive to the functional response of rivers, lakes and wetlands to climate-induced changes in temperature, flow/water-level and nutrient/organic matter loading. Special attention will be given to the use of species and assemblage traits as measures of functional response.

We will develop new tools to assess vulnerability to climate change that takes into account both site-specific threats and threats at the landscape scale, e.g. associated with the connectivity of freshwaters where improved connectivity can provide opportunities for migration and dispersal. The new scheme will be tailored especially for assessing the vulnerability of species, of habitats and of the conservation status of Natura 2000 sites listed in the HD.

Experimental Flumes at Alterra

The field experiments will be supported by laboratory and mesocosm experiments, analysis of major databases that enable time-space modelling, further analysis of long-term time-series assembled during the Euro-limpacs project and by evidence from palaeoecological studies where extreme events and abrupt transitions in the past have been recorded. All these approaches will be combined to help develop the process-based models needed to run scenarios for adaptive strategies and which are required for up-scaling from local to river basin. In this context the experimental and modelling approaches are inter-dependent.

Left: Experimental flumes at Alterra