Monitoring the Responses of Freshwater Ecosystems to Climate Change - Climate Change Impacts on Freshwater Ecosystems - page 85

The direct and indirect effects of climate change on the biota of lakes, rivers
and wetlands will depend on ecoregion, ecosystem type and other stressors
affecting the water body. Owing to the natural variability of surface waters and
the effects of many other stressors, no simple dose-response relationships among
climate change and biotic effects can be expected; the linkages between climate
change and biodiversity patterns cannot be understood without the overall,
complex picture.
The purpose of this chapter is to suggest indicators for the effects of climate
change on lake, river and wetland ecosystems that reflect the direction of their
pathways, relative importance, and magnitude of change. The term 'indicator' is
used here in a broad sense, i.e. a simple detectable sign of a complex process that
can be used as an early warning of ecosystem change. Indicators may be chemical,
hydrological, morphological, biological or functional parameters, which reflect
key processes influenced by climate change and are relatively simple to monitor.
There is a focus on parameters that are already used for monitoring programmes
under the Water Framework Directive, but other indicators (e.g. hydrological
parameters) are considered as well.
The selection of indicators is based on a literature review (up to 2007), in
which we first categorize and describe potential direct and indirect climate change
effects on lakes, rivers and wetlands. From this description a selection of
parameters judged to most clearly reflect the effects of climate change on
freshwater ecosystems is made. In two case studies, the susceptibility of selected
taxonomic groups to climate change effects is analysed.
Climate change impacts on the biota of lakes
Monitoring and assessing the effects of stress on lakes
Monitoring of lake ecosystems in Europe has changed significantly in recent
years. While formerly the use of physicochemical and selected biological
variables (such as chlorophyll) was most widespread, the EU Water Frame-
work Directive places emphasis on biological indicators. A variety of organism
groups (phytoplankton, macrophytes, benthic invertebrates and fish) have now
to be monitored, supplemented by hydromorphological and physicochemical
measurements.
Most biological assessment systems, developed for the purpose of the Water
Framework Directive, aim to reflect the deviation of the observed assemblage
from an undisturbed reference state, thus providing an integrated appraisal of a
water body's ecological quality. The current assessment systems are therefore
reflecting the impact of a variety of stressors. The impact of climate change has
rarely been considered in assessment systems and, as noted above, is not
specifically addressed by the Water Framework Directive. However, almost all
indices used to monitor the ecological status of European lakes will be affected
by climate change.
Climate change impacts will be among the most important stressors on
freshwaters in future, and will initiate chains of processes that are complex and