Monitoring the Responses of Freshwater Ecosystems to Climate Change - Climate Change Impacts on Freshwater Ecosystems - page 94

Climate change impacts on the biota of rivers
Monitoring and assessing the effects of stress on rivers
As with lakes, monitoring of European rivers has changed with the introduction
of the Water Framework Directive. Formerly, the use of physicochemical variables
and selected hydromorphological and biological indices using primarily
macroinvertebrates (such as Average Score per Taxon (ASPT) or Saprobic Indices)
was most widespread, while now several organism groups (phytoplankton for
large rivers, benthic algae, macrophytes, benthic invertebrates and fish) are being
monitored, supplemented by hydromorphological and physicochemical
variables.
The biological assessment systems for the Water Framework Directive reflect the
deviation of the observed assemblage from an undisturbed reference state; in the case
of rivers, the deviation is mainly caused by organic pollution, hydromorphological
degradation, eutrophication and acidification. While organic pollution was formerly
the most widespread stressor, hydromorphological degradation is now a main
concern, particularly in Central Europe. Acidification is mainly restricted to north-
west Europe, some Alpine regions and a number of other upland areas, although
eutrophication universally affects the lowland reaches of rivers in Europe.
Table 5.2 gives a selection of potential indicators for climate change impacts
for small rivers in cold, temperate and warm ecoregions of Europe. As for lakes,
many of the biotic indicators could be easily incorporated into routine monitoring
programmes, e.g. by adding indices reflecting the impact of temperature change
on benthic invertebrates, which are already monitored for the purposes of the
Water Framework Directive. However, physicochemical variables are most
appropriate as early warning indicators.
Hydrology
Changes in hydrology have been discussed in Chapters 3 and 4.
Primary production
Changed runoff and water temperature are expected to cause changes in riparian
vegetation (Hauer et al . 1997; Primack 2000) and may enhance macrophyte and
algal growth. Lower water levels and increased nutrient availability will lead to a
greater proportion of terrestrial plant species in floodplains (Hudon 2004). In
Fennoscandia, macrophyte species richness decreases with latitude and altitude,
mainly due to decreased July temperature. Thus, macrophyte biodiversity is
expected to respond strongly to climate change (Heino 2002).
Secondary production
Water temperature, flow regime, channel morphology and sedimentation, which
are all subject to impacts from climate change, are decisive factors for river
invertebrates and fish. Key variables are summer and maximum temperatures.