Aquatic Ecosystem Variability and Climate Change – A Palaeoecological Perspective - Climate Change Impacts on Freshwater Ecosystems - page 33

climate variability, and that contemporary changes are not as yet significantly
greater than those expected from natural variability.
The exceptions to this are lakes from high latitude and altitude where evidence
for unprecedented change is becoming compelling, associated with decreased ice
cover and increased productivity. For most other freshwaters situated in populated
regions of the world, the lake sediment record suggests that the effects of nutrient
enrichment, acid deposition, water abstraction and other human impacts,
operating at local and regional scales, remain the principal stresses, masking the
effects of climate change. Where climate change modifies processes in the same
way as human activity (e.g. in driving nutrient dynamics, controlling alkalinity
generation and modifying hydrological regimes), disentangling the role of climate
change from these other stressors may continue to be difficult.
However, in Europe and other regions of the world where pollutant loadings
are being reduced and lakes and streams are being progressively rehabilitated,
climate change could become a more important driver of freshwater ecosystem
structure and function in the future, potentially deflecting recovery trajectories
from pollution away from the pre-pollution reference state and towards a new,
uncertain state. The palaeoecological record in future will consequently serve not
only to provide an insight into how freshwater ecosystems have varied as a result
of past climate change but also to provide a measure of how different freshwater
ecosystems might become in future as a result of global warming.
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