Interaction of Climate Change and Acid Deposition - Climate Change Impacts on Freshwater Ecosystems - page 175

areas for decades to come. Further reductions are required if the goal is to permit
recovery of all impacted ecosystems.
Climate change is a confounding factor in that it can exacerbate or ameliorate
the rate and degree of acidification and recovery, both with respect to chemical
as well as biological effects. The absence of recovery following reduction in acid
deposition, therefore, may simply be the result of the confounding influence of
climatic variations. The time-scales of recovery from acid deposition are in many
respects similar to those of chronic changes in climate, in part because both
drivers act by affecting large pools of S, N, C and base cations in catchment soil.
But extreme climatic events, such as droughts, cause extreme responses that set
back the biological recovery process and slow down progress towards a stable
ecosystem. The interactions are complicated and manifold, and thus the outcomes
on ecosystems are difficult to predict and generalize.
Both acid deposition and climate change are caused by emissions of gases to
the atmosphere and are largely due to the same types of human activities -
burning of fossil fuels and other industrial processes. Clearly, there are
substantial 'co-benefits' to be gained: for example, reductions in emissions of
CO 2 by a switch to renewable energy sources will also bring about a reduction
in S and N emissions. At the policy level, much might be gained by coordinating
future emission controls, now dealt with separately under the United Nations
Economic Council for Europe (UNECE) Convention on Long-Range
Transboundary Air Pollution (LRTAP) and the UN Framework Convention on
Climate Change.
Society will take measures to ameliorate or mitigate the effects of climate
change. Some of these measures may indirectly affect the acidification of
sensitive freshwaters. For example, as illustrated by the modelling example
from Finland (Fig. 7.15), more intensive use of forests for biofuel may entail
release of N now stored in the soil to surface waters in the form of NO 3
accompanied by acidic cations. More research is needed on the effects of
adaptation and mitigation.
The mechanisms of the interactions between climate effects and acidification
effects are still, however, poorly understood. Experiments, continued monitoring
and analysis of long-term data series and modelling are complementary approaches
that lead to new insights and knowledge on possible interactions. Research is
particularly challenging in this field because the goal is to make projections for
the future under climatic conditions that for many ecosystems have never been
experienced previously. It is certain that climate change will have an increasing
impact on freshwaters in the foreseeable future and there will certainly be effects
not yet identified. Current assessments of total impact on freshwaters are probably
underestimated.
References
Aber, J.D., Nadelhoffer, K.J., Steudler, P. & Melillo, J. (1989) Nitrogen saturation in northern forest
ecosystems. Bioscience , 39 , 378-386.
Aber, J.D., Ollinger, S.V., Driscoll, C.T., et al . (2002) Inorganic nitrogen losses from a forested ecosystem
in response to physical, chemical, biotic, and climatic perturbations. Ecosystems , 5 , 648-658.