Freshwater Umbrella Research 2004-7

WP 4: Influence of climate change on the impacts of atmospheric deposition on upland freshwaters

Background

Climate is changing rapidly, beyond the range of previous natural variability. The Inter-governmental Panel on Climate Change has recently reviewed the evidence for climate change and concluded that the increase in global mean air temperature, about 0.6°C since the end of the 19th century, is predicted to intensify during the 21st century. For Europe, regional climate models reveal an additional temperature increase of up to 6°C by the late 21st century and an increase in the number of extreme events, such as droughts, floods and storms. Thus natural ecosystems, already under stress from land-use change and pollution, now face additional pressures from climate change, both directly and through interaction with other drivers of change. Such changes would significantly affect the hydrology, chemistry and ecology of lakes and rivers.

Predictions of the direct effects of climate change on aquatic ecosystems are very complex, and predicting these in combination with other human impacts poses an even greater challenge. Climate change affects the hydrological, physical, chemical and biological characteristics of all freshwaters, and is thereby a key influence on element cycling (nutrients, major ions, DOC, organic pollutants, metals), food webs and biodiversity. A central question is what are the likely changes to ecosystem structure and functioning that result from climate change that are independent of natural variability and the impact of other stressors? For lakes a key impact of climate change will be the effect of changing air temperature and wind patterns on the physical structure of the lake water column (e.g. ice cover, stratification and mixing and consequently on lake chemistry and biology). Additionally, substantial increases in the concentrations of DOC have been observed in surface waters draining peaty catchments across north-west Europe and have been attributed to climatic factors such as increased temperature and the frequency and severity of droughts (Freeman et al., 2001).

Despite major reductions in the emission of acidifying compounds, surface water acidification remains a serious threat to Europe's surface waters. Recovery is slow and recovery processes may increasingly be influenced by changing climatic patterns. The key issues are:

  • to determine the effects of long-term and seasonal changes in temperature and precipitation on the leaching of N, DOC and SO42-;
  • to determine the effects of increased frequency of episodic inputs of water and sea-salts on acidification pulses; and
  • to determine the effects of these factors on the recovery of acidified freshwaters

The distribution of POPs and metals may also be strongly influenced by future climate change. POPs are subject to a world-wide redistribution because of their volatility and chemical stability. In the last decade some organic pollutants have been observed to be transferred from temperate areas, where they were synthesised and used, to distant cold sites without significant dilution. Natural distillation and condensation processes are temperature dependent and that together with atmospheric transport lead to their deposition and accumulation in high altitude headwaters. A key question is the degree to which future climate change will influence the distribution patterns and mobility of organic pollutants in freshwater systems and lead to changes in the uptake and accumulation of these substances in freshwater food chains?

The EU funded Framework 6 Integrated Project to Evaluate the Impacts of Global Change on European Freshwater Ecosystems (Euro-limpacs) is concerned with the science required to understand and manage the ecological consequences of the interactions between climate change and pollution from atmospheric deposition. It addresses some of the above issues at the European scale but does not focus specifically on UK freshwaters or on upland systems impacted mainly by atmospheric deposition. This Task will therefore expand on the work done under Euro-limpacs to focus on these specific issues through literature review and summary of ongoing data analysis comparing water chemistry and biology with meteorological and climatic datasets. In addition, process understanding will be improved by experimental manipulations using existing roof infrastructure at the Afon Gwy. This work will complement the nitrate pathways and leaching mechanism work in WP3.

Work programme

The work programme for Work package 4 is split into two main tasks. Click on the links below for further information on an indivisual task

  • Task 4.1 - Literature review of climate impacts on atmospheric pollutant effects, including liaison with Euro-limpacs
  • Task 4.2 - Recovery and climate manipulation experiments at the Afon Gwy

References

  • Freeman C., Evans C.D., Monteith D.T., Reynolds B. and Fenner N. (2001) Export of organic carbon from peat soils. Nature 412, 785.