IMPACTS OF CLIMATE CHANGE ON WATER POLLUTION
Dave Sheahan
Centre for Environment, Fisheries and Aquaculture Science (Cefas), Pakefield, Lowestoft
Executive Summary
Climate change scenarios (Defra, 2002) indicate annual average temperature increases of 2 and 3.5°C by the 2080s; wetter winters (winter daily precipitation up to 20% heavier), and drier summers with the largest relative changes in the south and east where summer precipitation may decline by up to 50%. Sea levels are also expected to rise around the UK – between 26 and 86 cm by 2080s.
Changing climate has implications for land use and the fate and behaviour of anthropogenic and natural chemicals particularly with respect to their interaction with the hydrological cycle. Climate change may influence mobilisation and fate of chemicals applied to land, increasing discharge to surface and groundwater. Discharge volumes of storm water containing various contaminants may also increase. The bioavailability of sediment-associated contaminants present in the aquatic environment may also be changed by increases in temperature, changes in salinity regimes and increased storm events.
Until the 1970s the major biological impact on estuarine and coastal areas was probably the discharge of poorly treated sewage (Matthiesen & Law, 2002). Improved sewage effluent treatment has lead to a greater focus on chemical contaminants with specific modes of action and which often have subtle and chronic effects. These include products that remain active in treated sewage effluent discharges e.g. steroidal chemicals, pharmaceuticals and personal care products, chemicals present in surface runoff from agricultural land e.g. pesticides and nutrients, and contaminants arising from diffuse sources in surface runoff and storm overflows. With the increased development of ports and coastal areas handling of historically contaminated sediments is also an issue of increasing concern and its redistribution in the environment will be influenced by storm events.
Higher temperatures may make biodegradation of chemicals more rapid in water and contribute to reduction in toxic effects, but for many chemicals toxicity will increase with temperature as the rate at which a chemical is accumulated by an aquatic organism via food and respiratory or other body surfaces also increases.
Changes to rainfall patterns may result in changes to the movement and distribution of chemicals e.g. increased leaching of pesticides applied to agricultural land during certain periods of the year. Increased storm events during the winter will increase storm water flows in rivers and potentially inputs of untreated sewage effluent. Decreased river flows in the summer particularly in the South of England will result in higher relative contributions of treated sewage effluent. The biological oxygen demand will increase because of the increase in organic matter from treated sewage as well as any rise in temperature, which will increase bacterial respiration. Heavy storm events during summer periods are likely to result in flushing of untreated sewage effluent and diffuse pollutants from surface runoff in storm overflows.
Increased risk of flooding because of climate change has implications for the inundation of land that is contaminated. There may therefore be a greater risk of contaminants being remobilised in floodwater and of contaminated sediment and water reaching the freshwater and marine environment. Estimates indicate that there may be 100,000 sites affected by contamination in England and Wales with 5-20% requiring action to reduce risk of harm to people and the environment (EA, 2003). Contamination may arise through historic or recent industrial activity or due to natural processes. Just under half of the sites formally determined as contaminated thus far present a risk to controlled waters. The location of coastal industries e.g. power generation will need to take account of the increased risk of flooding in some coastal areas.
The use and fate in the marine environment of specific chemicals may also be influenced by climate change because of changes in farming practice (e.g. increased use of some pesticides) and consumer choice (e.g. increased use of UV sunscreens and fate and effects in the aquatic environment (Buser et al., 2006))
Level of Confidence
Low
Much monitoring effort has focussed on selected chemicals identified as of priority concern (e.g. metals such as mercury and organics such as hexachlorocyclohexane). In many cases, the concentration of these chemicals has declined with the introduction of tighter discharge consents and the improvement of sewage effluent treatment. With a few exceptions (e.g. in relation to sewage sludge disposal sites (Rees et al. 2006), Tributyltin (Rees et al. 2001) and steroidal chemicals), where contaminant-related biological effects are well characterised, changes in chemical concentrations have not been linked to changes in biological effects. Links between chemical concentrations, biological effects and climate change factors are not yet developed in the literature and where time series datasets do exist confidence in showing these links is low.
Key sources of Information
Impacts of Climate Change on Pollution in Marine Climate Change Impacts Annual Report Card 2006 (Eds. Buckley, P.J, Dye, S.R. and Baxter, J.M), Online Summary Reports, MCCIP, Lowestoft, www.mccip.org.uk