Climate change may result in a number of changes to physical and chemical processes in River Basins that ultimately result in increased pollution of transitional and coastal waters. The changes that occur will affect summer periods during which drought conditions, particularly in the South East of the UK are likely to result in the reduced dilution of chemicals present in sewage and other effluent discharges. More stormy conditions will affect summer and winter periods contributing to rapid runoff of chemicals from agricultural and urban areas and overflows from combined sewers. The predicted trend to drier summers, but more extreme rainfall events, will exacerbate the complementary problems of microbial delivery from livestock farming and sewage overflows (CSOs) producing intermittent and short term non-compliance in bathing and shellfish harvesting waters. Increased temperature and, in the longer term, decreased pH will affect the availability for accumulation by marine organisms of chemicals present in sediments and the water and will modify toxicity, in some cases reducing it (e.g. by increasing degradation) but in other cases increasing it (e.g. by enhancing uptake).

Most research effort so far has focused on modelling river water quality and climate change impacts, but the concepts and results can be extrapolated to estuaries and coastal waters. This work highlights such effects as:

• Water quality will be affected by changes in flow regime.
• Lower minimum flows imply higher concentrations downstream of point discharges.
• Increased storm events, especially in summer, could cause more frequent incidences of combined sewer overflows (CSOs) discharging highly polluted waters into waterbodies.
• More intense rainfall and flooding could result in increased suspended solids, sediment yields and associated contaminant metal fluxes.
• Invasive species - can alter the structure and function of ecosystems and this pressure may act in combination with the stress of contaminant exposure and altered physical parameters.

Many of the changes described above may result in deterioration of estuarine and coastal waters over a period of decades but in the shorter term breaches of current and emerging legislation are more likely to result. Climate change will therefore present a number of challenges to the Environment Agency and other organisations that have a broad range of duties to monitor, protect and improve estuaries and coastal waters. Increase in chemical and microbial pollution of coastal waters has the potential to impact on ecological quality, health, economic resource utilisation and compliance with EU Directives.

It is apparent that whilst many of the climate change influences on coastal waters have been hypothesised and prioritised and some patterns are emerging, existing evidence to support or refute these theories is still patchy. The current state of knowledge specifically on marine pollution is limited and the knowledge gaps are numerous and extensive.

What is already happening: Medium

In some areas, for example our current understanding of the inputs, behaviour and impact of ammonium, is reasonably good and would warrant a higher value for evidence and consensus. This is also the case for microbial contamination for which our knowledge of inputs and behaviour in the environment is better understood. But in other cases there is greater uncertainty e.g. for the distribution of priority pollutants and other chemicals from CSO inputs and the potential for toxicity enhancement through increased temperatures and reducing pH.

What could happen: Medium

Predictions for the future are limited in a number of areas by available research. More specific issues are developed in this report card than were presented previously.

What are the top priority knowledge gaps that need to be addressed in the short term to provide better advice to be given to policy makers?

Relating specifically to climate change and coastal pollution a number of knowledge gaps are apparent, many of which are cross-cutting to the different functions of the Environment Agency but also engage other organisations that contribute to improved understanding of marine processes. These include but are not limited to the following areas of research:

• Projected changes in the statistical distribution of river flows
• Estimates of the probabilities of changes in water quality and the probabilities of failing water quality standards including accurate and integrated, process-based prediction models for microbial pollutants in coastal catchments and near-shore receiving waters
• The joint probability of intense rainfall during or after a long period of dry weather and low river flow
• The possibility for higher effluent concentrations due to water re-use
• The possible changes to mixing and circulation of discharges from outfalls
• The potential for hypoxic episodes in coastal waters causing fish kills
• Increased distribution of contaminants due to increased sediment disturbance
• A better understanding of the effects of salinity, temperature and pH change upon chemical contaminants and their potential impact on marine organisms.
• In addition to the issue of coastal pollution per se, there is the wider aspect of the combined impacts of climatic variability and other stressors, such as chemical and microbiological pollutants, and the impact this may have on species distribution. In this context:
  • More research is required to evaluate the interactions between climate change and contaminants to better understand and predict how on-going and future climate changes may interact with anthropogenic impacts, including chemical and microbiological pollution.
  • Experimental studies and modelling efforts are needed to test various scenarios concerning transport, transfer and cycling of chemical pollutants and to assess the counteracting effects on important species including the impact on their well-being/fitness, and the potential effects on populations/ecosystems.

The potentially increased concentration of contaminants (such as ammonia, various organic chemicals and metals derived from CSO discharges) resulting from storm water inputs or due to reduced water flows may impact adversely on both commercial and recreational fisheries within estuaries.

Estuaries and other Transitional and Coastal waters are important nursery grounds for commercially important species, e.g. Bass, and unfavourable conditions through chemical intoxication could threaten commercial coastal fisheries and recreational sea angling.

Although shellfish have a greater tolerance to some contaminants they are inherently immobile and unable to avoid acute exposure. In addition the greater potential frequency of contamination of shellfisheries with sewage effluents, in particular the microbiological contamination, will mean that greater time and effort will have to be given to depuration of shellfish intended for consumption.

Salmonids are an important species with the recreational fishery also having a high social and commercial value (this issue is important because increased contamination of surface waters and their deoxygenation can influence fish avoidance well below lethal concentrations and may severely impact salmon runs in vulnerable rivers).

• There are over 12,000 full or part time fisherman in the commercial sector.
• The value of fish landed by UK vessels is £630m per annum of which about 20% -28% comes from the inshore fishery.
• The Scottish salmon farming industry is worth in excess £380m per annum.
• Although the landings of fin-fish have shown a steady decline over many years landings of key shellfish species (Nephrops, scallops and crabs) continue to rise.
• Cultivated shellfish total value for 2006 ~£23m to the UK economy (Shellfish Association, 2009).
• By comparison wild shellfish from near-shore intertidal and subtidal beds (cockles, mussels and oysters) have a relatively modest commercial value (although still >£6m per annum). The social value of these fisheries is much higher with many local communities having a long established affinity with fishing. The condition of many of these fisheries (Wash, South Wales, Morecambe Bay) is poor and although ammonia and other contaminants have not been identified as a key issue, any chemical stressors present could inhibit recovery (Shellfish Association, 2009).

The value of recreational sea angling is now approaching that of the commercial sector; a 2004 report estimated that recreational sea angling in the UK was worth £1,000m annually (PMSU, 2004).

Sheahan, D., J. Maud, A. Wither and C. Moffat. (2010) The potential impacts of climate change on estuarine and coastal pollution in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 10pp. www.mccip.org.uk/arc

Wither, A., C. Stapleton, M. Wyer, A. McDonald & D. Kay (2010) Microbial Pollution of Bathing and Shellfish Waters in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 13pp. www.mccip.org.uk/arc