Understanding the effects of climate change on water quality: a case-study assessment on rivers and lakes in England (WT0972). Final report 31st January 2013

Hutchins, Mike; Elliott, Alex; Caillouet, L.; Williams, Richard. 2013 Understanding the effects of climate change on water quality: a case-study assessment on rivers and lakes in England (WT0972). Final report 31st January 2013. NERC/Centre for Ecology & Hydrology, 29pp. (CEH Project no. C04523, Defra Contract WT0972)

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The main objective of the study was to quantify the effects that the climate likely to prevail in the 2050s might produce on the phytoplankton populations and water temperatures in lakes and rivers in England. There are four questions that are of importance to regulatory bodies: • How and when will climate change have a discernible and significant impact on water quality? • Will the changes require a change in monitoring or management practice? • How significant are these changes relative to other pressures? • How should these expected changes be planned for? The study has contributed to the first of these by using case studies based on three lakes and two rivers to demonstrate modelling tools and data sets that are available to be used for assessing climate change impacts on water quality. The climate related factors controlling phytoplankton growth are, air temperature (through river temperature), solar radiation and river flows (lake outflows). River flows are expected to change in the future in response to changing rainfall patterns and evaporation is likely to increase. Phytoplankton grow faster went there is more light and they have longer to grow in rivers and lakes if the water is moving more slowly through them (the residence time of the water is increased). Temperature changes will favour different species, with increases in water temperature favouring the potentially toxic Cyanobacteria species. A modelling approach was taken using the climate data based on and flow data derived from the UKCP09 scenarios. In total 11 scenarios of flow, air temperature and solar radiation (amongst other climate data) were available and these were run through the QUESTOR model for the rivers Thames and Ure (a tributary of the Yorkshire Ouse) and the PROTECH model for three contrasting lakes (Windermere, Bassenthwaite and Esthwaite). The flow regimes for each scenario had been generated from the data underpinning the UKCP09 scenarios as part of the Environment Agencies’ Future Flows Hydrology project, which gave the first spatially consistent set of projected flow data for the UK. Each of the 11 scenarios is equally likely and reflects the uncertainty in key parameters in the Hadley Centre’s climate model. The research also investigated the differences in simulating present day river temperature and algae concentrations when the river model was driven by future flows hydrology and climate data rather than the corresponding observed data. The aim was to assess how sensitive was the model to the simulations of current climate and hydrology. The PROTECH model is a well established process-based lake phytoplankton community model that includes cyanobacteria types in its configuration and has been applied to >20 lakes around the world. The version of the model used here had been successfully applied to the three case-study lakes in previous studies. The QUESTOR model is a semi-empirical, process based model, which has also been used for examining changes in water quality in UK rivers. The QUESTOR model has previously been used to model climate change impacts on dissolved oxygen and biochemical oxygen demand and has recently been extended to include impacts on phytoplankton reported here. In the case-study lakes with hydraulic retention times of >30-60 days (Windermere and Esthwaite), the symptoms of eutrophication (e.g. cyanobacteria blooms) became worse under the future climate scenarios without any increased nutrient loading to the lakes. Decreasing the nutrient load to these affected lakes (in the model) reduced the problem, showing that local management strategies can mitigate this problem. In the River Thames, the number of days when temperature, dissolved oxygen, biochemical oxygen demand and phytoplankton exceeded undesirable values (> 25 °C, < 6 mg L-1, > 4 mg L-1 and 0.03 mg L-1 respectively) is likely to increase (assuming no change in nutrient loads). However, there is considerable uncertainty around the level of the increase. In the River Ure, much smaller change in the occurrences of undesirable water quality are likely to occur in the future and some scenarios suggest no change. The analysis of the model results using the two sources of flow data (modelled versus observed) showed that “hydrological” errors were of less significance than those associated with the derivation and downscaling of climate model rainfall, air temperature and solar radiation variables. Errors associated with incomplete understanding of the water quality interactions in the river were also likely to be more substantial than those associated with hydrology, but less than those related to the climate model inputs. While lake modelling of phytoplankton is very well established, modelling of phytoplankton in rivers is still in an early phase and more work needs to be done to refine the model processes, particularly related to grazing and self shading effects. The model predictions are therefore subject to uncertainty associated with a lack of understanding and data about how to capture these processes better. The development of the Future Flows Hydrology methods and data sets has been an important part of the process of making the future predictions. Flow is a key driver for water quality and a coherent dataset and methods that can be applied nationally was essential. The quality of the data from climate models for generating the flows and defining the driving variables (air temperature and solar radiation) for the water quality modelling at the extremes of their distributions has been highlighted as the major source of uncertainty in the water quality model outputs. More work is required to define the accuracy of the climate data required for more certain water quality predictions. In carrying out this study, it has been demonstrated that there are methods for quantifying the effects of climate change on aspects of water quality in both lakes and rivers that make progress towards Defra goals in this area. Further model development and wider testing of these methods will be required before detailed management interventions can be recommended with any confidence.

Item Type: Publication - Report (UNSPECIFIED)
Programmes: CEH Topics & Objectives 2009 - 2012 > Water > WA Topic 1 - Variability and Change in Water Systems > WA - 1.3 - Model, attribute and predict impacts of climate and land cover change on hydrological and freshwater systems
CEH Sections: Boorman (to September 2014)
Funders/Sponsors: Defra
Additional Information. Not used in RCUK Gateway to Research.: The report and the technical summary are freely available on the Defra website - click on Official URL link
Additional Keywords: algae, phytoplankton, Thames, Ouse, Esthwaite, Bassenthwaite, Windermere
NORA Subject Terms: Ecology and Environment
Date made live: 27 Mar 2014 14:34 +0 (UTC)

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