Modelling water quality response to climate and large-scale land-use change using the world's longest water quality time series (1868 to date)

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Estimates suggest human activity has doubled the rate at which biologically available nitrogen enters the environment when compared to pre-industrial levels. This has led to nutrient enrichment of surface and groundwaters causing low dissolved oxygen levels, loss of habitat and freshwater and riparian biodiversity, lowered drinking water quality and, in some places, increased occurrence of algal blooms. Globally, Western Europe is regarded as a 'hot spot' of riverine nitrogen flux and some of the highest nitrate concentrations are found in UK rivers, particularly the River Thames. This is due to the population density, the extent of high-input agriculture within the country, and the small, relatively unimpeded nature of UK rivers. The potential for human impact on riverine nutrient and carbon fluxes by large-scale land-use and management change has been demonstrated, and suggested to be of potentially greater water quality significance than projected climate change impacts. Recent UK work has shown that groundwater-dominated river catchments exhibit a long-term (i.e. >30 year) nitrate response linked to agricultural intensification in the 1950s, 60s and 70s. This is particularly significant because groundwater flows are slow so transfers from the land to rivers via groundwater may take up to tens or even hundreds of years. In the past uncertainty about what is presently contained in the groundwater led to talk of a possible nutrient 'time bomb', due to affect rivers at some point in the future. It has been shown that groundwater-dominated river responses to changes in the catchment require many years of monitoring data (possibly going back further than the 1940s) in order to fully understand the rate and magnitude of land to river transfers. This has provided a crucial new perspective on the importance of long-term catchment function, but alarmingly, in England, there are few data from before the establishment of the water authorities in 1974 to support interpretation of such processes. In response to this researchers have used archived paper records to construct the world's longest water quality time series comprising monthly average nitrate concentrations for the River Thames upstream of London for the period 1868 to the present. This allows a unique insight into water quality changes affected by direct human influences over the period, the timing and character of catchment responses to changing land use and land management policy, and comparison of the magnitude of these influences with potential impacts of climate change over a sufficiently long period. The proposed research will use this Thames record to develop new methods and models, coupled with traditional statistical methods, to characterise and predict changes in river nutrient concentrations in both the short- and long-term. This will allow the rates at which groundwater nutrient transport can make land to river transfers and will help to identify whether projected climate change impacts will be as big a threat to water quality as large-scale changes in land use. This will enable freshwater and catchment scientists to gain a better understanding of long-term processes and will help policymakers to prioritise actions and make decisions. It will also show the ways in which monitoring programmes need to be managed to provide appropriate data, and the ways in which those data need to be interpreted if we are to manage our natural resources effectively and sustainably in the long-term.