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A strategic programme for NERC Lowland catchment research
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Hydrogeochemical functioning of permeable lowland catchments: summary

A fuller description of this project is also available.

Overview of project

The water environment faces increased pressures such as changes in land-use, increased demand for water supplies, and uncertainties over climate change. These pressures create significant challenges for managing catchments and this is recognised in the EU Water Framework Directive. An improved understanding of catchment processes is needed to develop of appropriate decision-support tools. This project has sought to achieve that goal through the integration of an extensively monitored field site with hydrochemical and hydrological measurements of ground and surface waters, coupled with the development of a catchment-scale model. Natural geological features have been found to be very important in the complex movement and interaction of surface and groundwaters. A wetland site has been found to be a biogeochemical hotspot but contributes little to the net nutrient flux within the catchment. Modelling studies suggest that changes in land use practices will not lead to river water quality improvements for several decades.

Aims

The overall aim of the project was to establish the main hydrological and hydrogeological controls on groundwater and surface water quality (including chemical transformations and flowpaths of the principal nutrients) and to produce an integrated modelling system describing the hydrochemical and nutrient functioning of lowland permeable catchments.  More about the aims of this project

Main findings and outputs

A new hydrogeological conceptual model of the Pang and Lambourn catchments has been developed

  • Dry valleys act as collectors of groundwater and feed it to the rivers.
  • The locations of springs in the Lambourn and Pang are controlled by lithological features such as: intersection of fracture lineaments or faults with valleys and karstic development of the Chalk.
  • Results suggest that matrix flow predominates in the unsaturated zone of the Chalk , but that fracture flow can contribute up to 30% of recharge water.
  • The shallow soil zone strongly attenuates infiltration fluxes and fracture flow is of limited significance.  More about the main findings of this project

Surface waters and riparian wetlands.

  • The major, minor and trace element chemistry is controlled by atmospheric and pollutant inputs from agriculture and sewage sources superimposed on a background signal linked to geological sources
  • Significant adsorption of phosphorus discharges from sewage treatment works by river bed sediments occurs within a few kilometres of the source; phosphorus uptake by biofilms is, in contrast, very limited.  More about the main findings of this project

Catchment-scale nutrient modelling.

  • Itegrated catchment models (INCA) were developed for the transport of nitrogen (INCA-N) and phosphorus (INCA-P), and for groundwater flow within the Chalk (INCA-Chalk).
  • A new conceptualisation of unsaturated zone processes has been developed with INCA-Chalk and incorporated within a GIS-based framework. This uses digital topography to characterise a distribution of unsaturated zone solute travel times.
  • INCA-Chalk has been run to evaluate long-term response for different scenarios of nutrient management and for different scenarios of future climate.  More about the main findings of this project
  • Travel times for nitrate can be of the order of many decades. Future models to represent nitrate transport in the Chalk and the response to management interventions must recognise this.

Description of activities

Field measurements

  • Hydrochemical monitoring of groundwater at Westbrook Farm
  • Natural chemical and isotopic tracers were used to determine dominant flowpaths from rainwater to soil and surface water to groundwater and to streams.
  • Piezometry.
  • Weekly sampling of in-stream water quality, with emphasis on nutrients.
  • Sampling of river bed sediments to determine phosphate concentrations.  More about the activities carried out by this project

Modelling activities

Areas of application

Implementation of the Habitats Directive and the Water Framework Directive.

Related and future work

Concepts developed in this study are being further explored under the NERC FREE thematic programme (Flood Risk from Extreme Events) with the project "Modelling groundwater flood risk in the Chalk aquifer from future extreme rainfall events" (NERC Reference: NE/E002307/1).

Researchers' details

Principal Investigator:

Co-investigators:

More researchers who worked on this project More researchers who worked on this project

Publications

All publications from this and other LOCAR projects are listed in the publications database.

Selected publications from this project are listed below. The full list of publications and recommended reading can be viewed in the full description page for this project Full publication list for this project

Selected publications

Gooddy D C, Darling W G, Abesser, C and Lapworth D J. 2006. Using Chlorofluorocarbons (CFCs) And Sulphur Hexafluoride (SF6) To Characterise Groundwater Movement And Residence Time In A Lowland Chalk Catchment. Journal of Hydrology, 330, 44-52.

Jackson B M, Wheater H S, Mathias S A, McIntyre N and Butler A P. 2006. A simple model of variable residence time flow and nutrient transport in the Chalk. Journal of Hydrology, 330, 221-234.

Neal C, Neal M, Leeks G J L, Old G, Hill L. and Wickham H. 2006. Suspended sediment and particulate phosphorus in surface waters of the upper Thames Basin, UK, Journal of Hydrology, 330, 142-154.

Neal C, Jarvie H P, Wade AJ, Neal M, Wyatt R, Wickham H, Hill L and Hewitt N. 2004. The water quality of the LOCAR Pang and Lambourn catchments. Hydrology and Earth System Sciences, 8(4), 614-635.

Mathias S A, Butler A P, McIntyre N, Wheater H S. 2005. The significance of flow in the matrix of the Chalk unsaturated zone. Journal of Hydrology, 310, 62-77.

Wilby R L, Whitehead P G, Wade A J, Butterfield D, Davis R J and Watts G. 2005. Integrated Modelling of climate change impacts on water resources and quality in a lowland catchment: River Kennet, UK. Journal of Hydrology, 330 (1-2): 204-220.

Full list of publications resulting from this project Full publication list for this project

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