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A strategic programme for NERC Lowland catchment research
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Fine sediment budgets and nutrient & contaminant transfer: summary

A fuller description of this project is also available.

Overview of project

Increased suspended sediment concentrations resulting from land use change have frequently been cited as important contributors to the degradation of Chalk stream ecosystems. Increased sediment fluxes are also frequently associated with increased nutrient and contaminant loadings. However current understanding of sediment sources and sediment mobilisation, transfer and storage within lowland groundwater-dominated catchments is limited. Detailed information on the fine sediment budgets of such catchments is an essential requirement for the development of effective sediment management strategies. In this project a novel integrated approach to data collection, involving sediment monitoring, sediment source fingerprinting and the use of fallout radionuclides to document sediment mobilisation and storage, has been successfully employed to establish the fine-grained sediment budgets of the three main LOCAR catchments.

This project found that surface erosion from cultivated land is generally the dominant sediment source, whereas the contribution from channel banks and other subsurface sources is commonly low. A large proportion of the mobilised sediment is sequestered within the catchments and their channel systems and only a very small proportion of the mobilised sediment is delivered to the catchment outlet.  A fuller overview of this project

Aims

Primary aims of this project were:

  • to assemble hitherto unavailable information on the fine sediment budgets and associated process dynamics of the three LOCAR catchments;
  • to use this assembled information as the basis for developing a sediment budget model for lowland catchments, to assist with catchment management; and
  • to establish the role of fine sediment transfer and storage in the transport and fate of nutrients and contaminants in lowland permeable catchments.  More about the aims of this project

Main findings

  • Sediment budgets between the two study catchments are broadly similar.
  • Gross surface erosion is higher on cultivated land than on pasture.
  • A substantial proportion of the mobilised sediment is sequestered within the fields and between the individual fields and river channel network.
  • The sediment contribution from banks and subsurface sources is relatively low and generally represents only about 1-5% of the suspended sediment output from the study catchments.
  • A large proportion of the fine sediment moving through the channel system enters temporary storage within the channel and is remobilised during high flow events
  • The estimated sediment delivery ratios for the study catchments are low (< ca. 5%).

Description of activities

Documenting soil erosion and sediment redistribution

  • The fallout radonuclide caesium-137 (Cs-137) was used to provide spatially distributed information on medium term (ca. 45 years) soil erosion and sediment redistribution rates.
  • Cs-137 reference inventories were established for all three study catchments.
  • A comprehensive programme of soil sampling along slope trandsects was used to characterise the spatial variability of caesium-137 inventories and to estimate gross and net erosion rates. More about the activities carried out by this project

Fingerprinting approach

  • The sediment transported by the study rivers was 'fingerprinted' by relating the geochemical properties of the suspended sediment to those of the potential sources.
  • Four potential sediment source types were identified within the study catchments.
  • Representative time integrated suspended sediment samples were collected at water quality monitoring stations at the outlets of the two study catchments and smaller subcatchments.
  • The relative contribution of the four source types to the suspended sediment yield at the catchment outlets was established.  More about the activities carried out by this project

Channel bed sampling and river monitoring

Areas of application

The sediment budgets established for the catchments provide important background information, which could be used to support the design of targeted sediment control and management strategies in these study catchments and similar areas.

Related work

Assessing the impact of climate change and land use change on catchment hydrology and soil erosion (Ben Thomas, PhD student, University of Exeter)

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

Collins A L and Walling D E. 2007. The storage and provenance of fine sediment on the channel bed of two contrasting lowland permeable catchments, UK. River Research and Applications, 23, 4, 429-450.

Collins A L and Walling D E. 2007. Fine-grained bed sediment storage within the main channel systems of the Frome and Piddle catchments, Dorset, UK. Hydrological Processes, 21, 11, 1448-1459.

Walling D E, Collins A L, Jones P A, Leeks G J L and Old G. 2006. Establishing fine-grained sediment budgets for the Pang and Lambourn LOCAR catchments, UK. Journal of Hydrology 330, 1-2, 126-141.

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

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