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A strategic programme for NERC Lowland catchment research
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Fine sediments, nutrient dynamics & biotic processes


Fine sediment and nutrient dynamics of lowland permeable streams: establishing the significance of biotic processes for sediment modification.

Overview of project

Fine sediment plays an important role in the transfer and fate of nutrients through river basins. In recent years, groundwater-fed rivers throughout lowland England have exhibited increases in both suspended sediment loads and concentrations of macro-nutrients linked to changes in land use and river management practices. These increases have resulted in a number of environmental problems, not least for stream biota, and there is an urgent need for improved understanding of the fine sediment dynamics of lowland permeable catchments. This project investigated the complex interactions between sediments, river flows and biota in reaches of the Frome and Piddle catchments, Dorset. It focused on the role of aquatic macrophytes and suspension feeding invertebrates in trapping and transforming sediments and nutrients associated with sediments. See a schematic diagram of the sediment trapping processes.


The overall aim of the project was to establish the significance of biotic processes for instream sediment and nutrient budgets in lowland permeable catchments. The research focused on providing a process-based understanding of (a) trapping and retention and (b) biological and biogeochemical transformations of fine sediment particles in contrasting reaches of the Frome and Piddle catchments, Dorset.

Main findings

The research was important in quantifying:

  • the degree Ranunculus plants modify flow in chalk streams
  • the associated spatial and temporal variability in the amount and character of fine particulate matter (especially its highly aggregated nature) that accumulates within chalk streams
  • the role of suspension-feeding invertebrates in sediment processing and retention; and
  • the biogeochemical processing within the trapped sediments and, in particular, the identification of chalk streams as significant sources of the greenhouse gases carbon dioxide, methane and nitrous oxide. This identified a hitherto unquantified agricultural impact beyond the well-known impacts of fertilizer enrichment and pesticide/herbicide application.

Description of activities

Researchers mapped in-channel vegetation and deposited sediments every month, and made monthly measurements of flows along river reaches using an electromagnetic flow meter. This was done throughout 2003 and 2004. Deposited fine sediments were sampled using Perspex corers. Sediment samples were analysed for organic matter content and laser diffraction was used to measure absolute and effective particle sizes. Detailed flow velocity profiles around and within a Ranunculus stand were constructed from measurements using a hotwire anemometry system. Experimental releases of stained corn pollen in the field and in the fluvarium at the River Laboratory, East Stoke, were undertaken to study the transport of fine particulate organic matter. Laboratory experiments at UCL investigated changes in blackfly larval faecal pellets through time under different treatment conditions. Methane emissions from the trapped fine sediments and gaseous exchange through Ranunculus stems were measured in-situ using gas ebullition samplers. Solutes and gases from sediment pore water were sampled using a minipore water probe system. A combined field and laboratory experimental approach was conducted to assess the potential for methane production and oxidation to take place beneath a Ranunculus stand.

Areas of application

  • Implementation of the Habitats Directive and the Water Framework Directive
  • Sediment and nutrient management in chalk streams.

Related and future work

Two PhD studentships based in the Department of Geography, Queen Mary, University of London, are currently investigating (a) transport of fine sediments in vegetated chalk streams and (b) stability of fine-grained bed sediments in lowland vegetated streams. These projects (2007-2010) are in collaboration with University College London (Professor Roger Wotton), Environment Canada (Dr Ian Droppo) and Natural England.

Researchers' details

Principal Investigator:

Co-Principal Investigator:



  • Dr J Cotton, Post-Doctoral Research Associate

Research Students:

  • L Warren
  • I Sanders


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

PhD theses

Warren, L. L. (2006) The Biogenic Transformation of Fine Sediments in Lowland Permeable Catchments. Unpublished PhD thesis, University College London.

Sanders, I. A. (2007) The source, transformation and fate of particulate organic matter in stands of the aquatic macrophyte Ranunculus spp. Unpublished PhD thesis, Queen Mary, University of London.

Refereed journal papers

Joyce, P., Warren, L. L. and Wotton, R. S. (2007) Faecal pellets in streams: their binding, breakdown and utlilization. Freshwater Biology 52: 1868-1880.

Sanders, I. A., Trimmer, M., Heppell, C. M., Cotton, J. A., Wharton, G., Hildrew, A. G. and Flowers, E. J. (2007) Emission of methane from chalk streams has potential implications for agricultural practices. Freshwater Biology 52: 1176-1186.

Wotton, R. S. and Warren, L. L. (2007) Impacts of suspension feeders on the modification and transport of stream seston. Fundamental and Applied Limnology / Archiv für Hydrobiologie 169: 231-236.

Clarke, S. J., Wharton, G. and Cotton, J. A. (2006) Spatial and temporal variations in the sediment habitat of Ranunculus spp. in lowland chalk streams - implications for using macrophytes as environmental monitors of sediment and water health? Water, Air & Soil Pollution: Focus 6: 393-401.

Cotton, J. A., Wharton, G., Bass, J. A. B., Heppell, C. M. and Wotton, R. S. (2006) The effects of seasonal changes to in-stream vegetation cover on patterns of flow and accumulation of sediment. Geomorphology 77: 320-334.

Sanders, I. A. and Trimmer, M. (2006) In-situ application of the 15NO3- isotope pairing technique to measure denitrification in sediments at the surface water - groundwater interface. Limnology and Oceanography: Methods 4: 142-152.

Wharton, G., Cotton, J. A., Wotton, R. S., Bass, J. A. B., Heppell, C. M., Trimmer, M., Sanders, I. A. and Warren, L. L. (2006) Macrophytes and suspension-feeding invertebrates modify flows and fine sediments in the Frome and Piddle Catchments, Dorset (UK). Journal of Hydrology 330: 171-184.

Wotton, R. S. and Wharton, G. (2006) Combining biology and hydrology - questions from an integrated study of chalk streams. In: Sediment dynamics and the hydromorphology of fluvial systems (Proceedings of a symposium held in Dundee, UK, July 2006). IAHS Publ. 306, 2006, pp. 331- 337.

Warren, L. L., Wharton, G. and Wotton, R. S. (2005) The role of faecal pellets in lowland permeable catchments. Internationale Vereinigung für theoretische und angewandte Limnologie 29: 167-169 (ISSN 0368-0770).

Recommended reading

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

Droppo, I. G. (2001) Rethinking what constitutes suspended sediment. Hydrological Processes 15 (9): 1551-1564.

Krishnappan, B. G. (2004) Erosion behaviour of fine sediment deposits. Canadian Journal of Civil Engineering, 31 (5): 759-766.

Naden, P. S., Rameshwaran, P., Mountford, O., Robertson, C. (2006) The influence of macrophyte growth, typical of eutrophic conditions, on river flow velocities and turbulence production. Hydrological Processes 20: 3915-3938.

Sand-Jensen, K. and Pedersen, O. (1999) Velocity gradients and turbulence around macrophyte stands in streams. Freshwater Biology 42: 315-328.

Wotton, R. S. (2005) The essential role of exopolymers (EPS) in aquatic systems. Oceanography and Marine Biology: An Annual Review 42: 57-94.

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