OR/13/031 Introduction

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Tye, A M, Hurst, M D, and Barkwith, A K A P. 2013. Nene phosphate in sediment investigation — Environment Agency project ref: 30258. (Water Framework Directive). British Geological Survey Internal Report, OR/13/031.

The introduction of the Water Framework Directive (Directive EC 2000/60/EC[1]) aims to prevent further deterioration, and to improve the quality of inland surface waters. One of its major aims is to promote ‘good ecological status (GES)’ with respect to biodiversity in rivers (Johnes et al. 2007[2]). Phosphate (PO4-P) is the major nutrient in rivers that is typically in shortest supply, and therefore has the greatest potential to limit river productivity (Mainstone & Parr, 2002[3]). Thus, excessive phosphate concentration in river waters is one of the most common reasons why GES is often not achieved (Withers & Haygarth, 2007[4]; Johnes et al. 2007[2]). Major inputs of phosphate in river waters are from point sources such as sewage treatment plants (Jarvie et al. 2006[5]; Neal et al. 2010[6]) or diffuse sources such as agricultural land where phosphate enters the river primarily attached to soil particles (Bilotta et al. 2010[7]; Quinton et al. 2010[8]). The most common pathways for agriculturally derived diffuse phosphorus contamination is either via soil erosion (Haygarth et al. 2006[9]; Quinton et al. 2010[8]) or through under field land drainage systems (Reid et al. 2012[10]; Bilotta et al. 2008[11]). Detrimental outcomes for rivers include (i) eutrophication leading to a loss in aquatic biodiversity, (ii) sediment deposition leading to enhanced plant growth and further siltation of the channel and (iii) potential future desorption of phosphate from the sediment to the water body (Jarvie et al. 2005[12]; McDowell et al. 2001[13]; McDowell et al., 2003[14]).

This report details work commissioned by the Environment Agency to examine sediment and Phosphorus dynamics in the six main WFD water bodies of the River Nene, which flows through Northamptonshire, Lincolnshire and Cambridgeshire, and out into the North Sea via the Wash. The Nene has a largely agricultural catchment, and its low relief, slow drainage and wide catchment give it a tendency to silt up. Large scale siltation of the river has been recorded and in 1930 the River Nene Catchment Board started to undertake extensive dredging (Meadows, 2007[15]). Within these water bodies, SRP concentrations are often greater than the limits suggested for Good Ecological Status (0.12 mg L-1 is considered by the EA as the high concentration) to be achieved. It is considered that a significant potential source of dissolved P in the River Nene is that stored in the river channel sediment. Therefore the Environment Agency wishes to investigate the extent that P associated with this sediment can contribute towards greater SRP concentrations in the River Nene as well as the volume of sediment deposits in the river channel. Sediment deposition and phosphate concentrations are intimately linked in determining ecological status as well as the wider functioning of the river in providing a range of ‘ecosystem services’. These include the role sediment and phosphate play in (i) maintaining navigability of the river to Northampton, (ii) the role phosphate plays in river bank macrophyte growth which can cause further siltation problems, (iii) the reduction of river channel capacity for flood alleviation and (iv) the reduction in amenity services such as angling and navigation. Results from this study will help inform future approaches and management with respect to both the effect phosphate has on GES, but also sediment management such as the desilting programme.

The study consists of three parts, these being (i) a sediment sampling program and laboratory analysis of the sediments for the six non-tidal part of the River Nene, (ii) a landscape modelling component that will produce first order estimates of sediment dynamics in the catchment and river channel and (iii) where we bring parts (i) and (ii) together to provide assessments of phosphate movement through the water bodies of the River Nene.

The objectives of each work package are given below:

Work Package 1: Sediment Sampling and laboratory analysis
The objectives of work package 1 were:

  • To derive first order estimates of sediment volumes in the six water bodies of the non-tidal River Nene
  • To determine mean concentrations of TP (TP) and Olsen extractable P (OEP) in the sediment of six water bodies along the River Nene
  • To determine the concentration of TP and OEP with depth from cores of sediment collected from six water bodies of the River Nene
  • To determine the Effective Phosphate Concentration (EPC0) for sediment samples from each of the six water bodies to assess whether sediments are a potential source or sink of phosphate
  • To determine the kinetics of phosphate sorption or desorption for each of the water bodies

Work Package 2: Sediment dynamics computer modelling
The objectives of work package 2 were to produce first order estimates of erosion and deposition within the Nene river channel for the six water bodies using a landscape evolution model that will:

  • Estimate the amount of sediment entering the River Nene
  • Determine the movement of sediment between the six water bodies of the River Nene as suspended sediment and bed load
  • Compare model estimates with literature values of sediment movement in the River Nene

Work package 3: Combining sediment movement and phosphorus dynamics
The outputs from work package 1 and 2 will be used to answer the fundamental questions as set out in the project specification. For each of the 6 water bodies (and for the total length of the six water bodies) we use our analyses and modelling to estimate:

  • The mass of TP in the sediment
  • The mass of OEP bound in the sediment
  • The volume of suspended and bed load sediment passing each water body
  • The potential mass of OEP released to the water column each year
  • Maps showing the erosion and deposition along with estimated depth of sediment along the main channel

References

  1. ↑ EC. 2000. Directive 2000/60/EC of the European Parliament and of the Council establishing a framework for the Community action in the field of water policy. Official Journal L 327, p.0001–0073 (22/12/2000).
  2. ↑ 2.0 2.1 Johnes, P J, Foy, R, Butterfield, D, and Haygarth, P M. 2007. Land use scenarios for England and Wales: evaluation of management optyions to support ‘good ecological status’ in surface waters. Soil Use and Management, 23 (suppl. 1), 176–194.
  3. ↑ Mainstone, C P, and Parr, W. 2002. Phosphorus in rivers — ecology and management. Science of the Total Environment, 282–283, 25–47.
  4. ↑ Withers, P J A, Haygarth, P M. 2007. Agriculture, phosphorus and eutrophication: a European Perspective. Soil Use and Management, 23(suppl. 1), 1–4.
  5. ↑ Jarvie, H P, Neal, C, and Withers, P J A. 2006. Sewage-effluent phosphorus: a greater risk to river eutrophication than agricultural phosphorus? Science of the Total Environment, 360, 246–253.
  6. ↑ Neal, C, Jarvie, H P, Withers, P J A, Whitton, B A, and Neal, M. 2010. The strategic significance of wastewater sources to pollutant phosphorus levels in English rivers and to environmental management for rural, agricultural and urban catchments. Science of the Total Environment, 408, 1485–1500.
  7. ↑ Bilotta, G S, Krueger, Brazier, R E, Butler, P, Freer, J, Hawkins, J M B, Haygarth, P M, Macleod, C J A, and Quinton, J N. 2010. Assessing catchment-scale erosion and yields of suspended solids from improved temperate grassland. Journal of Environmental Monitoring, 12, 731–739.
  8. ↑ 8.0 8.1 Quinton, J N, Govers, G, van Oost, K, and Bardgett, R D. 2010. The impact of agricultural soil erosion on biogeochemical cycling. Nature Geoscience, 3, 311–314.
  9. ↑ Haygarth, P M, Bilotta, G S, Bol, R, Brazier, R E, Butler, P J, Freer, J, Gimbert, L J, Granger, S J, Krueger, T, Macleod, C J A, Naden, P, Old, G, Quinton, J N, Smith, B, and Worsfield, P. 2006. Processes affecting transfer of sediment and colloids, with associated phosphorus, from intensively farmed grasslands: an overview of key issues. Hydrological Processes, 20, 4407–4413.
  10. ↑ Reid, D K, Ball, B, and Zhang, T Q. 2012. Accounting for the risks of phosphorus losses through tile drains in a phosphorus Index. Journal of Environmental Quality, 41(6), 1720–1729.
  11. ↑ Bilotta, G S, Brazier, R E, Haygarth, P M, Macleod, C J A, Butler, P, Granger, S, Krueger, T, Freer, J, and Quinton, J N. 2008. Rethinking the contribution of drained and undrained grasslands to sediment-related water quality problems. Journal of Environmental Quality, 37, 906–914.
  12. ↑ Jarvie, H P, Jürgens, M D, Williams, R J, Neal, C, Davies, J J L, Barrett, C, and White, J. 2005. Role of river bed sediments as sources and sinks of phosphorus across two major eutrophic UK river basins: the Hampshire Avon and Herefordshire Wye. Journal of Hydrology, 304, 51–74.
  13. ↑ McDowell, R, Sharpley, A, and Folmar, G. 2001. Phosphorus export from an agricultural watershed: Linking source and transport mechanisms. Journal of environmental Quality, 30, 1587–1595.
  14. ↑ McDowell, R W, Sharpley, A N, and Folmar, G. 2003. Modification of phosphorus export from an eastern USA catchment by fluvial sediment and phosphorus inputs. Agriculture, Ecosystems, and Environment, 99, 187–199.
  15. ↑ Meadows, I. 2007. Hydrology. In Synthetic Survey of the Environmental Archaeological and Hydrological record for the River Nene from its source to Peterborough. eds. Allen, P, Boismier, W A, Brown, A G, Chapman, A, and Meadows, I. Northamptonshire Archaeology, Report PNUM 3453.
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