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Understanding the controls on deposited fine sediment in the streams of agricultural catchments

Understanding the controls on deposited fine sediment in the streams of agricultural catchments
Understanding the controls on deposited fine sediment in the streams of agricultural catchments
Excessive sediment pressure on aquatic habitats is of global concern. A unique dataset, comprising instantaneous measurements of deposited fine sediment in 230 agricultural streams across England and Wales, was analysed in relation to 20 potential explanatory catchment and channel variables. The most effective explanatory variable for the amount of deposited sediment was found to be stream power, calculated for bankfull flow and used to index the capacity of the stream to transport sediment. Both stream power and velocity category were highly significant (p<<0.001), explaining some 57% variation in total fine sediment mass. Modelled sediment pressure, predominantly from agriculture, was marginally significant (p<0.05) and explained a further 1% variation. The relationship was slightly stronger for erosional zones, providing 62% explanation overall. In the case of the deposited surface drape, stream power was again found to be the most effective explanatory variable (p<0.001) but velocity category, baseflow index and modelled sediment pressure were all significant (p<0.01); each provided an additional 2% explanation to an overall 50%. It is suggested that, in general, the study sites were transport-limited and the majority of stream beds were saturated by fine sediment. For sites below saturation, the upper envelope of measured fine sediment mass increased with modelled sediment pressure. The practical implications of these findings are that (i) targets for fine sediment loads need to take into account the ability of streams to transport/retain fine sediment, and (ii) where agricultural mitigation measures are implemented to reduce delivery of sediment, river management to mobilise/remove fines may also be needed in order to effect an improvement in ecological status in cases where streams are already saturated with fines and unlikely to self-cleanse.
0048-9697
366-381
Naden, P.S.
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Murphy, J.F.
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Old, G.H.
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Newman, J.
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Scarlett, P.
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Harman, M.
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Duerdoth, C.P.
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Hawczak, A.
b2ecfea5-611b-44d5-afaf-f55160f67fe9
Pretty, J.L.
e3e537b2-eadd-41e4-bb4e-de36f4cee538
Arnold, A.
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Laizé, C.
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Hornby, D.D.
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Collins, A.L.
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Sear, D.A.
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Jones, J.I.
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Naden, P.S.
94009f2b-9d27-4341-9fdd-daffc281d76d
Murphy, J.F.
6f230e5a-143a-4563-953f-57a5eddd7797
Old, G.H.
458b0b14-f19c-46e2-a32c-573cb1817697
Newman, J.
373626fe-b2c7-40ee-a850-1c5f605d2fb4
Scarlett, P.
e2b53db4-b01c-426e-845c-286f2c1b68a0
Harman, M.
2366d51e-8c65-4264-9b90-a1f90e77e1b5
Duerdoth, C.P.
ef15369b-edc4-445c-8ca5-af77b5405d79
Hawczak, A.
b2ecfea5-611b-44d5-afaf-f55160f67fe9
Pretty, J.L.
e3e537b2-eadd-41e4-bb4e-de36f4cee538
Arnold, A.
f4dc0184-547e-4775-99a9-15083657a171
Laizé, C.
d32c62b7-c703-426f-b1b4-d451f9b655a2
Hornby, D.D.
3037e920-68b2-4265-9608-9630fd64be53
Collins, A.L.
eb72a479-2336-4268-a837-79d926239de3
Sear, D.A.
d26ed8c5-be98-450a-956c-c1332649e67f
Jones, J.I.
9acb09cb-4a0d-4fcd-99cc-9bf198d9d564

Naden, P.S., Murphy, J.F., Old, G.H., Newman, J., Scarlett, P., Harman, M., Duerdoth, C.P., Hawczak, A., Pretty, J.L., Arnold, A., Laizé, C., Hornby, D.D., Collins, A.L., Sear, D.A. and Jones, J.I. (2016) Understanding the controls on deposited fine sediment in the streams of agricultural catchments. Science of the Total Environment, 547, 366-381. (doi:10.1016/j.scitotenv.2015.12.079).

Record type: Article

Abstract

Excessive sediment pressure on aquatic habitats is of global concern. A unique dataset, comprising instantaneous measurements of deposited fine sediment in 230 agricultural streams across England and Wales, was analysed in relation to 20 potential explanatory catchment and channel variables. The most effective explanatory variable for the amount of deposited sediment was found to be stream power, calculated for bankfull flow and used to index the capacity of the stream to transport sediment. Both stream power and velocity category were highly significant (p<<0.001), explaining some 57% variation in total fine sediment mass. Modelled sediment pressure, predominantly from agriculture, was marginally significant (p<0.05) and explained a further 1% variation. The relationship was slightly stronger for erosional zones, providing 62% explanation overall. In the case of the deposited surface drape, stream power was again found to be the most effective explanatory variable (p<0.001) but velocity category, baseflow index and modelled sediment pressure were all significant (p<0.01); each provided an additional 2% explanation to an overall 50%. It is suggested that, in general, the study sites were transport-limited and the majority of stream beds were saturated by fine sediment. For sites below saturation, the upper envelope of measured fine sediment mass increased with modelled sediment pressure. The practical implications of these findings are that (i) targets for fine sediment loads need to take into account the ability of streams to transport/retain fine sediment, and (ii) where agricultural mitigation measures are implemented to reduce delivery of sediment, river management to mobilise/remove fines may also be needed in order to effect an improvement in ecological status in cases where streams are already saturated with fines and unlikely to self-cleanse.

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Published date: 2016
Organisations: Geography & Environment

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Local EPrints ID: 389589
URI: https://eprints.soton.ac.uk/id/eprint/389589
ISSN: 0048-9697
PURE UUID: 6d3f81cd-cbb0-44e4-868c-8e225dfe059b

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Date deposited: 09 Mar 2016 12:35
Last modified: 15 Jul 2019 20:42

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Contributors

Author: P.S. Naden
Author: J.F. Murphy
Author: G.H. Old
Author: J. Newman
Author: P. Scarlett
Author: M. Harman
Author: C.P. Duerdoth
Author: A. Hawczak
Author: J.L. Pretty
Author: A. Arnold
Author: C. Laizé
Author: D.D. Hornby
Author: A.L. Collins
Author: D.A. Sear
Author: J.I. Jones

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