Sediment targets for informing river cat

HYDROLOGICAL PROCESSES

Hydrol. Process. 25, 2112– 2129 (2011)

Published online 1 February 2011 in Wiley Online Library

(wileyonlinelibrary.com) DOI: 10.1002/hyp.7965

Sediment targets for informing river catchment management:

international experience and prospects

A. L. Collins,1,2* P. S. Naden,3 D. A. Sear,2

J. I. Jones,4

I. D. L. Foster5

and K. Morrow1

1 ADAS, Woodthorne, Wergs Road, Wolverhampton, West Midlands WV6 8TQ, UK

2 Department of Geography, University of Southampton, Highfield, Southampton S017 1BJ, UK

3 Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford, Oxon OX10 8ED, UK

4 School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK

5 School of Life Sciences, 115 New Cavendish Street, London W1W 6UW, UK

Abstract:

Sediment plays a pivotal role in determining the physical, chemical and biological integrity of aquatic ecosystems. A range of

factors influences the impacts of sediment pressures on aquatic biota, including concentration, duration of exposure, composition

and particle size. In recognition of the need to assess environmental status for sediment and mitigate excessive sediment

pressures on aquatic habitats, both water column and river substrate metrics have been proposed as river sediment targets.

Water column metrics include light penetration, turbidity, sediment concentration summary statistics and sediment regimes.

Substrate metrics include embeddedness, the fredle index and riffle stability. Identification of meaningful numeric targets

along these lines has, however, been undermined by various issues including the uncertainty associated with toxicological

dose-response profiles and the impracticalities of deploying statistically robust sampling strategies capable of supporting

catchment-scale targets. Many of the thresholds reported are based on correlative relationships that fail to capture the specific

mechanisms controlling sediment impacts on aquatic habitats and are stationary in nature. Temporal windows represented by

the key life stages of specific species must be given greater emphasis. Given such issues and the need to support the revision

of sediment targets for river catchment management, it is proposed that greater emphasis should be placed on developing

generic modelling toolkits with the functionality for coupling current or future projected sediment regimes with biological

response for a range of biota. Such tools should permit the identification of river catchment-specific targets within a national

context, based on biological effect and incorporate sufficient flexibility for utilizing updated physical, chemical, biological and

catchment attribute data. Confidence will continue to be required in compliance screening to ensure cost-effective management

programmes for avoiding disproportionate investment in impacted river catchments. Copyright  2011 John Wiley & Sons,

Ltd.

KEY WORDS sediment targets; river catchment; ecology; water policy; mitigation; compliance

Received 16 April 2010; Accepted 17 November 2010

INTRODUCTION

Excessive sediment pressures on aquatic habitats consti￾tute a significant ecosystem stressor. Enhanced sediment

inputs impact adversely upon fluvial aquatic ecosystems

by degrading habitat condition and directly impairing

biota (Cordone and Kelly, 1961; Newcombe and Mac￾Donald, 1991; Ryan, 1991; Bardonnet and Heland, 1994;

Wood and Armitage, 1997; Bilotta and Brazier, 2008).

Such impacts include the burial and suffocation of fish

eggs and larvae in conjunction with spawning gravel sil￾tation, gill clogging, impaired growth and histological

changes, as well as reduced predatory or feeding effi￾ciency and suppressed resistance to disease (Kemp, 1949;

Cordone and Kelly, 1961; Bisson and Bilby, 1982; Whit￾man et al., 1982; Redding and Schreck, 1983; Berg and

Northcote, 1985; Redding et al., 1987; Kondolf and Wol￾man, 1993; Bardonnet and Bagliniere, 2000; Harrod and

Theurer, 2002; Milner et al., 2003; Sear et al., 2008).

* Correspondence to: A. L. Collins, ADAS, Woodthorne, Wergs Road,

Wolverhampton, West Midlands WV6 8TQ, UK.

E-mail: [email protected]

River channel sedimentation can also have a deleterious

impact on macroinvertebrate populations (Ward et al.,

1998; Sharley et al., 2008) and macrophyte communities

(Clarke and Wharton, 2001). Fine sediment mobilization,

transfers and delivery play a critical role in the dispersal

and fate of nutrients (House, 2003; Collins et al., 2005;

Jarvie et al., 2006; Ballantine et al., 2009) and contam￾inants (Rees et al., 1999; Kronvang et al., 2003). Ele￾vated sediment inputs into watercourses from upstream

erosion and sediment mobilization can also result in a

range of undesirable so-called ‘off-site’ impacts, includ￾ing reduced navigability, the infilling of dams and reser￾voirs and increased water treatment costs. Both climate

and land use change represent important extrinsic drivers

for sediment mobilization and delivery (Houben et al.,

2006) and the expansion of agricultural land and intensi￾fication of farming practices have the potential to increase

sediment pressures on watercourses (Dearing et al., 1987;

Farnsworth and Milliman, 2003; Kasai et al., 2005).

Although enhanced sediment inputs to watercourses

are considered to represent an important cause of water

quality, habitat and biotic impairment, the impacts are

Copyright  2011 John Wiley & Sons, Ltd.