Sediments in streams can negatively impact benthic organisms through several mechanisms such as reducing oxygen availability and filling interstitial spaces. Excess sediments from anthropogenic sources or transport processes can directly harm organisms or alter flows and processes. Studies have found that deposited sediments reduce intra-gravel flow needed by salmonid eggs and pearl mussel lifecycles. Experiments adding sediments showed increased drift and reduced densities of invertebrates. Sediment deposition changes community composition and traits by selecting against certain taxa. Combined stressors like sediments and land use have greater effects and understanding their impacts on ecosystem functions and services is important for management and conservation.

1. Sediments and stream ecosystems
Steve Ormerod
?

2. Conceptual basics: sediment regimes

3. Montgomery & Buffington (1997)

4. Montgomery & Buffington (1997)
S J Ormerod

5. Ecological effects of excess sediments
Problems arise from:
i) Additional (anthropogenic) sediment delivery
ii) Transport in suspension
iii) Transport by saltation
iv) Settlement into interstices
v) Occlusion of surfaces
All can affect organisms directly, or by altering flow,
oxygen availability or other processes

6. Greig et al. 2005,
Postulated mechanisms of the effects of deposited sediments on salmonid eggs

7. Effects of sediment accumulation on two sets of salmon redds via interstitial flow
Greig et al. 2005,
Sediments
accumulate
Intra-gravel flow
declines

8. Pearl mussel life cycle:

9. (Geist & Auserwald 2007)

10. (Geist & Auserwald 2007)

11. Recent Welsh studies on sediments and their effects:
S. Larsen, I. P. Vaughan and S J Ormerod (2009) Scale-dependent effects of
fine sediments on temperate headwater invertebrates. Freshwater Biology, 54,
203-219
S. Larsen & S. J. Ormerod (2010) Low-level effects of inert sediments on
temperate stream invertebrates. Freshwater Biology, 55, 476-486
S. Larsen & S J Ormerod (2010) Combined effects of habitat modification on trait
composition and species nestedness in river invertebrates. Biological
Conservation, 143, 2638-2646
S. Larsen, G. Pace & S. J. Ormerod (2011) Experimental effects of sediment
deposition on the structure and function of macroinvertebrate assemblages in
temperate streams. River Research and Applications. 27, 257-267
S. Larsen and S. J. Ormerod (2014) Anthropogenic modification disrupts species
co-occurrence patterns in stream invertebrates. Global Change Biology, 20, 51-
60

12. Combined observations and
experiments to assess effects
of deposited sediments
Examined consequences for trait
diversity and composition
Considered emergent effects
for conservation and function

14. Larsen et al. 2009
Sediment deposition and
land use in the Usk catchment

15. Effects on invertebrate drift of sediment added experimentally at 4-5 kg per m2
Larsen & Ormerod 2010

16. Drift propensity increased by 200%
and density reduced by 30-60%
Larsen & Ormerod 2010

17. Larsen et al. 2009
Deposited sediment affects community composition and richness

18. Larsen et al. 2009
Sensitivity varies among different groups of organisms

19. Importance of organism ‘traits’…
S J Ormerod
S J Ormerod
S J Ormerod
S J Ormerod

20. Sediments systematically remove organisms with
Specific traits and reduce trait diversty

21. Trait consequences:
• Effects of sedimentation detectable only after accounting
for larger-scale land-use change
• Land use-change accompanied by losses of larger, long
lived organisms
• Sedimentation increased detritivores, herbivores, deposit
feeders and burrowers but reduced filterers, predators and
attached taxa declined.
• Trait diversity reduced by both sediments and land-use
change
Important ramifications for conservation and function?
Larsen et al.

22. +
Diversity in upland rivers for
ecosystem service sustainability
BESS: 4.4m Euros

23. Key ES flows
The Duress Ecosystems Services project:
Energy
pathways
Ecosystem
service
Biodiversity
(Gene to foodweb)
Biodiversity
stocks

24. Extensive large-scale data
and nested design
Fully multi-scale
approach:
Experimental channels >
catchments > region
Days > decades

25. Currently 3 replicate sets of channels in action
No 4 expected by 2015

26. More novel tools: Stable Isotopes for food web analysis
Basal
resources
Primary
consumers
Top
predators
Collection and preparation
of ~1500 samples for
analysis.

27. Change in
Distribution
1990-2010
Evidence of changes in stocks of river birds

28. Genes, populations, species,
ecosystem functions…
Microbes, invertebrates, fish,
birds.
Land use, climate…

29. +
What are the important future drivers and how
will these affect stocks and flows?
Future changes:
downscaling the
Duress scenarios

30. 2020
Markets influence high
Government influence high
Market or governance failure
2010
Free Market
Extensification
Transition
2050
Agri-environment
Production focussed
Collapse
Intensification
Prosser et al. unpubl
Scenarios to the 2050’s for uplandWales

31. Likely drivers of change for upland Wales
 Reviewed previous scenarios
and literature – publication in
review
 Identified drivers of change
through Expert Stakeholder
Workshop
 Already investigated 4
scenarios to the 2050’s for
upland Wales that apply to the
3 activity zones of the uplands.
high lands
ffrydd
valley lands

32. Ffridd Zone: Intensification Scenario
Land type: Ffridd
Agricultural LC= Other
Ownership = NRW and Common
Land
Designation = None
Land type: Ffridd
Agricultural LC= 5
Ownership = NA
Designation = None
Land type: Ffridd
Agricultural LC = 4
Ownership = NA
Designation: None
Land Type: Ffridd
Agricultural LC=4
Designation: Ancient woodland
N
Scenarios translated spatially across
Welsh catchments

33. 33
Example Scenarios - Agricultural intensification
Global food security forces policy to focus on production: Hill farming is now expected to be an important contributor to
the national livestock industry by providing breeding and finishing stock to lowland farming systems and fatstock for the
market. Environmental protection activity is limited to protected areas or areas with high tourism value.
Increased stock
densities and grazing
pressure
Conversion of temporary
grassland into permanent
grassland or fodder crops
Productivity increase through
drainage or exploitation of new
varieties of grasses and fodder
crops
Improvement of animal breeds to
maximise food production and
carcass specifications to meet
market needs
Common land maintained for
agricultural production
Greater inputs of fertiliser,
chemicals and pesticides to
boost productivity in Valley
bottoms and Ffridd
Reduction in features such as hedges,
woodland strips, lone trees, shrubs or
river margins to maximise available
land for production

34. 34
Example scenarios - Business as Usual
The farming management paradigm is initially dominant but policy aims to balance the aims of agricultural productivity
and environmental protection. Upland farming does not address UK food security specifically, but is managed for
supplying export markets - current production far outweighs local consumption . Environmental protection is limited to
small areas of land such as protected areas, areas with high tourism value, or areas requiring specific protection to
meet regulations.
Overgrazing continues
Proportion of farmers within
agri-environment schemes
increases but effectiveness
limited by difficulties in
managing landscape level
schemes
Resources required to support
upland farming are sourced
from other parts of UK or from
outside UK (feed, bedding)
Gradual reduction in sediment, nutrient and pesticide inputs to
upland rivers as agri-environment schemes are implemented
Upland areas remain largely
static with low tree cover but
natural regeneration occurs in
less productive parts of farms
in the ffridd and lowland areas
Common land maintained for
grazing

35. Conclusions
Clear evidence that deposited sediments affect
benthic river organisms: abundance, composition,
sensitive groups, trait composition and diversity
Potential interactions among stressors – notably
climate change
Potential for effects on ecosystem functions, services
and resilience – but understanding is rudimentary
Important to understand, predict and manage future
change