Siltflux workshop 1: Sediments and stream ecosystems - Steve Ormerod

Sediments and stream ecosystems Steve Ormerod

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Conceptual basics: sediment regimes

Montgomery & Buffington (1997)

Montgomery & Buffington (1997)

S J Ormerod

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

Greig et al. 2005,

Postulated mechanisms of the effects of deposited sediments on salmonid eggs

Effects of sediment accumulation on two sets of salmon redds via interstitial flow

Greig et al. 2005,

Sediments

accumulate

Intra-gravel flow

declines

Pearl mussel life cycle:

(Geist & Auserwald 2007)

(Geist & Auserwald 2007)

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-

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Combined observations and

experiments to assess effects

of deposited sediments

Examined consequences for trait

diversity and composition

Considered emergent effects

for conservation and function

Larsen et al. 2009

Sediment deposition and

land use in the Usk catchment

Effects on invertebrate drift of sediment added experimentally at 4-5 kg per m2

Larsen & Ormerod 2010

Drift propensity increased by 200%

and density reduced by 30-60%

Larsen & Ormerod 2010

Larsen et al. 2009

Deposited sediment affects community composition and richness

Larsen et al. 2009

Sensitivity varies among different groups of organisms

Importance of organism ‘traits’…

S J Ormerod

S J Ormerod S J Ormerod

S J Ormerod

Sediments systematically remove organisms with

Specific traits and reduce trait diversty

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.

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Diversity in upland rivers for ecosystem service sustainability

BESS: 4.4m Euros

Key ES flows

The Duress Ecosystems Services project:

Energy pathways

Ecosystem

service

Biodiversity

(Gene to foodweb)

Biodiversity stocks

Extensive large-scale data and nested design

Fully multi-scale approach: Experimental channels > catchments > region Days > decades

summer

winter

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

More novel tools: Stable Isotopes for food web analysis

Basal

resources

Primary

consumers

Top

predators

Collection and preparation

of ~1500 samples for

analysis.

Change in

Distribution

1990-2010

Evidence of changes in stocks of river birds

Genes, populations, species, ecosystem functions… Microbes, invertebrates, fish, birds.

Land use, climate…

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What are the important future drivers and how

will these affect stocks and flows?

Future changes:

downscaling the

Duress scenarios

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 upland Wales

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

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

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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

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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

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