Rothamsted Research where knowledge grows

Rothamsted Research where knowledge grows

Linking agricultural fine sediment pressure and

impacts on aquatic ecology for informing

catchment management across England and Wales

Adie Collins

The need for new management targets

• Freshwater Fish Directive (78/659/EC)

• annual mean suspended sediment concentration of 25 mg l-1

• repealed in 2013 • need for new

targets for informing catchment management

Background fine sediment pressures

‘Gap’ for reduction by

mitigation strategies

Current or future

projected sediment

stress

Natural ‘intrinsic’ sediment

stress

Sediment pressure

Time Ancient Modern

High

Low ‘Gap’ not

targeted by mitigation strategies

Background fine sediment pressures

Background fine sediment pressures

Fine sediment gap exceeding background

Revising targets for GES for fine sediment

Agricultural sediment mitigation under BAU

Mitigation methods for inorganic sediment

Establish cover crops in the autumn

Early harvesting and establishment of crops in the autumn

Cultivate land for crops in spring rather than autumn

Adopt reduced cultivation systems Cultivate compacted tillage soils

Cultivate and drill across the slope

Leave autumn seedbeds rough

Manage over-winter tramlines

Establish in-field grass buffer strips

Establish riparian buffer strips

Re-site gateways away from high-risk areas

Agricultural sediment mitigation measures

• catchment-specific revised sediment targets based on fish endpoint

• implications for meeting revised targets of

– business-as-usual

– new mitigation programmes

– climate change projections for 2020, 2030, 2050, 2080

Salmonid fish end point

Catchment Reach Redd

> 1 km2 100-50 m

< 1 m

Pressure SIDO-UK Routing

Salmonid fish end point

0

5

10

15

20

25

30

1 11 21 31 41 51 61 71 81 91 101 111 121 131 141

Days Since Fertilisation

DO

(m

gl-1

) /

Intr

agra

vel flow

(cm

hr-1

)

0

10

20

30

40

50

60

70

80

90

% F

illed v

oid

space

Dissolved Oxygen

Intragravel flow

Sediment accumulation

Management targets based on salmonids

• large reductions in

agricultural sediment loading required to reduce fine sediment infilling of the spawning substrate

• will require far more than BAU implementation of on-farm mitigation measures in some catchments

Fine sediment impacts: source / species

Key messages

• modern farming causes excess fine sediment loss to rivers

• modern background pressures can be used as targets or to correct the sediment gap using biological endpoints

• taking account of sediment source apportionment alone is not enough

• source-specific impacts exist

• species-specific impacts exist