Gammarus pulex&

Watercress Farming

Chalk Stream Headwaters Forum Oct 09

Melanie Dixon & Pete Shaw

Gammarus pulex (L.)

Bourne Rivulet – Gammaridae

Data courtesy of Environment Agency

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0.2km (east branch) 0.2km 2km

• PEITC

• Produced by crucifers e.g. watercress, broccoli, cabbage, rocket, kale.

• Plant defence against herbivores.

• Human health benefits.

Watercress (Nasturtium officianale (R.Br.))

Isothiocyanates

Gammarus pulexreproduction

• Exposed Gammarus pulex breeding pairs to PEITC solution or watercress wash water.

• Measured separation of pairs within a 2 hour period.

G. pulex precopular pairs

Response during 2h exposure

Pairsseparated

%

PEITC (1µl/l)

Wash water

Control

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0 15 30 45 60 75 90 105 120Time (mins)

After Exposure

• Were pairs able to re-form after return to clean water?

• Transient effect?

Watercress in flower

Pairs re-forming after 24h in clean water

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Washwater PEITC Control

Mea

n %

pairs re-formed after 24h

pairs at exposure end

Management to improve water quality

• E.g. settlement tank, parabolic screens, chlorine wash ceased.

• De-silted East channel, de-culverted discharge.

• Redirected factory wash water through watercress beds.

Parabolic screen above outfall

Survival in factory effluent

• Cages upstream & downstream of watercress bed.

• Factory wash water supplied bed.

• Borehole water supplied bed (control).

Gammarus pulex - Acute effect

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Borehole

supply

(control)

Below

control

bed

Wash

water

supply

Below

wash

water bed

Mea

n %

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mo

bil

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Re-direction of factory effluent

• ‘Treatment’ of wash water by passing though watercress beds before discharge is a positive measure

• Recent biological surveys indicate invertebrate populations recovering

Watercress farm outfall (Spring 08)

Bourne Rivulet – Gammaridae

Data courtesy of Environment Agency

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'89

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'98

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'04

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'06

'07

'08

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Nu

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0.2km (east branch) 0.2km 2km

We gratefully acknowledge the support of the Vitacress Conservation Trust and use of facilities at the Environment Agency Biological Effects Laboratory.

Vitacress Salads Ltd, Hampshire, UK