P Stripping of Agricultural Runoff

OrIntegrated Runoff Management Plans for Farms

Paul Quinn and Sebastian Tellier

The Rural P Problem

• Surplus P in the land bank• Saturation of P in the soil• P losses associated with sediment losses

• High P in ditch and river sediments – a ‘conveyer belt’

• Enough P to keep eutrophication risk high for the next 50 years

• WFD & P– has no chance unless a more proactive approach is taken

Addressing the problemTraditional approach

• Soil management and P applications• Land use change

OR a new paradigm

• P is locked into soil (soil amendment?) i.e for plant consumption only

• Stripped from the flow at source (in ponds and ditches)

• Suppress P impacts in rivers and lakes by scavenging P.

high

low

claypoor

clayrichlow

riskhighrisk

Nutrient Export Risk MatrixNutrient Export Risk Matrix

Fertiliser applications

and SoilManagement

Soil Type

Flow Connectivity and Remediation features

N lossor P loss

IRMP

Overall Vision

To create an Integrated Runoff Management Plan (IRMP) for a demonstration site at Nafferton Farm, where a series of proactive measures will be taken to control runoff flow paths and the physical and chemical properties of the water before the flow enters the Whittle Burn – thus reducing flood peaks and diffuse pollution levels.

IRMP Objectives• To control overland flow runoff from intensely farmed fields by using

strategically placed, within-field bioreactors/ponds;

• To reduce runoff from hardstandings by forcing flow back into fields containing bioreactors/ponds;

• To create a series of small and un-intrusive sediment traps within the ditch network and the sediment recovered and recycled to land;

• To create a phosphorus (P) stripping zone using ochre pellets (a recycled minewater treatment waste material). P saturated pellets, the trapped sediment and the ochre will be recycled back to land as fertilizer;

• To create a denitrifying potential to treat the bulk of the flow leaving Nafferton farm;

• To evaluate the potential of the storage and attenuation features to reduce the magnitude of flood risks as caused by UK farming systems.

Nafferton Farm Study

Catchment Area of 0.4km2

Temporary Water Storage

Pollution Remediation Zone: Cascading Sedimentation Ponds Ochre Zone (P stripping) Wetland (P & N stripping)

Fig. 1 General view of Nafferton farm and its Integrated Runoff and Sediment Management Plan

Gilchrist strip

Tank field

Drain intercepting the flow coming from farm hardstandings

Drain intercepting road runoff

15% of time10% of time

5% of time

Gate Flume

Instrumentation site 1: Crossroad Back Tank – Gilchrist Strip

15% of time

10% of time

5% of time

Drain

Gravel filled area to prevent ponding

HutHousing the mini-

analyser

Back field

Pond cell

Mire cell

PondMire Unit

PondMire 1

PondMire 2

PondMire 3

Ochre strip

Sediment trap

Ditch

Instrumentation site 2: Near the bottom of Gilchrist strip ditch

Ochre bag

Perspective view of the Ochre strip zone

Mire unit (view from above)

Dry weather flow outlet + 10%

Barrier (wood)

High flow storage water

Storage pond unit (cross section of outlet)

Dry weather flow outlet + 10%

Storage scenario 1: Baseflow event + 10-20%

Railway sleeper

Storage scenario 2: Storm event

Flume

Hut (housing the mini-Analysers)

20m

10-15m

Bridge

High Flow

Low Flow

Ditch Bottom

Pilot study 11 single bag ~ 25 kg ochre pellets

00.10.20.30.40.50.60.70.80.9

Date

TD

P m

g/l

TDP upstream

TDP downstream

0

0.050.1

0.150.2

0.250.3

0.350.4

0.45

Date

TP

mg

/l

TP upstream

TP downstream

Bag inserted

Major Event

Bag moved

P bag deployment• Easy to handle and deploy• Geotextile bag – 10 kg of ochre pellets

Pilot study 2

• 1 Ambient TP levels• 2 Disturbed TP levels

Little effect on TDP (though flows were quite high)

TP Results 412/07/2004

0

0.1

0.2

0.3

0.4

1 2Co

nce

ntr

atio

n (

mg

/l)

Upstream

Dow nstream

P stripping issues

• Sedimentation rates are very high

• Ditch preparation? Lined or not lined?

• Flashy hydrologic regime 10 l/s to 200 l/s.

can all the flow be processed (attenuated)?

• Sediment management plan

• Ochre recovery plan – when, how much?

• Benefits to agriculture

• Perception of putting waste to land

Scavenging P in rivers and lakes

• Gabions of ochre pellets in the water columnA – suspended in water columnB- resting on the channel bed (at a suitable location)• In place at times of high risk• removed from the water column and returned to land

P loss

Low flow level

flow

A

B

Bed Sediments

Proposed Runoff Plot Experiment Cockle Park Farm -10 plots

• Large scale soil amendment experiments• Biomass production and buffer strip impacts• Nutrient and metal fluxes

10 m

30 m control sludge ochre Sludge/

ochreLime 1 Lime 2

Conclusion• Huge potential but the waste to land issue needs to be

tackled

• Practical issues to be resolved.

• Remediation should work as part of a multi-disciplinary plan for all pollutants, biodiversity and flood reduction

• Defra funded schemes need to consider proactive measures compared to traditional passive methods.

• WFD - must strip P and protect larger rivers and lakes