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Constructed Farm Wetlands (CFWs) for remediation of farmyard runoff in Scotland: Water treatment efficiency, ecological

Constructed Farm Wetlands (CFWs) for remediation of farmyard runoff in Scotland: Water treatment efficiency, ecological value and cost-effectiveness. Fabrice Gouriveau The University of Edinburgh, School of GeoSciences fabrice.gouriveau@ed.ac.uk.

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Constructed Farm Wetlands (CFWs) for remediation of farmyard runoff in Scotland: Water treatment efficiency, ecological

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  1. Constructed Farm Wetlands (CFWs) for remediation of farmyard runoff in Scotland: Water treatment efficiency, ecological value and cost-effectiveness Fabrice Gouriveau The University of Edinburgh, School of GeoSciences fabrice.gouriveau@ed.ac.uk Supervisors: Dr. Kate Heal, Dr. Graham Russell, Dr. Andy Vinten

  2. Background • Agriculture is a major source of “diffuse” water pollution from arable fields, grasslands, farmyards, etc. • Constructed Farm Wetlands (CFWs) [Surface flow] are promoted to catch and treat contaminated farmyard runoff (e.g. yards, silage pits, roofs, tracks) However, the Scottish experience is limited and investigation is needed to understand existing systems and build more efficient ones…

  3. Research objectives • Study the link between farm practices, rainfall characteristics and quality & quantity of farmyard runoff • Assess spatially and temporally the water treatment performance of two CFWs • Assess their ecological value • Document the cost-effectiveness of CFWs • Contribute to the improvement of design guidance

  4. Work undertaken Two sites: CFW 1 and CFW 2, in south-east Scotland • Rainfall, water level and flow monitoring • Water sampling to assess pollutant loadings and removal: • Monthly grab samples • Storm event sampling • Samples analysed for: NO3-, NH4+, IP, TP, BOD5, TSS, FIOs • Ecological surveys • Aquatic macro-invertebrates (3 times a year) • Wetland vegetation (once a year) • Sediment sampling once a year • Interviews with farmers to assess acceptance, costs, problems

  5. CFW 1: Overview Farm 1: beef and arable farm – 125 cows Average annual rainfall ~ 870 mm Design (Treatment Volume): 2 x Vt = 2 x 1400 = 2800 m3 (Cost ~ £5000)

  6. CFW 1: Ponds Open ponds surrounded by Phragmites australis and Juncus effusus

  7. CFW 1: Wetland areas Wetland areas: grasses, watercress, rushes, etc.

  8. Inlets Outlet CFW 1: Final pond

  9. Not to scale N CFW 2: Overview Farm 2: dairy farm – 400 cows Annual average rainfall ~ 700 mm Design (Treatment Volume): 5 x Vt = 5 x 340 = 1700 m3 (Cost ~ £4000)

  10. Outlet Inlets Swale CFW 2: Swale and pond

  11. CFW 1: Water quality overview

  12. CFW 2: Water quality overview

  13. CFW 1: Spatial & temporal variability

  14. CFW 1: Storm-event sampling Treatment estimation: Rainfall ~ 20 mm in 15 h ; Vol. in = Vol. out ~ 500 m3 IP loading in = Ci x Vi = 0.60 x 500 ~ 300 g IP loading out = Co x Vo = 0.25 x 500 ~ 125 g  Treatment Efficiency for IP: 58 % mass removal

  15. CFW 2: Spatial & temporal variability

  16. CFW 2: Spatial & temporal variability

  17. CFW 2: Storm event sampling

  18. Macroinvertebrates QUALITY Very good Good Moderate Poor CFW 1 - Good ecological value (habitat heterogeneity, low contamination) CFW 2 - Moderate ecological value (low habitat heterogeneity, high contamination and rapid pH and DO changes)

  19. Summary of Findings CFW 1: Receiveslightly polluted runoff & discharges a good quality effluent meeting UK standards (except for nitrate and FIOs); good ecological value. Limitations: Farmyard runoff not fully intercepted; excess of field drainage & groundwater; preferential flow & sub-optimal use of the land CFW 2: Receives highly polluted runoff, achieves some treatment but discharges a poor quality effluent which does not meet UK standards; moderate ecological value. Limitations: Non-vegetated, too small, single cell, short HRT. But could be modified and planted to ensure better treatment. These CFWs are a low-cost option but design & performance could be improved

  20. Conclusions & Prospects • Lack of studies of performance of CFWs but increasing knowledge and data (e.g. Irish ICWs, Scottish CFWs) • Lack of clear water quality targets to be achieved by CFWs (common, site-specific or depending on receiving watercourse?) • Limited design guidance but CFW Design Manual in progress • Failure to implement CFWs according to design ; limited follow-up • Cost analysis need to be inclusive (construction, planting, maintenance, loss of land, SFP) and compared with other alternatives • Need for stronger financial incentives to support sustainable CFWs

  21. Design Suggestion • Deeper pond (sediment retention + spillage contingency) & shallow wetland cells connected by elbow pipes to control water level (<40 cm). • Wetland area/volume ? f (rainfall on impermeable surfaces, ~ 3 weeks residence time) Farmyard runoff Wetland cell 2 Wetland cell 1 Wetland cell 3 Pond 1 Pond 4 2 stage outflow

  22. Thank You for your Attention ! Many thanks to: David Kinloch Michie Studentship, Torrance Bequest, University of Edinburgh Development Trust, Scottish Environment Protection Agency (SEPA), Macaulay Institute, Scottish Agricultural College (SAC), Martha Lucía Gouriveau, Alan Frost, Rory Harrington, Marjan Van de Weg, Andrew Gray, John Morman, Rob Briers, Alison Cole, Carole Christian, Andrew Colman, James Sukias and all the farmers involved.

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