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 Supervisors: Dr. Kate Heal, Dr. Graham Russell, Dr. Andy Vinten

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

Research objectives 1)Study the link between farm practices, rainfall characteristics and quality & quantity of farmyard runoff 2)Assess spatially and temporally the water treatment performance of two CFWs 3)Assess their ecological value 4)Document the cost-effectiveness of CFWs 5)Contribute to the improvement of design guidance

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: NO 3 -, NH 4 +, IP, TP, BOD 5, 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

CFW 1: Overview Farm 1: beef and arable farm – 125 cows Average annual rainfall ~ 870 mm Design (Treatment Volume): 2 x V t = 2 x 1400 = 2800 m 3 (Cost ~ £ 5000)

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

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

CFW 1: Final pond Inlets Outlet

CFW 2: Overview Design (Treatment Volume): 5 x V t = 5 x 340 = 1700 m 3 (Cost ~ £ 4000) Farm 2: dairy farm – 400 cows Annual average rainfall ~ 700 mm Not to scale N

CFW 2: Swale and pond Swale Outlet Inlets

CFW 1: Water quality overview Mean inletMax inletMean outletMax outlet Treatment Efficiency (concentration) BOD 5 (mg l -1 ) < 0 % NH 4 + (mg l -1 ) % NO 3 - (mg l -1 ) % IP (mg l -1 ) % TSS (mg l -1 ) % FC (CFU/100 ml) > < 0 %

CFW 2: Water quality overview Mean inletMax inletMean outletMax outlet Treatment Efficiency (concentration) BOD 5 (mg l -1 ) % NH 4 + (mg l -1 ) % NO 3 - (mg l -1 ) % IP (mg l -1 ) % TSS (mg l -1 ) % FC (CFU/100 ml) > %

CFW 1: Spatial & temporal variability

CFW 1: Storm-event sampling Treatment estimation: Rainfall ~ 20 mm in 15 h ; Vol. in = Vol. out ~ 500 m 3 IP loading in = C i x V i = 0.60 x 500 ~ 300 g IP loading out = C o x V o = 0.25 x 500 ~ 125 g  Treatment Efficiency for IP: 58 % mass removal

CFW 2: Spatial & temporal variability

CFW 2: Storm event sampling

Macroinvertebrates 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) Poor Moderate Good Very good QUALITY

Summary of Findings CFW 1: Receives lightly 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

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

Design Suggestion Pond 4 D eeper 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 1 Wetland cell 2 Pond 1 2 stage outflow Wetland cell 3

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.