Managing diffuse pollution from farmyards with wetlands: implications for water quality and ecology Caroline Coletto (now Enviros Consulting Ltd.) Kevin Stewart Kate Heal School of GeoSciences The University of Edinburgh, Scotland

Why are farm wetlands required? Many drivers for addressing diffuse pollution: water quality and ecosystem degradation, health concerns, economic costs 65% of Scottish rivers at risk of failing WFD due to diffuse pollution from agriculture and forestry activities Farmyard runoff is a potential source of contaminants Diffuse pollution expected to become worse as result of climate change Wetlands = low-cost sustainable solution

Wetlands on 7 farms in River Tweed catchment, Scottish Borders CW1 CW7 CW6 CW5 CW4 CW3 CW2 Surface areas = m 2 Water volumes = m 3

Methods Water sampling at inlet and outlet –pH, conductivity, TSS, BOD, reactive P, NO 3 /NO 2, NH 4 -N National Pond Survey methodology –Macrophyte walk-over survey -> dominant species –Macroinvertebrate survey: 3-minute kick-sampling divided between 6 meso-habitats in each wetland Biodiversity indicators –Species richness, species rarity index (SRI), conservation value (CV) –Average score per taxon (ASPT) for macroinvertebrate data –Simpson and Shannon indices of diversity and evenness

Water chemistry results (1) Reduction in over-deep pond

Reduction of NO 3 to NH 4 -N in over-deep pond Water chemistry results (2)

% reduction by concentration from inlet to outlet Relatively clean inflow water Over-deep pond

Outlet concentrations compared with threshold values WetlandBOD (8 mg l -1 ) TSS (25 mg l -1 ) NH 4 -N (0.6 mg l -1 ) NO 3 -N (11.3 mg l -1 ) RP (0.07 mg l -1 ) EA River Ecosystem class 4 Min. conc. causing observable biological effects EA River Ecosystem class 2 EC Drinking water standard Mean conc. in minimally impaired ponds CW CW2 CW3 CW CW50.09 CW6> CW714

Ponds with series of basins retain SS CW7 CW2

Poor water treatment in ponds poorly implemented/high inflow concentrations CW4: Field drain 15 m from inlet => short-circuiting CW6: Design misinterpreted => water depth 3 m instead of 1.5 m

Macroinvertebrates Water beetle oologi/insekter/ekle_kryp/images/ insekter/dytiscidae.jpg Freshwater snail ages/weichtiere/schnecken /succinea/hydrobiidae_1_3 00.jpg Water boatman urse/ent425/spotID/Heteropt era/notonect01.jpg Stonefly nymph rmont_rivers/River%20sites/Im ages%20for%20Site/Alloperla_ concolor,I_DSC56.jpg Macrophytes Celery-leaved buttercup m/3467/ _94d8 aefb08.jpg?v=0 Iris pseudacorus knoch/Iris%20pseudacorus%20Sumpf- Schwertlilie%201.jpg Common reed s/bio/ecology/Phragmites %20australis jpg

Wetland vegetationAquatic macroinvertebrates

Main findings and recommendations Highest treatment efficiencies – CW1, 2 & 7 Highest biodiversity values – CW 1, 4 & 7 Common features of high-performing wetlands –≥ 3 wetland cells within system –Pre-treatment, e.g. settlement zones –Natural colonisation or planting of vegetation –Varied water depths Treatment efficiency expected to increase as wetlands mature

Concluding remarks Further research: –Link between water chemistry and ecology –Flood attenuation Pollution swapping (increased CH 4 and N 2 O emissions) depends on magnitude of N inputs Wetlands could offset expected increase in diffuse pollution as result of climate change