Natural Organic Matter. Chris Evans, Centre for Ecology and Hydrology, Bangor

Transcription

1 Natural Organic Matter Chris Evans, Centre for Ecology and Hydrology, Bangor

2 Welsh Water 2050 Strategic response 1. Safeguarding clean drinking water through catchment management Increased control of the quality of our raw product in the face of increased turbidity and run-off due to extreme weather events caused by climate change; ensuring raw water entering our treatment works is of a consistent and manageable quality (including managing cryptosporidium, natural organic matter causing disinfection by products and algal growth causing taste and odour complaints)

3 The challenge of rising DOC

4 DOC increases in Europe and North America DOC increases have occurred across large areas of Northern Europe and NE North America Increases have been observed in catchments draining forests, peatlands, upland grasslands and heathlands However, peatlands are in general the largest sources of freshwater DOC

5 Land-use impacts on Welsh peatlands Red = drained Black = undrained Around 10% of Welsh peatlands have been afforested At least 3000 km of drainage ditches Extensive areas of heavily modified bog and agricultural grassland on peat

6 DOC concentration/flux change Effects of drainage? Blanket bog Raised bog/fen Tropical peat 150% 100% 50% 0% Drainage Re-wetting -50% -100% Evans et al. (2016), IPCC (2013)

7 DOC responses to ditch-blocking, N Wales Hillslope Scale Paired Catchment Scale Evans et al. (in review)

8 Effects of managed burning? DOC vs recent burn area Yallop and Clutterbuck (2009)

9 Effects of a wildfire in Northern Ireland c) DOC Fire mg l Fire caused DOC to decrease, not increase This has also been observed elsewhere (and makes some sense) Overall, fire seems likely to affect DOC export (e.g. via plant species changes) but evidence base is fairly weak

10 Effects of recovery from acidification?

11 Effects of recovery from acidification? More DOC Less DOC Less acidic More acidic

12 Reservoirs as carbon reactors Lake/reservoir DOC input-output balances

13 DOM removal slows down over time:

14 Rapid light-driven removal of fresh DOM Dark Light

15 mg DOC/l Nutrient pollution causes DOC production: Farmland Stream: Adding N& P accelerates DOC production DARK LIGHT Agricultural stream LIGHT+P 14 LIGHT+N+P DARK+N Days Fovet et al. (in prep.)

16 CREW Project

17 CREW Reservoir DOM model Eq 1) Catchment DOC production: DOC catchment = DOC baseline x RDOC acidity x RDOC drainage x RDOC burning x RDOC forest x RDOC felling Eq 2) Effects of acid deposition: RDOC acidity = {exp(-α * ( ln(xso 4) ) + β)}/100 Eq 3) In-reservoir DOC removal: Water residence time DOC outflow = {(DOC inflow (DOC inflow f inert )} 0.5 (RT T ½ ) + (DOCinflow f inert ) DOC half-life Inert fraction Eq 4) In-reservoir DOC production: Internal P production DOC aquatic = (P external + P internal ) x {DOC:DOP} aquatic Catchment P input

18 Model simulations, Savalbeg WTW mg l a) Forest removal Inflow Inflow (forest removal) Outflow Outflow (forest removal)

19 16 Model simulations, West Water WTW 8 mg l -1 mg l Inflow Inflow (Re-wetting) Outflow Outflow (Re-wetting) b) Cessation of moorland burning Inflow Inflow (No burn) Outflow Outflow (No burn) mg l a) Peatland re-wetting Inflow Inflow (Re-wetting) Outflow Outflow (Re-wetting) mg l c) Reduced P levels Inflow Outflow Outflow (P removal) mg l b) Cessation of moorland burning Inflow 12 Inflow (No burn) 10 Outflow 8 Outflow (No burn) c) Reduced P levels mg l d) All measures combined Inflow 12 Inflow (all measures) 10 Outflow 8 Outflow (all measures)

20 FREEDOM Project Forecasting Risk to upland water treatment assets from the Environmental Exacerbation of Dissolved Organic Matter levels Aims: to equip Scottish Water, and ultimately the water industry as a whole, with scientifically robust knowledge and tools to enable the threats posed by rising DOM levels in water supplies to be addressed via a sustainable, resilient and costefficient combination of mitigative and adaptive solutions. Reservoir catchment input-output budgets (internal processes) Long-term data analysis (deposition impacts) Paired catchment studies (land-use impacts) Model development and testing (SW sites) Decision Support System & wider engagement (water industry)

21 NERC LOCATE project The role of aquatic C in the earth system New data on fluxes, character and processing of organic matter in UK rivers Conwy one of three focal study catchments New catchment models being developed

22 Conwy Observatory: Spectrolysers Hiraethlyn (Improved grassland) Conwy Marina (estuary mouth) Cwm Llanerch (Tidal limit) Glasgwm (Forest) Nant y Brwyn (Blanket bog) Llyn Conwy (lake)

23 Spectrolyser data, Sep 2016 Nant y Brwyn (blanket bog) Glascwm (forest on mineral soil) Hiraethlyn (Improved grassland) DOC response to rainfall was highly variable between sites, depending on soil type Despite a smaller flow peak, by far the largest DOC spike occurred in the farmland catchment

24 Concluding Questions Can catchment management reduce DOC export from the catchment, and if so how much? Are some future DOC increases unavoidable due to ongoing recovery from acidification or climate change? Could controlling P (or N) supply in catchments or reservoirs reduce both DOC production and taste & odour problems? Can we predict future water colour levels and therefore target catchment mitigation and/or capital investment in infrastructure? What controls DOC/water colour peaks, and can we develop realtime prediction systems to avoid high-doc (or high-sediment) water entering treatment systems?

25 Thanks for listening