Urban Water Security Research Alliance

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1 Urban Water Security Research Alliance Methane Emissions from Two Reservoirs in a Steep, Sub-Tropical Rainforest Catchment Brad Sherman and Phillip Ford Life Cycle Analysis and Integrated Modelling Project 15 September 2011

2 Emission intensity of water supply options Background Rainwater tanks (pumping) Water recycling (pumping) (pumping & treatment) Desalination Current water supply Reservoir CH4 emissions (pumping & treatment) (direct emissions) (tonnes CO 2 -e ML -1 ) GHG footprint of urban water cycle in SE Queensland (Hall et al. 2011) Reservoir CH 4 emission estimated to contribute ~ 32% of total direct + indirect emissions for current water supply Based on very limited data Low estimate was 1/2 as much High estimate was 10 times greater Need more data to reduce uncertainty of estimate Hall, M. R., West, J., Sherman, B., Lane, J., & de, H., David. (2011). Long-Term Trends and Opportunities for Managing Regional Water Supply and Wastewater Greenhouse Gas Emissions. Environmental Science & Technology, doi: /es103939a

3 Conceptual Model - CH4 Light Diffusion to atmosphere CH 4 Stream O 2 Oxidation of CH 4 to CO 2 by methanotrophs CH 4 CH 4 bubbles CO 2 & CH 4 Diffusion Discharge Organic matter CO 2 + CH 4 Sediment Expansive shallow systems! Deep systems!

4 Methane flux pathways F atm F bubble = (1- )F sed [CH4] epi F gradient = -k dch 4 /dz F biota dch 4 /dz [CH4] hypo F sed F sed

5 Thin boundary-layer diffusive flux CH4, CO2 atm atm water CH4, CO2 water Turbulence reduces water Water turbulence increases with wind speed Air-water flux increases with water turbulence

6 Field sites - Hinze Dam and Little Nerang Dam

7 Little Nerang Dam (Hinze Dam) Volume (ML) Surface Area (ha) Little Nerang Dam Hinze Dam Catchment Area (km 2 ) Domestic water supply for Gold Coast, SE Queensland Catchment vegetation ~ 80% forested Sub-tropical rainforest Warm and cool temperate rainforests Wet and dry sclerophyll forests ~ 20% grazing natural vegetation or modified pasture Strong rainfall gradient ~ 1 m p.a. at the dam (elevation 167 m) ~ 3 m p.a. at Springbrook (~ 8 km from dam, elevation 950 m) Very intense rainfall mm in 24 h not uncommon 5.6 m in 1974!

8 Field sites LND05 NW embayment LND05 dam wall LND west embayment LND Node 1 Hinze11 Hinze12 Hinze13 LND Met Hinze10 Hinze05 Hinze04 LND PB02 PB transect LND08 PBT05 PBT04 PBT03 PBT02 PBT01 LND06 LND EAST 01 LND PB01 LND PB03 Little Nerang Dam 0 m 400 m LND EAST 02 LND09 LND EAST 03 LND10 LND11 Hinze07g, h Hinze06 Hinze06 b, f Hinze07 0 m Hinze09 Hinze08 Hinze07f Hinze06i Hinze06h Hinze Dam 1000 m 2000 m GC profile site Flux chamber site Hinze03 Hinze02 Hinze01

9 Field monitoring program Picarro gas analyser for CH4 & CO2 Kestrel weather monitor for local wind speed Met station / thermistor chain Floating chamber / Nortek ADV

10 The floating chamber in action!

11 Flux chamber measurement Bubble events CH 4 (ppmv) :50:00 12:00:00 12:10:00 Diffusive flux only Flux is directly proportional to the slope Use linear regression if measurement is only a diffusive flux Use end point concentrations if measurement contains bubble fluxes

12 Floating Chamber data - diffusive flux only 445 LND10 19 Jan LND09 19 Jan 2010 CO 2 (ppmv) slope = R 2 = 0.97 CO 2 (ppmv) slope = R 2 = 0.94 CH 4 (ppmv) :37 10:38 10:39 10:40 10:41 10:42 10:43 10:44 10:45 10: Note: higher ambient CH4 at LND10 slope = R 2 = :37 10:38 10:39 10:40 10:41 10:42 10:43 10:44 10:45 10:46 CH 4 (ppmv) :02 11:03 11:04 11:05 11:06 11:07 11:08 11:09 11:10 11: slope = R 2 = :02 11:03 11:04 11:05 11:06 11:07 11:08 11:09 11:10 11:11 Heterotrophic CO2 is emitted 420 m + 25 minutes Autotrophic CO2 is consumed

13 Spatial variability - Little Nerang Dam LND10 distal east arm LND05 dam wall LND EAST 03 LND09 LND Node 1 LND EAST 01 LND EAST 02 LND05 NW embayment LND west embayment LND Met LND06 Burford / confluence LND PB01 0 m 400 m LND PB03 CH 4 Flux (mg-ch 4 m -2 d -1 ) Feb 2010 LND PB02 LND08 distal west arm NW embayment LND Node 1 West embayment Met Stn LND06 LND08 LND09 LND10

14 Spatial variability in high flux region CH 4 Flux (mg-ch 4 m -2 d -1 ) Depth 1 Mar PBT PBT PBT PBT04 LND PB02 PB transect line 280 PBT05 3 m 10 m 10 m 11 m 4 m PBT05 PBT04 PBT03 PBT02 PBT01 LND PB01 LND PB03 LND08 distal west arm Feb LND06 Burford / confluence 11 LND EAST LND EAST 02 LND EAST LND PB03 LND PB02 LND PB01 Confluence LND EAST01 LND EAST02 LND EAST03 CH 4 Flux (mg-ch 4 m -2 d -1 ) 0 m 200 m

15 Reservoir scale spatial variability CH4 Flux (mg-ch4 m -2 d -1 ) Scaled Instantaneous 2-3 Dec 2009 CH4 Flux (mg-ch4 m -2 d -1 ) Scaled Instantaneous Jan Scaled 1-8 June LND05 LND Node 1 LND Met LND06 LND08 LND EAST03 LND EAST04 LND10 LND05 LND Met LND06 LND08 LND Scaled 24 Feb -1 Mar CH4 Flux (mg-ch4 m -2 d -1 ) Instantaneous 1 LND Node 1 West embayment NW embayment LND Met LND06 LND PB01 LND PB02 PBT01 PBT02 PBT03 PBT04 PBT05 LND PB03 LND08 LND EAST01 LND EAST02 LND EAST03 LND09 LND10 LND05 West embayment NW embayment LND Met LND06 LND08 LND09 LND10 CH4 Flux (mg-ch4 m -2 d -1 ) Instantaneous CH 4 Flux increases by 100x from dam to upstream ends

16 Spatial variability - Little Nerang Dam pch 4 increases towards upstream ends

17 LND PB03 Temporal variability - Little Nerang Dam Flux CH 4 (mg m -2 d -1 ) hours LND10 Fluxes can vary by a factor of 3-10 within 20 minutes when bubbles are present 10 Flux CH 4 (mg m -2 d -1 ) Measurements 20 minutes apart :33: :51: :08: :56: :14: :42: :02: :20: :32: :43:00 9 hours :55: :12: :28: :55: :13: :35: :59: :59: :11: :17: :37:30 LND06 Seasonal trends No trend at LND10 Decrease at LND06 in winter? Notice very large (x 10) difference between consecutive days at LND06! :26: :44: :33: :49: :08: :56: :14: :30: :49:02 LND05 dam wall :06: :23: :41: :59: :30: :50: :06: :00: :18: :35: :43: :02: :20: :37: :54: :36: :52: :37: :49: :06: :05: :22:00 LND EAST 03 LND09 LND10 distal east arm LND Node 1 LND EAST 01 LND EAST 02 LND05 NW embayment LND west embayment LND Met LND06 Burford / confluence LND PB m

18 Spatial variability - Hinze Dam CH 4 Flux (mg-ch 4 m -2 d -1 ) Hinze Dam Feb 2010 Hinze11 Hinze12 Hinze13 1 Hinze06 Hinze07 Hinze eruption Hinze08 Hinze09 Little variability in east arm (Hinze01 - Hinze05) High emissions / high variability in west arm 100 x variation within m Hinze07g, h Eruption Hinze06 Hinze06 b, f West arm receives fresh organic matter East arm receives discharge from Little Nerang Dam Hinze10 Hinze11 Hinze12 Hinze05 Hinze04 Hinze03 Hinze07 Hinze02 Hinze01 Hinze09 Hinze08 Hinze07f Hinze06i Hinze06h Hinze m GC profile site Hinze Dam CSIRO GHG study sites Flux chamber site To Little Nerang Dam Hinze05 Hinze04 Hinze03 Hinze02 Hinze01

19 What do high emissions look like? Continuous disturbance of surface by bubbles spatially random over time large area ( > 10 4 m 2 ) CH4 flux O( mg m 2 d -1 ) Rare massive eruption of bubbles unknown frequency (1-2 d -1?) small area (< 100 m 2 ) short duration (1-5 minutes) CH4 flux O( mg m 2 d -1 )?? instantaneous

20 Mean reservoir CH4 fluxes 500 Flux CH 4 (mg m -2 d -1 ) Little Nerang Dam Area-weighted means Little Nerang Dam mg m -2 d Dec Jan 24 Feb - 1 Mar June All data Hinze Dam Flux CH 4 (mg m -2 d -1 ) Hinze Dam mg m -2 d Feb 30 June - 1 July 16 July 13 Aug All data

21 Conclusions - Spatial variability 64% of emissions comes from 6% of reservoir area 78% of flux from 9% of reservoir area Emissions highest at presumed deposition zones at upstream end of storages High emissions in arms receiving new organic matter from catchment Arms with another reservoir upstream did not show this effect Organic matter supply more important than depth per se PB Transect had highest emission at deepest site (centre) Western embayment - lowest emitter, shallow site, hard bottom

22 Conclusions - Temporal variability Total reservoir flux dominated by ebullition Bubble fluxes at a site vary over an hour by up to a factor of 10 between measurements Repetitive sampling required to capture stochastic bubble events Longer-term bubble trap deployments No consistent seasonal trends observed Little water temperature variation Dec - Mar Lowest diffusive emissions at deepest sites in winter Possible thermal regulation of methanogenesis High bubble emissions observed in well-oxygenated water column during winter conditions

23 Conclusions Little Nerang Dam ( mg m -2 d -1 ) is amongst the highest CH4-emitting reservoirs in the world Hinze Dam (37-64 mg m -2 d -1 ) is a relatively high emitter (especially when compared to Tasmanian storages) Hypothesis Steep catchment with high rainfall and high litter flux High proportion of labile carbon is washed into the storage rather than degrading on the landscape or in river channels Interception by a reservoir provides sufficient residence time for labile carbon to be degraded to CH 4 prior to arrival in downstream storages

24 Acknowledgements UWSRA, WfHC provided funding Seqwater support Laurie Fairall, Deb Gale, James Udy CSIRO Danny Hunt, Chris Drury, Mat Dunbabbin, Murray Hall, Shiroma Maheepala UQ Alistair Grinham Monash Water Studies Centre Mike Grace, Todd Scicluna, Perran Cook

25 Urban Water Security Research Alliance THANK YOU