Fluxes: measurements and modeling Schlesinger and Bernhardt Pg 135-150 Gustin flux paper Denmead, 2008 Baldocchi, 2012 Flux C time Amount of material transferred from one reservoir to the other Source Sink Budget-balance of sources and sinks 1
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Transport phenomena Flux = amount of a given quantity that flows through a unit area per unit time (a vector). Examples: Heat flux (J m -2 s -1 ) Volumetric flux (m 3 m -2 s -1 ) Chemical flux (mol m -2 s -1 ) Mass flux (g m -2 s -1 ) source e.g. hydrologic cycle sink 3
Global water cycle Pools (km 3 ) Fluxes (km 3 yr -1 ) 26,350,000 2 373,000 413,000 New figure and numbers S and B Figure 10.1 Evaporation from the oceans ranges from 4 mm day -1 in the tropics to <1 mm d -1 at the poles. Runoff = ppt ET- groundwater The relative balance of ppt and evaporation differs between regions. 4
Precipitation hard to model and predict Solid and dashed lines rain gauge Dots-models Chahine Gimeno et al (2011) Understanding evaporation source regions and continental precipitation Satellite data Isotopes Flux analyses Humidity Climate change Intensified hydrologic cycle Changing circulation patterns 5
It s more complicated than it seemed at first! We have to consider both temporal and spatial scale Satellite A train Leaf Cells Individual plant Scales of fluxes Landscape Globe 6
Approaches for scaling fluxes Bottom up- scaling with empirical data Bottom up-scaling with processes Top down-apply air concentrations and model to get at what is driving exchange Top down-remote sensing Northern Wetlands Study (NOWES) To assess the importance of Northern Wetlands as sources of biogenic gases to the atmosphere under current and future climate scenarios 7
Northern Wetlands Study (NOWES) To assess the importance of Northern Wetlands as sources of biogenic gases to the atmosphere under current and future climate scenarios Mass Balance Everything has to go somewhere Boundary A substance entering a defined region has three possible fates inputs Sinks Sources Accumulation outputs 1) It gets to leave unchanged 2) It may accumulate Accumulation = Input Output Sinks + Sources rate rate rate rate rate 3) It may change or be removed (sink) or some may be added (source) 8
Methods for quantifying fluxes Air approach but similar for water/ soil ( Baldocchi, 2012) 1. Deposition collectors (dry and wet) 2. Flux chambers (enclosures)-net flux Static (equilibrium) Dynamic (flow through) 3. MicroMet (tower) approach-net flux Gradient method (MBR) Eddy covariance Eddy accumulation (REA) Horizontal flux (MMB) Unidirectional Flux Deposition 9
Collectors Unidirectional or Net Flux chambers C out C in Flux C Q C A out in 10
Mass Balance Where; C = pollutant concentration (g/m 3 ) C in = Pollutant concentration in incoming air ( g/m 3 ) q s = emission rate of pollutant or flux (g/m 2 s) H = Mixing height (m) L = Length of Box (m) W = Width of box (m) U = Average wind speed (m/s) C(0) = concentration in the box initially t = time Steady State At steady state dc/dt = 0 C = q s L/uH + C in Non Steady State C(t) = q s L/uH (1 e ut/l + C in ) + C(0) e ut/l Alert,NU Reno,NV 11
Flow Through Chamber Flux= Q(C out -C in )/A Mass Balance Static Chamber flux measurement Static Chambers mass Balance Flux= (ΔC/Δt ) V/A (ng/m 2 s) 12
Baldocchi (2012) Fast flux measurements isotopes C, O, carbonyl sulfide OCS to partition fluxes between plants and soil CH4 and N2O to assess microbial activity in the soil Hydrocarbons, ozone, nitrogen oxides to assess pollutant loads To interpret trace gas fluxes Need meteorology, land use and disturbance, state of vegetation and soil Surface Layer Turbulence & Fluxes Reynolds averaging F ' ' F q w K F H E C ' ' c T w c K p ' ' w c K C Fluxes V p H q 2 ( w / m ) z C 2 ( ng / m s) z T 2 ( w / m ) z Deposition velocity = V d =F C /C L(m) is the Monin Obukov Length, ratio of mechanical to buoyancy forces 3 u* T C L kgh p z/l =0 neutral z/l>0 stable z/l<0 unstable (m/s) 13
Aerodynamic Gradient Method F K C Z C u* k( C2 C1) F K z ln( z d / z d) Stable Neutral H z d 4. 7 L H 0 Unstable 2 1 x H 2ln 2 3 u* T C L kgh p 2 1 h2 h1 1 z d x 15 L L(m) is the Monin Obukov Length where g = acceleration due to gravity (9.81 m/s 2 ) H = sensible heat flux (W/m 2 ) = air density (kg/m 3 ) T = temperature (K) Cp = specific heat at constant pressure (J/kg.K) 0.25 14
Net flux Gradient measurement (MBR) Net flux Eddy covariance/correlation Instantaneous change in vertical wind velocity and atmospheric gas concentration 15
Net flux?relaxed eddy accumulation Updraft Deadband Downdraft Fugitive Emissions from Coal Seam Gas exploration Experimental approach Flux tower measures atmospheric turbulent parameters at a rate of 20 times per second, concurrent with concentrations of CH 4, CO 2 and H 2 O. Eddy covariance technique facilitates the calculation of turbulent fluxes and energy balance parameters in real time. These data are needed for the modelling approaches applied. 16
Modelling Approach: Backward Lagrangian Stochastic model (WindTrax) Inputs: friction velocity u*, K M Obukhov stability length L, Surface roughness length z 0, wind speed wind direction u u* m z k( z d ) measured concentration Measured background concentration u ' ' u w u z 3 u * T C p L kgh 2 * Output: Source strength Q (g/s) or are flux (g/m 2 s) Micromet mass balance upwind mast downwind mast wind direction horizontal flux vertical flux surface x All require v specific ground characteristics 17
How can we possibly get at regional and global fluxes from a limited number of ground measurements? Multi-scale measurements http://modis.gsfc.nasa.gov/ 18
methodology page http://fluxnet.ornl.gov/introduction Mercury example Stamenkovic/Hartmann PhD 19
Do plants take up or emit mercury to the atmosphere? JStamenkovic - Dissertation Defense Is the exchange cuticular or stomatal? Species differences? Environmental controls? Measuring mercury (Hg) exchange C out C in Flux C Q C A out in 20
Four plant species: Andropogon gerardii Sorghastrum nutans Rudbeckia hirta Populus tremuloides RH: 25% Soil [Hg]: 0.02 / 0.90 g g -1 RH: 7-62% (avg. 25%) Light / Dark Ambient / Scrubbed air [CO 2 ]: 360, 613, 846 ppm [Hg]: 0, ambient, 2x, 5x (0-12 ng m -3 ) P. tremuloides 20 clean air ambient Hg exchange air Hg (ng m -3 ) 15 10 5 Air Hg clean / ambient air Light / Dark Hg Flux (ng m -2 h -1 ) 0 549 550 551 552 553 554 555 556 10 0-10 -20-30 -40 Stomatal movement and gas exchange Pnet ( mol m -2 s -1 ) 20 15 10 5 0-5 549 550 551 552 553 554 555 556 21
Foliar Hg flux (ng m -2 h -1 ) air Hg concentration (ng m -3 ) EcoCELL- unfortunately blank too high to use data collected from this large chamber Ecologically Controlled Enclosed Lysimeter Laboratory Large flow-through gas-exchange chamber Flux ~ concentration differential, air flow, area 5.5 m 7.3 m Air intake 4.5 m EcoCELL 22
Components vs net flux Hg flux [ng m -2 hr -1 ] 8 6 4 2 0 mesocosm 1 mesocosm 2 mesocosm 3 mesocosm 4-2 Bare soil Plant shoot Chamber net Components vs net flux Hg flux [ng m -2 hr -1 ] 8 6 4 2 0 mesocosm 1 mesocosm 2 mesocosm 3 mesocosm 4? Litter correction 77% -2 Bare soil Plant shoot Chamber net Plant litter soil 23
Tallgrass prairie monoliths a net sink for atmospheric Hg + 0.099 g ha -1 yr -1-0.025 g ha -1 yr -1 + 0.074 g ha -1 yr -1 Litter-and-plant covered soil: 0.025 g ha -1 yr -1 130 g ha -1 Soil storage* Precipitation: 0.029 g ha -1 yr -1 Uptake in vegetation (ephemeral storage): 0.070 g ha -1 yr -1 litterfall 0.13 g ha -1 Root pool* Leaf Individual plant Role of vegetated systems in biogeochemical cycling of mercury Soil flux Landscape Biome Globe Continental / Global scale 24
Background biomes in the US GRASSLAND (Stamenkovic et al. in press) DESERT (Ericksen et al. 2006) DECIDUOUS FOREST (Kuiken et al. 2008) Classification and regression tree Rule-based model biome swc < 2 forest 0.2 ± 0.1-0.2 ± 0.1 0.8 ± 0.4 swc < 25 0.1 ± 0.1 1.1 ± 0.5 temperature irradiance % swc Hg flux 25
Spring Summer Fall Winter Hg flux rate (ng Hg m 2 h 1 ) NET ANNUAL EXCHANGE dry deposition of ~11 tons Hg g Hg m 2 JStamenkovic - Dissertation Defense max LAI leaf mass/area (100 g m -2 ) leaf [Hg] (25 ng g -1 ) 26
Vegetated systems are a net sink for atmospheric mercury 146 wet deposition fire, 10-15 hydrothermal systems 5-7 Atmosphere Contiguous United States metric tonnes Hg per year 11 (?) Land storage Pacyna & Pacyna 2006, Brunke et al. 2001 Engle et al. 2006 Fluxes Measured in different ways Concentrations/time Concentration/area/ time A concentration does not give you a flux 27
Global carbon cycle Pools (10 15 g C) Fluxes (10 15 g C yr -1 ) Global nitrogen cycle Pools (10 15 g N) Fluxes (10 12 g N yr -1 ) 28
Global phosphorus cycle Pools (10 15 g P) Fluxes (10 12 g P yr -1 ) Global sulfur cycle Pools (10 15 g S) Fluxes (10 12 g S yr -1 ) 29