CENTER FOR EMBEDDED NETWORKED SENSING UCLA USC UCR CALTECH UCM Sap Flow – Lots of ways to do it

Water diffuses “down-hill” from high to low concentration (  c) over a distance (  x) Everything diffuses like Fick’s First Law: Flow rate  cxcx Some Physics

Flow rate   w (psi) = the “concentration” of water  w (pure water) = 0.0 mega-Pascals  w (everything else) = negative MPa   w  x

 w (wet soil)  -0.1 MPa  w (atmosphere)  -95 MPa

 w (wet soil)  -0.1 MPa  w (root)  -0.5 MPa  w (stem)  -0.6 MPa  w (branch)  -0.8 MPa  w (atmosphere)  -95 MPa

 w (wet soil)  -0.1 MPa  w (root)  -0.5 MPa  w (stem)  -0.6 MPa  w (branch)  -0.8 MPa  w (atmosphere)  -95 MPa HIGH WATER FLOW Transpiration (day) stomata open resistance low

 w (wet soil)  -0.1 MPa  w (root)  -0.1 MPa  w (stem)  -0.1 MPa  w (branch)  -0.1 MPa  w (atmosphere)  -95 MPa No/little transpiration (night) stomata closed resistance high very low water flow

 w (dry soil)  -1.5 MPa  w (root)  -1.9 MPa  w (stem)  -2.0 MPa  w (branch)  -2.2 MPa  w (atmosphere)  -95 MPa Low water flow Low transpiration (stressed) stomata closed? resistance medium

Different water sources High soil water content Low soil water Transpiration for 3 hours only Transpiration for 12 hours Equal rates of water transport

Buy a pre-built system = $$,$$$ Sap Flow – Lots of ways to do it

Do it yourself = less $, but more work Building sap flow probes

Heated probe drops in temperature (relative to unheated probe) when sap flows. Heated probe temperature is higher during low or no sap flow. Measurement systems

Installation

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,6,1255,44.32,22.99,10.58,2.424,4.369,6.43,-.014,8.63,7.48,6.69,6.693,6.929,-.047,9.19,6.913,26.22,8.51,9.86,6.876,8.11,0,28.75,27.8,-6999,-6999,-6999,29.29,25.47 Data!

Temperature difference trace

zero sap-flow points (night) Temperature difference trace

Daily zero sap-flow subtracted Temperature difference trace

Sap flow: u = × Z where Z = (  T 0 –  T) /  T Units of sap flow: m 3 H 2 O m -2 sap wood area s -1 Empirical transformation

Sap flow trace

Units of sap flow: m 3 H 2 O m -2 sap wood area s -1 1 m 3 H 2 O = 1000 liters 10 cm sap wood thickness 80 cm diam  r 2 -  r 2 = m 2 Multiply results by 4900 Units of sap flow: liters s -1 Units transform

Sap flow – nice units

Is sap flow decreasing?

Interpreting sap flow: micromet

$6000 $15 $320 Light (PAR) sensing

Interpreting sap flow: micromet dew point = 9.1°C dew point = 15.3 °C

Interpreting sap flow: micromet

Interpreting sap flow: um? But note: temperature fluctuations even when no power is applied to the heated probe – temperature gradients!