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Algorithm

The calculations require the user to enter data in three steps, and results are then displayed in the fourth step.

Step 1: selection of the hydrological regime of the studied pool:
a) non-steady-state (no inflow to the pool, the water table decreases due to progressive evaporation) or
b) steady-state model (inflow equals evaporation).

Step 2: selection of the option for δA value determination:
1) the most accurate approach – it is required to known δ
A value based on field analyses;
2) δ
A calculated from stable isotope composition for precipitation (δRain) for the studied pool and season;
3) δ
A calculated from δRain and the slope of LEL. The selection in this step will determine what data need to be used in step 3.

Step 3: entering analysed stable isotope composition of water:
δ
P –initial value for water in the pool (for non-steady state) or value for water inflowing to the pool (for steady state)
δ
L – final value for water in the pool (for non-steady state) or a pool value (for steady state)

and measured parameters: T – temperature; h – relative humidity of air (as fraction); δA – the stable isotope composition of moisture in ambient air (if known); dRain –the stable isotope composition of precipitation (if δA is not known); LEL – if known for the study area.

Step 4: After entering all required variables, the calculated results will be displayed as a fraction of the evaporated volume f, or as fraction evaporation over inflow E/I, depending on the selected model. Along with results, the intermediate parameters, calculated based on entered variables, will be listed: kinetic isotope fractionation constant – Ck; kinetic isotope fractionation factor - εk; equilibrium isotope fractionation factor – ε*, total isotope fractionation - ε, fractionation factor - α, limiting isotopic composition – δ* and parameter m.

The full algorithm is avilable as a research paper (free access)

Skrzypek G, Mydłowski A, Dogramaci S, Hedley P, Gibson JJ, Grierson PF, 2015. Estimation of evaporative loss based on the stable isotope composition of water using Hydrocalculator. Journal of Hydrology 523, 781–789.

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 Python Pool, Dolphin Island, Western Australia 

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