 |
| Titel |
Modelling the water balance of a precise weighable lysimeter for short time scales |
| VerfasserIn |
Johann Fank, Gernot Klammler, Gerhard Rock |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105342
|
| Publikation (Nr.) |
 EGU/EGU2015-4864.pdf |
|
|
|
|
|
| Zusammenfassung |
| Precise knowledge of the water fluxes between the atmosphere and the soil-plant system and
the percolation to the groundwater system is of great importance for understanding and
modeling water, solute and energy transfer in the atmosphere-plant-soil-groundwater system.
Weighable lysimeters yield the most precise and realistic measures for the change of stored
water volume (δS), Precipitation (P) which can be rain, irrigation, snow and dewfall and
evapotranspiration (ET) as the sum of soil evaporation, evaporation of intercepted water and
transpiration. They avoid systematic errors of standard gauges and class-A pans. Lysimeters
with controlled suction at the lower boundary allow estimation of capillary rise (C) and
leachate (L) on short time scales.
Precise weighable large scale (surface >= 1 m2) monolithic lysimeters avoiding
oasis effects allow to solve the water balance equation (P – ET – L + C ± δS =
0) for a 3D-section of a natural atmosphere-plant-soil-system for a certain time
period. Precision and accuracy of the lysimeter measurements depend not only on the
precision of the weighing device but also on external conditions, which cannot be
controlled or turned off. To separate the noise in measured data sets from signals
the adaptive window and adaptive threshold (AWAT) filter (Peters et al., 2014) is
used.
The data set for the years 2010 and 2011 from the HYDRO-lysimeter (surface = 1Âm2,
depth = 1Âm) in Wagna, Austria (Klammler and Fank, 2014) with a resolution of 0,01 mm for
the lysimeter scale and of 0,001 mm for the leachate tank scale is used to evaluate
the water balance. The mass of the lysimeter and the mass of the leachate tank is
measured every two seconds. The measurements are stored as one minute arithmetic
means.
Based on calculations in a calibration period from January to May 2010 with different
widths of moving window the wmax – Parameter for the AWAT filter was set to 41 minutes.
A time series for the system mass (“upper boundary”) of the lysimeter has been calculated by
adding lysimeter mass and the leachate tank mass for every minute. Based on the
resolution of the scales and an evaluation of noise in periods without precipitation and
evaporation a dmin-value of 0.002 to filter the leachate tank measurements and a
dmin-value of 0.012 was used to filter the lysimeter weight data and the upper boundary
data. A mandatory requirement for the quantification of P or ET from lysimeter
measurements is that in a reasonably small time interval, either P or ET is negligible.
With this assumption, every increase in upper boundary data is interpreted as P.
Every increase of seepage mass is interpreted as L, every decrease as C. δS is
evaluated from filtered lysimeter mass. ET is calculated using the water balance
equation.
The evaluation results are given as water balance components time series on a minute
scale. P measured with the lysimeter for the two years 2010 and 2011 is 105Â% of
precipitation measured with a standard tipping bucket gauge 100Âm beside the lysimeter.
While P during the summer season (April to September) is very close to standard
precipitation measurement, P during the winter season is more than 120Â% of tipping bucket
precipitation. Meissner et al. (2007) showed that P includes precipitation of dewfall and rime.
A detailed evaluation of the HYDRO-Lysimeter in Wagna showed, that precipitation in the
night and not recognized with the standard tipping bucket (interpreted as dew or rime) is
about 1Â% of P, the highest monthly sums (>Â1Âmm) are recognized from August to
November.
Klammler, G. and Fank, J.: Determining water and nitrogen balances for beneficial
management practices using lysimeters at Wagna test site (Austria). Science of the Total
Environment 499 (2014) 448–462.
Meissner, R., Seeger, J., Rupp, H., Seyfarth, M., and Borg, H.: Measurement of dew, fog,
and rime with a high-precision gravitation lysimeter, J. Plant Nutr. Soil Sci. 2007, 170,
335–344.
Peters, A., Nehls, T., Schonsky, H., and Wessolek, G.: Separating precipitation and
evapotranspiration from noise – a new filter routine for high-resolution lysimeter data.
Hydrol. Earth Syst. Sci., 18, 1189–1198, 2014. |
|
|
|
|
|
|