What does it mean when lc-excess value in soil water larger than zero? This LMWL is from a neighboring area and was generated with 2-year precipitation isotopic data out of my study period for there is no enough precipitation isotopic data in my research. Suprisingly, there is some locations with lc-excess values larger than zero. So I wonder is it OK to use this index to quantify evaporation? If not, is there is an alternative?
Thanks for your answers.
Hi Qin Liu,
The question is how comparable the location where the precipitation was sampled is in comparison to the location where you sampled the soil water.
The LMWL might be different depending on elevation, snow/rain amount, temperature, humidity, continental/oceanic influence. To me, it seems to be saved to go with the original metric, the d-excess, if no local precipitation is available. However, one needs to be careful with the interpretation about the temporal Dynamics of fractionation intensity due to evaporation from the soil. You'll be able to detect clear fractionation signals though d-excess
To answer your original question about lc-excess > 0, this could for example result from dew, if I understand the isotope dynamics from dew formation correctly.
Matthias Sprenger Hi, Dr Sprenger, thank you so much for your answers.
The two small catchments are closely located ( about 5 km away from each other) and they have similar elevation and topography.
I observed this phenomon in 0-10 cm and 10-20 cm soil layers (lc-excess>0) in two campaigns one week after rainfall events in summer. So I suppose this might be owing to the precipitation input, which might be orginally slightly lying above the LMWL. Meanwhile, results from dews are also possible. I'll further check the precipitation isotopes if they are available. Then, here comes another two questions. (1) How many data do we need to generate a proper LMLW? (2) Is there a range or confidence level in using lc-excess to identify evaporation, which could take some uncertainties into account.
Thank you again for your help.
Regards,
Qin
5 km should not cause a problem, yes!
I agree that looking into the precipitation data and its variation will probably help explaining the soil water dynamics.
Regarding the uncertainty, please see the original conference abstract that the lc-excess stems from. Landwehr & Coplen present on their second page a lc-excess*, which takes into account the standard deviation based on the analytical errors from the 2H and 18O analyses.
Is the precipitation from "open sky" collectors or from "throughfall" collectors?
- Badges
- Science topic