Discussion of Present Isotopic Hydrograph Separation (IHS) Method

Runoff sources and dominant flow paths are still poorly understood in most catchments. Consequently, isotope hydrograph separation methods are widely used to improve our understanding about runoff generation. Isotope hydrograph separation (IHS) is based on the mass balance equation of water flux and isotope tracer concentration. The isotope analysis machine (for example, mass spectrum) available can only get the delta-value of the isotope tracer. An analysis is presented for quantifying the error in two- and three- component tracer-based hydrograph separation. This analysis compared the error between ratio balance method and mass balance method in computing mixed fractions to determine which method is more accurate. In the ratio balance method, the ratio of isotope tracer in used in concentration mass balance equation; comparatively, in the mass balance method, the concentration of isotope tracer is used in the same equation. Many studies about two- and three-component tracer-based hydrograph separation are used to illustrate the application of the analysis. Because of the abundance of rare isotopes are so negligible, the difference between two methods is small in the isotopic hydrograph separation studies. In scientific research, it is not appropriate to substitute ratio for concentration in the isotope tracer concentration mass balance equation. Therefore, we recommend the use of mass balance method in the application of isotope hydrograph separation research to improve the degree of accuracy.