Identification of potential end-members and their apportionment from
downstream high-frequency chemical data
Abstract
High-frequency chemical measurements in streamwater give detailed
information on the different hydrochemical processes occurring in the
catchment. They can provide clues about the end-members (water sources)
whose mixing produces the ionic stream concentrations observed. To
identify and quantify the end-members and their respective contribution
to streamwater chemistry, we developed a new methodology, termed
“IQEA” (Identification and Quantification of End-members and their
Apportionment). It consists in the resolution by a minimization process
of an objective function based on downstream high-frequency chemical
data and the size of the shape of a pre-defined fixed number of three
end-members. We applied the IQEA method on the high-frequency
concentration dataset of nitrates and calcium from the ORACLE-Orgeval
Observatory in France. The results were compared with field data
obtained from various potential end-members. The IQEA methodology
yielded robust and very satisfactory results, apart from an exceptional
flood event that occurred during the 2 years of measurements used in
this study. While the IQEA model treats concentration and discharge
datasets independently, its results show a strong relationship between
the dominant end-member computed and the hydrological features.