Storage-Discharge Characteristics of Headwaters by Tracer Analysis: A Case Study in the Vallon de Nant over the Recession Period 2022

The objective of my Master thesis is to investigate how hydrochemical as well as isotopic tracers can be related to differences in storage and discharge of several springs in the Vallon de Nant catchment during the summer recession period from June until October 2022. The research process was divided into water quality and water quantity analysis. In the water quantity part, the spatial as well as temporal variation of the discharge, determined by salt dilution measurements during seven sampling campaigns, as well as the recession constants, defining the storage-release rate, are discussed, while in the water quality analysis it is explained how the ion concentration as well as the isotopic composition of the collected water samples and some field parameters vary spatially as well as temporally. The investigations have showed that a low depletion of heavy isotopes, giving indication of a high proportion of rain, as well as high electrical conductivity values, highlighting a long residence time of water in the subsurface, and low discharge rates indicate a shallow water flowing path; additionally, warm temperatures and a comparably high concentration of calcium and nitrate, but a low sodium concentration are characteristic for a shallow water storage-discharge pattern, which is also expressed in low recession constants. Overall, it can be concluded that at most of the monitored springs the results of the water quality and of the water quantity analysis are coherent and suggest the same storage-discharge pattern, but there are also cases where the identified tracers do not accurately correspond to the results of the recession analysis due to reasons such as influences of an artificial water catchment or in case of a tributary, due to several different contributing water origins, in which cases more profound research is essential.

Description of the files

• water_quality_variables.csv includes the results of the water quality analysis, which was performed at three different stations along the mainstream, at four springs and at one tributary in the Vallon de Nant catchment during the research period from July until October 2022.

Columns:

• station [-]
• day [-]
• month [-]
• year [-]
• fluoride [mg/l]: mean fluoride concentration of two collected water samples
• chloride [mg/l]: mean chloride concentration of two collected water samples
• nitrite [mg/l]: mean nitrite concentration of two collected water samples
• nitrate [mg/l]: mean nitrate concentration of two collected water samples
• phosphate [mg/l]: mean phosphate concentration of two collected water samples
• sulfate [mg/l]: mean sulfate concentration of two collected water samples
• sodium [mg/l]: mean sodium concentration of two collected water samples
• ammonium [mg/l]: mean ammonium concentration of two collected water samples
• potassium [mg/l]: mean potassium concentration of two collected water samples
• magnesium [mg/l]: mean magnesium concentration of two collected water samples
• calcium [mg/l]: mean calcium concentration of two collected water samples
• dDmean [‰]: mean deuterium composition of two collected water samples
• d17Omean [‰]: mean ¹⁷O composition of two collected water samples
• d18Omean [‰]: mean ¹⁸O composition of two collected water samples
• detex [‰]: deuterium excess
• Icex [‰]: line conditioned excess
• pH [-]: mean pH value of two subsequent measurements
• electrical conductivity [µS/cm]: mean electrical conductivity of two subsequent measurements
• temperature [°C]: mean temperature of two subsequent measurements

• discharge_springs.csv includes the results of the water quantity analysis, which was performed at four springs and at one tributary in the Vallon de Nant catchment during the research period from July until October 2022.

Columns:

• station [-]
• day [-]
• month [-]
• year [-]
• dis [l/s]: Mean of two subsequent discharge measurements at the springs
• sd [l/s]: Standard deviation between two discharge measurements at the springs

• stations.csv includes the metadata of the monitored sampling stations in the Vallon de Nant catchment, in particular, of three stations along the mainstream, four springs and one tributary.

Columns:

• station_id [-]
• type [-]: differentiation between mainstream, springs and tributary
• lat [WGS84]: decimal latitude of the station in the WGS84
• lon [WGS84]: decimal longitude of the stations in the WGS84
• elevation [m.a.s.l.]: elevation of the sampling stations in meters above sea level