Analysis of Event-based Hydrological Processes at the Hydrohill Catchment Using Hydrochemical and Isotopic Methods

Abstract

Abstract. Hydrochemical and isotopic techniques have been widely applied in hydrological sciences because isotopic tracers can identify water sources and hydrochemical tracers can discern runoff flow paths. To better understand the hydrological process, we combined hydrochemical and isotopic techniques under controlled experimental conditions to investigate hydrological process from rainfall to runoff in the Hydrohill experiment catchment, a typical artificial catchment in Chuzhou, China. Hydrochemical and isotopic data, i.e., pH, electric conductivity (EC), total dissolved solids (TDS), anions (Cl−, NO3-, SO42- and HCO3-), cations (K+, Na+, Ca2+ and Mg2+) and dissolved Si, 18O and D in water samples were collected during a rainfall event in 2016, and used to determine the hydrochemical and isotopic characteristics of rainfall and runoff components. We applied EC, TDS, SO42-, Ca2+, Mg2+, 18O and D as tracers to investigate rainfall-runoff processes in the experimental catchment. Runoff flow paths could be well identified by the relationship between 18O and EC, TDS, SO42-, Ca2+ and Mg2+. The quantity of flow flux and mass fluxes of main hydrochemical and isotopic tracers gauged at the catchment outlet shows applicable tracers (Ca2+, Mg2+, SO42-, and 18O) are mainly from deep groundwater runoff (from soil layer of 60–100 cm beneath ground surface). Contributions of the event water and pre-event water to the total runoff during the rainfall-runoff process are different. The quantitative results were very encouraging as a basis to develop hydrological models for further study.

Concentration–Discharge Relationships in Runoff Components during Rainfall Events at the Hydrohill Experimental Catchment in Chuzhou, China

“…The value for Na + was larger in rainfall than in SR and SSR30, though the highest concentration value of Na + was still in the deepest flow path, SSR100. Further information about the basic characteristics of ions is presented in several previous studies about the hydrochemistry in Hydrohill catchment [29,30], though this is the first study to focus on the C-Q relationship in runoff components. Analysis of C-Q relationships reveals that concentrations of Na + , Ca 2+ , Mg 2+ , SO 4 2− , and HCO 3 − in the four runoff components had a negative relationship with discharge (Figure 5).…”

“…The SO 4 2− in the rainfall at the Hydrohill catchment comes primarily from the atmosphere. After entering the soil, a series of reactions, such as SO 2 and H 2 S oxidation, sulfur-containing animal and plant residues decompose protein, sulfur-containing animal and plant residues decomposing protein, etc., occur in the soil [29]. In addition to the rainfall replenishment, primary sources of HCO 3 − in the soil are the dissolution of CO 2 , microbial activities, and the weathering decomposition of carbonates [34].…”

“…the basic characteristics of ions is presented in several previous studies about the hydrochemistry in Hydrohill catchment[29,30], though this is the first study to focus on the C-Q relationship in runoff components.Water 2020, 12, x FOR PEER REVIEW 6 of 14…”