Hydrological response of karst stream to precipitation variation recognized through the quantitative separation of runoff components

Abstract

Various water transmitting media are related to highly variable water source compositions, which limit the understanding of the aquifer structure and hydrological processes in a karst catchment. This study aims to understand the variation in water contribution by matrix, fissure, and conduit flows during storm and seasonal scales based on discharge, electrical conductivity (EC), and nitrate measurements of stream water in a typical dolomite catchment during 2017–2018 and discusses the hydrological response mechanism of a karst aquifer to rainfall characteristics. Time-series analyses of discharge and EC indicated that the rapid response time (mean lag time < 1 h) was mainly controlled by rainfall intensity, and the lag time decreased significantly when the rainfall intensity was lower than 15 mm/h. However, the mean discharge was dominated by the rainfall amount and antecedent moisture state. Hydrograph separation based on nitrate indicates that the contribution of soil water was irrelevant for recharging the stream during a non-rain period, whereas epikarst water contributed more than 83.2% of the total flow during a rainfall event. As indicated by the EC frequency distribution analyses, the contribution ratios of the surface, conduit, fissure, and matrix flows were 1:1.8:2.1:7.1, 1:1.6:5.3:6.3, and 0:0:0:1 during stormy, heavy, and light rainfall events, respectively. These parameters indicate that the degree of karstification was low in the karst aquifer. Seasonal frequency distribution analyses of EC indicate that higher rainfall amounts and rainfall intensities during the wet season promoted the contribution of conduit flow to approximately 11.4% of the total flow; however, matrix flow dominated the recharge of the streamflow and its contribution was more than 55.6% during each season. Our results suggest that the permeability of the epikarst matrix dominates the storage and transfer functions in dolomite karst aquifers with low karstification.