Characterizing Hydrological Functioning of Three Large Karst Springs in the Salem Plateau, Missouri, USA

Spring discharge hydrographs can provide information on karst aquifer connectivity and responses to precipitation. However, few studies have conducted time-series analyses of spring hydrographs over multi-decadal time scales. We examine daily discharge for three large karst springs and daily precipitation for adjoining weather stations during 1928–2019 in the Salem Plateau of southern Missouri, one of the major karst regions in the USA. For different time periods, we conducted baseflow index calculations and time-series (autocorrelation, spectral density, and cross-correlation with precipitation) analyses for discharge data, and Mann–Kendall (MK) trend analyses for discharge and precipitation data. Hydrograph separation indicates discharge is baseflow-dominated (86–94%) at all three springs. The memory effect is lower for Bennett Spring (with an auto-correlation lag time 29–41 days) than for Big Spring (60–92 days) and Greer Spring (77–112 days). Spectral density analysis indicates that annual signals dominate all three springs. Cross-correlation analysis shows a quicker response to precipitation at Bennett Spring (0–1 days) than at Big and Greer springs (1–2 days). MK trend analysis shows significant increases in discharge for all three springs over multiple decades, but not for the period 2007–2019. Increased discharge accompanies regional increases in precipitation, but may also reflect increased recharge associated with reversion of farmland to forest.