Quantifying floodwater impacts on a lake water budget via volume-dependent transient stable isotope mass balance

Abstract. Isotope mass balance models have undergone significant developments in the last decade, demonstrating their utility for assessing spatial and temporal variability hydrological processes revealing value baseline assessment remote and/or flood-affected settings where direct measurement of surface water fluxes to lakes (i.e. stream gauging) are difficult perform. In this study, we demonstrate that isotopic modelling can be used provide evidence relative importance floodwater inputs temporary subsurface storage at ungauged lake systems. A volume-dependent transient model was developed an artificial (named A) southern Quebec (Canada). This typically receives substantial during spring freshet period as ephemeral hydraulic connection with a 150 000 km2 large watershed is established. First-order flux estimates allow impacts highlighted within annual budget. The has revealed groundwater account 60 %–71 % 39 %–28 total A, respectively, which demonstrates inherent dependence on groundwater. However, when considering potential floodwater, partitioning between tends equalize, budget found more resilient quantity quality changes. Our findings suggest not only impact its dynamics springtime but also significantly influence long-term help inform, understand, predict future variations. From global perspective, knowledge useful establishing regional-scale management strategies maintaining lakes, predicting response recharge systems such settings, mitigating due land use climate