Stable isotope (δ¹⁸O, δ²H) signature of river runoff, groundwater, and precipitation in three river basins in the center of East European Plain

Abstract. Empirical study of the isotopic features of river runoff were conducted at three hydrological posts in three different river basins: the Zakza river in the center of East European Plane (southwest of Moscow), the Dubna river (north of Moscow) and the Sosna Bystraya river in the south of central region. Samples of river water, groundwater, and precipitation for the October 2019–October 2021 were collected at weekly intervals. At total 332 samples of river water, 275 samples of groundwater and 194 samples of precipitation were collected. Precipitation was collected as an integral sample of all precipitation fallen during the week before sampling date. For each precipitation samples, the total amount of precipitation and air temperature, weighted by precipitation amount, are given according to weather station in river basin. During the observation period, there were two completely different conditions in terms of runoff formation. First, from October 2019 to October 2020, there was an unusually low spring freshet followed by a big rain flood in July. From October 2020–October 2021, there was a normal intra-annual flow pattern with high spring freshet. A significant supply of melted snow during spring freshet is the key factor influencing water regimes in these three river basins; varying degrees of anthropogenic flow regulation are also present. The new height frequency and complete data of stable isotope signature of river runoff component can help to study the response of a river runoff to climate change.