Hydrological connectivity between water bodies and the effect on DOM migration patterns after a rainstorm event in the Qinghai-Tibetan plateau

The effect of global climate warming on the Qinghai-Tibetan Plateau (QTP) has resulted in degradation of permafrost. This has in turn impacted water flow in the rivers and the formation of numerous lakes due to the erosion and migration of river channels. The connectivity between the rivers, groundwater, and these lakes was not investigated due to the complex landscape conditions. To overcome this difficulty, we investigated the connectivity between these water bodies after a bracted rainstorm event that would maximize the effects of disconnected surface water in the system. We followed the effects of the rainstorm event in 45 consecutive watersheds, spanning from the source of the Yellow River (5277 m asl) to its plateau exit (4060 m asl). Data on terrain and meteorological parameters together with analyses of δ²H, δ¹⁸O, ²²²Rn, and dissolved organic matters (DOM) (a₃₅₀, I, II, III, IV, V, C1) in samples from the rivers, lakes, rainfall, permafrost, groundwater, and soil were used. The results indicate that decreasing watershed slope and permafrost degradation and increasing river channel gradient enhance the groundwater recharge to the lakes and Yellow River. The upstream lakes gradually shift from receiving terrestrial-side groundwater to being recharged by riverside groundwater moving downstream in the watersheds. This suggests that more groundwater and groundwater-derived DOM are discharged into the Yellow River. The main DOM components are humic substances (>90 %) that originate from the vegetation in the river buffer zone (0–3 km). These findings provide, for the first time, insight into the complex connectivity between the river and its associated lakes in the QTP during a rainstorm event. The study adds a new perspective of the plateau hydrology and transport pathways of the organic carbon.