Riverine Isoscapes Modeling in the Yangtze River Basin, China: Insights Into Basin Processes and Source-Water Contributions

Abstract

The utilization of surface water isoscapes facilitates the characterization of source-water contributions and hydrological processes within a basin. However, intricate river network topology poses significant challenges in applying this approach to large and complex basins. In this study, a spatial stream network model (SSNM) was employed to create isoscapes of surface waters using 852 river isotopic data across the Yangtze River Basin (YRB). Results showed that precipitation and river water δ¹⁸O values displayed a similar trend, characterized by the lowest (highest) values in the upper (lower) reaches of the YRB. River water δ¹⁸O exhibited multiple spatial dependencies regarding the flow-connected, flow-unconnected, and Euclidean spatial relationships from the shape of semivariograms, indicating basin processes within the river network and terrestrial landscape across the YRB. The riverine δ¹⁸O isoscapes were predicted by coupling environmental covariates including hydrologic, climatic drivers, and landscapes with spatial autocovariance structures across the YRB. The predictive accuracy of isoscapes from SSNM was distinctly improved from 66% using linear model to 87%. Maps of source contributions from SSNM showed higher contribution from meltwater of glacier/permafrost in the upper reaches of YRB (>60%). In contrast, precipitation and groundwater were the main contributing recharge sources due to the distributed aquifer and evaporative effects on river water in the mid-lower reaches of YRB. The findings present a novel approach for the representation of isoscapes in large-scale, intricate basins, offering valuable evidence for provenance studies and basin management.