山东省沂源县螳螂河流域水体氢氧同位素对蒸发效应的指示作用OA

This study takes the Tanglanghe River Basin in Yiyuan county,Shandong Province as the study area.To investigate the influence of evaporation on the regional water cycle,the stable isotopic compositions of groundwater and surface water samples collected along the Tanglanghe River were systematically measured in August 2024 and April 2025.The analytical results reveal distinct seasonal variations and spatial patterns in the isotopic signatures,highlighting the indicative significance of δ18O and deuterium excess(d-excess)for evaporation processes in the basin.The major findings are summarized as follows. (1)During the wet period in August 2024,which coincides with the peak of the East Asian Summer Monsoon rainfall,the δD-δ18O trend line for all water bodies in the basin lies to the Global Meteoric Water Line(GMWL).Notably,both the slope and intercept of the local water line derived from this period are higher than those of the previously established Local Meteoric Water Line(LMWL).This statistical relationship strongly indicates that atmospheric precipitation is the predominant and direct source of recharge for the basin's hydrological system.Therefore,the Tanglanghe River can be definitively classified as a rain-fed fluvial system,with its flow regime primarily dictated by the timing and magnitude of precipitation events within its catchment area.In stark contrast,during the dry period of April 2025,the isotopic compositions of all sampled water bodies exhibited a pronounced enrichment in the heavier isotopes(δ18O and δD).This systematic shift toward heavier isotopic values directly reflects the dominance of intense evaporation under arid conditions. (2)Building on this temporal contrast,a marked distinction also exists between the isotopic behavior of groundwater and surface water within the Tanglanghe River Basin.Groundwater samples exhibit a notably narrow range of variation in both δD and δ18O values,and these values demonstrate minimal seasonal fluctuation in samples between the wet and dry periods.This temporal and spatial homogeneity reflects the profound regulatory capacity,storage effect,and mixing homogenization inherent to subsurface flow systems.Conversely,surface water display pronounced seasonal isotopic variability.During the wet period,surface water isotopes are relatively depleted(more negative δ-values),whereas during the dry period,they are significantly enriched(more positive δ-values).Specifically,the isotopic enrichment ranking during the wet period is groundwater＞river water＞reservoir water(from less negative to more negative),whereas this order reverses dramatically in the dry period to river water＞reservoir water＞groundwater.This pattern indicates that the water is directly recharged by atmospheric precipitation.During the wet period,runoff is rapid and residence time is short,resulting in inadequate mixing and homogenization of seasonal signals.In the subsequent dry season,the reservoir experiences particularly intense evaporation due to its larger exposed surface area and extended hydraulic retention time,leading to heavy isotope enrichment. (3)Further analysis of environmental controls on isotopic fractionation revealed a significant negative correlation between δ18O values and water temperature.Notably,this relationship proved statistically stronger than the correlation observed between deuterium excess(d-excess)and temperature,underscoring the greater sensitivity of δ18O to thermal dynamics during evaporation. (4)Finally,by leveraging the isotopic mass balance approach and the distinct isotopic enrichment observed between the wet and dry periods,the proportion of water loss due to evaporation along the main stem of the Tanglanghe River during the dry period of April 2025 was estimated.The calculated evaporative loss fraction ranges from 4.62％to 19.40％.A distinct spatial trend is evident,with the evaporation ratio progressively increasing from the upstream reaches toward the downstream sections.This downstream increase in evaporative loss is governed by two primary factors.First,the intensity of groundwater recharge,as substantial groundwater inflow,characterized by more depleted and stable isotope signatures,can buffer the evaporation signal.Second,variations in the morphology of the river surface,including wider channel widths and slower flow velocity,increase the exposure time and the surface area available for evaporation flux,thereby accelerating isotope enrichment.