Seasonal variability of stable isotopes in the Changjiang (Yangtze) river water and its implications for natural climate and anthropogenic impacts

Abstract

Background: Seasonal variations of stable hydrogen and oxygen isotopes in river water can be used to indicate hydrological processes and the water cycle in the river basin. This study presents a high-resolution time series of stable oxygen isotopic record (δ 18 O) in the lower Changjiang (Yangtze) River mainstream and aims to investigate the regional water cycle concerning natural climate changes and anthropogenic activities. Results: The river water δ 18 O shows apparent seasonal variations, which is overall higher during the dry season and lower during the flood season. This basin-scale seasonal variation of δ 18 O in precipitation over the Changjiang catchment is calculated based on the long-term meteorological and hydrological data. The seasonal variation of δ 18 O in the lower Changjiang river water is largely constrained by monsoon-induced precipitation, but is more directly controlled by the mixing of waters from the upper reaches and the tributary lakes in the middle valley. Conclusions: The relative contributions of waters from the upstream and tributary lakes to the lower Changjiang mainstream have been considerably altered by the construction of Three Gorges Dam via the regulation of river discharges. A comparison of river water isotopic records with water discharges from the lakes suggests that it takes about 2 weeks (~ 17 days) for the Changjiang river water to circumvent the mid-lower reaches of the catchment before traveling to the sea. This study suggests that the stable hydrogen and oxygen isotopes can be harnessed as sensitive indicators for water cycling within a large catchment that is driven primarily by natural forcing though subject to substantial human impacts.

Evaporation Processes in the Upper River Water of the Three Gorges Reservoir: Evidence from Triple Oxygen Isotopes

“…The study area is located in the Three Gorges Reservoir (TGR), which is a typical basin of evolution from river to lake. , The influence of reservoir construction on the river carbon cycle, biological diversity, and allocation of water sources continues to attract the attention of scholars. − Isotope techniques have become major tracers for the studies of various geochemical processes, − such as the effects of climate change and human activities on the water cycle, , the mixing processes between tributaries and main streams, , and the hydrological effect of reservoirs. , However, the data of isotopes in the TGR and even in the Yangtze River are still limited, which is insufficient to reveal the signatures of the water cycle and the regulatory effect of the Three Gorges Dam (TGD) on the TGR Basin . In the Yangtze River Basin, triple oxygen isotopes are only involved in the study of atmospheric precipitation at the headwaters and upper reaches of the Yangtze River , but are scarce in studies on river water.…”

Spatiotemporal variations of seawater <i>δ</i>¹⁸O and <i>δ</i>D in the Western North Pacific marginal seas near Japan

“…δ 18 O and δD of the Chengjiang freshwater exhibit seasonality (Wang et al, 2019), with the δ 18 O and δD values of −7.9 ± 0.58 and −50.4 ± 5.81‰, respectively, during the dry season (winter) and −10.9 ± 0.39 and −76.9 ± 2.95‰, respectively, during the wet season (summer). This variation is slightly different near the river mouth (Li et al, 2020) because the contribution from two lakes changes the δ 18 O values at the river month. However, in general, δ 18 O is lower during the dry season than the wet season.…”

Nutrient Dynamics under the Coupling Effects of Damming and Urbanization in the Three Gorges Reservoir: Status, Sources, and Driving Factors

“…The mineralization of organic nitrogen in soil and groundwater recharge is the primary source of Y store . In the TGR basin, rainfall is the major contributor to surface river water during flood periods, with groundwater recharge playing a limited role. , Additionally, the presence of nitrogen stored in sediments can also contribute to the riverine N flux. , However, the high temperatures in the wet season will lead to stratification within the water column and hinder vertical solute exchange. Y store showed a decreased trend (p < 0.01 and r = −0.714, Table S5) as the operation time increased.…”

“…In the TGR basin, rainfall is the major contributor to surface river water during flood periods, with groundwater recharge playing a limited role. 56,69 Additionally, the presence of nitrogen stored in sediments can also contribute to the riverine N flux. 70,71 However, the high temperatures in the wet season will lead to stratification within the water column and hinder vertical solute exchange.…”