Stable Isotope Composition of River Waters across the World

Abstract

Stable isotopes of O and H in water are meaningful indicators of hydrological and ecological patterns and processes. The Global Network of Isotopes in Precipitation (GNIP) and the Global Network of Isotopes in Rivers (GNIR) are the two most important global databases of isotopes in precipitation and rivers. While the data of GNIP is almost globally distributed, GNIR has an incomplete spatial coverage, which hinders the utilization of river isotopes to study global hydrological cycle. To fill this knowledge gap, this study supplements GNIR and provides a river isotope database with global-coverage by the meta-analysis method, i.e., collecting 17015 additional data points from 215 published articles. Based on the newly compiled database, we find that (1) the relationship between δ18O and δ2H in river waters exhibits an asymmetric imbricate feature, and bifurcation can be observed in Africa and North America, indicating the effect of evaporation on isotopes; (2) multiple regression analysis with geographical factors indicates that spatial patterns of river isotopes are quite different across regions; (3) multiple regression with geographical and meteorological factors can well predict the river isotopes, which provides regional regression models with r2 of 0.50 to 0.89, and the best predictors in different regions are different. This work presents a global map of river isotopes and establishes a benchmark for further research on isotopes in rivers.

Isotopic temporal and spatial variations of tropical rivers in Thailand reflect monsoon precipitation signals

“…Red (blue) points represent the stations in the northeastern (southern) region values at stations NE5 and NE6, which are in the mainstream of the Mekong River, were significantly lower than at other NE stations not on the Mekong River(Figure 3b).Global river d-excess varies between −47.1‰ and 64.9‰, with an average of 3.0‰ (IAEA, 2019). Most of the d-excess values in river waters across the globe (about 83%) are lower than the global precipitation average of 10‰(Nan et al, 2019). In the present study, the d-excess in river waters across Thailand ranged from −9.1‰ to 16.0‰, with an average value of 4.1 ± 5.3‰.…”

“…These irrigated waters experienced remarkably high evaporation with higher δ 18 O values and lower d-excess relative to precipitation (Figure 7). Previous studies (Kendall & Coplen, 2001;Nan et al, 2019;Zhu et al, 2018) documented that most d-excess values in rivers are lower than 10‰. This might be attributable to the damming effect, as reservoirs feed the tributaries of these rivers.…”

“…The global river water line (GRWL) was described by Nan et al (2019) with ranged from 4.84 to 7.52 ( Figure 6), lower than the GRWL (8.03 ± 0.01).…”

“…The effects of these factors on precipitation isotopes have been identified in previous studies and given names such as the altitude effect, temperature effect, and amount effect (Bershaw, 2018; Dansgaard, 1964; Le Duy, Heidbüchel, Meyer, Merz, & Apel, 2018; Pfahl & Sodemann, 2014; Xia et al, 2018). These isotopic effects can also be seen in river waters (Nan, Tian, Hu, Wang, & Zhao, 2019), implying that precipitation is the primary source of global river waters. River water isotopes have been found to be closely correlated with the stable isotopes in precipitation (Kendall & Coplen, 2001).…”

“…The aridity index and relative humidity significantly influence the isotopic composition of river waters (Nan et al, 2019). The controls on the global spatiotemporal distributions of river water isotopes have been investigated (Nan et al, 2019) based on the Global Network of Isotopes in Rivers (GNIR). However, the GNIR data are sparse in tropical regions such as Thailand (Halder, Terzer, Wassenaar, Araguás-Araguás, & Aggarwal, 2015b), and monsoon influences on tropical river isotopes have not been previously investigated.…”