Comparing deuterium excess to large-scale precipitation recycling models in the tropics

Precipitation recycling is essential to sustaining regional ecosystems and water supplies, and it is impacted by land development and climate change. This is especially true in the tropics, where dense vegetation greatly influences recycling. Unfortunately, large-scale models of recycling often exhibit high uncertainty, complicating efforts to estimate recycling. Here, we examine how deuterium excess (d-excess), a stable-isotope quantity sensitive to recycling effects, acts as an observational proxy for recycling. While past studies have connected variability in d-excess to precipitation origins at local or regional scales, our study leverages >3000 precipitation isotope samples to quantitatively compare d-excess against three contemporary recycling models across the global tropics. Using rank-correlation, we find statistically significant agreement ($$\bar \tau = 0.52$$ τ ¯ = 0.52 to $$0.70$$ 0.70 ) between tropical d-excess and recycling that is strongly mediated by seasonal precipitation, vegetation density, and scale mismatch. Our results detail the complex relationship between d-excess and precipitation recycling, suggesting avenues for further investigation.

Influence of Evaporation on the Hydrogen and Oxygen Stable Isotopes in an Enclosed Water Body: A Case Study

It is of great significance to study the influence of evaporation on the protection and management of regional water resources. In this study, water samples have been collected from a typical enclosed water body, Liuxi, a small brook in the campus of Suzhou University in May and June, and then analyzed for their hydrogen and oxygen stable isotopes. The results indicate that the samples collected in June have higher d18O and dD values relative to the samples collected in May, and both of them have d18O and dD values plotted at the right of the meteoric line, in combination with their lower deuterium excess (d-excess) values relative to the meteoric line, implying that the water has been influenced by evaporation. Moreover, the d-excess values showed decreasing and increasing in different sampling sites, which was demonstrated to be influenced by different extents of evaporation. Based on the calculation, the residual water quantities were 70–75% and 51–70% for May and June relative to the initial water, which indicates that about 10% of the water had evaporated during May and June.

Isotopic composition of precipitation and groundwater onshore of the Rio del Rey Basin, southwest Cameroon: local meteoric lines and recharge

The link between rainfall and groundwater recharge in the Rio del Rey Basin, which is of socio-economic importance to Cameroon, is poorly understood. Accordingly, the stable isotopes in monthly rainfall from January to December 2012 (in Lobe and Mundemba) and 52 surface water and groundwater samples were investigated. High values of δ18O and δD were recorded in the dry period (February to March), and the least values of δ18O and δD were observed in the wet period (September). This indicates that different condensation processes primarily influenced stable isotopes in rainfall as a function of the difference in moisture sources. The relationship between δD and δ18O defined the Lobe meteoric water line as δD = 7.97 δ18O + 12.48 and Mundemba water line as δD = 7.75 δ18O + 10.79. The similarity of their slopes to the global meteoric line suggests that the isotopic composition of investigated rains was not significantly affected by evaporation during precipitation. The ranges in deuterium-excess of precipitation from 5.8 to 16.56‰ suggest the source of vapour is from the Atlantic Ocean. The groundwater isotope values (ranging from −3.81 to −2.52‰ for δ18O) plotted close to and along the GMWL, showing that its isotopic composition is of meteoric origin under rapid recharge conditions. The isotopic similarity between groundwater and June–August rains suggests a significant recharge during this period.