A laboratory study investigating the effects of dilution by precipitation on dissolved inorganic carbon and stable isotope evolution in surface waters

Abstract

Surface waters are a major pathway of carbon cycling between the atmosphere and the earth's surface. Yet studies describing water column processes that affect carbon cycling do not consider the effects of dilution by precipitation. In this study, we conducted a laboratory experiment in which we prepared undiluted (100%) and snowmelt diluted 25, 50, and 75% by volume of samples of NaHCO solution and lake and river water and then exposed them to the laboratory atmosphere for up to 1000 h. We aim to determine how dilution by precipitation followed by water-atmosphere CO interaction affects DIC and δC evolution. Dilution resulted in decreased pH, solutes, and DIC concentrations according to the dilution proportion. The decreased pH perturbed the carbonate equilibrium resulting in CO outgassing. In all the samples, there was continuous enrichment in the δC composition. Isotopic evolution by CO loss in the > 50% snowmelt-diluted samples lasted for about 10 h, while it took about 400 h for the diluted samples to evolve to a similar isotopic composition as the undiluted samples. Our laboratory results suggest that the effects of precipitation dilution should not be ignored in studying DIC evolution in surface waters during periods where precipitation dilution exceeds 50% by volume.

Carbon dioxide, methane, and dissolved carbon dynamics in an urbanized river system

“…The concentration of DIC decreased with increasing river discharge ( r = −0.66, p < 0.01, Figure 5c) as the increasing runoff after precipitation diluted the DIC pool (Abongwa & Atekwana, 2018; Cai et al, 2015; Lee et al, 2017; Reiman & Xu, 2019; Zhong et al, 2017). The imported DIC in high flow was characterized by low concentration and lower δ 13 C, likely from organic‐derived CO 2 (Cerling et al, 1991; Leith et al, 2014; Reiman & Xu, 2019).…”

“…The surface water evaporation of rivers and lower runoff water input in drier periods could increase the contribution of deep groundwater DIC (Atkins et al, 2017;Barth et al, 2003). Maximum values of [DIC] and δ 13 C-DIC were observed in the extremely dry period (Figures 2c and 4b The concentration of DIC decreased with increasing river discharge (r = À0.66, p < 0.01, Figure 5c) as the increasing runoff after precipitation diluted the DIC pool (Abongwa & Atekwana, 2018;Cai et al, 2015;Lee et al, 2017;Reiman & Xu, 2019;Zhong et al, 2017).…”

“…Maximum values of [DIC] and δ 13 C-DIC were observed in the extremely dry period (Figures 2c and 4b) when groundwater would have dominated flow. Consequently, groundwater DIC can be associated with The concentration of DIC decreased with increasing river discharge (r = À0.66, p < 0.01, Figure 5c) as the increasing runoff after precipitation diluted the DIC pool (Abongwa & Atekwana, 2018;Cai et al, 2015;Lee et al, 2017;Reiman & Xu, 2019;Zhong et al, 2017).…”

Hydrological and runoff formation processes based on isotope tracing during ablation period in the source regions of Yangtze River

“…This result showed that dilution not only plays an important role in the precipitation effect, but it also affects river water. However, the dilution effect was also significant when precipitation was the major recharge source for river water (Abongwa and Atekwana, 2018;.…”

“…It was found that the contribution of glacier and snow meltwater to runoff in spring was as high as 82 %. Boucher and Carey (2010) systematically studied runoff segmentation in permafrost basins. Maurya et al (2011) found that the average contribution of meltwater to runoff was 32 % in typical glacial basins on the southern slope of the Himalayas.…”