How Arsenic Affects Life in Hot Springs by Changing Nutrient Cycles

Greg Howard
1st February, 2024

How Arsenic Affects Life in Hot Springs by Changing Nutrient Cycles

Arsenic, a common contaminator of groundwater.

Photo adapted from: Tomihahndorf / CC BY SA (Source)
Arsenic contamination of groundwater is a widespread problem affecting millions globally, particularly in regions relying on wells for drinking water. While the presence of arsenic is known, the precise natural processes controlling its levels – how it moves, changes form, and interacts with other elements – remain poorly understood, especially in geothermal areas where arsenic concentrations are naturally high. Researchers at China University of Geosciences (Beijing)[1] have investigated these processes in the Guide Basin, China, to better understand how arsenic becomes mobilized in groundwater. The study focused on geothermal groundwater, which is water heated by the Earth’s internal heat. This water often contains elevated levels of arsenic and other dissolved substances. The researchers analyzed water samples and the microbial communities present along the natural flow path of the groundwater, from where it enters the ground (recharge area) to where it emerges (discharge area), noting how arsenic levels and microbial composition changed. The core finding is that arsenic’s behavior is tightly linked to the activity of microorganisms and their interactions with carbon, nitrogen, and sulfur cycles. Specifically, the study revealed significant shifts in the types of microbes present as arsenic concentrations increased along the groundwater flow path. In the recharge area, where arsenic levels are lower, microbes capable of oxidizing arsenic – converting it to a less harmful form – were abundant. These arsenic oxidizers were often found alongside microbes involved in denitrification (removing nitrogen from water) and carbon fixation (converting carbon dioxide into organic matter). This suggests a process where arsenic oxidation is coupled with these other microbial activities. However, as the groundwater flowed and arsenic levels rose in the discharge area, a different set of microbes dominated. Here, microbes involved in ammonification (producing ammonia from organic matter) and organic carbon biodegradation (breaking down organic carbon) were more prevalent. The researchers found strong correlations between arsenic(III), ammonium, bicarbonate, and these microbial groups, indicating that microbial processes were contributing to arsenic mobilization – essentially releasing it from solid materials into the water. This research builds upon earlier work demonstrating the importance of microbial activity in arsenic transformation[2]. Previous studies showed that bacteria can resist, oxidize, and transport arsenic, and that the presence of specific genes, like aoxB (involved in arsenic oxidation) and arsB (involved in arsenic transport), is linked to arsenic resistance levels. The current study expands on this by showing how these microbial processes are not isolated events, but are integrated into broader biogeochemical cycles. Furthermore, the findings align with observations in other geothermal environments where hydrogen sulfide (H2S) can inhibit arsenic oxidation[3]. While not directly studied in the Guide Basin, the principle remains relevant: the chemical environment significantly influences which microbes can thrive and, consequently, how arsenic is transformed. The study also echoes findings from broader investigations of subterranean microbial life[4], which highlight the vast diversity of microorganisms in groundwater and their crucial role in driving essential Earth processes. The researchers propose that hydrological disturbances – changes in groundwater flow – could disrupt this delicate microbial balance and lead to increased arsenic mobilization. For example, increased groundwater extraction, as seen in the Mekong Delta[5], could alter the flow paths and potentially release arsenic trapped in underground sediments. The study emphasizes that understanding these complex microbial interactions is crucial for predicting and mitigating arsenic contamination in groundwater resources.

EnvironmentBiochemEcology

References

Main Study

1) Metabolic coupling of arsenic, carbon, nitrogen, and sulfur in high arsenic geothermal groundwater: Evidence from molecular mechanisms to community ecology.

Published 1st February, 2024

https://doi.org/10.1016/j.watres.2023.120953

Related Studies

2) Genes involved in arsenic transformation and resistance associated with different levels of arsenic-contaminated soils.

https://doi.org/10.1186/1471-2180-9-4

3) Autecology of an arsenite chemolithotroph: sulfide constraints on function and distribution in a geothermal spring.

Journal: Applied and environmental microbiology, Issue: Vol 73, Issue 21, Nov 2007

4) Thousands of microbial genomes shed light on interconnected biogeochemical processes in an aquifer system.

https://doi.org/10.1038/ncomms13219

5) Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence.

https://doi.org/10.1073/pnas.1300503110


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