The study shows that the loss of these plants, which control arsenic in sediments, can worsen contamination. Using advanced techniques, the team monitored how plant death and root decomposition lead to arsenic release back into the water, highlighting a previously underestimated process.
Arsenic is a toxic metalloid linked to skin lesions and cancers, and contaminated drinking water remains one of the most serious exposure routes worldwide. In many lakes and rivers, arsenic accumulates in bottom sediments after entering from natural mineral weathering or human activities such as industrial discharge and irrigation return flows. Under stable, oxygenated conditions, these sediments can function as long-term sinks for arsenic, often by binding it to iron and manganese oxides. However, when environmental conditions shift—such as reduced oxygen levels or warming bottom waters—arsenic can be released back into the water column. Submerged macrophytes are key ecosystem engineers in these environments: their roots leak oxygen into otherwise anoxic sediments, promoting iron plaque formation that traps arsenic. Yet these same plants are in sharp global decline, and what happens to sediment-bound arsenic when their roots die and decompose has remained poorly understood.
A study (DOI:10.48130/een-0025-0003) published in Energy & Environment Nexus on 16 October 2025 by Qin Sun’s & Shiming Ding’s team, Hohai University & Southeast University, sheds light on the unexpected consequences of macrophyte loss and underscores the need for new approaches to managing water quality in aquatic ecosystems.
To explore how the transition from the rhizosphere to the detritusphere affects As dynamics in sediments, a variety of techniques were employed, including high-resolution chemical imaging, Mössbauer spectroscopy, and microbial community analysis through high-throughput sequencing and qPCR. Oxygen penetration depths and redox conditions in sediments were monitored during different stages of macrophyte growth and root decomposition. During plant growth, oxygen penetration reached depths of 12.5–18.5 mm, and sediment redox potential (Eh) increased from 211.48 mV to 279.60 mV. However, as roots decomposed, oxygen release ceased, and the sediments transitioned to anaerobic conditions, reducing oxygen penetration to 6 mm and decreasing the Eh to 167.81 mV. The impact of this transition was also evident in arsenic concentrations. While soluble arsenic levels decreased significantly during root growth, they rose sharply after plant death, with a flux increase from −0.61 ng/cm²/day during growth to 12.43 ng/cm²/day in the detritusphere. Spatially, labile As flux in the rhizosphere was lower than in bulk sediments, but it increased approximately twofold in the detritusphere, indicating the release of arsenic as the root system decomposed. Additionally, Fe and As speciation analyses revealed that arsenic was primarily bound to Fe plaques, with a substantial loss of As from these plaques following plant decay, as Fe(III) minerals were reduced to Fe(II) in the anaerobic detritusphere. Microbial community shifts further influenced arsenic cycling: Fe-oxidizing bacteria predominated in the rhizosphere, whereas Fe-reducing bacteria became more abundant in the detritusphere, contributing to the release of arsenic. Overall, these results highlight a shift from arsenic sequestration to mobilization upon plant death, driven by changes in redox conditions and microbial activity.
These findings reveal an overlooked pathway for arsenic contamination: the transition from living root zones to decaying detritus around dying aquatic plants. The loss or die-back of submerged macrophytes, which typically trap arsenic, may inadvertently release it into the water. With macrophytes already declining by one-third in many lakes, this shift could explain unexpected spikes in arsenic and other pollutants in recovering or managed water bodies.
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References
DOI
10.48130/een-0025-0003
Original Source URL
https://doi.org/10.48130/een-0025-0003
Funding information
This study was funded by the National Natural Science Foundation of China (U2102210, 42407535, and 42277393), the China Postdoctoral Science Foundation (GZB20230782, 2024M763366), the Basic Research Program of Jiangsu (BK20241697), the Key Research and Development Program of Jiangxi Province (20223BBG74003), and the Long-term Program for Innovative Leading Talents of Jiangxi Province (jxsq2023101034).
About Energy & Environment Nexus
Energy & Environment Nexus is a multidisciplinary journal for communicating advances in the science, technology and engineering of energy, environment and their Nexus.