Instability in a carbon pool driven by multiple dissolved organic matter sources in a eutrophic lake basin: Potential factors for increased greenhouse gas emissions

Enhanced pollution control using sediment microbial fuel cells for ecological remediation

Sediment Microbial Fuel Cell (SMFC) technology is an innovative approach to facilitate the degradation of sedimentary organic matter by electroactive microorganisms, transforming chemical energy into electrical energy and modulating the redox potential at the sediment-water interface, consequently controlling the release of endogenous pollutants. The synergistic effects of various environmental factors and intrinsic conditions can significantly impact SMFC performance. This review provides a comprehensive overview of SMFC development in research and application for water environment treatment and ecological remediation, a perspective rarely explored in previous reviews. It discusses optimization strategies for SMFC implementation, emphasizing advancements in novel or cost-effective electrode materials, the dynamics of microbial communities, and the control of typical pollutants. The review suggests a virtuous cycle path for SMFC development, highlighting future research needs, including integrating cross-disciplinary approaches like artificial intelligence, genomics, and mathematical modeling, to enhance the deployment of SMFC in real-world environmental remediation.

Cyanobacteria decay alters CH4 and CO2 produced hotspots along vertical sediment profiles in eutrophic lakes

Cyanobacteria-derived organic carbon has been reported to intensify greenhouse gas emissions from lacustrine sediments. However, the specific processes of CH4 and CO2 production and release from sediments into the atmosphere remain unclear, especially in eutrophic lakes. To investigate the influence of severe cyanobacteria accumulation on the production and migration of sedimentary CH4 and CO2, this study examined the different trophic level lakes along the middle and lower reaches of the Yangtze River. The results demonstrated that eutrophication amplified CH4 and CO2 emissions, notably in Lake Taihu, where fluxes peaked at 929.9 and 7222.5 μmol/m2·h, mirroring dissolved gas levels in overlying waters. Increased sedimentary organic carbon raised dissolved CH4 and CO2 concentrations in pore-water, with isotopic tracking showing cyanobacteria-derived carbon specifically elevated CH4 and CO2 in surface sediment pore-water more than in deeper layers. Cyanobacteria-derived carbon deposition on surface sediment boosted organic carbon and moisture levels, fostering an anaerobic microenvironment conducive to enhanced biogenic CH4 and CO2 production in surface sediments. In the microcosm systems with the most severe cyanobacteria accumulation, average CH4 and CO2 concentrations in surface sediments reached 6.9 and 2.3 mol/L, respectively, surpassing the 4.7 and 1.4 mol/L observed in bottom sediments, indicating upward migration of CH4 and CO2 hotspots from deeper to surface layers. These findings enhance our understanding of the mechanisms underlying lake sediment carbon emissions induced by eutrophication and provide a more accurate assessment of lake carbon emissions.

Transition of organic matter from allochthonous to autochthonous alters benthic nutrient dynamics via microbial food webs

The impoundment of rivers by dams has significantly modified sedimentation patterns and trophic structures. As a result, the algal-derived organic matter (OM), as opposed to terrestrial-derived OM, plays an increasingly important role along the river-reservoir gradient. This study utilized water-sediment microcosms to explore the impacts of allochthonous and autochthonous OM deposition on benthic nutrient dynamics mediated by microbial food webs. Our results revealed that OM addition led to increased fluxes of NH4+ and CO2, with the highest flux induced by cyanobacteria OM, followed by diatom and allochthonous OM. N2 release flux was promoted by allochthonous and diatom OM deposition but inhibited by cyanobacteria OM deposition. The amendment of autochthonous OM increased the activity of dehydrogenase and urease, while allochthonous OM with a higher C/N ratio enhanced the catalytic abilities of polyphenol oxidase and β-glucosidase. Furthermore, OM deposition significantly reduced microbial community richness and diversity, except for eukaryotic richness, and induced pronounced changes in bacterial and eukaryotic community structures. Allochthonous OM deposition stimulated the utilization of bacteria and protozoan on native OM, resulting in a positive priming effect of 26.78 %. In contrast, diatom and cyanobacteria OM additions exerted negative priming effects of -44.53 % and -29.76 %, respectively. Bayesian stable isotope mixing models showed that diatom OM was primarily absorbed by protozoan and metazoan, while cyanobacteria OM was more easily decomposed by bacteria and transferred to higher trophic levels through microbial food webs. In addition, bacterial ammonification accounted for 74.5 % of NH4+ release in the allochthonous OM deposition treatment, whereas eukaryotic excretion contributed separately 83.3 % and 83.1 % to NH4+ release in the diatom and cyanobacteria OM addition treatments. These findings highlight the significance of accounting for the regulatory capacity of OM deposition when studying benthic metabolism within river-reservoir systems.