Suchergebnisse

Abstract
Background
Nanoscale zero-valent iron (nZVI) is commonly used for remediation of groundwater contaminated by chlorinated ethenes (CEs); however, its long-term reactivity and subsurface transport are limited. A novel nZVI–AC material, consisting of colloidal activated carbon (AC) with embedded nZVI clusters, was developed with the aim of overcoming the limitations of nZVI alone.

Results
Application of a limited amount of nZVI–AC to an oxic, nitrate-rich, highly permeable quaternary aquifer triggered time-limited transformation of CEs, with noticeable involvement of reductive dechlorination. Reductive dechlorination of CEs was dominantly abiotic, as an increase in the concentration of vinyl chloride (VC) and ethene did not coincide with an increase in the abundance of reductive biomarkers for complete dechlorination of CEs (Dehalococcoides, Dehalogenimonas, VC reductase genes vcrA and bvcA). Application of nZVI–AC under unfavourable hydrochemical conditions resulted in no dramatic change in the microbial community, the reducing effect resulting in temporal proliferation of nitrate and iron reducers only. At a later stage, generation of reduced iron induced an increase in iron-oxidizing bacteria. High concentrations and a continuous mass influx of competing electron acceptors (nitrate and dissolved oxygen) created unfavourable conditions for sulphate-reducers and organohalide-respiring bacteria, though it allowed the survival of aerobic microorganisms of the genera Pseudomonas, Polaromonas and Rhodoferax, known for their ability to assimilate VC or cis-1,2-dichloroethene. A potential for aerobic oxidative degradation of CE metabolites was also indicated by detection of the ethenotroph functional gene etnE.

Conclusions
This pilot study, based on the application of nZVI–AC, failed to provide a sustainable effect on CE contamination; however, it provided valuable insights into induced hydrogeochemical and microbial processes that could help in designing full-scale applications.

Abstract
Background
The N2-fixing cyanobacterium, Aphanizomenon flos-aquae is a globally distributed bloom causing species that degrades water quality of fresh and marine water bodies. Overcoming phosphorus (P) deficiency is one of the ecological advantages for bloom-forming cyanobacteria. It remains unclear to what extent can A. flos-aquae alleviate P deficiency by regulating P using strategies.

Results
Based on in situ observations of extracellular alkaline phosphatase (APase) in A. flos-aquae via enzyme-labeled fluorescence in freshwater bodies in China, Poland and Czechia, we further investigated responses of isolated A. flos-aquae to different P supplies (dissolved inorganic P (Pi) as +DIP, dissolved organic α-glycerophosphate and β-glycerophosphate as +DOPα and +DOPβ, P-free condition as P-depleted). The significantly negative relationships between percentage of APase producing cells and soluble reactive P concentration in both fields and cultures suggested that the excretion of APase in cyanobacterium was regulated by ambient Pi supply. Suffering from P deficiency in the P-depleted treatments, A. flos-aquae showed the highest APase activity but a vigorous growth at the early culture stage, which might also benefit from the formation of polyphosphate body (PPB) and the decrease of cell P quota. In the +DOP treatments, the coordination of dissolved DOP mineralization and continuous prompt utilization of PPB might contribute to a maintenance but not reproduction of A. flos-aquae when relying on DOP, since the specific growth rate kept around 0 cells L−1 day−1 at the second half culture period and the highest cell density reached only 13.38% of that in +DIP treatments while photochemical efficiency was comparable during the whole experiment. Luxury uptake of phosphate as PPB in the +DIP treatments was consistent to the canonical view of polyphosphate as P storage.

Conclusion
Aphanizomenon flos-aquae could achieve an instantaneous growth in response to P deficiency with the coordination of P utilization strategies, while it maintained a long-term sustainable growth but not reproduction under sole DOP supply. Persistent and active reproduction could only be achieved in high Pi supply, which implying that an effective consequence can be expected for combating the bloom of A. flos-aquae when controlling P supply.