Assessment of microbial activity in water based on hydrogen peroxide decomposition rates

This study proposes a new and simple assay that allows rapid assessment of microbial activity in water samples. The assay consists of standardized hydrogen peroxide (H₂O₂) addition to a water sample and subsequent spectrophotometric determination of H₂O₂ reduction over time. The H₂O₂ decomposition rate constant reflects the level of enzymatic activity from planktonic and particle-associated bacteria as well as algae and protozoans. The proof of concept was verified on water samples from recirculating aquaculture systems (RAS), showing that the vast majority of H₂O₂ decomposition was related to microbial activity. Only 3% of the total H₂O₂ decomposition was related to abiotic processes when 0.20 μm sterile filtered RAS water was compared with unfiltered RAS water. Planktonic bacteria (size range 0.20–1.6 μm) accounted for 16% of H₂O₂ decomposition, while bacterial aggregates, particle-associated bacteria and microbiota above 1.6 μm were responsible for the remaining 81%. H₂O₂ decomposition rate constants were positively correlated to BOD₅ (r = 0.893; p < 0.001; n = 18) and to the number of 1–30 μm micro particles (r = 0.909; p < 0.001; n = 72) in RAS water, substantiating the biologically mediated decomposition processes in the water phase. The H₂O₂ decomposition assay thus represents a new alternative to existing methods that allows rapid (1–2 h) and simple quantification of microbial activity in fresh- and saltwater samples from aquaculture systems. Potential applications of the assay are discussed.     

双齿围沙蚕(Perinereis aibuhitensis Grube)典型自然栖息地的沉积环境特征

在山东沿海选取了双齿围沙蚕(Perinereis aibuhitensis Grube)的典型栖息地——河口潮间带,通过测定、分析不同潮区(高潮区、中潮区和低潮区)和同一潮区不同深度(5 cm、15 cm、25 cm和50 cm)沉积物中H2S、有机物、碳、氮、含水率以及粒度等指标,对其沉积环境特征进行了研究.结果显示,高潮区沉积物H2S浓度显著低于其他2个潮区(P＜0.05),25 cm深度处的沉积物H2S浓度显著高于其他深度(P＜0.05).3个不同潮区的间隙水中H2S浓度和含水率无显著性差异(P＞0.05),不同深度沉积物的间隙水中H2S浓度和含水率也无显著性差异(P＞0.05).低潮区有机物含量和氮含量显著低于中潮区和高潮区(P＜0.05),不同潮区之间的碳含量无显著性差异(P＞0.05),不同深度的沉积物中有机物含量、氮含量和碳含量随深度的增加而逐渐升高.粉砂在3个潮区以及各个潮区不同深度的沉积物中所占的比例均为最大,砂所占比例最小.低潮区沉积物的中值粒径显著高于其他2个潮区(P＜0.05),而不同深度沉积物的中值粒径无显著差异(P＞0.05).实验显示,本研究所选取的双齿围沙蚕典型自然栖息地沉积物中的H2S含量较高,并且随沉积物深度的增加而逐渐升高.沉积物中的有机物和碳含量极显著相关,碳氮含量显著相关.沉积物粒度分类属粘土质粉砂,高潮区沉积物的中值粒径显著小于低潮区,可能是造成高潮区沉积物的有机物含量和含水率显著高于低潮区的原因之一.