Dynamics of macrozoobenthos assemblages in the Fubao Bay of Lake Dianchi and their relation to organic pollutants

A two-year-long investigation on the dynamics of the structure and biodiversity of macrozoobenthos was conducted in the Fubao Bay of Dianchi Lake, Southwest China. A high level of organic pollution has been detected in this Bay for the last 10 years. In all, 31 benthic taxa belonging to eight families and 20 genera were identified. Oligochaeta dominated this ecosystem, comprising 53 to 99% of the total abundance and 75 to 99% of the total wet biomass. The standing crop of the solely dominant species Limnodrilus hoffmeisteri rose sharply in the two-year period: It increased from 46% of the total abundance to 73% and from 73% of the wet biomass to 99% in second year. One-way analysis of variance (ANOVA) revealed that there was no significant difference (p > 0.05) in the richness value for all and the most predominant groups between the two years. However, significant differences were detected between the total and oligochaete abundances (p < 0.05). The standing crop was the lowest (188.72 ind/m2 and 0.20 g/m2) in October, 2006 and the highest (14931.7 ind/m2 and 39.33 g/m2) in January, 2008. The annual mean standing crop increased nearly 10 times in density and eight times in wet biomass between the two years, and this increase was mainly contributed by oligochaetes. Analyses of three diversity indices and the K-dominance curve revealed that there was a significant difference between the two years. Multiple regression analysis indicated that the dynamics of the biomass of macrozoobenthos could be largely attributed to nitrate nitrogen.Key words: Macrozoobenthos, structure, biodiversity, Dianchi Lake, organic pollution

A simple miniaturised photometrical method for rapid determination of nitrate and nitrite in freshwater

A rapid, simple miniaturised photometrical method was developed for the determination of nitrate and/or nitrite in freshwater samples. All procedures, including sample buffering, reduction by copperised cadmium granules, colour development and absorbance determination, were completed in a 96-well microplate. The factors governing the nitrate reduction and its recovery were investigated in detail, and the optimised analysing conditions were established. Nitrate was quantitatively reduced by copperised cadmium granules with a high reduction efficiency (96.59 +/- 0.96%). The proposed method gave a linear calibration ranging from 0.01 to 1.50 mg L-1 for NO2--N and 0.02 to 1.50 mg L-1 for NO3--N. The detection limits for nitrite and nitrate were 2 and 4 mu g L-1, respectively. The proposed method allowed at least 48 samples to be simultaneously analysed in duplicate, with good precision, within 90 min for nitrate and 30 min for nitrite, and was successfully applied to actual freshwater sample analysis with a recovery of 98.02 +/- 1.04% for nitrite and 99.72 +/- 1.39% for nitrate. This method produced accurate results comparable to standard methods, provided a much higher sample throughput than conventional methods and could be routinely used in actual freshwater sample monitoring. (C) 2010 Elsevier B.V. All rights reserved

A laboratory study on risk assessment of microcystin-RR in cropland

The persistence time and risk of microcystin-RR (MC-RR) in cropland via irrigation were investigated under laboratory conditions. In order to evaluate the efficiency of the potential adsorption and biodegradation of MC-RR in cropland and the persistence time of MC-RR for crop irrigation, high performance liquid chromatography (HPLC) was used to quantify the amount of MC-RR in solutions. Our study indicated that MC-RR could be adsorbed and biodegraded in cropland soils. MC-RR at 6.5 mg/L could be completely degraded within 6 days with a lag phase of 1 - 2 days. In the presence of humic acid, the same amount of MC-RR could be degraded within 4 days without a lag phase. Accordingly, the persistence time of MC-RR in cropland soils should be about 6 days. This result also suggested the beneficial effects of the organic fertilizer utilization for the biodegradation of MC-RR in cropland soils. Our studies also demonstrated that MC-RR at low concentration ( 100 mu g/L) significantly inhibited the growth of plants. High sensitivity of the sprouting stage plants to MC-RR treatments as well as the strong inhibitory effects resulting from prolonged irrigation further indicated that this MC-RR growth-inhibition may vary with the duration of irrigation and life stage of the plants. (c) 2007 Published by Elsevier Ltd.The persistence time and risk of microcystin-RR (MC-RR) in cropland via irrigation were investigated under laboratory conditions. In order to evaluate the efficiency of the potential adsorption and biodegradation of MC-RR in cropland and the persistence time of MC-RR for crop irrigation, high performance liquid chromatography (HPLC) was used to quantify the amount of MC-RR in solutions. Our study indicated that MC-RR could be adsorbed and biodegraded in cropland soils. MC-RR at 6.5 mg/L could be completely degraded within 6 days with a lag phase of 1 - 2 days. In the presence of humic acid, the same amount of MC-RR could be degraded within 4 days without a lag phase. Accordingly, the persistence time of MC-RR in cropland soils should be about 6 days. This result also suggested the beneficial effects of the organic fertilizer utilization for the biodegradation of MC-RR in cropland soils. Our studies also demonstrated that MC-RR at low concentration ( 100 mu g/L) significantly inhibited the growth of plants. High sensitivity of the sprouting stage plants to MC-RR treatments as well as the strong inhibitory effects resulting from prolonged irrigation further indicated that this MC-RR growth-inhibition may vary with the duration of irrigation and life stage of the plants. (c) 2007 Published by Elsevier Ltd

Prediction and elucidation of the population dynamics of Microcystis spp. in Lake Dianchi (China) by means of artificial neural networks

Lake Dianchi is a shallow and turbid lake, located in Southwest China. Since 1985, Lake Dianchi has experienced severe cyanabacterial blooms (dominated by Microcystis spp.). In extreme cases, the algal cell densities have exceeded three billion cells per liter. To predict and elucidate the population dynamics ofMicrocystis spp. in Lake Dianchi, a neural network based model was developed. The correlation coefficient (R 2) between the predicted algal concentrations by the model and the observed values was 0.911. Sensitivity analysis was performed to clarify the algal dynamics to the changes of environmental factors. The results of a sensitivity analysis of the neural network model suggested that small increases in pH could cause significantly reduced algal abundance. Further investigations on raw data showed that the response of Microcystis spp. concentration to pH increase was dependent on algal biomass and pH level. When Microcystis spp. population and pH were moderate or low, the response of Microcystis spp. population would be more likely to be positive in Lake Dianchi; contrarily, Microcystis spp. population in Lake Dianchi would be more likely to show negative response to pH increase when Microcystis spp. population and pH were high. The paper concluded that the extremely high concentration of algal population and high pH could explain the distinctive response of Microcystis spp. population to +1 SD (standard deviation) pH increase in Lake Dianchi. And the paper also elucidated the algal dynamics to changes of other environmental factors. One SD increase of water temperature (WT) had strongest positive relationship with Microcystis spp. biomass. Chemical oxygen demand (COD) and total phosphorus (TP) had strong positive effect on Microcystis spp. abundance while total nitrogen (TN), biological oxygen demand in five days (BOD5), and dissolved oxygen had only weak relationship with Microcystis spp. concentration. And transparency (Tr) had moderate positive relationship with Microcystis spp. concentration.Lake Dianchi is a shallow and turbid lake, located in Southwest China. Since 1985, Lake Dianchi has experienced severe cyanabacterial blooms (dominated by Microcystis spp.). In extreme cases, the algal cell densities have exceeded three billion cells per liter. To predict and elucidate the population dynamics ofMicrocystis spp. in Lake Dianchi, a neural network based model was developed. The correlation coefficient (R 2) between the predicted algal concentrations by the model and the observed values was 0.911. Sensitivity analysis was performed to clarify the algal dynamics to the changes of environmental factors. The results of a sensitivity analysis of the neural network model suggested that small increases in pH could cause significantly reduced algal abundance. Further investigations on raw data showed that the response of Microcystis spp. concentration to pH increase was dependent on algal biomass and pH level. When Microcystis spp. population and pH were moderate or low, the response of Microcystis spp. population would be more likely to be positive in Lake Dianchi; contrarily, Microcystis spp. population in Lake Dianchi would be more likely to show negative response to pH increase when Microcystis spp. population and pH were high. The paper concluded that the extremely high concentration of algal population and high pH could explain the distinctive response of Microcystis spp. population to +1 SD (standard deviation) pH increase in Lake Dianchi. And the paper also elucidated the algal dynamics to changes of other environmental factors. One SD increase of water temperature (WT) had strongest positive relationship with Microcystis spp. biomass. Chemical oxygen demand (COD) and total phosphorus (TP) had strong positive effect on Microcystis spp. abundance while total nitrogen (TN), biological oxygen demand in five days (BOD5), and dissolved oxygen had only weak relationship with Microcystis spp. concentration. And transparency (Tr) had moderate positive relationship with Microcystis spp. concentration

Understanding wastewater treatment mechanisms: a review on detection, removal, and purification efficiencies of faecal bacteria indicators across constructed wetlands

The specific mechanisms of faecal bacterial removal by constructed wetland (CW) mechanisms are inadequately understood. In several circumstances, CWs have been compared to &quot;black box&quot; systems involving poorly understood waste removal mechanisms despite being an emerging environmentally friendly waste management approach. This has therefore attracted numerous scientific studies to further unlock CWs&#39; functional mechanisms and to increase its efficiencies. This review paper covers detailed information on the status of detection techniques and removal efficiencies of faecal coliforms, with an emphasis on Escherichia coli. A comprehensive literature search was undertaken that involved a comparative review of various study results and critical analysis of previous scientific and review papers. The ultimate objective is to shed further light on the role of wetlands on wastewater purification for improved aquatic ecosystem health and clean water for humans and other organisms.</p

Chemical transformation of silver nanoparticles in aquatic environments: Mechanism, morphology and toxicity

Silver nanoparticles (Ag NPs) have been inevitably introduced into ecological environment during their extensive applications in daily human life. Thermodynamically, Ag NPs are unstable and transform into other species under various aqueous conditions. Ag NPs and their transformation products pose potential threats to environment and humans. However, the complex environmental conditions and transformations of Ag NPs complicate their human health and environmental risk assessment. To bridge the knowledge gap, four essential environmental transformations, oxidative dissolution, sulfidation, chlorination and photoreduction, of Ag NPs are reviewed herein. The mechanism, morphology and size change, as well as the toxicity of Ag NPs during these transformations under certain aqueous conditions are detailed. In particular, these environmental transformations have shown strong correlations that are discussed. The transformation, fate, bioavailability, morphology and toxicity of Ag NPs are critical factors and should be considered in a complete human health and environmental risk assessment of Ag NPs. The fluctuation of these factors in the realistic environment is also vital and should be considered. (C) 2017 Elsevier Ltd. All rights reserved

Efficacy of macrophyte dominated wastewater inclosure as post-treatment alternative in domestic wastewater quality polishing for eradication of faecal pathogenic bacteria pollution

Variation in microbial strains and pathogenicity within wetland ecosystem is a topic that needs more considerable attention due to the rising climate change and in human population. Despite many current studies focusing on wetlands ecology, there is still inadequate documentation that are specific to the relationship between bacterial abundance, diversity and pathogenicity, as well as the principles and roles of aquatic plants in wastewater polishing. To provide an understanding on the fate and virulence of members of Enterobacteriaceae and Enterococcaceae in a winter tolerant macrophyte dominated artificial wetland system, this study evaluated the efficacy of macrophyte dominated Wastewater Polishing Pond Inclosures (WPPIs) in influencing the abundance, survival and pathogenicity of faecal bacterial pathogens. The study reveals that WPPIs provides more than 95% reduction of pathogenic forms of Escherichia coli as well as Enterococcusfaecalis and Enterococcusfaesium. WPPIs provides a good sustainable and environment friendly alternative approach in wastewater polishing and the efficiency is a factor of macrophytes percentage cover. Therefore, the application of WPPIs in domestic wastewater polishing is recommended for sufficient pollution control on aquatic ecosystems that receive enormous effluents from a highly populated urban set up with huge domestic wastewater generation. (C) 2017 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers

Vertical distribution of Fe and Fe(III)-reducing bacteria in the sediments of Lake Donghu, China

In lake sediments, iron (Fe) is the most versatile element, and the redox cycling of Fe has a wide influence on the biogeochemical cycling of organic and inorganic substances. The aim of the present study was to analyze the vertical distribution of Fe and Fe(III)-reducing bacteria (FeRB) in the surface sediment (30 cm) of Lake Donghu, China. At the 3 sites we surveyed, FeRB and Fe(II)-oxidizing bacteria (FeOB) coexisted in anoxic sediments. Geobacter-related FeRB accounted for 5%-31% of the total Bacteria, while Gallionella-related FeOB accounted for only 0.1%-1.3%. A significant correlation between the relative abundance of poorly crystalline Fe and Geobacter spp. suggested that poorly crystalline Fe favored microbial Fe(III) reduction. Poorly crystalline Fe and Geobacter spp. were significantly associated with solid-phase Fe(II) and total inorganic phosphorus levels. Pore water Fe(II) concentrations negatively correlated with NO3- at all sites. We concluded that Geobacter spp. were abundant in the sediments of Lake Donghu, and the redox of Fe might participate in the cycling of nitrogen and phosphorus in sediments. These observations provided insight into the roles of microbial Fe cycling in lake sediments

Root Radial Oxygen Loss and the Effects on Rhizosphere Microarea of Two Submerged Plants

Radial oxygen loss (ROL) has been suggested to be a major process to protect plants exposed to the anaerobic by-products of soil anaerobiosis. The aim of the present study was to test the effects of root ROL from two submerged plants (Hydrilla verticillata and Vallisneria spiralis) on the rhizosphere oxygen profile and rhizosphere microarea. Phospholipid fatty acids (PLFAs) of sediment samples were used to characterize and quantify the microbial community. The results showed clearly that there were significant differences between the two plants in radial oxygen loss, which affected rhizosphere physicochemical parameters and the microbial community. Rhizosphere total biomass, bacteria, gram-positive bacteria, actinomycetes, and microbial diversity of V. spiralis were significantly higher than those of H. verticillata. The present study highlights root ROL as a key parameter affecting the microbial community of the rhizosphere microarea.</p