Insights into how characteristics of dissolved algal organic matter affect the efficiency of modified clay in controlling harmful algal blooms.

Dissolved algal organic matter (dAOM) originating from harmful algal blooms (HABs) can deteriorate the quality of municipal water supplies, threaten the health of aquatic environments, and interfere with modified clay (MC)-based HABs control measures. In this study, we explored the composition of dAOM from Prorocentrum donghaiense, a typical HAB organism, and assessed the influence of dAOM on MC flocculation. Our results suggested that dAOM composition was complex and had a wide molecular weight (MW) distribution. MW and electrical properties were important dAOM characteristics affecting flocculation and algal removal efficiency of MC. Negatively charged high-MW components (>50 kDa) critically affected algal removal efficiency, reducing the zeta potential of MC particles and leading to small and weak flocs. However, the effect of dAOM depended on its concentration. When the cell density of P. donghaiense reached HAB levels, the high-MW dAOM strongly decreased the algal removal efficiency of MC.

Harvesting of Microcystis flos-aquae using chitosan coagulation: Influence of proton-active functional groups originating from extracellular and intracellular organic matter.

Algogenic organic matter (AOM) produced by Microcystis cells inhibits coagulation harvesting; however, the harvesting inhibitory mechanisms at the functional groups level remain to be determined. This study fractionated extracellular organic matter (EOM) and intercellular organic matter (IOM) from Microcystis flos-aquae into five different hydrophilic and hydrophobic fractions and investigated their inhibition of chitosan coagulation harvesting. The proton-active functional groups in the inhibitory fractions were further analysed by potentiometric titration, and the interaction between these functional groups and chitosan was elucidated. The results showed that the harvesting inhibition of M. flos-aquae cells was dominated by HPI in AOM due to its high charge density, which resulted in greater consumption of coagulant. Potentiometric titration results suggested that the proton-active functional groups of both HPIEOM and HPIIOM consist mainly of phosphodiester, carboxylic, phosphoryl and amine/hydroxyl functional groups, and the harvesting inhibition of HPI on M. flos-aquae cells at pH 6.5 was mainly due to the deprotonation of phosphodiester and carboxylic functional groups. Moreover, carboxylic functional groups with stronger polarity could enhance the intermolecular interaction between HPI and chitosan more effectively than phosphodiester at pH 6.5. Preventing the deprotonation of carboxylic functional groups by adjusting the pH to 4.3 could effectively alleviate the harvesting inhibition caused by HPI. These findings revealed the inhibition mechanism of AOM on the coagulation harvesting of M. flos-aquae cells from the perspective of deprotonation of proton-active functional groups, which may provide important insights for assessing the role of AOM in the coagulation harvesting of Microcystis cells.

Effect of shear rate on floc characteristics and concentration factors for the harvesting of Chlorella vulgaris using coagulation-flocculation-sedimentation.

Coagulation-based separation has been increasingly applied to microalgal harvesting because of its competitive cost and high scalability. The characteristics of flocs formed during coagulation/flocculation are critical for efficient harvesting. However, few studies have been devoted to systematically investigating the structural characteristics of microalgal flocs and their influences on subsequent settling performance. In this paper, the dynamic mean size and fractal dimension, strength, regrowth and settling performance of Al3+ coagulated Chlorella vulgaris flocs were characterized at various flocculation shear rates. The influence of shear rate on floc characteristics was revealed. An appropriate shear rate (9 s-1) produced more desirable microalgal flocs (in terms of size and compactness), with better settling performance and a higher concentration factor, than higher or lower shear rates, favoring their separation and subsequent harvesting. At this condition, the concentration factor reached 13.50, which was a 177.21% improvement over the 4.87 reached at a low shear rate.

Evaluation of potential factors affecting deriving conductivity benchmark by utilizing weighting methods in Hun-Tai River Basin, Northeastern China.

Specific conductivity is an increasingly important stressor for freshwater ecosystems. Interacting with other environmental factors, it may lead to habitat degradation and biodiversity loss. However, it is still poorly understood how the effect of specific conductivity on freshwater organisms is confounded by other environmental factors. In this study, a weight-of-evidence method was applied to evaluate the potential environmental factors that may confound the effect of specific conductivity on macroinvertebrate structure communities and identify the confounders affecting deriving conductivity benchmark in Hun-Tai River Basin, China. A total of seven potential environmental factors were assessed by six types of evidence (i.e., correlation of cause and confounder, correlation of effect and confounder, the contingency of high level cause and confounder, the removal of confounder, levels of confounder known to cause effects, and multivariate statistics for confounding). Results showed that effects of dissolved oxygen (DO), fecal coliform, habitat score, total phosphorus (TP), pH, and temperature on the relationship between sensitive genera loss and specific conductivity were minimal and manageable. NH3-N was identified as a confounder affecting deriving conductivity benchmark for macroinvertebrate. The potential confounding by high NH3-N was minimized by removing sites with NH3-N > 2.0 mg/L from the data set. Our study tailored the weighting method previously developed by USEPA to use field data to develop causal relationships for basin-scale applications and may provide useful information for pollution remediation and natural resource management.

[Community Structure Characteristics of Eukaryotic Planktonic Algae in Liaohe River Through High-throughput Sequencing].

Eukaryotic phytoplankton plays an important ecological function in river ecosystem. The 18S rRNA gene V4 variable region of the environmental samples in Liaohe river was sequenced by using 454 pyrosequencing technology. The reprehensive sequences of OTUs were annotated, and then the OTUs list was compared to the species list obtained by microscope observation. The phylogenetic tree was constructed based on the reprehensive sequences of OTUs and 18S rRNA genes of eukaryotic phytoplankton algae obtained from GenBank. The community structure characteristics of eukaryotic phytoplankton and its environmental impact indicators were further studied. In this study, we got 167901 high-quality sequences of 18S rRNA gene V4 region. These sequences were annotated to 424 OTUs, including 134 eukaryotic algae. The results of the high-throughput sequencing showed that bacillariophyta and chlorophyta were the dominant groups of the total phyla. The high-throughput sequencing also revealed the presence of Charophyta, Cryptophyta, Haptophyta and Chrysophyceae which were not observed by optical microscope. The phylogeny analysis clustered the Cryptophyta and Pyrroptata at phylum level. The different genera of Cryptophyta and part of families or genera of Pyrroptata were clustered and distinguished by phylogeny analysis. The results of RDA showed that NH4+-N, PO43-P and NO3- were the most important environmental factors that affected the community structure. This study provided a new perspective to understand the diversity, community structure and influence factors of eukaryotic phytoplankton in Liaohe river. The study also indicated that high-throughput sequencing has great application potential in investigation of phytoplankton and the water environment quality assessment in Liaohe river.

[Impact of Talc Ore Mining on Periphyton Community Structure and Water Environment].

In order to explore the impact of Talc ore mining on aquatic ecosystems, periphyton communities and environmental factors from control portion, impacted portion and recovery portion separately were investigated and analyzed. Samples were collected from upstream Tanghe River (an important tributary of Tazi River) in November 2015, April 2016, and July 2016. Mann-Whitney U test was applied to compare the differences in environmental factors and periphyton community structures among three portions. Spearman correlation analysis, canonical correspondence analysis, and t-value biplot analysis were used to determine the relationship between the environmental factors and periphyton community structures. In the control and recovery portions, mass concentrations of magnesium (Mg), selenium (Se), arsenic (As), iron (Fe), molybdenum (Mo), bicarbonate ion (HCO3-), nitrate ion (NO3-), power of hydrogen (pH) and electric conductivity (EC), were the highest, and in the impacted portion, mass concentrations of potassium(K), sodium (Na), strontium (Sr), barium (Ba), silicon dioxide (SiO2), and dissolved oxygen (DO) were the lowest. The mass concentrations of Mg, Mo, As, EC, and HCO3- were significantly different (P<0.05) among the three portions. In control and recovery portions, the periphyton density, species richness, diatom siltation index, and relative abundance of Achnanthes sp. were the highest, while in the impacted portion, the percentage of handle diatom, the relative abundance of Surirella sp., and relative abundance of Navicula sp. were the lowest. Species richness of periphyton was significantly different (P<0.05) among the three portions. In summary, Mg, EC, and HCO3- from Talc Ore mining had significant impacts on periphyton assemblage structure.

[Responses of the Benthic Diatom Community to Nutrients and the Identification of Nutrient Thresholds in Three Aquatic Ecoregions of the Huntai River, Northeast China].

Benthic diatom communities and nutrient gradients were investigated from 287 sampling sites in three aquatic ecoregions (AE) of the Huntai River to characterize the spatial distribution of nutrients and the benthic diatom communities. Locally weighted scatterplot smoothing (LOWESS) was used to analyze the thresholds for nitrogen and phosphorus. The results showed that:① The concentration of ammonia nitrogen and total phosphorus significantly differs in the three AEs, and shows a tendency of AEⅠ < AE Ⅱ < AE Ⅲ. ② To reveal the structure of benthic diatom communities, various benthic diatom indexes, including the sportive diatom percentage, sensitive diatom percentage, stipitate diatom percentage, Pielou evenness index, specific polluosensitivity index (IPS), biological diatom index (IBD), and generic diatom index (IDG) were analyzed. The sportive diatom percentage varied significantly in AEI, AEⅡ, and AE Ⅲ, with the highest percentage observed in AEⅢ and the lowest in AEⅠ. However, the other six indexes exhibited an opposite trend. All revealed that AE Ⅲ has been seriously damaged, while AEⅠ is less disturbed than AEⅡ and AE Ⅲ. ③ LOWESS fitting curves show thresholds for ammonia nitrogen (NH4+ -N) in the three aquatic ecoregions as 0.13, 0.30, and 1.98 mg·L-1, respectively and for total phosphorous (TP) were 0.04, 0.06, and 0.20 mg·L-1. All results were tested by independent-sample T tests. This study will provide assistance for effectively protecting the benthic diatom community in different aquatic ecoregions and also provide a theoretical basis for water management.