Thi Thuy Duong

Dynamics of benthic diatom colonization in a cadmium/zinc-polluted river (Riou-Mort, France)

Periphytic diatom communities were sampled from glass substrates immersed along a gradient of organic and metallic pollution. We investigated the influence of nutrients and a combination of nutrients and metals on biofilms and diatom communities settling on the glass over three weeks. Biofilm was characterized through organic biomass, chlorophyll-a concentrations and metal content; structure of diatom assemblages was assessed by studying densities, mean biovolumes and taxonomic composition. Exposure to organic pollutants re- sulted in an increase of biomass (dry weight, chlorophyll-a concentrations and diatom densities) and diatom com- munity structure was similar to that at an unpolluted site relative to nutrient concentrations. Cyclotella meneghi- niana was dominant and the species Nitzschia palea, Navicula gregaria and Melosira varians were well-repre- sented. Downstream of the metal-contamination source, biofilm biomass, as well as chlorophyll-a concentrations, decreased as cadmium and zinc content got higher (up to 60 µgCd/g dry weight and 1400 µgZn/g dry weight). Concurrently, the size distribution of diatoms, changing from larger to smaller individuals, reflected changes in the taxonomic composition of the assemblages where Eolimna minima was found in high proportions. Statisti- cally significant amounts of abnormal frustules were also enumerated in the metal-polluted environment (p < 0.05).

Experimental toxicity and bioaccumulation of cadmium in freshwater periphytic diatoms in relation with biofilm maturity.

A study was undertaken to examine cadmium accumulation in freshwater biofilm, its effects on biofilm development and on diatom community structure in laboratory experimental conditions. A suspension of a biofilm originated from the Riou-Mort River (South West France) was inoculated into three experimental units containing clean glass substrates under laboratory conditions. Settling and already developed biofilms were exposed to a Cd concentration of 100 microg L(-1). Metal accumulation (total and intracellular metal content) in biofilms, dry weight and ash-free dry mass, diatom cell density and diatom community composition were analyzed. Both total and intracellular Cd accumulated by the biofilm throughout the experiment increased with duration of metal exposure. Biofilms in the course of maturation were showed higher Cd content and less effective development than settled biofilms. However diatom communities in younger biofilms exposed to Cd increased their tolerance to Cd by a highly significant development of Nitzschia palea. In contrast, Cd exposure had different effect in installed biofilm and taxonomic composition. These results indicate that mature biofilm may limit Cd accumulation into its architecture and protect diatom communities from the effects of metals.

Seasonal effects of cadmium accumulation in periphytic diatom communities of freshwater biofilms.

The relationships between diatom species and cadmium (Cd) accumulated in biofilms of the Riou-Mort River (SW, France) were studied in July 2004 and March 2005. Biofilms were sampled from artificial substrates immersed along a metallic pollution gradient during 20 days. Dynamics of diatom communities and cadmium accumulation were followed by collecting samples after 4, 7, 14 and 20 days of biofilm colonization. Cd accumulation in biofilms during experiment was significantly higher in Cd polluted station (Joanis) than in reference station (Firmi) for both seasons. Periphytic diatom composition varied between sites and seasons. At Firmi station, seasonal dynamics of diatom communities were stable with the dominance of Cyclotella meneghiniana and Melosira varians in July and Surirellabrebissonnii and Navicula gregaria in March. At Joanis station, diatom communities mainly responded to high levels of metal by a high proportion of small, adnate species. Positive correlations between Eolimna minima, Nitzschia palea, Encyonema minutum, Surirella angusta, and Gomphonema parvulum and cadmium accumulation were observed, indicating that these species are tolerant to high levels of cadmium. On the other hand, negative correlations of C. meneghiniana, N. gregaria, Navicula lanceolata, M. varians and Nitzschia dissipata with cadmium qualify them as sensitive diatom species. Periphytic diatom composition through the presence of specific species highlight metal tolerant indicator diatom groups which will be meaningful for biomonitoring pollution in natural aquatic systems.

Consistency in Diatom Response to Metal-Contaminated Environments

Diatoms play a key role in the functioning of streams, and their sensitivity to many environmental factors has led to the development of numerous diatom-based indices used in water quality assessment. Although diatom-based monitoring of metal contamination is not currently included in water quality monitoring programs, the effects of metals on diatom communities have been studied in many polluted watersheds as well as in laboratory experiments, underlying their high potential for metal contamination assessment. Here, we review the response of diatoms to metal pollution from individual level (e.g. size, growth form, and morphological abnormalities) to community structure (replacement of sensitive species by tolerant ones). These potential effects are then tested using a large, multi-country database combining diatom and metal information. Metal contamination proved to be a strong driver of the community structure, and enabled for the identification of tolerant species like Cocconeis placentula var. euglypta, Eolimna minima, Fragilaria gracilis, Nitzschia sociabilis, Pinnularia parvulissima, and Surirella angusta. Among the traits tested, diatom cell size and the occurrence of diatom deformities were found to be good indicators of high metal contamination. This work provides a basis for further use of diatoms as indicators of metal pollution.

Total organic carbon fluxes of the Red River system (Vietnam)

Abstract Riverine transport of organic carbon from terrestrial ecosystems to the oceans plays an important role in the global carbon cycle. The Red River is located in Southeast Asia where river discharge, sediment loads and fluxes of elements (carbon, nitrogen and phosphorus) associated with suspended solids have been dramatically altered over past decades as a result of reservoir impoundment and land use, population, and climate change. Dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations were measured monthly at four stations of the Red River system from January 2008 to December 2010. The results reveal that POC changed synchronically with total suspended solids (TSS) concentration and with the river discharge, whereas no clear trend was observed for DOC concentration. The mean value of total organic carbon (TOC = DOC + POC) flux in the delta of the Red River was 31.5 × 1013 ± 4.0 × 1013 MgC.yr−1 (range 27.9–35.8 × 1013 MgC.yr−1 which leads to a specific TOC flux of 2012 ± 255 kgC.km−2.yr−1 during this 2008–2010 period. About 80% of the TOC flux was transferred to the estuary during the rainy season as a consequence of the higher river water discharge. The high mean value of the POC:Chl‐a ratio (1585 ± 870 mgC.mgChl‐a−1) and the moderate C:N ratio (7.3 ± 0.1) in the water column system suggest that organic carbon in the Red River system is mainly derived from erosion and soil leaching in the basin. The effect of two new dam impoundments in the Red River was also observable with lower TOC fluxes in 2010 compared with 2008. Copyright

Inhibition effect of engineered silver nanoparticles to bloom forming cyanobacteria

Silver nanoparticle (AgNP) has a wide range antibacterial effect and is extensively used in different aspects of medicine, food storage, household products, disinfectants, biomonitoring and environmental remediation etc. In the present study, we examined the growth inhibition effect of engineered silver nanoparticles against bloom forming cyanobacterial M. aeruginosa strain. AgNPs were synthesized by a chemical reduction method at room temperature and UV–Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscope (TEM) showed that they presented a maximum absorption at 410 nm and size range between 10 and 18 nm. M. aeruginosa cells exposed during 10 d to AgNPs to a range of concentrations from 0 to 1 mg l−1. The changes in cell density and morphology were used to measure the responses of the M. aeruginosa to AgNPs. The control and treatment units had a significant difference in terms of cell density and growth inhibition (p < 0.05). Increasing the concentration of AgNPs, a reduction of the cell growths in all treatment was observed. The inhibition efficiency was reached 98.7% at higher concentration of AgNPs nanoparticles. The term half maximal effective concentration (EC50) based on the cell growth measured by absorbance at 680 nm (A680) was 0.0075 mg l−1. The inhibition efficiency was 98.7% at high concentration of AgNPs (1 mg l−1). Image of SEM and TEM reflected a shrunk and damaged cell wall indicating toxicity of silver nanoparticles toward M. aeruginosa.

CO 2 partial pressure and CO 2 emissions from the lower Red River (Vietnam)

The Red River (Vietnam) is a good example of a South-East Asian river system, strongly 17 affected by climate and human activities. This study aims to quantify the spatial and seasonal 18 variability of carbon dynamic and CO2 outgassing at the water-air interface of the lower Red River 19 system. The monitoring of water quality and CO2 emission were carried out for 24h cyclings at the five 20 stations during the dry and monsoon seasons. The riverine water pCO2 was supersaturated with CO2 in 21 contrast to the atmospheric equilibrium (400 ppm), averaging about 1588.6 ± 884.6 ppm, thus resulting 22 in a water–air CO2 flux of 26.9 ± 18.4 mmol m -2 day. The CO2 outgassing rate was characterized by 23 significant spatial variations, highest at Hoa Binh station (Da River) due to the dam impoundment and 24 the highest river flow. Surprisingly, CO2 outgassing was higher in the day time (30.4 ± 21.2 mmol m 25 2 day) than in the night time (23.3 ± 15.4 mmol m day), probably as a result of the combined effect 26 of higher wind speed and water temperature in the day time. Seasonal differences were also observed, 27 higher in the wet season (30.7 ± 23.1 mmol m day) than in the dry season (23.0 ± 12.2 mmol m 28 2 day), due to higher river discharges and higher external inputs of organic matters from watersheds. 29 Conversely during dry season, temperature was among the main factors influencing C dynamic, with 30 higher pCO2 and fluxes, probably as a result of increased metabolic rates. 31

Anticyanobacterial phenolic constituents from the aerial parts of Eupatorium fortunei Turcz

Abstract Four thymol derivatives and two phenolic compounds were isolated from the aerial parts of Eupatorium fortunei. The new structures were elucidated to be 7,8,9-trihydroxythymol (1), and 8,10-didehydro-7,9-dihydroxythymol (2) by means of MS and NMR analysis. The known compounds were identified as 8,9,10-trihydroxythymol (3), 10-acetoxy-8,9-dihydroxythymol (4), o-coumaric acid (5) and 4-(2-hydroxyethyl)benzaldehyde (6). Compound 3 showed strongest inhibitory effect on the growth of Microcystis aeruginosa in comparison with CuSO4.