Ecosystem Modeling Applied to Nutrient Criteria Development in Rivers

Threshold concentrations for biological impairment by nutrients are difficult to quantify in lotic systems, yet States and Tribes in the United States are charged with developing water quality criteria to protect these ecosystems from excessive enrichment. The analysis described in this article explores the use of the ecosystem model AQUATOX to investigate impairment thresholds keyed to biological indexes that can be simulated. The indexes selected for this exercise include percentage cyanobacterial biomass of sestonic algae, and benthic chlorophyll a. The calibrated model was used to analyze responses of these indexes to concurrent reductions in phosphorus, nitrogen, and suspended sediment in an enriched upper Midwestern river. Results suggest that the indexes would respond strongly to changes in phosphorus and suspended sediment, and less strongly to changes in nitrogen concentration. Using simulated concurrent reductions in all three water quality constituents, a total phosphorus concentration of 0.1 mg/l was identified as a threshold concentration, and therefore a hypothetical water quality criterion, for prevention of both excessive periphyton growth and sestonic cyanobacterial blooms. This kind of analysis is suggested as a way to evaluate multiple contrasting impacts of hypothetical nutrient and sediment reductions and to define nutrient criteria or target concentrations that balance multiple management objectives concurrently. Any opinions, findings, conclusions, or recommendations expressed in this article are those of the authors alone, and do not necessarily reflect the views of the U.S. Environmental Protection Agency or of the U.S. Government.     

Does quinone or phenol enrichment of humic substances alter the primary compound from a non-algicidal to an algicidal preparation?

Dissolved organic matter (DOM) has been shown to affect phytoplankton species directly. These interactions largely depend on the origin and molecular size of DOM and are different in prokaryotes and eukaryotes. In a preceding study, however, two humic substance preparations did not adversely affect coccal green algae or cyanobacterial growth even at high concentrations of dissolved organic carbon (DOC). These results contradicted previous findings, showing a clear, negative response of different phototrophs to much lower DOC concentrations. To test whether or not at least defined building blocks of humic substances (HSs) are effective algicidal structures, we enriched two humic preparations with hydroquinone and p-benzoquinone, respectively, and exposed two different green algae, Pseudokirchneriella subcapitata and Monoraphidium braunii, and two cyanobacterial species, Synechocystis sp. and Microcystis aeruginosa, to the unmodified and enriched HSs. As response variables, growth rates in terms of biomass increase, chlorophyll-a content, and photosynthetic yield were measured. The highest concentration (4.17 mM DOC) of the modified HSs clearly inhibited growth; the cyanobacterial species were much more sensitive than the green algal species. However, realistic ecological concentrations did not adversely affect growth. Aerating the exposure solution for 24 h strongly reduced the inhibitory effect of the modified HSs. The algicidal effect was obviously caused by monomers and not by polymerised high molecular weight HSs themselves. Furthermore, the maximum quantum yield (Φ PSII max) was stimulated in the green algal species by low and medium DOC concentrations, but reduced in the cyanobacterial species upon exposure to higher HS concentrations. The quinone- and phenol-enriched HSs only showed algicidal activity at high concentrations of 4.17 mM DOC and lost their effects over time, presumably by oxidation and subsequent polymerisation. This study confirms that the applied humic substances themselves are not effective algicides even if enriched in effective structures.     

太湖竺山湾春季浮游细菌群落结构及影响因素

为研究太湖竺山湾春季浮游细菌群落结构,利用高通量测序对竺山湾4个采样点(雅浦港、沙塘港、竺山湖南和椒山)浮游细菌的16S rRNA基因进行序列测定.结果表明:测序文库的覆盖率很高,测序结果完全可以代表样本的真实情况;椒山的物种丰富度最高,但物种分布均匀度较低;竺山湾主要优势菌门为蓝藻门(Cyanobacteria)、放线菌门(Actinobacteria)、变形菌门(Proteobacteria)和拟杆菌门(Bacteroidetes),蓝藻门平均丰度高达64.73%,正处于水体复苏阶段,已有蓝藻水华暴发态势.属水平优势细菌主要有鱼腥藻属(Anabaena)、hgc I_clade、CL500-29_marine_group、微囊藻属(Microcystis)、聚球藻属(Synechococcus)和分枝杆菌属(Mycobacterium);运用冗余分析(RDA)探讨浮游细菌与环境因子的关系,结果表明,水温、Chl-a、NH+4-N、DO和PO3-4-P是影响浮游细菌群落的主要环境因子,其中,DO能显著影响微囊藻属,营养盐和水温对其也有一定程度影响.     

Biodegradation of multiple cyanobacterial metabolites in drinking water supplies

The fate of multiple cyanobacterial metabolites was assessed in two Australian source waters. The saxitoxins were the only metabolites shown to be non-biodegradable in Myponga Reservoir water, while microcystin-LR (MCLR) and geosmin were biodegradable in this water source. Likewise, cylindrospermopsin (CYN) was shown to be biodegradable in River Murray water. The order of ease of biodegradability followed the trend: MCLR > CYN > geosmin > saxitoxins. Biodegradation of the metabolites was affected by temperature and seasonal variations with more rapid degradation at 24 °C and during autumn compared with 14 °C and during winter. A microcystin-degrading bacterium was isolated and shown to degrade four microcystin variants within 4 h. This bacterium, designated as TT25, was shown to be 99% similar to a Sphingopyxis sp. based on a 16S rRNA gene fragment. Isolate TT25 was shown to contain a homologue of the mlrA gene; the sequence of which was 99% similar to that of a previously reported microcystin-degrader. Furthermore, isolate TT25 could degrade the microcystins in the presence of copper sulphate (0.5 mg L⁻¹ as Cu²⁺) which is advantageous for water authorities dosing such algicides into water bodies to control cyanobacterial blooms.     

太湖蓝藻水华预警监测技术体系的探讨

太湖蓝藻水华已经成为一个社会和政府共同关注的环境问题.为确保太湖地区饮水安全,提高政府应对蓝藻水华的能力,对太湖水源地蓝藻进行预警监测是判断蓝藻水华发展趋势以及制定相应的对策的重要手段.文章分析了蓝藻水华暴发的过程和蓝藻水华的监测技术,结合政府部门的实际,提出了太湖引用水源地蓝藻水华预警监测体系,对整个太湖地区乃至全国富营养化水体的水质预警具有重要的参考价值.     

The role of extracellular organic matter on the cyanobacteria ultrafiltration process

The membrane fouling caused by extracellular organic matter (EOM) and algal cells and organic matter removal of two typical cyanobacteria (M. aeruginosa and Pseudoanabaena sp.) during ultrafiltration (UF) process were studied in this work. The results showed that EOM had a broad molecular weight (Mw) distribution and the irreversible membrane fouling was basically caused by EOM. Moreover, humic acid and microbial metabolites were major components of EOM of two typical cyanobacteria. Since EOM could fill the voids of cake layers formed by the algal cells, EOM and algal cells played synergistic roles in membrane fouling. Fourier transform infrared spectroscopy analysis indicated that the CH₂ and CH₃ chemical bonds may play an important role in membrane fouling caused by EOM. Interestingly, the cake layer formed by the algal cells could trap the organic matter produced by algae and alleviate some irreversible membrane fouling. The results also showed that although the cake layer formed by the algal cells cause severe permeate flux decline, it could play a double interception role with UF membrane and increase organic matter removal efficiency. Therefore, when using UF to treat algae-laden water, the balance of membrane fouling and organic matter removal should be considered to meet the needs of practical applications.     

Environmental impact of two successive chemical treatments in a small shallow eutrophied lake: Part II. Case of copper sulfate

The appearance of cyanobacteria ( > 10 colony per ml) was not prevented after alum treatment. In order to prevent cyanobacteria efflorescences in a small shallow polymictic lake (Courtille, France), copper sulfate was applied. Treatment level was 63 microg 1(-1) as Cu2+ from CUSO4, 5 H2O. Cyanobacteria were kept under control during the summer. Microcystis sp. completely disappeared, which allowed swimming in the lake throughout the tourist season. Microcystis only reappeared 2 months after the treatment. Copper content in the water column only returned to its background level 2 months after copper addition. This high residence time of copper in the water might have been caused by complexation and adsorption of copper on natural organic matter, whose level was high in the ecosystem studied. A mechanism of transfer of 'truly' dissolved copper towards particulate copper has been underlined and explains the disappearance of this fraction of copper in the water column.     

人工浮岛在丁香湖水质改善中的应用

针对丁香湖水体恶化产生蓝藻的问题,在湖中设置人工浮岛对水质进行改善,浮岛植物以凤眼莲为主,辅以美人蕉等搭配.人工浮岛运行后,对水体中TN、TP指标净化效果良好,TN的去除率为48.1%～52.1%,TP的去除率为55.0%～64.4%,而且具有一定的景观效果.     

Toxicology and detection methods of the alkaloid neurotoxin produced by cyanobacteria, anatoxin-a

Freshwater resources are under stress due to naturally occurring conditions and human impacts. One of the consequences is the proliferation of cyanobacteria, microphytoplankton organisms that are capable to produce toxins called cyanotoxins. Anatoxin-a is one of the main cyanotoxins. It is a very potent neurotoxin that was already responsible for some animal fatalities. In this review we endeavor to divulgate much of the internationally published information about toxicology, occurrence and detection methods of anatoxin-a. Cyanobacteria generalities, anatoxin-a occurrence and production as well as anatoxin-a toxicology and its methods of detection are the aspects focused in this review. Remediation of anatoxin-a occurrence will be addressed with a public health perspective. Final remarks call the attention for some important gaps in the knowledge about this neurotoxin and its implication to public health. Alterations of aquatic ecosystems caused by anatoxin-a is also addressed. Although anatoxin-a is not the more frequent cyanotoxin worldwide, it has to be regarded as a health risk that can be fatal to terrestrial and aquatic organisms because of its high toxicity.