Biocidal activity of algal toxins against immature mosquitoes

Extracts of two species of green algae, filamentousRhizoclonium hieroglyphicum Kütz and a phytoplankton,Chlorella ellipsoidea Gerneck, obtained with solvents in the laboratory were assayed againstAedes aegypti L.,Culex quinquefasciatus Say, andCuliseta incidens (Thomson). On extraction with petroleum ether, groundR. hieroglyphicum yielded an active crude extract which was chromatographed on a neutral alumina column and eluted consecutively with petroleum ether, benzene, and methanol. All three eluted fractions were found to induce significant mortality in test mosquito species. The benzene-eluted fraction was the least toxic. The methanol-eluted fraction was the most toxic to all species and exhibited juvenile hormone-like activity; it also caused morphogenetic changes in emerging adults. All three fractions delayed the rate of development of mosquito larvae by 2–5 days. Three supernatants ofC. ellipsoidea obtained on different occasions were tested against first instars ofC. quinquefasciatus. After the confirmation of their activity, all supernatants were extracted with diethyl ether, combined, and assayed against first- and fourth-stage larvae of the three mosquito species. The first-stage larvae ofC. quinquefasciatus andC. incidens were approximately three times more suspectible than those ofA. aegypti. However, fourth-stage larvae of the former two species were about twice as susceptible to the extract as those of the latter species. Dead first-stage larvae of all the species had a shrunken appearance. In general,C. ellipsoidea extract was quicker acting than that ofR. hieroglyphicum.     

The estimation of bioavailable phosphorus in particulate forms by ultrasonic treatment

The concentration of bioavailable phosphorus (BAP), which is readily available to algae, has been reported to be important to the severity of eutrophication. Because time‐consuming conventional methods have constrained sample processing, a rapid method of estimating BAP is required. We investigated an extraction method using 0.1 M NaOH in combination with ultrasonic treatment to estimate BAP in agricultural soils and suspended sediments. The extraction process was less time‐consuming than conventional methods. The relevance of the extraction methodology to the growth of P‐starved Microcystis aeruginosa was confirmed by observing the growth of this alga in cultures amended with extracted samples of soil or sediment as the sole P source. Cell growth in media containing samples extracted with ultrasonic treatment was similar to growth in media containing samples extracted with conventional methods. The results suggest that ultrasonic extraction is a promising method for rapidly obtaining BAP from agricultural soils and suspended sediments.     

Reconstruction of Windermere Sewage-Treatment Works

This sewage-treatment works, which is located within the Lake District National Park, on the shores of England's largest lake, receives flows from the villages of Windermere, Bowness and Troutbeck and serves a population which can double from winter to summer.
The paper describes the logistical and other aspects of undertaking construction works within the confines of an existing site whilst maintaining treatment to incoming flows. The background and regulatory influences on the design of the scheme are covered, together with details of the new treatment units and the provision of facilities to strip phosphate from the effluent.     

Recycling algae to improve species control and harvest efficiency from a high rate algal pond

This paper investigates the influence of recycling gravity harvested algae on species dominance and harvest efficiency in wastewater treatment High Rate Algal Ponds (HRAP). Two identical pilot-scale HRAPs were operated over one year either with (HRAP_r) or without (HRAP_c) harvested algal biomass recycling. Algae were harvested from the HRAP effluent in algal settling cones (ASCs) and harvest efficiency was compared to settlability in Imhoff cones five times a week. A microscopic image analysis technique was developed to determine relative algal dominance based on biovolume and was conducted once a month. Recycling of harvested algal biomass back to the HRAP_r maintained the dominance of a single readily settleable algal species (Pediastrum sp.) at >90% over one year (compared to the control with only 53%). Increased dominance of Pediastrum sp. greatly improved the efficiency of algal harvest (annual average of >85% harvest for the HRAP_r compared with ∼60% for the control). Imhoff cone experiments demonstrated that algal settleability was influenced by both the dominance of Pediastrum sp. and the species composition of remaining algae. Algal biomass recycling increased the average size of Pediastrum sp. colonies by 13-30% by increasing mean cell residence time. These results indicate that recycling gravity harvested algae could be a simple and effective operational strategy to maintain the dominance of readily settleable algal species, and enhance algal harvest by gravity sedimentation.     

湘西花垣县大脑坡铅锌矿地质特征与容矿空间分析

大脑坡铅锌矿床是近年来在花垣铅锌矿田内新发现的又一超大型铅锌矿,为进一步查明该矿区成矿地质条件,查明与成矿有关的地层、岩相、构造、矿体形态以及分布、容矿空间特征,在该矿区开展了勘探工作,通过1∶2 000专项地质填图、钻探、坑探、取样测试等,详细查明了该矿的地质特征及容矿空间特征,为同类型矿床的寻找奠定了基础。     

The low TN:TP ratio,a cause or a result of Microcystis blooms?

An enclosure experiment in the shallow, subtropical Lake Donghu, China, was performed in the summer of 2001 to examine the effect of TN:TP (total phosphorus) ratios and P-reduction on the occurrence of Microcysitis blooms. The treatments were performed with enough amounts of N but with different amounts of P in the water column and sediment. Microcystis blooms occurred in the enclosures either with an initial TN:TP <29 or TN:TP>29 where the nutrients (N, P) were high enough. Microcysitis blooms never occurred in the treatments with low P concentration in spite of the presence of sufficient N. The P-rich sediments served as an important source for the P supply in the water column, and such a process was activated greatly by the outburst of Microcystis blooms which pumped up selectively P from the sediments and thus decreased the TN:TP ratios. Therefore, the low TN:TP ratio is not a cause but rather a result of Microcystis blooms.     

Processes of nitrogen loss from fertilizers applied to flooded rice fields on a calcareous soil in north-central China

Losses of nitrogen were investigated after applications of ammonium bicarbonate and urea to flooded rice at transplanting. Ammonia (NH₃) volatilization was determined by direct micrometeorological methods, and total loss of fertilizer nitrogen (N) was measured by¹⁵N balance. All the loss appeared to be in gaseous forms, since there was no evidence of leaching and runoff was prevented. The difference between N loss and NH₃ loss was thus assumed to be denitrification loss.Both NH₃ volatilization and denitrification losses were large, being 39% and 33%, respectively, of the ammonium bicarbonate N, and 30% and 33%, respectively, of the urea N applied by farmers' methods.Ammonia fluxes from the field fertilized with ammonium bicarbonate were very high for two days, and then declined rapidly as the NH₃ source in the floodwater diminished. Moderate fluxes from the field fertilized with urea continued over 6 days, but calculations showed that NH₃ transfer from floodwater to atmosphere was retarded during the middle period of the experiment, particularly on day 2 when a thick algal scum appeared on the water surface. The results indicate that this algal mass obstructed the transport of NH₃ across the water-air interface until the scum was dispersed by wind action. Nevertheless, the prolonged NH₃ losses on the urea treatment were due primarily to high floodwater pH values promoted by the strong algal growth during the daylight hours.Nitrogen-15 balance studies showed that incorporation of fertilizer into drained soil substantially increased recoveries of fertilizer N in rice plants and soil compared with incorporation of fertilizer in the presence of standing floodwater. Ammonia loss measurements on these treatments when urea was applied suggested that the improvement in fertilizer N efficiency was due mainly to reductions in NH₃ loss.     

Model assumptions limit implications for nitrogen and phosphorus management

A recent Science paper concluding “phosphorus load reduction will make Erie more toxic” is misleading because it ignores historical lake behavior, and is based on a cellular-level model that excludes lake-level processes which influence phytoplankton community composition and toxicity. The inferences made from models are inherently limited by the assumptions underlying those models. We identify major assumptions, several of which are implicit, that were involved in extrapolating this cellular-level model to make lake-level inferences. An active adaptive management program will evaluate future nutrient load modifications if emerging evidence from well-vetted data and models indicate updates are appropriate.     

海藻类联产品的制备与开发

介绍了海藻类资源的综合利用情况及海藻类联产品碘、甘露酵、海藻酸钠的用途、联合制备方法、经济效益分析和联产品的开发前景。指出推广应用褐藻胶是海藻类资源有效利用的前提。