[Seasonal Variation on Nutrient Limitation for Phytoplankton Growth in a Coastal River-Reservoir System, Southeast China].

A comprehensive analysis was conducted using a dataset obtained from October in 2013 to October in 2014 monitoring in 20 headwater streams of Jiulong River and four reservoirs, situated in such a coastal river-reservoir system in Southeast China suffering from intensive anthropogenic disturbance. In-situ monitoring, GIS and statistical analysis were coupled in this study to identify the spatiotemporal variations of nutrients & phytoplankton abundance and community structure, the differentiation of nitrogen & phosphorus limitation of phytoplankton growth, and the seasonal variations in nutrient limitation of phytoplankton growth. The results showed that there were obvious spatiotemporal variations in terms of nutrients & phytoplankton abundance and community structure in the 20 headwater streams and four reservoirs. The concentration of nitrogen was higher in winter and spring whereas lower in summer and autumn for both 20 headwater streams and four reservoirs. However, the concentration of phosphorus showed an opposite trend. The phytoplankton's abundance was the highest in summer for four reservoirs while it was higher in winter and spring, lower in summer and autumn in the 20 headwater streams. Meanwhile, the main trend in the succession of phytoplankton was from Bacillariophyta in autumn, winter and spring to Chlorophyta in summer in Tingxi reservoir, from Chlorophyta-Cryptophyta in winter and spring to Chlorophyta-Cyanophyta in summer and autumn in Jiangdong reservoir. No obvious trend exhibited in phytoplankton succession in Shidou-Bantou reservoir and 20 headwater streams. The Redundancy analysis (RDA) ordination plots well displayed the phytoplankton's community structure and its relationships with environmental factors. Besides, according to linear regression analysis there was a closer correlation between chlorophyll-a and nutrients in four reservoirs than in 20 headwater streams. In four reservoirs, N limitation was preliminarily observed in autumn whereas P limitation exhibited in winter.

[Studies for killing the oceanic harmful organisms in ship's ballast water using hydroxyl radicals].

With a physical method of strong electric-field discharge, O2 in air and H2O at gas state are ionized and dissociated into a number of activated particles such as *OH, O2+, H2O+, etc, which are injected into a part of ballast water to form the dissolved *OH. High concentration of *OH solution was injected into the main pipe of discharge ballast water to effectively and fast kill the oceanic harmful organisms and bacteria in the course of conveying ship's ballast water. In the 10 t x h(-1) experimental system of ship's ballast water, the experiments were carried out for killing the plankton and bacteria using *OH radicals. The *OH concentration is 0.65 mg x L(-1) for 100% killing efficiency. At the same time, cell morphology changes of Chaetoceros muelleri and Nitzschia closterium were observed by a microscope. The cells of algae in their cellular wall, cellular membrane or cell protoplasm were greatly destroyed using *OH radicals.

[Rapid elimination of surface organophosphorous pollutants using hydroxyl radical].

According to the frequency of contamination accident for organic compounds in recent years, two kinds of organophosphorus pesticides dichlorvos and omethoate, as the simulated organic pollutants, were rapidly eliminated using spraying hydroxyl radical produced by strong electric-field ionization discharge method on an aluminium flat plate about 160 cm2. The high concentration aqueous *OH solution was produced from H2O(gas) and O2 with plasma reaction. In a condition, where pH is 6 and the initial densities of dichlorvos and omethoate on the simulation plane are both 60 microg x cm(-2), when the spray density of *OH reaches 3.9 microg x cm-2, removal efficiencies of dichlorvos and omethoate are 90%, and mineralization rates are 64% and 72%, respectively. The effect of pH for removal efficiency was also investigated. The results found that the removal efficiency of organophosphorus pollutants first decreased slowly and then increased fast with the increase of pH from 2 to 12 and the lowest removal rate appeared when pH close to neutral. The degradation rates of dichlorvos and omethoate both ascend by 21% and 26% respectively with pH 12 than that of pH 6. Four factors and three levels orthogonal test indicated that the degradation by *OH played a major role at the surface oxidation removal rapid of organophosphorus pollutants in a short period of time.

[Study on the degradation of phenol wastewater using hydroxyl radical produced by plasma and the course by UV spectra].

The phenol wastewater with high concentration was treated by hydroxyl radical produced by a strong ionization discharge plasma in the present article. Salicylic acid used as molecular probe to determine the concentration of hydroxyl radical. The phenol elimination efficiency of wastewater whose initial concentration was 1 21 5 mg x L(-1) could reach 99.11% when the concentration of hydroxyl radical was 1 037 mg x L(-1); while the initial concentration of 8 853 mg x L(-1) of phenol wastewater dropped to 6 250 mg x L(-1) under the same conditions, that is, 1 mg hydroxyl radicals could oxidize 2.5 mg of phenol. The smaller the initial phenol concentration, the higher the removal. However, the higher the initial concentration, the greater the absolute quantity of treatment. And the relation between the changes including pH value and the conductivity and the concentration of hydroxyl radical was stated and explained. With the concentration of hydroxyl radicals increasing, the pH value of wastewater changed from close to neutral to acidity gradually. The higher the concentration of hydroxyl radical, the stronger the acidity of wastewater. When continuing the increase in the concentration of hydroxyl radical, the change began to smooth. With the addition of hydroxyl radical, as is different from other phenomena, there was a tiny descending stage before ascending as shown on the conductivity curve, indicating that phenol had been oxidized and generated the organic acids continuously. Catechol, hydroquinone and benzoquinone are the important compounds of the intermediate products as shown by the analysis of UV spectra and chromatography. The final UV spectra curve indicated that there were little organic compounds containing conjugated structure in the treated wastewater.