[Nitrogen and Phosphorous Adsorption Characteristics of Suspended Solids Input into a Drinking Water Reservoir via Typhoon Heavy Rainfall].

During typhoon "Mujigae" in October 2015, water samples and surface sediments were collected from Gaozhou Reservoir, a drinking water reservoir, for simulation and analysis of the kinetics of suspended solids adsorption to nitrogen and phosphorus and the adsorption isotherms of suspended solids with different particle sizes and different concentrations. The results showed no obvious nitrogen adsorption of suspended solids of Gaozhou Reservoir. However, the adsorption effect to phosphorus by suspended solids was significant and the equilibrium time of phosphorus adsorption was 10 hours. The adsorption capacity of phosphorus increased with the decrease of sediment particle size when particle sizes were less than 0.25 mm, whereas it increased with the increase of suspended solids concentration when the concentration was in the range of 0.2-2.0 kg·m-3. The adsorption isotherm of suspended solids to phosphorus conformed to the Langmuir and Freundlich models, and the maximum adsorption capacity increased with the decrease of suspended solids particle sizes, which increased with the increase of suspended solids concentrations. The maximum adsorption capacity of suspended solids to phosphorus was 0.073-1.776 mg·g-1. These results indicated that the increase of suspended solids concentration due to the heavy rainfall of the typhoon promoted the adsorption of suspended solids to phosphorus, which reduced eutrophication in Gaozhou Reservoir.

[Eutrophication and Characteristics of Cyanobacteria Bloom in the Summer in Guishi Reservoir].

Large-scale cyanobacteria bloom occurred in the summer of 2014 in the Guishi Reservoir that is an important drinking water source for Hezhou City. The dynamic change regularity, external pollution sources, and the phytoplankton community characteristics during the bloom were investigated to evaluate the eutrophication in the reservoir and to present effective prevention and control measures. The results showed that nitrogen and phosphorus concentrations increased year by year; water quality on some sites has been out of class Ⅱ of national water quality standards; and the main pollution source was the agricultural non-point sources. Phytoplankton cell density was in the range of 8.60×106-5.36×108 cells·L-1 and chlorophyll a concentrations reached 74.48 µg·L-1 during the bloom. The dominant species was Microcystis wesenbergii whose density reached 5.36×108 cells·L-1. The cell density decreased over time and concentrated on the surface and at the depth of 2 m underwater. The total phytoplankton cell density was strongly correlated to total phosphorus, total nitrogen, nitrate nitrogen, and the permanganate index, and was inversely correlated to transparency. The water in the Guishi Reservoir was not polluted by microcystic toxins. Moreover, Guishi Reservoir is in a meso-eutrophic state; therefore, the prevention and control of the cyanobacteria bloom should focus on weather conditions and on reducing the input of nitrogen and phosphorus to keep the nutrient levels low.

[Phytoplankton community structure and eutrophication risk assessment of Beijiang River].

To study the distribution of phytoplankton and water quality of Beijiang River, the community structure of phytoplankton was investigated and analyzed in wet and dry seasons. The results showed that a total of 74 species belonging to six phyla, 29 family and 48 genera of phytoplankton were identified, including 58 species of five phyla, 23 family and 41 genera in wet season and 59 species of six phyla, 26 family and 40 genera in dry season. Phytoplankton community structure in Beijiang River was represented by Bacillariophyta, Chlorophyta and Cyanophyta. Bacillariophyta dominanted the phytoplankton, and the dominant species were Aulacoseira granulate, Fragilaria virescens, Surirella biseriata, Nitzschia amphibia, Navicula simplex, Cyclotella meneghiniana, Synedra ulna, Gomphonema angustatum and Cymbella tumida. There was little difference in phytoplankton density between both seasons with the mean values being 3.54 x 10(5) and 4.87 x 10(5) cells L(-1) in dry and wet seasons, respectively. Based on the RDA results, DO, permanganate index, nitrogen and phosphorus were the important environmental factors affecting the distribution of phytoplankton in Beijiang River. The water quality of Beijiang River was classified as oligo-mesotrophic level even if this river was subjected to nitrogen and phosphorus pollution mainly from agricultural non-point source.