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To study the effect of biomass particle size on the rate and ability of phosphorus removal from aqueous solution by MgO-loaded Phragmites australis biochar (MBC), MBC was prepared using 0.0-0.5, 1.0-2.0, and 6.0-8.0 mm Phragmites australis particles as the feedstock and MgCl 2 as the modification material. The MBC was characterized using FTIR, XRD, and SEM techniques. Kinetic and isotherm experiments of phosphate (PO 4 3- -P) adsorption from aqueous solution by the MBC were conducted, and the experimental data were fitted with various kinetic and isotherm models. The results showed that the adsorption rate of PO 4 3- -P by the MBC increased with the increase in biomass particle size. The amount of PO 4 3- -P adsorbed by the MBC prepared from 0.0-0.5, 1.0-2.0, and 6.0-8.0 mm particles reached 15.4%, 25.8%, and 80.8%, respectively, within 2 h. The biomass particle size did not affect the maximum PO 4 3- -P adsorption capacity (249.0-254.7 mg·g -1 ) of the MBC. MBC prepared from the 6-8 mm particles retained the complete cell wall structure of the Phragmites australis , and a large number of micropores and mesopores were generated during pyrolysis, thereby forming a hierarchical, regular, and well-connected pore structure. MBC prepared from the 0.0-0.5 mm and 1.0-2.0 mm particles had inferior pore structures with inferior pore connectivity, which affected the diffusion rate of PO 4 3- ions inside the MBC and limited the PO 4 3- -P adsorption rate. Therefore, when using waste Phragmites australis harvested from a constructed wetland to produce MBC and remove phosphorus from water, the Phragmites australis should be crushed into 6-8 mm particles. Over-crushing deteriorates the pore structure of the produced MBC and reduces the removal rate of phosphorus by the MBC.

When low-concentration rural sewage is treated biologically, the effluent total nitrogen (TN) concentration often does not meet the discharge limit because of its low carbon-to-nitrogen ratio (C/N). To solve this problem, a laboratory-scale anoxic/oxic (A/O) biofilter packed with Arundo donax and activated carbon as the anoxic and aerobic column fillers (No. 2) was operated for treatment of simulated rural sewage and advanced nitrogen removal, while an ordinary gravel-packing A/O biofilter (No. 1) was set up as the control group. The results were as follows. When the influent chemical oxygen demand (COD), ammonia nitrogen (NH 4 + -N), and TN concentrations were (79.47±14.21), (34.49±2.08), and (34.73±3.87) mg·L -1 , respectively, the No. 1 and No. 2 reactors achieved removal efficiencies of (88.00±7.00)% and (89.00±10.00)%, (90.00±2.00)% and (97.00±7.00)%, and (37±15)% and (68±7)%, respectively. The results revealed that using Arundo donax and activated carbon new fillers could significantly enhance NH 4 + -N and TN removal. High-throughput sequencing results indicated that the microorganisms involved in the nitrification process in the No. 1 reactor mainly belong to Proteobacteria, whereas those in the No. 2 reactor belong to Proteobacteria and Nitrospirae. In addition, the main denitrification bacterial phyla in the anoxic column of the No. 1 reactor were Chloroflexi, Proteobacteria, Bacteroidetes, and Planctomycetes, whereas those in the anoxic column of the No. 2 reactor were primarily Bacteroidetes, Proteobacteria, Firmicutes, and Patescibacteria. Quantitative real time polymerase chain reaction (qPCR) results showed that the microbial nitrification ( amoA and Nitrospira 16S rDNA), denitrification ( narG , nosZ , nirS , and nirK ), and anaerobic ammonium oxidation functional genes (ANAMMOX) in the No. 2 reactor were significantly higher than those in the No. 1 reactor. All the genes, except for the narG and nosZ genes, had one to two orders of magnitude of improvement in the No. 2 reactor compared to those in the No. 1 reactor.

The effect of ammonia-nitrogen in water on phosphorus removal by magnesium modified biochar (MBC) was developed to increase the utilization of wetland plants. The crystal structures were measured by X-ray powder diffraction (XRD). MBC was prepared using reed as the biomass feedstock, which was modified with magnesium chloride. The raw biochar (BC) was prepared as a control. The removal of phosphate from solution using four different methods, i.e. MBC, BC, BC, and MgCl 2 solutions (BC+Mg 2+ ) and MgCl 2 solutions (Mg 2+ ), under different nitrogen to phosphorus molar ratios and initial phosphorus concentrations was investigated in batch experiments. The results demonstrated that the phosphorus removal efficiency of the four treatment methods, which followed the order of MBC>>BC+Mg 2+ ≈Mg 2+ >BC. NH 4 + in the solution, promoted phosphorus removal by MBC. In addition, the larger the ratio of nitrogen to phosphorus and the higher the initial phosphorus concentration, the stronger the phosphorus removal capacity of MBC was. In the three treatments with MBC, BC+Mg 2+ , and Mg 2+ , the XRD analysis showed that NH 4 + reacted with Mg 2+ and PO 4 3- in the solution to form MgNH 4 PO 4 ·6H 2 O at N:P=5 or 10, promoting the removal of phosphorus. For recycling purposes, waste biomass from constructed wetlands could be used to produce MBC and treat polluted water rich in ammonium and phosphate. Moreover, the ammonium-nitrogen promotes the phosphate removal by MBC. The results from this study provide a new theoretical basis and data support for the treatment of water eutrophication.

The inherent relationship between land use pattern and inflow water quality is essential for nonpoint source pollution study. Response of inflow river quality to land use pattern in Northern part of Lake Erhai Watershed was analyzed in aspects of land use composition and configuration using spatial analysis and statistical analysis methods. The results indicated that as land use composition indexes, average slope and vegetation area percentage had significant relationship with TN and TP of inflow rivers. As land use configuration indexes, patch density, patch density of agriculture land and landscape shape index of water had significant relationship with TP and NH 4 + -N of inflow rivers. Response of inflow river quality to land use pattern was better at class level than at landscape level. Water quality response indicators were TP in rainy season and NH 4 + -N in dry season, of which regression adjustment coefficient R 2 was 0.761 and 0.978, respectively. Response of inflow river quality to land use pattern was better in dry season than in rainy season, and the water quality response indicators were TN, TP and NH 4 + -N. Improving vegetation coverage and agriculture land intensive degree and avoiding human disturb to natural water area especially in dry season were suggested in nonpoint source pollution control of northern watershed of Lake Erhai Watershed. Later research on relationship between land use configuration and inflow river quality should better be at class level.

We studied the relationship between agricultural land and water quality of inflow river in Erhai Lake Basin, by means of spatial and statistical analysis, from the perspective of comprehensive agricultural land and the area percentage of different types of agricultural land. The obtained results indicated that inflow water quality showed a significant spatial difference, the inflow TP pollution in the western inflow rivers of Erhai Basin was serious. The major pollution indicators in the northern and southern inflow rivers (except for D3) were organic matter and nitrogen. The area percentage of agricultural land had a significantly indicative effect on the water quality of inflow river. The area percentage of comprehensive agricultural land negatively correlated with permanganate index, NH4(+) -N, TN and TP contents in wet season, the correlation coefficients were - 0.859, - 0.565, - 0.693, - 0.181. It negatively correlated with permanganate index and NH4(+) -N content in dry season, the correlation coefficients were - 0.384, - 0.328. It had positive relationships with and TN, TP content in dry season, the correlation coefficients were 0.221 and 0.146. The area percentage of different types of agricultural land had an obviously indicative effect on the inflow water quality. Farmland positively correlated with TN and TP contents both in wet and dry seasons. The correlation coefficients between farmland and TN, TP were 0.252, 0.581 in rainy season and were 0.149, 0.511 in dry season. It had positive and negative relationships with permanganate index, NH4(+) -N content in wet season and dry season, respectively. The correlation coefficients between farmland and permanganate index, NH4(+) -N were 0.388, 0.053 in rainy season and were -0.137, -0.147 in dry season. Forest land exhibited an opposite performance to that of farmland. The correlation coefficients between forest land and TN, TP, permanganate index, NH4(+) -N were - 0.526, - 0.275, - 0.469, -0.155 in rainy season and were -0.012, -0.100, 0.282, 0.151 in dry season. Fishpond had a weakly indicative effect on TN and TP contents. Meadowland and orchard had a similar performance with that of farmland in wet season, but were opposite to that of farmland in dry season. Therefore, management for farmland, meadowland and orchard in the north and south during wet season should be emphasized during the agricultural nonpoint source control in Erhai Lake Basin.

Sixty topsoil composite samples (0-20 cm) have been collected in 3 258 km2 surrounding area of Chaohu Lake. The concentrations of organic material (OM), total nitrogen (TN) and total phosphorus (TP) were determined, and their spatial distribution characteristics were studied by geo-statistics software named GS 7.0 +, Surfer 8.0 and Mapinfo 8.5. The correlations of these 3 kinds of nutrient were analyzed by SPSS 17.0 at the same time. Results showed that the average omega (OM), omega (TN) and omega (TP) in topsoil around Chaohu Lake were 19 500 mg x kg(-1), 1 027 mg x kg(-1) and 483 mg x kg(-1). The omega (OM) and omega (TN) in topsoil in the east of Chaohu Lake were both higher than those in the west of the lake, while omega (TP) was reverse. The omega (TP) in topsoil around Hangbu-Fengle River and Baishitianhe River which located in the southwest of Chaohu Lake was higher than that in any other rivers and with the serious soil erosion. Hence, to control the TP released by nonpoint pollution, attention should be paid on these two rivers. Furthermore, the semivariogram models of omega (OM), omega (TN) and omega (TP) followed linear model and they all had a strong spatial autocorrelation, the ratios of nugget to sill were 0.015, 0.202 and 0.128, respectively. The characteristics of spatial distribution of omega (OM), omega (TN) and omega (TP) were similar. Moreover, the Pearson correlation analysis showed that omega (OM), omega (TN) and omega (TP) were significantly correlated. The omega (TN) and omega (TP) can be calculated by two recommended formulas, and the results were acceptable in daily non-pint pollution management.

Batch culture experiments were used to study the effect of leachate from sediment of Yanghe reservoir on the growth of Microcystis and Anabaena isolated from Yanghe reservoir. The results showed that the growth of Microcystis was significantly inhibited when the addition of anaerobic leachate from sediment in M11 culture medium was high (> or = 20% V/V). The maximum biomass of Microcystis was lower than that grown in pure M11 culture medium. But there was an obvious promotion on the growth of Anabaena when anaerobic leachate from sediment was added. The growth rate of Anabaena increased 36.6%, 47.2% and 36.0%, respectively, compared to M11 culture medium when adding 2%, 20% and 50% (V/V) anaerobic leachate. Compared to adding anaerobic leachate, aerobic leachate had no influence on the growth of Microcystis, while the growth rate of Anabaena was promoted by aerobic leachate. The growth rate of Anabaena increased 37.2% compared with M11 when adding 20% (V/V) of aerobic leachate. But after addition of Fe-citrate to the mixed culture medium (50% M11 culture medium +50% anaerobic leachate), the maximum biomass of Microcystis significantly increased. The results suggest that high organic matter concentration decreases iron availability for Microcystis.

The dominance of gas-vacuolated cyanobacteria is often attributed to their buoyancy and buoyancy in response to environmental conditions. Lake simulator experiments (4 m high and 1 m diameter) and pyrex bottle experiments (10 L) were applied to investigate the buoyancy regulation and vertical distribution of Planktothrix mougeotii in eutrophic lakes at 28 degrees C. During light phase, the filaments stratify in the 2-3 m after 8 h light exposure and the biomass at the layer attach maximum after 12 h light exposure. During dark phase, the filaments are tent to migrate to the surface. 20% of filaments migrate to the surface after 12 h and 50% of filaments migrate to the surface after 48 h. The buoyancy regulation under light condition is that filaments stratify in 10 micromol x (m2 x s)(-1) layers, and the filaments above the layer sink down, while those suspended below the layer float up. The amplitude of diel changes in buoyancy is related to photon irradiance, and the change of buoyancy in light [100 micromol x (m2 x s)(-1)]/ dark is higher than its in light [25 micromol x (m2 x s)(-1)]/ dark. Carbohydrate ballasting may be the only mechanism for buoyancy changes in Planktothrix mougeotii filaments during the period.

Two methods including filtration (vacuity is 0.02 MPa) and centrifugation ( < 500 r/min) were applied to concentrate algal biomass, and capillary compression tube and the concentrated algae suspensions, critical pressure distribution of gas vesicles in six cyanobacteria were also investigated. The results showed that unicellular Microcystis aeruginosa cells couldn't be concentrated effectively by filtration or centrifugation, but colony of Microcystis wesenbergii and Microcystis flosaquae, and filament of Planktothrix mougeotii could be concentrated by centrifugation and filtration respectively. Both filtration and centrifugation had a negligibly impact on gas vesicles content of cells, and the loss of gas vesicles was lower than 7%. The mean critical pressure values of five strains Microcystis were very close, which ranged from 0.64 to 0.67 MPa, and the mean critical pressure of P. mougeotii was 0.715 MPa. All of the six cyanobacteria were isolated from three shallow lakes, and their mean critical pressure values were lower than those cyanobacteria that inhabit in deep lakes or reservoirs. At the same condition of illumination density and temperature, turgor pressures of two unicellular Microcystis were higher than those of colonial Microcystis.

Not only population density of phytoplankton but also its community structure were influenced by iron limitation. The growth and competition of a cyanobacterium Microcystis aeruginosa and a green alga Scenedesmus quadricauda at different iron and EDTA concentrations were investigated using batch cultures. The results showed that the growth of M. aeruginosa was significantly inhibited whereas S. quadricauda wasn't when EDTA at high concentrations (> or = 13.5 micromol/L), and consequently, it favored the dominance of S. quadricauda. Moreover, increasing iron concentration from 3 micromol/L to 18 micromol/L could greatly alleviate the growth inhibition of M. aeruginosa while increasing concentration of other microelements e.g. B, Mn, Zn, Cu, Mo didn't. These results suggest that high EDTA concentration decreases iron availability for M. aeruginosa, but not for S. quadricauda. The reason that the two algae respond to high EDTA concentrations differently is that their adsorption strategies for iron should be different.