Geographic pattern of phytoplankton community and their drivers in lakes of middle and lower reaches of Yangtze River floodplain, China.

Disentangling the relative contributions of deterministic and stochastic processes was critical to compressive understanding of underlying mechanism governing geographic pattern and assembly of phytoplankton community, while it was seldom performed in connected lakes under human pressure. Here, we investigated phytoplankton community pattern in relation to environmental and spatial factors over 81 lakes located in the middle and lower reaches of Yangtze River (MLYR) floodplain, where many lakes suffered from eutrophication and cyanobacterial blooms. A majority of MLYR lakes had higher phytoplankton abundance surpassing 107 cells/L and were dominated by common bloom-forming cyanobacterial genera, including Pseudanabaena, Microcystis, Merismopedia, Dolichospermum, Limnothrix, and Raphidiopsis. Phytoplankton community exhibited a striking geographical pattern both for taxonomic and functional compositions, while functional groups were less sensitive, and dissimilarity in communities displayed no significant increases with increasing geographical distance. Further, species richness explained much higher percentage of community variations than species turnover, indicating a reduced effect of environmental filtering of phytoplankton species with tolerance to similar environments in connected MLYR lakes. Both deterministic and stochastic processes governed assembly and biogeographic of phytoplankton community. Variation partition analysis showed that spatial factors exhibited greater influence on phytoplankton community compared to environmental variables. The stronger influence of spatial factors was further demonstrated by Mantel test and neutral community model. These findings indicate that deterministic and stochastic processes exhibited similar biogeographic patterns for phytoplankton community in MLYR lakes, but stochastic process was overwhelmingly dominated. Moreover, a large proportion of unexplained variation implies that complex interactions exist to shape assembly mechanism of phytoplankton community in MLYR lakes.

[Denitrification Rates and nirS-type Denitrifying Bacteria Community Structure Characteristics of Bulk and Rhizosphere Soil in Spring and Summer in the Alpine Wetlands of the Qinghai-Tibet Plateau].

Denitrification is a key process in the nitrogen cycle of ecosystems. Most existing studies of nitrogen emissions and denitrifying bacterial communities are carried out in ecosystems with significant human interference, yet few focus in natural ecosystems with low human disturbance. Here, the denitrification rates and characteristics of nirS-type denitrifying bacterial communities in rhizosphere and bulk soils from alpine wetland plants at different altitudes(Tangke, Jiuzhi, Maduo, and Dari) and seasons(spring and summer) in the Yellow River source region of the Qinghai-Tibet Plateau were investigated. The 15N isotope tracer technique was used to estimate the denitrification rates, and high-throughput sequencing technology was used to determine the composition and relative abundance of nirS-type denitrifying bacterial communities. We also investigated the environmental factors(temperature and altitude) and soil physical and chemical properties(pH, soil organic carbon, ammonia, nitrate, and nitrite) controlling the denitrification and related microorganisms. The results show that the denitrification rates of alpine wetland soils ranged from 0.80 to 14.98 nmol·(g·h)-1, and the contribution to the total N2 production ranged from 11.23% to 71.16%. The soil samples from Tangke, Jiuzhi, and Dari showed higher denitrification rates in rhizosphere soils than the corresponding bulk soils(P<0.05). Proteobacteria was the most dominate denitrifying bacteria phylum. At the genus level, unclassified Proteobacteria(2.86%-29.41%) showed the highest relative abundance, indicating that unique unidentified bacteria may dominate denitrification in these wetland soils. The genera with the next highest relative abundances were Pseudomonas(2.45%-26.52%) and Cupriavidus(0%-34.14%). Distance-based redundancy analysis showed that the community structure of the nirS-type denitrifying bacteria was mainly affected by altitude, pH, and nitrite concentrations; Pearson correlation analysis showed that denitrification rates and the Shannon index are significantly negatively correlated with soil pH(P<0.05), and the relative abundance of the main denitrifying bacterial genera were influenced by temperature and soil pH(P<0.05). This study provides valuable insights for understanding the nitrogen cycle in the unique alpine wetlands of the Qinghai-Tibet Plateau.

[Research on the threshold of Chl-a in Lake Taihu based on microcystins].

Water samples were collected in Lake Taihu from June to October in 2013 in order to investigate the threshold of chlorophyll a (Chl-a). The concentrations of three microcystins isomers (MC-LR, MC-RR, MC-YR) were detected by means of solid phase extraction and high performance liquid chromatography-tandem mass spectrometry. The correlations between various MCs and eutrophication factors, for instance of total nitrogen (TN), total phosphorus (TP), chlorophyll a, permanganate index etc were analyzed. The threshold of Chl-a was studied based on the relationships between MC-LR, MCs and Chl-a. The results showed that Lake Taihu was severely polluted by MCs and its spatial distribution could be described as follows: the concentration in Meiliang Bay was the highest, followed by Gonghu Bay and Western Lake, and Lake Center; the least polluted areas were in Lake Xuhu and Southern Lake. The concentration of MC-LR was the highest among the 3 MCs. The correlation analysis indicated that MC-LR, MC-RR, MC-YR and MCs had very positive correlation with permanganate index, TN, TP and Chl-a (P < 0.01). The threshold value of Chl-a was 12.26 mg x m(-3) according to the standard thresholds of MC-LR and MCs in drinking water. The threshold value of Chl-a in Lake Taihu was very close to the standard in the State of North Carolina, which demonstrated that the threshold value provided in this study was reasonable.

[Measurement of dissolved organic nitrogen with nanofiltration pretreatment and its distribution characteristics in landscape water].

In this study, we present a nanofiltration (NF90, NF270) pretreatment to increase the precision of dissolved organic nitrogen (DON) measurements in water samples. The variations of DON measurements with and without NF pretreatment were investigated. And the effects on the removal of dissolved inorganic nitrogen (DIN) by NF90 and NF270 were compared. As shown in the results, the average removal rates reached 30.7%, 55.9% of NH4(+)-N, 50.0%, 73.1% of NO3(-) -N and 42.9%, 72.0% of NO2(-)-N for NF90 and NF270 pretreatment, respectively. NF270 was obviously more effective to remove the DIN species. Concentrations of DON measured using traditional methods varied from 0.09 to 0.46 mg x L(-1), with negative concentration (-0.08 mg x L(-1)) at site 2 and the DIN/TDN ratio ranged from 85.3% to 105%; while the concentrations of DON measurements varied from 0.03 to 0.58 mg x L(-1), and the DIN/TDN ratio ranged from 76.1% to 90.6% for NF90 pretreatment and varied from 0.10 to 0.59 mg x L(-1), and the DIN/TDN ratio ranged from 47.5% to 84.5% for NF270 pretreatment. The results indicated that nanofiltration pretreatment could effectively remove the DIN species, decrease the standard deviation of DON measurements and increase the precision of DON measurements. The distribution of DON in water samples of Beijing Olympic Forest Park was investigated. The results showed that there was seasonal variation in the concentrations of DON in landscape water from the Olympic Forest Park. And there was significant difference between the north and south part. The DON concentrations were less than 0.2 mg x L(-1) in November, March and May and higher in July in the north part, while the DON concentrations were lower in May and higher in November and March in the south part, ranging from 0.40-0.65 mg x L(-1).

[Characteristics of organic phosphorus fractions in different trophic sediments of lakes, China].

In this study, the characteristics of organic phosphorus fractions in sediments of seven lakes with different drainage basin feature, ecological structure, and polluted levels from different regions were investigated, and the relationships between organic phosphorus (Po), inorganic phosphorus (Pi) and bioavailable characters were also discussed. The difference of the related content of Po in different sediments indicated the discrepancy of phosphorus sources and biogeochemical cycles in different lakes. Organic matter (OM) was significantly correlated with Po (R2 = 0.80, p < 0.01), and except for Lake Qilu, OM was significantly correlated with labile Po, moderately labile Po and nonlabile Po in all studied sediments (R2 were 0.85, 0.52, 0.80 respectively, p < 0.01). The moderately labile Po and nonlabile Po were the main fraction of Po in all studied lakes, and the relative contributions to total Po were 15.12%-66.73% and 27.99%-77.72%, respectively. The mean proportion of labile Po was 6.1% in studied sediments. The rank order of Po fractions was residual Po > HCl-Po > fulvic acid-Po > humic acid-Po > NaHCO3-Po with mean relative proportion 8.3:3.1:2.2:1.8:1.0. Labile Po was significantly correlated with total phosphorus (TP), Pi , Po, NaHCO3-Pi and NaOH-Pi . Furthermore, Labile Po was also significantly correlated with T), Po and NaOH-Pi in all studied sediments, which suggested that labile Po was transformed into bioavailable phosphorus and the nonlabile Po may become a potential source of available phosphorus, although it was considered as highly resistant fraction.

[Rapid determination of chemical components in interstitial water of lake sediments using near-infrared spectroscopy].

The near infrared reflectance spectra (NIRS) of interstitial water samples of lake sediments in Chaohu lake were determined by near-infrared reflectance spectrometry. The respective near NIRS calibration models for predicting total nitrogen (TN), total organic carbon (TOC), phosphorus ( PO3(3-)), ammonia nitrogen(NH3-N) and silicate (SiO3-) were built using partial least squares (PLS) algorithm with two spectral pretreatment tools including, wavelet compression combining orthogonal signal correction (OSC) and orthogonal signal correction (OSC) combining wavelet compression. The correlation coefficients between measured values and predicted values in calibration set for TN, NH3-N, PO3(3-), TOC and SiO3(3-) were 0.975, 0.989, 0.937, 0.862 and 0.888, respectively. RMSEC (root mean square error of the calibration) for TN, NH3-N, PO3(3-), TOC and SiO3- were 0.353, 0.238, 0.031 3, 2.005 and 2.674 mg x L(-1), respectively. The correlation coefficients between measured values and predicted values in validation set for TN, NH3-N, PO3(3-), TOC and SiO3- were 0.912, 0.918, 0.773, 0.337 and 0. 856, respectively. RMSEP(root mean square error of the prediction)for TN, NH3-N, PO3(3-), TOC and SiO3- were 1.424, 0.945, 0.081, 7.866 and 4.273 mg x L(-1), respectively.

[Rapid determination of nutrient components in lake sediments using near infrared spectroscopy].

The lake sediments record important environmental evolution information of lake in recent 100 years. However, a rapid and precise combination analytical method measuring nutrient components in lake sediments can not be established. The near infrared reflectance spectra (NIRS) of sediment coring samples were determined by near-infrared reflectance spectrometry. The respective near NIRS calibration models for predicting total carbon (TC), total nitrogen (TN), total organic carbon (TOC) and total phosphorus (TP) were built first in China using partial least squares (PLS) algorithm with six spectral pretreatment tools including first-order derivate, wavelet denoise, orthogonal signal correction (OSC), wavelet denoise combining orthogonal signal correction (OSC), first-order derivate combining orthogonal signal correction (OSC), and orthogonal signal correction (OSC) combining wavelet compression. The results showed that although NIR all calibration models can not well predict TOC, the first-order derivate combining OSC spectral calibration model had a good prediction for TC and TN, and for TP OSC spectral calibration model was good. The correlation coefficients between measuring values and predicted values in validation set for TC, TN and TP were 0.76, 0.87 and 0.81, respectively. RMSEP (Root mean square error of the prediction) for TC, TN and TP were 0.13%, 0.0082% and 0.012%, respectively. The study has an important significance of driving the domestic researches on spectroscopy characteristic of lake sediments and establishment of rapid analytical technique determining nutrient components of lake sediments.

A hybrid inexact optimization approach for solid waste management in the city of Foshan, China.

An interval-parameter two-stage chance-constraint mixed integer linear programming (ITCMILP) model is provided for supporting long-term planning of solid waste management in the City of Foshan, China. The ITCMILP is formulated by integrating interval-parameter, two-stage, mixed integer, and chance-constraint programming methods into a general framework, and can thus deal with multiple uncertainties associated with model parameters, constraints and objectives. Three scenarios are examined, covering combinations of various system conditions and waste management policies. Scenario 1 is designed for comparison purposes. Scenarios 2 and 3 correspond to situations when the existing landfill's life is to be extended. The results demonstrate that the centralized composting and incinerating facilities are desired for treating the organic waste flows. The tradeoff among system cost, violation risk, and the related policy implications are also analyzed. The results obtained could help decision makers gain in-depth insights into the impact of uncertainties on long-term solid waste management in the City of Foshan.

[Phosphorus adsorption and regeneration of electric arc furnace steel slag as wetland medium].

The long-term phosphorus (P) adsorption and retention capacities of electric arc furnace (EAF) steel slag materials derived from one batch and a 278-d column experiments with a synthetic P solution were compared. The investigations of the regeneration of the P adsorption capacity by water level decrease was conducted. It was revealed column experiment on a long-term basis can determine P saturation of EAF accurately. And the results can be used for realistic estimations of constructed wetland systems (CWS) longevity. EAF slag showed a high afinity for P, reaching a saturation value of 1.65 g/kg. Regeneration experiment of the P adsorbing capacity by this material showed that, after 4 weeks of water level decrease, EAF steel slag was able to increase its initial P adsorption capacity to 2.65 g/kg. A sequential P fractionation experiment was performed to quantify the proportion of P bound to mineral compounds in EAF. From the most loosely bound to the most strongly bound P fraction, P1 was associated with resin extractable (13%), Fe extractable (0.5 mol/L Na2CO3, 39%), Al extractable (0.1 mol/L NaOH, 21%), Ca extractable (1 mol/L HCl, 13%), and Ca in a stable residual pool (concentrated hot HCl, 14%). X-ray fluorescence analyses of EAF steel slag chemical composition revealed that the continuous application of a P solution resulted in 300% and 170% increases in K2O and P2O5, respectively. Al2O3 and FeO increased by 8%, while the portion of CaO remained unchanged. The investigated properties (P retention potential, regeneration of P adsorption, P fractionation) provide useful data about the suitability of slag material as a media for longterm P removal and dry-wet operation can improve P retention capacity of EAF to prolong the longevity of full-scale CWS.

[Study on dynamic spectral characteristics of humic acid in municipal solid wastes composting].

In the present study, the compost consisted of residual MSW with metal, plastic and glass removed. The composting process was assisted using industrial technology. During the composting, humic acid (HA) was extracted and purified. The spectroscopic characteristics of the HA were determined by using UV, FTIR, and fluorescence spectroscopy. During the composting process, the HA fluorescence spectra exhibited a sharp reduction in relative fluorescence intensity at the short wavelength region, and the primary peak shifted from 335 nm at the initial stage to 458 nm at the final stage of composting, thereby approaching the main peak at 460-480 nm for HA in soil. The FTIR spectra exhibited a reduction in polysaccharides and aliphatic components, and a relative increase in aromatic components; while the HA UV spectra revealed an increase in conjugation and the degree of humification. However, compared with the E4 /E6 value and the spectroscopic characteristics of HA in soil, the HA in the MSW compost has a relatively low molecular weight, a simpler structure and a relatively low degree of aromatic condensation, which also implies that the HA in compost is highly active.

[Relationship between the nitrogen removal and oxygen demand in constructed wetlands].

A simplified model of sequential N transformations and sink was applied to investigate the relationship between the nitrogen removal and oxygen demand to verify the validity of full nitrification-denitrification mechanism in a newly-built multi-stages constructed wetlands. Average net rates of N mineralization ranged from 0.01 to 0.28 g x (m2 x d)(-1), nitrification from 0.50 to 1.54 g x (m2 x d)(-1), denitrification from 0.41 to 1.13 g x (m2 x d)(-1)(3.4% approximately 35.4% of measured N removal in different stage) and plant assimilation from 0.07 to 0.26 g x (m2 x d)(-1) in the five tanks. Nitrification and denitrification occurred concurrently with BOD removal, even in the first stage receiving the higher-strength wastewater. Surprisingly, net areal nitrification rates, was correlated with BOD removal rates positively. Nitrification rates were also correlated linearly with average NH4+-N concentrations in the cascade tanks. The nitrogenous oxygen demand (NOD) required to support full nitrification of ammonia and mineralized Org-N in the wetland was in the upper range of that expected to be able to be supplied through surface and plant-mediated oxygen transfer. Some potential alternative nitrogen removal pathways with reduced overall oxygen requirements that have relevance to constructed wetlands were discussed.