[Decomposition of Myriophyllum aquaticum and the Associated Release of Nitrogen and Phosphorus].

Decomposition of wetland plants could release pollutants, which may affect the removal efficiency and effluent quality of constructed wetlands. The experimental decomposition test of Myriophyllum aquaticum was carried out for 60 d using nylon bags, and release characteristics of nitrogen and phosphorus during the decomposition process were studied. The results showed that the decomposition rate of M. aquaticum was fastest during the first 0-4 d, with a weight loss of 30%, while the degradation rate slowed gradually during the period 4-60 d, with weight loss of 31%. The fitting first-order kinetic decomposition rate constant was 0.0142 d-1, and the calculated time to degrade 50% of dry matter was 48.8 d. The water pH decreased rapidly from 7.60 to 5.63 during 0-4 d, stabilized during 4-32 d, and finally increased to 7.03 (which was close to the control sample without M. aquaticum). The dissolved oxygen concentration decreased rapidly from 6.30 mg·L-1 to 0.61 mg·L-1 during 0-4 d, and remained in an anaerobic state. The total nitrogen concentration in the water increased rapidly to 12.7 mg·L-1 within 2 h, gradually decreased to 5.80 mg·L-1 during 2 h-32 d, and then finally increased slightly. The phosphorus concentration increased rapidly to 18.4 mg·L-1 at the beginning of the experiment, and then gradually stabilized. The main forms of nitrogen and phosphorus released by M. aquaticum were organic nitrogen (accounting for 65.7%-94.7% of total nitrogen) and inorganic phosphorus (accounting for 61%-89% of total phosphorus), respectively. The total nitrogen content of M. aquaticum increased from 24.3 mg·g-1 to 60.5 mg·g-1 with increasing degradation time; the total phosphorus decreased initially from 6.09 mg·g-1 to 2.94 mg·g-1 and then remained constant. These trends may have been related to the fixation of nitrogen by attached microorganisms. Therefore, suitable harvesting and management strategies should be adopted for wetland plants to reduce secondary pollution.

[Removal Performance and Mechanism for Treating Phosphorus in Agricultural Wastewater by Three Adsorbents].

To screen the optimal absorbents for P removal from agricultural wastewater, the P adsorption capacity of bentonite, red soil, and slag was studied using synthetic wastewater. Combing the properties of three adsorbents measured by SEM, XDS, and BET methods, the isothermal adsorption, adsorption kinetics, and Ca2+ release capacity were analyzed to elucidate the mechanisms of P adsorption. The results showed that the P adsorption capacity of slag was higher than that of bentonite and red soil, and the Langmuir isotherm model was able to better fit the adsorption data (R2>0.96). The P theoretical saturation sorption capacity of slag was higher (16.87 mg·g-1) than that of bentonite (1.21 mg·g-1) and red soil (0.92 mg·g-1) (P<0.05). The results for adsorption kinetics indicated that slag rapidly removed 95.6% of P from 10 mg·L-1 solution, and the Elovich equation fit the data well (R2=0.812). The adsorption kinetics of P on bentonite and red soil were better described by the pseudo-second-order kinetic equation (R2=0.982 and 0.959, respectively). The Ca2+ release capacity of slag (10.46 mg·g-1) was significantly higher compared to bentonite (0.31 mg·g-1) and red soil (0.03 mg·g-1) (P<0.05). The P adsorption capacity of red soil was 0.26 mg·g-1 when the pH value was 3, and it decreased as the pH values increased. At the initial pH of 7.0, the P adsorption capacity of bentonite was about 0.01 mg·g-1, lower than 0.04 mg·g-1 at pH 3, and 0.05 mg·g-1 at pH 11. The initial pH value had little effect on the P adsorption capacity of slag. The P-loaded bentonite, red soil, and slag were effectively regenerated by using CaCl2 solution, and bentonite was easier to reuse compared to red soil and slag. The key factors affecting the P adsorption capacity of the three adsorbents were physical and chemical properties, such as crystal structure and the content of metal ions, Ca2+ release capacity, and initial pH. These findings demonstrated that slag was a better choice for P removal compared to bentonite and red soil and could be used as an effective P adsorbent for agricultural wastewater treatment.

[Photosynthetic mechanism of tea yield and quality affected by different habitats]. / ç”Ÿå¢ƒå¯¹èŒ¶å¶å“è´¨å’Œäº§é‡å½±å“çš„å ‰åˆç”Ÿç†æœºåˆ¶.

To understand photosynthetic mechanism of tea yield and quality, an experiment was conducted with four different typical habitats, including three intercropping patterns (S1:Osmanthus-Tea, S2:Michelia-Tea, S3:Osmanthus-Michelia-Tea) and a control (CK) at Changsha Agricutural Observation Station of Chinese Academy of Sciences. The photosynthetic physiological and ecological characteristics of tea yield and quality were examined. The results showed that the habitats S1, S2, S3 reduced the leaf temperature (TL), photosynthesis active radiation flux (PAR), net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (gs), as well as the tea polyphenol content. Habitats S1, S2, S3 significantly increased leaf relative humidity (RHS), total amino-acid content of tea, and the yield and quality of tea, with a pattern of S3>S1>S2>CK. The leaves in habitats S1 and S3 could be made into high-grade green tea and famous green tea respectively. Comprehensive indicators showed that habitat S3 is an ideal intercropping pattern for high quality and high yield of tea garden.

[Comparison Between Atmospheric Wet-only and Bulk Nitrogen Depositions at Two Sites in Subtropical China].

Atmospheric emissions of reactive nitrogen (N) species are at high levels and have caused high N deposition in China in recent years. In this study, atmospheric wet-only and bulk N depositions were monitored simultaneously in a two-year study at an agricultural site (HN) and a forest site (XS) in the Jinjing River catchment in Changsha County, Hunan Province in subtropical China. The differences in concentration and deposition of NH4+-N, NO3--N, DON, and TN between wet-only and bulk N depositions were compared, and the correlation between wet-only and bulk N depositions was analyzed, with the aim of estimating atmospheric wet N deposition based on bulk N deposition. During the monitoring period, NH4+-N was the dominant species in both wet-only and bulk deposition at the sampling sites. The average values of total N (TN) depositions for wet-only and bulk depositions at HN were 26.2 and 28.9 kg·(hm2·a)-1, respectively. The proportions of NH4+-N, NO3--N, and DON in TN in wet-only deposition were 49.7%, 31.3%, and 19.0%, respectively, while the proportions in the bulk deposition were 48.7%, 31.6%, and 19.7%, respectively. The average values of TN depositions for wet-only and bulk depositions at XS were 23.6 and 27.8 kg·(hm2·a)-1, respectively. The proportions of NH4+-N, NO3--N, and DON in TN in wet-only deposition were 53.9%, 34.78%, and 11.4%, respectively, while they were 49.6%, 31.6%, and 18.9%, respectively, for bulk deposition. The concentrations of N species in wet-only and bulk depositions were significantly and negatively correlated with precipitation, while the amount of N deposition was significantly and positively correlated with precipitation. The concentrations of N species in wet-only deposition had a significant linear correlation with those in the bulk deposition at the two sites (R2>0.82). According to the regression equation for wet-only and bulk N deposition at the monitoring sites, the proportions of NH4+-N, NO3--N, and TN in wet-only to bulk deposition were 0.875, 0.774, and 0.852, respectively, at HN and 0.859, 0.783, and 0.819, respectively, at XS. These values were mainly related to the amount of wet-only N deposition and the pollution level of atmospheric particulate N species at the monitoring sites. In the subtropical region of China, atmospheric wet N deposition can be overestimated by 10% to 18% when the atmospheric bulk N deposition is used to replace the wet N deposition. Based on the regression equation between atmospheric bulk N deposition and wet N deposition, the atmospheric wet N deposition can be estimated well using the atmospheric bulk N deposition data.

[Physiological Characteristics and Nitrogen and Phosphorus Uptake of Myriophyllum aquaticum Under High Ammonium Conditions].

Ammonium nitrogen (NH4+-N) at high concentrations is toxic to plants. In order to explore the NH4+-N tolerance of Myriophyllum aquaticum (M. aquaticum) and its ability of nitrogen (N) and phosphorus (P) uptake, this study used a nutrient solution with three NH4+-N levels (70, 210, 420 mg·L-1) to incubate M. aquaticum for 21 d. The characteristics of plant physiology and N and P uptake of M. aquaticum were measured. At NH4+-N of 70 mg·L-1, M. aquaticum grew healthily, and shoot height and biomass linearly increased with the increase incubation time. Relative shoot height and biomass of M. aquaticum were 40.56 cm and 17.82 g·hole-1 on day 21, respectively. Compared to the control with 70 mg·L-1 ammonium, malondialdehyde (MDA) content of M. aquaticum was significantly increased; chlorophyll and soluble sugar contents were also high at NH4+-N of 210 mg·L-1. M. aquaticum suffered from the NH4+-N stress. However, the stress of 210 mg·L-1 NH4+-N did not affect its normal growth and there was no significant difference in the relative growth rate of the shoot height and biomass compared with the control. At NH4+-N of 420 mg·L-1, MDA contents of M. aquaticum doubled and the shoot height and biomass growth rate were only 27.4% and 17.9% of those for 70 mg·L-1 NH4+-N, indicating that M. aquaticum was subjected to serious stress that caused unhealthy growth or even death. At three NH4+-N levels, the ranges of N and P content of M. aquaticum were 30.7-53.4 mg·g-1 and 3.8-7.7 mg·g-1, respectively, which indicated that M. aquaticum had a high uptake capacity of N and P. M. aquaticum is an ideal wetland plant that has a good application prospect for constructed wetlands in biological treatment of high-ammonia wastewater.

Anaerobic ammonium oxidation in sediments of surface flow constructed wetlands treating swine wastewater.

Anaerobic ammonium oxidation (anammox) was suggested to be involved in the nitrogen (N) removal process in constructed wetlands (CWs). Nevertheless, its occurrence and role in CWs treating swine wastewater have not been well evaluated yet. In this study, we investigated the diversity, activity, and role of anammox bacteria in sediments of mesoscale surface flow CWs (SFCWs) subjected to different N loads of swine wastewater. We found that anammox bacteria were abundant in SFCW sediments, as indicated by 7.5 × 105 to 3.5 × 106 copies of the marker hzsB gene per gram of dry soil. Based on stable isotope tracing, potential anammox rates ranged from 1.03 to 12.5 nmol N g-1 dry soil h-1, accounting for 8.63-57.1% of total N2 production. We estimated that a total N removal rate of 0.83-2.68 kg N year-1 was linked to the anammox process, representing ca. 10% of the N load. Phylogenetic analyses of 16S ribosomal RNA (rRNA) revealed the presence of multiple co-occurring anammox genera, including "Candidatus Brocadia" as the most common one, "Ca. Kuenenia," "Ca. Scalindua," and four novel unidentified clusters. Correlation analyses suggested that the activity and abundance of anammox bacteria were strongly related to sediments pH, NH4+-N, and NO2--N. In conclusion, our results confirmed the presence of diverse anammox bacteria and indicated that the anammox process could serve as a promising N removal pathway in the treatment of swine wastewater by SFCWs.

[Interception Effect of Vegetated Drainage Ditch on Nitrogen and Phosphorus from Drainage Ditches].

In order to effectively intercept and remove nitrogen (N) and phosphorus (P) from agricultural water, Canna glauca, Sparganium stoloniferum, Juncus effusus, Hydrocotyle vulgaris, and Myriophyllum elatinoides were planted in an agricultural drainage ditch. The temporal and spatial variations of the dissolved N and P concentrations were monitored during the whole experimental period. In addition, the contents of N and P in sediments and plants were compared among different plant plots. The results showed the effluent TN and TP concentrations in the vegetated drainage ditch were lower than the surface water environmental quality standards for class IV and class II . The average removal rates of TN and TP in water were 64.3% and 69.7%, respectively. The average sediment interceptions in 2010 and 2011 reached 40,400 kg, containing 52.4 kg of N and 21.4 kg of P. The amounts of sediment N and P in five plant plots exhibited the descending order: Canna glauca > Hydrocotyle vulgaris > Sparganium stoloniferum > Myriophyllum elatinoides > Juncus effuses. The accumulated N and P amounts assimilated by five kinds of aquatic plants reached 7.9 kg · a⁻¹ and 1.4 kg · a⁻¹, respectively. Compared with other plants, Canna glauca and Myriophyllu elatinoides had the highest ratios of above-ground and below-ground tissues, and the strongest absorption capacity of N and P was also observed in these two plants. Therefore, the vegetated drainage ditch has good interception effect on N and P pollutants. Furthermore, Canna glauca and Myriophyllum elatinoides can be considered as the optimal plants for N and P uptake.

[Study on phosphorus adsorption characteristic of sediments in an ecological ditch].

Sediments properties and phosphorus (P) adsorption capacities were compared among the samples of 0-5 cm and 5-15 cm layers from the ecological ditch vegetated with Cenetlla asiatica, Sparganium stoloniferum and a natural agricultural ditch with weeds. The results showed the 0-5 cm sediment vegetated with Cenetlla asiatica had higher concentrations of oxalate extracted Fe, Al and P than those vegetated with Sparganium stoloniferum or weeds. The parameters calculated from the Freudlich and Langmiur isotherms showed the equilibrium phosphate concentration (EPC0) ranged from 0.009 to 0.031 mg x L(-1). Cenetlla asiatica in the 0-5 cm layer had the maximum values of 352.2 L x kg(-1) and 562.7 mg x kg(-1) for Freundlich adsorption constant (K(f)) and Langmuir sorption maximum (S(max)), respectively, which proved it had the highest P adsorption capacity. The regression analysis showed P sorption parameters had significant relationship to oxalate-extracted Fe, clay content and DPS (P < 0.05). It was thus clear that aquatic plants influenced sediment properties and P adsorption capacity, and the practice of growing proper plants in ecological ditch could reduce the risk of P loss in non-point source pollution.