Linzhang Yang

Nitrogen Runoff and Leaching Losses During Rice-Wheat Rotations in Taihu Lake Region, China*

Abstract Although nitrogen (N) loss through runoff and leaching from croplands is suspected to contribute to the deterioration of surrounding water systems, there is no conclusive evidence for paddy soils to prove this hypothesis. In this study, field plot experiments were conducted to investigate N losses through runoff and leaching for two consecutive years with 3 N fertilization rates in rice (Oryza sativa L.)-wheat (Triticum aestivum L.) rotations in the Taihu Lake region, China. A water collection system was designed to collect runoff and leachates for both the rice and wheat seasons. Results showed that dissolved N (DN), rather than particulate N (PN), was the main form of N loss by runoff. The NO3−-N concentration in runoff was between 0.1 and 43.7 mg L−, whereas the NH4+-N concentration ranged from below detection limit to 8.5 mg L−. Total N (TN) loads by runoff were 1.0–17.9 and 5.2–38.6 kg ha− during rice and wheat seasons, respectively, and the main loss occurred at the early growing stage of the crops. Nitrogen concentrations in leachates during the rice seasons were below 1.0 mg L− and independent of the N application rate, whereas those during the wheat season increased to 8.2 mg L− and were affected by the fertilizer rate. Annual losses of TN through runoff and leaching were 13.7–48.1 kg ha-1 from the rice-wheat cropping system, accounting for 5.6%–8.3% of the total applied N. It was concluded that reduction in the N fertilization rate, especially when the crop was small in biomass, could lower the N pollution potential for water systems.

Mechanisms of removing pollutants from aqueous solutions by microorganisms and their aggregates: A review

With the publics enhanced awareness of eco-safety, environmentally benign measures based on microorganisms and microbial aggregates have become more accepted as methods of removing pollutants from aquatic systems. In this review, the application of microorganisms and microbial aggregates for removing pollutants from aqueous solutions is introduced and described based on mechanisms such as assimilation, adsorption, and biodegradation. The advantages of and future studies regarding the use of microorganisms and microbial aggregates to remove pollutants are discussed. Due to the limitation of a single microorganism species in adapting to heterogeneous conditions, this review demonstrates that the application of microbial aggregates consisting of multiple photoautotrophic and heterotrophic microorganisms, is a promising method of removing multiple pollutants from complex wastewaters and warrants further research.

Methylene blue adsorption onto swede rape straw (Brassica napus L.) modified by tartaric acid: Equilibrium, kinetic and adsorption mechanisms

The aim of this study was to develop a promising and competitive bioadsorbent with the abundant of source, low price and environmentally friendly characters to remove cationic dye from wastewater. The swede rape straw (Brassica napus L.) modified by tartaric acid (SRSTA) was prepared, characterized and used to remove methylene blue (MB) from aqueous solution at varied operational conditions (including MB initial concentrations, adsorbent dose, etc.). Results demonstrated that the equilibrium data was well fitted by Langmuir isotherm model. The maximum MB adsorption capacity of SRSTA was 246.4 mg g(-1), which was comparable to the results of some previous studied activated carbons. The higher dye adsorption capacity could be attributed to the presence of more functional groups such as carboxyl group on the surface of SRSTA. The adsorption mechanism was also discussed. The results indicate that SRSTA is a promising and valuable absorbent to remove methylene blue from wastewater.

Basic dye adsorption onto an agro-based waste material - Sesame hull (Sesamum indicum L.)

The aim of this project was to establish an economical and environmentally benign biotechnology for removing methylene blue (MB) from wastewater. The adsorption process of MB onto abandoned sesame hull (Sesamum indicum L.) (SH) was investigated in a batch system. The results showed that a wide range of pH (3.54-10.50) was favorable for the adsorption of MB onto SH. The Langmuir model displayed the best fit for the isothermal data. The exothermic adsorption process fits a pseudo-second-order kinetic model. The maximum monolayer adsorption capacity (359.88 mg g(-1)) was higher than most previously investigated low-cost bioadsorbents (e.g., peanut hull, wheat straw, etc.). This study indicated that sesame hull is a promising, unconventional, affordable and environmentally friendly bio-measure that is easily deployed for removing high levels of MB from wastewater.

Evaluating Adsorption and Biodegradation Mechanisms during the Removal of Microcystin-RR by Periphyton

Microcystin-RR (MCRR) is among the cyanobacterial toxins of significant concern due to their negative effects on water quality and human health. In this study, periphyton dominated by bacteria and diatoms was applied to remove MCRR from water. The maximum removal rate of MCRR by periphyton was observed in the first day (the latent adaptation period). Within this period, 85.2%, 73.3%, 83.5%, and 86.5% of the total MCRR removed (through adsorption and biodegradation) was by the adsorption of periphyton when the periphyton biomasses were 1.32 g, 3.96 g, 6.60 g, and 9.24 g, respectively. The amount of MCRR adsorbed increased with the increasing ratio of periphyton biomass to MCRR in solution. The adsorption process fitted well to the Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models, implying that the bioadsorption process has mechanistic relevance. The MCRR adsorption by periphyton is physical in nature and thermodynamically spontaneous. This study provided strong evidence that adsorption was the main mechanism for the removal of MCRR and other microcystins by periphyton and similar microbial aggregates in the latent adaptation period. Thereafter, biodegradation of periphyton dominated the toxin removal process. These results show that periphyton can be employed for an environmentally benign and effective solution for MCRR removal.

Allelopathic control of cyanobacterial blooms by periphyton biofilms

Periphyton biofilms are natural mixtures comprised of photoautotrophic and heterotrophic complex microorganisms. In this work, the inhibition effects of periphyton biofilms on cyanobacterial blooms were studied in pilot and field trials. Results show that the cyanobacterial species responsible for the blooms had an upper nutrient concentration threshold, below which it could not effectively compete with other organisms in the periphyton. The disappearance of the cyanobacterial blooms was due to the allelopathy between the cyanobacteria and periphyton biofilm. In particular, it was found that the periphyton biofilm could produce water-soluble allelochemicals such as indole and 3-oxo-α-ionone to significantly inhibit the growth of the cyanobacteria. These allelochemicals are able to damage the thylakoid membranes of the cyanobacteria, interrupt the electron transport in photosystem II, decrease effective quantum yields, and eventually lead to the failure of photosynthesis. A comprehensive discussion on the ecological consequences of these findings is also presented. This work demonstrates the potential of periphyton biofilm to be used as an environmentally friendly ecological engineering solution for (i) the control of cyanobacterial blooms and (ii) a transitional means for the construction of beneficial conditions for ecosystem restoration. In addition, this work provides significant insights into the competitive relationships between algae and biofilms.

Adsorption of dyestuff from aqueous solutions through oxalic acid-modified swede rape straw: Adsorption process and disposal methodology of depleted bioadsorbents

Swede rape straw (Brassica napus L.) was modified by oxalic acid under mild conditions producing an efficient dye adsorbent (SRSOA). This low-cost and environmental friendly bioadsorbent was characterized by various techniques and then applied to purify dye-contaminated aqueous solutions. Equilibrium study showed that the Langmuir model demonstrated the best fit to the equilibrium data and the methylene blue (MB) adsorption capacity calculated by this model was 432mgg(-1). The adsorption process and mechanism is also discussed. To properly deal with the dye-loaded bioadsorbents, the disposal methodology is discussed and a biochar based on depleted bioadsorbents was for the first time produced and examined. This method both solved the disposal problem of contaminant-loaded bioadsorbents and produced an useful adsorbent thereafter. The study indicates that SRSOA is a promising substitute for ACs in purifying dye-contaminated wastewater and that producing biochars from contaminant-loaded bioadsorbents maybe a feasible disposal method.

Anthropogenic Impact on Surface Water Quality in Taihu Lake Region, China

Abstract Taihu Lake region is one of the most industrialized areas in China, and the surface water is progressively susceptible to anthropogenic pollution. The physicochemical parameters of surface water quality were determined at 20 sampling sites in Taihu Lake region, China in spring, summer, autumn, and winter seasons of 2005–2006 to assess the effect of human activities on the surface water quality. Principal component analysis (PCA) and cluster analysis (CA) were used to identify characteristics of the water quality in the studied water bodies. PCA extracted the first three principal components (PCs), explaining 80.84% of the total variance of the raw data. Especially, PC1 (38.91%) was associated with NH 4 -N, total N, soluble reactive phosphorus, and total P. PC2 (22.70%) was characterized by NO 3 -N and temperature. PC3 (19.23%) was mainly associated with pH and dissolved organic carbon. CA showed that streams were influenced by urban residential subsistence and livestock farming contributed significantly to PC1 throughout the year. The streams influenced by farmland runoff contributed most to PC2 in spring and winter compared with other streams. PC3 was affected mainly by aquiculture in spring, rural residential subsistence in summer, and livestock farming in fall and winter seasons. Further analyses showed that farmlands contributed significantly to nitrogen pollution of Taihu Lake, while urban residential subsistence and livestock farming also polluted water quality of Taihu Lake in rainy season. The results would be helpful for the authorities to take sound actions for an effective management of water quality in Taihu Lake region.

Environmentally benign periphyton bioreactors for controlling cyanobacterial growth.

Microporous suspended bioreactors immobilized with periphytons were submerged between sediments and overlying water to control phosphorus release and cyanobacterial (Microcystis aeruginosa) growth. The results showed that the periphyton mainly consisted of bacteria and diatoms. The application of periphyton bioreactor decreased the levels of exchange phosphorus (Exch-P) in sediments from 1.69 to 0.49 mg g(-1) and total phosphorus (TP) from 0.75 to 0.30 mg L(-1). The significant reduction of the total dissolved phosphorus (TDP) content was not only beneficial for the decrease of the cyanobacterial growth, but also stimulates the periphyton to produce natural cyanobacterial inhibitors such as gallic acid and ethyl-2-methylacetoacetate. These synergistic effects led to the growth inhabitation of M. aeruginosa when the initial concentrations of M. aeruginosa were less than 119.3 microg L(-1). This study provides an environmentally-friendly and publically acceptable method of controlling bacterial blooms when compared to traditional addition of chemicals.

Land Use and Soil Organic Carbon in China’s Village Landscapes

Abstract Village landscapes, which integrate small-scale agriculture with housing, forestry, and a host of other land use practices, cover more than 2 million square kilometers across China. Village lands tend to be managed at very fine spatial scales (≤ 30 m), with managers both adapting their practices to existing variation in soils and terrain (e.g., fertile plains vs. infertile slopes) and also altering soil fertility and even terrain by terracing, irrigation, fertilizing, and other land use practices. Relationships between fine-scale land management patterns and soil organic carbon (SOC) in the top 30 cm of village soils were studied by sampling soils within fine-scale landscape features using a regionally weighted landscape sampling design across five environmentally distinct sites in China. SOC stocks across Chinas village regions (5 Pg C in the top 30 cm of 2 × 106 km2) represent roughly 4% of the total SOC stocks in global croplands. Although macroclimate varied from temperate to tropical in this study, SOC density did not vary significantly with climate, though it was negatively correlated with regional mean elevation. The highest SOC densities within landscapes were found in agricultural lands, especially paddy, the lowest SOC densities were found in nonproductive lands, and forest lands tended toward moderate SOC densities. Due to the high SOC densities of agricultural lands and their predominance in village landscapes, most village SOC was found in agricultural land, except in the tropical hilly region, where forestry accounted for about 45% of the SOC stocks. A surprisingly large portion of village SOC was associated with built structures and with the disturbed lands surrounding these structures, ranging from > 18% in the North China Plain to about 9% in the tropical hilly region. These results confirmed that local land use practices, combined with local and regional variation in terrain, were associated with most of the SOC variation within and across Chinas village landscapes and may be an important cause of regional variation in SOC.