Fertilizer additions (N-rate) have increased surface runoff of nitrogen (R-TN) from croplands, which is eventually transferred to rivers. This pollution further contributes to ecological degradation and and health risks of drinking waters. Despite this recognition, little is known about the spatial pattern of R-TN from croplands and the drivers of its variation. On the basis of 210 site-years of measurements at 41 sites in Chinese paddy fields, we examined the nonlinear response of R-TN to N-rate and the effects of environmental factors on R-TN, R-TN per unit nitrogen fertilizer additions (RR), and background N runoff (R-0). The results show that (i) R-TN-N-rate relationship deviates from linearity and the parameters vary by climate and soil attributes; (ii) Observed variation of R-TN is better explained by precipitation and clay content (48%) than N-rate and its interaction (17%); (iii) The R-TN is 1.09 +/- 0.36 Tg N yr(-1) for Chinese paddy fields in 2008, to which R-0 contributes more than 50%, and the corresponding average RR is 6.8 +/- 1.7% (1 - sigma), 30% lower than the linear model. This study therefore suggests that the future policies for agricultural N runoff need to account for local environmental conditions rather than solely attempting to reduce N fertilizer applications. (C) 2016 Elsevier B.V. All rights reserved.
As China’s largest CO 2 emission source, power sector has a large scale of power exchange, which results in the issue of interprovincial CO 2 emissions transfer embodied in power transmission. Based on interprovincial detailed power exchange data, a bottom-up method which takes into account the fuel mix of exported electricity is developed to calculate provincial CO 2 emissions embodied in power transmission. Provincial CO 2 emissions from power sector associated in consumption perspective in 2007, 2010 and 2012 are analyzed and compared with those in production based perspective. The calculation shows that total CO 2 emissions embodied in interprovincial power exchange is 532 Tg in 2012, accounting for 14% of total emissions from power sector. The embodied emissions have risen by 94% between 2007 and 2012. The general transfer pathway of embodied CO 2 emissions is from eastern China to western China with long-range power transmission. The disparities between consumption and production based CO 2 emissions are significant in some provinces. The production based CO 2 emissions from power sector of Inner Mongolia are 195 Tg higher than those of the consumption based, while the consumption based emissions of Beijing are 484% larger than those of the production based. This study also reveals an increasing trend of CO 2 emissions from both production and consumption principles for most provinces over the period 2007–2012.
Various multivariate methods were used to analyze datasets of river water quality for 11 variables measured at 20 different sites surrounding Lake Taihu from 2006 to 2010 (13,200 observations), to determine temporal and spatial variations in river water quality and to identify potential pollution sources. Hierarchical cluster analysis (CA) grouped the 12 months into two periods (May to November, December to the next April) and the 20 sampling sites into two groups (A and B) based on similarities in river water quality characteristics. Discriminant analysis (DA) was important in data reduction because it used only three variables (water temperature, dissolved oxygen (DO) and five-day biochemical oxygen demand (BOD5)) to correctly assign about 94% of the cases and five variables (petroleum, volatile phenol, dissolved oxygen, ammonium nitrogen and total phosphorus) to correctly assign >88.6% of the cases. In addition, principal component analysis (PCA) identified four potential pollution sources for Clusters A and B: industrial source (chemical-related, petroleum-related or N-related), domestic source, combination of point and non-point sources and natural source. The Cluster A area received more industrial and domestic pollution-related agricultural runoff, whereas Cluster B was mainly influenced by the combination of point and non-point sources. The results imply that comprehensive analysis by using multiple methods could be more effective for facilitating effective management for the Lake Taihu Watershed in the future.
Both planktonic and sediment bacterial assemblages are the important components of freshwater lake ecosystems. However, their spatiotemporal shift and the driving forces remain still elusive. Eutrotrophic Dianchi Lake and mesotrophic Erhai Lake are the largest two freshwater lakes on the Yunnan Plateau (southwestern China). The present study investigated the spatiotemporal shift in both planktonic and sediment bacterial populations in these two plateau freshwater lakes at different trophic status. For either lake, both water and sediment samples were collected from six sampling locations in spring and summer. Bacterioplankton community abundance in Dianchi Lake generally far outnumbered that in Erhai Lake. Sediment bacterial communities in Erhai Lake were found to have higher richness and diversity than those in Dianchi Lake. Sediments had higher bacterial community richness and diversity than waters. The change patterns for both planktonic and sediment bacterial communities were lake-specific and season-specific. Either planktonic or sediment bacterial community structure showed a distinct difference between in Dianchi Lake and in Erhai Lake, and an evident structure difference was also found between planktonic and sediment bacterial communities in either of these two lakes. Planktonic bacterial communities in both Dianchi Lake and Erhai Lake mainly included Proteobacteria (mainly Alpha-, Beta-, and Gammaproteobacteria), Bacteroidetes, Actinobacteria, Cyanobacteria, and Firmicutes, while sediment bacterial communities were mainly represented by Proteobacteria (mainly Beta- and Deltaproteobacteria), Bacteroidetes, Chlorobi, Nitrospirae, Acidobacteria, and Chloroflexi. Trophic status could play important roles in shaping both planktonic and sediment bacterial communities in freshwater lakes.
Aerobic methane-oxidizing bacteria (MOB) play a crucial role in mitigating the methane emission from lake ecosystems to the atmosphere. However, the distribution of methanotrophic community in shallow and eutrophic lake and its influential factors remain essentially unclear. The present study investigated sediment methanotrophic microorganisms at different sites in eutrophic freshwater Dianchi Lake (China) in two different seasons. The abundance, diversity, and structure of sediment methanotrophic community showed a profound spatial and seasonal variation. The pmoA gene copy number in lake sediments ranged from 8.71 +/- 0.49 x 10(4) to 2.09 +/- 0.03 x 10(7) copies per gram of dry sediment. Sediment methanotrophic communities were composed of Methylococcus and Methylobacter (type I methanotrophs) and Methylosinus (type II methanotrophs), while type I MOB usually outnumbered type II MOB. Moreover, ammonia nitrogen was found to be a potential determinant of methanotrophic community structure in Dianchi Lake.
Ordered two-dimensional arrays of silver adatoms with tunable metal atom density stabilized by 1,4-diethynyl-2,5-dimethylbenzene, a terminal alkyne, were prepared on Ag(111) and scrutinized by scanning tunneling microscopy and density functional theory calculations. Stabilization of the adatom arrays was attributed to the substrate-mediated electron localizations of the Ag adatom and terminal alkynyl in the molecule.
The nanostructures of a series of conjugated oligo(p-phenylene-ethynylene)s (OPE) adsorbed on a surface were thoroughly studied using scanning tunneling microscopy (STM). These oligomers have different backbone lengths and side chains. As a result, various nanostructures displaying periodic linear patterns at a single molecule level were obtained. Based on careful measurements on the STM images in combination with density functional theory (DFT) calculations, it could be found that the vertical and parallel distances between neighboring oligomers were responsible for the specific arrangement of the backbone and side chains. The results showed that these molecular designs strongly affect their self-assembled structure, which is important to clarify the structure-property relationship in the nanoscience field.