Coupling coordination and interaction between urbanization and eco-environment in Cheng-Yu urban agglomeration, China.

We built a comprehensive evaluation index system of urbanization in Chengdu-Chongqing (Cheng-Yu) urban agglomeration from four subsystems, including the economic, social, ecological, and urban and rural coordination. The comprehensive evaluation index system of eco-environment was constructed by combining ecological environment carrying capacity and ecological flexibi-lity. The coupling coordination degree model was applied to quantify the coupling coordination degree between urbanization and eco-environment in the prefecture-level cities of Cheng-Yu urban agglo-meration from 2005 to 2018. With GIS spatial analysis, phenomenon analysis and Tapio model, we analyzed the interaction type, evolution path and path of decoupling between urbanization and eco-environment in the prefecture-level cities of Cheng-Yu urban agglomeration. The results showed that the urbanization quality of Cheng-Yu urban agglomeration showed a trend of fluctuation and rise during the study period. Both Chengdu and Chongqing as high value areas showed "double-core" radia-ting to the surrounding areas. The eco-environment quality showed a slowly rising trend. The spatial pattern was a " U " shape with a north opening, high perimeter and low center. The degree of coupling coordination between the urbanization system and the eco-environment system was rising, with a spatial pattern of low in the middle and high in the east and west. The overall level of coupling coordination was relatively high. The type of coupling coordination degree was gradually evolving from near-disorder and reluctant coordination to moderate coordination. The evolution paths of urbanization and eco-environmental interaction were divided into two categories: stable and changing. The stable type included 20 cities in 5 subcategories, with Chengdu, Deyang, Mianyang, etc. being always well-coordination. The change type included 16 cities in 9 subcategories. The coordination degree of Chongqing main urban area, Tongliang and most other cities was improved, showing "rising" development. Hechuan, Zigong and a few other cities showed "sinking" development. The growth rates of both ecological environment and urbanization were positive. The decoupling state of urbanization and ecological environment was mainly characterized by weak decoupling and expansion connection.

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Unreasonable application of nitrogen fertilizer to cropland decreases nitrogen use efficiency of crop. A large amount of nitrogen loss to environment through runoff, leaching, ammonia volati-lization, nitrification-denitrification, etc., causes water and atmospheric pollution, poses serious environmental problems and threatens human health. The type of nitrogen fertilizer and its application rate, time, and method have significant effects on nitrogen loss. The primary reason for nitrogen loss is attributed to the supersaturated soil nitrogen concentration. Making full use of environmental nitrogen sources, reducing the application rate of chemical nitrogen fertilizers, applying deep placement fertilizing method, and applying organic fertilizers with chemical nitrogen fertilizers, are effective practices for reducing nitrogen loss and improving nitrogen use efficiency. It is suggested that deve-loping new high efficiency nitrogen fertilizers, enhancing nitrogen management, and strengthening the monitoring and use of environmental nitrogen sources are the powerful tools to decrease nitrogen application rate and increase efficiency of cropland.

[Community structure characteristics of phytoplankton and related affecting factors in Hengshan Reservoir, Zhejiang, China].

In order to reveal the community structure characteristics of phytoplankton and the relationships with environmental factors in Hengshan Reservoir, the phytoplankton species composition, abundance, biomass and 12 environmental factors at 4 sampling sites were analyzed from March 2011 to February 2012. A total of 246 phytoplankton species were identified, which belong to 78 genera and 7 phyla. The dominant species were Melosira varians, M. granulate, Cyclotella meneghiniana, Asterianella formosa, Synedra acus, Achnanthes exigua, Ankistrodesmus falcatus, Oscillatoria lacustris, Cryptomonas erosa, Chroomonas acuta, Phormidium tenue and Microcystis aeruginosa, etc. Seasonal variations of species were obvious. The annual abundance and biomass of the phytoplankton were 0.51 x 10(5)-14.22 x 10(5) ind x L(-1) and 0.07-1.27 mg x L(-1), respectively. The values of the Margelef index, Pielou index and Shannon index of the phytoplankton community were 1.10-3.33, 0.26-0.81 and 0.51-2.38, respectively. The phytoplankton community structure was of Bacillariophyta-Cryptophyta type in spring and winter, of Chlorophyta-Cyanophyta type in summer, and of Bacillariophyta type in autumn. Canonical correlation analysis (CCA) showed that temperature, transparency, chemical oxygen demand and pH had the closest relationships with the phytoplankton community structure in the reservoir. Water quality evaluation showed that Hengshan Reservoir was in a secondary pollution with a meso-trophic level.