Search

City is a kind of social-economic-natural complex ecological systems.Urban ecological land is an important component of urban ecosystem,which plays a key role to guarantee urban social-economy sustainable development,provide urban ecosystem services and improve residents′ quality.The rapid spread of urban area and intensive human activities have significantly changed the urban land use structure and ecological land quantity,thus seriously impacted the urban ecological service and human living environment.However,little information was available on the influence of urban land structure on ecosystem services in resource-exhausted cities.Through the remote sensing,GIS technology and evaluation method of ecological service value,the variations of land use structure and ecological service value were assessed in a typical resource-exhausted city—huaibei during 1987 to 2007 in this study.The results showed that from1987 to 2007,the total area and structure of ecological land in this city were drastically changed,with the proportion of ecological land area decreased from 91.45% to 71.86%.From 1987 to 2000,the area of farmland substantially reduced,but the areas of forest,water and built-up lands increased.While from 2000 to 2007,the area of farmland increased but the area of forest and water significantly reduced.Although there were no obvious changes of total areas of the built-up land in this period,the aggregation level of the built-up land increased significantly.However,the comprehensive land use dynamic degree of huaibei city has a decreasing tendency from 1987 to 2007,which reflecting the gentle land circulation during this period.Moreover,in these 20 years,urban ecological service value increased between 1987 and 2000 then decreased since 2000.The maximum value of ecological service appeared in 2000,which was 31.32×108 yuan.During 2000 to 2007,the ecosystem services of waste treatment and water conservation function mainly provided by water and forest have the greatest contribution.The variation of ecological service value during 1987—2000 was mainly due to the impacts of coal mining,which occupied large area of cultivated land and made the surface area sinking into desolated beaches or depression,thus caused the significantly reduction of food production services.Meanwhile,the increasing of wetlands from sink area and woodland by ecological constructions such as returning farmland to forest and artificial afforestation made other ecosystem services obviously improved.From 2000 to 2007,the increasing urban expansion and population growth convert a large sum of ecological land to built-up area,resulting the decreasing of the ecosystem services values.In addition,the distribution of urban ecological land significantly influenced the spatial variability ecological service value.The higher service value areas were mainly distributed on the south part of huaibei city where farmland and forestland is relatively concentrated,while lower service value areas were mainly concentrated in the built-up area.Thus it can be seen that urban land use structure change greatly influenced ecological services,and the results can provide certain scientific basis to the optimization of the landscape pattern and reasonable control of urban land in the huaibei city.

The concept of urban green space,which comprises gardens and parks,urban forestry,urban agriculture,greenways,waterfront greenbelt,and roof greening,is different from traditional garden greenland,and forms functional eco-networks.On the other hand,the ecological and environmental impacts of urbanization extend over large areas even though the areal percentage of urban land in regional land-cover maps is typically quite small.Urban land use changes altered the green space patterns dramatically,and sequentially influenced urban landscape structure and ecosystem services.With the concern of high speed of urbanization and serious urban environmental problems,a common consensus has been achieved that the spatio-temporal dynamics of urban green space patterns are important factors to social,economic and ecological functions of urban ecosystems.Many countries have formulated urban landscaping as an essential part of the strategy of sustainable development.Nevertheless,under most circumstances,the green spaces were built more arbitrarily than based upon scientific analyses.Therefore,study on the quantitative methods of urban green space patterns revealed broad applications in protecting and planning green space structure and functions,which could further promote urban human settlements. Among various quantitative methods of urban green space patterns,detecting methods of green space changes under urbanization was a hotspot.Urban development and suburbanization had shrunk the size of green spaces and got the green patches fragmented.In terms of measuring green space fragmentation,it was of prime importance to select appropriate fragmentation metrics and improve the method of weighting to aggregate to get an unique fragmentation score.Contrary to landscape fragmentation,improvement in green space connectivity rehabilitated and optimized network structure,which could further enhance ecosystem services supply.Recently,assessment of green space connectivity had been transited from metric-based approaches to the coupling of both landscape metrics and models,and an increasing number of researches focused on the network scenario analysis of urban green spaces had gradually formed an united methodological framework for reconstruction of urban eco-networks.Meanwhile,accessibility analysis of urban green spaces was an important researching topic to assess the spatial interactions between residential land use and urban green spaces,and could help to identify the truly underserved areas lacking opportunities of accessing green spaces which was critical for effective urban planning and development.Moreover,spatial-temporal gradient analysis,combined with quantified landscape metrics,was judged to be the most appropriate way of relating the spatial pattern of urban green spaces to urbanization and underlying human processes,and of determining their influence on ecological attributes of the environment.Three sampling methods were commonly used for detecting the gradient changes of green space patterns: buffer gradient analysis,directional transects and moving window method.For comparative studies on the spatial variations of green space patterns along urban-rural gradients,multiple approaches of mapping peri-urban areas should be addressed in a scientific way. In the final section,suggestions for future researches were put forward,which highlighted the importance of quantifying green space patterns spatially explicit at multiple scales.In order to achieve these goals,the so-called local analysis,combined with quantified landscape metrics and accessibility measurements,which was often conducted at grid level,patch level and local areas according to the research objectives respectively,was widely used.Considering the scale effects involved in the spatial analysis associated with urbanization,multi-scale methods of quantifying green space patterns need to be carried out both at diverse spatial grains and extents to facilitate comparisons among different cities and periods of time.In addition,the quantification of green space patterns should also be integrated with planning or policy issues,as well as be applied to evaluating ecosystem services.In other words,quantifying green space patterns could not only serve as guidelines in terms of decision making,but help evaluating the impacts of regional development policies on future ecological benefits and ecosystem services.

Uniform NaYF4∶18%Yb,0.5%Tm nanocrystals were synthesized via thermal decomposition method following high temperature,and then a change of the nanocrystals was made from oil-soluble to water-soluble by ligand-exchanged method.X-ray diffraction(XRD) analyses showed that the samples were β-NaYF4 nanocrystals.The TEM images exhibited that the nanocrystals had an average size of 35 nm.Under 980 nm near-infrared laser excitation,the samples showed intense ultraviolet upconversion emission.5-photon upconversion fluorescence of the Tm3+ ions in the nanocrystals was stronger than 4-photon and 3-photon upconversion fluorescence.Due to special optical properties and small size,the water-soluble nanocrystals would show potential applications in the biomedical field.

The ultraviolet upconversion luminescence properties of the Tm3+ ion sensitized by the Yb3+ ion were studied,in fluoride glass as excited by a 980 nm continuous wave diode laser.Red,blue,and even ultraviolet emissions were observed with ZrF4-BaF2-LaF3-A1F3-NaF glass,and it was also found that the peaks at 291,347,363,454,475,643,687 and 804 nm correspond to the transitions of 1I6→3H6,1I6→3F4,1D2→3H6,1D2→3F4,1G4→3H16,G4→3F4,3F3→3H6,and 3H4→3H6,respectively.According to the relationship between the pump power and the upconversion peaks intensity,347 nm and 363 nm ultraviolet emissions are five photon and four photon processes respectively.The research results show that the ZrF4-BaF2-LaF3-A1F3-NaF glass of the Tm3+ ion sensitized by the Yb3+ ion can effectively transform the near-infrared waveband laser to the ultraviolet.