Exploring the regional differences of ecosystem health and its spatial relationships with urban forms in China.

A deeper understanding of the regional differences and driving factors behind ecosystem health (EH) is of vital for ecosystem management and restoration. Although a considerable number of studies have focused on this topic, few studies have explored the spatial relationship and scale effect between urban forms and EH from the perspective of urban scale, agglomeration and irregularity. Therefore, this study first constructed an improved evaluation framework by integrating vigor, organization, resilience and ecosystem services supply-demand ratio to measure the EH level in China at the county scale during 1995-2015, and then evaluated and compared the spatial relationships between five urban form metrics and EH based on the spatial regression model at the national, regional, urban agglomeration and city scales. The results showed that the level of EH in China spatially decreased from the southeast to the northwest, and displaying significant spatial agglomeration. At the national scale, the fragmentation and complexity of urban form exerted the greater negative influence on EH than urban expansion scale. At the regional scale, controlling urban expansion scale and enhancing landscape connectivity were conducive to the improving of EH in the central and eastern regions. At the urban agglomeration scale, the regularity and compactness of urban form played a key role in the sustainable development of regional and national urban agglomerations. At the city scale, large cities can improve environmental quality by limiting the size of core patches and reducing the complexity of urban shape. This paper can provide a scientific guidance for ecosystem protection and urban high-quality development.

Composition and sources of heavy metals in aerosol at a remote site of Southeast Tibetan Plateau, China.

Knowledge of the elemental composition of aerosols at remote sites is important for evaluating the influence of anthropogenic activities. In this study, the elemental composition and sources of total suspended particles (TSP) at Yaze, a remote site in the southeastern Tibetan Plateau (TP), were investigated. The results showed that the mean elemental concentrations at Yaze were relatively low compared with those in other areas of the TP. Seasonal variations in the studied elements was characterized by low and high concentrations during the monsoon and non-monsoon periods, respectively. The enrichment factors (EFs) for some heavy metals at Yaze were slightly higher than those at Nam Co station (inland TP) but much lower than those at Mt. Yulong (southeastern TP) and in the Indian megacity of Delhi, indicating fewer anthropogenic influences at the study site relative to sites close to severely polluted regions. For the studied elements, three major sources were identified: crustal origins (e.g., Al and Fe), anthropogenic origins (e.g., Zn and Cd) and mixed origins (e.g., As and Bi). Further analysis by potential source contribution functions showed that the local TP was the primary source for elements of crustal origins. Correspondingly, the typical heavy metals were mainly attributed to pollution emitted from anthropogenic activities and transported over long-range from both South and Southeast Asia. This work demonstrates the transport of heavy metals from external sources to remote sites in the southeastern TP. These results are also useful for interpreting the historical profiles of heavy metals in the ice cores of the TP.

Overestimation of anthropogenic contribution of heavy metals in precipitation than those of aerosol samples due to different treatment methods.

Due to increased anthropogenic activities in recent decades, many heavy metal elements have been emitted into the atmosphere and transported to remote regions. The Enrichment factors (EFs) is a normally used method for evaluating the source of heavy metal elements. However, because of some flaws of this method (e.g., higher solubility of heavy metals elements than reference elements in dilute acid), the anthropogenic contributions of some heavy metal elements in the precipitation sample were overestimated. To address this issue, EFs of heavy metal elements of aerosol, precipitation and snowpit samples in a typical remote area of the Tibetan Plateau (TP) were compared. The results showed that the EF values of many heavy metal elements in precipitation and snowpit samples were close to that of aerosol samples treated with dilute acid but usually much higher than those of totally dissolved aerosol samples. Moreover, EF values of most heavy metal elements in the ice core at the margin of the TP were higher than those at central TP, indicating that signal of long-range transport anthropogenic emitted heavy metal elements is weak and may be covered by natural mineral dust sources at glacier region. Therefore, the threshold EF values for determining anthropogenic sources of heavy metal elements in precipitation and ice core samples should be higher than those of aerosols. This study provides new knowledge on investigating anthropogenic sources of heavy metals in precipitation samples at both the TP and other regions of the world.

Coupling coordination analysis and spatiotemporal heterogeneity between urbanization and ecosystem health in Chongqing municipality, China.

Rapid urbanization has seriously disturbed the structure and function of ecosystems and caused many eco-environmental problems, in turn, these problems also reduce the quality of urbanization and threaten the sustainable development of urban. Currently, most studies only focus on the impact of urbanization on ecosystem components (i.e., structure, functions or services), few studies have explored the coordination and spatiotemporal heterogeneity between urbanization and ecosystem health from a systematic view. Therefore, in viewing of this, this study integrated coupling coordination degree model (CCDM) and geographically and temporally weighted regression (GTWR) to measure the interaction relationship and spatiotemporal heterogeneity between urbanization and ecosystem health (UAEH) in Chongqing at the county scale from 1997 to 2015. Results showed that: 1) the degree of coordination between UAEH in Chongqing increased gradually from 1997 to 2015, developed from the moderately unbalance stage to moderately balance stage, and experienced a transition from urbanization lag to ecosystem health lag. Moreover, the coupling coordination degree showed a decreased spatial trend from the western to the eastern of Chongqing. 2) The restriction effect between UAEH gradually weakened from 1997 to 2015, and the synergistic effect between them gradually strengthened. Additionally, the interaction between UAEH tended to converge, and the negative effects between UAEH were mainly distributed in the central and western of Chongqing. In these area, population urbanization aggravated the deterioration of the natural ecosystem, in turn, the decline of ecosystem vigor and resilience also restricted the sustainable development of urbanization. Finally, this study also puts forward some corresponding policy recommendations based on each region's coupling type.

[Nitrate-Nitrogen Pollution Sources of an Underground River in Karst Agricultural Area Using 15N and 18O Isotope Technique].

The objectives of this study were to reveal the sources of nitrate and the ratio of karst in an agricultural basin based on a 15N and 18O isotope technique and quantitative calculation of the IsoSource model. From May to October 2017, six sampling points in the Qingmuguan river basin, Chongqing, were monitored every 24 d. Results showed that there was a great risk of nitrate pollution in the underground river system, because most NO3--N concentrations of the sampling points exceeded the threshold. Spatially, NO3--N concentrations in the underground river increased from upstream to downstream. Temporally, NO3--N concentrations of Fishpond and Yankou Ponor upstream and Jiangjia Spring downstream were impacted by agricultural fertilizer from May to June and fluctuated from June to September due to precipitation. With decreased agricultural activities, NO3--N concentrations gradually decreased after September. NO3--N concentrations were high in midstream soil water. Daluchi, in the middle and lower reaches, maintained relatively low NO3--N concentrations with stable fluctuations. Dual 15N and 18O isotopic compositions suggested that the upstream nitrates were derived from soil organic nitrogen and a mixture of manure and sewage. The midstream nitrates originated from soil organic nitrogen and NH4+ from fertilizer and rain. Nitrates in the middle and lower reaches were derived from the mixing of manure and sewage, soil organic nitrogen, and NH4+ from fertilizer and rain. Jiangjia Spring, the outlet of the underground river, was seriously polluted by nitrates. It is believed that soil organic nitrogen, NH4+ in fertilizer and rain, the mixing of manure and sewage, and NO3- in precipitation were the main nitrate sources in the outlet. Nitrate source contribution of the outlet was calculated with the IsoSource model. The calculation results showed that manure and sewage, soil organic nitrogen, NH4+ in fertilizer and rain, and NO3- in precipitation contributed 46.4%, 32.6%, 18.6%, and 2.4%, respectively.

Stable isotopic composition reveals the spatial and temporal dynamics of discharge in the large river of Yarlungzangbo in the Tibetan Plateau.

Spatial and temporal variability in stable isotopic compositions (δ18O and δD) in river water of the Yarlungzangbo was investigated to identify major hydrological processes along the river channel and evaluate the isotopic response to discharge variation. The results show geographic, distinct isotopic evolutions in the Yarlungzangbo system. Along the main stem, river δ18O exhibits a decreasing trend from the headwaters to the middle reach but an increasing one from the middle to the lower reaches, and main flows demonstrate much greater δ18O-δD slope and intercept compared to the global meteoric water line (GMWL) and reported local meteoric water lines (LMWLs) for sites within the basin. These results are found to be consistent with the isotopic characteristics of stream and river waters collected across the entire drainage basin. Water mixing appears to be the dominant hydrological process along the Yarlungzangbo, and the pattern of isotopic change in individual river reaches closely reflects that of precipitation in corresponding part of the river basin. The isotopic variability along the main stem observed during the synoptic survey is evidenced to hold through time by a time-series investigation at three key hydrological stations. River water at such three stations shows a strong isotopic response to discharge variability. In general, river δ18O tends to be negatively correlated with discharge, highlighting a typical monsoon precipitation-driven isotope-discharge pattern. Specifically, we found their individual discharge-weighted average δ18O values likely vary in a similar rate with the ratio of mean discharge in monsoon season (JAS) to that in pre-monsoon season (MJ) on a yearly basis, indicating a specific relationship between average river isotopic composition and discharge seasonality throughout their drainage areas (i.e. the middle-lower Yarlungzangbo basin). This study thus demonstrates the usefulness of isotopic data for assessing hydrodynamics over a less explored, complex and high-altitude large river catchment.

[Geochemical Characteristics of Lateral Hyporheic Zone Between the River Water and Groundwater, a Case Study of Maanxi in Chongqing].

The hyporheic zone is a place where river water and groundwater mutually exchange and mix. It plays an important role in protecting the ecology and water quality of river water and groundwater. In order to study the geochemical characteristics of lateral hyporheic zone in river and ground water, water temperature, dissolved oxygen, pH, electrical conductivity were measured automatically at the hyporheic zone of Maanxi in Chongqing. The concentrations of ions in water and elements in sediment within the hyporheic zone were also analyzed. The results showed that the hydrochemical species of lateral hyporheic zone in Maanxi was HCO3-Ca·Mg. Affected by the infiltration of river water, the coefficient variations of water temperature, dissolved oxygen, pH and electrical conductivity in the hyporheic zone were lower than those observed in the river under the buffer action. Along with the farther distance from the riverbank, an anoxia redox environment was formed in the hyporheic zone due to a physical, chemical and biological interactions. An acid and alkali environment was also formed with a decreasing pH trend near the riverbank and hyporheic zone. Under its influence, concentrations of K+, NH4+-N, NO3- and SO42- decreased. Mn, electrical conductivity, and the concentrations of Ca2+, Mg2+, Ba2+ and Sr2+ firstly increased and then decreased, while the concentrations of Fe, Al3+ were elevated. Affected by the long-time interaction of river water and groundwater, the elementary concentrations in the sediment were relatively high at the place of about 30 cm away from the riverbank. This consequently formed a hydrogeochemical gradient in the hyporheic zone. The boundary of the hyporheic zone was inferred at 30 to 50 cm away from the riverbank, whereas the boundary of shallow hyporheic zone was located at 10 cm away from the riverbank. In the process of river water recharging groudnwater, hyporheic zone of river and groundwater played an important role in the purification of water quality.

[Nitrate storage and transport within a typical karst aquifer system in the paralleled ridge-valley of east Sichuan].

In order to investigate the nitrate storage and transport in the karst aquifer system, the hydrochemical dynamics of Qingmuguan underground river system was monitored online by achieving high-resolution data during storm events and monthly data in normal weather. The principal component analysis was employed to analyze the karst water geochemistry. Results showed that nitrate in Jiangjia spring did not share the same source with soluble iron, manganese and aluminum, and exhibited different geochemical behaviors. Nitrate was derived from land surface and infiltrated together with soil water, which was mainly stored in fissure, pore and solution crack of karst unsaturated zone, whereas soluble iron, manganese and aluminum were derived from soil erosion and directly recharged the underground river through sinkholes and shafts. Nitrate transport in the karst aquifer system could be ideally divided into three phases, including input storage, fast output and re-inputting storage. Under similar external conditions, the karstification intensity of vadose zone was the key factor to determine the dynamics of nitrate concentrations in the groundwater during storm events. Nitrate stored in the karst vadose zone was easily released, which would impair the aquatic ecosystem and pose seriously threats to the local health. Thus, to strengthen the management of ecological system, changing the land-use patterns and scientifically applying fertilizer could effectively make a contribution to controlling mass nutrient input from the surface.