Qinling Mountains is not only the geographical boundary between North and South China, but also the boundary between subtropical and warm temperate zones. It plays an important role in the geo-ecological pattern of China. However, there is controversy about the specific location of this geographical boundary in academic community due to the complexity, transition and heterogeneity of the transitional zone, as well as the differences in the delimitation indicators and research purposes. To further reveal the characteristics of the North-South transitional zone and clarify the specific location of the geo-ecological boundary between North and South China, combined with SRTM topographic data, temperature and precipitation data, Pinus massoniana forest and Pinus tabulaeformis forest, which represent subtropical coniferous forests in South China and temperate coniferous forest in North China respectively, were chosen to analyze their spatial distributions in the Qinling-Daba Mountains and the climatic conditions at their boundary with the climatic indexes of annual precipitation, the coldest month (January) average temperature, the warmest month (July) average temperature and the annual average temperatures. The results show that: (1) Pinus massoniana and Pinus tabulaeformis forests and the climate indicators of their boundary can be used as one of the vegetation-climate indicators for the delimitation of subtropical and warm temperate zones. The boundary between the subtropical coniferous forest (Pinus massoniana forest) and temperate coniferous forest (Pinus tabulaeformis forest) in Qinling-Daba Mountains is located along the south slope of Funiu Mountain to the north edge of Hanzhong Basin (the south slope of Qinling Mountains) at an altitude of 1000-1200 m, where the climatic indictors are stable: the annual precipitation is about 750-1000 mm; the annual average temperature is about 12-14 ℃; the coldest monthly average temperature is 0-4 ℃; and the warmest monthly average temperature is about 22-26 ℃. (2) It could be more scientifically to delimitate the boundary of subtropical and warm temperate zones in China by comprehensively considering the vegetation-climate indicators. Additionally, the boundary between subtropical and warm temperate zones in Qinling-Daba Mountains should be a transitional zone consisting of the boundaries of coniferous forests, broad-leaved forests and shrubs between subtropical and warm temperate zones. The results provide a scientific basis for the selection of delimitation indicators of subtropical and warm temperate zones.

As a link between the atmosphere and the geosphere, the hydrological cycle is affected by both climate change and Land Use/Cover Change (LUCC). However, most existing research on runoff response focused mainly on the impact of the projected climate variation, neglecting the influence of future LUCC variability. Therefore, the objective of this study is to examine the co-impacts of both projected climate change and LUCC on runoff generation. Firstly, the future climate scenarios under BCC-CSM1.1 and BNU-ESM are both downscaled and corrected by the Daily Bias Correction (DBC) model. Secondly, the LUCC scenarios are predicted based on the Cellular Automaton-Markov (CA-Markov) model. Finally, the Soil and Water Assessment Tool (SWAT) model is used to simulate the hydrological process under different combinations of climate and LUCC scenarios, with the attempt to quantitatively evaluate the impacts of climate change and LUCC on runoff generation. In this study, the Hanjiang River basin is used as the case study area. The results show that: (1) compared with the base period (1966-2005), the annual rainfall, daily maximum and minimum air temperatures during 2021-2060 will have an increase of 4.0%, 1.8 ℃, 1.6 ℃ in RCP4.5 scenario, respectively, while 3.7%, 2.5 ℃, 2.3 ℃ in RCP8.5 scenario, respectively. (2) During 2010-2050, the area proportions of forest land and construction land in the study area will increase by 2.8% and 1.2%, respectively, while those of farmland and grassland will decrease by 1.5% and 2.5%, respectively. (3) Compared with the single climate change or LUCC scenario, the variation range of future runoff under both climate and LUCC is the largest, and the influence of climate change on future runoff is significantly greater than that of LUCC. This study is helpful to maintain the future water resources planning and management of the Hanjiang River basin under future climate and LUCC scenarios.

Greenhouse gases from permafrost have a significant impact on global climate change. The in situ static dark chamber and gas chromatography techniques were used to monitor the fluxes of carbon dioxide (CO₂), methane (CH₄), and nitrous dioxide (N₂O) from the typical forest soils of Larix gmelini, Pinus sylvestris, and Betula platyphylla in the permafrost regions of the Greater Hinggan Mountains. The experiment was conducted during the growing season (May to September) of 2016 and 2017. The dynamic characteristics of greenhouse gas fluxes and the controlling factors were comparatively analyzed. The results showed that soil CO₂, CH₄, and N₂O fluxes of the three forest types were 65.88-883.59 mg·m^-2·h^-1, -93.29--2.82 μg·m^-2·h^-1, and -5.31-45.22 μg·m^-2·h^-1, respectively. The soils from the three typical forests were all sources for CO₂ and N₂O, and sink for CH₄ during the entire observation period. Soil CO₂ and CH₄ fluxes changed significantly among different forest types and between the two observation periods. The soil CO₂ fluxes of the three forest types were mainly controlled by soil temperature and were found to have a significantly positive correlation with the soil temperature at 5, 10, and 15 cm (P < 0.01). The soil CH₄ fluxes were affected by soil water content and soil temperature. The correlations were significant in the soils at 10 and 15 cm (P < 0.05). Moreover, the air temperature controlled and regulated soil N₂O fluxes. The soil N₂O fluxes in the Betula platyphylla forest showed a significantly negative correlation with the soil temperature at 15 cm (P < 0.05). The emission rate of soil CO₂ and N₂O accelerated with increasing temperature, while the absorption rate of CH₄ decreased, enhancing the atmospheric greenhouse effect. The global warming potential of greenhouse gases was calculated based on the 100-year time scale, where the soil greenhouse gases of the three forest types exhibited a positive feedback on climate warming.

The Tang Po Lakes, consisting of a great number of small lakes and swamps, which had widely spread upon the Central Hebei Plain during the Northern Song Dynasty, was an awesome geographical landscape in North China in history. It has a significant meaning for understanding the regional environmental change in the North China Plain. The researchers employed an interdisciplinary procedure to unveil the spatial pattern and changing process of the Tang Po system in history. Based on GIS, this paper integrated the traditional historical geographic method, which mainly focused on the scrutiny of all sorts of historical records, with analysis of modern soil survey, archaeological survey, remote sensing images, and the references in the published research. In this way the spatial distribution of Tang Po Lakes on the Central Hebei Plain during the Northern Song Dynasty has been carefully examined and scientifically reconstructed for the first time. The paper showed that the Northern Song government constructed the Tang Po system at the end of the 10th century by fully taking advantage of local natural lakes and swamps originally located in the depression zone of the Central Hebei Plain which adjoined to its northern border, in order to prevent the invasion from the Liao Dynasty in north. In the mid-11th century, the Tang Po system reached its maximum extent, which spanned more than 260 kilometers from the eastern coast to the western mountain foot. The Tang Po system, which was composed of many small lakes, swamps, pits, diches, and even rice paddies, could be divided into nine sub-regions, and watered by the Tanghe River, the Shahe River, the Shenshui River, the Yishui River, the Hutuo River, and the Yuhe River. The whole Tang Po system was deliberately connected and maintained by the complex artificial facilities, such as dams, embankments, reservoirs, sluice gates, and channels. In the early 12th century the Northern Song Dynasty was in decline, the Tang Po system collapsed and was broken into three separate parts which had existed till the late Qing Dynasty. The Tang Po system of the Northern Song Dynasty has ever been the biggest man-made lake system in Chinese history, which had a magnificent impact on the regional water system and local environment of the Central Hebei Plain.

In order to analyze the spatio-temporal evolutions of Dongting Lake in modern times, this paper investigated the temporal changes of the riparian lake areas in Dongting Lake area since the late Qing Dynasty using various historical maps and remote sensing data since 1896 AD (the 22nd year during the Emperor Guangxu's reign in the Qing Dynasty). The remote sensing data interpretation, statistical analysis and historical comparison methods were used to test the accuracy of the remote sensing based lake areas with the observation data from the Ministry of Water Resources of China. The results showed that the overall error rate was only 0.62%, and after 1896, the riparian lake areas in Dongting Lake decreased from 5126.37 km² to 2702.74 km², with an annual atrophy rate of 48.19%. The 53 years before the founding of the People's Republic of China was a period of obvious lake shrinkage, with an annual average decrease of 15.66 km². The 1950s was a period of rapid atrophy (134.33 km² per year), and the 1960-1970s was a period of rapid shrinkage, with an annual rate of 21.66 km². The riparian lake areas in Dongting Lake only reduced by 5.10 km² since the 1980s. In terms of the areas for each lake, the East Dongting Lake was the lake with the largest shrinkage (922.60 km²) since 1935, followed by the Muping Lake (a decrease of 588.05 km²), and the South Dongting Lake (decrease of 448.37 km²). The change in areas of Qili Lake was relatively small in recent decades. The areas of Dongting Lake increased by 10.50 km² during 1998-2002 due to the implementation of returning farmland to lake. In general, the evolution of riparian lakes in Dongting Lake area since the late Qing Dynasty was characterized by the closure and separation of Datong Lake, the replacement of the embankments for the South Dongting Lake, the local remains of the West Dongting Lake, the three-sided enclosure of East Dongting Lake and the limited operation of returning farmland to lake after the catastrophic flood in 1998. This study may provide data and technical support for the ecological restoration and environmental protection strategy of the Yangtze River Basin.