The study took northern Shaanxi, a key region of Grain for Green Project, as the research area. We firstly analyzed the spatiotemporal patterns of cropland during 2000-2013 using the remotely sensed time series cropland. The RUSLE model was improved by taking terraced fields as a parameter, and then the soil erosion modulus (SEM) was simulated using the calibrated model. Finally, the impacts of the Grain for Green Project on the soil erosion were assessed by comparing SEM changes in shifted and unshifted cropland. The results indicated that, the SEM across the areas of "Grain for Green" decreased by 22.70 t/hm ² from 2000 to 2010, accounting for 47.08% of that from the returned cropland in 2000. In the same period, the SEM from the unreturned cropland decreased by 10.99 t/hm ², accounting for 28.60% of that from the unreturned land in 2000. For the whole study area, the SEM of different land use types averagely decreased by 14.51 t/hm ², which is 41.87% of the SEM in northern Shaanxi in 2000. We concluded that "Grain for Green" could effectively reduce the SEM in northern Shaanxi and made the most contribution to soil protection. The Grain for Green Project entered a consolidation period after 2000 (during 2010-2013 in this study), and changes of the SEM during this period were thus relatively low.

The existing studies on potential evaluation of urban land intensive use mainly adopt the multi-index comprehensive evaluation approach, which has defects such as insufficient basis, incomparability of results and difficulty in reflecting dynamic changes. In view of this, this study introduced the theory and method of technical efficiency measurement into the potential evaluation of urban land intensive use. The potential of urban land intensive use can be defined as the land savings or output growths potential brought by the possible improvement of technical efficiency. Based on measuring the technological efficiency of urban land use with the SFA method, this paper constructed the quantitative evaluation models of land saving and output growth potential of urban land intensive use, and then measured and analyzed the scale and proportion of land saving and output growth potential in the Beijing-Tianjin-Hebei region during 2006-2015. The results show that the potential scale of urban land intensive use in the study area is very large and continuously increasing. The annual average of land saving potential scale is 709.80 km ², and the net increment in the 10 years is 543.96 km ², while the output growth potential scale is 420.76 billion yuan (the constant price in 2005), and the net increment in the 10 years is 342.86 billion yuan. The results also indicate that the potential proportion of urban land intensive use in the Beijing-Tianjin-Hebei region is quite high and continuously rising. The annual average of land saving potential proportion is 21.80%, or an increase of 10.56 percentage points in the 10 years, while the annual average of output growth potential proportion is 26.12%, or an increase of 14.73 percentage points in the 10 years. The potential ranking between the 13 cities is stable and the gap is widening, showing the general rule that it is more difficult for developed cities and easier for underdeveloped cities to explore potentialities, as well as the Matthew effect that it is easier for the easy and more difficult for the difficult. The research can provide scientific guidance for the practice and management of urban land intensive use and facilitate the dialogue and exchange between intensification evaluation and efficiency measurement.

Using daily temperature observations from the National Meteorological Information Center of China, we analyzed the spatiotemporal variation in actual heating energy efficiency in areas south and north of the Qinling Mountains-Huaihe River (hereafter Qinling-Huanhe Line) over the period 1960-2016. The dynamic heating index, defined as the difference between fixed and dynamic heating energy consumption during the entire heating season, was used. Specifically, we analyzed the spatiotemporal response of actual heating energy efficiency to the Arctic Oscillation (AO) index, where changes in the circulation pattern bring frigid winter air to eastern China in the negative phase, resulting in increased heating energy demand. The results showed that: (1) spatial pattern of heating energy consumption in areas south and north of the Qinling-Huaihe Line was high in the eastern and southern regions, but low in the western and northern regions. The signal of decreasing heating energy demand in the lower latitudes of the region occurred earlier than in the higher latitudes. (2) On the whole, actual regional heating energy efficiency showed a decreasing trend that was corresponded with regional warming. In the north, however, the decreasing trend was weaker than in the south during the study period. This implies that residents continued to adopt a fixed-date strategy in the heating season, thus heating energy waste would increase consistently throughout the seven sub-regions, especially in the south. (3) Comparing the situation before and after climate change, i.e., 1960-1990 versus 1990-2016, we found that substantial changes were not evident in the spatial pattern of heating energy consumption in areas south and north of the Qinling-Huaihe Line. Nevertheless, there were differences in the response of temperature variations to climate change. The lower reaches of the Yangtze River, the Hanjiang River Basin, and the Wushan Mountains were some areas where heating energy waste was slowly increasing. A faster increase in heating energy waste mainly occurred in the eastern Huaihe Plain, the northwestern lower Yellow River Basin, and the Qinling-Bashan Mountains. (4) Actual heating energy efficiency had a close relationship with AO in the south-north transitional zone of China. Over the past 57 years, the AO alternated between positive and negative phases. Starting in the 1990s, the AO tended to be more of a positive phase pattern, in which higher pressure at the mid-latitudes drove warm air farther north, bringing warmer winters to the Qinling-Huaihe region, and thus decreased heating energy consumption. Spatially, the most sensitive responses of heating energy efficiency to climate change occurred in the southern Huaihe Plain and the northern regions of the lower Yangtze River Basin. In future, we should mitigate the risks of extreme climate change in sharply negative phases of the AO warrant attention, and develop policies concerning household heating in the south-north transitional zone of China.

Identifying the sources and fate of nitrogen in groundwater is challenging in areas with diverse land use types and multiple potential inputs. The Abujiaohe river basin in China's Sanjiang Plain, which has mixed land use types, including forestland, upland, paddy fields, and residential areas, was selected as the study area. Multiple environmental tracers, including hydrochemical and stable isotopes of nitrate (δ ¹⁵N-NO₃ ^- and δ ¹⁸O-NO₃ ^-) from groundwater, were examined. A biplot approach (δ ¹⁵N-NO₃ ^- and δ ¹⁸O-NO₃ ^-) combined with multivariate statistical analysis of hydrochemical data was used to investigate the sources and fate of nitrogen in groundwater. The results showed that severe nitrogen pollution—the highest concentration found in this study exceeded the national limit by four times—was present in both towns and agricultural areas. Land use was not only the dominant determining factor of nitrogen concentration and groundwater chemistry type, but also had a key impact on the regional nitrogen cycle and nitrogen sources. In the forestland, dominant nitrate was mainly derived from organic nitrogen nitrification in the soil. In residential areas, excessive NO₃ ^- with high Cl ^- concentrations derived from manure and septic waste, which was controlled by the nitrification process. In paddy fields, low NO₃ ^-, combined with high NH₄ ⁺ and stable isotopes of nitrate concentrations, was observed. The linear relationship between δ ¹⁵N-NO₃ ^- and δ ¹⁸O-NO₃ ^-indicated that the occurrence of significant denitrification led to the limited presence of isotopic tracer. The uplands, affected by multiple factors such as rainfall and denitrification, had a more complex N cyclic process. Ultimately, multivariate statistical analysis results showed that the reduction of nitrogen fertilizer input was the main reason for nitrogen pollution. Therefore, the combined approach of using nitrogen isotopic ratios and conventional multivariate statistical analysis allowed for the more reliable separation of nitrogen sources in groundwater. This approach can help us to initiate more targeted remediation strategies.

Wind-driven soil erosion results in land degradation, desertification, atmospheric dust, and sandstorms. The Hunshandake Sandy Land, an important part of the Two Barriers and Three Belts project, plays important roles in preventing desert and sandy land expansion and in maintaining local sustainability. Hence, assessing soil erosion and soil accumulation moduli and analyzing the dynamic changes are valuable. In this paper, Zhenglan Banner, located on the southern margin of the Hunshandake Sandy Land, was selected as the study area. The soil erosion and accumulation moduli were estimated using the ¹³⁷Cs and ²¹⁰Pb_ex composite tracing technique, and the dynamics of soil erosion and soil accumulation were analyzed during two periods. The results are as follows: (1) the regional ¹³⁷Cs reference inventory was 2123.5±163.94 Bq·m ^-2, and the regional ²¹⁰Pbex reference inventory was 8112±1787.62 Bq·m ^-2. (2) Based on the ¹³⁷Cs isotope tracing analysis, the erosion moduli ranged from -483.99 to 740.31 t·km ^-2·a ^-1. Based on the ²¹⁰Pb_ex isotope tracing analysis, the erosion moduli was from -441.53 to 797.98 t·km ^-2·a ^-1. (3) Compared with the 1920-1970s, since the 1970s lower soil erosion moduli and accumulation moduli were observed. Therefore, the activities of local sand dunes weakened, and the quality of the local ecological environment improved. The multi-isotope composite tracing technique combining the tracers ¹³⁷Cs and ²¹⁰Pb_ex has potential for similar soil erosion studies in arid or semiarid regions around the world.