[Distribution Characteristics and Ecological Risk Assessment of Soil Heavy Metals in Typical Watersheds of the Qinghai-Tibet Plateau].

The Qinghai-Tibet Plateau is an extremely vulnerable area that is sensitive to human activities. In recent years, more and more human disturbances have been detected in this area. This study analyzed the spatial distribution and ecological risks of 7 heavy metals (Cr, Ni, Cu, Zn, As, Cd, and Pb) in two regions, namely the Bailong River and Yellow River and their two tributaries (BY region) in Gannan and the Yarlung Zangbo River and its two tributaries (YZ region) in Tibet. In terms of spatial distribution, concentrations of the seven heavy metals were higher in the east and lower in the west of the BY region. The average concentrations all exceeded the background value of the Qinghai-Tibet Plateau, especially for Cd (4.50 times) and As (2.83 times). High Pb concentrations were mainly found in water, urban and rural residential land, and industrial and construction land. In the YZ region, heavy metal concentrations were lower along the river, while high-altitude areas exhibited higher heavy metal concentrations. The average concentrations of Ni, Zn, As, and Cd exceeded the background values of the Qinghai-Tibet Plateau, especially that of Cd (3.13 times), which mostly exhibited high values in water coverage areas. The geo-accumulation index method and the potential ecological risk index method show that the degree of As and Cd pollution was relatively high in the BY region in Gannan, with the greatest potential ecological risk occurring in the water coverage area. In the YZ region in Tibet, the degree of Cd pollution was high, with the highest potential ecological risk also occurring in the water coverage area. This study provides significant guidance for the environmental protection, sustainable development, and utilization of soil under different types of land use in the Qinghai-Tibet Plateau.

Characteristics of drought vulnerability for maize in the eastern part of Northwest China.

Based on information distribution and diffusion method theory and combined with the standardized precipitation index and relative meteorological yield data, meteorological factors and social factors were comprehensively considered to assess the vulnerability of maize (Zea mays) to drought. The probability distribution curve of meteorological drought degree (MDD) and relative meteorological yield in the eastern part of Northwest China (Gansu, Ningxia and Shaanxi) from 1978 to 2016 were obtained, using a two-dimensional normal information diffusion method to construct the vulnerability relationship between MDD and relative meteorological yield. The drought vulnerability curve of maize in the study area was obtained. The probability distribution of MDD was multiplied by the fragility curve and summed to obtain the multi-year average risk. The MDD probability distribution curve showed that the probability of moderate drought in Shaanxi was relatively high, followed by Gansu and Ningxia. The probability distribution of Gansu was more discrete. The probability of strong meteorological drought in Ningxia was high, followed by Shaanxi and Gansu. Probability distribution of relative meteorological yield for maize in Gansu Province was highly discrete, with thick tailings, large uncertainties, and more extreme values, which were strongly affected by meteorological conditions, followed by Shaanxi and Ningxia. Taking meteorological drought as the cause and maize damage as the result, the vulnerability relationship between MDD and drought damage was obtained. With an increased MDD, the relative meteorological yield of maize gradually declined. From the average value, when MDD was less than -2.60, the relative meteorological yield of maize was reduced within 15%; when MDD was greater than -2.60, the relative meteorological yield of maize increased within 10%. When the degree of meteorological drought exceeded -2.2, maize was most vulnerable to drought in Shaanxi followed by Ningxia and Gansu. When meteorological drought was less than -2.2, maize was most vulnerable to drought in Shaanxi followed by Gansu and Ningxia. The expected values of relative meteorological production in Gansu, Ningxia, and Shaanxi were 1.36%, 2.48%, and -1.76%, respectively; therefore, Shaanxi had the highest maize drought risk, followed by Gansu and Ningxia. This research had a clear physical background and clear risk connotations. The results provide a data foundation and a theoretical basis for drought disaster reduction for maize in the study area.

[Effects of climate warming on oil flax growth and water use efficiency in semi-arid region of Loess Plateau, Northwest China].

By using the site-specific observation data of oil flax growth and related meteorological records in semi-arid region of Loess Plateau, this paper studied the effects of climate change on the oil flax growth, and analyzed the relationships between the oil flax water use efficiency and meteorological condition. In this region, the annual precipitation displayed a decreasing trend, and its climatic trend rate was -15.80 mm (10 a)(-1), with an annual periodic change of 3 a and 6 a, whereas the annual air temperature had an increasing trend, and its climatic trend rate was 0.36 degrees C (10 a)(-1). In crop growth period, the aridity index displayed a marked increasing trend, its climatic trend rate was 0.12 (10 a)(-1), and the aridity tendency was more obvious from the beginning of 1990s to the year 2009. From sowing to maturation, oil flax needed 120-150 d, 1700-2100 degrees C d of > or = 0 degrees C accumulated temperature, 200-250 mm precipitation, and 1000-1300 h sunshine hours. The main meteorological factors affecting the oil flax growth in the region were air temperature and precipitation. The increase of air temperature shortened the prophase vegetative growth stage, whereas the increase of air temperature and the decrease of precipitation extended the reproductive growth stage, causing the extension of the whole growth period of the oil flax. The air temperature in the oil flax whole growth period except at seeding stage and maturing stage had negative effect on the yield formation, being more obvious at squaring stage, whereas the precipitation in the whole growth period except at blooming stage had positive effect on the yield formation, being more obvious at seeding stage. The water use efficiency of the oil flax was significantly positively correlated with the air temperature and sunshine hours at seeding stage as well as the aridity index from squaring stage to maturing stage, and negatively correlated with the precipitation from squaring stage to maturing stage. In the study region, the aridity index from May to July was the key factor affecting the water use efficiency of oil flax.

[Effects of climate change on potato growth in semi-arid region of Loess Plateau, China].

Based on the 1988-2008 located observation and 2007-2008 encrypted observation of potato growth and the 1957-2008 meteorological observation in semi-arid region of Loess Plateau, this paper studied the effects of climate change on the potato growth in this region. In 1957-2008, the annual precipitation in this region had a descending trend, with a linear fitting rate of the annual precipitation change curves being - 13.359 mm x (10 a)(-1), while the annual mean temperature displayed an ascending trend, with a linear fitting rate of the annual mean temperature change curves being 0.239 degrees C x (10 a)(-1). During potato growth period, the aridity index displayed a marked ascending trend, and the linear fitting rate of the aridity index change curves was 0.102 x (10 a)(-1). The growth rate of potato tuber became faster from the 96th day after sowing, reached the maximum on the 110th day, and turned slower from the 124th day. The interval from sowing to seedling emergence was shortened by 1-2 d x (10 a)(-1), and that from inflorescence formation to reaping and of whole growth period was lengthened by 9-10 d x (10 a) (-1). In the study region, climate warming shortened the vegetative growth stage, but lengthened the reproductive growth stage and whole growth period of potato.

[Responses of subalpine meadow Poa botryoides to climate change].

Based on the field plot observation and related meteorological data, the effects of climate change in 1985-2005 on the growth and development of subalpine meadow Poa botryoides in Maqu County of Gansu Province were analyzed. The results showed that during study period, the annual precipitation in the Maqu County had a decreasing trend, with a rate of -9.895 mm x (10 a)(-1) and a cycle of 3 years, while the annual air temperature had an increasing trend, with a rate of 0.341 degrees C x (10 a)(-1). The aridity index of P. botryoides in growth season had an obvious increasing trend, with a rate of 0.036 x (10 a)(-1), and the tendency was more markedly from the beginning of the 1990s to 2005. The period from reviving to ripeness of P. botryoides was 140-150 d, and the requirements of accumulated temperature above 0 degree C, precipitation, and sunshine duration in this period were 1000 degrees C-1200 degrees C, 400-450 mm, and 1000-1100 h, respectively. The growth rate of P. botryoides turned to higher at 54 d after reviving, reached the highest at 80 d after reviving, and became lower at 104 d after reviving. Under the effects of climate warming, the phenophase of P. botryoides was advanced by 15 d x (10 a)(-1) at heading stage, 7-8 d x (10 a)(-1) at flowering stage, 8-9 d x (10 a)(-1) at ripeness stage, and 3 d x (10 a)(-1) at withering stage. Climate change made the P. botryoides yield in study area have greater variation and higher unsteadiness.

[Responses of winter wheat growth to winter warming in Gansu Province].

Based on the observation data of the air temperature at Tianshui and Xifeng in 1951-2005 and of the phenology of winter wheat at Tianshui and Xifeng in 1981-2003, the tendency of winter warming in past 50 years and the responses of winter wheat growth to climate warming in Gansu Province were analyzed. The results showed that the growth and development of winter wheat were seriously influenced by winter warming. In recent 20 years or more, the overwintering mortality of winter wheat dropped to <2% , overwintering days reduced by 7-8 days, whole growth period shorted by 8-10 days, and jointing-flowering period extended by 7 days, which would benefit the production of winter wheat and the utilization of climatic resource. However, the higher winter temperature and lesser precipitation also made the grain yield instable and the plant diseases and insect pests more frequent, resulting in more uncertain factors in winter wheat safe production.