Soil organic carbon storage and soil CO<Subscript>2</Subscript> flux in the alpine meadow ecosystem

High-resolution sampling, measurements of organic carbon contents and ¹⁴C signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau, and application of ¹⁴C tracing technology were conducted in an attempt to investigate the turnover times of soil organic carbon and the soil-CO₂ flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12×10⁴ kg C hm⁻² to 30.75×10⁴ kg C hm⁻² in the alpine meadow ecosystems, with an average of 26.86×10⁴ kg C hm⁻². Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO₂ flux ranges from 103.24 g C m⁻² a⁻¹ to 254.93 gC m⁻² a⁻¹, with an average of 191.23 g C m⁻² a⁻¹. The CO₂ efflux produced from microbial decomposition of organic matter varies from 73.3 g C m⁻² a⁻¹ to 181 g C m⁻² a⁻¹. More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%281.23% of total CO₂ emitted from organic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming, the storage, volume of flow and fate of the soil organic carbon in the alpine meadow ecosystem of the Tibetan Plateau will be changed, which needs further research. Supported by the National Natural Science Foundation of China (Grant Nos. 40231015, 40471120 and 40473002) and the Guangdong Provincial Natural Science Foundation of China (Grant No. 06300102)     

策勒绿洲与荒漠交错带达木沟剖面近4ka来干湿波动记录

位于塔克拉玛干沙漠南缘策勒绿洲与荒漠交错带的达木沟剖面高分辨率地记录了这一区域近４ｋａ来的环境演变历史。虽然,可以反映干湿波动的Ｒｂ／Ｓｒ比值曲线明显地反映了近４ｋａ来本地区持续干旱化的特征,且有后期加剧的趋势。但年代学及剖面沉积特征的研究还表明,在此期间仍有若干次相对湿润与干旱化加剧时期的波动。     

初冬季节青藏高原清水河地区甲烷排放率变化(英)

As the globally largest area covered by high altitudinal permafrost, the Qinghai-Tibet Plateau may contribute substantially to atmospheric CH4 budget when global warming. Preliminary observations on CH4 emission at Qingshuihe from November 5 to 14, 1995 show that alpine grassland may be a small source for atmospheric CH4 during early winter. The emission rates of CH4 from moist grassland surface varied from-16. 1 to 23. 9 μg. m-2h-1, with an average of 1. 82 μg. m-2h-1. Emission rates of CH4 from water surface of Qingshuihe River were from -21. 0 to 37. 1 μg. m-2h-1, with an average of 1. 56 μg. m-2h-1. The emission rates of CH at 30 to 200 cm in depth ranged from-69. 0 to 36. 0 μg. m-2h-1, with the average rate at these depths varying from -2. 15 to 2. 04 μg' m-2h-1. The mean emission rates of CH4 in the active layer and permafrost indicate the lower part of active layer tends to release CH4, CH4 is absorbed at low rates in the middle section and in the vicinity of permafrost table, and net fluxes of CH4 is emitted from the soils in the upper part. During the observation periods, the methane concentrations in static chambers and emission rates of grassland and water surface displayed noticeable diurnal variations. The water/ice content may play important role in the spatial variations of methane emission rates. The emission rates of methane is weakly correlated with the ground temperatures at sampling depths and air temperatures. The observed emission rates of methane from the comparatively dry and sandy grassland soils are quite low compared with that observed in the permafrost regions in the high latitudes.     

Sex expression and growth rates in natural populations of the desert soil crustal mossSyntrichia caninervis

The low elevation Mojave Desert cryptobiotic crust is dominated by the mossSyntrichia caninervis. In 16 populations of this moss, stem height and population were significantly associated with sex expression, with longer stems expressing sex more frequently and producing more perichaetia. The above-ground age of stems ranged up to 10 years, with a mean growth rate across populations of 0.36 mm year⁻¹. The overall stem sex ratio, as a proportion of the total number of stems, was 0.30♀: 0♂: 0.70 non-expressing. The probability of expressing sex in a given season was 0.09. The absence of sexual reproduction (no sporophytes) and likely absence of the male sex from the area indicate that the non-expressing plants are female individuals. The slow growth rates, low rates of sex expression, absence of male plants, and absence of sexual reproduction in this crustal species may help explain why re-establishment of mosses on desert soils can take decades.     

Processes of the deposition and vicissitude of Mu Us Desert, China since 150 ka B.P.

“Milanggouwan stratigraphical section” named lately takes down 27 cycles of alternately evolutionary histories of desert depositions in the Mu Us area with the fluviolacustrine facies and palaeosols since 150 ka B. P. Studies show that the sedimentary form was induced by the growth and decline and confrontation each other between the winter monsoon and the summer monsoon of East Asia in the past 150 ka. Project supported by the National Natural Science Foundation of China (Grant No. 49473192).     

An analysis of change in alpine annual maximum discharges: implications for the selection of design discharges

The paper presents an analysis of 17 long annual maximum series (AMS) of flood flows for Swiss Alpine basins, aimed at checking the presence of changes in the frequency regime of annual maxima. We apply Pettitt's change point test, the nonparametric sign test and Sen's test on trends. We also apply a parametric goodness‐of‐fit test for assessing the suitability of distributions estimated on the basis of annual maxima collected up to a certain year for describing the frequency regime of later observations. For a number of series the tests yield consistent indications for significant changes in the frequency regime of annual maxima and increasing trends in the intensity of annual maximum discharges. In most cases, these changes cannot be explained by anthropogenic causes only (e.g. streamflow regulation, construction of dams). Instead, we observe a statistically significant relationship between the year of change and the elevation of the catchment outlet. This evidence is consistent with the findings of recent studies that explain increasing discharges in alpine catchments with an increase in the temperature controlling the portion of mountain catchments above the freezing point. Finally, we analyse the differences in return periods (RPs) estimated for a given flood flow on the basis of recent and past observations. For a large number of the study AMS, we observe that, on average, the 100‐year flood for past observations corresponds to a RP of approximately 10 to 30 years on the basis of more recent observation. From a complementary perspective, we also notice that estimated RP‐year flood (i.e. flood quantile (FQ) associated with RP) increases on average by approximately 20% for the study area, irrespectively of the RP. Practical implications of the observed changes are illustrated and discussed in the paper. Copyright © 2011 John Wiley & Sons, Ltd.     

Water balance change for a re-vegetated xerophyte shrub area/Changement du bilan hydrique d’une zone replantée d’arbustes xérophiles

Abstract

Abstract Water balances for a re-vegetated xerophyte shrub (Caragana korshinskii) area were compared to that of a bare surface area by using auto-weighing type lysimeters during the 1990–1995 growing seasons at the southeast Tengger Desert, Shapotou, China. The six-year experiment displayed how major daily water balance components might vary for a bare and a re-vegetated sand dune area. Evapotranspiration from the C. korshinskii lysimeter represented a major part of the water balance. The average annual ET/P ratios varied between 69 and 142%. No seepage was observed for the vegetated lysimeter. For the bare lysimeter, on the other hand, 48 mm or 27% of observed rainfall per year occurred as seepage. These results suggest that re-vegetating large sandy areas with xerophytic shrubs could reduce soil water storage by transpiration. Also, the experimental results indicate that re-vegetating large sandy areas could significantly change groundwater recharge conditions. However, from a viewpoint of desert ecosystem reconstruction, it appears that natural rainfall can sustain xerophytic shrubs such as C. korshinskii which would reduce erosion loss of sand. However, re-vegetation has to be balanced with recharge/groundwater needs of local populations.     

不同石漠化等级的孢粉组合特征及其生态指示意义——以花江实验区为例

以贵州省关岭县南部北盘江试验示范为例,分析了不同等级石漠化土地上的表土孢粉组合特征,揭示了孢粉组合特征与石漠化等级的相互关系。结果显示:石漠化地区的孢粉组合具有鲜明的特征,乔木与灌木合占16.1%,草本与蕨类植物合占58.9%,这反映了石漠化地区以草蕨类植物为主的植被状况;孢粉组合与石漠化等级呈良好的相关性,草蕨类植物随石漠化等级的升高比重由41%增加到77.6%,种类由14种增加到27种,乔木花粉所占比重由6.9%降到2.6%,植物种类不变;孢粉组合反映出三出凤尾蕨等蕨类植物对岩溶石漠化生态环境的适应性和代表性。     

干旱高山区地电化学法寻找铜镍矿研究——以青海化隆拉水峡铜镍矿区为例

为解决干旱高山区的深部找矿问题和探索地电化学法在干旱高山区寻找隐伏铜镍矿产的可行性,在青海化隆拉水峡铜镍矿区开展了地电提取测量法、土壤离子电导率测量法寻找隐伏铜镍矿的试验研究,通过对已知矿体的地电化学法找矿试验,在隐伏铜镍矿体上测出了清晰的地电化学异常。对矿区的深部及外围的找矿预测中,在A区发现3个地电化学Ni、Cu及电导率异常,在B区发现3个地电化学Cu异常、1个Ni异常、3个电导率异常,在C区发现了3个地电化学Cu异常、2个地球化学Ni异常、3个电导率异常,推测在上述地电化学异常区内寻找隐伏铜镍矿会有新的突破。     

青藏高原多年冻土活动层土壤水分对高寒草甸覆盖变化的响应

对青藏高原高寒草甸30%、60%和93%三种覆盖度下,多年冻土活动层的土壤水分随季节变化的观测研究,结果表明:多年冻土活动层土壤水分分布对植被覆盖变化响应强烈.年内不同时期,植被覆盖度为65%和30%的土壤表层20cm深度内水分含量及分布相似,每次降水后30%覆盖度土壤水分的变率略大于65%覆盖度的;而93%覆盖度土壤水分在年内解冻开始到冻结前均小于前两种覆盖类型;植被覆盖度越小,土壤冻结和融化响应时间越早,响应历时也越短;浅层土壤冻结和融化对植被覆盖度的响应程度较强,接近深层土壤冻结和融化对植被覆盖度的响应程度降低.覆盖度为30%和65%土壤水分在整个冻结过程的减少幅度比93%覆盖度土壤大10%～26%,而融化期水分增加幅度更大为1.5%～80%;土壤冻融的相变水量对植被覆盖度变化响应明显,植被覆盖度降低,土壤冻结和融化相变水量增大.由于受植被蒸腾与地表蒸散发和土壤温度梯度的影响,融化期土壤剖面的水分重新分配,总体上呈现水分向剖面上部和底部迁移,剖面中部60～80cm深度左右的土壤出现"干层".