Short-term variation of CO2 flux in relation to environmental controls in an alpine meadow on the Qinghai-Tibetan Plateau

[1] The alpine meadow ecosystem on the Qinghai-Tibetan Plateau may play a significant role in the regional carbon cycle. To assess the CO2 flux and its relationship to environmental controls in the ecosystem, eddy covariance of CO2, H2O, and energy fluxes was measured with an open-path system in an alpine meadow on the plateau at an elevation of 3,250 m. Net ecosystem CO2 influx (Fc) averaged 8.8 g m(-2) day(-1) during the period from August 9 to 31, 2001, with a maximum of 15.9 g m(-2) day(-1) and a minimum of 2.3 g m(-2) day(-1). Daytime Fc averaged 16.7 g m(-2) day(-1) and ranged from 10.4 g m(-2) day(-1) to 21.7 g m(-2) day(-1) during the study period. For the same photosynthetic photon flux density (PPFD), gross CO2 uptake (Gc) was significantly higher on cloudy days than on clear days. However, mean daily Gc was higher on clear days than on cloudy days. With high PPFD, Fc decreased as air temperature increased from 10degreesC to 23degreesC. The greater the difference between daytime and nighttime air temperatures, the more the sink was strengthened. Daytime average water use efficiency of the ecosystem (WUEe) was 8.7 mg (CO2)(g H2O)(-1); WUEe values ranged from 5.8 to 15.3 mg (CO2)(g H2O)(-1). WUEe increased with the decrease in vapor pressure deficit. Daily albedo averaged 0.20, ranging from 0.19 to 0.22 during the study period, and was negatively correlated with daily Fc. Our measurements provided some of the first evidence on CO2 exchange for a temperate alpine meadow ecosystem on the Qinghai-Tibetan Plateau, which is necessary for assessing the carbon budget and carbon cycle processes for temperate grassland ecosystems.

尾波干涉法精确测量地震波速变化的方法及实验研究

The coda of seismic waves consists of that part of the signal after the directly arrivials. In a finite medium, or in one that is strongly heterogeneous, the coda is dominated by waves which have repeatedly sampled the medium. Small changes in a medium which may have no detectable influence on the first arrivals are amplified by this repeated sampling and may thus be detectable in the coda. Because of this, coda wave is widely used in detecting micro variations in medium。 In this paper, we give a general view of the theory and application of coda wave, especially coda wave interferometry. We focus on discussing the application of coda wave interferometry on data source of active situ experiment。 First, we apply coda wave interferometry in a short time period situ experiment which last for three days. We also apply the method of coda wave interferometry in a situ experiment which last for one month. Daily circle variations of seismic velocity around the experiment site were obtained, and we also observed that the velocity variations in the experiment site have a significant correlation with the environment factors, including air temperature, barometric pressure, solid earth tide and the level of rainfall. We find that the velocity variation during this period is up to 10-3. The relationship between velocity variation and changes in air temperature, barometric pressure and solid earth tide was analyzed with least square linear fitting .The velocity has no dependence on the air temperature. But velocity has a change of 10-6--10-7 when the barometer or earth tide change per Pa. Generally, we conclude the work and results of previous researchers, and we also display our works and results. We hopes to contribute to the future research of coda wave interferometry.

东北四海龙湾玛珥湖啊1500年来长链烯酮不饱和度温标与古水温重建

The alkenone unsaturation paleothermometer is an important proxy to reconstruct water temperature, and is widely applied to reconstructing sea surface temperature in most oceanographic settings. Recent research indicates that long chain alkenone is preserved in lacustrine sediments, and the alkenone unsaturation has good relationship with mean annual temperature in studied lakes. Thus, the alkenone unsaturation could be used as a temperature proxy to reconstruct temperature in limnic systems. In this study, we analyzed long chain alkenone from the varved sediments in Lake Sihailongwan, northeastern China. Based on the counting varves, we established time scale during the past 1500 years. The distribution pattern in the sediment is similar with the previous study in lacustrine environment. The ratio of C37:4 methyl ketone to the sum of C37 alkenones is high. Based on the published temperature- alkenone unsaturation equation, we reconstructed the mean air temperature and July water temperature during the past 1500 years. Three major cold periods are in AD560-950, AD 1540-1600 and AD1800-1920. Three major warm periods are AD450-550, AD 950-1400 and AD 1600-1800. The Medieval Warm Period was a significant warm periods. However, the traditional “Little Ice Age” was not a persistent cold period, and interrupted by relative longer warm period. The temperature variations in this study show a general similar pattern with the summer temperature reconstruction from Shihua Cave and the winter temperature from historical documents. The temperature variations from long chain alknone record show a good agreement with solar activity (10Be data from ice core and sunspot number from tree rings). It may suggest that solar activity is most important forcing in the studied area.

西藏高原草原化嵩草草甸生态系统呼吸及碳平衡

The soil respiration and net ecosystem productivity of Kobresia littledalei meadow ecosystem was investigated at Dangxiong grassland station, one grassland field station of Lhasa Plateau Ecosystem Research Station. Soil respiration and soil heterotrophic respiration were measured at the same time by using Li6400-09 chamber in growing season of year 2004. The response of soil respiration and its components, i.e. microbial heterotrophic respiration and root respiration to biotic and abiotic factors were addressed. We studied the daily and seasonal variation on Net Ecosystem carbon Exchange (NEE) measured by eddy covariance equipments and then the regression models between the NEE and the soil temperature. Based on the researches, we analyzed the seasonal variation in grass biomass and estimated NEE combined the Net Ecosystem Productivity with heterogeneous respiration and then assessed the whether the area is carbon source or carbon sink. 1.Above-ground biomass was accumulated since the grass growth started from May; On early September the biomass reached maximum and then decreased. The aboveground net primary production (ANPP) was 150.88 g m~" in 2004. The under-ground biomass reached maximum when the aboveground start to die back. Over 80% of the grass root distributed at the soil depth from 0 to 20cm. The underground NPP was 1235.04 g m"2.. Therefore annual NPP wasl.385X103kg ha"1, i.e.6236.6 kg C ha"1. 2. The daily variation of soil respiration showed single peak curve with maximum mostly at noon and minimum 4:00-6:00 am. Daily variations were greater in June, July and August than those in September and October. Soil respiration had strong correlation with soil temperature at 5cm depth while had weaker correlation with soil moisture, air temperature, surface soil temperature, and so on. But since early September the soil respiration had a obviously correlation with soil moisture at 5cm depth. Biomass had a obviously linearity correlation with soil respiration at 30th June, 20th August, and the daytime of 27th September except at 23lh October and at nighttime of 27th September. We established the soil respiration responding to the soil temperature and to estimate the respiration variation during monsoon season (from June through August) and dry season (May, September and October). The regression between soil respiration and 5cm soil temperature were: monsoon season (June through August), Y=0.592expfl()932\ By estimating , the soil daily respiration in monsoon season is 7.798gCO2m"2 and total soil respiration is 717.44 gCC^m" , and the value of Cho is 2.54; dry season (May, September and October), Y=0.34exp°'085\ the soil daily respiration is 3.355gCO2m~2 and total soil respiration is 308.61 gCC^m", and the value of Cho is 2.34. So the total soil respiration in the grown season (From May to October) is 1026.1 g CO2IT1"2. 3. Soil heterogeneous respiration had a strong correlation with soil temperature especially with soil temperature at 5cm depth. The variation range in soil heterogeneous respiration was widely. The regression between soil heterogeneous respiration and 5cm soil temperature is: monsoon season, Y=0.106exp ' 3x; dry season, Y=0.18exp°"0833x.By estimating total soil heterotrophic respiration in monsoon season is 219.6 gCC^m"2, and the value of Cho is 3.78; While total soil heterogeneous respiration in dry season is 286.2 gCCbm"2, and the value of Cho is 2.3. The total soil heterotrophic respiration of the year is 1379.4kg C ha"1. 4. We estimated the root respiration through the balance between soil respiration and the soil heterotrophic respiration. The contribution of root respiration to total respiration was different during different period: re-greening period 48%; growing period 69%; die-back period 48%. 5. The Ecosystem respiration was relatively strong from May to October, and of which the proportion in total was 97.4%.The total respiration of Ecosystem was 369.6 g CO2 m" .we got the model of grass respiration respond to the soil temperature at 5cm depth and then estimated the daytime grass respiration, plus the nighttime NEE and daytime soil respiration. But when we estimated the grass respiration, we found the result was negative, so the estimating value in this way was not close. 6. The estimating of carbon pool or carbon sink. The NPP minus the soil heterogeneous respiration was the NEE, and it was 4857.3kg C o ha"1, which indicated that the area was the carbon sink.