Assessment of iron(II) binding by a cryptoendolithic bacterial community: Implications for iron cycling in the Jurassic Navajo Sandstone     

《Journal of Arid Environments》2013

Previous work showed the cryptoendolithic microbial communities of the Colorado Plateau act to harden the surfaces of Jurassic Navajo Sandstone outcrops via the production of extracellular polymeric substances (EPS). It is our hypothesis that EPS produced in these systems serve to trap ions and maintain hydration. EPS isolated from in vitro and in vivo biofilms bind 200–600 nmol of ferrous iron per 10 g of biofilm sample. Initial characterizations of the EPS used preparations from two distinct microbial cultures grown in semi-submerged conditions with EPS harvested from approximately one-half of each culture immediately, the remaining biofilm was allowed to dry before the EPS was harvested. Analysis of ferrous iron binding of the four preparations showed that the culture dominated with non-filamentous cells only produced a chelating moiety after desiccation. Conversely, the second culture dominated by filamentous cells produced a ferrous iron binding activity when semi-submerged. Biochemical characterization showed that the extracted EPS was acidic, containing 37% uronic acid. Neither the EPS nor the biofilms had the ability to retain water though an increase in the rate of water loss was noted. We conclude that EPS produced by these communities are involved in nutrient capture as well as stabilization.  相似文献   

青藏高原植被覆盖变化及其与气候变化的关系   总被引：4，自引：0，他引：4  

刘军会  高吉喜  王文杰 《山地学报》2013,31(2):234-242

近几十年来,全球气候变化对青藏高原植被覆盖产生了重要影响。基于青藏高原1981—2005年遥感影像及同期气象数据,结合生态学模型,分析了青藏高原植被覆盖度变化趋势及其与气候变化的关系。结果显示,25 a间,青藏高原温度升高、降水量增加,植被覆盖度呈"整体升高、局部退化"趋势;地表植被改善区主要位于植被低覆盖区,退化区主要位于高覆盖区;从不同植被类型看,除针叶林、阔叶林受采伐影响覆盖度下降外,其他植被覆盖度均不同程度的上升;植被覆盖度变化与同期降水量变化、温度变化均呈正相关,且具有明显的区域差异。  相似文献   

Soil erosion and its response to the changes of precipitation and vegetation cover on the Loess Plateau   总被引：8，自引：2，他引：6  

Wenyi?Sun  Quanqin?ShaoEmail author  Jiyuan?Liu 《地理学报(英文版)》2013,23(6):1091-1106

Soil erosion is a major threat to our terrestrial ecosystems and an important global environmental problem. The Loess Plateau in China is one of the regions that suffered more severe soil erosion and undergoing climate warming and drying in the past decades. The vegetation restoration named Grain-to-Green Program has now been operating for more than 10 years. It is necessary to assess the variation of soil erosion and the response of precipita- tion and vegetation restoration to soil erosion on the Loess Plateau. In the study, the Revised Universal Soil Loss Equation （RUSLE） was applied to evaluate annual soil loss caused by water erosion. The results showed as follows. The soil erosion on the Loess Plateau between 2000 and 2010 averaged for 15.2 t hm-2 a 1 and was characterized as light for the value less than 25 t hm-2 a-1. The severe soil erosion higher than 25 t hm-2 a-~ was mainly distributed in the gully and hilly regions in the central, southwestern, and some scattered areas of earth-rocky mountainous areas on the Loess Plateau. The soil erosion on the Loess Plateau showed a deceasing trend in recent decade and reduced more at rates more than 1 t hm 2 a 1 in the areas suffering severe soil loss. Benefited from the improved vegetation cover and ecological construction, the soil erosion on the Loess Plateau was significantly declined, es- pecially in the east of Yulin, most parts of Yah＇an prefectures in Shaanxi Province, and the west of Luliang and Linfen prefectures in Shanxi Province in the hilly and gully regions. The variation of vegetation cover responding to soil erosion in these areas showed the relatively higher contribution than the precipitation. However, most areas in Qingyang and Dingxi pre- fectures in Gansu Province and Guyuan in Ningxia Hui Autonomous Region were predomi- nantly related to precipitation.  相似文献   

Spatial coupling relationships of gas hydrate formation in the Tibetan Plateau     

Qiang Zhou  WanLun Li  WeiTao Chen  YongJiang Wang 《寒旱区科学》2013,5(6):0691-0697

At present, gas hydrates are known to occur in continental high latitude permafrost regions and deep sea sediments. For middle latitude permafrost regions of the Tibetan Plateau, further research is required to ascertain its potential development of gas hydrates. This paper reviewed pertinent literature on gas hydrates in the Tibetan Plateau. Both geological and ge- ographical data are synthesized to reveal the relationship between gas hydrate formation and petroleum geological evo- lution, Plateau uplift, formation of permafrost, and glacial processes. Previous studies indicate that numerous residual basins in the Plateau have been formed by original sedimentary basins accompanied by rapid uplift of the Plateau. Ex- tensive marine Mesozoic hydrocarbon source rocks in these basins could provide rich sources of materials forming gas hydrates in permafrost. Primary hydrocarbon-generating period in the Plateau is from late Jurassic to early Cretaceous, while secondary hydrocarbon generation, regionally or locally, occurs mainly in the Paleogene. Before rapid uplift of the Plateau, oil-gas reservoirs were continuously destroyed and assembled to form new reservoirs due to structural and thermal dynamics, forcing hydrocarbon migration. Since 3.4 Ma B.P., the Plateau has undergone strong uplift and extensive gla- ciation, periglacier processes prevailed, hydrocarbon gas again migrated, and free gas beneath ice sheets within sedi- mentary materials interacted with water, generating gas hydrates which were finally preserved under a cap formed by frozen layers through rapid cooling in the Plateau. Taken as a whole, it can be safely concluded that there is great temporal and spatial coupling relationships between evolution of the Tibetan Plateau and generation of gas hydrates.  相似文献   

Effects of initial soil water content and saturated hydraulic conductivity variability on small watershed runoff simulation using LISEM     

Wei Hu  Dongli She  Ming'an Shao  Kwok P. Chun  Bingcheng Si 《水文科学杂志》2013,58(6):1137-1154

Abstract

Soil water content (θ) and saturated hydraulic conductivity (K_s) vary in space. The objective of this study was to examine the effects of initial soil water content (θ_i) and K_s variability on runoff simulations using the LImburg Soil Erosion Model (LISEM) in a small watershed in the Chinese Loess Plateau, based on model parameters derived from intensive measurements. The results showed that the total discharge (TD) and peak discharge (PD) were underestimated when the variability of θ_i and K_s was partially considered or completely ignored compared with those when the variability was fully considered. Time to peak (TP) was less affected by the spatial variability compared to TD and PD. Except for TP in some cases, significant differences were found in all hydrological variables (TD, PD and TP) between the cases in which spatial variability of θ_i or K_s was fully considered and those in which spatial variability was partially considered or completely ignored. Furthermore, runoff simulations were affected more strongly by K_s variability than by θ_i variability. The degree of spatial variability influences on runoff simulations was related to the rainfall pattern and θ_i. Greater rainfall depth and instantaneous rainfall intensity corresponded to a smaller influence of the spatial variability. Stronger effects of the θ_i variability on runoff simulation were found in wetter soils, while stronger effects of the K_s variability were found in drier soils. For accurate runoff simulation, the θ_i variability can be completely ignored in cases of a 1-h duration storm with a return period greater than 10 years, while K_s variability should be fully considered even in the case of a 1-h duration storm with a return period of 20 years.