Current Location:home > Browse



Your conditions: Geography(79)

1. chinaXiv:201904.00091 [pdf]

Dynamics of infiltration rate and Field-Saturated soil hydraulic conductivity in a Wastewater-Irrigated cropland

Siyi Zhang; Isaac Hopkins; Li Guo; Henry Lin
Subjects: Geosciences >> Geography

The maintenance of a soil’s infiltration rate (IR) and field-saturated hydraulic conductivity (Kfs) is crucial for the long-term sustainable functioning of wastewater-irrigated lands. However, an effective procedure for reliably measuring in situ soil Kfs remains elusive. To address this issue, this study investigated the DualHead Infiltrometer (DHI), a novel instrument for automatically determining IR and Kfs, and compared it with a traditional Double-Ring Infiltrometer (DRI) under various field conditions. In the initial phase, we optimized the procedure and settings for the DHIs in a cropland that has been spray-irrigated with secondary-treated wastewater for decades in central Pennsylvania. Results showed that our optimized procedure, which used a single, long pressure cycle, yielded more robust measurements of IR than the originally recommended sequence of two short pressure cycles. The values of Kfs measured by the DHIs with optimized settings were similar to those measured by DRIs under many (but not all) field conditions, due to their differences in infiltration surface areas, operational procedures, length of infiltration time, and soil spatiotemporal variability. Viscosity-corrected Kfs on the irrigated cropland was 123.8±94.0 mm h-1, higher than that on the adjacent non-irrigated cropland (103.2±94.6 mm h-1), but the difference was not statistically significant, owing to the high degree of soil spatiotemporal variability and our limited number of measurements. Nevertheless, the higher Kfs values measured on irrigated cropland reflect observed changes in soil structure (e.g., soil pore characteristics) that have resulted from decades of irrigation. Seasonal variations in Kfs values existed between winter and summer conditions, but IRs during all seasons remained much higher than the current spray-irrigation rate (4.25 mm h-1), suggesting that the soil is still capable of handling the routine irrigation, even during winter. However, the coefficients of variation exceeded 67.0% across the field sites investigated and the time periods covered by our measurements were limited. As this specific site is permitted to discharge treated wastewater year-round, caution must still be exercised to ensure that soil Kfs remains high enough to prevent runoff generation, especially during winter frozen conditions.

submitted time 2019-09-06 Hits12071Downloads1116 Comment 0

2. chinaXiv:201909.00017 [pdf]

基于建设开发适宜性评价的干旱区绿洲城市增长边界的划定 —以乌鲁木齐市为例

Subjects: Geosciences >> Geography

科学合理地划定城市增长边界是控制城市无序蔓延、减少土地利用效率低下的有效途径,也是目前我国空间规划探索的重要内容之一。城市增长边界划定应依据区域不同资源环境本底条件和建设开发水平,因地制宜地选择合适的指标和方法,才能更准确地反映出城市发展的实际和需求,起到切实的指导作用。干旱区城市的发展受绿洲-荒漠生态系统影响作用显著,城市扩张过程中人地矛盾较为突出,城市增长边界划定必须体现资源环境-经济社会发展的协调性。本文以乌鲁木齐市为例,基于资源环境底线和城市发展潜力评价相叠加的研究思路,尝试探索干旱区绿洲城市增长边界划定的可行方法,结果表明:① 限制性评价和适宜性评价相结合的方法,可以很好地划定干旱区绿洲城市增长边界;② 将绿洲区域作为土地潜力的评价单元,对于干旱区绿洲城市划定城市增长边界更加合理和适用;③ 城市增长边界划分为刚性边界和阶段性边界可以指导城市土地的开发。

submitted time 2019-09-05 From cooperative journals:《干旱区研究》 Hits289Downloads11 Comment 0

3. chinaXiv:201909.00019 [pdf]


Subjects: Geosciences >> Geography

基于天山山区53个气象站点,31个CMIP5全球气候模式,集合逐年平均气候资料、社会经济和自然地形等资料,利用FLUS模型,预估了2050年RCP2.6、RCP4.5和RCP8.5排放情景下天山山区土地利用变化。结果表明:① FLUS模型能够较好地模拟研究区历史土地利用变化,具有较高的模拟精度。② 与基准期(1970—1999年)相比,3种情景下多年平均气温升高了1.67~2.16 ℃,其中春季和夏季增温幅度较小,秋季和冬季增温幅度较大。多年平均降水量增加22~25 mm,3种情景下个别年份较基准期出现降水减少现象,但总体呈增加趋势。③ 2050年RCP2.6、RCP4.5和RCP8.5的预估结果与2017年实测土地利用结果相比,天山山区冰雪面积分别减少29.2%、34.6%、38.4%。前2种情景城市用地面积增幅不大,部分耕地转换为城市用地和草地,林地面积少量增加。而RCP8.5情景下城市用地面积为2017年的近3倍,部分林地转换为草地。3种情景下水体总面积略有增加,未利用地呈减少趋势。

submitted time 2019-09-05 From cooperative journals:《干旱区研究》 Hits284Downloads11 Comment 0

4. chinaXiv:201909.00004 [pdf]


Subjects: Geosciences >> Geography

青藏高原是全球地理环境最为特殊的区域之一,研究全新世以来青藏高原文化遗址时空演变及其原因,对于理解极端环境下的人类响应与适应具有重要意义。基于ArcGIS空间分析,运用核密度估计、平均最邻近指数和全局空间自相关等地理统计方法,研究了全新世以来青藏高原14 339处文化遗址的时空演变。结果表明:各时期遗址最近邻指数均小于1,全局Moran’s I的取值介于0~1之间,遗址存在正的空间自相关,且属于集聚分布的模式;遗址分布重心经历了由高原腹地(旧石器时期)—东南边缘谷地(新石器时期)—东部地域(青铜器时期以来)的转变;遗址分布形态特征则经历了均匀广布型(旧石器时期)、边缘河谷型(新石器时期)、河谷集聚型(青铜器时期)、退化分散型(吐蕃部落时期)、半月广布型(吐蕃王朝时期)、斑块广布型(元代)、连片集聚型(明清时期)的变化过程;青藏高原各时期遗址时空分布演变是海拔、气候变化、植被等自然环境,以及生产方式、技术、战争、人口迁移、政治政策等社会经济因素共同作用的结果。

submitted time 2019-09-02 From cooperative journals:《干旱区研究》 Hits321Downloads25 Comment 0

5. chinaXiv:201909.00005 [pdf]

A drought resistance index to select drought resistant plant species based on leaf water potential measurements

SayedJamaleddin KHAJEDDIN
Subjects: Geosciences >> Geography

The water deficit in arid and semi-arid regions is the primary limiting factor for the development of urban greenery and forestation. In addition, planting the species that consume low levels of water is useful in arid and semi-arid regions that have poor water management measures. Leaf water potential (Ψ) is a physiological parameter that can be used to identify drought resistance in various species. Indeed, Ψ is one of the most important properties of a plant that can be measured using a pressure chamber. Drought avoiding or drought resistant species have a lower Ψ than plants that use normal or high levels of water. To determine drought resistance of species that are suitable for afforestation in arid urban regions, we evaluated twenty woody species in the Isfahan City, central Iran. The experimental design was random split-split plots with five replications. The species were planted outdoor in plastic pots and then subjected to treatments that consisted of two soil types and five drip irrigation regimes. To evaluate the resistance of each species to drought, we used the Ψ and the number of survived plants to obtain the drought resistance index (DRI). Then, cluster analysis, dendrogram, and similarity index were used to group the species using DRI. Result indicates that the evaluated species were classified into five groups: (1) high water consuming species (DRI>–60 MPa); (2) above normal water consuming species (–60 MPa≥DRI>–90 MPa); (3) normal water consuming species (–90 MPa≥DRI>–120 MPa); (4) semi-drought resistant species (–120 MPa≥DRI>–150 MPa); and (5) drought resistant species (DRI≤–150 MPa). According to the DRI, Salix babylonica L., Populus alba L., and P. nigra L. are high water consuming species, Platanus orientalis L. and Albizia julibrissin Benth are normal water consuming species, and Quercus infectoria Oliv. and Olea europaea L. can be considered as drought resistant species.

submitted time 2019-08-30 From cooperative journals:《Journal of Arid Land》 Hits1364Downloads18 Comment 0

6. chinaXiv:201909.00006 [pdf]

Allometric biomass equations of Larix sibirica in the Altay Mountains, Northwest China

LI Yuanyuan
Subjects: Geosciences >> Geography

Boreal forests are important carbon sinks and have tremendous potential to mitigate climate change. Aboveground biomass of Siberian larch (Larix sibirica Ledeb.) stands in the Altay Mountains, Northwest China was studied and allometric equations that are related to the biomass of aboveground components using diameter at breast height (DBH) or both DBH and height (H) as independent variables for L. sibirica trees were derived in this paper. A linear simultaneous equation system by using either DBH or both DBH and H (DBH&H) indices, was used to ensure additivity of the biomass of individual tree components, and was fitted for L. sibirica. Model performance was validated using the jackknifing test. Results indicate that the goodness-of-fit for the regressions was lowest for the needles (R2 ranging from 0.696 to 0.756), and highest for the stem wood (R2 ranging from 0.984 to 0.997) and the aggregated biomass components (R2 ranging from 0.994 to 0.995). The coefficient of determination for each component was only marginally improved in terms of model fit and performance in the biomass equations that used DBH&H as the independent variables compared to that used DBH as the independent variable, and needles yielded an even worse fit. Stem biomass accounted for the largest proportion (87%) of the aboveground biomass. Based on the additive equations that used DBH as the single predicitor in this study, the mean aboveground carbon stock density and the carbon storage values of L. sibirica forests were 74.07 Mg C/hm2 and 30.69 Tg C, respectively, in the Altay Mountains. Empirical comparisons of published equations for the same species growing in the Altay Mountains of Mongolia were also presented. The mean aboveground carbon stock density estimated for L. sibirica forests was higher in the Chinese Altay Mountains than in the Mongolian Altay Mountains (66.00 Mg C/hm2).

submitted time 2019-08-30 From cooperative journals:《Journal of Arid Land》 Hits1434Downloads20 Comment 0

7. chinaXiv:201909.00007 [pdf]

Community phylogenetic structure of grasslands and its relationship with environmental factors on the Mongolian Plateau

Subjects: Geosciences >> Geography

The community assembly rules and species coexistence have always been interested by ecologists. The community phylogenetic structure is the consequence of the interaction process between the organisms and the abiotic environment and has been used to explain the relative impact of abiotic and biotic factors on species co-existence. In recent years, grassland degradation and biodiversity loss have become increasingly severe on the Mongolian Plateau, while the drivers for these changes are not clearly explored, especially whether climate change is a main factor is debated in academia. In this study, we examined the phylogenetic structure of grassland communities along five transects of climate aridity on the Mongolian Plateau, and analyzed their relations with environmental factors, with the aims to understand the formation mechanism of the grassland communities and the role of climatic factors. We surveyed grassland communities at 81 sites along the five transects, and calculated their net relatedness index (NRI) at two different quadrat scales (small scale of 1 m2 and large scale of 5 m2) to characterize the community phylogenetic structure and analyze its relationship with the key 11 environmental factors. We also calculated the generalized UniFrac distance (GUniFrac) among the grassland communities to quantify the influence of spatial distance and environmental distance on the phylogenetic β diversity. The results indicated that plant community survey using the large scale quadrat contained sufficient species to represent community compositions. The community phylogenetic structure of grasslands was significantly overdispersed at both the small and large scales, and the degree of overdispersion was greater at the large scale than at the small scale, suggesting that competitive exclusion instead of habitat filtering played a major role in determination of community composition. Altitude was the main factor affecting the community phylogenetic structure, whereas climatic factors, such as precipitation and temperature, had limited influence. The principal component analysis of the 11 environmental factors revealed that 94.04% of their variation was accounted by the first four principal components. Moreover only 14.29% and 23.26% of the variation in community phylogenetic structure were explained by the first four principal components at the small and large scales, respectively. Phylogenetic β diversity was slightly significantly correlated with both spatial distance and environmental distance, however, environmental distance had a less explanatory power than spatial distance, indicating a limited environmental effect on the community phylogenetic structure of grasslands on the Mongolian Plateau. In view of the limited effect of climatic factors on the community phylogenetic structure of grasslands, climate change may have a smaller impact on grassland degradation than previously thought.

submitted time 2019-08-30 From cooperative journals:《Journal of Arid Land》 Hits1811Downloads23 Comment 0

8. chinaXiv:201909.00008 [pdf]

Shrub modulates the stoichiometry of moss and soil in desert ecosystems, China

LI Yonggang
Subjects: Geosciences >> Geography

Desert mosses, which are important stabilizers in desert ecosystems, are distributed patchily under and between shrubs. Mosses differ from vascular plants in the ways they take up nutrients. Clarifying their distribution with ecological stoichiometry may be useful in explaining their mechanisms of living in different microhabitats. In this study, Syntrichia caninervis, the dominant moss species of moss crusts in the Gurbantunggut Desert, China, was selected to examine the study of stoichiometric characteristics in three microhabitats (under living shrubs, under dead shrubs and in exposed ground). The stoichiometry and enzyme activity of rhizosphere soil were analyzed. The plant function in the above-ground and below-ground parts of S. caninervis is significantly different, so the stoichiometry of the above-ground and below-ground parts might also be different. Results showed that carbon (C), nitrogen (N) and phosphorus (P) contents in the below-ground parts of S. caninervis were significantly lower than those in the above-ground parts. The highest N and P contents of the two parts were found under living shrubs and the lowest under dead shrubs. The C contents of the two parts did not differ significantly among the three microhabitats. In contrast, the ratios of C:N and C:P in the below-ground parts were higher than those in the above-ground parts in all microhabitats, with significant differences in the microhabitats of exposed ground and under living shrubs. There was an increasing trend in soil organic carbon (SOC), soil total nitrogen (STN), soil available phosphorous (SAP), and C:P and N:P ratios from exposed ground to under living shrubs and to under dead shrubs. No significant differences were found in soil total phosphorous (STP) and soil available nitrogen (SAN), or in ratios of C:N and SAN:SAP. Higher soil urease (SUE) and soil nitrate reductase (SNR) activities were found in soil under dead shrubs, while higher soil sucrase (STC) and soil β-glucosidase (SBG) activities were respectively found in exposed ground and under living shrubs. Soil alkaline phosphatase (AKP) activity reached its lowest value under dead shrubs, and there was no significant difference between the microhabitats of exposed ground and under living shrubs. Results indicated that the photosynthesis-related C of S. caninervis remained stable under the three microhabitats while N and P were mediated by the microhabitats. The growth strategy of S. caninervis varied in different microhabitats because of the different energy cycles and nutrient balances. The changes of stoichiometry in soil were not mirrored in the moss. We conclude that microhabitat could change the growth strategy of moss and nutrients cycling of moss patches

submitted time 2019-08-30 From cooperative journals:《Journal of Arid Land》 Hits1109Downloads19 Comment 0

9. chinaXiv:201909.00009 [pdf]

Effects of different tillage and straw retention practices on soil aggregates and carbon and nitrogen sequestration in soils of the northwestern China

WU Jun
Subjects: Geosciences >> Geography

Soil tillage and straw retention in dryland areas may affect the soil aggregates and the distribution of total organic carbon. The aims of this study were to establish how different tillage and straw retention practices affect the soil aggregates and soil organic carbon (SOC) and total nitrogen (TN) contents in the aggregate fractions based on a long-term (approximately 15 years) field experiment in the semi-arid western Loess Plateau, northwestern China. The experiment included four soil treatments, i.e., conventional tillage with straw removed (T), conventional tillage with straw incorporated (TS), no tillage with straw removed (NT) and no tillage with straw retention (NTS), which were arranged in a complete randomized block design. The wet-sieving method was used to separate four size fractions of aggregates, namely, large macroaggregates (LA, >2000 μm), small macroaggregates (SA, 250–2000 μm), microaggregates (MA, 53–250 μm), and silt and clay (SC, <53 μm). Compared to the conventional tillage practices (including T and TS treatments), the percentages of the macroaggregate fractions (LA and SA) under the conservation tillage practices (including NT and NTS treatments) were increased by 41.2%–56.6%, with the NTS treatment having the greatest effect. For soil layers of 0–5, 5–10 and 10–30 cm, values of the mean weight diameter (MWD) under the TS and NTS treatments were 10.68%, 13.83% and 17.65%, respectively. They were 18.45%, 19.15% and 14.12% higher than those under the T treatment, respectively. The maximum contents of the aggregate-associated SOC and TN were detected in the SA fraction, with the greatest effect being observed for the NTS treatment. The SOC and TN contents were significantly higher under the NTS and TS treatments than under the T treatment. Also, the increases in SOC and TN levels were much higher in the straw-retention plots than in the straw-removed plots. The macroaggregates (including LA and SA fractions) were the major pools for SOC and TN, regardless of tillage practices, storing 3.25–6.81 g C/kg soil and 0.34–0.62 g N/kg soil. Based on the above results, we recommend the NTS treatment as the best option to boost soil aggregates and to reinforce carbon and nitrogen sequestration in soils in the semi-arid western Loess Plateau of northwestern China.

submitted time 2019-08-30 From cooperative journals:《Journal of Arid Land》 Hits1378Downloads18 Comment 0

10. chinaXiv:201909.00010 [pdf]

Determining the spatial distribution of soil properties using the environmental covariates and multivariate statistical analysis: a case study in semi-arid regions of Iran

Subjects: Geosciences >> Geography

Natural soil-forming factors such as landforms, parent materials or biota lead to high variability in soil properties. However, there is not enough research quantifying which environmental factor(s) can be the most relevant to predicting soil properties at the catchment scale in semi-arid areas. Thus, this research aims to investigate the ability of multivariate statistical analyses to distinguish which soil properties follow a clear spatial pattern conditioned by specific environmental characteristics in a semi-arid region of Iran. To achieve this goal, we digitized parent materials and landforms by recent orthophotography. Also, we extracted ten topographical attributes and five remote sensing variables from a digital elevation model (DEM) and the Landsat Enhanced Thematic Mapper (ETM), respectively. These factors were contrasted for 334 soil samples (depth of 0–30 cm). Cluster analysis and soil maps reveal that Cluster 1 comprises of limestones, massive limestones and mixed deposits of conglomerates with low soil organic carbon (SOC) and clay contents, and Cluster 2 is composed of soils that originated from quaternary and early quaternary parent materials such as terraces, alluvial fans, lake deposits, and marls or conglomerates that register the highest SOC content and the lowest sand and silt contents. Further, it is confirmed that soils with the highest SOC and clay contents are located in wetlands, lagoons, alluvial fans and piedmonts, while soils with the lowest SOC and clay contents are located in dissected alluvial fans, eroded hills, rock outcrops and steep hills. The results of principal component analysis using the remote sensing data and topographical attributes identify five main components, which explain 73.3% of the total variability of soil properties. Environmental factors such as hillslope morphology and all of the remote sensing variables can largely explain SOC variability, but no significant correlation is found for soil texture and calcium carbonate equivalent contents. Therefore, we conclude that SOC can be considered as the best-predicted soil property in semi-arid regions.

submitted time 2019-08-30 From cooperative journals:《Journal of Arid Land》 Hits1363Downloads13 Comment 0

12345678  Last  Go  [8 Pages/ 79 Totals]