The effects of water flow and temperature on thermal regime around a culvert built on permafrost

Temperature and water flow through a culvert beneath the Alaska Highway near Beaver Creek,Yukon,were measured at hourly intervals between June and October 2013.These data were used to simulate the effect of the culvert on the thermal regime of the road embankment and subjacent permafrost.A 2-D thermal model of the embankment and permafrost was developed with TEMP/W and calibrated using field observations.Empirical relations were obtained between water temperatures at the entrance to the culvert,flow into the culvert,and water temperatures inside the structure.Water temperatures at the entrance and inside the culvert had a linear relation,while water temperatures inside the culvert and water flow were associated by a logarithmic relation.A multiple linear regression was used to summarize these relations.From this relationship,changes in the flow rate and water temperatures at the entrance of the culvert were simulated to obtain predicted water temperatures in the culvert.The temperatures in the culvert were used in the thermal model to determine their effects on the ground thermal regime near the culvert.Variation of ±10% in water flow rate had no impact on the thermal regime underneath the culvert.Variation of water temperature at the entrance of the culvert had a noticeable influence on the thermal regime.A final simulation was conducted without insulation beneath the culvert.The thaw depth was 30 cm with insulation,and 120 cm without insulation,illustrating the importance of insulation to the ground thermal regime.     

Terrestrial heat flow and lithospheric thermal structure in the Chagan Depression of the Yingen-Ejinaqi Basin,north central China

The Chagan Depression in the Yingen-Ejinaqi Basin, located at the intersection of the Paleo-Asian Ocean and the Tethys Ocean domains is an important region to gain insights on terrestrial heat flow, lithospheric thermal structure and deep geodynamic processes. Here, we compute terrestrial heat flow values in the Chagan Depression using a large set of system steady-state temperature data from four representative wells and rock thermal conductivity. We also estimate the “thermal” lithospheric thickness, mantle heat flow, ratio of mantle heat flow to surface heat flow and Moho temperature to evaluate the regional tectonic framework and deep dynamics. The results show that the heat flow in the Chagan Depression ranges from 66.5 to 69.8 mW/m², with an average value of 68.3 ± 1.2 mW/m². The Chagan Depression is characterized by a thin “thermal” lithosphere, high mantle heat flow, and high Moho temperature, corresponding to the lithospheric thermal structure of “cold mantle and hot crust” type. We correlate the formation of the Yingen-Ejinaqi Basin to the Early Cretaceous and Cenozoic subduction of the western Pacific Plate and the Cenozoic multiple extrusions. Our results provide new insights into the thermal structure and dynamics of the lithospheric evolution in central China.     

Response and recovery of the Eel River, California, and its tributaries to floods in 1955, 1964, and 1997

Northwestern California is prone to regional, high magnitude winter rainstorms, which repeatedly produce catastrophic floods in the basins of the northern Coast Ranges. Major floods on the Eel River in 1955 and 1964 resulted in substantial geomorphic changes to the channel, adjacent terraces, and tributaries. This study evaluated the changes and the effects of a moderate flood in 1997 through field observations and examination of aerial photographs that spanned from 1954 to 1996. The purpose was to document the nature and magnitude of geomorphic responses to these three floods and assess the rates and controls on the recovery of the Eel River and its tributaries. Channel widening from extensive bank erosion was the dominant geomorphic change along the lower Eel River during major floods. As a result of the 1964 flood, the largest amount of widening was 195 m and represented an 80% change in channel width. Channel narrowing characterized the periods after the 1955 and 1964 floods. More than 30 years after the 1964 flood, however, the river had not returned to pre-flood width, which suggests that channel recovery required decades to complete. A long recovery time is unusual given that the Eel River is located in an area with a “superhumid” climate and has an exceptionally high sediment yield. This long recovery time may reflect highly seasonal precipitation and runoff, which are concentrated in 3–5 months each winter. In contrast to the main stem of the Eel River, the dominant effects of floods on the tributaries of the Eel River were rapid aggradation of channel bed and valley floor followed by immediate downcutting. Dendrogeomorphic data, aerial photographs, and field observations indicate that thick wedges of gravel, derived largely from hillslope failures in upper reaches of the tributaries, are deposited at and immediately upstream of the mouths of tributaries as the stage of the Eel River exceeded that of the tributaries during major floods. In the waning stages of the flood, the tributaries cut through the gravel at a rate equal to the lowering of the Eel and generated unpaired terraces and nickpoints. The complete process of deposition and incision can occur within a few days of peak discharge. Although reworking of some sediment on the valley floor may continue for years after large floods, channel morphology in the tributaries appears to be a product of infrequent, high magnitude events. The morphology of the tributary channel also appears to be greatly influenced by the frequency and magnitude of mass wasting in headwater areas of small basins.     

冬夏季温度和降水变化对青海湖全新世环境变化的影响初探

青海湖是国内最大的内陆湖泊,位于青藏高原东北缘,因其处在东亚夏季风、印度季风和西风带的交替控制区域,对气候变化十分敏感,成为古环境变化研究的热点地区。有关青海湖的形成演化、环境变化和水文变化的研究也存在多种观点。本研究再分析了青海湖已报道的古环境指标和气候模式模拟的夏季、冬季温度和降水变化,力图更加全面地理解青海湖全新世以来的古环境变化。研究发现早全新世11~8 ka夏季降水量和表面蒸发量较大,冬季降水稀少,湖泊水位只有十余米深,使得青海湖周边风沙活动频繁。并且,早全新世的气候不稳定,经历了频繁和较大幅度的波动。全新世气候适宜期出现在8~6 ka,古环境指标指示这一时期为温暖湿润的气候环境,湖盆内植被以森林草原为主,湖泊水位不断上升。青海湖地区的夏季降水自6 ka开始减少,然而冬季降水增加,同时夏季温度和蒸发量减少,使得湖区植被组成由森林草原向高山草甸转变,湖区大范围形成古土壤。湖区古环境条件在晚全新世距今1.5 ka开始恶化,冬季和夏季降水同时减少,湖泊水位下降,风沙活动再次加强。     

基于遥感的银川市建成区城市扩展及其热环境变化分析

为研究银川市城市建成区扩展对热环境的影响,基于1989、1999、2010年和2017年Landsat系列遥感数据,采用建筑用地指数(IBI)提取4个年份的城市建成区信息,获取了城市形态演化指标,利用热红外波段反演不同年份的地表温度;在此基础上,分析了城市扩展和热环境变化的时空演变特征,探讨了城市扩展和热环境之间的响应关系。结果表明:(1)1989—2017年银川市城市建成区扩展面积达506.13 km2,各时期的扩展速度和扩展强度差异明显,城市扩展具有"缓慢—快速—稳步"的阶段性特征,城市空间形态趋于紧凑化,向着稳定状态发展,城市整体向东部和北部扩展,重心整体向东北方向迁移约5.54 km。(2)热岛范围随着城市扩展不断扩大,较高温区域所占热岛比例呈先减小后增加的趋势,高温和特高温占比表现出先增加后减小的特征,热岛强度逐渐向较高温区转移,城市热岛效应得到缓解;热岛空间分布显示,热岛逐渐由兴庆区老城区蔓延至贺兰县和西夏区,且兴庆区热岛逐渐演化为相互独立的小次级热岛,强度有所降低;28 a间银川市城市热岛比例指数(URI)表现出先上升后下降的特征,整体呈上升趋势。(3)热岛区域在空间分布...     

基于空间PCA的兰州市热环境人文驱动因素分析

在城市化过程中,人类社会、经济活动的加剧使城市地表热力景观呈现出高度的空间异质性。目前对城市热环境形成、演变的驱动机制、热岛效应与地表覆被变化的定量关系研究大多还是从对某些影响因子的测定入手,缺乏对区域热环境系统全面、综合的评价与分析。利用多源空间数据,以干旱区河谷型城市兰州为研究对象,在探讨热环境的空间格局基础上,运用空间主成分分析方法替代传统的多准则判断方法,分析了人类活动对城市热环境的影响特征。结果表明:兰州市人类活动对热环境的影响因子可以归纳为4种相对独立的基本要素,即景观格局、工业布局、城市建筑以及地表覆盖。影响兰州市中心城区热环境的最核心要素是景观格局,四个因子的线性模型较好地模拟了热环境的空间变化,定量揭示了兰州中心城区人类活动对热环境的影响机制。     

Biological and Geochemical Record of Anthropogenic Impacts in Recent Sediments from Lake Pupuke, Auckland City, New Zealand

Frozen sediment cores from Lake Pupuke in Auckland City, New Zealand, contain a high resolution decadal to annual scale record of changing lake paleoenvironments and geochemistry that reflects changing landuse and hydrology in the catchment over the past c. 190 years. A reliable chronology is available from AMS ¹⁴C and ²¹⁰Pb dating of the sediments, with the timing of the older part of the record supported by the first appearance of pollen of introduced Pinus and Plantago lanceolata associated with European settlement of Auckland in the early 1840s. Diatom stratigraphy, sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions commensurate with European development of the Lake Pupuke catchment, in particular enhanced algal productivity controlled by the influx of nutrients after c. 1920 AD. Attempts to prevent nuisance algal blooms in 1933, 1934 and 1939 using CuSO₄ addition produced Cu spikes in the sediment that allowed confirmation of the accuracy of the ²¹⁰Pb chronology. Hence, the elemental and isotopic composition of the Lake Pupuke sediments reflect the timing of significant anthropogenic activities, rather than climatic variations, that have occurred within the watershed over the past c. 190 years. The comparison of records of land use change in the catchment with the multi-proxy record of changes in the sediments usually allowed unambiguous identification of the signatures of change and their causes.     

南京市内部旅游客流空间测度与模拟

将传统分析方法与空间数据分析方法相结合,建立空间数据模型,采用Surfer动态图,实态模拟南京旅游客流空间分布格局。研究发现:①南京市内部旅游流位序—规模分布非常典型。流量规模参数|q|大于1,但一直趋于减小,说明极化作用、不均衡发展仍是旅游流空间格局演变中主要特征。②南京市旅游流呈现显著的空间集聚特征。1995~2005年间,全局Moran’sI指数有一定的波动,1995年Moran’sI最小,2001年后,全局Moran’sI快速扩大。城市内部旅游流空间关联程度逐渐增强,局域范围内具有强烈的空间自相关特征。Local Moran’sI显著性检验表明,南京旅游流在局域范围内具有强烈的空间自相关特征。“高高”象限由1995年4个增至2005年8个;“低高”象限由1995年2个增至2005年8个,而“高低”象限变化不明显。③通过R型和Q型因子分析,识别了4个重要的旅游集聚场和扩散场,但首级集聚场和扩散场强度非常大。首级核旅游吸引力具有较广的吸引范围,且吸引景区级别较高。其它3个核吸引范围呈现分片区特征。扩散场分布相对均衡且“大分散、小集聚”。④根据研究结果构建了南京城市内部旅游流空间变化模式。20世纪90年代中期以来,南京市内部旅游流空间变化模式呈现出空间层次性、动态变化性特征。旅游流空间分布呈现从少数旅游节点向多数旅游节点转变,旅游节点体系逐渐发育成熟。     

升金湖枯水期滩地土壤CO2-C释放通量及有机碳稳定性研究

湿地是陆地生态系统的重要组成部分,在陆地碳库和固碳中具有重要作用。全球湿地碳库的稳定对减少土地利用变化引起的温室气体释放及减缓气候变化具有重要意义。以升金湖国家级自然保护区的典型滩地为研究对象,采用静态箱—气相色谱法对土壤CO₂释放通量进行观测和测定,并进一步分析土壤有机碳库的分布,探讨了滩地土壤呼吸动态和碳库稳定性。研究结果表明,升金湖0～20 cm滩地土壤有机碳含量为11.47～22.25 g/kg,有机碳密度为3.78～4.58 kg/m²,平均有机碳密度为4.11 kg/m²,土壤CO₂-C释放通量为111.7～499.5mg/（m².h）;滩地土壤有机碳密度和CO₂-C释放通量高于周边地区的水稻土土壤,且其有机碳稳定系数偏低,这表明升金湖滩地土壤有机碳库自身具有较高的稳定性,这是滩地土壤有机碳保持的一种机制,在气候变暖背景下,滩地土壤有机碳库的脆弱性将增加。