Epigenetic gorges in fluvial landscapes

Epigenetic gorges form when channels that have been laterally displaced during episodes of river blockage or aggradation incise down into bedrock spurs or side‐walls of the former valley rather than excavating unconsolidated fills and reinhabiting the buried paleovalley. Valley‐filling events that promote epigenetic gorges can be localized, such as a landslide dam or an alluvial/debris flow fan deposit at a tributary junction, or widespread, such as fluvial aggradation in response to climate change or fluctuating base‐level. The formation of epigenetic gorges depends upon the competition between the resistance to transport, strength and roughness of valley‐filling sediments and a river's ability to sculpt and incise bedrock. The former affects the location and lateral mobility of a channel incising into valley‐filling deposits; the latter determines rates of bedrock incision should the path of the incising channel intersect with bedrock that is not the paleovalley bottom. Epigenetic gorge incision, by definition, post‐dates the incision that originally cut the valley. Strath terraces and sculpted bedrock walls that form in relation to epigenetic gorges should not be used to directly infer river incision induced by tectonic activity or climate variability. Rather, they are indicative of the variability of short‐term bedrock river incision and autogenic dynamics of actively incising fluvial landscapes. The rate of bedrock incision associated with an epigenetic gorge can be very high (>1 cm/yr), typically orders of magnitude higher than both short‐ and long‐term landscape denudation rates. In the context of bedrock river incision and landscape evolution, epigenetic gorges force rivers to incise more bedrock, slowing long‐term incision and delaying the adjustment of rivers to regional tectonic and climatic forcing. Copyright © 2008 John Wiley & Sons, Ltd.     

The importance of local‐scale openness within regions dominated by closed woodland

New and existing pollen data from Wales, UK, are used to assess the level of landscape openness at the regional and local scale. At the regional scale, the existing pollen data support the high‐forest model of vegetation structure by 6000 cal. yr. BC prior to any palynological signal for anthropogenic impact in the region. New data from two sites in southwest Wales follow the general regional pattern of early to middle Holocene vegetation succession, but are striking owing to maintenance of high non‐arboreal pollen percentages (NAPs) throughout the mid‐Holocene. It is argued that these NAPs indicate that a significant degree of openness can be found at the local level (and beyond the confines of the peat‐forming site) within regions characterised by closed woodland. It is possible that woodland development in these areas may have been suppressed by reduced drainage, although the role of grazing animals in maintenance of clearings cannot be assessed. Implications for this local degree of openness are discussed, in particular the significance of vegetation heterogeneity at the local scale for the construction of place or locale for prehistoric communities. Copyright © 2006 John Wiley & Sons, Ltd.     

INTERSTATE HIGHWAY EXIT MORPHOLOGY: NON-METROPOLITAN EXIT COMMERCE ON 1-75*

The commercial non-metropolitan exit clusters of America's interstate highway system exhibit regularities of basic form, scale, mix of services provided, and the ordinal placement of establishments relative to the exit proper. An examination of 354 exits serving 1-75 indicates the typical morphology of interstate exit clusters.     

基于地理国情普查的县域景观格局分析与优化建议——以佛山市三水区为例

快速城镇化进程带来城市地表覆盖类型及其空间组合关系的剧烈变化,由此造成资源短缺、环境污染、生态恶化等诸多问题。景观格局分析与优化方法对合理利用和优化配置土地资源至关重要,而地理国情普查为此提供基础数据支撑。本文选取景观斑块水平和景观类型水平指数,基于地理国情普查数据,对佛山市三水区地表覆盖景观类型特征和景观格局特征进行量化分析。研究结果表明:三水区水域和林地构成景观基质,山水城市特征明显;城乡人文景观优势度相对较高,城市开发对生态景观破碎化作用显著;三水区土地综合整治工作有待加强。     

黄河流域湿地景观时空演变格局分析

湿地景观的时空演变及其驱动因素研究是湿地生态恢复与保护的重要参考,本文利用1980—2015年7期黄河流域土地利用数据构建黄河流域湿地矢量数据集,基于景观格局指数对黄河流域湿地的时空演变特征进行定量和定性分析;采用转移矩阵对每两个时期湿地资源的转移类型和数量进行计算与分析。研究结果表明,①1980—2015年,黄河流域湿地率为3.5%,其中自然湿地率约为2.0%,即黄河流域的湿地类型以自然湿地为主。②斑块面积结果显示,黄河流域湿地总面积减少了312.74km²,表现为人工湿地增加,自然湿地减少;自然湿地中沼泽湿地呈增加状态,主要是在2005—2010年增加了979.22km²,滩地呈减少状态,减少了1218.19km²,主要发生在1990—1995年和2005—2010年。斑块密度结果显示,随着河渠和滩地受人为活动影响程度的加大,两者的斑块破碎化程度逐渐加大。最大斑块指数结果显示,水田是黄河流域的主导湿地类型,沼泽和湖泊是自然湿地中的主导湿地类型。③黄河流域湿地类型与非湿地之间转换是黄河流域景观转换的主要组成部分,其中沼泽与滩地是面积发生变化的主要湿地类型。     

玛河流域景观生态风险评价与时空分异

以玛纳斯河流域作为研究区,结合特殊的干旱区山地-绿洲-荒漠系统(Mountain-Oasis-Desert System简称MODS),综合考虑遥感影像数据光谱信息和纹理特征,将研究区分为耕地、林地、草地、水体、裸地、居民地、工业用地和冰川/永久积雪等8个景观类型,利用FRAGSTATS软件计算景观指数,引入生态风险的指数,将研究区划为低、较低、中、较高、高生态风险区五级,评估其景观格局的生态风险时空变化特征。结果表明:1)1990—2015年间,玛纳斯河流域景观变化主要表现为耕地、建设用地的增加以及水体、冰川/永久积雪面积的缩减;2)玛纳斯河流域的景观生态风险等级空间分布具有明显的差异,较低风险区的面积变化较为明显,低、较低生态的风险区比重有所上升,除此以外,林、草地类型各生态风险的等级所占比重的起伏波动具有明显的差异。建议应当合理地利用土地资源,尽量保护林地、草地等景观脆弱行较低的原生景观类型,禁止为开垦耕地而破坏林地、草地;增加土地的利用效率,更要对高等、较高生态风险区加强监管。     

新疆乌恰康苏地区构造地貌与景观生态格局研究

新疆乌恰康苏地区位于西昆仑山与西南天山对冲作用形成的盆山耦合带,其构造地貌具有显著的山地-平原分布格局特征.文章以"3S"技术为基础进行构造地貌填图,划分新疆乌恰康苏地区的景观类型,研究构造地貌对该区域景观生态格局的影响.采用垂向山地-平原构造地貌为指标,划分5个景观类;以土地利用类型+植被覆盖为指标,划分6个景观型;...     

河流生态系统结构功能整体性概念模型

在完善与整合现有河流生态系统结构功能概念及模型的基础上,提出河流生态系统结构功能整体性概念模型。水文情势、水力条件和地貌景观格局是对河流生态系统结构与功能具有关键影响的3大生境要素,结构功能模型的核心是建立以3大生境要素为构架的生命支持系统与河流生命系统之间的相互作用和相互制约关系,同时考虑由于人类活动引起生境要素变化对于河流生态系统的影响。河流生态系统结构功能整体性概念模型由以下4种模型组成:河流四维连续体模型、水文情势-河流生态过程耦合模型、水力条件-生物生活史特征适宜模型以及地貌景观空间异质性-生物群落多样性关联模型,这4种模型的一体化整合,基本概括了河流生态系统结构功能的整体特征。     

镇赉县土地利用结构调整

基于遥感与GIS进行吉林省镇赉县土地利用现状调查与生态适宜性评价, 通过分析二者差异提出土地利用调整方向及对策, 进一步优化土地利用结构。研究结果显示, 镇赉县宜林地和宜牧地的利用现状主要是盐碱地, 其次为耕地, 很少用于林地与草地; 宜农地和宜农、林、牧地利用格局单一, 耕林草比例不合理; 土地利用结构调整方向为盐碱地治理、退耕还林还草与土地利用格局优化。结合自然环境特点分析, 调整后的土地利用模式有农林复合、林草复合及开发水田等3种, 农、林、牧用地比例接近3∶1∶1, 空间格局交替安排。     

鲁中南岱崮地貌的成因及演化——以抱犊崮为例解析

鲁中南抱犊崮地区,山体陡峭挺拔,风景秀丽,以有鲁南小泰山之称的抱犊崮为代表,山体顶部主要由古生代寒武纪九龙群张夏组灰岩组成,其下分布由长清群馒头组砂岩、砂质页岩、泥质灰岩、薄层灰岩及朱砂洞组灰岩、泥质灰岩等。“崮”的成因主要是古生代寒武纪灰岩经受了强烈的地壳切割和抬升运动,并遭受长期的侵蚀、溶蚀、重力崩塌和风化剥蚀等多重地质作用而形成抱犊崮所具有的岱崮地貌,作为地质遗迹和地质地貌景观,具有重要的地学研究价值,也是潜力巨大的旅游资源。