Modern Diatom Assemblages in Surface Sediments from Estuarine Systemsin the Southeastern Buenos Aires Province, Argentina

Paleoecological reconstructions of Holocene sea-level changes in Argentinean coastal regions were based mainly on ecological data gathered from other regions, as there was a lack of information on modern estuarine diatom distributions. The aim of the present work was to assess the spatial variation of diatom assemblages in two representative estuaries of Argentina in order to gather ecological information for paleoecological reconstructions in the region. The two selected estuaries have different geomorphologic features and salinity regimes: Mar Chiquita Lagoon is shallow, which prevents the development of a stable salinity gradient as it occurs in the Quequén Grande River. Surface sediment samples were taken from selected stations representative of the environmental gradient from the inlet to the inner reaches of both estuaries. Cluster analysis defined three diatom zones at Mar Chiquita: marine/brackish assemblages dominate the inlet (zone I), where salinity, tidal range and current speed are higher. The brackish/freshwater tychoplankton Staurosira construens var. venter and Staurosirella pinnata dominate the inner lagoon (zone II), where environmental conditions are very variable and concentrations of suspended sediments are higher. Brackish/freshwater euryhaline diatoms dominate the headwaters (zone III). On the other hand, the Quequén Grande River was divided into three diatom zones: coastal taxa are distributed at the inlet (zone I), while the middle estuary (zone II) is dominated by brackish/freshwater euryhaline taxa. At the upper estuary region (zone III), freshwater diatoms dominate, and the halophobous Nitzschia denticula increased in abundance values. Diatom distributions were most closely related to the salinity gradient at Quequén Grande River than at Mar Chiquita Lagoon. Fossil data of a sequence from Mar Chiquita Lagoon (Las Gallinas Creek) were compared to the modern data set in order to search for analogies between fossil and modern diatom assemblages. DCA results showed that fossil diatom assemblages have modern counterparts. Most diatom assemblages of Las Gallinas Creek fall within Mar Chiquita zone III, representing a shallow brackish/freshwater environment, with low salinity fluctuations (~1–9‰) and no tidal influence. Therefore, our modern diatom data provide useful analogs to interpret paleoenvironments in the region.     

莱州湾南岸滨海湿地变化及其原因分析

以1992年和2004年的TM遥感影像为数据源,从景观生态学角度,对1992年和2004年的莱州湾南岸湿地及其变化进行了研究。结果表明,与1992年相比,2004年研究区湿地面积减少了32．339km2,其中,自然湿地面积减少了246．189km2,而人工湿地面积却增加了213．851km2,至2004年,人工湿地面积已占研究区湿地总面积的78．22％;湿地景观多样性指数下降了0．1077,景观优势度指数和景观破碎化指数分别上升至0．109和0．0089。自然湿地被大面积垦殖,湿地淡水资源不足,大规模开采沿海卤水资源,环境污染加剧,风暴潮等自然灾害频发,是导致研究区自然湿地萎缩的主要因素。     

Post-glacial vegetation history of the Mission Mountains,Montana

A pollen record from Rock Lake in the Mission Mountains, northwestern Montana reveals a four-zone sequence reflecting Holocene vegetation change. Chronologic control is provided by two well-known tephras, Glacier Peak (11 200 yr B.P.) and Mazama (6800 yr B.P.). The presence of Glacier Peak tephra above the basal inorganic sediments indicates deglaciation prior to 11 200 yr B.P. Colonizing vegetation (Zone I) after the fall of Glacier Peak tephra was dominated byArtemisia (sage) andAlnus (alder). The presence ofAbies needles,Picea needles, and oneTaxus needle in the core demonstrates that these taxa were at Rock Lake at the time Zone II sediments were deposited. The increase inPinus,Picea, andAbies pollen in Zone II (10 850-4750 yr B.P.) suggests warmer and drier conditions prevailed, and may record the Hypsithermal. The pervasiveness ofPicea andAbies pollen in Pollen Zone III (4750-3350 yr B.P.) suggests the emergence of the modern subalpine forest. Pollen Zone IV (3350 yr B.P.-present) is characterized by relatively little change in the pollen assemblages. One noted change, however, is the increase of Cyperaceae (sedge), which may indicate an expansion of shore-line around the lake, possibly reflecting increased precipitation.This is the 5th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.     

北京丰台区土地利用变化及其经济驱动力分析

采用GIS技术和统计分析技术,基于1984、1992和1995～2001年土地利用图件和数据,分析了1984年以来北京丰台区土地利用变化历史过程及其空间分异特征。土地利用变化的基本特点是农业用地面积大幅度下降,非农用地面积快速增加,且随着时间的推移,变化高峰地域在由内向外传递。对1999年土地利用类型数据与经济产值数据匹配结果表明:土地经济产出效益巨大差异的存在是驱动丰台区土地利用从农业用地,尤其是耕地向非农业用地转化的最大动力所在。利用1992～2001年的非农业用地与固定资产投资、人口,二、三产业增加值进行的相关分析显示,固定资产投资、人口增长和第二产业的发展对非农业用地扩展有着显著的作用。     

新疆博尔塔拉河表土孢粉组合与植被关系研究

博尔塔拉河流域位于中哈边境,其植被和土壤具有十分明显的垂直分布和区域性差异,根据该流域一条自西向东沿着海拔高度从210 m 到3 235 m 长约200多km的样带上所采集的人为干扰较少的49 个表土花粉样品的孢粉组合图式和现代植被样方调查资料,探讨了博尔塔拉河流域植被与表土花粉之间的关系。该区孢粉谱从上至下可划分为6个带,分别对应高山草甸带、亚高山草甸草原带、森林灌丛带、灌丛草原带、荒漠草原带、荒漠植被带。值得注意的是第6个孢粉带因含有具湿地特征的隐域性植被类型花粉组分,故又分成2个亚带,即荒漠植被亚带Ⅵ₁和荒漠植被亚带Ⅵ₂。森林灌丛植被带上限的云杉花粉含量明显比该带下限的含量高,表明云杉花粉的传播在沟谷地区受山谷风的影响较大。与此同时,将孢粉数据与气象数据相结合,分析结果得出比较有代表性的云杉属(Picea)、桦属(Betula)、藜科(Chenopodiaceae)、麻黄属(Ephedra)等花粉,与降水量和温度的关系较为密切。     

南设得兰群岛西海域S_(11)岩芯沉积物中碎屑矿物及沉积作用的探讨

本文对南设得兰群岛西海域S_(11)钻孔岩芯中的重、轻矿物作了描述,按矿物在垂直方向上的变化和优势矿物种确定矿物组合类型,并将晚更新世到全新世的341cm沉积地层划分为四层:1.上火山碎屑矿物沉积层,2.中火山碎屑矿物沉积层,3.火成碎屑矿物沉积层(深海砂层),4.下火山碎屑矿物沉积层。本文还讨论了物质来源和深海砂层的可能成因。     

1992-2015年中亚五国土地覆盖与蒸散发变化

1991年苏联解体,中亚五国独立使得土地覆盖与蒸散发格局发生深刻变化。以中亚五国为研究区,采用欧空局气候变化项目（CCI）土地覆盖和全球陆地数据同化系统（GLDAS）蒸散发数据,分析1992-2015年土地覆盖与蒸散发时空变化特征,进一步研究耕地蒸散耗水特征。结果表明：① 中亚五国土地覆盖变化具有阶段性特征,耕地扩张引起土地覆盖格局变化。1992-2003年耕地快速增加（1.1万km ²/a）,林地和草地大幅减少。2003-2015年耕地增速趋缓（0.3万km ²/a）,林地和草地有一定恢复,裸地和水体持续减少,城镇用地持续增长。耕地共增加12.3万km ²,林地和草地分别减少4.0万km ²和2.3万km ²,且集中于哈萨克斯坦中北部。裸地减少3.5万km ²,集中于哈萨克斯坦西南部,水体减少3.1万km ²,集中在咸海湖泊。乌兹别克斯坦耕地减少、裸地增加,吉尔吉斯斯坦、塔吉克斯坦和土库曼斯坦土地覆盖变化幅度较小;② 中亚五国蒸散发变化与土地覆盖格局基本一致。蒸散发总体呈增加态势（6 mm/a）,1992-2003年快速增加（11.3 mm/a）,2003-2015年缓慢上升（2.4 mm/a）。中亚五国年蒸散发达到276.8 mm,东南部的吉尔吉斯斯坦（347.3 mm）和塔吉克斯坦（302.9 mm）最高,中北部的哈萨克斯坦（297.9 mm）次之,西南部的乌兹别克斯坦（211.0 mm）和土库曼斯坦（150.0 mm）最低;③ 中亚五国蒸散耗水结构受耕地面积大小的影响。中亚五国耕地蒸散耗水的贡献由24.7%增至27.9%,土库曼斯坦耕地蒸散耗水仅占本国的11%,其他国家均超过25%。草地、林地和裸地的蒸散耗水贡献降低,但哈萨克斯坦、吉尔吉斯斯坦和塔吉克斯坦仍以草地和林地蒸散耗水为主（≥ 50%）,土库曼斯坦（61.3%）和乌兹别克斯坦（46.4%）的裸地蒸散耗水占绝对优势。本文明确了中亚五国土地覆盖连续动态变化过程,细化各国土地覆盖与蒸散发特征及差异,增强对土地覆盖与蒸散发现状的认识,可为水土资源管理和生态环境保护提供数据参考。     

1993～2003年厦门市湿地动态变化及其驱动因素分析

通过对厦门市1993年TM遥感影像和2003年ETM 遥感影像的解译分析和数据统计,从湿地面积动态变化和湿地消长情况等方面,用单一土地利用动态度等指标对1993~2003年期间厦门市的湿地变化进行了研究。结果表明,1993~2003年期间厦门市天然湿地面积减少了2103hm2,其中有954hm2(滩涂864hm2)转变为非湿地,有1149hm2转变为人工湿地;而人工湿地面积增加了2775hm2,其中养殖场面积从1993年的5778hm2迅猛增加到2003年的9768hm2,年均增长率为6.91%,水库与水塘和盐田则分别减少了961hm2和254hm2。有27.74%、11.41%、9.33%和3.63%的养殖场面积分别是由非湿地、滩涂、盐田和水库与水塘转变而来的;有54.37%的盐田转变成了养殖场,有33.24%、30.24%的红树林转变为非湿地、养殖场,有10.35%、8.64%的滩涂转变为养殖场、非湿地。对社会经济驱动因素的分析表明,经济发展、人口增长和农业生产比较利益因素极大影响着厦门市湿地的动态变化。     

Competition,contingency, and destabilization in urban assemblages and actor-networks

This intervention contributes to recent work in urban geography that integrates the conceptual frameworks of assemblages and actor-network theory by highlighting two additional directions that require a more rigorous and detailed theorization. The first direction concerns the relationship between contingency and necessity in urban assemblages and actor-networks and this paper delineates four specific propositions as a starting point for further reflection. The second direction suggests that urban assemblages and actor-networks require a more explicit vocabulary for thinking about competition and cooperation within and between cities. To this end, the paper introduces a new concept – delayed asymmetric counterforces – that can foster a better understanding of competition-induced urban change and destabilization. The novel concept is developed in conjunction with a typology of delays in competitive urban dynamics, which helps illuminate how delayed asymmetric counterforces are both a cause and an effect of the complexity inherent in the urban realm.     

近30年苏北滨海滩涂湿地演变特征与空间格局

苏北滨海滩涂湿地位于现代长江口与废黄河口之间,是最典型的淤泥质平原海岸,其演变特征及空间格局具有鲜明的特征。本文选用1980年、1992年、2008年的TM 和ALOS影像为主要数据源,构建了基于空间分割和转移矩阵分析模型,研究了近30年来苏北滨海滩涂湿地的演变特征及其空间格局。结果表明： ①苏北滨海滩涂发生了巨大变化,近30年间滩涂总面积减少了1273.11 km²,平均每年减少45.47 km²;滩涂湿地侵蚀/淤积面积约965.14 km²,0 m等深线冲刷后退减少的面积约为307.97 km²。②苏北滨海滩涂湿地区域差异性明显。南北方向上可划分为6个自然地理单元,东西方向上可划分为3个区域。③苏北滨海滩涂湿地演变中,湿地转型、湿地丧失和湿地演替分别占总面积的38.39%、14.80%、20.51%;其中天然湿地减少354.1 km²,人工湿地增加1061.45 km²,非湿地增加253.09 km²。④滩涂湿地主要植被群落演替特征和空间分布也呈现出差异性。湿地演替主要发生在净变区,与对应岸段的海岸侵蚀/淤积类型基本吻合。     

沉积物记录的亚高山湖泊环境变化——以鄂东南云中湖为例

根据云中湖27 cm长沉积岩芯进行元素、粒度和硅藻多指标分析以及²¹⁰Pb测年,结合流域气候和人类活动等历史资料,反演1958年以来云中湖在气候变化和人类活动影响下的环境变化。冗余分析结果显示云中湖沉积硅藻组合变化与Al、Fe、Pb和温度四个变量显著相关。硅藻属种聚类分析的结果表明云中湖环境变化经历了两个阶段：1958-1993年间喜碱性水体的Achnanthes minutissima和Fragilaria nanana属种大量出现与较高CIA指数响应于气候调控下的流域侵蚀过程;1993年以来气候变暖与旅游发展引起入湖营养盐增加是Cyclotella pseudostelligera和Aulacoseira alpigena等中—富营养硅藻种增殖的主要诱因。重建亚高山湖泊在气候变化以及人类活动影响下湖泊生态系统的演化,为保护亚高山湖泊生态环境和改善流域水质提供参考。     

Reconstructing past eutrophication trends from diatoms and biogenic silica in the sediment and the pelagic zone of Lake Constance, Germany

In Lake Constance, phosphorus concentrations and the seasonal development of phytoplankton communities in water samples from the pelagic zone were regularly recorded since the 1950's. Before the 1950's, there were occasional investigations of plankton communities since 1896. We compared these data with the sedimentary record in two sediment cores. Then, the eutrophication history of Lake Constance was inferred from diatoms. The record of biogenic silica in the cores is discussed with respect to diatom biomass increase.Diatom assemblages in the sediment cores precisely reflected the pelagic diatom development for the period 1971--1992. Both sediment cores and the water samples have a high interannual variability of diatom assemblages. Below a sediment depth of 27 cm (AD 1920), more than 50% of the diatoms were partly corroded, and we limited the reconstruction of trophic state changes to the interval of 1920--1993. Oligotrophic conditions of Lake Constance were indicated by the dominance of various Cyclotella taxa from 1920 to 1940. Since 1939/1940, increasing abundance of it Tabellaria fenestrata showed oligotrophic to mesotrophic conditions. Between 1953 and 1956, increasing Stephanodiscus hantzschii and disappearing Cyclotella indicated advanced eutrophication and total phosphorus values ranged between 8--10 mg m-3 during turnover in late winter. Further eutrophication was shown by disappearing T. fenestrata and increasing S. minutulus in 1963. Maximum TP concentrations of 87 mg m-3 occurred in 1979/80 and was accompanied by increasing abundances of Aulacoseira granulata. From 1986 to 1992, reoccurrence of Tabellaria fenestrata and Cyclotella indicate some recovery of Lake Constance.Biogenic silica and diatom abundances were similar among cores but indicate a 3--4 fold increase of diatom biomass only. This was far below the estimate of biomass increase from sedimentary pigment data (25 fold) and the estimate of phytoplankton data from the literature (70 fold).     

上海东部地区晚第四纪沉积的孢粉组合及古环境

通过对上海东部地区南汇鹤鸣孔、东海1井、高桥G2孔3口钻井晚第四纪地层的孢粉研究,划分出了6个孢粉组合带和3个亚带,恢复了本地区植被演替、气候波动的6个阶段:第1阶段晚更新世晚期,反映气候凉冷稍湿;第2阶段前北方期,反映气候温凉略湿;第3阶段北方期,反映气候温和略干;第4阶段大西洋期,反映气候热暖潮湿;第5阶段亚北方期,反映气候温暖略干; 第6阶段亚大西洋期,反映气候温暖湿润。这为本地区晚第四纪古植被、古气候、古环境的重建提供了重要的孢粉学资料。     

Can severely fragmented patches of riparian vegetation still be important for arid-land bird diversity?

The vegetation of riparian habitats is often distinct from that of the surrounding landscape, thus representing unique habitat for a variety of biota. Although highly mobile, birds often exhibit distinct species assemblages associated with habitat. Therefore, degradation or removal of riparian habitat, particularly in arid environments, may threaten bird diversity. Along the Vaal River, South Africa, mining and agriculture have reduced natural riparian habitat to ca. 9% of its former extent in the Northern Cape Province. We surveyed bird assemblages within intact riparian, savanna and bush-thickened habitats along the Vaal River to ascertain their importance to bird diversity. Avian abundance and species richness did not differ between the three habitats. Species composition of riparian bird assemblages was significantly different to that of savanna and bush-thickened habitats, however, which were not significantly different from each other, and more species were characteristic of riparian habitat (17 species) than bush-thickened (seven species) or savanna (one species) habitats. Of three species reaching the south-western limit of their African distribution, all occurred in riparian habitat. Thus, despite its fragmented nature, the riparian vegetation on the Vaal still supports an important component of avian diversity, and a landscape-level approach is required to manage this relatively rich, arid-land, river.     

1984-2008年北京湿地景观格局驱动机制(英文)

The landscape pattern of Beijing wetlands has undergone a significant change as a result of natural and artificial elements.Supported by remote sensing and GIS technology,using multi-temporal TM images from 1984 to 2008 in Beijing,this paper analyzed the dynamic characteristics of wetlands landscape pattern through selected typical indices including patch area,patch average area,fractal dimension index,diversity,dominance,contagion indices and the spatial centroids of each wetlands type were calculated.Finally,the paper explored the evolution mode and driving factors of wetland landscape pattern.The results were obtained as follows:the total wetland area increased during the period 1984-1996,then decline from 1996 to 2004.The wetland area in 1994 accounted for only 47.37% of that in 2004.The proportion of artificial wetland area was larger than that of natural wetland.The proportion of reservoir wetland was 33.50% to 53.73% and had the maximum average area.pond and paddy field wetland type with the least average area accounted for 16.46% to 45.09% of the total wetland area.The driving forces of the natural river wetland were mainly natural elements;its fractal dimension index was greater than the others.The Shannon diversity index of wetland landscape increased from 1.11 in 1992 to 1.34 in 2004,indicating that the difference between proportions of each wetland type decreased and areas of each wetland type were evenly distributed.The contagion index went down from 65.59 to 58.41,indicating that the connectivity degraded.Miyun Reservoir had the largest area and its area change had a great impact on the location of the centroid.Wetland resources degenerated gradually from the joint effects of natural and artificial factors.During the period 2006-2008,the precipitation increased and the drought condition was relieved.The government implemented series of positive policies to save water resources,and the wetland area increased.     

Diatom-temperature transfer functions based on the altitudinal zonation of diatom assemblages in Papua New Guinea: a possible tool in the reconstruction of regional palaeoclimatic changes

Indirect and direct gradient ordination techniques were used to study the relationship between present-day benthic and periphytic diatom assemblages and environmental factors along an altitudinal gradient in Papua New Guinea. Both within the screened initial data-set and a narrowly-defined subset of soft-water lakes, shifts in diatom assemblages are clearly related to altitudinal differences. This relation is used to construct transfer functions for inferring altitude (and hence average water temperature) from the diatom records. Calibration by canonical correspondence analysis (CCA) and simple weighted averaging calibration proved to be superior to models using WA with tolerance downweighting and to a simple WA model based on a selection of 52 indicator taxa. From the calibration models and the linear relationship between altitude and epilimnetic water temperature, the average lake water temperature can be predicted with an accuracy of 3.2°C. After further refinement, a transfer function for palaeotemperature based on diatoms would be of potential value for climatic reconstructions in tropical regions.     

湿地水文学研究进展及科学前沿问题

湿地水文过程控制湿地的形成与演化,湿地水文情势制约着湿地环境的生物、物理和化学特征,从而影响到湿地类型分异、湿地结构与功能,湿地水文研究是认识湿地生态系统的结构、过程与功能的主要内容。湿地水文情势分析涉及湿地的降雨-径流、湿地蒸散发、湿地地下水运移等主要过程。湿地水循环及水量平衡是湿地水文情势和过程研究的综合,关系到湿地水文循环过程的各个方面。湿地水文过程、边际效应和参数特征及对不同尺度水周期的响应与功能差异等是现代湿地水文研究的重要科学问题。     

Late-glacial and early-Holocene Coleoptera assemblages as indicators of local environment and climate at Kråkenes Lake, western Norway

Thirty-six Coleoptera (beetle) taxa and other insects were identified from the late-glacial and early-Holocene sediments at Kråkenes Lake. Compared with other Scandinavian late-glacial sites, this is a rather sparse record. The water beetles found in the Allerod are characteristic of a poorly vegetated clear-water lake. The terrestrial fauna is indicative of dwarf-shrub and moss vegetation. A marked decline in the number of species at the start of the Younger Dryas was rather rapid, probably over less than 80 calendar yrs. No obligate tundra species replaced the Allerod fauna. Most of the Younger Dryas is virtually devoid of beetles. The increase in numbers and diversity of both aquatic and terrestrial species at the Younger Dryas/Holocene transition is very rapid. After an initial pioneer stage, beetles associated with dwarf-shrub heath and willow scrub appeared, but no obligate tree or forest taxa were recorded.Mutual Climatic Range (MCR) temperature reconstructions suggest that the Allerod was colder and more continental than present. The near absence of beetles in the Younger Dryas probably reflects very cold conditions. A rapid temperature rise at the start of the Holocene resulted in a warmer and more continental climate than present.     

Spatiotemporal wetland changes and their threats in North Central Ethiopian Highlands

Wetlands are important environmental resources for rural livelihoods in Ethiopia. The study investigated spatiotemporal change of wetlands, drivers and effects in North Central Ethiopian Highlands. Landsat satellite imageries of 1984, 1993, 2000, and 2013 were used to analyse wetland changes over the last three decades. Practical observations, interviews and discussions with local communities and officers were also conducted to address the main objective. Furthermore, secondary data on crop yields were collected to supplement the primary data. The study shows that wetlands have been converted into built‐up areas and farmlands. Wetlands in the study area experienced annual loss across the entire study period. Consequently, the area size of wetlands decreased from 7.4 per cent in 1984 to 2.6 per cent in 2013. About 66 per cent of the total wetlands was lost within 30 years mainly due to farmland encroachment and urban expansions. The highest rate of wetland change was recorded between 2000 and 2013. Such wetland changes increased conflicts among land users. However, the converted wetlands increased short‐term benefits due to wetland recession agriculture. To conclude, wetland resources are under enormous threats, and challenge the sustainability of livelihoods. Thus, integrated and adaptive wetland restoration policies could improve the degraded wetlands.     

北京丰台区农村居住用地变化及与人口相关模型

采用GIS技术和统计分析技术，基于1984年，1992年，1996年和1999年4期土地利用图件和数据，分析了1984－1999年期间北京丰台区农村居住用地变化过程及地域分异特征；提出并应用特征均值探讨了农村人均居住用地和人居密度变化的过程和趋势，以行政村为基本单元，利用1999年农村居住用地数据与对应的农村人口数据建立了表达式为Sv=11.324e^0.0006pv的农村居住用地与人口相关模型；用1992年数据对模型进行检验和误差分析的结果表明，模型适用地域为北京近郊且不邻近卫星城镇的农村区。