Henderson Island prehistory: colonization and extinction on a remote Polynesian island

Situated at the extreme margin of the Indo-West Pacific biotic province, the four islands of the isolated Pitcairn Group hold interest for biogeographers and archaeologists alike. Human settlement may have been as early as the 8th century AD for the uplifted limestone island of Henderson, the most pristine island of its kind. An archaeological survey of the Pitcairn Islands is provided, while Henderson is examined in detail. Recent extensive excavations provide a record of change during 600 years of human occupation. Adaptation to the ecologically-marginal conditions is documented by artefacts, more than 150000 vertebrate bones, molluscs and subfossil plant remains recovered from stratigraphic contexts. The effects of prehistoric human occupation on the pristine environment are revealed by Polynesian plant and animal introductions, bird extinctions and range reductions, possible over-predation of marine molluscs, exploitation of sea turtles, and large-scale burning for swidden agriculture. The origin of human colonists is documented by analysing imported artefacts by geochemical characterization (x-ray fluorescence analysis). The human abandonment of Henderson, by the seventeenth century, is viewed in the context of prehistoric regional dynamics.     

Biomarkers in Zebra mussel for monitoring and quality assessment of Lake Maggiore (Italy)

Three different biomarkers (acetylcholinesterase (AChE), ethoxy resorufin-O-deethylase (EROD) and DNA strand breaks) were measured in Zebra mussel (Dreissena polymorpha) specimens collected in April 2005 at six different sampling sites on Lake Maggiore, the second largest Italian lake in terms of depth and volume, in order to assess the spatial variation of exposure to man-made contaminants. Mussels maintained at fixed laboratory conditions were used as controls to eliminate potential interference due to environmental factors. Biomarker data were also supported by the analysis of several chemicals (six dichlorodiphenyltrichloroethane (DDTs), 23 polychlorinated biphenyls (PCBs), 14 polybrominated diphenyl ethers (PBDEs), 11 polycyclic aromatic hydrocarbons (PAHs) and hexachlorobenzene (HCB)) measured in the mussel soft tissues by gas chromatographic analyses. We found a negative correlation between temperature and AChE activity, while any measured environmental or physiological factor seemed to influence EROD activity and DNA strand breaks. A positive relationship was found between EROD activity and all of the measured chemicals, except for PAHs, which correlated with the amount of DNA strand breaks. Significant differences were noted for all biomarkers, both among sampling stations and between control and experimental data, even if the general level of variability was low. The biomarkers showed a distinct pattern of spatial variation, but the evaluation of DNA strand breaks was the strongest discriminating power between sites. In addition, the comparison between AChE and EROD activity measured in 2005 was compared with results obtained in a previous study carried out over the same sampling period in 2003. Results indicated a strong influence of temperature on AChE activity and probable interference of substrate inhibition of EROD activity, pointing out the need to take care in the interpretation of data comparisons. The results obtained with two different metrics used for the measure of DNA strand breaks is also discussed, as well as the relationship between EROD activity data and potential genotoxicity.     

Phytoplankton of a recently landlocked brackish-water lagoon of Lake Tanganyika: a systematic account

The planktonic flora of a recently landlocked brackish-water lagoon of Lake Tanganyika was studied. 273 Taxa were observed including 5 new ones: Trachelomonas dubia Swir. emend. Defl. var. colliundulata Caljon, Tr. gatumbana Caljon, Tr. komarovii Skv. var. bicollaris Caljon, Chroomonas angusta Caljon, Scourfieldia chlorolateralis Caljon. Diatoms were qualitatively the most important group (37.7%) followed by the Chlorophyta (23.0%), the Euglenophyta (19.4%) and the Cyanophyta (13.6%). This algal composition compares well with that of other African water-bodies of similar ionic composition and salinity but shows a more important development of Euglenophyta taxa.Many typical brackish-water and marine algal taxa were observed.The algal flora was mainly composed of cosmopolitan and subcosmopolitan taxa (89%) and a small number of tropical and subtropical taxa (11%).     

Limnological studies in a large,deep, oligotrophic lake (Lake Ohrid,Yugoslavia). A summary of nutritional radiobioassay responses of the pelagial phytoplankton

In situ carbon-14 bioassay techniques were used during 1972–1974 to estimate nutritional preferences and requirements of the pelagial phytoplankton in Lake Ohrid, Yugoslavia.Bioassay measurements, conducted spatially and temporally, and corrected appropriately, showed a strong stimulation to phytoplankton photosynthesis rates during most seasons in epilimnetic waters following microadditions of inorganic silica and iron. Photosynthetic stimulation was additive for individual elements and synergistic when simultaneous additions were made. Marked stimulation occurred for both elements during the spring, especially in upper hypolimnetic waters (50–75 m) and correlated strongly with dominant diatom populations.The addition of an organic chelator, nitrilotriaceticacid (NTA), commonly stimulated photosynthetic rates and, frequently, as deep as 15o m, considerably below the depth of optimal light availability for photosynthesis. With minor exception, the simultaneous addition of this chelator and inorganic iron were always capable of producing stimulatory responses.Inorganic phosphorus was preferred over nitrogen and generally found to be more stimulatory. Phosphorus stimulation was restricted primarily to periods of spring and summer production. The addition of glucose, acetate and glycine produced positive responses, while the addition of several vitamins showed little effect except for a stimulation from microamounts of B₁₂. The addition of two organic growth substances, Gibberellic acid (GA) and Indoleacetic acid (IAA), both stimulated phytoplankton photosynthesis.The results of more than 140 bioassay measurements indicate the pelagial phytoplankton are severely restricted nutritionally due to specific physical-chemical interactions occurring in Lake Ohrid. Similar mechanisms have been postulated and evaluated in other hand-water lake systems. In spite of the great depth of the lake (300 m+) and probable age, these mechanisms are undoubtedly responsible for the low phytoplankton production occuring in the lake.     

Potential role for microbial ureolysis in the rapid formation of carbonate tufa mounds

Modern carbonate tufa towers in the alkaline (~pH 9.5) Big Soda Lake (BSL), Nevada, exhibit rapid precipitation rates (exceeding 3 cm/year) and host diverse microbial communities. Geochemical indicators reveal that carbonate precipitation is, in part, promoted by the mixing of calcium-rich groundwater and carbonate-rich lake water, such that a microbial role for carbonate precipitation is unknown. Here, we characterize the BSL microbial communities and evaluate their potential effects on carbonate precipitation that may influence fast carbonate precipitation rates of the active tufa mounds of BSL. Small subunit rRNA gene surveys indicate a diverse microbial community living endolithically, in interior voids, and on tufa surfaces. Metagenomic DNA sequencing shows that genes associated with metabolisms that are capable of increasing carbonate saturation (e.g., photosynthesis, ureolysis, and bicarbonate transport) are abundant. Enzyme activity assays revealed that urease and carbonic anhydrase, two microbial enzymes that promote carbonate precipitation, are active in situ in BSL tufa biofilms, and urease also increased calcium carbonate precipitation rates in laboratory incubation analyses. We propose that, although BSL tufas form partially as a result of water mixing, tufa-inhabiting microbiota promote rapid carbonate authigenesis via ureolysis, and potentially via bicarbonate dehydration and CO₂ outgassing by carbonic anhydrase. Microbially induced calcium carbonate precipitation in BSL tufas may generate signatures preserved in the carbonate microfabric, such as stromatolitic layers, which could serve as models for developing potential biosignatures on Earth and elsewhere.     

环鄱阳湖城市群城乡建设用地的承载能力评价及空间格局匹配

土地承载力是土地管理和可持续利用的重要研究领域之一,城乡建设用地是土地利用类型的重要组成部分,其结构与布局是否合理对土地可持续利用至关重要.本研究以环鄱阳湖城市群为研究区,进行城乡建设用地开发适宜性评价,核算城乡建设用地可承载临界值,计算可承载城乡建设用地丰度,并与现状城乡建设用地进行空间格局匹配性分析,得到研究区各个县(市、区)的剩余开发强度和空间匹配度.结果表明: 研究区城乡建设用地开发适宜性评价结果等级中,最适宜区、较适宜区、较不适宜区和不适宜区面积分别为3130.62、2477.29、867.03和29509.14 km².研究区城乡建设用地可承载临界值(可开发强度)为16.6%,各个县(市、区)的值在7.7%～100%,各县(市、区)可承载城乡建设用地丰度在0.15～1.30.研究区剩余开发强度为12.3%,空间匹配度为0.76;各个县(市、区)剩余开发强度在4.9%～53.5%,空间匹配度在0.11～1.00,地区差异较大.此研究有助于明确现状开发状态与合理开发状态之间的关系,可为城乡建设用地的精细化管理、制定空间格局优化调控政策提供依据.     

贵州省石阡鸳鸯湖国家湿地公园越冬鸳鸯数量、分布及日行为初探

为了解贵州省石阡鸳鸯湖国家湿地公园越冬鸳鸯Aix galericulata的种群密度、日行为特征及人为干扰对其的影响,于2017年10月—2018年3月,采用直接计数法对鸳鸯数量、性比及人为干扰下的种群密度进行了22次调查。越冬中期,种群数量稳定在755只±17只,性比为1.14∶1,各条河沟的数量之间的差异具有高度统计学意义(X^2=84.041,df=5,P<0.01),即大河、小河与坝坎为鸳鸯分布及活动的主要区域;种群密度与人为干扰次数呈极显著负相关(R=-0.799,n=90,P<0.01),在人为干扰次数为1次±1次的区域,种群密度为42只/hm^2±3只/hm^2～53只/hm^2±14只/hm^2,当人为干扰次数达到7次±3次时,几乎没有鸳鸯活动。同时采用瞬时扫描法对鸳鸯的8种越冬行为进行了34 d(442 h)的观察,共记录各行为136 933次。取食、休息和修整为鸳鸯的主要行为;除了修整,鸳鸯在保育区与非保育区的各行为时间分配差异有高度统计学意义(P<0.01);越冬日行为节律极具规律性,取食高峰在07∶00—08∶00、14∶00—15∶00和17∶00—18∶00;休息高峰在13∶00—14∶00和15∶00—16∶00;飞行高峰在06∶00—07∶00(飞回湖区)和18∶00—19∶00(飞往夜栖地);修整在各时间段发生均较为频繁。     

基于海岛生态脆弱性模拟的朱家尖岛空间管控对策

近10年来,桥隧连陆型海岛数量快速增长,这类工程的建设改善了海岛的交通可达性,使得海岛旅游人口快速增长,实现了海岛经济的快速发展.而旅游人口的快速增加和海岛土地利用结构的变化,使得海岛生态脆弱性增加.为实现海岛生态系统的科学管理,科学评价和预测海岛生态系统脆弱性变化趋势及敏感区域,制定不同区域的生态系统管理方式显得尤为迫切.本研究构建了海岛生态脆弱性评价模型,评估了朱家尖岛生态脆弱性现状,以2015年作为基期模拟未来20年旅游人口和土地利用变化,以及未来20年的海岛生态脆弱性变化,在此基础上分析脆弱性变化的敏感区域,并提出相应的管理措施.结果表明:朱家尖岛目前的生态系统处于良好状态,中度和重度脆弱性面积相对较小.随着朱家尖岛旅游人口增加和岛陆开发强度的增强,海岛生态系统趋于脆弱,其中,高脆弱性面积增加,低脆弱性面积减少.针对脆弱性评估的结果结合敏感性分析,将朱家尖岛划分为禁止开发区、限制开发区和有条件开发区,以实现精细化管理.     

Species succession and the development of a lacustrine fish community in an ephemeral lake

Here, we present a gillnet survey of Lake Liambezi a 370 km² shallow ephemeral floodplain lake situated in north-eastern Namibia, which is fed irregularly by the upper Zambezi and Kwando Rivers during years of high flooding. The lake dried up in 1985 and, with the exception of sporadic minor annual inundation events, remained dry until 2007. We describe the temporal succession of fish species over an 8 year period from initial inundation 2007 to maturation in 2014. The succession of the fish community did not follow the typical pattern of opportunistic strategists during colonisation, to periodic strategists that are eventually succeeded by equilibrium strategists. Instead, the evolution of the fish community was characterised by three distinct phases. The first phase involved the inundation and colonisation of the lake in 2007, followed by its decline until the floods that filled the lake in 2009. During this phase the lake was colonised by fishes from the adjacent upper Zambezi and Chobe River floodplains. Fish communities predominantly comprised floodplain specialists including the barbs Enteromius paludinosus and Enteromius poechii, the mormyrid Marcusenius altisambesi and catfishes Schilbe intermedius and Clarias gariepinus. The filling of the lake in the March 2009 floods marked the beginning of the second, successional phase. The barbs declined in abundance and the alestid Rhabdalestes maunensis underwent explosive population growth between 2009 and 2010, but populations crashed equally rapidly and were replaced by Brycinus lateralis which, together with S. intermedius went on to dominate the fish community 2011–2014. Larger, slower growing tilapiine cichlids increased steadily in abundance and became the dominant components in a 2700 t y^–1 artisanal fishery that developed on the lake. The fish community in the ephemeral Lake Liambezi is clearly influenced by numerous factors including connectivity, lake level fluctuations, competition and the effects of fishing, which may disrupt typical succession processes in floodplain ecosystems.