Using Diatoms as Ecological and Paleoecological Indicators in Riverine Environments

2007 ◽  
Vol 13 ◽  
pp. 121-130
Author(s):  
Jeffery R. Stone
Keyword(s):  
Spatial Distribution ◽  
Environmental Changes ◽  
Climatic Factors ◽  
Diatom Assemblages ◽  
Meandering River ◽  
Rates Of Change ◽  
Terminal Lakes ◽  
Riverine Systems ◽  
The Impact ◽  
Selection Of

Fossil diatom assemblages are useful for reconstructing past environmental changes in riverine systems. However, few studies have attempted to utilize paleolimnological techniques in these settings. Analysis of sediments from riverine environments can provide key information predating the impact of human development, which cannot be acquired by other means. Paleolimnological techniques can be used to determine the natural variability in these systems and to estimate the magnitude and rates of change that the environment may have undergone as a result of anthropogenic or climatic factors, and to provide realistic goals for management of negatively-impacted systems.Reconstructing past riverine settings requires an understanding of the factors that control the spatial distribution of diatoms in riverine settings; this paper discusses the impact of resources, stressors, and disturbance events, which are the primary controls on the distribution of benthic diatoms in modern riverine environments. A selection of case studies that utilize paleolimnological techniques to infer past stream hydrology are also discussed; these examples encompass the use of fossil diatom assemblages from sediments recovered from lowland floodplain and meandering river systems, estuarine environments, fluvial lakes, arctic deltaic environments, and terminal lakes.

scholarly journals Spatial distribution patterns of soil total phosphorus influenced by climatic factors in China’s forest ecosystems

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jie Zhu ◽  
Anchi Wu ◽  
Guoyi Zhou
Keyword(s):  
Spatial Distribution ◽  
Forest Ecosystems ◽  
Climatic Factors ◽  
Critical Role ◽  
Effect Of Temperature ◽  
P Concentration ◽  
Single Effect ◽  
The Impact ◽  
P Distribution ◽  
Total P

AbstractPhosphorus (P) is an important element in terrestrial ecosystems and plays a critical role in soil quality and ecosystem productivity. Soil total P distributions have undergone large spatial changes as a result of centuries of climate change. It is necessary to study the characteristics of the horizontal and vertical distributions of soil total P and its influencing factors. In particular, the influence of climatic factors on the spatial distribution of soil total P in China’s forest ecosystems remain relatively unknown. Here, we conducted an intensive field investigation in different forest ecosystems in China to assess the effect of climatic factors on soil total P concentration and distribution. The results showed that soil total P concentration significantly decreased with increasing soil depth. The spatial distribution of soil total P increased with increasing latitude and elevation gradient but decreased with increasing longitude gradient. Random forest models and linear regression analyses showed that the explanation rate of bioclimatic factors and their relationship with soil total P concentration gradually decreased with increasing soil depths. Variance partitioning analysis demonstrated that the most important factor affecting soil total P distribution was the combined effect of temperature and precipitation factor, and the single effect of temperature factors had a higher explanation rate compare with the single effect of precipitation factors. This work provides a new farmework for the geographic distribution pattern of soil total P and the impact of climate variability on P distribution in forest ecosystems.

Effects of Didymosphenia geminata blooms on benthic diatom assemblages in the Restigouche River Watershed, eastern Canada

Botany ◽  
2015 ◽  
Vol 93 (5) ◽  
pp. 317-323 ◽  
Author(s):  
Branaavan Sivarajah ◽  
Joshua Kurek ◽  
Kathleen M. Rühland ◽  
John P. Smol
Keyword(s):  
Benthic Diatom ◽  
Diatom Assemblage ◽  
Diatom Assemblages ◽  
Eastern Canada ◽  
Didymosphenia Geminata ◽  
Assemblage Composition ◽  
River Watershed ◽  
And Function ◽  
Riverine Systems ◽  
The Impact

Nuisance Didymosphenia geminata (Lyngbye) M. Schmidt (didymo) blooms were first reported in 2006 from the Restigouche River Watershed (RRW), eastern Canada. Although government agencies and recreational users are concerned about these blooms, little is known about the impact on biota and (or) the structure and function of the relatively pristine riverine systems of the RRW. Here, we assess whether didymo blooms affect overall benthic diatom assemblage composition by examining epilithic samples from middle stretches of the Patapedia and Upsalquitch rivers. Significant (albeit minor) differences (P < 0.05) in diatom assemblage composition between sites, with and without didymo blooms, were only observed from the Patapedia River. Rarefied diatom species diversity (Hill’s N2) and rarefied richness did not differ significantly among sites, regardless of the presence or absence of blooms. Our data show that didymo blooms have minimal effect on benthic diatom assemblage composition in the RRW.

scholarly journals Relict inland mangrove ecosystem reveals Last Interglacial sea levels

2021 ◽  
Vol 118 (41) ◽  
pp. e2024518118
Author(s):  
Octavio Aburto-Oropeza ◽  
Carlos Manuel Burelo-Ramos ◽  
Exequiel Ezcurra ◽  
Paula Ezcurra ◽  
Claudia L. Henriquez ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Sea Level ◽  
Environmental Changes ◽  
Terrestrial Ecosystems ◽  
Mangrove Ecosystem ◽  
Last Interglacial ◽  
Sea Levels ◽  
Climatic Oscillations ◽  
Floristic Data ◽  
The Impact

Climatic oscillations during the Pleistocene played a major role in shaping the spatial distribution and demographic dynamics of Earth's biota, including our own species. The Last Interglacial (LIG) or Eemian Period (ca. 130 to 115 thousand years B.P.) was particularly influential because this period of peak warmth led to the retreat of all ice sheets with concomitant changes in global sea level. The impact of these strong environmental changes on the spatial distribution of marine and terrestrial ecosystems was severe as revealed by fossil data and paleogeographic modeling. Here, we report the occurrence of an extant, inland mangrove ecosystem and demonstrate that it is a relict of the LIG. This ecosystem is currently confined to the banks of the freshwater San Pedro Mártir River in the interior of the Mexico–Guatemala El Petén rainforests, 170 km away from the nearest ocean coast but showing the plant composition and physiognomy typical of a coastal lagoon ecosystem. Integrating genomic, geologic, and floristic data with sea level modeling, we present evidence that this inland ecosystem reached its current location during the LIG and has persisted there in isolation ever since the oceans receded during the Wisconsin glaciation. Our study provides a snapshot of the Pleistocene peak warmth and reveals biotic evidence that sea levels substantially influenced landscapes and species ranges in the tropics during this period.

scholarly journals Environmental migration and country security: Theoretical analysis and empirical research

2021 ◽  
Vol 234 ◽  
pp. 00010
Author(s):  
Iryna Didenko ◽  
Kseniia Volik ◽  
Tetiana Vasylieva ◽  
Serhiy Lyeonov ◽  
Nataliia Antoniuk
Keyword(s):  
Environmental Changes ◽  
Climatic Factors ◽  
The United States ◽  
The Philippines ◽  
Negative Consequences ◽  
Population Movements ◽  
Environmental Migration ◽  
Lack Of Information ◽  
Ecological Migration ◽  
The Impact

The article considers the impact of environmental changes on population migration and security of countries. Theoretical aspects of Environmental migration, in particular its essence and types, are studied. The main directions of scientific research in this field are considered. In particular, much attention is about finding ways to adapt to changes in the environment and minimize the negative consequences of these changes to achieve sustainable development in both regions and countries. The study found that internal population movements are mainly due to climatic factors such as storms and floods. It was determined that in 2019, about 52% of new mixing was caused by storms and 40% - by floods. Countries for which the phenomenon of ecological migration is most characteristic are India, the Philippines, the United States, China, and Indonesia. The main problems that arise in the study of Environmental mobility of the population are identifiedThey are mainly related to the lack of information and statistical base for conducting qualitative and diverse research.

Influence of climatic factors on silver fir xylogenesis along the Italian Peninsula

IAWA Journal ◽  
2019 ◽  
Vol 40 (2) ◽  
pp. 259-S3 ◽  
Author(s):  
Serena Antonucci ◽  
Sergio Rossi ◽  
Fabio Lombardi ◽  
Marco Marchetti ◽  
Roberto Tognetti
Keyword(s):  
Environmental Changes ◽  
Climatic Factors ◽  
Abies Alba ◽  
Growth Dynamics ◽  
Growing Season ◽  
Effect Of Temperature ◽  
Ecological Indicator ◽  
Silver Fir ◽  
Xylem Differentiation ◽  
The Impact

ABSTRACTXylem phenology has been widely recognised as an ecological indicator of the impact of environmental changes on forest ecosystems, especially at the edge of a species distribution. We investigated xylem phenology of silver fir (Abies alba Mill.) in three sites in Italy, between the 38th and 46th parallels. The phases of xylem phenology were assessed weekly on wood microcores collected from March to November 2015 to calculate timing and duration of xylem cell production. The effect of temperature and precipitation on xylem phenology were sequentially included in stepwise regressions and used to predict the duration of each phenological phase under three future climatic scenarios at different concentrations of greenhouse gases (RCP 2.6; 4. 5; 8. 5). A growing season of 163 days was detected in the southern site that was longer compared to the central (132 days) and northern (120 days) sites. A longer duration of xylogenesis was mostly related to a delayed completion of xylem differentiation in autumn rather than an earlier onset of cambium reactivation in spring. Overall, 67–76% of the duration of phenological phases was controlled by growing season precipitation, while 24 –33% was influenced by minimum temperature. Inclusion of both the above factors in the modelling exercise simulated a lengthening of the silver fir growing season during the 21st century. A longer duration of xylogenesis was envisaged in the scenario RCP 8. 5, especially in the central site. Population and climate gradients need to be considered when addressing phenological shifts and growth dynamics of silver fir in Mediterranean mountains.

scholarly journals The Impact of Climatic Factors on Spatial Distribution of Scorpion Stings in Ardabil Province, North-West of Iran; 2012 - 2017

2018 ◽  
Vol In Press (In Press) ◽  
Author(s):  
Eslam Moradiasl ◽  
Davoud Adham ◽  
Hossein Solimanzadeh ◽  
Abedin Saghafipour ◽  
Hadi Eghbal
Keyword(s):  
Spatial Distribution ◽  
Climatic Factors ◽  
North West ◽  
Scorpion Stings ◽  
The Impact

scholarly journals Cenozoic aridization in Central Eurasia shaped diversification of toad-headed agamas (Phrynocephalus; Agamidae, Reptilia)

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e4543 ◽  
Author(s):  
Evgeniya N. Solovyeva ◽  
Vladimir S. Lebedev ◽  
Evgeniy A. Dunayev ◽  
Roman A. Nazarov ◽  
Anna A. Bannikova ◽  
...  
Keyword(s):  
Body Size ◽  
Environmental Changes ◽  
Climatic Factors ◽  
Phylogenetic Analyses ◽  
Late Oligocene ◽  
Central Eurasia ◽  
Biogeographic History ◽  
Middle Asia ◽  
History Of ◽  
The Impact

We hypothesize the phylogenetic relationships of the agamid genusPhrynocephalusto assess how past environmental changes shaped the evolutionary and biogeographic history of these lizards and especially the impact of paleogeography and climatic factors.Phrynocephalusis one of the most diverse and taxonomically confusing lizard genera. As a key element of Palearctic deserts, it serves as a promising model for studies of historical biogeography and formation of arid habitats in Eurasia. We used 51 samples representing 33 of 40 recognized species ofPhrynocephaluscovering all major areas of the genus. Molecular data included four mtDNA (COI,ND2,ND4,Cytb; 2,703 bp) and four nuDNA protein-coding genes (RAG1,BDNF,AKAP9,NKTR; 4,188 bp). AU-tests were implemented to test for significant differences between mtDNA- and nuDNA-based topologies. A time-calibrated phylogeny was estimated using a Bayesian relaxed molecular clock with nine fossil calibrations. We reconstructed the ancestral area of origin, biogeographic scenarios, body size, and the evolution of habitat preference. Phylogenetic analyses of nuDNA genes recovered a well-resolved and supported topology. Analyses detected significant discordance with the less-supported mtDNA genealogy. The position ofPhrynocephalus mystaceusconflicted greatly between the two datasets. MtDNA introgression due to ancient hybridization best explained this result. MonophyleticPhrynocephaluscontained three main clades: (I) oviparous species from south-western and Middle Asia; (II) viviparous species of Qinghai–Tibetan Plateau (QTP); and (III) oviparous species of the Caspian Basin, Middle and Central Asia.Phrynocephalusoriginated in late Oligocene (26.9 Ma) and modern species diversified during the middle Miocene (14.8–13.5 Ma). The reconstruction of ancestral areas indicated thatPhrynocephalusoriginated in Middle East–southern Middle Asia. Body size miniaturization likely occurred early in the history ofPhrynocephalus. The common ancestor ofPhrynocephalusprobably preferred sandy substrates with the inclusion of clay or gravel. The time of Agaminae radiation and origin ofPhrynocephalusin the late Oligocene significantly precedes the landbridge between Afro-Arabia and Eurasia in the Early Miocene. Diversification ofPhrynocephaluscoincides well with the mid-Miocene climatic transition when a rapid cooling of climate drove progressing aridification and the Paratethys salinity crisis. These factors likely triggered the spreading of desert habitats in Central Eurasia, whichPhrynocephalusoccupied. The origin of the viviparous Tibetan clade has been associated traditionally with uplifting of the QTP; however, further studies are needed to confirm this. Progressing late Miocene aridification, the decrease of the Paratethys Basin, orogenesis, and Plio–Pleistocene climate oscillations likely promoted further diversification withinPhrynocephalus. We discussPhrynocephalustaxonomy in scope of the new analyses.

scholarly journals Impact of Environmental Factors on Selection of Defence Services Officers

2017 ◽  
Vol 5 (3) ◽  
pp. 200-207
Author(s):  
Ravinder Kumar Gosain ◽  
Parul Agarwal ◽  
Pradeep Singh Siwach
Keyword(s):  
Environmental Factors ◽  
Environmental Changes ◽  
Service Selection ◽  
Armed Forces ◽  
Jel Classification ◽  
Middle Level ◽  
Economic Changes ◽  
Senior Officers ◽  
The Impact ◽  
Selection Of

Objective - "Change is the only constant" is a cliché but it is important to identify the factors which are changing to emerge as challenges before the military leadership of tomorrow. The societies are bound to be affected by the changes taking place in the environment. Generally, every society is affected by the four types of environmental factors. These are political, social, economic and technological. Since in India, democracy is deep rooted and the philosophy of the defence forces is same and has neither changed nor is likely to change, this factor is not under study here. So, the purpose is to study the impact of other environmental factors on selection of Defence Services Officers. Methodology/Technique - The study has been carried out by personally visiting all the Service Selection Centres of the Indian Armed Forces and presenting a questionnaire to large number of junior, middle and senior level serving and retired officers at various places. Only 449 officers responded which included 190 junior officers, 133 middle-level officers and 126 senior officers. The response was put through SPSS software system and analysed. Findings - The analysis clearly revealed that environmental changes in the society over a period of time do impact the qualities in the youth which have direct bearing on their selection for officers in the armed forces. Since the selection is based on finding the officers like qualities available or trainable in the youth, the impact of environmental factors is directly affecting the intake of the youth resulting in deficiency of officers' cadre in the armed forces. Novelty - The research contributes to develop scientific knowledge in environmental change effect on selection of defence officers. Type of Paper - Empirical Keywords: Qualities; Environment; Socio-Economic Changes; Armed Forces. JEL Classification: H56, J11.

Methods for Restricting Maximum Exposure Rate in Computerized Adaptative Testing

Methodology ◽  
2007 ◽  
Vol 3 (1) ◽  
pp. 14-23 ◽  
Author(s):  
Juan Ramon Barrada ◽  
Julio Olea ◽  
Vicente Ponsoda
Keyword(s):  
Measurement Accuracy ◽  
Computerized Adaptive Testing ◽  
Computation Time ◽  
Adaptive Testing ◽  
Exposure Rate ◽  
Control Parameters ◽  
The Impact ◽  
Two Alternatives ◽  
Selection Of ◽  
Maximum Exposure

Abstract. The Sympson-Hetter (1985) method provides a means of controlling maximum exposure rate of items in Computerized Adaptive Testing. Through a series of simulations, control parameters are set that mark the probability of administration of an item on being selected. This method presents two main problems: it requires a long computation time for calculating the parameters and the maximum exposure rate is slightly above the fixed limit. Van der Linden (2003) presented two alternatives which appear to solve both of the problems. The impact of these methods in the measurement accuracy has not been tested yet. We show how these methods over-restrict the exposure of some highly discriminating items and, thus, the accuracy is decreased. It also shown that, when the desired maximum exposure rate is near the minimum possible value, these methods offer an empirical maximum exposure rate clearly above the goal. A new method, based on the initial estimation of the probability of administration and the probability of selection of the items with the restricted method ( Revuelta & Ponsoda, 1998 ), is presented in this paper. It can be used with the Sympson-Hetter method and with the two van der Linden's methods. This option, when used with Sympson-Hetter, speeds the convergence of the control parameters without decreasing the accuracy.

Holocene diatom assemblages from Dunderbukhta sediments, West Svalbard

2019 ◽  
pp. 242-245
Author(s):  
Ksenya V. Poleshchuk ◽  
Zinaida V. Pushina ◽  
Sergey R. Verkulich
Keyword(s):  
Environmental Changes ◽  
Ecological Groups ◽  
Diatom Assemblages ◽  
Diatom Analysis ◽  
Diatom Flora ◽  
Sediment Samples ◽  
Ecological Zones ◽  
Middle Holocene ◽  
Temperature Trends

The diatom analysis results of sediment samples from Dunderbukta area (Wedel Jarlsberg Land, West Svalbard) are presented in this paper. The diatom flora consists of four ecological groups, which ratio indicates three ecological zones. These zones show environmental changes of the area in early–middle Holocene that is demonstrating periods of regression and temperature trends.

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