Cyclostephanos Dubius Research Articles

Diatom records in sediments for eutrophication process of Lake Xian'nv, China since the mid-20th century

<p>To well understand the eutrophication process for inland lakes where more lands had been used for agriculture and industry without adequate environmental protections, 9 surface sediments and 1 core sediment in Lake Xian’nv which was located in the middle of Jiangxi Province were chosen. Combined with 210Pb and 137Cs geochronology, nutrient index including total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), Carbon nitrogen ratio (C/N), diatoms assembles and TDI index of eutrophic diatoms were compared quantitatively and conducted to elucidate the eutrophication process using statistical methods. The results showed a total of 155 years from 1863 to 2018 were recorded from the entire sediment core. The nutrient level in 23 centimeters below the surface of the sediment core where was synchronized with reservoir construction indicated TN, TP, TOC, and Carbon nitrogen ratio had been gradually increased since the construction of Dam. In surface sediments, the three diatoms with higher average relative abundance were Achnanthidium minutissimum, Navicula Bory, and Aulacoseira granulata with a value of 54.2 %, 29.4 %, and 15.3 % respectively. Significant changes of the diatom communities from 1955 to 2009 had been recorded, where diatom communities could be classified into four distinct periods. In the first few years after the reservoir was built, the dominant diatoms were epiphytic and benthic diatom communities represented by Navicula cincta、Fragilaria ulna, and Cocconeis placentula in zone I on the bottom floor covered from 1955 to 1961. However, planktonic diatom communities were dominant after 1983 which were mainly constituted by Aulacoseira alpigena、Cyclostephanos dubius、Cyclotella meneghiniana, and Cyclotella radiosa . Both TDI index of eutrophic diatoms and Principal Component Analysis (PCA) revealed the succession from benthic diatoms to planktonic diatoms and changes in nutrient levels.</p>

Species composition of summer diatoms complex of Ceratophyllum demersum L. epiphyton in the Pripyat river (The national park «Pripyatsky»)

The diatom complex of the Ceratophyllum demersum L. epiphyton collected in July 2010 from Pripyat river includes 58 species. They belong to 3 classes, 9 orders, 13 families, 23 genera. The dominants (of the number of valves in the preparation) were Cocconeis lineata Ehrenberg (34,8%), Cyclostephanos dubius (Fricke) Round (11,3%), subdominants – Сocconeis euglipta Ehrenberg (8,8%), Aulacoseira ambigua (Grunow) Simonsen (5,9%) and Gyrosigma spencerii (Bailey ex Quekett) Griffith et Henfrey (5,6%).

DNA barcoding reveals a new species of Stephanodiscus Ehrenberg

The taxonomic situation of the species complex around Stephanodiscus minutulus/parvus is controversial. Insufficient species description and fossil type material contribute to persistent confusion. Håkansson & Kling (1990) described S. binatus as another morphologically similar species in this group. Following the reinvestigation of the type materials of S. minutulus and S. parvus by Houk et al. (2014), it seems that these names are often falsely applied to S. binatus. Monoclonal strains of the S. minutulus/parvus/binatus species complex from European water bodies were established for morphological and molecular analyses. Most of the strains belonged to S. binatus, which seems to be very common in meso- to eutrophic waters in middle Europe. Differing in the barcoding markers, the remaining strains represented a new species, S. neglectus sp. nov., morphologically similar to S. binatus. Stephanodiscus minutulus and S. parvus were not found. Seven strains of S. neglectus sp. nov., seven strains of S. binatus and two strains of Cyclostephanos invisitatus were subjected to detailed morphometric investigation. Four strains of Stephanodiscus hantzschii, Stephanodiscus neoastrea, Cyclostephanos dubius were also included in the molecular analysis. The morphological differential diagnosis of S. neglectus sp. nov. from S. binatus is difficult, but the molecular results show that the species are distinctly different. Using three different loci the distance between the new species and S. binatus equals the distance between S. binatus and S. hantzschii.

Diatom assemblage responses to multiple environmental stressors in a deep brackish plateau lake, SW China.

Eutrophication, climate change, water level fall, fish introduction, and salinity have been widely recorded to impact lake ecosystems around the world. However, the combined responding pattern in the lake ecosystem to the above multiple environmental stressors is not well understood. Here, we present diatom assemblage and geochemical indicators (total organic carbon (TOC), total nitrogen (TN), and total phosphorous (TP)) in lake sediment to investigate the long-term trends in the aquatic ecosystem in response to multiple environmental stressors in Lake Chenghai, a deep brackish lake located on Yunnan-Guizhou Plateau, SW China, during the past 80years. We identified 8 genera and 15 species of diatom reaching a relative abundance of ≥ 2% in at least one sample, with the dominant taxa such as Cyclotella rhomboideo-elliptica and Aulacoseira alpigena through the sediment core. There was a clear shift in the diatom community from oligotrophic species of C. rhomboideo-elliptica to eutrophic species such as Cyclotella meneghiniana and Cyclostephanos dubius becoming dominant since ca. 1998 CE. In addition, the changes in the fish introduction, water level, temperature, and salinity also resulted in the variation in abundance of planktonic and benthic diatoms. The increase in the abundance of diatoms of C. rhomboideo-elliptica since ca. 1986 CE may be related to the decline in water level and increasing fish production. For one thing, the decline in water level reduces the concentrations of benthic diatoms but increases the relative biomass of planktonic diatoms. For another, the increasing fish production results in the decrease in the zooplankton biomass, thus reducing the predation pressure on planktonic algae. Besides, some specific species such as C. meneghiniana may respond to the increased nutrient release and increased salinity since ca. 1998 CE. Combined, our findings demonstrate that trophic level is the main driver of diatom assemblage changes, and other environmental variables including water level, fish introduction, and climate warming also contribute to diatom community variation in this brackish plateau lake during the last 80years.

Response of epilithic diatom assemblages to weir construction on the Nakdong River, Republic of Korea

In South Korea, sixteen multifunctional weirs were constructed on four major rivers (Han, Nakdong, Geum, Yeongsan) from 2009 to 2012. Hydrological changes resulting from weir construction altered the physical, chemical, and biological characteristics of natural large rivers. We aimed to investigate the variation in epilithic assemblages responding to changes in physicochemical, meteorological, and hydrological variables in the eight weir (lentic) sections of the Nakdong River, which is the longest river in South Korea. Sampling was conducted to determine the influence of environmental parameters on community composition, and to monitor the seasonality of environmental and biological patterns.A total of 173 taxa including 26 major epilithic diatom taxa were identified. Among them, nutrient-tolerant diatom species were characterized by Cyclostephanos dubius, Navicula gregaria, Fragilaria crotonensis, Aulacoseira granulata, Melosira varians, Navicula minima, Nitzschia amphibia, Amphora pediculus, and Nitzschia inconspicua. These species were primarily dominant in the midstream and downstream weir sections of the river adjacent to urban-industrial land use zones relating to nutrient enrichment. Moreover, preference for longer hydraulic retention time (HRT) was identified in C. dubius, N. gregaria, and F. crotonensis, in addition to its tolerance for high nutrition. Redundancy analysis based on the relative abundance of diatom taxa demonstrated that the diatom assemblage composition was closely related to total nitrogen (TN), total phosphorus (TP), phosphate phosphorus (PO4-P), electrical conductivity, precipitation, water discharge, and HRT. Variation partitioning analysis further revealed that hydrological-meteorological variables play a synergistic role in enhancing the function of physical and chemical variables in structuring diatom assemblage composition soon after weir construction. A generalized linear model using the Akaike’s information criterion also suggests that the trophic diatom index (TDI) could indicate the water quality status in the weir sections, as the TDI was positively correlated (p < 0.05) with nutrients (TN and PO4-P). Our findings inform the applicability of using the TDI for efficiently monitoring and managing the water quality of consecutive weir sections of the Nakdong River and the weir systems of other rivers in temperate regions.

DNA metabarcoding reveals multiple co-occurring species in

Spring diatom blooms dominate the annual cycle of phytoplankton abundance in temperate freshwater systems. Many researchers have questioned whether severe blooms are attributable to a single species and warrant the identification of similar, concurrently occurring organisms. Here, we investigated spring diatom blooms in a temperate freshwater system (Yeongsan River, South Korea) that is thought to predominantly include the diatom Stephanodiscus hantzschii. Water samples were collected from four different sites during the blooms that occurred in March 2015. We analysed physicochemical and biological parameters and examined the species composition of the spring blooms using DNA metabarcoding via pyrosequencing. Our results revealed that several diatom species co-occurred during the blooms: Cyclotella sp. was the most frequently detected, followed by Cyclostephanos dubius and Discostella sp., whereas Stephanodiscus was only detected at two stations with low occurrence. These results suggest the coexistence of many diatoms during spring blooms in the Yeongsan River; however, Cyclotella sp. was responsible for the spring bloom attributed to S. hantzschii. DNA metabarcoding can be a useful tool for resolving species identities in spring diatom blooms in temperate freshwater systems. In addition, the co-occurrence of similar species should be considered when implementing efforts to monitor and control spring blooms.

Response of the Diatom Flora of the Hel Peninsula Vicinity, Puck Bay, Baltic Sea, to Anthropopressure

The subject of this study was the diatom taphocoenoses preserved in the surface sediments of the northern part of Puck Bay, southern Baltic Sea. Three subbotom sedimentary cores ZP1/0518, ZP2/0518 and ZP3/0414 collected in the vicinity of the Hel Peninsula from a water depth of 65 m, 47 m and 50.2 m, respectively were analyzed with respect to diatom flora. Over 500 valves of diatoms were counted in each sample in order to estimate the percentage abundance of particular taxa. Habitat, salinity, trophy and saproby requirements of all identified species were established according to literature. The percentage content of distinguished ecological groups was counted in each core. Diatomological analysis indicates that the diatom flora observed in muddy and silty sediments of the study area was generally abundant, taxonomically diverse and well preserved. However, some valves were mechanically broken or/and chemically destroyed. In all cores anthropogenic assemblage with small sized planktic diatoms tolerating higher nutrient and pollution concentration as well as lower transparency of water column predominated. The most important components were euhalobous species Thalassiosira levanderi and mesohalobous one Cyclotella choctawhatcheeana. Both species achieved the highest frequency (up to ca. 80% and 38%, respectively) in core ZP1/0518. Other eutraphentic, α/β mesosaprobous taxa belonged to oligohalobous halophilous (Actinocyclus normanii f. subsalsa, Cyclotella atomus, C. meneghiniana) and oligohalobous indifferent (A. normanii f. normanii, Cyclostephanos dubius, Aulacoseira spp.) were observed rarely. Benthos was also dominated by diatoms preferring the high content of nutrients and organic matter. This group was represented by marine/brackish-water taxa (i.e. Catenula adhaerens, Cocconeis hauniensis, C. scutellum, Diploneis didyma, D. smithii, D. stroemii, Opephora krumbeinii) and freshwater ones (i.e. Amphora copulata, A. pediculus, Cocconeis neodiminuta, C. neothumensis). Our results clearly indicate the apparent human impact on the structure of the diatom flora in the northern part of the Puck Bay. At least two sources of anthropopressure can be determined in the vicinity of Hel Peninsula i.e. (1) at a local scale harbor in Hel city and municipal sewage linked to development of tourism, and (2) at a regional scale the Vistula River waters, which is the major source of pollution in the Gulf of Gdańsk.

Species composition of diatom algae of the periphyton in the oxbow lake Teremshino (National park “Pripyatsky”)

The diatom complex of periphyton, collected in July 2015 from the oxbow Lake Teremshino, includes 66 species. They belong to 3 classes, 12 orders, 19 families, 34 genera. The dominant species is Cyclostephanos dubius (Fricke) Round (60,0 % of the relative number of valves).

Aulacoseira pseudomuzzanensis sp. nov. and other centric diatoms from post iron ore mining reservoirs in Poland

Post iron ore mining reservoirs in Łęczyca (Poland) can be considered extreme habitats because they are characterized by high pH, conductivity, and sulfate, sodium and potassium concentrations. We observed high abundances in these water bodies of several centric diatom species that are otherwise known from less extreme environments. These included Thalassiosira duostra, Cyclostephanos dubius, Stephanodiscus binatus, Stephanodiscus invisitatus, Stephanodiscus parvus, Stephanodiscus hantzschii, Lindavia aff. balatonis, Discostella woltereckii, Discostella pseudostelligera, and Cyclotella meneghiniana, revealing the eurytopic nature of these species. Morphological differences between populations from extreme habitats and their counterparts from less extreme environments may indicate phenotypic responses of eurytopic taxa to the differing environmental regimes, or the presence of distinct, more stenotopic taxa. In both cases, this could be relevant for biomonitoring. For this reason, we carefully observed the morphological variability of our target taxa in the Łęczyca reservoir samples compared with literature accounts from less extreme habitats, and in some cases, with type material of the species concerned. Specimens similar to Aulacoseira muzzanensis α-chains were observed. Following comparison with the type material of Melosira muzzanensis Meister (≡A. muzzanensis), we concluded that the Łęczyca populations are sufficiently different to be recognized as a separate species, here described as Aulacoseira pseudomuzzanensis sp. nov. The importance of identifying centric diatoms to species level for water management surveys is emphasized, even for those taxa that are difficult to identify using only LM.

东北镜泊湖硅藻对近现代气候变化和人类干扰的响应过程

PDF HTML阅读 XML下载 导出引用 引用提醒 东北镜泊湖硅藻对近现代气候变化和人类干扰的响应过程 DOI: 10.5846/stxb201610272185 作者: 作者单位: 浙江师范大学,中科院南京地理与湖泊研究所,浙江师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（41372184，41672173，41701218） Diatom response to climate changes and anthropogenic disturbances in Jingpo Lake (NE China) Author: Affiliation: Zhejiang Normal University,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:全球气候变暖和人类活动加剧已经导致中国大量湖泊生态系统功能退化，而目前对东北地区湖泊生态系统变化的认识主要源于短期的监测。以东北镜泊湖为例，通过沉积记录和现代监测资料，分析一个多世纪以来以硅藻群落为代表的湖泊生态系统对气候波动和区域人类活动的响应过程。研究结果表明，在人类干扰显著加强之前，风力扰动是镜泊湖硅藻群落变化的一个重要因子，表现为Aulacoseira属种取代小型浮游种（Cyclostephanos、Stephanodiscus和Discostella）成为优势种。20世纪70年代以来，Asterionella formosa、Nitzschia palea和Fragilaria crotonensis的相继增加则反映了流域农业活动加剧、农业化肥大量施用以及污水排放导致的湖泊营养水平升高。温度的持续上升已经引起东北地区一些湖泊硅藻群落结构发生显著变化，但镜泊湖的硅藻记录却未显示这一气候变化的信号。考虑湖泊-流域形态和人类活动的不同，研究认为近几十年气候变化对镜泊湖硅藻群落结构的影响被强烈的人类干扰所掩盖而未显现出来。 Abstract:Climate warming and intensified human activities have led to the deterioration of lake environments and the degradation of lake ecological services in China over the past few decades. In northeast (NE) China, up to now, information about lake ecological changes responding to climate changes and human activities has derived mainly from short-term observations. In the present study, we choose Jingpo Lake in NE China as the study area. Sediment records and paleolimnological methods, in combination with long-term meteorological observations, were used to determine the patterns of diatom community responses to climate changes and anthropogenic disturbances. The history of diatom assemblage changes over the past 130 years was reconstructed from the sediment of Jingpo Lake. The result was then compared with other diatom records from NE China to evaluate the impacts of climate changes and human activities on diatom community shifts. Our diatom records show a distinct shift from small-type planktonic species (e.g., Cyclostephanos dubius, Cyclostephanos tholiformis, Stephanodiscus parvus, Stephanodiscus invisitatus, Discostella pseudostelligera) to a genus of heavy frustules (Aulacoseira), implying that wind strength played an important role in diatom assemblage changes before the expansion of human activities. Since the end of the 1960s, successive increases in the abundance of Asterionella formosa, Nitzschia palea, and Fragilaria crotonensis have reflected intensified agricultural activities, fertilizer usage, and sewage discharge, which have resulted in a trend to eutrophication. The meteorological observations of the past 60 years reveal obvious climate warming in NE China, especially since the mid-1970s. Previous studies have shown that diatom communities in Lake Xiaolongwan and Erlongwan (NE China) have clearly responded to climate warming, while diatoms in Jingpo Lake have not responded in a similar way. Lake Xiaolongwan and Erlongwan have similar climate conditions to those at Jingpo Lake but much smaller basins and catchments. Additionally, human activities in the catchments of Lake Xiaolongwan and Erlongwan are much less intense. Therefore, it can be speculated that the impacts of climate warming on the diatom community shift in Jingpo Lake have been obscured by intense human disturbances. Additionally, intensified human activity has become the dominant factor leading to the ecological threshold being crossed in Jingpo Lake. 参考文献 相似文献 引证文献

Paleolimnology of a freshwater estuary to inform Area of Concern nutrient delisting efforts

The St. Louis River Estuary (SLRE), a freshwater estuary bordering Duluth, Minnesota, Superior, Wisconsin, and the most western point of Lake Superior (46.74°, − 92.13°), has a long history of human development since Euro-American settlement ~ 200 years ago. Due to degradation from logging, hydrologic modification, industrial practices, and untreated sewage, the SLRE was designated an Area of Concern in 1987. Action has been taken to restore water quality including the installation of the Western Lake Superior Sanitary District in 1978 to help remove beneficial use impairments. A better understanding of historical impacts and remediation is necessary to help document progress and knowledge gaps related to water quality, so a paleolimnological study of the SLRE was initiated. Various paleolimnological indicators (pigments, diatom communities, and diatom-inferred phosphorus) were analyzed from six cores taken throughout the SLRE and another from western Lake Superior. Reductions in eutrophic diatom taxa such as Cyclotella meneghiniana and Stephanodiscus after 1970 in certain cores suggest an improvement in water quality over the last 40 years. However, in cores taken from estuarine bay environments, persistence of eutrophic taxa such as Cyclostephanos dubius and Stephanodiscus binderanus indicate ongoing nutrient problems. Sedimentary pigments also indicate cyanobacteria increases in bays over the last two decades. Diatom model-inferred phosphorus and contemporary monitoring data suggest some of the problems associated with excess nutrient loads have been remediated, but modern conditions (internal phosphorus loading, changing climate) may be contributing to ongoing water quality impairments in some locations. The integrated record of biological, chemical, and physical indicators preserved in the sediments will aid state and federal agencies in determining where to target their resources.

Use of Diatom Communities as Indicators of Conductivity and Ionic Composition in a Small Austral Temperate River System

The aim of this study was to determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories. Samples were collected on two occasions from 22 sampling sites within the Bloukrans River system, Eastern Cape Province, South Africa. The data collected were subjected to multivariate statistical technique, i.e. CCA, to determine environmental gradients along which the diatom species were distributed as well as to elucidate hypothesised differences in community structure per stream order. Significant differences between the two sampling periods were observed in dissolved oxygen, temperature, Na, B, Ca, Zn, Cu, Cr, K, Fe, phosphate, conductivity, salinity and nitrate, while significant stream order variation was observed for conductivity, salinity, Mg, Ca and sediment nitrates. Study sites were grouped into two broad categories (stream order 1 and 2/3 sites) based on CCA. As pollution increased, low to moderate pollution-tolerant species such as Fragilaria tenera, Cyclostephanos dubius and Gyrosigma acuminatum were replaced by high pollution-tolerant species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. This shows that diatom assemblages are appropriate indicators of ionic composition/conductivity and hydromorphological characteristics (e.g. stream size) of running waters. The results highlight the importance of creating regional calibration datasets which will make it possible to develop procedures to determine conductivity and ion concentration effects on biota.

Surface–sediment diatom assemblages of the urban ponds of St. Petersburg, Russia

The diatom assemblages of the surface sediments have been studied in 53 urban ponds and lakes of St. Petersburg for the first time. In total, 350 species and infraspecific taxa have been registered; the species of Achnanthidium, Cocconeis, Cyclostephanos, Cyclotella, Gomphonema, Lemnicola, Navicula, Nitzschia, and Stephanodiscus genera were the most common. The wide distribution of small centric planktonic taxa, Cyclostephanos dubius, C. invisitatus, Cyclotella pseudostelligera, Stephanodiscus hantzschii, and S. minutulus, is preconditioned by the depletion of dissolved silica, which is a result of the high phosphorus load. The high abundance of macrophytes in the shallowest sites favors the dominance of epiphytic Fragilaria, Staurosira, and Staurosirella taxa. Bottom-living diatoms in the shallow eutrophic and hypereutrophic urban ponds are light-limited; this is a result of either macrophytes or phytoplankton development. Alkaliphilous and alkalibiontic species prevail among the pH-indicative species, while eutraphentic and hypereutraphentic diatoms, as well as those thriving in a wide range of trophic conditions, dominate over other trophic groups. The β- and α-mesosaprobic species are the most common saprobity-indicative taxa.

Direct versus indirect climate controls on Holocene diatom assemblages in a sub-tropical deep, alpine lake (Lugu Hu, Yunnan, SW China)

The reconstruction of Holocene environmental changes in lakes on the plateau region of southwest China provides an understanding of how these ecosystems may respond to climate change. Fossil diatom assemblages were investigated from an 11,000-year lake sediment core from a deep, alpine lake (Lugu Hu) in southwest China, an area strongly influenced by the southwest (or the Indian) summer monsoon. Changes in diatom assemblage composition, notably the abundance of the two dominant planktonic species, Cyclotella rhomboideo-elliptica and Cyclostephanos dubius, reflect the effects of climate variability on nutrient dynamics, mediated via thermal stratification (internal nutrient cycling) and catchment-vegetation processes. Statistical analyses of the climate–diatom interactions highlight the strong effect of changing orbitally-induced solar radiation during the Holocene, presumably via its effect on the lake's thermal budget. In a partial redundancy analysis, climate (solar insolation) and proxies reflecting catchment process (pollen percentages, C/N ratio) were the most important drivers of diatom ecological change, showing the strong effects of climate–catchment–vegetation interactions on lake functioning. This diatom record reflects long-term ontogeny of the lake-catchment ecosystem and suggests that climatic changes (both temperature and precipitation) impact lake ecology indirectly through shifts in thermal stratification and catchment nutrient exports.

Diatom Seasonality and Sedimentation in a Subtropical Alpine Lake (Lugu Hu, Yunnan-Sichuan, Southwest China)

The diatom succession and sedimentation during 2011 in a subtropical, deep alpine lake (Lugu Hu, Southwest China) were studied. The seasonal patterns in diatom assemblages were related to light, nutrient availability, and thermal regime. Peaks in the concentration of the planktonic diatoms (Asterionella formosa and Cyclotella ocellata) occurred in the metalimnion during autumn when light penetration was greater and silica concentrations were higher. The spring peak of Cyclostephanos dubius appeared to be a result of the combination of a well-mixed water column, higher nutrient concentration, and low light availability. Its sedimentation in late spring suggests that the sinking rates of C. dubius increased rapidly with the onset of stratification. However, the minimal catches of A. formosa and C. ocellata in sediment traps during autumn suggest they were still actively growing with very low sedimentation losses. The catch of benthic Fragilaria species in sediment traps during early spring and autumn reflected their resuspension from shallow water and transfer into pelagic zone as thermal stratification breaks down. The results provide important information for the interpretation of paleolimnological records from the lakes in Southwest China.

Diatom response to Asian monsoon variability during the Holocene in a deep lake at the southeastern margin of the Tibetan Plateau

Diatom analysis was applied to a 5.56‐m‐long sediment core, spanning the last 7.8 ka, from Lake Chenghai on the southeastern margin of the Tibetan Plateau. Diatom assemblages are dominated by Cyclotella rhomboideo‐elliptica, Cyclostephanos dubius and small fragilarioid and periphytic taxa. These diatom taxa are interpreted to be sensitive to changes in trophic status and/or turbulence of the water column that are probably related to variations in precipitation and temperature induced through the Asian monsoon. High abundances of C. dubius, Staurosirella pinnata and periphytic taxa suggest higher trophic status (mesotrophic) and stronger turbulence in the water column in the middle Holocene (7.8–4.5 ka BP). During the period of 4.5–2.3 ka BP, a decline in C. dubius, S. pinnata and periphytic taxa, and an increase in C. rhomboideo‐elliptica with the appearance of Cyclotella ocellata suggests a response to decreasing trophic level (more oligotrophic). After 2.3 ka BP, the persistent increases in C. rhomboideo‐elliptica and the loss of Cyclotella ocellata mirrored a further decrease in trophic level (oligotrophic). The main changes in the diatom assemblages in the Lake Chenghai sediment core reflect direct and indirect climate forcing and in particular, the strength of monsoonal precipitation, which in turn corresponds to orbitally induced variability in Northern Hemisphere summer solar insolation since 7.8 ka BP.

Pleistocene Stephanodiscaceae Diatoms from Deposits in El Fayoum Depression, Egypt

Diatomite samples in the Pleistocene deposits collected from three different localities in El Fayoum depression, reveal the predomi-nance of Cyclostephanos and Stephanodiscus from Stephanodiscaceae. Stephanodiscus spp. were regarded with high frequencies in the western region of Lake Qarun and the dominan-cy is lowered in the eastern part while Cyclo-stephanos was present with less frequency. Stephanodiscus was represented by two species S. aegyptiacus and S. minutulus while Cyclo-stephanos found as one species C. dubius. Mor-phological variations of fossil species were de-scribed using light and scanning electron mi-croscopy. The results show both morphological differences and similarities between the ob-served species. Observing the investigated taxa with light microscope they show similarities, while observation with the SEM shows distinct differences. The presence of Stephanodiscus minutulus with large number indicates that the paleoecological environment was alkaline fresh-water nature and also suggested that the lake at this time was a different water levels or different degree of transparency. Recording of Cyclo-stephanos dubius in the diatomaceous earth of the studied site proved that this area was char-acterized by both high conductivity and high nutrients concentration during the Pleistocene era.

Components of the Subsurface Sediments with Emphasis of Diatoms Frequency and Their Palaeoecological Significance at the Tennis Island and Its Environs, Western Port Said, Egypt

Objective: The study gives a view of the major textural and compositional components of subsurface sediments around Tennis Island and its environs. It provides data on distribution and frequency of diatoms in the subsurface sediment as well as describes and combines the achieved results of paleo-environment processes and its response to water level change. Methodology: Twelve subsurface sediment samples were collected to show major textural and compositional components as well as describing diatom flora around a unique natural ecosystem called Tennis Island. Results: The grain size analysis of the collected samples revealed a high content of fine sand, mud (silt and clay) and characterized by low organic matter (average 10.4%) and widely varied content of CaCO3, with an average of 53.8%. 39 diatom species belonging Original Research Article Gaballah and Aboulela; JSRR, Article no. JSRR.2014.004 564 to 25 genera were identified. Analogue for the island with high proportion of Planktonic species compared to benthic ones was established. Planktonic species represented by dominant forms like Cyclostephanos dubius; Cyclotella meneghiniana and Cyclotella stelligera. The non Planktonic species were Navicula alpina; Campylodiscus spp. and Diplonies bombus; while the other benthic forms were often sparse. Island is influenced by water input from the sea and drains from the south. Conclusion: The study revealed that diatoms experience climate change directly and indirectly through changes in sea water level, tectonic activity and trophic status.

Use of siliceous algae as biological monitors of heavy metal pollution in three lakes in a mining city, southeast China

Abstract In order to assess the ecological status of three lakes in a historical mining city (SE China), water metal concentrations and surface sedimentary diatoms and chrysophyte cysts were analyzed in 20 sampling sites. The significant correlations between the algal indices and the cumulative criterion unit (CCU) scores confirmed the importance of heavy metals in shaping algae communities. In the metal-polluted sites, diatom assemblages were dominated by metal-tolerant species, such as Nitzschia palea and Nitzschia perminuta. In the unpolluted samples, diatom assemblages were characterized by Cyclostephanos dubius, Discostella pseudostelligera and Aulacoseira species (mainly A. alpigena, A. granulata and A. ambigua). These dominant taxa in the unpolluted samples might be sensitive to metal contamination but tolerant of eutrophication. In addition, nonspherical cysts were much more abundant in the polluted sites, indicating that their presence should be indicative of metal contamination in this region. This study provides some clues for future metal pollution assessment through the use of siliceous algae in metal polluted lakes.

Natural and human-induced environmental changes in Eastern Europe during the Holocene: a multi-proxy palaeolimnological study of a small Latvian lake in a humid temperate zone

This study uses the Holocene lake sediment of Lake Ķūži (Latvia, Vidzeme Heights) for environmental reconstruction with multi-proxy records including lithology, computerised axial tomography scan, grain-size analysis, geochemistry, diatoms and macrofossils, supported by AMS radiocarbon dating. Numerical analyses (PCA; CONISS) reveal three main phases in the development of the lake. Response to the Lateglacial–Holocene transition in Lake Ķūži took place around 11,300 cal. BP. Organogenic sedimentation started with distinctive 5-cm-thick peat layer and was followed by lacustrine sedimentation of carbonaceous gyttja. Several findings of the peat layer with similar dated age and position at different absolute altitudes indicate that lake basin was formed by glaciokarstic processes. In the Early Holocene (until around 8,500 cal. BP), the lake was shallow and holomictic, surrounded by unstable catchment with erosion and inflow events. Predominance of diatom species of Cyclotella and Tabellaria, large numbers of respiratory horns of phantom midge pupae (Chaoboridae), high Fe/Mn ratio, as well as the presence of laminated sediments indicates the transition to a dimictic and oligo-mesotrophic lake conditions with high water level, anoxia in the near-bottom and stable catchment in the Middle Holocene (8,500–2,000 cal. BP). This contrasts with many hydrologically sensitive lakes in Northern and Eastern Europe in which the water level fell several meters during this period. During the Late Holocene (from 2,000 cal. BP to the present), the lithological and biotic variables reveal major changes, such as the increase in erosion (coarser grain-size fraction) and eutrophication [diatoms Aulacoseira ambigua (Grun.) Sim., Stephanodiscus spp., Cyclostephanos dubius (Fricke) Round]. Characteristics of lake-catchment system during the Late Holocene reflect anthropogenic signal superimposed on the natural forcing factors. To date, the Late Quaternary palaeolimnological reconstructions using lake sediment has been limited in the Baltic region. Therefore, findings from Lake Ķūži provide important information about environmental and climatic changes that took place in this part of Eastern Europe. This study shows that the relative importance of climate and local factors has varied over the time and it is essential to consider the lake basin topography, catchment size and land cover as potential dominant forcing factors for changes in sedimentary signal.