Fragilaria Crotonensis Research Articles

Phytoplankton Functional Groups Variation and Influencing Factors in a Shallow Temperate Lake.

The present study was carried out in Luoma Lake, a shallow lake in temperate eastern China. Based on a two-year study, the dynamics of phytoplankton functional groups and influencing factors were analyzed. A total of 178 taxa were identified and sorted into 20 codons, according to the phytoplankton functional group classification. In order to find the environmental factors driving phytoplankton variations, fifteen groups were analyzed in detail using redundancy analysis. Groups P (Fragilaria crotonensis), X2 (Chlamydomonas globosa, C. microsphaera and Chroomonas acuta), and MP (Navicula rotaeana) were dominant during low temperature periods, whereas groups X2, S1 (Pseudanabaena limnetica), and W1 (Euglena sp.) were dominant during high temperature periods. Water temperature, total phosphorus, and ammonium were the significant driving factors explaining phytoplankton succession. Furthermore, total phosphorus and ammonium could be broadly used in risk management for potential algal blooms in Luoma Lake.

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

Paleolimnological assessment of nutrient enrichment on diatom assemblages in a priori defined nitrogen- and phosphorus-limited lakes downwind of the Athabasca Oil Sands, Canada

<p>As the industrial footprint of the Athabasca Oil Sands Region (AOSR) continues to expand, concern about the potential impacts of pollutants on the surrounding terrestrial and aquatic ecosystems need to be assessed. An emerging issue is whether recent increases in lake production downwind of the development can be linked to AOSR activities, and/or whether changing climatic conditions are influencing lake nutrient status. To decipher the importance of pollutants, particularly atmospheric deposition of reactive nitrogen (Nr), and the effects of climate change as potential sources of increasing lake production, lakes from both within and outside of the nitrogen deposition zone were analyzed for historical changes in diatom assemblages. Lake sediment cores were collected from <em>a priori</em> defined nitrogen (N) - and phosphorus (P) - limited lakes within and outside the N plume associated with the AOSR. Diatom assemblages were quantified at sub-decadal resolution since ca. 1890 to compare conditions prior to oil sands expansion and regional climate warming, to the more recent conditions in each group of lakes (Reference and Impacted, N- and P-limited lakes). Analyses of changes in assemblage similarity and species turnover indicates that changes in diatom assemblages were minimal both within and across all lake groups. Small changes in percent composition of planktonic taxa, particularly small centric taxa (<em>Discostella </em>and <em>Cyclotella</em> species) and pennate taxa, such as <em>Asterionella formosa</em> and <em>Fragilaria crotonensis</em>, occurred in some of the lakes. While these changes were consistent with potential climate effects on algal growth, water column stability and other factors; the timing and direction of biotic changes were variable among sites suggesting that any apparent response to climate was lake dependent. The absence of a consistent pattern of diatom changes associated with receipt of reactive nitrogen or intrinsic nutrient-limitation status of the lake suggest that downwind AOSR emissions had no demonstrable effect on diatom composition. </p>

Diatom communities in thermo-mineral springs of Galicia (NW Spain)

The species composition of diatom assemblages was studied in five unpolluted thermo-mineral springs in Galicia (NW Spain). Three are considered hot and two cold, and some contain hydrogen sulphide. A total of 68 taxa (24 genera) have been recorded. The Shannon–Wiener diversity index (H′) ranged between 0.63 and 2.01. The nMDS ordination showed that diatom assemblage composition was influenced mostly by conductivity, temperature and hydrogen sulphide concentration. Diatom assemblages found in the Galician springs differed from those in springs of other geographical locations with similar physical and chemical characteristics. The most species-rich genera were Nitzschia and Achnanthidium with 10 and 8 species, respectively. Achnanthidium exiguum and Achnanthidium saprophilum had the widest distribution. Denticula thermalis and Achnanthidium caledonicum were found in environments with relatively low mineralization and low temperature, whereas Rhopalodia gibberula, Rhopalodia operculata and Fragilaria crotonensis were found in mineral-rich springs with high temperatures. Achnanthidium exiguum, A. saprophilum, Achnanthes coarctata, Achnanthes exigua var. elliptica, Mayamaea atomus, Eunotia implicata, Gomphonema minusculum, Gomphonema minutum and Cosmioneis pusilla were present in the spring with high H2S content.

Water quality assessments: A case study of plankton and macrobenthic invertebrates of Porto-Novo and parts of Gulf of Guinea

Aspects of physico-chemical characteristics, plankton and macro invertebrates of Porto-Novo and Gulf of Guinea were studied in September 2012 with a view to determine the quality of water using plankton indices. Standard methods were used to determine the physico-chemical parameters. The mean water quality parameters studied were temperature (36.71oC), pH (7.63), transparency (1.97m), total dissolved solids (10.0mg/L), dissolved oxygen (4.73mg/L) and salinity (38.58‰) for Gulf of Guinea. Five divisions; Cyanophyta, Bacillariophyta, Chlorophyta, Euglenophyta and Pyrrhophyta were recorded for both bodies of water with diatoms and dinoflagellates dominating the spectrum. The phytoplankton ofPorto-Novo recorded abundance of Gomphonema spp., Fragilaria crotonensis, Synedrasp. and Nitzschia sp.(diatoms) while that of Gulf of Guinea recorded Ceratium spp. and Gonyaulax spinifera (dinoflagellates). For the zooplankton, Acartia clausii (a copepod) and Penilla avirostris Dana (Cladocera) were the highest in both occurrence and abundance especially at Porto-Novo. The population of benthic fauna was low (20 individuals) dominated by bivalve, Tivela tripla.Keywords: Microalgae, zooplankton, benthos, Porto-Novo, Gulf of Guinea

Effects of winter severity on spring phytoplankton development in a temperate lake (Lake Erken, Sweden)

Phytoplankton seasonal succession has been linked to a variety of serial environmental changes, especially weather- and climate-induced physical forcing. This study compared spring phytoplankton dynamics after winters of different severity (cold, normal, and warm) in Lake Erken, Sweden. The spring diatom bloom was dominated by different functional groups: group A (centric diatoms 5–10 μm) after cold winters, B (centric diatoms >15 μm) after normal winters, and P (Aulacoseira granulata, Fragilaria crotonensis) after warm winters. Our results suggest that weather-related processes were the primary external drivers accounting for differences in spring phytoplankton dynamics in Lake Erken. Spring phytoplankton are influenced by overwintering species from the last autumn that can initiate the following spring bloom. Average taxonomic distinctness of the spring community was assessed using a new biodiversity measurement that incorporates taxonomic relatedness information. This value was lower than expected after warm and cold winters, which had winter air temperature 1°C deviation from an average value calculated over 21 years. Such winters increased the level of disturbance or stress to the lake, resulting in a spring with less diverse phytoplankton by narrowing the niche for species with various ecological requirements.

Phytoplankton composition of the water and gastrointestinal tract of the mussel Diplodon enno (Ortmann, 1921) from São Francisco river (Bahia, Brazil).

The knowledge on diet composition of the freshwater mussel Diplodon enno (Ortmann) would aid in its culture and propagation allowing, this way, the replacement of natural endangered populations in Brazil. Microalgae are the main food source for captive mussels and unionids have displayed an ability to sort algae based on the cellular characteristics prior to ingestion. The main objective of the present work is to analyze the phytoplankton composition of the water from and of the gastrointestinal contents of the mussel D. enno, as an initial step for development of a suitable rearing diet. Therefore, water samples and bivalve specimens were collected from S. Francisco River, city of Paulo Afonso, Bahia, Brazil. The microalgal composition found in water and stomach/gut content samples was very diverse being represented by the following divisions: Cyanophyta, Chlorophyta, Dinophyta and Heterokontophyta (Diatoms). Concerning the relative abundance of microalgae divisions, it is possible to state, for the water and gastrointestinal contents, that Cyanophyta represents 15% and 14%, Chlorophyta 54% in both, Heterokontophyta 31% and 27% and Dinophyta 0% and 5%, respectively. According to the Brazilian CETESB criteria for phytoplankton species classification, 50% of Cyanophyta and 15% of Chlorophyta species observed in the water samples were classified as "very frequent", as were 68% of Heterokontophyta and 33% of Chlorophyta species in the gut/stomach tract samples. Focusing at a species level, although in the water only Coelastrum sp. and Chroococcus sp. were observed in 100% and 75% of the samples, respectively, in the gastrointestinal tract the species Staurastrum sp., Aulacoseira sp., Scenedesmus sp. and Fragilaria crotonensis occurred in 80% to 100% of the samples. The present results showed that D. enno feeds not only on small chlorophytes microalgae, due to their convenient size that facilitates higher feeding rates, but also on large size diatoms, due to a possible nutritional advantage for the bivalves. Thus, a diet composed by large diatoms and small chlorophytes microalgae may be considered as the most reasonable for the maintenance of D. enno populations.

Phytoplankton composition of the Itaparica and Xingó reservoirs, São Francisco River, Brazil.

The installation of dams causes changes to the integrity of rivers and to the water cycle, performing an instrumental role in the organization of biological communities, including that of phytoplankton. In the present study, we analyzed the taxonomic composition of phytoplankton in two hydroelectric reservoirs on the São Francisco River, Itaparica and Xingó reservoirs. Samples were collected at quarterly intervals between December 2007 and September 2009, at 12 sampling stations in each reservoir, totaling 92 samples. We identified 110 species in the Itaparica reservoir and 136 in the Xingó reservoir, of which diatoms followed by green algae, played a major contribution to both reservoirs. Most of the species is rare and/or occasional. In the Itaparica reservoir, there were no very frequent species, although in the Xingó this category was represented by the diatoms Aulacoseira granulata (Ehrenberg) Simonsen and Fragilaria crotonensis Kitton. These results show that, despite the similarity in the composition of phytoplankton, the reservoirs studied certainly differed regarding their environmental conditions.

Variation of phytoplankton functional groups modulated by hydraulic controls in Hongze Lake, China.

Hongze Lake is a large, shallow, polymictic, eutrophic lake in the eastern China. Phytoplankton functional groups in this lake were investigated from March 2011 to February 2013, and a comparison was made between the eastern, western, and northern regions. The lake shows strong fluctuations in water level caused by monsoon rains and regular hydraulic controls. By application of the phytoplankton functional group approach, this study aims to investigate the spatial and temporal dynamics and analyze their influencing factors. Altogether, 18 functional groups of phytoplankton were identified, encompassing 187 species. In order to seek the best variable describing the phytoplankton functional group distribution, 14 of the groups were analyzed in detail using redundancy analysis. Due to the turbid condition of the lake, the dominant functional groups were those tolerant of low light. The predominant functional groups in the annual succession were D (Cyclotella spp. and Synedra acus), T (Planctonema lauterbornii), P (Fragilaria crotonensis), X1 (Chlorella vulgaris and Chlorella pyrenoidosa), C (Cyclotella meneghiniana and Cyclotella ocellata), and Y (Cryptomonas erosa). An opposite relationship between water level and the biomass of predominant groups was observed in the present study. Water level fluctuations, caused by monsoonal climate and artificial drawdown, were significant factors influencing phytoplankton succession in Hongze Lake, since they alter the hydrological conditions and influence light and nutrient availability. The clearly demonstrated factors, which significantly influence phytoplankton dynamics in Hongze Lake, will help government manage the large shallow lakes with frequent water level fluctuations.

Climate change impeded the re-oligotrophication of the Saidenbach Reservoir

Regular ecological investigations usually on a fortnightly basis have been carried out at the Saidenbach Reservoir (SE Germany) and its tributaries since 1975. The data show a sudden decrease in the phosphorus import of over 60% in 1990, resulting in the abrupt change of the trophic state from eutrophic to weakly mesotrophic. Contrary to expectations, the average annual phytoplankton abundance did not decrease but almost doubled on average over the years after 1990. This was primarily due to mostly warmer winters after 1990 causing longer spring overturns, which minimized sedimentation losses, enabled better utilization of the phosphorus reserves, and resulted in higher yields of the diatom-dominated phytoplankton spring mass development. In the summers after 1990, the mass growth of the diatom Fragilaria crotonensis, which in the past used to dominate in this season and effectively transported phosphorus to the sediment by settling, was considerably reduced because of lower P supply and stronger stratification. However, the decrease in the biomass of Fragilaria was overcompensated by the increased abundance of cyanobacteria. They benefitted not only from declining phosphorus competition by Fragilaria but also from higher thermal stability and temperature in the epilimnion. Hence, even higher summer biomasses were observed despite considerably lowered phosphorus import. The analysis of the long-term dataset clearly illustrates the deciding impact of hydrophysical factors on the phytoplankton growth, also under nutrient deficient conditions. The altered mixing and stratification pattern caused by climate change did not only prevent the re-oligotrophication of the reservoir but even enhanced the phytoplankton production. It seems that global warming modifies the interplay between physical and nutrient limitation mechanisms and the limits and models used in the past to classify trophic-state levels have to be verified. The study shows the enormous significance and indispensability of uninterrupted ecological long-term datasets, including reliable data of the ecosystem's organismic structure, for research about the consequences of climate change.

Effects of glacier meltwater on the algal sedimentary record of an alpine lake in the central US Rocky Mountains throughout the late Holocene

The effects of alpine glaciers on the hydrology, physical features, and biogeochemistry of lakes have been investigated over contemporary time scales. However, the influence of these factors on algal communities over longer time scales remains unclear, yet is critical to paleolimnological interpretation of environmental change in alpine regions. We examined sedimentary algal pigments and fossil diatom assemblages in two proximal lakes with equivalent local climates, one glacier-fed and one snow-fed, in the central Rocky Mountains (USA) to determine how glacier meltwater has altered algal records over the last 3,000 years. Differences between the records of the two lakes intensified during the Medieval Climate Anomaly and the Little Ice Age, with the glacier-fed lake exhibiting an overall increase in fossil algal pigment concentrations and greater diatom assemblage turnover. Starting 1,000 years ago, the glacier-fed lake in this study showed evidence of nitrogen enrichment from glacier meltwater, as indicated by increasing relative abundances of Asterionella formosa and, to a lesser extent, Fragilaria crotonensis. Since the Little Ice Age, diatom species richness declined in the glacier-fed lake, and further decreased following the 1950s, while assemblage turnover increased. These results demonstrate that glaciers can strongly alter the algal sedimentary record and should be considered when interpreting high-elevation lake records.

Spatio-temporal study of phytoplankton cell viability in a eutrophic reservoir using SYTOX Green nucleic acid stain

Despite the global importance of phytoplankton primary production, the ecological role of cell death as an important loss process in phytoplankton is poorly understood. To assess the significance of cell death in phytoplankton, we studied cell viability of dominant species in the canyon-shaped eutrophic Řimov Reservoir (Czech Republic) at weekly and biweekly intervals from April to October 2011. Surface samples were taken from the lacustrine zone (near the dam, low nutrient level) and transition zone (near the river inflow, high nutrient level) of the reservoir. Moreover, samples from euphotic depth (1% of surface irradiance) were taken from the lacustrine zone. We used the membrane-impermeant nucleic acid dye SYTOX Green to examine seasonal and spatial differences in phytoplankton cell viability. Three species (diatoms Asterionella formosa, Fragilaria crotonensis, and cyanobacterium Aphanizomenon flos-aquae) were studied in detail. There was no difference in Asterionella cell viability among sampling sites. In the lacustrine zone, Fragilaria and Aphanizomenon exhibited lower viability than in the transition zone. In addition, Aphanizomenon viability was significantly lower at the euphotic depth. Nutrient levels were revealed as a factor influencing Fragilaria viability, while light availability was more important for Aphanizomenon. Our results evidenced that the importance of cell death, in particular phytoplankton taxa, varies both spatially and temporally. Moreover, our study indicates that coexisting taxa may differ in their capacity to cope with different environmental stressors.

Phytoplankton composition changes during water level fluctuations in a high-altitude, tropical reservoir

To understand the responses of phytoplankton to water level fluctuations (WLFs) in tropical conditions at high altitude, limnological monitoring was performed monthly in Valle de Bravo (VB) reservoir, a waterbody affected by relatively strong WLFs due to water scarcity in central Mexico during 2008–2009. The thermal behaviour of the reservoir was warm, monomictic (Nov–Feb), and water levels fell to 12 m below capacity. Observed hypolimnetic temperature increases in VB are considered indirect evidence of boundary mixing events, previously attributed to internal waves driven by strong diurnal winds along a 7 km fetch. Unusually low biomasses were observed during circulation, probably due to low light availability (Zeu/Zmix < 1), grazing, and relatively low temperatures (<20 °C). In contrast, enhanced phytoplankton biomass was observed throughout stratification, which could be explained by nutrient inputs to the epilimnion through boundary mixing, as previously proposed for VB, and by higher (>20 °C) temperatures. Dominant species were Cyclotella ocellata, Fragilaria crotonensis, Woronichinia naegeliana, and Microcystis wesenbergii. Nitrogen-fixing cyanobacteria (Nostocales), a recurrent problem in this reservoir, were markedly less abundant than during high-water periods (2002–2005), probably due to dissolved inorganic nitrogen (DIN) inputs from the hypolimnion. A profuse formation of heterocysts was observed at the same time that DIN and the DIN to soluble reactive phosphorus ratio (DIN:SRP) were low (<2 μmol L−1 and ~1 respectively), suggesting heterocyst development could be a complementary proxy to assess DIN limitation. Intense water level decreases in this reservoir resulted in increasing biomasses of planktonic diatoms and a significant decrease in noxious algae such as Nostocales, thus ameliorating the water quality of the reservoir.

Quagga mussel (Dreissena rostriformis bugensis) selective feeding of phytoplankton in Saginaw Bay

Experiments from May to December measuring selective grazing and egestion of different phytoplankton taxa in natural Saginaw Bay (Lake Huron) seston by shallow-water morph quagga mussels (Dreissena bugensis rostriformis) showed that the mussels were highly selective filter feeders and that their net clearance rates on different species ranged widely, resulting in food consumption that was strongly driven by seasonal phytoplankton dynamics. Overall, net clearance rates by quagga mussels on the entire phytoplankton assemblage were similar to those observed for zebra mussels (Dreissena polymorpha) during the 1990s. Phytoplankton taxon, rather than size, was more important to food selection since quagga mussels cleared similar sized but different species of algae at very different rates. In contrast to many studies with zebra mussels, larger-sized algae such as Dinobryon divergens, Aulacoseira italica, Fragilaria crotonensis, and Anabaena were cleared at high rates and rejected at lower rates than many smaller species within the same broad taxonomic group. We suspect that these differences between dreissenid species do not stem from species differences but methodological factors and phytoplankton composition of systems studied. Small-sized diatoms, green algae with thick cell walls (Scenedesmus and Oocystis), and colonial cyanobacteria with gelatinous sheaths (Aphanocapsa, Chroococcus, and Microcystis) were cleared at low rates and rejected in high proportion in pseudofeces or feces during all seasons. We describe the likely mechanisms of pre- and post-ingestive behavior that explain these differences, which relate to phytoplankton size, morphology, cell wall characteristics, and chemical composition. Changes in the Great Lakes phytoplankton communities are consistent with mussel grazing preferences.

A comparison of the character of algal extracellular versus cellular organic matter produced by cyanobacterium, diatom and green alga

This study investigated characteristics of algal organic matter (AOM) derived from three species (cyanobacterium Microcystis aeruginosa, diatom Fragilaria crotonensis and green alga Chlamydomonas geitleri) which dominate phytoplanktonic populations in reservoirs supplying drinking water treatment plants. Algal growth was monitored by cell counting, optical density and dissolved organic carbon concentration measurements. Extracellular organic matter (EOM) released at exponential and stationary growth phases and cellular organic matter (COM) were characterised in terms of specific UV absorbance (SUVA), peptide/protein and non-peptide content, hydrophobicity and molecular weight (MW). It was found that both EOM and COM were predominantly hydrophilic with low SUVA. COM was richer in peptides/proteins, more hydrophilic (with about 89% of hydrophilic fraction for all three species) and had lower SUVA than EOM. MW fractionation showed that both EOM and COM of all three species contain large portions of low-MW (<1 kDa) compounds and high-MW (>100 kDa) polysaccharides. Peptides/proteins exhibited narrower MW distribution than non-peptide fraction and it widened as the cultures grew. The highest amount of peptides/proteins with a significant portion of high-MW ones (22%) was observed in COM of M. aeruginosa. The results imply that the knowledge of AOM composition and characteristics predetermine which processes would be effective in the treatment of AOM laden water.

Paleolimnological reconstruction of change in a subtropical lake: a comparison of the subfossil record to limnological data

Paleolimnological reconstruction of change in a subtropical lake: a comparison of the subfossil record to limnological data Paleolimnological techniques permit the reconstruction of past environmental and biological conditions in aquatic ecosys- tems. However, more studies that include comparisons with historical and limnological records are needed, particularly in subtropical and tropical regions, to validate the links between extant and subfossil indicator communities. We performed a paleolimnological study to reconstruct environmental changes over the last 11 years in Lake Rodo, a subtropical, hypereu- trophic shallow lake located in Uruguay (34 ◦ 54 � 45 �� S, 56 ◦ 10 � 01 �� W), which was subjected to rehabilitation measures and from which limnological data were available. Analyses of the composition and abundance of fossil diatoms divided the record into three time periods that coincided with events during the history of Lake Rodo and its rehabilitation. The most abundant species were Aulacoseira granulata, Synedra acus, Aulacoseira granulata var. angustissima, Achnanthidium minutissimum, Stephanodiscus hantzschii and Fragilaria crotonensis. Indices of planktonic/benthic subfossil diatoms and of diversity re- flected changes in the transparency of lake water and in the diversity of habitats available for growth. Records of diatom abundances from phytoplankton and sediment samples were highly correlated; these results highlight the value of diatoms as bioindicators for reconstructing environmental conditions even on short time scales (sub-decadal). Our results also show important differences between temperate and subtropical systems and highlight the need for caution when attempting to apply ecological data determined in other regions.

낙동강 중·하류의 식물플랑크톤 군집구조 분석

A seasonal variation of phytoplankton community in the middle-lower part of the Nakdong River was studied in four sampling stations at monthly intervals from January to December 2012. We identified 40 genera 72 species of phytoplankton. Among these, diatoms were 36 species (50.0%), green algae 20 species (27.8%), blue-green algae 9 species (12.5%) and others 7 species (9.7%), respectively. The phytoplankton standing crops were recorded a maximum of 29,640 cells/mL at the Mulgeum (St. 4) in June and a minimum of 236 cells/mL at the Goryung (St. 1) in October. Also, Standing crops were increased with proceeding from middle part to lower part. Ecological important species were Stephanodiscus hantzschii, Cyclotella meneghiniana, Synedra acus, Aulacoseira granulata, Pediastrum sp. and Microcystis aeruginosa. Seasonal succession of phytoplankton represented that Stephanodiscus hantzschii was dominant species in winter, Cyclotella meneghiniana, Synedra acus was dominant species in spring, Microcystis aeruginosa, Cyclotella meneghiniana, Fragilaria crotonensis, Synedra acus, Aulacoseria granulata was dominant species in summer, and Aulacoseria granulata, Cyclotella meneghiniana, Fragilaria crotonensis was dominant species in autumn. In the community analysis, diversity index and dominant index were higher May~July and December~February, respectively. Also, diversity index and dominant index were decreased and increased with proceeding from middle part to lower part.

Spatial heterogeneity of diatom silicification and growth in a eutrophic reservoir

Summary Diatoms are one of the most important phytoplankton groups. As they grow, diatoms use silicon to produce a siliceous frustule, which protects the cell. During April–November 2011, at 1–3 week intervals, we estimated diatom silicification rates at two distinct sites along the longitudinal profile of the canyon‐shaped eutrophic Římov Reservoir (Czech Republic): (i) a nutrient‐depleted lacustrine zone near the dam and (ii) a nutrient‐rich transition zone upstream near the river inflow. Diatom silicification was estimated using the 24‐h in situ incubation of natural phytoplankton assemblage with a fluorophore 2‐(4‐pyridyl)‐5‐{[4‐(2‐dimethylaminoethyl‐aminocarbamoyl)methoxy]phenyl}oxazole (PDMPO) which fluorescently stains the newly synthesised diatom frustules. Diatoms contributed an average c. 40% to the total phytoplankton biovolume in the lacustrine zone, but only c. 20% in the transition zone where a cyanobacterial bloom developed during summer. Asterionella formosa and Fragilaria crotonensis were the most abundant diatom species, while Aulacoseira italica, Nitzschia acicularis, Synedra acus and Stephanodiscus sp. were less important. Silicification rates of all diatom species were significantly higher in the transition zone than at the dam. The intensity of PDMPO fluorescence per diatom cell was tightly related to the growth rates of three diatom species calculated from changes in cell counts during the incubation. The PDMPO technique can thus be used as a proxy for diatom growth. Growth rates of the two most abundant diatom species were positively correlated with daily light exposure but not with nutrient concentrations.

Okrzemki środkowego plejstocenu w osadach jeziornych z Krępca (Wyżyna Lubelska)

Osady jeziorne z profilu Krepiec 13 kolo Łecznej zostaly uznane na podstawie analizy pylkowej (Z. Janczyk-Kopikowa, 1980) za rownowiekowe z osadami z Ciechanek Krzesimowskich, ktore wedlug A. Środonia (1969) reprezentują interglacjal lubelski. W nawiązaniu do podzialu palinologicznego opisywanego profilu dokonano korelacji wydzielonych okresow rozwoju roślinności wyzszej z fazami rozwoju okrzemek – diatomofazami (KI, K2, K3). W obrebie diatomofaz wyrozniono ponadto ich cześci oraz subdiatomofazy reprezentujące poszczegolne etapy rozwoju jeziora interglacjalnego. MIDDLE PLEISTOCENE DIATOMS FROM LACUSTRINE DEPOSITS FROM KRĘPIEC (LUBUN UPLAND) A thick packet of lacustrine deposits, about 20 m thick, was found at depth from 21.15 m to 41.50 m in the Krepiec 13 borehole column. They are represented by silts varying in lithology and with intercalations of gyttja, peat and peaty silts. They are underlain by sands with boulders, resting on till, and overlain by sands, peats, clay silts, chalk gravels and sandy silts. The pollen analysis, carried out by Z. Janczyk-Kopikowa (in print), has shown that the Krepiec borehole column comprises Interglacial deposits coeval with those from Ciechanki Krzesimowskie. According to A. Środon (1969), the latter do not correspond to the Masovien I Interglacial but to the Lublin Interglacial. On the basis of palynological subdivision of the studied borehole column, the differentiated periods of development of higher plants were correlated with phases of development of diatoms – diatom phases (K1, K2, K3). The diatom phases were further subdivided into parts and diatom subphases representing individual stages in evolution of the interglacial lake (Fig. 2). The bulk of the studied lacustrie deposits from Krepiec, comprising diatom phases Kl, K2A and K3A, are characterized by predominance of nannoplankton diatoms Stephanodiscus and Cyclotella in the dominant group (Tables I – IV). Fragilaria crotonensis , Asterionella formosa and Synedra ulna and S. acus are fairly common in the subdominant group. Middle part of the studied column (diatom phase K2B) displays a transitional stage in the development of the lake, characterized by decrease of plankton, accompanied by increase in number of littoral, mainly epiphytic, and rheophilous species typical of flowing water. Upper part of the section (diatom phase K3B) is characterized by predominance of Melosira italica and Epithemia zebra and, subsequently, Synedra ulna and Fragilaria construens . The development of these species indicates a marked shallowing, eutrophication of waters in the lake, and its overgrowing by macrophytes. The changes are related to further amelioration of climate, recorded as an Interglacial optimum in the pollen spectrum (III) by Z. Janczyk-Kopikowa (in print). The Krepiec section seems most close to that of the Lichwm Interglacial from Gwoznica in south-western Byelorussia (G.G. Gruzman et al., 1975).

The impact of cattle farming best management practices on surface water nutrient concentrations, faecal bacteria and algal dominance in the Lake Oconee watershed

AbstractThe objective of this study was to assess water quality in the Lake Oconee watershed and evaluate the best management practices used by cattle farms to reduce water contamination. Inorganic nutrient concentrations, algal abundance and faecal bacteria were highest in the cattle farming areas. The diatom community where cattle had no access was dominated by Achnanthidium minutissimum (Kützing) Czarnecki and Fragilaria crotonensis Kitton, and in sites where cattle were allowed direct access to the lake, Asterionella formosa Hassal, Nitzschia palea (Kützing) Smith and Navicula rostellata Kützing dominated. The latter three taxa are well‐known high‐nutrient diatoms. High populations of green algae (coccoid Desmidiaceae) were found where cattle had access. Sources of faecal pollution were identified using polymerase chain reaction detection, with Bifidobacterium adolescentis as a marker of human faecal pollution and Bacteroides (BoBac) indicating cattle faecal pollution. Overall, riparian buffers were most effective at reducing pollution from cattle operations.