Thecamoebian Assemblages Research Articles

Environmental evolution of the Miocene palaeolake of Venta del Moro (Valencia, Spain): a study of foraminifers, thecamoebians (Arcellinida) and ostracods

ABSTRACT The Venta del Moro site (Valencia, Spain) is especially known for its rich content in Late Miocene fossil mammals but it also holds other fossil vertebrates, invertebrates and plants. A micropalaeontological study of a 70-cm long sedimentary section carried out in the lacustrine beds of the site has yielded 2 foraminifer, 7 thecamoebian and 19 ostracod taxa (two of these last probably new species). A constrained cluster analysis allowed the recognition of three consecutive zones based on their micropalaeontological content. The variation of the microfossil assemblages closely matches lithology and reflects environmental changes in a palaeolake that was subject to a gradual drying process. Anoxic bottom conditions at the base of the sequence (Zone 1) prevented the occurrence of aerobic benthic microorganisms. Later, the appearance of ostracods and thecamoebians (Zone 2) documents the increasing oxygenation of the lake and suggests a permanent freshwater to slightly brackish lake with low temperature and stream influence. The dominance of foraminifers and the changes in the thecamoebian and ostracod assemblages in the upper part of the sequence (Zone 3) reflect more stable and oxygenised conditions and probably increasing temperature and evaporation in oligohaline temporary waters, during the final drying phase of the lake.

THECAMOEBIANS (TESTATE AMOEBAE) AS PROXIES OF ECOSYSTEM HEALTH AND RECLAMATION SUCCESS IN CONSTRUCTED WETLANDS IN THE OIL SANDS OF ALBERTA, CANADA

Thecamoebian (testate amoebae) assemblages in samples collected in August 2007 and June 2008 from Suncor Energy Inc. Constructed Wetlands Test Facility, Fort McMurray, Alberta were found to respond to varying levels of oil sands process-affected water/materials (OSPW/OSPM). Oil sands process affected material is characterized by elevated conductivity and naphthenic acid concentrations, and a strong relationship was found between thecamoebian assemblages and both of these impact-indicator constituents (r 2 =0.707 and r 2 =0.743, respectively). Wetlands highly impacted by OSPM contained low-diversity assemblages dominated by centropyxid thecamoebians (Centropyxis aculeataandC. constricta) andArcella vulgaris. Less-impacted sites, in contrast, had higher relative abundance and more-diverse assemblages dominated by difflugiid thecamoebians, primarilyDifflugia oblonga,D. urceolata, andCucurbitella tricuspis. Thecamoebian assemblages responded quickly to a deliberate reduction in the rate of OSPW input to some sample sites between 2007 and 2008, with increases in species diversity and relative abundance of difflugiids. At sites with little annual change in water quality, the thecamoebian assemblages were comparable, indicating reproducibility of thecamoebians as a contamination proxy. Canonical Correspondence Analysis (CCA) revealed the strong controls of Na/(Ca+Mg), Na/SO 4 , naphthenic acids, Na, alkalinity, and conductivity on the thecamoebian communities, although many of these are intercorrelated. Rmode cluster analysis emphasized the interannual similarity of the thecamoebian faunas at the same sites and the community changes at sites where the OSPW character changed. Q-mode cluster analysis showed that four main thecamoebian strains and species (Centropyxis constricta ‘‘aerophila’’,Centropyxis aculeata‘‘discoides’’,Cucurbitella tricuspis, Difflugia oblonga‘‘glans’’) significantly influence assemblage composition. The study suggests that thecamoebians are useful environmental proxies capable of gauging the impact of oil sands materials in reclaimed areas and have the potential to monitor the progression of aquatic reclamation initiatives. They also appear to be useful in gauging the success of various reclamation mitigation options, such as fertilization. The addition of nutrients resulted in higher species diversity and greater relative abundance of difflugiid thecamoebians than at a parallel site that had not been fertilized, suggesting a faster improvement in aquatic ecosystem health with nutrient loading. The rapid generation time of these protists, together with their apparent sensitivity to OSPM, make thecamoebians useful biomonitors of the progression of aquatic reclamation in oil sands operations.

Early Permian glacio-marine thecamoebian assemblages from the northwest Himalayas, India

Abstract. Diverse assemblages of thecamoebians are reported here from the Early Permian Manjir Formation of the northwest Himalaya in India. These thecamoebian tests were found in palynological preparations and are assigned an Early Permian age based on co-occurrence of age-diagnostic palynomorphs. Several of them show very close morphological affinity with extant thecamoebian genera, such as Amphitrema, Arcella, Centropyxis, Cyclopyxis, Cucurbitella, Difflugia and Trinema. This fauna lived in shallow-marine environments during the Early Permian deglacial phase of the widespread Late Carboniferous–Early Permian glaciation of Gondwana. The extant forms used for morphological comparison with the fossil forms were recorded from lakes and ponds in various parts of India. This study supports the current hypothesis of minimal evolution in thecamoebian lineages through geological time, and this group of protists has survived through long geological time and several mass extinction events without any significant morphological change. Stratigraphical and palaeontological evidence indicates that this fauna lived in the shallow-marine environments along the northwestern margin of Indian Gondwana during the deglacial phase of Late Carboniferous–Early Permian glaciation.

Biogeographic variation in Thecamoebian ( Testate amoeba ) assemblages in lakes within various vegetation zones of Alberta, Canada

Thecamoebians (Testate amoebae) have proven to be valuable proxies commonly used in environmental and paleoenvironmental studies. A better understanding of their geographic distribution and environmental parameters influencing this distribution is required for further thecamoebian research. Thecamoebians were analyzed from twelve lakes spanning five drainage basins and four vegetation zones, representing a variety of environmental and limnological parameters in Alberta, Canada. Species diversity is low throughout the study sites, ranging from 1.35 to 2.17, with various strains of Difflugia oblonga, Centropyxis constricta and Centropyxis aculeata dominating the fauna. Climate, as reflected in the vegetation zones, appears to be an influencing factor on species and strain distributions. Low-diversity assemblages strongly dominated by C. aculeata and C. constricta,characterize lakes in the rocky mountain region. Slightly, more diverse assemblages dominated by D. oblonga and Cucurbitella tricuspis characterize lakes in the grassland region. The highest Thecamoebian diversity was found in both the Boreal Forest and Parkland zones. The Boreal Forest is dominated by D. oblonga together with C. constricta,C. tricuspis and C. aculeata, while the Boreal Parkland is dominated by D. oblonga along with C. constricta and C. aculeata. Key words: Thecamoebians, Testate amoebae, Biogeographic, Alberta

Controls on the contemporary distribution of lake thecamoebians (testate amoebae) within the Greater Toronto Area and their potential as water quality indicators

Thecamoebians were examined from 71 surface sediment samples collected from 21 lakes and ponds in the Greater Toronto Area to (1) elucidate the controls on faunal distribution in modern lake environments; and (2) to consider the utility of thecamoebians in quantitative studies of water quality change. This area was chosen because it includes a high density of kettle and other lakes which are threatened by urban development and where water quality has deteriorated locally as a result of contaminant inputs, particularly nutrients. Fifty-eight samples yielded statistically significant thecamoebian populations. The most diverse faunas (highest Shannon Diversity Index values) were recorded in lakes beyond the limits of urban development, although the faunas of all lakes showed signs of sub-optimal conditions. The assemblages were divided into five clusters using Q-mode cluster analysis, supported by Detrended Correspondence Analysis. Canonical Correspondence Analysis (CCA) was used to examine species-environment relationships and to explain the observed clusterings. Twenty-four measured environmental variables were considered, including water property attributes (e.g., pH, conductivity, dissolved oxygen), substrate characteristics, sediment-based phosphorus (Olsen P) and 11 environmentally available metals. The thecamoebian assemblages showed a strong association with phosphorus, reflecting the eutrophic status of many of the lakes, and locally to elevated conductivity measurements, which appear to reflect road salt inputs associated with winter de-icing operations. Substrate characteristics, total organic carbon and metal contaminants (particularly Cu and Mg) also influenced the faunas of some samples. A series of partial CCAs show that of the measured variables, sedimentary phosphorus has the largest influence on assemblage distribution, explaining 6.98% (P < 0.002) of the total variance. A transfer function was developed for sedimentary phosphorus (Olsen P) using 58 samples from 15 of the studied lakes. The best performing model was based on weighted averaging with inverse deshrinking (WA Inv, rjack2 = 0.33, RMSEP = 102.65 ppm). This model was applied to a small modern thecamoebian dataset from a eutrophic lake in northern Ontario to predict phosphorus and performed satisfactorily. This preliminary study confirms that thecamoebians have considerable potential as quantitative water quality indicators in urbanising regions, particularly in areas influenced by nutrient inputs and road salts.

Thecamoebians from the small streams of the Boubín area (Šumava Mts, Czech Republic)

From 1999–2005, seventy-eight samples were collected from the small streams in the area of the Boubin Mountain including also the natural preserve “Boubinsky prales” (Boubin primeval forest) (Sumava Mts, Czech Republic). Nineteen species of thecamoebians were identified in the samples; the most abundant species were Centropyxis orbicularis, Pontigulasia compressa, Centropyxis aculeata, Difflugia oblonga and Centropyxis arcula. Species composition of assemblages as well as ecological affinities of the most common taxa are comparable with data from the previously analysed streams in the Sumava Mts. This correlation improves the quality of data for environmental preferences of thecamoebian assemblages contained in the streams and these can be used for interpretation of ancient environments. Though species composition of assemblages changes gradually, two end-member assemblages can be defined. For both assemblages, environmental conditions were defined: Lower-diversity assemblages dominated by centropyxids originated mainly from standing water with low content of organic debris. Relative abundances of C. orbicularis showed negative correlations with abundances of other Centropyxis spp. which may indicate different ecological affinities of this species. Centropyxis orbicularis may tolerate higher levels of fine organic debris in stream sediments. Assemblages with common to abundant occurrences of P. compressa and/or D. oblonga prefer running water. Difflugia oblonga dominated in samples with higher content of fine organic debris. Relation between test size of D. oblonga and flow rate was recorded: large D. oblonga prevailed in standing water while small specimens dominated in fast streams.

Ecology of testate amoebae (thecamoebians) in subtropical Florida lakes

Fifty-seven surface sediment samples from 35 Florida lakes were collected to study testate amoebae. Seven genera, 17 species, and 28 strains were identified in the 46 sediment samples from 31 lakes that contained testate rhizopods. Seven species accounted for C90% of the individuals in all samples. Sediment total phosphorus (TPsed), organic matter (OM), and total carbon:total nitrogen ratio (TC:TN) were measured to assess the effect of these variables on thecamoebian assemblages. OM content was the only sediment variable that influenced presence/ absence of thecamoebians. Samples with \5% OM contained no thecamoebians. Lakes with multiple surface sediment samples showed high Morisita-Horn similarity values (0.74-0.99), indicating that all sites at which samples were collected in a lake pro- vided representative thecamoebian assemblages. No relationship was observed between thecamoebian diversity indices and sediment variables. Lake trophic state and pH were examined to explore potential water column influences on thecamoebian communities. Highest thecamoebian diversity indices were found in mesotrophic to eutrophic lakes with pH near 8.0. These results suggest that water column conditions have a greater influence on thecamoebian assem- blages than do sediment variables. We used multivariate analysis to evaluate the relations between water quality variables and testate rhizopod assem- blages. Canonical correspondence analysis (CCA) showed that alkalinity and pH are the water column variables that most influence the relative abundance of species. Thecamoebians thus hold promise as bioin- dicators of acidification in Florida lakes. Thecamoe- bian remains in lake sediment cores should be useful to infer past anthropogenic shifts in lake pH.

THECAMOEBIANS FROM THE UPPER VLTAVA RIVER (SUMAVA MOUNTAINS, CZECH REPUBLIC): SPECIES COMPOSITION OF ASSEMBLAGES VS. ENVIRONMENT IN STREAMS

Research Article| October 01, 2007 THECAMOEBIANS FROM THE UPPER VLTAVA RIVER (ŠUMAVA MOUNTAINS, CZECH REPUBLIC): SPECIES COMPOSITION OF ASSEMBLAGES VS. ENVIRONMENT IN STREAMS Katarína Holcová Katarína Holcová Department of Geology and Paleontology, Charles University in Prague, Albertov 6, CZ-128 43 Praha 2, Czech Republic, E-mail: Holcova@natur.cuni.cz Search for other works by this author on: GSW Google Scholar Author and Article Information Katarína Holcová Department of Geology and Paleontology, Charles University in Prague, Albertov 6, CZ-128 43 Praha 2, Czech Republic, E-mail: Holcova@natur.cuni.cz Publisher: Cushman Foundation for Foraminiferal Research Received: 23 Sep 2005 Accepted: 11 Jun 2007 First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 © 2007 Journal of Foraminiferal Research Journal of Foraminiferal Research (2007) 37 (4): 287–299. https://doi.org/10.2113/gsjfr.37.4.287 Article history Received: 23 Sep 2005 Accepted: 11 Jun 2007 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Katarína Holcová; THECAMOEBIANS FROM THE UPPER VLTAVA RIVER (ŠUMAVA MOUNTAINS, CZECH REPUBLIC): SPECIES COMPOSITION OF ASSEMBLAGES VS. ENVIRONMENT IN STREAMS. Journal of Foraminiferal Research 2007;; 37 (4): 287–299. doi: https://doi.org/10.2113/gsjfr.37.4.287 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract Between 1999 and 2002, thecamoebian assemblages were analyzed in one hundred samples collected from tributaries of the Upper Vltava River (Šumava Mts., Czech Republic, Middle Europe). The Šumava Mountains comprise the largest forest complex in Central Europe that is still preserved in a near natural condition. Diverse fresh-water environments (springs, wetlands, peat bogs, creeks, rivers and ponds) characterize the area.Thecamoebian tests were picked from dried 36–500 μm residues. In total, eighteen thecamoebian species were identified. The number of species per sample varies from one to thirteen, and the assemblages are characterized by dominance of Centropyxis orbicularis, C. aculeata, Pontigulasia compressa, Difflugia oblonga and Centropyxis arcula. A negative correlation (r = − 0.67) is notable between abundances of centropyxids and P. compressa. The negative correlation is caused by the different environmental conditions preferred by each taxon. Assemblages dominated by centropyxids originate mainly from standing water, whereas assemblages with common to abundant occurrences of P. compressa prefer running-water environments and substratum without coarse organic debris.Following a flood event in August 2002, thecamoebian assemblages were more diverse and abundant. While reworking of thecamoebian tests from different biotopes during flooding probably caused the increase in diversity, a boom in the population of Centropyxis orbicularis after the flood event confirmed the opportunistic character of this species.Boundary abundances of diagnostic species defined for flowing and standing waters in the forest area (= more than 20% of Pontigulasia compressa for flowing water and more than 50% of centropyxids for standing water) can be applied in interpretation of ancient environments. Similarly, changes in thecamoebian assemblages before and after the flood event can be used in paleoecology. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Paleolimnological Evidence of Terrestrial and Lacustrine Environmental Change in Response to European Settlement of the Red River Valley, Manitoba and North Dakota*

Limnological and terrestrial changes in three floodplain lakes are correlated with settlement of the Red River valley in Manitoba and North Dakota. Distinctive pollen, diatom and thecamoebian assemblages provide proxy evidence of the ecological changes from pre- to post-settlement periods in Horseshoe Lake, Lake Louise and Salt Lake. In the pre-settlement period (Zone I), prior to ~1812, grass and Quercus pollen dominate and are indicative of a tall grass prairie-oak riparian forest ecosystem. Diatom and thecamoebian assemblages suggest oligo- to mesotrophic limnological conditions, and more brackish water than presently occurs in Horseshoe Lake. The onset of the post-settlement period (Zone II) corresponds to distinctive terrestrial and limnological changes. A sharp decline in Quercus at the base of this zone correlates with documented regional riparian deforestation, whereas the increase in the weed taxa Salsola, Brassica, Rumex and Ambrosia is associated with the introduction of European agricultural practices and cereal grasses. Diatom and thecamoebian assemblages indicate progressive floodplain lake eutrophication, as well as increased salinity in Salt Lake. Salt Lake is the most brackish lake and supports the brackish-water foraminifera Trochammina macrescens cf. polystoma. Increased erosion and run off in the watershed has caused a more than twofold increase in lake basin sedimentation between the pre-settlement and post-settlement periods.

Characterization of Guaraguaçú River (Paraná, Brazil) based on the distribution of foraminiferal and thecamoebian assemblages and sedimentological analysis

Abstract

Evidence for possible precursor events of megathrust earthquakes on the west coast of North America

Megathrust earthquakes in western North America may be preceded by a precursor phase several years prior to megathrust, induced earthquakes. For example, on 27 March 1964, a 9.2 magnitude (on the Richter scale) earthquake occurred on the coast of Alaska. Changes in foraminifera and diatom assemblages at Girdwood Flats, Alaska, provide evidence of a precursor to this earthquake, thereby detailing a previously unknown sequence of events. We describe further evidence of precursor phases from marshes in Turnagain Arm, Alaska, United States, and farther south in Netarts Bay, Oregon, United States; this is the first time that two widely spaced locations have been examined for earthquake-related precursor stages. The Alaska earthquake offers the possibility to compare a modern sequence (A.D. 1964) of events with the geologic record. The Netarts Bay marsh has experienced no modern earthquake that could be used for comparison, but the nature of megathrust zones implies that the modern and ancient events should be physically similar. New cores examined from Turnagain Arm include both the 1964 earthquake and an event identified and dated at 1800 yr B.P. Prior to the 1964 event, the foraminifera and thecamoebian assemblages changed from a forest phase to a mildly brackish stage; this sequence was dated as being 15 yr or less in length, using Pb210 and Cs137 dating techniques. The event at 1800 yr B.P. was also associated with a similar precursor stage, indicating a small subsidence prior to the megathrust earthquake–related subsidence event. In Netarts Bay a new core was taken at a previously cored site to make use of carbon-14 dates and the assurance that at least four events were known to have occurred over the past 3000 yr. The new core contains four transitions, each identified by a mineralic deposit, often sharply bounded below and gradationally overlain by marsh peat. Transition in this context refers to the section of core analyzed, ∼15 cm above and below each of the four sand layers. Foraminiferal assemblage analyses indicate that these units represented a high marsh prequake phase followed by a lower marsh precursor stage, the earthquake-related deposition (sand layer), and then a rebound back into postquake marsh deposits. Sand deposits with either no or few foraminifera are inferred as tsunami/earthquake–related deposition stages. These transitions in two widely separated geographic areas (Alaska and Oregon) indicate that similar mechanisms operate for large megathrust earthquakes at subduction zones from Alaska to northern California in the Cascadia Subduction Zone, thus implying that precursor events also occur and can be detected by foraminiferal zonation all along this area. In a recent article ([Dragert et al., 2001][1]), scientists from the west coast suggested that “slow” or “silent” earthquakes they measured with continuous geographical positioning systems might be indicators of megathrust earthquakes. The transitions we document may be the prehistoric representations of these “silent” quakes. Foraminiferal evidence may help by allowing, more accurate positioning of seismometers along the west coast of North America and thereby lead to more precise and timely earthquake prediction methods. [1]: #ref-14

Diatom and thecamoebian signatures of Red River (Manitoba and North Dakota) floods: Data collected from the 1997 and 1999 spring freshets

Overbank deposits that aggraded during the severe and moderate Red River, Manitoba and North Dakota floods of 1997 and 1999 were examined to characterize the typical diatom and thecamoebian flood assemblages. The deposits contain diatom assemblages dominated by Nitzschia spp., Stephanodiscus spp. and Navicula spp. as well as large quantities of Hantzschia amphioxys, Luticolaimbricata and L. mutica and lesser amounts of Aulacoseira italica, A. granulata, A. ambigua, Cyclotella meneghiniana, Amphora montana and Synedra ulna. Samples collected from the Red River in late summer are dominated by the plankton Cyclotella atomus, species of Stephanodiscus, Cyclostephanos sp. 1 (cf. delicatus), Cyclotella meneghiniana, Nitzschia reversa and Nitzschia acicularis. Late summer, floodplain lake plankton are dominated by Fragilaria capucina, Cocconeis placentula, Stephanodiscus parvus/minutulus and Cyclotella atomus. Red River thecamoebian flood assemblages are dominated by Cyclopyxis spp., with lesser amounts of Centropyxis aculeata and Arcella vulgaris. Late summer water samples from the Red River contain very few thecamoebian remains. The majority of the taxa present are Centropyxis aculeata, Arcella vulgaris and Cyclopyxis spp. Floodplain lakes are dominated by benthic thecamoebians, especially Difflugia oblonga and Cucurbitella tricuspis, a eutrophic indicator. The results of this baseline study suggest that diatom and thecamoebian assemblages can characterize flood deposits, within floodplain lake basins, during both very high and moderately high flood years, and that these assemblages are inherently different from those typically found in lakes along the Red River.

HYDRODYNAMIC CIRCULATION IN THE ESTUARIES OF ESTACAO ECOLOGICA JUREIA-ITATINS, BRAZIL, INFERRED FROM FORAMINIFERA AND THECAMOEBIAN ASSEMBLAGES

Research Article| January 01, 2003 HYDRODYNAMIC CIRCULATION IN THE ESTUARIES OF ESTAÇÃO ECOLÓGICA JURÉIA-ITATINS, BRAZIL, INFERRED FROM FORAMINIFERA AND THECAMOEBIAN ASSEMBLAGES Wânia Duleba; Wânia Duleba 1Departamento de Geologia Sedimentar e Ambiental, Instituto de Geociências, Universidade de São Paulo, 05508-080 São Paulo, SP, Brazil. E-mail: waduleba@uol.com.br Search for other works by this author on: GSW Google Scholar Jean-Pierre Debenay Jean-Pierre Debenay 2Université d’Angers, Laboratoire de Géologie and LEBIM (Laboratoire d’Etude des Bio-Indicateurs Marins), île d’Yeu, France. E-mail: debenay@univangers.fr Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (2003) 33 (1): 62–93. https://doi.org/10.2113/0330062 Article history received: 18 Jun 2001 accepted: 16 Jan 2002 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Wânia Duleba, Jean-Pierre Debenay; HYDRODYNAMIC CIRCULATION IN THE ESTUARIES OF ESTAÇÃO ECOLÓGICA JURÉIA-ITATINS, BRAZIL, INFERRED FROM FORAMINIFERA AND THECAMOEBIAN ASSEMBLAGES. Journal of Foraminiferal Research 2003;; 33 (1): 62–93. doi: https://doi.org/10.2113/0330062 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract Depth measurements and chemical, sedimentological and microfaunal analyses were conducted in two microtidal estuaries, devoid of anthropogenic pollution, in the ecological reserve of Juréia-Itatins (E.E.J.I.). The spatial and temporal (summer and winter) variations in the composition of foraminifera and thecamoebian assemblages relative to hydrographic and sedimentological parameters were studied and compared with microfaunal data from other estuarine areas. Canonical correspondence analysis (CCA) was used to assess the relationship between microfaunal and abiotic variables. The distribution patterns of foraminifera and thecamoebians corresponded most strongly to bottom salinity and bottom temperature. The species distribution in the microtidal estuaries of E.E.J.I. was similar to that reported from macrotidal estuaries (Argentine and temperate regions) but differed from that observed in other tropical and subtropical microtidal estuaries of Brazilian and African coasts. Distribution patterns of foraminiferal and the-camoebian assemblages facilitated the development of hydrodynamic models of water circulation in the two estuaries. Such modeling would have been very difficult using only hydrological and chemical data because of the complex and highly variable water circulation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Holocene environmental history of thermokarst lakes on Richards Island, Northwest Territories, Canada: Theocamoebians as paleolimnological indicators

Richards Island, Northwest Territories, Canada, is characterized by thermokarst lakes which record Holocene limnological change. This study is the first report of thecamoebian assemblages and continuous annual lake water temperatures from these Arctic lakes. Ecological environments on Richards Island are influenced by a climatic gradient resulting from the contrasting influences of the cold Beaufort Sea to the north and the warm waters of the Mackenzie Delta to the east and west. This climatic gradient in turn influences modern thecamoebian assemblages, and is an indication of the complexity involved in interpreting past conditions from core material in this area. Population abundance and species diversity of thecamoebian assemblages on Richards Island are not significantly different from those reported from temperate and semi-tropical latitudes. However, certain assemblage characteristics, such as large and coarse agglutinated tests, dominance of assemblages by one or two species and low morphological variation are interpreted to be diagnostic of Arctic conditions. Thecamoebian assemblages in core material from the area indicate that the local paleolimnological conditions may have changed within the last 3 ka, and this is unrecorded in previously reported pollen data. Paleoenvironmental interpretations in a permafrost landscape have to take into account morphological instability of thermokarst lakes, which can be the cause of paleolimnological and consequently faunal change. In this area ecosystem development is clearly related to geomorphology and local climatic effects and is not exclusively controlled by regional climate change.

A variable lacustrine environment in Lake Winnipeg, Manitoba: Evidence from modern thecamoebian distribution

Thecamoebians (testate protozoan) were examined in 18 surface sediment samples from the North and South basins and the Narrows of Lake Winnipeg, Manitoba. Significantly higher numbers of thecamoebians and tintinnids in the North Basin compared to the Narrows and South Basin are attributed to the effects of urban development around the South Basin of Lake Winnipeg. Human population growth in this area has led to increased nutrient concentration in runoff, causing eutrophication of the southern lake, which in turn allows for increased algal productivity. Cucurbitella tricuspis is found in large abundances in the South Basin, particularly close to the inlet of the Red and Assiniboine rivers. High abundances of this species have been attributed to eutrophic conditions, which this species appears to withstand more successfully than other species. Increases in domestic waste output, that have led to elevated heavy metal concentrations in lake bottom sediments of the South Basin, may have resulted in lower abundances of thecamoebians, further reducing competition. Strong currents in the Narrows cause a slightly coarser substrate and sweep away food sources such as phytoplankton. This results in a lower faunal abundance and slightly lower species richness of thecamoebians. Robust species such as the coarse-grained Difflugia viscidula and species which feed on bacteria such as Centropyxis aculeata show increased abundances. Modern thecamoebian assemblages are comparable to Late Holocene faunal associations in terms of species composition. Individual species abundances, however, have changed. For example, in the North Basin the Late Holocene dominance of Difflugia manicata is replaced by various strains of Difflugia oblonga during recent times. A common species of the South Basin from Late Holocene to recent times is Difflugia globulus. It would appear that faunal differences between basins are the result of differences in algal food sources.

Microfossil analysis of sediments representing the 1964 earthquake, exposed at Girdwood Flats, Alaska, USA

Abstract Diatom, pollen, foraminifera and thecamoebian assemblages from an outcrop of peat and silt at Girdwood Flats, in the upper Turnagain Arm of the Cook Inlet, Alaska, record four phases of relative land and sea-level changes. The first phase is the development of freshwater swamp above high marsh sediments during relative land uplift, caused by strain accumulation along the locked portion of the Alaska-Aleutian subduction zone. In second phase, the top 2 cm of the peat, all microfossil groups record pre-seismic relative sea-level rise (relative land subsidence). The third phase is rapid land subsidence, 1.7 m, during the earthquake of March 1964 that initiated intertidal silt accumulation above the peat. The final phase is the colonisation of mudflat by salt marsh communities during post-seismic land uplift. The microfossil data compare favourably with sequences from Washington, Oregon and British Columbia that record late Holocene submergence events caused by earthquakes. The comparable changes in microfossil assemblages record the different phases of relative land and sea-level changes and the magnitude of land subsidence caused by each earthquake (expressed relative to the tidal range at the site). These results raise the question whether preseismic sea-level rise represents any kind of warning of large earthquakes.

Thecamoebians in Lake Winnipeg: a tool for Holocene paleolimnology

Holocene sediments in Lake Winnipeg are expressed in the lower Lake Agassiz sequence which is unconformably overlain by the Lake Winnipeg sequence. Nine sites, covering the North and South basins and the connecting Narrows, were selected for analysis of Holocene changes in thecamoebian faunae. Only the Lake Winnipeg sequence contains thecamoebians. This study indicates that biologic productivity and consequently the type of organic material in the sediments is the main control on thecamoebian taxa in Lake Winnipeg. Other factors controlling the distribution of thecamoebians are water chemistry and turbidity. Inorganic sediment geochemistry and water temperature do not appear to significantly influence the thecamoebian fauna of Lake Winnipeg. Variations in the abundance of key thecamoebian species along a north-south transect divide Lake Winnipeg into three distinct areas. The North Basin has remained relatively unchanged since the retreat of Lake Agassiz as indicated by the domination of Difflugia manicata throughout its history. This species appears to prefer Cyanophyta and diatoms as its food source. In the Narrows harsh conditions created by turbid waters and lack of algal food taxa result in Centropyxis aculeata replacing Difflugia manicata as the dominant species. In the South Basin three thecamoebian assemblages are recognized. Cucurbitella tricuspis, indicative of eutrophic conditions, dominates the most recent sediments of the South Basin. The underlying sediments are characterized by Difflugia globulus. In Lake Winnipeg this species is not a cold climate (arctic) indicator as suggested elsewhere but instead seems to prefer sediments containing green and yellow-green algal material. A Centropyxis-Arcella Assemblage occurs only at the base of the southernmost core where it is indicative of an early phase of hyposaline conditions as developed in shallow pools during the southward transgression of Lake Winnipeg. This study illustrates the usefulness of thecamoebians as paleolimnological indicators. Environmental changes are more significant in the restricted South Basin resulting in distinct thecamoebian assemblages. In contrast, the North Basin provided a stable environment throughout the late Holocene reflected in only subtle faunal changes.

Agglutinated foraminifera and thecamoebians from the Late Carboniferous Sydney coalfield, Nova Scotia: paleoecology, paleoenvironments and paleogeographical implications

Agglutinated foraminifera and arcellaceans (“thecamoebians”) were examined from Carboniferous (late Westphalian-Stephanian) cyclothems in the Sydney Basin of Nova Scotia. Four distinctive assemblages are documented from the coal-bearing strata, and indicate deposition took place on an extensive coastal platform. The eastern part of the basin is dominated by Ammobaculites-Ammotium assemblages that indicate estuarine-low marsh paleoenvironments. Relationships between test size, grain size within the test, and grain size of the substrate are used to differentiate between upper mudflat and lower mudflat sub-facies within estuarine facies. Mixed assemblages dominated by Trochammina, Ammotium and Ammobaculites indicate vegetated substrates, analogous to modern lower marsh environments, and flanked the estuarine system in the eastern and western areas of the basin. Rich Trochammina and thecamoebian assemblages are restricted to the western area of the basin, indicating deposition within the upper part of the tidal range. Trochammina assemblages, typically found underlying coal seams, may indicate vegetated substrates equivalent to modern high marsh facies. Thecamoebian assemblages, dominated by an agglutinated difflugid type, indicate freshwater paleoenvironments. Encystment of the thecamoebian populations suggests paleoenvironments were short lived.