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Lake Development and Limnological Response to Prehistoric and Historic Land-Use in Diss, Norfolk, U.K.
Journal of Ecology
Abstract
The lake was mildly nutrient-rich (mesotrophic) early in its history. The lower part of the core shows large variations in diatom concentrations and distinct lithological changes, including broad bands of silt and short sections of laminated sediments, which suggest fluctuating lake levels in the early Holocene. Increased concentrations of the blue-green algal pigment oxcillaxanthin indicate the expansion of Oscillatoria about 6000 years BP, probably in response to increased stabilization of the water column. The subsequent preservation of >3 m of laminated sediments in the mid-Holocene and extremely high pigment concentrations indicate a long period of moderate water levels and seasonal hypolimnetic oxygen depletion. Increased pigment concentrations and percentages of diatom taxa characteristic of moderately enriched lakes correlate with pollen evidence of widespread deforestation. Rapid and sustained eutrophication of the mere probably resulted from increased nutrient inputs caused by forest clearance. The mere remained eutrophic throughout the remainder of its history. Subsequent shifts in the diatom community indicate limnological responses to agricultural practices associated with Cannabis cultivation and later to the growth of a town around the mere. -from Author
... P. ocellata's dominance is linked to its opportunistic tendencies, small size and slow sinking rates, allowing it to thrive in wide-ranging conditions (Rioual et al. 2007;Malik and Saros 2016) (Supplementary Table S2). It's occurrence alongside N. gracilis, indicates high light intensity, which these species favour (Fritz 1989;Malik and Saros 2016), and consequently, that the period of mixing is limited (as this would reduce water clarity and light availability through sediment resuspension), but sufficient to allow low quantities of L. comta to be sustained in the plankton. A brief occurrence of S. parvus at ~ 2926 ± 28 cal. ...
... A second shift from P. ocellata to S. parvus between ~ 2767 and 2755 ± 28 cal. BP also indicates increased turbulence (triggering declining light availability due to reduced water clarity, needed for photosynthesis Kilham et al. 1986;Kilham 1990;Bradbury et al. 2002;Rioual et al. 2007)) and littoral input, potentially from wind-induced wave activity at the shoreline, which may have driven the increased quantity of N. gracilis at this point (Fritz 1989). Deeper and prolonged annual mixing episode(s) could also explain the changes in the varve preservation during this period, where varves are interpolated, as varve preservation requires anoxic/suboxic bottom water (Zolitschka et al. 2015). ...
... Alongside this, N. gracilis almost disappears from the record at ~ 2754 ± 28 cal. BP, indicating that light intensity is reduced (Fritz 1989), supporting the interpretation of increased turbulence (Supplementary Table S2). From 2621 ± 29 cal. ...
Understanding atmospheric response to radiative forcing, including the intensity and distribution of wind patterns is critical as this might have important implications in the coming decades. Long-term episodes of reduced solar activity (i.e. Grand Solar Minima, GSM) have triggered rapid climate change in the past, recorded in proxy-based records, including varved sediments from Meerfelder Maar, Germany, where the Homeric GSM (~2800 years ago) was studied. This study reconstructs windy conditions during the same GSM from Diss Mere, another varved record in England, to support the solar-wind linkage in the North Atlantic-European region. We use diatoms as proxies for windiness and support the palaeolimnological and palaeoclimate interpretation with a multi-proxy chironomids and pollen) evidence. The diatom assemblage documents a shift from Pantocsekiella ocellata dominance to Stephanodiscus parvus and Lindavia comta, indicating a shift to more turbulent waters from ~2767 ± 28, linked to increased windiness. This shift is synchronous with changes in 14C production, linked to solar activity changes during the GSM. Both proxy records reflect a rapid and synchronous atmospheric response (i.e. stronger winds) at the onset and during the GSM in the North Atlantic and continental Europe. In order to test whether this solar-wind linkage is consistent during other GSMs and to understand the underlying climate dynamics, we analyse the wind response to solar forcing at the two study sites during the Little Ice Age, a period that includes several GSMs. For this, we have used a reconstruction based on a 1200-year-long simulation with an isotope-enabled climate model. Our study suggests that wind anomalies in the North Atlantic-European sector may relate to an anomalous atmospheric circulation in response to long-term solar forcing leading to north-easterlies modulated by the East Atlantic pattern.
... This multi-proxy study gives detailed insight into effects of catchment changes (pedogenesis, vegetation succession, and anthropogenic land-use) on sedimentary P forms and aquatic primary producers throughout the Holocene, and is a good example of the strong connectivity between a small lake and its catchment area (e.g., Fritz 1989, H akansson and Regn ell 1993, Luoto et al. 2012. Besides climate-driven changes in the catchment vegetation, three stages with different intensities of human activities can be distinguished: (1) low disturbance caused by domestic grazing during the Early/Mid Neolithic (~3600 to~2600 BC), (2) higher disturbance because of animal husbandry and some grain cultivation during the Late Bronze and Pre-Roman Iron Age (~800 BC to AD~100) with clear effects on the catchment vegetation and the lake and (3) strong disturbance caused by domestic grazing, intensified crop cultivation and, in particular, by retting of fiber plants (especially hemp) during the Middle Ages and Renaissance (AD~1000 tõ 1700), which resulted in almost complete catchment deforestation and substantial changes in Lake Fuglsø. ...
... Elevated nutrient concentrations (i.e., at least mesotrophic conditions) since the early Holocene have been observed in other temperate lakes too (Fritz 1989, Nisbeth et al. 2019). In the case of Lake Fuglsø, we infer that this was caused by the high catchment : lake area ratio, relatively steep topography and sandy soils, which together resulted in high influx of nutrients and organic material to the lake during periods of open landscape. ...
... Stephanodiscus parvus and Asterionella formosa increased, resulting in diatom assemblages similar to those before human impacts and indicating that Lake Fuglsø was undisturbed and had Si-poor, P-rich, and likely organic-/humic-rich water (Fritz 1989, Thackeray et al. 2008. Prolonged stratification, facilitated by reduced wind fetch due to the reforested catchment, probably supported the dominance of low Si-demanding planktonic diatom species by impairing Si recycling from the hypo-to the epilimnion during most of the growth season (Radbourne et al. 2019). ...
This paleolimnological study aims to investigate how natural processes and anthropogenic land‐use changes have affected sedimentary phosphorus (P) forms and primary producers in a small, temperate lake (Lake Fuglsø, Denmark) throughout the Holocene. Our multi‐proxy approach uses pollen, X‐ray fluorescence scanning, carbon (C) and nitrogen contents and stable isotopes, sequential P extraction, ³¹P nuclear magnetic resonance spectroscopy, pigments, diatoms, and plant macrofossils from a ¹⁴C‐dated sediment record. We found three periods of human impact: (1) low disturbance from domestic grazing during the early/mid Neolithic (~3600 to ~2600 BC), (2) higher disturbance because of animal husbandry and some grain cultivation during the Late Bronze and Pre‐Roman Iron Age (~800 BC to AD ~100), and (3) strong disturbance caused by domestic grazing, intensified crop cultivation and, in particular, by retting of fiber plants during the Middle Ages and Renaissance (AD ~1000 to ~1700). Cultural eutrophication during the latter phase caused unprecedented changes in the lake, including altered species composition, high production, and strongly accelerated sediment accumulation rates. Generally, catchment deforestation was related to elevated proportions of metal (iron, aluminum, calcium)‐bound P forms in the sediment, while high tree cover correlated with elevated proportions of P forms associated with organic material (“organic” P, humic‐bound P, refractory organic P) and loosely bound P. During phases with forest in the catchment, silicon (Si) inputs to the lake were insufficient and diatom frustules were mostly absent in the sediments. In contrast, diatoms thrived in the lake when the landscape was open and erosional Si influx was high. This study is the first to show long‐term (~eight millennia) and recurring Si limitation of diatoms, a finding that may explain the absence of diatoms in sediment records of other sites too. In summary, human land‐use with preceding deforestation accelerated the transport of nutrients and elements from the terrestrial to the aquatic environment, leading to substantial and irreversible changes in Lake Fuglsø. Our study is a good example of the tight links between catchment processes and lake status, indicating that catchment dynamics should be considered in lake restoration projects, particularly for lowland lakes with high catchment : lake area ratios.
... Samples were examined at 1000× magnification using a Leica DMBL, and where possible, a minimum of 300 diatom valves were counted per sample. Identifications were made following Krammer andLange-Bertalot (1986, 1991), Lange-Bertalot (2001), and Krammer (2002), Fritz (1989) and online resources (http:// crati cula. ncl. ...
... The calcite layer in the varves show coarse grains at the base and fine calcite grains at the top, representing the decreasing grain size observed from May to October in the sediment traps. The transition between the calcite layer and dark organic layer is diffuse as calcite grains still occur in the dark layer but intermixed with a wide range of diatoms species (including benthic species) and terrestrial OM remains (Fritz 1989). This suggests resuspension is one of the dominant deposition processes during this season (Roeser et al. 2021). ...
Diss Mere is a small natural lake located in the centre of the town Diss in Norfolk (England). The lake, which has been exposed to different stressors including climate variability and changing land use, has significant recreational, historical and environmental value. The Diss Mere sediments are annually-laminated for most of the Holocene (2.1–10.3 ka BP), which allows the study of the lake evolution and its response to changing environmental conditions at an exceptionally high resolution. As with many mid-latitude, alkaline lakes, Diss Mere’s sediments are formed of biogenic-calcite varves. We have conducted a 3.5-year lake-monitoring survey including sediment trapping to identify the main drivers and seasonal processes contributing to lake sedimentation. Our results demonstrate that the modern lake is still producing seasonally-differentiated sediments today, however, are unable to be preserved as varves due to the permanent oxygenation of the lake bottom through gradual lake shallowing. Seasonal sediment fluxes follow a general pattern of (i) an early spring-diatom bloom; (ii) spring precipitation of medium-coarse calcite grains; (iii) summer precipitation of smaller endogenic calcite grains; and (iv) an autumn algal bloom and endogenic calcite precipitation intermixed with benthic diatoms and micrite. Whilst calcite precipitates throughout the whole year, peaks are observed in the epilimnion during the summer. This study shows that a modern analogue approach can be applied to the varves revealing their potential for environmental and climate reconstruction and highlights the significance of monitoring surveys for modern analogue approaches to palaeolimnological research.
... Samples were examined at 1000× magnification using a Leica DMBL, and where possible, a minimum of 300 diatom valves were counted per sample. Identifications were made following Krammer andLange-Bertalot (1986, 1991), Lange-Bertalot (2001), and Krammer (2002), Fritz (1989) and online resources (http:// crati cula. ncl. ...
... The calcite layer in the varves show coarse grains at the base and fine calcite grains at the top, representing the decreasing grain size observed from May to October in the sediment traps. The transition between the calcite layer and dark organic layer is diffuse as calcite grains still occur in the dark layer but intermixed with a wide range of diatoms species (including benthic species) and terrestrial OM remains (Fritz 1989). This suggests resuspension is one of the dominant deposition processes during this season (Roeser et al. 2021). ...
The oscillatory behaviour of the climate system on decadal timescales before the instrumental record is hard to quantify. However, knowledge of this variability is important for putting current changes in context and for supporting reliable future predictions. Here we investigate the recurrent component of Holocene climate variability in the North Atlantic sector from 10,500 to 2,000 years ago by conducting a frequency analysis of both an annually laminated climate record from a lake in England and outputs from a long transient simulation of the Atlantic meridional overturning circulation. We find consistent decadal variability over the past 6,700 years and before 8,500 years before present, probably reflecting predominance of solar and ocean forcings. Between these dates, climate variability was dampened on decadal timescales. Our results suggest that meltwater discharge into the North Atlantic and the subsequent hydrographic changes, from the opening of the Hudson Bay until the final collapse of the Laurentide Ice Sheet, disrupted the decadal cyclic signals for more than a millennium. Given the current acceleration of the Greenland Ice Sheet melting in response to global warming, this study provides long-term evidence of potential challenges predicting future patterns of the climate system.
... A produção de sólidos em bacias hidrográficas depende de diversos fatores, seja de origem natural como o tipo de solo, geologia, geomorfologia, clima (WANG et al., 2004;TUNDISI et al., 2004;HESTIR et al., 2015), como pela ação antrópica, principalmente representado pelo uso e ocupação da terra (FRITZ, 1989;BRAMLEY et al., 2002;AHEARN et al., 2005;LIU et al., 2015). A intervenção antrópica nos ecossistemas terrestre e aquático tem gerado uma série de problemas ambientais. ...
O sensoriamento remoto é uma técnica cada vez mais utilizada para obter informações ambientais. Assim, avaliamos a resposta espectral da água submetida a diferentes concentrações de Totais de Sólidos em Suspenção (TSS). O experimento foi conduzido em um ambiente controlado com o uso de uma caixa de água, a qual foram adicionadas frações de Latossolo Vermelho. Os dados de TSS oscilaram de zero, água limpa, até 318 mg/l. Os dados de reflectância foram obtidos com o uso do espectrorradiômetro FieldSpec (400 a 900 nm). O aumento de TSS levou a dois efeitos distintos quanto a reflectância de acordo com a faixa espectral: i) diminuição da reflectância na faixa de 400 a 525 nm e ii) aumento na reflectância nos comprimentos de onda maiores do que 525 nm. Este quadro proporcionou correlações significativas e negativa para o intervalo de 400 a 510 nm e significativas e positivas entre 584 e 822 nm. Foram testadas diferentes funções matemáticas para a estimativa de TSS a partir da reflectância nos comprimentos de onda que apresentaram as melhores correlações. O melhor modelo foi o polinomial com R² de 0,82 em 741 nm. Portanto, o TSS, constituído de Latossolo Vermelho, altera a reflectância da água a níveis possíveis de serem detectados com recursos de sensoriamento remoto, principalmente na borda vermelha e infravermelho próximo.
... Whilst many studies have shown that early societies have modified catchments (e.g. removal of vegetation for agricultural purposes) and therefore water chemistries of lakes in Europe (Fritz, 1989), tropical America (Anselmetti et al., 2007) and North America (Ekdahl et al., 2004), the study of human impacts on lacustrine ecosystems and the onset of cultural eutrophication in eastern Africa, has been limited to the larger lakes, such as lake Victoria (Verschuren et al., 2002) and Malawi (Hecky, 2000). The only exception to this is a comparative study of data over a 30-year span (1971-2000) at Lake Saaka, near Fort Portal, which suggested that eutrophication had occurred over the time period in question. ...
This paper explores deeper dimensions of fluorosis and seeks to develop a clear communitydriven policy framework around fluorosis. It aims at redistributive policies that will lead to
resource benefits to the local residents. The work will provide the foundation necessary to
lobby for the implementation of policies that favor rainwater harvesting at household level.
Exploitation of water for energy production needs to be redefined and readdressed properly.
Naivasha geothermal exploration and fluorosis is used as the case study. Mount Longonot’s
previous volcanic events were a blessing and a curse to the geographical area in that, it is the
reason for geothermal potential and is also the generator of observed high fluoride aquifers
of the area. Geothermal energy production has always required water in the form of steam to
produce energy and therefore, legislation should be able to induce good quality and affordable
consumption water as well as wastewater treatment in Naivasha.
... Hence, a wealth of studies has investigated eutrophication, and how lake system structure and functioning have responded to intensive modern agricultural practices and urbanisation in recent centuries (e.g., Lotter, 1998;Langdon et al., 2006;Bennion and Simpson, 2011;Anderson et al., 2014). Far fewer, however, have focused on the impact of early land use on lakes over millennia (Fritz, 1989;Bradshaw et al., 2005). Studies of early human impacts can help to resolve debates about how, where and whether humans significantly changed their environment (Ruddiman, 2013;Lewis and Maslin, 2015;ArchaeoGLOBE Project, 2019). ...
Although humans have impacted their environment over millennia, details of these impacts, especially on aquatic systems, is still surprisingly scarce despite potential disturbance by early land use. This study examined a high-resolution radiocarbon-dated Holocene record from the Danish Lake Væng, using geochemical and biological proxies, and related the observed impacts to other lake records with catchment disturbance. The results indicate a lengthy and varying history of aquatic eutrophication linked to human activity. Modest impacts on the lake coincided with the first signs of landscape disturbance during the Neolithic (c. 4500 cal. yrs BP). Observed impacts intensified in the Late Bronze and Pre-Roman Iron Age. Viking Age/Medieval deforestation and erosional inputs to the lake associated with new ploughing technology (1200 cal. yrs BP), however, led to a major reorganisation of the aquatic ecosystem. Filamentous bloom-forming cyanobacteria, common today in heavily culturally impacted lakes, reached a historical maxima. The lake ecosystem subsequently recovered somewhat but remains eutrophic to date. The erosion record from Lake Væng shows a striking similarity with other Danish lake records, especially the notable increase in Medieval Period catchment inputs, which are observed in other European lacustrine records. Numerous European lowland lakes may have shifted into a degraded ecological state millennia ago, but degradation intensified during the onset of the Medieval Period. Hence, assuming pre-industrial conditions as relatively pristine reference baselines for more recent cultural eutrophication could be flawed in landscapes intensively used by humans for millennia.
... (and, to a lesser extent, Asterionella sp.) most likely reflects changes in lake circulation with a subsequent redistribution of nutrients across the water column (e.g. Baier et al., 2004;Fritz, 1989;Zahrer et al., 2013). The relatively low Mn/Fe values at Poggensee do not point towards more bottom-water oxygenation, yet this signal might be blurred by fluctuations in lake productivity. ...
Estimating the environmental and societal impact of recent volcanic eruptions is a task aided by direct measurements and historical sources. Beyond the reach of first-hand accounts, our understanding of pre-historic volcanism is often hindered by dating uncertainties inherent to geological archives. Here, we minimize dating errors by analyzing the annually laminated sequences of two Central European lakes, Poggensee and Woseriner See. We focus on environmental transformations that occurred in the decades preceding and following the deposition of the Icelandic Saksunarvatn tephra, dated between ca. 10,300 and 10,200 cal. BP. As a first result, we provide two new independent age determinations for the ash layer detected in both sequences. Our estimates (10,264 ± 24 cal. BP at Poggensee and 10,282 ± 45 cal. BP at Woseriner See) place the age of this tephra deposit closer to Greenland estimates than to continental ones, possibly reducing the chronological gap between the multiple fallout events that characterize the Saksunarvatn Ash. A high resolution palaeoenvironmental characterization was carried out via pollen, thin sections and geochemical analysis. Both sequences show traces of a contemporaneous disturbance event dated to ca. 18 years before tephra deposition. In addition, environmental impact compatible with a cooling event is discernible for ca. 15 years following tephra deposition. While independent climate mechanisms can be responsible for the observed trends, we explicitly focus on exploring volcanic eruptions as a possible leading driver. A consistent agreement across all proxies is lacking in the pre-tephra record, yet sulfur enrichment and acidification processes allow us to suggest volcanism as a plausible trigger. Combined with the post-tephra cooling, the two sedimentary records depict a possible scenario of multi-decadal, continuous volcanic impact.
Archaeological and palaeoecological evidence relating to human activity in the English Midlands is scant compared to elsewhere in Britain. Knowledge of human activity in pre-Roman and Roman times is often fragmentary and disparate in parts of the region where it could be assumed that the resident population was small with little Roman impact. To examine these contentions, a palaeoenvironmental investigation from Aqualate Mere near Newport, Staffordshire, has been undertaken on the sediment record extending back to c. 1300 cal. BC. An analysis of microfossils, microscopic charcoal, sediment chemistry and mineral magnetism from a core dated by ¹⁴C, SCPs, ²¹⁰Pb and ¹³⁷Cs has provided an opportunity to reconstruct land use changes and atmospheric pollution from the later prehistoric period onwards. The results challenge the idea this region was a backwater as there is near-continuous agricultural activity around the mere since the Late Bronze Age through to modern times. This is characterised by phases of woodland decline, an intensification of farming, soil erosion, evidence for possible eutrophication and regional lead pollution.
The project aims to popularize in Poland analyzes often applied in archaeological research - mainly environmental approaches and the study of artifacts, by publishing, organizing workshops, and lectures by invited scientists from various fields related to archaeology.
In the edited volume: Mikroprzeszłość. Badania specjalistyczne w archeologii; published at the end of 2021 (written in Polish), 21 chapters present various scientific analyzes used in archeology (environmental approaches and the study of artifacts), from sampling at archaeological sites to laboratory analyses based on examples from Polish prehistoric and historic sites.
Fossil diatom assemblages from the sediment/water interface in 105 Minnesota lakes were compared with measurements of alkalinity, sulphate, total phosphorus, transparency, and water depth at the sample site. Similar assemblages were placed together using cluster analysis and comparisons of environmental variables between diatom clusters were made using an analysis of variance. Total alkalinity and transparency showed the greatest difference among clusters. Samples from shallow eutrophic prairie lakes were dominated by Melosira granulata, Stephanodiscus niagarae and, occasionally, by Stephanodiscus hantzschii. Deep oligotrophic lakes had modest percentages of Cyclotella comta. Dilute acid lakes were dominated either by Melosira distans and M. italica or by Tabellaria fenestrata, Cyclotella stelligera, and in some cases C. glomerata. Assemblages with Cyclotella glomerata and Synedra nana were found in naturally meromictic lakes. Stephanodiscus hantzschii showed a preference for extremely eutrophic lakes. The relationships between recently deposited diatom assemblages and the lake environmental conditions studied here can be used to evaluate the extent of past environmental change in lakes.
Investigations have been made of Late-Weichselian and Flandrian deposits in Blelham Tarn, Lancashire and other parts of its basin. Pollen and diatom analyses have been made of several cores and samples taken from the inflows. Pollen analysis has been used as a basis for chronology. The vegetational history of the region and past diatom flora of the tarn and ‘kettle-hole’ are discussed. During the Late-Weichselian, in pollen zones I and III, the vegetation was dominated by herbs of open habitats, whilst in pollen zone II birch woodland developed. The diatom flora consisted mainly of non-planktonic forms with Fragilaria spp. dominant. In the Early-Flandrian (pollen zones IV–VI) birch woodland developed and was succeeded by a mixed oak forest. Differences are shown in the pollen spectra from the ‘kettle-hole’, marginal and open water regions of the tarn. The planktonic/non-planktonic (P/NP) diatom ratio slowly increased in the tarn. However, dominance was retained by the non-planktonic forms. This increase in P/NP ratio did not occur in the ‘kettle-hole’ region. A new diatom variety Melosira distans var. blelhamensis appeared in the flora. At the opening of pollen zone VIIa Alnus rapidly increased, and for the first time planktonic diatoms became dominant in the open waters of the tarn. In littoral regions non-planktonic forms, in particular Achnanthes minutissima var. cryptocephala, remained dominant. Sphagnum-sedge peat accumulated in the ‘kettle-hole’. Diatoms are scarce in this peat. During the Late-Flandrian (pollen zone VIIb to the present day) the local vegetation was an older mixed oak forest. However, more open vegetational conditions gradually developed as shown by the increase in herbaceous pollen. Dominance was held in the open waters by the planktonic diatoms. The littoral regions favoured the growth of Achnanthes minutissima var. cryptocephala. Sphagnum-sedge peat continued to accumulate in the ‘kettle-hole’. Other limnological aspects considered include the tarn's trophic condition, productivity, alkalinity, the transparency of its waters and tarn level changes. In the past the tarn covered a much wider area. Field evidence shows that man has interfered with the drainage system.
S ummary
The diatom flora of a core taken from the region of the central buoy in Esthwaite has been analysed quantitatively and qualitatively. The diatom flora of the sediments laid down from the early zones of the Late‐glacial to the present day can be subdivided into five periods characterized by indicator species and variations in diatom productivity. The zones in Esthwaite have been compared with those from Windermere and Kentmere and shown to agree in general features, indicating a similar historical development for all three lake basins. The diatom periods show good correlation with the zoning derived from pollen analysis; and the change at the Boreal‐Atlantic Transition from base‐rich to base‐poor status, which was first detected in Kentmere, has been substantiated in Esthwaite. Comparison with the present‐day diatom flora suggests that a transition to eutrophic conditions, detected in late Post‐glacial time, is still occurring.
Core samples taken from Late Devensian and Flandrian deposits at Melynllyn have been investigated. One profile was sampled at fairly close intervals for diatom and pollen analyses, and a series of radiocarbon dates was obtained. An absolute diatom counting method was used, which enabled the results to be expressed both in terms of annual diatom deposition and as percentages of the diatom sum. The diatom succession indicates that a change from alkaline to circumneutral conditions took place early in the Flandrian period. Diatoms characteristic of acidic, oligotrophic waters have been well established in the tarn from mid Flandrian times to the present day. Pollen analysis serves chiefly as a means of correlating the deposits with those from other sites in the Snowdonia region, although some features of the pollen diagrams are discussed. The data indicate that erosion was accelerated in the drainage basin of the tarn following the decline in Ulmus pollen percentages.
Two profiles of the diatom assemblages in lake sediments of Late Devensian age have been analysed in detail to substantiate a zonation based upon the diatom assemblages from the nearby Loch Sionascaig site, in northern Scotland. The profiles bear out the original divisions into three diatom assemblage zones and indicate some subdivisions; there is close correlation with stratigraphic, pollen and chemical changes. The Cam Loch assemblages did not include the planktonic phase found in the Sionascaig Diatom Zone 2 sediments of Allerød age, despite the proximity of the two sites and a geological location that would suggest a possibly richer environment.
It is concluded that the best pioneer forms are those of cosmopolitan distribution and that in the benthos at least there was an alkaline environment with sufficient nutrient status for diatoms typical of present day eutrophic lakes to occur during the period of greatest diatom diversity. The open water planktonic environment probably remained nutrient‐poor with little diatomaceous plankton, a condition resembling some present‐day alpine lakes.
The final cold phase of the late‐glacial is characterized by the temporary disappearance of many taxa and the presence of several indicator taxa. Solifluction of the surrounding land surface is indicated by the presence of some subaerial forms. This is also a feature of an earlier slight climatic recession indicated by correlation of pollen and diatom analyses and now correlated with the Bølling/Allerød stade.
Three cores were taken from the deposits of Llyn Clyd and two cores from Llyn Glas, using a Mackereth corer. Samples taken at approximately 10 cm intervals have been analysed for pollen and diatoms. Pollen analysis has been used as a means for correlating deposits in the two tarns. The data show that changes have occurred in the diatom flora of both tarns but these changes are less pronounced than in some lowland bodies of water. Llyn Glas appears to have had more stable conditions throughout its development than Llyn Clyd.
The recent history of Little Round Lake, a small meromictic lake in southeastern Ontario, is considered. Pollen analyses were used to identify past changes in terrestrial vegetation, whilst limnological conditions were interpreted on the basis of diatom and chrysophyte microfossils. Contemporaneous with the arrival of European settlers (ca. A. D. 1850), the predisturbance assemblage of oligotrophic Cyclotella diatoms was replaced by Synedra spp., which then succeeded to a eutrophic flora dominated by Stephanodiscus hantzschii. Meanwhile, synuracean algae were almost completely excluded. Over the last 30 years, the algal microfossils indicate that the lake underwent a marked return to oligotrophy. Evidence is presented which suggests that this shift was related to the cultural enhancement of meromixis by the seepage of road salt.
Four thousand eight hundred years ago hemlock (Tsuga canadensis) populations were decimated throughout eastern North America. We have studied the effects of this loss from the terrestrial community on three Southern Ontario lakes: Little Round Lake, Sunfish Lake, and McKay Lake. This study includes the use of cladocerans, diatoms, chrysophytes, and bacterial pigments to assess the limnologic changes that occurred in these lakes. Each lake experienced a change in trophic status that coincided with the loss of hemlock from its catchment, but the change in the aquatic biota was different in each lake. The lakes' size may have been the most influential factor governing the response to this terrestrial disturbance.
Scales and bristles ofMallomonas crassisquama (Asmund) Fott andM. elongata Reverdin are reported from the laminated sediments of Laukunlampi, a small kettlehole lake in N. Karelia, Finland. The white
summer laminae in the deeper sediment are composed almost entirely ofM. crassisquama scales and bristles. The taxonomy, ecology and distribution ofM. crassisquama andM. elongata are briefly discussed and factors influencing the preservation of scales and bristles in sediments are considered. It is
suggested that analysis of sedimentary associations of scales, bristles and cysts could be used to improve cyst taxonomy inMallomonas.
KeywordsMallomonas scales and bristles–laminated sediments