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1.
Water chemistry and surface sediments were analyzed from 41 shallow lakes representing three previously-defined hydrological
categories in the Slave River Delta, Northwest Territories, Canada, in order to identify relationships between hydrological
and limnological conditions and their associations with recently deposited diatom assemblages. Evaporation-dominated lakes are physically removed from the influence of the Slave River, and are characterized by high alkalinity and high concentrations
of nutrients and ions. In contrast, flood-dominated lakes tend to receive a pulse of floodwater from the Slave River during the spring thaw and have low alkalinity and low concentrations
of most nutrients and ions. Exchange-dominated lakes are variably influenced by floodwaters from the Slave River and seiche events from Great Slave Lake throughout the
spring thaw and open-water season, and are characterized by a broad array of limnological conditions that are largely dependent
on the strength of the connection to these sources of floodwater. Specific diatom ‘indicator’ taxa have been identified that
can discriminate these three hydrological lake categories. Evaporation-dominated lakes are associated with high relative abundance
of common epiphytic diatom taxa, while diatoms indicative of flood- and exchange-dominated lakes span a wide range of habitat
types (epiphytic, benthic) but also include unique planktonic diatoms (Stephanodiscus and Cyclostephanos taxa) that were not found in surface sediments of evaporation-dominated lakes. The planktonic diatom taxa originate from
the Slave River, and thus are indicative of river influence. In complex, remote, freshwater ecosystems like the Slave River
Delta, integration of results from hydrological and limnological approaches provides a necessary foundation to assess present,
past and future hydroecological responses to changes in river discharge and climate. 相似文献
2.
3.
We present a paleolimnological record spanning the Holocene from a small lake on Russell Island (Lake PW02), in the central
Canadian Arctic Archipelago (74.07° N, 97.77° W, 182 m asl). Fragilarioid diatom types in the genera Pseudostaurosira, Staurosira and Staurosirella constitute >90% of valves in fossil samples. Using modern biogeographic data which specify the temperature optima of the
Fragilarioid diatom taxa, we present new inferences about the timing of paleoclimatic changes in the central Arctic islands.
The early Holocene was characterized by maximum values for sediment organic matter, and lower ratios of Staurosirella pinnata to Staurosira construens v. venter, suggesting warm summer air temperatures between about 9500−6500 cal year BP. Influxes of biogenic silica and diatom valves
decreased following 4000 cal year BP, the sediment accumulation rate slowed and diatom taxa of the littoral zone diversified,
suggesting cooler summers and more persistent lake ice. Variations in the species composition of the assemblages indicate
paleoclimatic changes that are in broad agreement with other paleoenvironmental records from the Arctic including melt records
from the Agassiz Ice Cap. Although autecological data remain incomplete for Fragilarioid taxa, our results indicate differences
in these taxa in responses to paleoenvironmental change and underline the potential for the increased use of these taxa in
paleoenvironmental reconstructions. The record from Lake PW02, as in other records from Arctic lakes with low algal diversity
throughout the Holocene, shows a pronounced increase in diatom diversity since the 1920s, and diatom production since the
1970s far exceeds any recorded during the Holocene. 相似文献
4.
Surficial sediments of three northern Egyptian lakes (Manzala, Burullus and Edku) show differences in diatom assemblages deposited in different sites of these lakes. A total of 172 species and varieties belonging to 58 genera were identified and counted from 62 samples. Of these, 163 diatom taxa were recorded from Manzala Lake sediments, 147 taxa were found in Burullus Lake sediments, and 117 taxa were identified in Edku Lake sediments. The considerable variation in the composition and distribution of the diatom assemblages among these lakes was mainly related to differences in the water quality, salinity, the concentration of nutrients and climatic changes. The planktonic diatom Cyclotella meneghiniana was dominant in the majority of the samples from Manzala Lake, but dominant in only a few samples from the middle parts of Burullus and Edku lakes. The non-planktonic epiphytic taxa Cocconeis placentula and Epithemia sorex were the subdominant species in the surface sediments, especially in shallow and marginal parts of the lakes. Multivariate statistical techniques (hierarchical ascending clustering and canonical correspondence analysis) were used to identify ecological groups of diatoms and to investigate which environmental variables were important in explaining the variation between these groups. Eight ecological groups containing distinctive diatom assemblages reflect current environmental conditions; especially saltwater intrusion in the north and nutrient-rich freshwater in the south. 相似文献
5.
Karlyn S. Westover Sherilyn C. Fritz Tatyana A. Blyakharchuk Herbert E. Wright 《Journal of Paleolimnology》2006,35(3):519-541
The sedimentary diatom records of three shallow lakes in the Altai Mountains, southern Siberia, were examined to assess the
nature and timing of Holocene environmental changes. Few paleoenvironmental records, especially reconstructions not based
on pollen, have been reported from this region. The lakes differ in elevation, annual precipitation, and catchment vegetation.
Diatom assemblages in all lakes were dominated for the entire period of record by small benthic species of Pseudostaurosira Williams & Round, Staurosira Ehrenberg, and Staurosirella Williams & Round. Planktonic taxa only occur in very low abundances (<5%). The most diverse diatom flora was found in Dzhangyskol,
which is situated at the lowest elevation within a forested catchment. A lack of detailed information on the ecological preferences
of the dominant taxa and the complexity of environmental drivers make direct interpretation of the diatom record difficult.
However, other proxies suggest that dramatic shifts in dominance between Staurosira elliptica and Staurosirella pinnata in Grusha Ozero reflect millennial-scale variability in climate. Together, chironomids and diatoms provide evidence of a
cooling possibly correlative to the Younger Dryas Stade and subsequent early-Holocene warming consistent with pollen evidence
of afforestation, which also is likely linked to increased humidity. By ~6000 cal year BP, the transition to a cooler, more
continental climate had begun. The diatom record of Akkol shows significantly less variation in diatom community composition,
but biogenic silica accumulation rates, a proxy for diatom productivity, appear to reflect climatic variability driven by
insolation trends over the past 8000 years. Long-term variability in Dzhangyskol is not clearly linked to climate. 相似文献
6.
Cladocera as indicators of trophic state in Irish lakes 总被引：1，自引：0，他引：1
We examined the impact of lake trophic state on the taxonomic and functional structure of cladoceran communities and the role
of nutrient loading in structuring both cladoceran and diatom communities. Surface sediment assemblages from 33 Irish lakes
were analysed along a gradient of total phosphorus concentration (TP; 4.0–142.3 μg l−1), using a variety of statistical approaches including ordination, calibration and variance partitioning. Ordination showed
that the taxonomic structure of the cladoceran community displayed the strongest response to changes in lake trophic state,
among 17 measured environmental variables. Trophic state variables chlorophyll-a and TP explained about 20% of the variance in both cladoceran and diatom assemblages from a set of 31 lakes. Procrustes analysis
also showed significant concordance in the structure of cladoceran and diatom communities (P < 0.001). Thus, lake trophic state affects the taxonomic structure of both primary and secondary producers in our study lakes.
We also found a significant decrease in relative abundance of taxa associated with both macrophytes and sediments, or sediments
only, along the TP gradient (r = −0.49, P = 0.006, n = 30), as well as an increase in the proportion of the planktonic group (r = 0.43, P = 0.017, n = 30). This suggests that cladoceran community structure may also be shaped by lake trophic state indirectly, by affecting
habitat properties. We found no relationship between lake trophic state and the relative abundance of each of three cladoceran
groups that display different body size. We compared community structure between bottom and top sediment samples in cores
from six Irish lakes. Results revealed similar trajectories of nutrient enrichment over time, as well as a strong shift in
cladoceran functional structure in most systems. This study confirms that Cladocera remains in lake sediments are reliable
indicators of lake trophic state. This study also highlights the fact that taxonomic and functional structure should both
be considered to account for the multiple factors that shape cladoceran communities. 相似文献
7.
Banks Island (N.W.T.) has become a focal point for climate change studies in the Canadian Arctic. However, long-term climatic
and environmental data are very sparse from this large island, as they are for the entire southwestern region of the Canadian
Arctic Archipelago. In this paleolimnological study, diatom species assemblage shifts documented in cores collected from a
pond and a lake on Banks Island were interpreted to represent a response to climate warming commencing in the nineteenth century.
We found that, although the timing and overall nature of the species changes in the two cores were consistent, the signal
was muted in the deeper site likely as a result of differences in ice cover extent and duration between lakes and ponds. A
high-resolution study was also conducted from a second pond, at sub-decadal resolution, that only spanned the last ∼60 years.
In the deeper lake site, Fragilaria construens and F. pinnata dominated the assemblages, similar to those noted in other high Arctic regions where lakes are characterized by extended
ice cover. In contrast, Denticula kuetzingii dominated the shallower ponds and, in the case of the pond core representing the longer time period, this taxon increased
in the post-1850 sediments, likely coincident with climate warming. In all cores, diatom assemblages became more diverse and
Achnanthes species (particularly A. minutissima) increased from ∼1850 to the present, similar to changes documented in other Arctic regions. Beta diversity values calculated
for the diatom species changes indicated that assemblage shifts in the Banks Island cores were of similar magnitude to those
recorded in other Arctic regions with high species turnover, such as Ellesmere Island. A diatom-based Total Nitrogen (TN)
transfer function previously developed for Banks Island was applied to the three 210Pb dated cores as an exploratory tool for inferring past changes in nitrogen concentrations. In both the lake and pond cores,
diatom-inferred TN concentrations tended to increase in the more recent sediments, as may be expected with warming; however
these trends were not very distinct. 相似文献
8.
Shallow lakes have been described as existing in two alternative equilibrium states, dominated by either submerged plants
or phytoplankton. Causes of, often catastrophic, shifts between these states have been widely debated but may often result
from displacement of the dominant community by stochastic influence. In Australian cut-off river meanders (also known as ‘billabongs’),
anecdotal and palaeolimnological evidence suggests widespread loss of aquatic macrophytes since European occupation of the
region c. post-1800. Our detailed and high-resolution stratigraphic study of a sediment core from Hogan’s Billabong (Murray
River, Australia) seeks to identify the causes of the loss of aquatic macrophytes. Little direct evidence of the past extent
and composition of submerged macrophyte communities was recovered. Nevertheless, results derived from other sediment proxies,
including declines in the abundance of epiphytic diatoms and in plant-associated invertebrates, provide further indirect evidence
of macrophyte disappearance. Despite limitations with radiometric dating, the sequence of events in the derived record suggests
that a period of high abiotic turbidity, leading to a critical reduction in water transparency and caused by widespread erosion
during the late 19th century, is the most likely factor contributing to loss of submerged vegetation from this billabong. 相似文献
9.
Inferences of past climate from the fossil record in lakes rely on the accurate quantification of a relationship of fossilizing organisms to their environment. Whereas the relationship of diatoms to water chemistry parameters has been modeled in many systems, few studies adequately address the relationship of diatoms to physical properties, such as water depth or hydrology, that may be more directly tied to climate. We examined the composition of modern diatoms in surface sediments of 75 isolated ponds (mostly Carolina bays) of the Atlantic Coastal Plain to: (1) assess the influence of physical and chemical variables on the distribution of diatoms among ponds of the region, and (2) develop a model that predicts hydroperiod (a measure of pond permanence) from diatom assemblages. We constructed two hydroperiod calibration models: the first infers hydroperiod from the weighted-average optima and tolerances of taxa along the hydroperiod gradient, the second bases inferences on the hydroperiod estimates of compositionally similar samples. Both approaches incorporate a-priori and post-hoc tests of assumptions often inherent in the construction of transfer functions. Diatom assemblage composition had strong, approximately linear relationships to hydroperiod, water depth, and calcium concentration in non-metric multidimensional ordination space; effects of other variables, including pH, were non-linear or ambiguous. Overall, the assemblages reflected the dilute, acidic chemical characteristics of bays. The assemblages contained differing abundances of euterrestrial, benthic and planktonic taxa, depending on a pond's susceptibility to drying. A weighted-averaging regression model based on taxon-specific hydroperiod optima generated adequate, unbiased hydroperiod inferences from diatom species composition (r2 = 0.81). This model may be used to infer past drought episodes from fossil diatom assemblages at appropriate sites on the Atlantic Coastal Plain. 相似文献
10.
A late Holocene diatom stratigraphy of Bottom Pond (37°05′S, 12°17′W) was studied and interpreted to infer paleolimnological
and climate changes on Tristan da Cunha, South Atlantic. The diatom flora of Bottom Pond is dominated by meroplanktonic Aulacoseira alpigena and A. distans and a benthic/epiphytic flora including Achnanthes spp., Naviculadicta spp., Eunotia taxa and Frustulia rhomboides. The flora also includes an important terrestrial and aerophytic component, consisting of several Diadesmis spp., Navicula lapidosa, Nitzschia terrestris and some Pinnularia spp., at times dominating the flora. Peaks of high terrestrial diatom abundances and low abundances and concentrations of
Aulacoseira spp., correspond to periods of increased magnetic susceptibility and are interpreted to be the result of increased catchment
erosion and/or precipitation leading to enhanced in-wash of species living in the soils around the lake. The diatom record
of Bottom Pond most likely registers both local responses to increased erosion in the catchment as well as climatic change
of a more regional character. Comparisons with the geochemical record in 2nd Pond on Nightingale Island show a correspondence
between the two data sets at 2,000–1,750 cal yrs BP, most likely evidence of increased precipitation in the Tristan da Cunha
region. The Tristan da Cunha archipelago is situated at the northern limit of the Southern hemisphere west wind belt and stronger
and/or a northward shift of the westerlies, are probably the main causes of the precipitation changes. 相似文献
11.
Linda Ampel Barbara Wohlfarth Jan Risberg Daniel Veres Melanie J. Leng Päivi Kaislahti Tillman 《Journal of Paleolimnology》2010,44(2):397-404
The sedimentary record from the paleolake at Les Echets in eastern France allowed a reconstruction of the lacustrine response
to several abrupt climate shifts during the last glacial period referred to as Dansgaard–Oeschger (DO) cycles. The high-resolution
diatom stratigraphy has revealed distinct species turnover events and large fluctuations in stable oxygen isotope values in
diatom frustules, as a response to DO climate variability. More or less identical species compositions became re-established
during each DO stadial and interstadial phases, respectively. However, the relative abundance of the most dominant species
within these assemblages varies and might indicate differences in climatic conditions. Interstadial phases are characterized
by identical species successions. Transitions from stadial to interstadial conditions show a distinct Fragilaria–Cyclotella succession, which resembles the diatom regime shifts that have been recognized in some lakes in the Northern Hemisphere since
the mid-nineteenth century. 相似文献
12.
Holocene diatom flora and stratigraphy from sediment cores of two Antarctic lakes (King George Island) 总被引：6，自引：0，他引：6
The diatom stratigraphy of Holocene sediment cores from two Antarctic lakes (Mondsee, Tiefersee; 62° 10 S/58° 50 W) of King George Island was investigated. The diatom assemblages were dominated by cosmopolitan species. The flora was composed of three main components: 1) taxa of submersed bryophytic habitats, which also occur in the bryophilic diatom flora of southern South America; 2) species of various terrestrial habitats, including some specific subantarctic taxa; 3) species distributed in coastal inland waters influenced by sea-spray.Changes in sediment pattern and diatom species composition seemed to reflect climatic changes. At least three different core sections were distinguished in both lakes: Two sections rich in mosses occur between approx. 7000–4700 B.P. and from 3200 B.P. to present, in general resembling present day conditions. In between is a section of high allochthonous content with generally low diatom concentrations and rising percentages of aerophilic, halophilic and alkaliphilic diatoms. An increase of melt water discharge, possible sea-spray influence, and lake- level fluctuations are discussed.Three new taxa are described: Achnanthes metakryophila nov. spec., Achnanthes renei nov. spec., Navicula australomediocris nov. spec. The taxonomy of selected taxa is discussed. 相似文献
13.
In North America, land use practices of the last two centuries have strongly influenced aquatic communities and freshwater quality, but the impacts of prehistoric land use on freshwater resources remain poorly documented. Here we investigate the influence of prehistoric and historical land use on Horseshoe Lake, Illinois, USA, an oxbow lake in a floodplain of the Mississippi River that is adjacent to Cahokia, the largest prehistoric indigenous population center north of Mexico. Diatom assemblages from Horseshoe Lake’s sedimentary record track shifts in aquatic environmental conditions over the last ca. 1600 years. During the period of prehistoric population growth and agricultural intensification associated with Cahokia’s emergence (ca. 600–1200 CE), the relative abundance of Aulacoseira granulata—a planktonic diatom associated with shallow eutrophic lakes—increased. Following the abandonment of Cahokia in the 14th century CE, the diatom flora of the lake shifted from planktonic Aulacoseira taxa to the epiphytic taxa Cocconeis and Gomphonema. This shift in diatom assemblages is consistent with a reduction of nutrient inputs to the lake and/or reduced fishing pressure as prehistoric populations abandoned the area. Following the intensification of historic settlement after 1800 CE, diatom assemblages shift to epipelic species of small Staurosira and Fragilaria, indicating a reduction in aquatic macrophytes and increased turbidity. Our results document prehistoric indigenous impacts on a freshwater system beginning nearly 1000 years before European colonization of the Americas and demonstrate the antiquity of human impacts on freshwater resources in North America. 相似文献
14.
Kristopher R. Hadley Marianne S. V. Douglas Robert McGhee Jules M. Blais John P. Smol 《Journal of Paleolimnology》2010,44(1):85-93
Until recently, major anthropogenic impacts on freshwater ecosystems were believed to be rare in North America prior to the
period of European colonization. However, recent paleolimnological and archaeological data collected from the Canadian Arctic
suggest that the whaling activities of Thule Inuit, who lived in small, nomadic communities, altered freshwater ecosystems
centuries earlier. Using a comparative paleolimnological approach from two ponds situated adjacent to a former Thule winter
settlement on south-eastern Bathurst Island (Nunavut, Arctic Canada), we record marked ecological changes in pond ecology
due to eutrophication from the Thule’s activities. The geography of our study site provided an interesting and rare opportunity
for a comparative paleolimnological study of long-term Thule impacts on polar limnology, because our two study ponds (only ~50
m apart) were nearly identical in size and in geological and climatic settings, but differed markedly in the magnitude of
Thule influence. Here, we recorded striking changes in diatom species assemblages, spectrally-inferred primary production,
and nutrient geochemistry, indicating eutrophication in a small pond draining 18 Thule whale houses. Input of marine-derived
nutrients from sea mammal carcasses used by the Thule for both sustenance and the construction of winter settlements, as well
as other anthropogenic activities, coincided with a notable increase in the eutrophic diatom taxon Stephanodiscus minutulus, whereas no comparable changes were recorded in the nearby control pond for the duration of the sedimentary record. Although
the diatom changes recorded in the affected site persisted after the period of Thule occupation, the most recent sediments
and water chemistry suggest that the pond has largely recovered to near pre-impact conditions. 相似文献
15.
Diatom-inferred lake level from near-shore cores in a drainage lake from the Experimental Lakes Area,northwestern Ontario,Canada 总被引：1，自引：0，他引：1
We inferred late Holocene lake-level changes from a suite of near-shore gravity cores collected in Lake 239 (Rawson Lake),
a headwater lake in the Experimental Lakes Area, northwestern Ontario. Results were reproduced across all cores. A gravity
core from the deep central basin was very similar to the near-shore cores with respect to trends in the percent abundance
of the dominant diatom taxon, Cylcotella stelligera. The central basin, however, does not provide a sensitive site for reconstruction of lake-level changes because of the insensitivity
of the diatom model at very high percentages of C. stelligera and other planktonic taxa. Quantitative estimates of lake level are based on a diatom-inferred depth model that was developed
from surficial sediments collected along several depth transects in Lake 239. The lake-level reconstructions during the past
~3,000 years indicate that lake depth varied on average by ±2 m from present-day conditions, with maximum rises of ~3–4 m
and maximum declines of ~3.5–5 m. The diatom-inferred depth record indicates several periods of persistent low levels during
the nineteenth century, from ~900 to 1100 AD, and for extended periods prior to ~1,500 years ago. Periods of inferred high
lake levels occurred from ~500 to 900 AD and ~1100 to 1650 AD. Our findings suggest that near-shore sediments from small drainage
lakes in humid climates can be used to assess long-term fluctuations in lake level and water availability. 相似文献
16.
Linda Randsalu-Wendrup Daniel J. Conley Jacob Carstensen Lars-Anders Hansson Christer Brönmark Sherilyn C. Fritz Preetam Choudhary Joyanto Routh Dan Hammarlund 《Journal of Paleolimnology》2014,51(3):437-448
In this study, we demonstrate that an integrated approach, combining palaeolimnological records and limnological monitoring data, can increase our understanding of changing ecological patterns and processes in shallow lakes. We focused on recent regime shifts in shallow Lake Krankesjön, southern Sweden, including the collapse of the clear-water state in 1975 and its subsequent recovery in the late 1980s. We used diatom, hydrocarbon and biogenic silica sediment records, in concert with limnological data sets on nutrient concentrations, water clarity, chlorophyll-a and water depth, to investigate the shifts. The shift from clear to turbid conditions was abrupt and occurred over 1 to 2 years, whereas recovery of the clear-water state was more gradual, taking 4–5 years. In 1978, shortly after the first regime shift in water clarity, the diatom community underwent a significant shift. It became less diverse, with decreased abundance of epiphytic and planktonic taxa. Despite rising phosphorus concentrations and lower abundance of submerged macrophytes, Lake Krankesjön has remained in the clear-water state over the past 20 years, although this state seems to be increasingly unstable and susceptible to collapse. The complex reactions of the entire lake ecosystem to major changes in lake-water clarity, as shown by the palaeolimnological variables investigated in this study, emphasize the importance of careful lake and catchment management if a stable, clear-water state is desired. 相似文献
17.
We examined changes at the community and population level of sedimentary diatoms over a wide temporal and spatial gradient
of metal pollution encountered in cores from three lakes in the Abitibi mining region (Québec, Canada). Diatom communities
on the whole appeared to be very tolerant of metal contamination, as shown by diatom cell accumulation rates decreasing only
under the most severe conditions of contamination, which were found from the 1930s to the 1980s in Lac Dufault (cadmium, up
to 94 μg/g dry sediment; Cu, up to 8600 μg/g; Zn, up to 9000 μg/g). Under the moderate conditions of contamination observed
in the other two lakes and in the most recent sediment of Lac Dufault, diatom cell accumulation rates tended to increase over
values typical of the pre-mining period. However, there were increasing rearrangements of the community composition along
the contamination gradient. Under moderate metal enrichment, the diatom community of Lac Vaudray experienced only subtle changes,
with Cyclotella stelligera, albeit decreasing, remaining the dominant taxon. In the intermediately contaminated Lac Caron, several benthic taxa, noticeably
Cymbella silesiaca and several Fragilaria species, rose in taxonomic importance. The most extreme contamination observed in Lac Dufault led to a severely impoverished
community almost entirely represented by Achnanthes minutissima and Brachysira vitrea. With increasing levels of contamination, there was a shift from planktonic to benthic taxa and morphotypes and a consistent
decrease in the siliceous stomatocysts/diatom frustules ratio. These trends suggest that littoral zones may represent an
important refugium under conditions of high contamination. Responses to metal stress were in general more evident at the population
than at the community level. Cyclotella stelligera and B. vitrea had a consistent negative and positive response, respectively, along the gradient and are the most promising indicators of
metal pollution for this region. 相似文献
18.
Swan Lake is a small kettle lake located on the Oak Ridges Moraine; a moraine that is recognized as an important source of
ground water for the nearby and rapidly expanding Greater Toronto Area. A paleolimnological reconstruction using pollen and
diatoms from the lake sediments showed significant changes in biological community composition through the last ∼400 years.
Alterations in the diatom and pollen assemblages were most dramatic ca. A.D. 1850, correlating with the highest sediment flux
in the lake between the period ca. A.D. 1850 and A.D. 1870. These changes were directly linked to regional deforestation and
agricultural activities associated with European settlement. The pollen record from ca. A.D. 1850 to present day indicated
that tree species (e.g. Pinus spp., Tsuga canadensis) were declining, while grass (Poaceae) and invasive species (e.g. Ambrosia) were increasing. Around A.D. 1850, the diatom flora changed from an assemblage dominated by large, benthic species (e.g.
Sellaphora pupula, Pinnularia cf. maior, and Stauroneis phoenicenteron) to an assemblage characterized by smaller, tychoplanktonic (e.g. Fragilaria tenera, Staurosirella pinnata) and epiphytic (e.g. Achnanthidium minutissimum, Rossithidium linearis) taxa. This diatom community change supports the intermediate disturbance hypothesis which predicts a high level of diversity
and richness following an intermediate to intense disturbance of short duration. Phosphorus concentrations in Swan Lake were
inferred using a diatom-based regional calibration model, and the results indicated marked changes in lake water chemistry
through time (from below detection limits before land clearance and settlement to 19.3 μg l−1 in the current sediments), which were concurrent with episodes of regional deforestation and land-use change. Although the
sediment and biological records indicate that the lake ecology has stabilized over the last 30–50 years, paleolimnological
records show that the water quality and biology of Swan Lake has changed dramatically and not returned to pre-settlement conditions.
Swan Lake presents a detailed record of the impact created by deforestation and urban development with a population of <50
individuals per km2. Detailed paleolimnological studies like Swan Lake, in tandem with global human footprint studies, can create realistic estimates
of land-use impacts at the global scale. 相似文献
19.
Differential diatom dissolution in Late Quaternary sediments from Lake Manyara,Tanzania: an experimental approach 总被引：3，自引：0，他引：3
Philip Barker 《Journal of Paleolimnology》1992,7(3):235-251
Diatom dissolution in saline lakes represents an important obstacle to the quantitative reconstruction of water chemistry and climate from lake sediment archives. This problem is here approached experimentally by artificially dissolving diatom-bearing core sediment from Lake Manyara, Tanzania. Manyara holds one of the longest continuous palaeolimnological records from tropical Africa although its interpretation is based on a fragmentary diatom record due to frustule dissolution. These experiments have revealed clear changes in assemblage composition as dissolution operated differentially with respect to diatom taxa. Differential dissolution has considerable impact on the water chemistry estimates derived from transfer functions. Taphonomy, rather than environmental change, may have been responsible for minor fluctuations in the diatom assemblages from Manyara, although major palaeohydrological changes during the Late Pleistocene and Early Holocene can be identified. Particularly well represented by MANE-87 is a period of intermediate lake level between 27 500 and 23 000 14C yr BP which has regional palaeohydrological significance. 相似文献
20.
Christopher M. Donar Robert K. Neely Eugene F. Stoermer 《Journal of Paleolimnology》1996,15(3):237-243
A 43 cm by 5 cm diameter sediment core sample was obtained from Ford Lake reservoir in Washtenaw County, Michigan, and sectioned at 1 cm intervals. The purpose of this study was to determine whether diatom communities in this reservoir have undergone quantifiable changes in abundance and composition since its creation. Thirty-one cm of this core appeared to represent material deposited since the creation of the reservoir based on changes in diatom abundance, the physical composition of the sediment and the change in biogenic SiO2 concentration. Fortyseven species of diatoms were identified total concentrations of diatom remains varied from 1×104 g-1 to 1×107 g-1. Prior to the establishment of the reservoir, the diatom flora was dominated by benthic taxa. Benthic diatoms were numerous throughout the entire core, but eutrophic taxa (e.g., Aulacoseira italica, Aulacoseira granulata, Stephanodiscus niagarae, Fragilaria crotonensis) dominated much of the core after the reservoir's creation. Total diatom density increased about tenfold in the about the first 10–15 years after the reservoir's creation before declining markedly. 相似文献