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1.
Richard W. Battarbee David Morley Helen Bennion Gavin L. Simpson Michael Hughes Viktorija Bauere 《Journal of Paleolimnology》2011,45(4):405-414
We describe a palaeolimnological meta-database (“LakeCores”) that includes information for lakes in Europe that have been
cored for studies of recent environmental change. Only cores with intact mud-water interfaces and good chronologies for the
last ~100–200 years are currently included. The information provided in the database includes the general characteristics
of the lakes cored, the methods used for dating and analysis and the bibliographic source of the information selected. At
present the database contains information on 1847 studies from 975 sites. Here we use the database to identify cores for which
diatom-based pH and total phosphorus (TP) reconstructions have been derived and, from an inspection of the relevant papers,
we compile summary data for the timing and extent of acidification and eutrophication of lakes across Europe. We show that
there were few cases of acidification and eutrophication in Europe prior to about 1850, and therefore that conditions prior
to 1850 can be used for reference with respect to current attempts to restore surface waters to “good ecological status”.
We also show the extent to which pH and TP levels have changed across the continent both for all lakes, and, in the case of
TP, for lakes of different types covering a range of alkalinities, altitudes, water depths and surface areas. 相似文献
2.
Bianca B. Perren N. John Anderson Marianne S. V. Douglas Sherilyn C. Fritz 《Journal of Paleolimnology》2012,48(1):223-239
Holocene paleolimnological records (diatoms, organic content, spectrally inferred sediment chlorophyll-a) from three West Greenland lakes (~67°N) situated along a transect from the outer coast to a nunatak at the periphery of the Greenland Ice Sheet are used to explore the nature of regional postglacial lake development and its relationship to Holocene climate evolution. The lakes were deglaciated asynchronously by approximately 4?ka (earliest on the coast) and thus their sediment records document different starting points of Holocene ontogeny, both temporally and paleoclimatically. Despite similar time-transgressive characteristics of the diatom stratigraphies, overarching climatic factors, principally effective moisture, and eolian inputs, govern individual lake development. The transition to Neoglaciation between 5.6 and 4?ka BP marks a shift toward a cooler, moister, windier climate from the aridity and higher temperatures of the mid-Holocene (8?C6?ka BP). A shift toward increased aridity, windiness, and eolian activity is documented in the interior lakes over the last 500?years. These lake records demonstrate the sensitivity of freshwater lakes in arid regions to changes in effective moisture and highlight the role of wind and eolian activity in Arctic lake environments. 相似文献
3.
Empirical models for describing recent sedimentation rates in lakes distributed across broad spatial scales 总被引:1,自引:0,他引:1
Soren Brothers Jesse C. Vermaire Irene Gregory-Eaves 《Journal of Paleolimnology》2008,40(4):1003-1019
Over the last 20 years there has been a surge of interest in paleolimnology and as a result a large accumulation of lake sedimentation
records. This emerging archive has allowed us to develop empirical models to describe which variables explain significant
variation in sedimentation rates over the past ∼150 years across large spatial scales. We hypothesized that latitude would
be a significant explanatory variable of profundal zone lake sedimentation rates across a temperate to polar gradient. We
further hypothesized that along a more longitudinally-constrained dataset (i.e. east coast of North America), latitude would
explain a greater proportion of the variance. To test these hypotheses, we collated data from 125 natural, average-sized lakes
(with surface area <500 km2) by recording authors’ estimates of sedimentation rates (measured as mm/year) or by digitizing recent sediment profiles and
calculating sedimentation rates over the past ∼150 years. We found that, at both scales, latitude was the strongest predictor
of lake sedimentation rates (full dataset: r
2 = 0.28, P = 0.001, n = 125; east coast dataset: r
2 = 0.58, P < 0.001, n = 43). By conducting a multiple linear regression analysis, we found that 70% of the variance in sedimentation rates from
the east coast transect was explained by latitude and elevation alone. This latter model is of sufficient strength that it
is a robust predictive tool. Given that climate and land-use strongly co-vary with latitude and that both of these factors
have previously been shown to influence lake sedimentation rates, it appears that latitude is a surrogate measure for climate
and land-use changes. We also show support for land-use as an important variable influencing sedimentation rates by demonstrating
large increases in recent versus Holocene accumulation rates. These results indicate that it is possible to make generalizations
about sedimentation rates across broad spatial scales with even limited geographic data. 相似文献
4.
Neil L. Rose David Morley Peter G. Appleby Richard W. Battarbee Tiiu Alliksaar Piero Guilizzoni Erik Jeppesen Atte Korhola Jaan-Mati Punning 《Journal of Paleolimnology》2011,45(4):447-468
Sediment accumulation rate (SAR) is an important physical parameter in all lakes and increases have been observed in many
over the last c.100 years. This has been ascribed to changes in land-use and land-management causing accelerated catchment
soil erosion and an increase in autochthonous organic matter production. The EU Water Framework Directive requires that assessment
of biological, hydromorphological and chemical elements of water quality should be based on the degree to which present day
conditions deviate from those expected in the absence of significant anthropogenic influence, termed reference conditions.
Currently however, the reference condition for sediment accumulation rate for lakes of different types is undefined. To improve
our understanding of the controls on SARs we compiled SAR and lake typology data for 207 European lakes derived from 210Pb dated cores to assess how rates have changed through time (in 25 year classes) both overall and for lakes of different
types. Seventy-one percent of these sediment cores showed surface SARs higher than “basal” (mainly nineteenth century) rates,
11% showed no change while 18% showed a decline. Lakes were then classified into lake-types using four variables: alkalinity
(3 classes), altitude (3 classes), maximum depth (2 classes) and lake area (2 classes). This generated a possible 36 lake
classes of which 25 were represented in the dataset. Nine lake-types contained >10 lakes. Little change in SAR occurred prior
to 1900 and most increases occurred in more recent periods, in particular 1950–1975 and post-1975. This indicates a general
acceleration in SAR in European lakes during the second half of the twentieth century. Reference SARs were estimated for six
lake-types with the highest number of sites. European mountain lakes had the lowest reference SAR (0.005 ± 0.003 g cm−2 yr−1) while lowland, high alkalinity sites had the highest (0.03–0.04 g cm−2 yr−1). SARs for other lake-types ranged between 0.012 and 0.024 g cm−2 yr−1. Using the mountain lake-type as an example, the 1850 reference SAR appears to show good agreement with available data for
lakes beyond Europe indicating these values may be more broadly applicable. Contemporary SARs in lakes of all classes showed
exceedence over their defined reference SAR. This may be partly due to diagenetic processes. Greatest exceedences were found
in shallow, low altitude lakes and these are considered to be the ones under the greatest threat from continued elevation
of SAR. It is considered that climate change may play a progressively more important role in driving SAR in the future. 相似文献
5.
青藏高原不同时段气候变化的研究综述 总被引:2,自引:2,他引:0
1 Introduction The annual mean world temperature increased by about 0.6℃ from the late 1800s to the 1980s (Wang, 1994). The global environmental change is marked with “global warming” and its possible effects on the ecosystem as well as the production … 相似文献
6.
Wei Zhong Jibin Xue Jun Ouyang Yanming Zheng Qiaohong Ma Xuefeng Yu 《Journal of Paleolimnology》2010,44(3):777-788
Two cores were recovered from raised peat bogs on the tropical northern Leizhou Peninsula, south China. Multiple sediment
variables including organic matter (OM) content, the stable carbon isotope signature of OM, low-frequency magnetic susceptibility
and degree of humification, indicate that the regional paleoclimate played an important role in determining the nature of
peat that accumulated. Based on comparison with other climate proxies, the bulk peat δ13C record was interpreted as an indicator of variation in the East Asian (EA) summer monsoon, and to a lesser extent, the Indian
summer monsoon, during the last glacial period between ~49 and 10 cal ka BP. More negative bulk δ13C values reflect wetter and warmer conditions, and thus a strong EA summer monsoon. More positive values indicate drier and
cooler conditions. A warm and wet period occurred between ~46 and 28 cal ka BP, implying a strengthening of the EA summer
monsoon. A climate shift occurred at ~22 cal ka BP and the driest and coldest period appeared between ~19 and 16 cal ka BP,
suggesting weakening of the EA summer monsoon. After ~12 cal ka BP, climate shifted towards wetter and warmer conditions again.
It has been suggested that variations in orbitally induced solar insolation played a role in the last glacial climate of the
study region. Several millennial—scale arid and cold phases characterized by C4 plants, or by more positive δ13C values during periods when C3 plants dominated, show agreement with the Greenland GISP2 ice core and the Chinese stalagmite
records. Interactions between high northern latitude cold air advection and summer moisture transported across the tropical
ocean, and the migration of the mean position of the Intertropical Convergence Zone (ITCZ) would have favored these millennial–scale
phases. Additionally, changes in heat transport to the North Atlantic would also have influenced climate in the region. 相似文献
7.
I. Mazzini C. Faranda M. Giardini C. Giraudi L. Sadori 《Journal of Paleolimnology》2011,45(2):243-256
We present a Holocene record of climate and environmental change in central New York (USA) inferred using lithologic and stable
isotope data from two sediment cores recovered in Cayuga Lake. The record was divided into three intervals: (1) early Holocene
(~11.6–8.8 ka), (2) Hypsithermal (~8.8–4.4 ka), and (3) Neoglacial (~4.4 ka to present). The early Holocene began abruptly,
with rising lake level and relatively deep water. Between ~10.8 and 9.2 ka, cool and dry conditions prevailed at a time of
maximum solar insolation. This anomaly has been referred to as the “post-Younger Dryas climate interval” and lasted ~1,600 years,
the approximate length of one “Bond cycle.” The Hypsithermal was the warmest, wettest and most biologically productive interval
of the Holocene in central New York. The Hypsithermal was characterized by centennial to multi-centennial-scale variability.
The 8.2 ka event is one such variation. The Neoglacial was an interval of generally cooler and dryer conditions, falling lake
levels, and several prominent climate anomalies. At approximately 2.4 ka, δ13C of bulk organic matter increased abruptly by 5‰ as lake level declined, and the lake flora was dominated by Chara sp. during the coldest interval of the Neoglacial. Numerous sediment variables display increased variability ~2.0 ka, which continues
today. Archaeological data from the literature suggest that Native American populations may have been large enough to impact
land cover by about 2.4 ka and we hypothesize that the “Anthropocene” began at about that time in central New York. We also
found paleolimnological evidence for the Medieval Warm Period (~1.4–0.5 ka), which was warmer and wetter than today, and for
the Little Ice Age (~500–150 years ago), a period with temperatures colder than today. 相似文献
8.
Mirko Dreßler Anja Schwarz Thomas Hübener Sven Adler Burkhard W. Scharf 《Journal of Paleolimnology》2011,45(2):223-241
Fossil diatoms from lake sediments have been used to infer both past trophic state and climate conditions. In Europe, climate
reconstructions focused on northern and alpine regions because these areas are climatically sensitive and anthropogenic impact
was low. In contrast, anthropogenic impact was often high in the central European lowlands, such as northern Germany, beginning
in the Neolithic Age, ~3700 BC. Since that time, trophic state change was the main factor that affected diatom assemblages
in central European lowland lakes. Therefore, it was considered difficult or impossible to identify climate changes in the
region using sedimented diatoms. We used diatom assemblage changes, diatom-inferred total phosphorus concentrations and the
relative abundance of planktonic diatoms from sediments of three lakes that differ in their location, size, morphology, catchment
area and current trophic state to test whether we could distinguish between trophic state and climate signals over the past
5,000 years in northern Germany. In this study, changes in trophic state and climate were well differentiated. In the study
lakes, relative abundance of planktonic diatoms seems to be linked to the length of lake mixing phases. Planktonic diatom
abundance decreased during years with shorter mixing duration, and these shorter mixing times probably reflect colder winters.
The diatom-inferred periods of short mixing phases from 1000 BC to AD 500 and from AD 1300 to 1800 coincide well with two
known cooling phases in Europe and the North Atlantic region. 相似文献
9.
Solar and anthropogenic imprints on Lake Masoko (southern Tanzania) during the last 500 years 总被引:1,自引:0,他引:1
Yannick Garcin David Williamson Laurent Bergonzini Olivier Radakovitch Annie Vincens Guillaume Buchet Joël Guiot Simon Brewer Pierre-Etienne Mathé Amos Majule 《Journal of Paleolimnology》2007,37(4):475-490
The Masoko crater-lake in southern Tanzania provides a continuous record of environmental changes covering the last 500 years.
Multi-proxy studies were performed on a 52 cm sediment core retrieved from the deepest part of the lake. Magnetic, organic
carbon, geochemical proxies and pollen assemblages indicate a dry climate during the ‘Little Ice Age’ (AD 1550–1850), confirming
that the LIA in eastern Africa resulted in marked and synchronous hydrological changes. However, the direction of response
varies between different African lakes (low versus high lake-levels), indicating strong regional contrasts that prevent the
clear identification of climate trends over eastern Africa at this time. Inferred changes in Masoko lake-levels closely resemble
the record of solar activity cycles, indicating a possible control of solar activity on the climate in this area. This observation
supports previous results from East African lakes, and extends this relationship southward. Finally, anthropogenic impact
is observed in the Masoko sediments during the last 60 years, suggesting that human disturbance significantly affected this
remote basin during colonial and post-colonial times. 相似文献
10.
A high resolution multi-proxy record of pronounced recent environmental change at Baker Lake,Nunavut
A. S. Medeiros C. E. Friel S. A. Finkelstein R. Quinlan 《Journal of Paleolimnology》2012,47(4):661-676
Arctic aquatic systems are considered to be especially sensitive to anthropogenic disturbance, which can have cascading effects
on biological communities as aquatic food-web structure is altered. Bio-indicators that respond to major limnological changes
can be used to detect and infer major environmental change, such as climate warming, with the use of paleolimnological techniques.
A multi-proxy approach was used to quantify recent environmental changes at Baker Lake, Nunavut, Arctic Canada. Analyses of
fossilized remains of chironomids and diatoms were conducted on a sediment core of 20 cm in length sampled at 0.5-cm intervals.
A new surface sediment training set of subfossil chironomid assemblages from 65 lakes across the eastern Canadian Arctic generated
a robust (r
jack2 = 0.79) surface water paleotemperature transfer function. The transfer function was applied to stratigraphic intervals from
the Baker Lake sediment core to generate a paleotemperature reconstruction of sub-decadal resolution. The surface water temperature
reconstruction inferred a 2°C increase in mid-summer surface water temperature for Baker Lake over the last 60 years, which
was corroborated by the local instrumental record spanning the period of 1950–2007 AD. The chironomid record shows a recent
decline of several cold-water taxa and appearance of warm-water indicators. This shift in community structure began circa
1906 AD, and intensified after 1940 AD. The corresponding fossil diatom record showed an increase in small planktonic Cyclotella taxa over the past 60 years, intensifying in the last 5 years, which also suggests a warmer climate and longer ice-free periods.
The shifts in the diatom assemblages began later than the shifts in the chironomid assemblages, and were of lower magnitude,
reflecting differences in the mechanisms in which these two indicators respond to environmental change. 相似文献
11.
A knowledge of pre-disturbance conditions is important for setting realistic restoration targets for lakes. For European waters
this is now a requirement of the European Council Water Framework Directive where ecological status must be assessed based
on the degree to which present day conditions deviate from reference conditions. Here, we employ palaeolimnological techniques,
principally inferences of total phosphorus from diatom assemblages (DI-TP) and classification of diatom composition data from
the time slice in sediment cores dated to ~1850 AD, to define chemical and ecological reference conditions, respectively,
for a range of UK lake types. The DI-TP results from 169 sites indicate that reference TP values for low alkalinity lakes
are typically <10 μg L−1 and in many cases <5 μg L−1, whilst those for medium and high alkalinity lakes are in the range 10–30 and 20–40 μg L−1, respectively. Within the latter two alkalinity types, the deeper waters (>3 m mean depth) generally had lower reference
TP concentrations than the shallow sites. A small group of shallow marl lakes had concentrations of ~30 μg L−1. Cluster analysis of diatom composition data from 106 lakes where the key pressure of interest was eutrophication identified
three clusters, each associated with particular lake types, suggesting that the typology has ecological relevance, although
poor cross matching of the diatom groups and the lake typology at type boundaries highlights the value of a site-specific
approach to defining reference conditions. Finally the floristic difference between the reference and present day (surface
sample) diatom assemblages of each site was estimated using the squared chord distance dissimilarity coefficient. Only 25
of the 106 lakes experienced insignificant change and the findings indicate that eutrophication has impacted all lake types
with >50% of sites exhibiting significant floristic change. The study illustrates the role of the sediment record in determining
both chemical and ecological reference conditions, and assessing deviation from the latter. Whilst restoration targets may
require modification in the future to account for climate induced alterations, the long temporal perspective offered by palaeolimnology
ensures that such changes are assessed against a sound baseline. 相似文献
12.
Amanda R. Lusas Brenda L. Hall Thomas V. Lowell Meredith A. Kelly Ole Bennike Laura B. Levy William Honsaker 《Journal of Paleolimnology》2017,57(4):321-341
Prediction of future Arctic climate and environmental changes, as well as associated ice-sheet behavior, requires placing present-day warming and reduced ice extent into a long-term context. Here we present a record of Holocene climate and glacier fluctuations inferred from the paleolimnology of small lakes near Istorvet ice cap in East Greenland. Calibrated radiocarbon dates of organic remains indicate deglaciation of the region before ~10,500 years BP, after which time the ice cap receded rapidly to a position similar to or less extensive than present, and lake sediments shifted from glacio-lacustrine clay to relatively organic-rich gyttja. The lack of glacio-lacustrine sediments throughout most of the record suggests that the ice cap was similar to or smaller than present throughout most of the Holocene. This restricted ice extent suggests that climate was similar to or warmer than present, in keeping with other records from Greenland that indicate a warm early and middle Holocene. Middle Holocene magnetic susceptibility oscillations, with a ~200-year frequency in one of the lakes, may relate to solar influence on local catchment processes. Following thousands of years of restricted extent, Istorvet ice cap advanced to within 365 m of its late Holocene limit at ~AD 1150. Variability in the timing of glacial and climate fluctuations, as well as of sediment organic content changes among East Greenland lacustrine records, may be a consequence of local factors, such as elevation, continentality, water depth, turbidity, and seabirds, and highlights the need for a detailed spatial array of datasets to address questions about Holocene climate change. 相似文献
13.
The “greatest lake period” means that the lakes are in the stage of their maximum areas. As the paleo lake shorelines are
widely distributed in the lake basins on the Tibetan Plateau, the lake areas during the “greatest lake period” may be inferred
by the last highest lake shorelines. They are several, even tens times larger than that at present. According to the analyses
of tens of lakes on the Plateau, most dating data fell into the range of 40-25 ka BP, some lasted to 20 ka BP. It was corresponded
to the stage 3 of marine isotope and interstitial of last glaciation. The occurrence of maximum areas of lakes marked the
very humid period on the Plateau and was also related to the stronger summer monsoon during that period. 相似文献
14.
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
15.
The status of tropical glaciers is enormously important to our understanding of past, present, and future climate change,
yet lack of continuous quantitative records of alpine glacier extent on the highest mountains of tropical East Africa prior
to the 20th century has left the timing and drivers of recent glacier recession in the region equivocal. Here we investigate
recent changes (the last 150–700 years) in lacustrine sedimentation, glacier extent, and biogeochemical processes in the Rwenzori
Mountains (Uganda- Democratic Republic of Congo) by comparing sedimentological (organic and siliciclastic component determined
by loss-on-ignition; LOI) and organic geochemical profiles (carbon and nitrogen abundance, ratio, and isotopic composition
of sedimentary organic matter) from lakes occupying presently glaciated catchments against similar profiles from lakes located
in catchments lacking glaciers. The siliciclastic content of sediments in the ‘glacial lakes’ significantly decreases towards
the present, whereas ‘non-glacial lakes’ generally show weak trends in their siliciclastic content over time, demonstrating
that changes in the siliciclastic content of glacial lake sediments primarily record fluctuations in glacier extent. Radiometric
dating of our sediment cores indicates that prior to their late 19th-century recession Rwenzori glaciers stood at expanded
‘Little Ice Age’ positions for several centuries under a regionally dry climate regime, and that recession was underway by
1870 AD, during a regionally wet episode. These findings suggest that the influence of late 19th century reductions in precipitation
in triggering Rwenzori glacier recession is weaker than previously thought. Our organic geochemical data indicate that glacier
retreat has significantly affected carbon cycling in Afroalpine lakes, but trends in aquatic ecosystem functioning are variable
among lakes and require more detailed analysis. 相似文献
16.
Kathleen R. Stoof-Leichsenring Annett Junginger Lydia A. Olaka Ralph Tiedemann Martin H. Trauth 《Journal of Paleolimnology》2011,45(3):353-367
Lake Naivasha, Kenya, is one of a number of freshwater lakes in the East African Rift System. Since the beginning of the twentieth
century, it has experienced greater anthropogenic influence as a result of increasingly intensive farming of coffee, tea,
flowers, and other horticultural crops within its catchment. The water-level history of Lake Naivasha over the past 200 years
was derived from a combination of instrumental records and sediment data. In this study, we analysed diatoms in a lake sediment
core to infer past lacustrine conductivity and total phosphorus concentrations. We also measured total nitrogen and carbon
concentrations in the sediments. Core chronology was established by 210Pb dating and covered a ~186-year history of natural (climatic) and human-induced environmental changes. Three stratigraphic
zones in the core were identified using diatom assemblages. There was a change from littoral/epiphytic diatoms such as Gomphonema gracile and Cymbella muelleri, which occurred during a prolonged dry period from ca. 1820 to 1896 AD, through a transition period, to the present planktonic Aulacoseira sp. that favors nutrient-rich waters. This marked change in the diatom assemblage was caused by climate change, and later
a strong anthropogenic overprint on the lake system. Increases in sediment accumulation rates since 1928, from 0.01 to 0.08 g cm−2 year−1 correlate with an increase in diatom-inferred total phosphorus concentrations since the beginning of the twentieth century.
The increase in phosphorus accumulation suggests increasing eutrophication of freshwater Lake Naivasha. This study identified
two major periods in the lake’s history: (1) the period from 1820 to 1950 AD, during which the lake was affected mainly by
natural climate variations, and (2) the period since 1950, during which the effects of anthropogenic activity overprinted
those of natural climate variation. 相似文献
17.
Charles E. UmbanhowarJr Philip Camill Jeffrey A. Dorale 《Journal of Paleolimnology》2011,45(2):151-166
Few studies have assessed the relative importance of landscape, land use history, climate, and regional heterogeneity on lake
ecosystem processes, despite the likelihood that interactions among these factors must be important for controlling lake dynamics.
We used 14 sediment measures from 20 lake cores in a climatically sensitive region of the prairie-forest border in southern
Minnesota to (1) assess relationships between modern lake productivity (Carlson’s Trophic State Index [TSI]), modern land-use,
catchment, and lake morphometry, and (2) contrast regional responses to climatic transitions from the ‘Medieval Climatic Anomaly’(1000–1350)
to the ‘Little Ice Age’ (1350–1800) to ‘Modern’(~1980–1996 AD). TSI was significantly positively correlated with modern sedimentation
rate, and accumulation rates of organic matter (OM), biogenic silica (BSi), and total phosphorus (TP). TSI was not significantly
correlated with “modern” land cover, catchment, or lake morphometry characteristics, but total organic N(N) was negatively
correlated with percent cultivation in the catchment area and negatively correlated with δ15N of bulk organic matter in sediment. Regional, among-lake heterogeneity was high over the past 1,000 years, but Little Ice
Age (LIA) cooling appeared to result in an approximately 20% decline in OM, BSi and TP accumulation, while warming and cultural
eutrophication of the past 150 years corresponded to a 200–400% increase in accumulation rates as well as an 80% increase
in carbonates and a small but significant 10% drop in C/N ratios consistent with greater in-lake productivity. Our results
indicate that climate does have regional effects on lake ecosystems but that among-lake variability is high, reflecting the
importance of local factors and suggesting a need for (1) more explicit definition of what ‘regional’ means, (2) a focus on
degree as well as direction of change, and (3) estimating accumulation rates based on multiple lakes and multiple cores within
lakes. 相似文献
18.
Pierre Giresse Makaya Mvoubou Jean Maley Alfred Ngomanda 《Journal of Paleolimnology》2009,41(2):369-392
Seven vibro-cores were collected from three shallow lakes of the Gabon (Kamalété, Nguène, Maridor) along a 300-km west–east
transect close to the Equator. These lakes are located in very distinct landscapes: coastal forest-savanna mosaic, rain forest
and savanna with colonising forest, respectively. Core chronologies were established by radiocarbon dating. Study of these
lacustrine archives (textural variables, clay minerals, organic matter components, δ13C, pollen) allowed comparison of late Holocene environmental changes recorded at each site and with results from other studies.
Lake Kamalété indicates minor climatic deterioration (increased drying and greater seasonality) between 1,410 and 500 cal.
years BP, which is also recognised in southern Cameroon and east-central Africa. Lake Nguène was surrounded by dense moist
forest throughout the last 4,110 years, but shows significant deterioration from ~2,800 cal. years BP, a phenomenon seen at
nearby sites. Lake Maridor shows a decline of forest initiated a little after 3,800 cal. years BP, which indicates timing
that is distinct from the two other sites. This was probably a response to local conditions (i.e. outlet damming). Although
the three lakes display generally parallel climatic trends perhaps linked to SST oscillations, there is not perfect coherence
between these three sites. Differences among the three basins may be attributable to local factors like groundwater hydrology
and slope instabilities of such shallow lake systems in this equatorial region. 相似文献
19.
Robert G. Hatfield Barbara A. Maher Jacqueline M. Pates Philip A. Barker 《Journal of Paleolimnology》2008,40(4):1143-1158
We examine sediment dynamics in an upland, temperate lake system, Lake Bassenthwaite (NW England), in the context of changing
climate and land use, using magnetic and physical core properties. Dating and analysis of the sedimentary records of nine
recovered cores identify spatially variable sedimentation rates across the deep lake basin. Mineral magnetic techniques, supported
by independent geochemical analyses, identify significant variations both in sediment source and flux over the last ∼2100 years.
Between ∼100 years BC and ∼1700 AD, sediment fluxes to the lake were low and dominated by material sourced from within the
River Derwent sub-catchment (providing 80% of the hydraulic load at the present day). Post-1700 AD, the lake sediments became
dominantly sourced from Newlands Beck (presently providing ∼10% of the lake’s hydraulic load). Three successive, major pulses
of erosion and increased sediment flux appear linked to specific activities within the catchment, specifically: mining activities
and associated deforestation in the mid-late nineteenth century; agricultural intensification in the mid-twentieth century
and, within the last decade, the additional possible impact of climate change. These results are important for all upland
areas as modifications in climate become progressively superimposed upon the effects of previous and/or ongoing anthropogenic
catchment disturbance. 相似文献
20.
土地利用变化时空模型的图谱方法--以黄河三角洲为例 总被引:12,自引:0,他引:12
Changesinlandcoverandland-usehaveimpactsandimplicationsatlocal,regionalandglobalscalesbecauseofthewaytheyalterbiophysical,biogeochemicalandhydrologicalstatesandprocesses(Alcamoetal.,1996;Li,1996).Since1990,scientistsathomeandabroadhavebeenpayingattentiontoresearchesonland-useandland-coverchange(LUCC)(Turneretal.,1990;MeyerandTurner,1994),butresearchisnotenoughon"spaceandprocess"ofLUCC(Turneretal.,1995).Spatialrelationshipbetweenvariablesyethasnotbeenestablished(Bockstael,1996).Soitispara… 相似文献