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1.
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
2.
Emiliya P. Kirilova Maarten van Hardenbroek Oliver Heiri Holger Cremer André F. Lotter 《Journal of Paleolimnology》2010,43(4):829-842
We present a palaeolimnological study encompassing five centuries of trophic-state change of the dike-breach lake De Waay
located on the Rhine-Meuse delta (the Netherlands). Diatom-inferred total phosphorus (TP) concentrations indicate hypertrophic
epilimnetic conditions (>300 μg l−1 TP) since the formation of the lake in the fifteenth century until the end of the eighteenth century. Cladocera data support
the reconstructed trophic state and indicate turbid conditions in lake De Waay during this period. High inferred TP concentrations
as well as the amount of Ti in the sediment reflect numerous flooding events. From the nineteenth century onwards reconstructed
TP concentrations decreased to 40–150 μg l−1 due to improvements in sewage and dike systems that considerably diminished direct river flooding and seepage-derived nutrients.
As a consequence, the increased stability of littoral habitats led to an increased diversity of the Cladocera assemblages.
The most significant decrease in TP concentrations to ~40 μg l−1 occurred between about 1900 and 1930. This mesotrophic phase was a consequence of the isolation of the lake from catchment
drainage and the introduction of a highly elaborate flood control during this period. However, since the mid twentieth century
a eutrophication trend is preserved in the record, likely related to increased agricultural activity in the vicinity of the
lake. Our results emphasize that land-use and trophic-state history must be taken into account when evaluating the ecological
status of lakes for water management and protection actions, especially for lakes in landscapes that are strongly modified
by human action. 相似文献
3.
Piero Guilizzoni Aldo Marchetto Andrea Lami Stefano Gerli Simona Musazzi 《Journal of Paleolimnology》2011,45(4):433-445
We propose a palaeolimnological method for inferring past total phosphorus (TP) concentrations in lake water from spectrophotometrically-measured
sedimentary pigments, particularly total carotenoids (TC). Our approach is based on a highly significant statistical correlation
(P < 0.0001) between pigment concentrations (total carotenoids) in the surface sediment of 28 Italian lakes (subalpine, large,
deep, shallow, volcanic) and TP concentrations measured in these lakes at overturn when the core was collected. A transfer
function was developed from this “training” set, and used to estimate past TP concentrations from pigment concentrations in
sediment cores. The results generally agreed with TP values as measured by long-term water quality monitoring programs. Contrasting
results were obtained by a comparison with diatom-inferred TP. While the diatom model showed a tendency to overestimate TP
values higher than 100 μg l−1, the pigment model correctly estimated TP in lakes when TP was <100 μg l−1, but not when lakes were rich in macrophytes. In fact, lakes with extensive populations of aquatic submersed macrophytes
and epiphytes are outliers in terms of the TC versus TP relationship. The root mean square error of prediction of the pigment
model is lower than those derived from certain diatom—based inference models. The predicted and residual values are not related
to the estimated values and their average is not statistically different from zero. Errors were estimated via a ‘leave-one-out’
re-sampling technique. The proposed method permits rapid and relatively inexpensive determination of reference trophic conditions. 相似文献
4.
Fasong Yuan Yongwei Sheng Tandong Yao Chaojun Fan Junli Li Hui Zhao Yanbin Lei 《Journal of Paleolimnology》2011,46(2):291-307
Stable isotopes (δ18O and δD) are useful tracers for investigating hydrologic and climatic variability on a variety of temporal and spatial scales.
Since the early isotopic studies on mountainous glaciers in the late 1960s, a great deal of information has been generated
on the isotopic composition of rainfall, snow, ice, surface waters, and lake carbonate sediments across the Tibetan Plateau.
However, measurements of δ18O and δD values of lake water are scarce. Here we present a new dataset of δ18O and δD values of lake waters collected from 27 lakes across the plateau during a reconnaissance survey in summer 2009. δ18O and δD values of lake water range from −19.9 to 6.6‰ and from −153 to −16‰, respectively. The average values of δ18O and δD are −6.4 and −72‰, considerably greater than those of precipitation observed in this region. The derived Tibetan
lake water line, δD = 5.2δ18O − 38.9, is significantly different from the global meteoric water line. Most of the lakes, including some freshwater lakes,
contain water with negative values of d-excess (d). There is a negative correlation between d and total dissolved solids (TDS). Each of these findings indicates that evaporation-induced isotopic enrichment prevails
in Tibetan lakes. Moreover, we develop an isotope modeling scheme to calculate E/P ratios for Tibetan lakes, using a combination
of existing isotopic fractionation equations and the Rayleigh distillation model. We use the intersection of the local evaporation
line and GMWL as a first approximation of δ18O and δD values of lake water inputs to infer an E/P ratio for each lake. Our modeling calculations reveal that although variable
from lake to lake, the water budget across the plateau is positive, with an average E/P of 0.52. This is in good agreement
with other observational and model data that show varying degrees of increases in lake size from satellite imagery and significant
decreases in lake salinity in many lakes on the plateau over the last several decades. Together with the new isotopic dataset,
the proposed modeling framework can be used to examine and quantify past changes in a lake’s hydrologic balance from the isotopic
record of downcore carbonate sediments in the region. 相似文献
5.
Biogeochemical records of paleoenvironmental changes in Nainital Lake,Kumaun Himalayas,India 总被引:1,自引:0,他引:1
Preetam Choudhary Joyanto Routh Govind J. Chakrapani Bhishm Kumar 《Journal of Paleolimnology》2009,42(4):571-586
Rapid urbanization and increased tourism around Nainital Lake in the Kumaun Himalayan region in north India has raised concerns
about sediment and water pollution. Lead-210 dated sediment cores from the lake represent ~95 years of accumulation and yield
a mean sedimentation rate of ~4.7 mm year−1. Total organic carbon (TOC), percent N and S and their atomic C/N and C/S ratios, stable isotopes (δ13C, δ15N, and δ34S), and specific biomarkers (n-alkanes and pigments) were measured in the core. Organic matter is primarily derived from in-lake algal production and TOC
flux varies from 1.0 to 3.5 g m−2 year−1. Sediments are anoxic (Eh −328 to −187 mV) and have low (0.10–0.30 g m−2 year−1) N, but high (0.37–1.0 g m−2 year−1) S flux. Shifts in δ13C, δ15N, and δ34S suggest in-lake microbial processes dominated by denitrification and sulfate reduction. The sediments are dominated by short-chain
hydrocarbons with low Carbon Preference Index values. The pigments indicate a gradual shift to cyanobacterial domination of
the phytoplankton community in recent years. Despite an increase in external input of nutrients, the trophic state of the
lake has remained largely unchanged, and the perceived human-induced impacts are limited. 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.
8.
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
9.
Diatom-based total phosphorus (TP) and pH transfer functions for the Irish Ecoregion 总被引:2,自引:0,他引:2
Guangjie Chen Catherine Dalton Manel Leira David Taylor 《Journal of Paleolimnology》2008,40(1):143-163
A 72-lake diatom training set was developed for the Irish Ecoregion to examine the response of surface sediment diatom assemblages
to measured environmental variables. A variety of multivariate data analyses was used to investigate environmental and biological
data structure and their inter-relationships. Of the variables used in determining a typology for lakes in the Irish Ecoregion,
alkalinity was the only one found to have a significant effect on diatom assemblages. A total of 602 diatom taxa were identified,
with 233 recorded at three or more sites with abundances ≥1%. Generally diatom data displayed a high degree of heterogeneity
at the species level and non-linear ecological responses. Both pH and total phosphorus (TP) (in the ranges of 5.1–8.5 and
4.0–142.3 μg l−1 respectively) were shown to be the most significant variables in determining the surface sediment diatom assemblages. The
calibration models for pH and TP were developed using the weighted averaging (WA) method; data manipulation showed strong
influences on model performances. The optima WA models based on 70 lakes produced a jack-knifed coefficient of determination
(r
2
jack) of 0.89 with a root mean squared error (RMSEP) of 0.32 for pH and r
2
jack of 0.74 and RMSEP of 0.21 (log10 μg l−1) for TP. Both models showed strong performances in comparison with existing models for Ireland and elsewhere. Application
of the pH and TP transfer functions developed here will enable the generation of quantitative water quality data from the
expanding number of palaeolimnological records available for the Irish Ecoregion, and thus facilitate the use of palaeolimnological
approaches in the reconstruction of past lake water quality, ecological assessment and restoration. 相似文献
10.
Trace metals and polycyclic aromatic hydrocarbons (PAH) were analyzed in sediment cores from three central Alberta lakes to
determine the contributions of local coal-fired power plants to contaminant loadings. In Wabamun Lake, with four power plants
built since 1950 within a 35-km radius, sediment concentrations of mercury, copper, lead, arsenic and selenium have increased
by 1.2- to 4-fold. Trace metal enrichments were less pronounced in Lac Ste. Anne and Pigeon Lake, situated 20 km north and
70 km south of Wabamun Lake, respectively. Total Hg flux to Wabamun Lake sediments (21–32μg m−2 yr−1) has increased 6-fold since 1950, compared to 2- and 1.5-fold increases in Lac Ste. Anne and Pigeon Lake, respectively, since
circa 1900. Total PAH flux to surface sediments was 730–1100μg m−2 yr−1 in Wabamun Lake, 290–420μg m−2 yr−1 in Lac Ste. Anne, and 140–240μg m−2 yr−1 in Pigeon Lake. Without adoption of pollution-abatement technology that compensates for increases in generating capacity,
continued expansion of coal-burning industry in Alberta will result in increased contaminant deposition, primarily from local
sources. 相似文献
11.
A decade of widespread increases in surface water concentrations of total organic carbon (TOC) in some regions has raised
questions about longer term patterns in this important constituent of water chemistry. This study uses near-infrared spectroscopy
(NIRS) to infer lake water TOC far beyond the decade or two of observational data generally available. An expanded calibration
dataset of 140 lakes across Sweden covering a TOC gradient from 0.7 to 24.7 mg L−1 was used to establish a relationship between the NIRS signal from surface sediments (0–0.5 cm) and the TOC concentration
of the water mass. Internal cross-validation of the model resulted in an R
2 of 0.72 with a root mean squared error of calibration (RMSECV) of 2.6 mg L−1. The TOC concentrations reconstructed from surface sediments in four Swedish lakes were typically within the range of concentrations
observed in the monitoring data during the period represented by each sediment layer. TOC reconstructions from the full sediment
cores of four lakes indicated that TOC concentrations were approximately twice as high a century ago. 相似文献
12.
Arsenic contamination of lake sediments in Florida: evidence of herbicide mobility from watershed soils 总被引:1,自引:0,他引:1
Thomas J. Whitmore Melanie A. Riedinger-Whitmore Joseph M. Smoak Keith V. Kolasa Ethan A. Goddard Richard Bindler 《Journal of Paleolimnology》2008,40(3):869-884
Organic arsenical herbicides, which include monosodium methylarsonate (MSMA), have been applied to golf courses and lawns
throughout Florida, USA, since the 1950s. These products convert rapidly to inorganic forms of arsenic (As) in soils and are
mobilized readily. Leachates have been known to contaminate groundwater and surface waters, although past studies have not
examined whether use of these products has led to significant As accumulation in lake sediments. We used paleolimnological
methods to document the depositional history and inventories of total As in sediments and porewaters of Little Lake Jackson
in Florida, which is adjacent to three golf courses. Six sediment cores, four of which were 210Pb dated, showed porewater total As concentrations as high as 435 μg l−1, and dry-sediment total As concentrations as high as 148 mg kg−1. Approximately 537 kg of total As is present in >19,000 metric tons of sediment (dry mass), and an additional 18 kg of As
is dissolved in 10.8 × 104 m3 of porewaters. Total As content in surface sediments (mean = 47.3 mg kg−1) exceeds the consensus-based sedimentary concentration for probable toxicity effects in freshwater benthic fauna. Surface
and subsurface waters flow to the lake from topographically higher areas to the west, where golf courses and residential areas
are located. Total As concentrations were elevated highly in monitoring wells and in a stream that flows between the golf
courses and lake, but As was below detection limits in wells that were located at the distal perimeter of the golf courses.
Subsurface and surface waters exit the lake towards topographically lower areas to the east. Nearly all As in sediments remains
bound in the solid phase, indicating that As sedimentary profiles largely reflect depositional history. Sedimentary As concentrations
are correlated strongly with aluminum and iron, which suggests that As was scavenged from lake waters during the past. Sedimentary
As concentrations increased until the 1980s, then declined somewhat to the present time. Dissolved As was scavenged efficiently
from the water column when hypolimnetic waters were oxygenated persistently, but after eutrophication led to a seasonally
anoxic hypolimnion in the 1980s, apparently less As was co-precipitated, and more was lost to hydrological outflow. Arsenic
accumulation in sediments might be common in areas where As derived from organic arsenical herbicide applications is directed
by shallow water tables towards adjacent lakes. 相似文献
13.
N. Kazancı S. A. G. Leroy S. Öncel Ö. İleri Ö. Toprak P. Costa S. Sayılı C. Turgut M. Kibar 《Journal of Paleolimnology》2010,43(1):89-110
Freshwater Lake Ulubat (z
mean = 1.5–2.0 m and Area = ~138 km2), NW Anatolia, Turkey was filled in by fine-to-medium-grain silts during the late Holocene. Deposition in Lake Ulubat has
been 1.6 cm year−1 for the last 50 years, but the sedimentation rate over the last ~1,600 years was lower (0.37 mm year−1). The organic matter and carbonate contents of the infill show cyclic changes that reflect environmental fluctuations. The
silt-dominated lithology and the vertically uniform heavy metal distributions are probably due to wind-controlled sedimentation
in the lake. Heterogeneous mud, derived from a large, mountainous drainage basin, is deposited in the lake mostly during summer,
June to October, when conditions are hot and calm. Winter months are stormier and sediments are re-suspended due to the shallow
water depth and the effect of waves on the lake bottom. It is likely that re-suspended sediments, particularly fine-grained
particles, together with the heavy metals, are transported out of the lake via the outlet, especially during periods of high
lake level. This resuspension and removal process probably caused the lake sediments to become silt-dominated and depleted
in heavy metals. The role of broad shallow lakes in sequestering sediments and heavy metals can be described more accurately
when wind data are considered. Such information may also be helpful for land-use planning in downstream areas. 相似文献
14.
Jane M. Reed Francesc Mesquita-Joanes Huw I. Griffiths 《Journal of Paleolimnology》2012,47(2):251-275
Diatoms (Bacillariophyceae; single-celled algae) and ostracods (Ostracoda; shelled microcrustacea) are known for their sensitivity
to salinity. In palaeolimnology, the potential has yet to be tested for quantifying past salinity, lake level, and by inference,
climate change, by application of multiple-indicator transfer functions. We used weighted averaging techniques to derive diatom
(n = 91; r
2
= 0.92) and ostracod (n = 53; r
2
= 0.83) conductivity transfer functions from modern diatom, ostracod and water chemistry data collected in lakes of central,
western and northern Turkey. Diatoms were better represented across the full gradient than ostracods, at intermediate levels
of conductivity in particular, but both transfer functions were statistically robust. Because transfer functions are not infallible,
we further tested the strength and simplicity of salinity response and the potential for identifying characteristic associations
of diatom and ostracod taxa in different parts of the salinity gradient, to improve palaeoclimate reconstruction. We identified
a subset of 51 samples that contained both diatoms and ostracods, collected at the same time from the same habitat. We used
Two-Way Indicator Species Analysis of a combined diatom-ostracod data set, transformed to achieve numerical equivalence, to
explore distributions in more detail. A clear ecological threshold was apparent at ~3 g l−1 salinity, rather than at 5 g l−1, the boundary used by some workers, equating to the oligosaline-mesosaline boundary. Other salinity boundaries were poorly
defined, indicating lack of a simple, well-defined salinity response. We did, however, define characteristic associations
of taxa, to facilitate the distinction to be drawn between a hydrologically open, fresh lake and an oligosaline lake, in palaeoenvironmental
reconstruction. Over the rest of the salinity gradient, we highlighted the potential for the multi-proxy approach to strengthen
ostracod-based reconstruction in particular, to overcome the problem of broad apparent tolerance ranges in common halophilic
taxa such as Limnocythere inopinata, which often dominate in low-diversity fossil assemblages. The combination of multi-proxy quantitative reconstruction, complemented
by qualitative understanding of ecological responses generated by the analysis, remains a powerful tool in Quaternary palaeoclimate
research. 相似文献
15.
Atmospheric deposition of reactive nitrogen (Nr) has enriched oligotrophic lakes with nitrogen (N) in many regions of the
world and elicited dramatic changes in diatom community structure. The lakewater concentrations of nitrate that cause these
community changes remain unclear, raising interest in the development of diatom-based transfer functions to infer nitrate.
We developed a diatom calibration set using surface sediment samples from 46 high-elevation lakes across the Rocky Mountains
of the western US, a region spanning an N deposition gradient from very low to moderate levels (<1 to 3.2 kg Nr ha−1 year−1 in wet deposition). Out of the fourteen measured environmental variables for these 46 lakes, ordination analysis identified
that nitrate, specific conductance, total phosphorus, and hypolimnetic water temperature were related to diatom distributions.
A transfer function was developed for nitrate and applied to a sedimentary diatom profile from Heart Lake in the central Rockies.
The model coefficient of determination (bootstrapping validation) of 0.61 suggested potential for diatom-inferred reconstructions
of lakewater nitrate concentrations over time, but a comparison of observed versus diatom-inferred nitrate values revealed
the poor performance of this model at low nitrate concentrations. Resource physiology experiments revealed that nitrogen requirements
of two key taxa were opposite to nitrate optima defined in the transfer function. Our data set reveals two underlying ecological
constraints that impede the development of nitrate transfer functions in oligotrophic lakes: (1) even in lakes with nitrate
concentrations below quantification (<1 μg L−1), diatom assemblages were already dominated by species indicative of moderate N enrichment; (2) N-limited oligotrophic lakes
switch to P limitation after receiving only modest inputs of reactive N, shifting the controls on diatom species changes along
the length of the nitrate gradient. These constraints suggest that quantitative inferences of nitrate from diatom assemblages
will likely require experimental approaches. 相似文献
16.
The analysis of chironomid taxa and environmental datasets from 46 New Zealand lakes identified temperature (February mean air temperature) and lake production (chlorophyll a (Chl a)) as the main drivers of chironomid distribution. Temperature was the strongest driver of chironomid distribution and consequently produced the most robust inference models. We present two possible temperature transfer functions from this dataset. The most robust model (weighted averaging-partial least squares (WA-PLS), n = 36) was based on a dataset with the most productive (Chl a > 10 μg l−1) lakes removed. This model produced a coefficient of determination () of 0.77, and a root mean squared error of prediction (RMSEPjack) of 1.31°C. The Chl a transfer function (partial least squares (PLS), n = 37) was far less reliable, with an of 0.49 and an RMSEPjack of 0.46 Log10μg l−1. Both of these transfer functions could be improved by a revision of the taxonomy for the New Zealand chironomid taxa, particularly the genus Chironomus. The Chironomus morphotype was common in high altitude, cool, oligotrophic lakes and lowland, warm, eutrophic lakes. This could reflect the widespread distribution of one eurythermic species, or the collective distribution of a number of different Chironomus species with more limited tolerances. The Chl a transfer function could also be improved by inputting mean Chl a values into the inference model rather than the spot measurements that were available for this study. 相似文献
17.
Georg Schettler Jens Mingram Jörg F. W. Negendank Liu Jiaqi 《Journal of Paleolimnology》2006,35(2):271-288
Palaeovariations of the atmospheric 210Pb flux in Northeast China (Long Gang area, Jilin province), quantified by high resolution 210Pb measurements on seasonally laminated sediments of Lake Sihailongwan are presented on decadal scale. The mean flux of unsupported
210Pb between 1790 and 1970 for the centre of the lake basin is 517 Bq m−2 yr−1 with maximum deviations between −23% and +27% of this value. Flux rates above this average were found between 1783 and 1813,
around 1836, and between 1860 and 1901. The mean 210Pbexc flux rates derived were clearly lower around 1821, 1908, 1930, and 1953. The 210Pbexc flux reached its minimum of 344 Bq m−2 yr−1 during the period 1977–1982. The atmospheric flux of unsupported 210Pb is correlated with the precipitation frequency during the summer monsoon and shows coinciding variability with geochemical
proxies that document the groundwater inflow into the lake. Al2O3-rich dust of remote provenance scavenged by wet-deposition in the rainy season is the major carrier of the atmospheric 210Pbexc flux. 相似文献
18.
Alexandra Rouillard Peter Rosén Marianne S. V. Douglas Reinhard Pienitz John P. Smol 《Journal of Paleolimnology》2011,46(2):187-202
We developed an inference model to infer dissolved organic carbon (DOC) in lakewater from lake sediments using visible-near-infrared
spectroscopy (VNIRS). The inference model used surface sediment samples collected from 160 Arctic Canada lakes, covering broad
latitudinal (60–83°N), longitudinal (71–138°W) and environmental gradients, with a DOC range of 0.6–39.6 mg L−1. The model was applied to Holocene lake sediment cores from Sweden and Canada and our inferences are compared to results
from previous multiproxy paleolimnological investigations at these two sites. The inferred Swedish and Canadian DOC profiles
are compared, respectively, to inferences from a Swedish-based VNIRS-total organic carbon (TOC) model and a Canadian-based
diatom-inferred (Di-DOC) model from the same sediment records. The 5-component Partial Least Squares (PLS) model yields a
cross-validated (CV) RCV2 R_{CV}^{2} = 0.61 and a root mean squared error of prediction (RMSEP
CV
) = 4.4 mg L−1 (11% of DOC gradient). The trends inferred for the two lakes were remarkably similar to the VNIRS-TOC and the Di-DOC inferred
profiles and consistent with the other paleolimnological proxies, although absolute values differed. Differences in the calibration
set gradients and lack of analogous VNIRS signatures in the modern datasets may explain this discrepancy. Our results corroborate
previous geographically independent studies on the potential of using VNIRS to reconstruct past trends in lakewater DOC concentrations
rapidly. 相似文献
19.
Modern assessment and monitoring of aquatic ecosystems is increasingly based on biota and the “reference condition” approach,
in which the observed values (O) of biological variables are compared to those expected in the absence of human disturbance (E). To use this approach, correct estimation and validation of reference conditions are critical. Because appropriate modern
or historical data are never available for this approach, palaeolimnological data offer an alternative. We used a calibration
data set from 73 profundal sites in semi-pristine Finnish lakes to construct a regression model for estimating expected values
for the chironomid Benthic Quality Index (BQI)—a macroinvertebrate metric widely used in bioassessment—from environmental
variables that are insensitive to human disturbance. For comparison, reference values were estimated using the European legislative
rationale based on a priori lake typology. Performance of the alternative approaches was assessed by internal ‘leave-one-out’
cross-validation using the calibration set and by external cross-validation using independent palaeolimnological data on BQI
values representing the historical pristine status of 24 lake basins. Additionally, for 19 of these sites, which vary in their
degree of human impact, the ratio of present BQI to that in pristine condition, which shows the degree of actual change, if
any, was calculated from palaeolimnological data and compared with the O/E ratios based on the present chironomid data and estimated E. A linear regression model with mean depth and mean/maximum depth ratio as independent variables estimated the reference
values of BQI much closer to the observed ones (r
2 = 0.58, RMSEP = 0.65 and r
2 = 0.71 RMSEP = 0.55; for internal and external cross-validation, respectively) than did the typology approach (r
2 = 0.28, RMSEP = 0.86; r
2 = 0.10, RMSEP = 0.97). The regression approach also yielded O/E ratios more similar to the actual ones (r
2 = 0.79, RMSEP = 0.09) than did the typology approach (r
2 = 0.62, RMSEP = 0.23). Our results strongly support the use of lake morphometric variables and modelling instead of categorical
lake typology for the establishment of reference conditions for profundal macroinvertebrate communities and demonstrate the
utility of palaeolimnological data in the validation of reference values and assessment methods. 相似文献
20.
Ulrike Herzschuh Steffen Mischke Hanno Meyer Birgit Plessen Chengjun Zhang 《Journal of Paleolimnology》2010,43(4):739-750
The apparent isotope enrichment factor εmacrophyte of submerged plants (εmacrophyte–DIC = δ13Cmacrophyte − δ13CDIC) is indicative of dissolved inorganic carbon (DIC) supply in neutral to alkaline waters and is related to variations in aquatic
productivity (Papadimitriou et al. in Limnol Oceanogr 50:1084–1095, 2005). This paper aims to evaluate the usage of εmacrophyte inferred from isotopic analyses of submerged plant fossils in addition to analyses of lake carbonate as a palaeolimnological
proxy for former HCO3
− concentrations. Stable carbon isotopic analysis of modern Potamogeton pectinatus leaves and its host water DIC from the Tibetan Plateau and Central Yakutia (Russia) yielded values between −23.3 and +0.4‰
and between +14.0 and +6.5‰, respectively. Values of ε
Potamogeton–DIC (range −15.4 to +1.1‰) from these lakes are significantly correlated with host water HCO3
− concentration (range 78–2,200 mg/l) (r = −0.86; P < 0.001), thus allowing for the development of a transfer function. Palaeo-ε
Potamogeton–ostracods values from Luanhaizi Lake on the NE Tibetan Plateau, as inferred from the stable carbon isotope measurement of fossil Potamogeton pectinatus seeds (range −24 to +2.8‰) and ostracods (range −7.8 to +7.5%) range between −14.8 and 1.6‰. Phases of assumed disequilibrium
between δ13CDIC and δ13Costracods known to occur in charophyte swards (as indicated by the deposition of charophyte fossils) were excluded from the analysis
of palaeo-ε. The application of the ε
Potamogeton–DIC-HCO3
− transfer function yielded a median palaeo-HCO3
− -concentration of 290 mg/l. Variations in the dissolved organic carbon supply compare well with aquatic plant productivity
changes and lake level variability as inferred from a multiproxy study of the same record including analyses of plant macrofossils,
ostracods, carbonate and organic content. 相似文献