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1.
All the chironomid head capsules in a sediment sample are normally extracted to determine the concentration of chironomids.
This method may be tedious since a sample may contain hundreds of head capsules. We have tested a method to estimate the concentration
of chironomids in sub-samples and assessed the potential taxonomic bias generated when only a part of each sediment sample
is sorted. To allow calculation of concentrations, a known quantity of exotic markers (microspheres with diameter 149–350 μm)
was added to the sample. The number of head capsules in the total sample was estimated according to the ratio between the
retrieved numbers of microspheres to head capsules in the sub-sample. According to our results, the chironomid concentrations
estimated from sub-samples were statistically similar to the concentrations obtained by processing the full sample. Also,
a sub-sample containing at least 75 head capsules was likely to have similar taxa abundances and taxa richness as the full
sediment sample. These results indicate that exotic markers may be added to chironomid samples for representative concentration
estimation. The method may potentially be used for other biological groups than chironomids. 相似文献
2.
Maarten van Hardenbroek Oliver Heiri Jonathan Grey Paul L. E. Bodelier Frederike Verbruggen André F. Lotter 《Journal of Paleolimnology》2010,43(2):235-245
We used a series of experiments to determine whether stable carbon isotope analysis of modern and fossil larval head capsules
of chironomids allowed identification of their dietary carbon source. Our main focus was to assess whether carbon from naturally
13C-depleted methane-oxidizing bacteria (MOB) can be traced in chironomid cuticles using stable carbon isotope analysis. We
first showed that a minimum sample weight of ~20 μg was required for our equipment to determine head capsule δ13C with a standard deviation of 0.5‰. Such a small minimum sample weight allows taxon-specific δ13C analyses at a precision sufficient to differentiate whether head capsules consist mainly of carbon derived from MOB or from
other food sources commonly encountered in lake ecosystems. We then tested the effect of different chemical pre-treatments
that are commonly used for sediment processing on δ13C measurements on head capsules. Processing with 10% KOH (2 h), 10% HCl (2 h), or 40% HF (18 h) showed no detectable effect
on δ13C, whereas a combination of boiling, accelerated solvent extraction and heavy chemical oxidation resulted in a small (0.2‰)
but statistically significant decrease in δ13C values. Using culturing experiments with MOB grown on 13C-labelled methane, we demonstrated that methanogenic carbon is transferred not only into the larval tissue, but also into
chironomid head capsules. Taxon-specific δ13C of fossil chironomid head capsules from different lake sediments was analyzed. δ13C of head capsules generally ranged from −28 to −25.8‰, but in some instances we observed δ13C values as low as −36.9 to −31.5‰, suggesting that carbon from MOB is traceable in fossil and subfossil chironomid remains.
We demonstrate that stable carbon isotope analyses of fossil chironomid head capsules can give insights into dietary links
and carbon cycling in benthic food webs in the past and that the method has the potential to reconstruct the importance of
MOB in the palaeo-diet of chironomid larvae and, indirectly, to infer past changes in methane flux at the sediment water interface
in lakes. 相似文献
3.
Sieving samples for chironomid analysis with a 150 μm mesh was shown to greatly reduce sample preparation time, and use of
only larger specimens did not affect chironomid-inferred salinities in African lakes. Here, we tested if this method is suitable
for temperature reconstruction in colder lakes at higher latitudes. Removal of specimens <150 μm in two training sets, one
from Canada and one from Sweden, had little impact on the performance statistics of the calibration models. Chironomid abundance,
however, decreased greatly because more than half of the head capsules in assemblages were <150 μm. This had major impacts
on the temperature reconstructions. Inferences were on average 2°C warmer with the modified models (all specimens >150 μm)
than those obtained with the full model (all specimens >100 μm). General patterns of temperature change were also altered.
For Lake 7 on Southampton Island, Canada, a cooling trend was reconstructed with the full Canadian model while the modified
Canadian model yielded a warming trend. When only specimens >150 μm were used, two to three times more wet sediment was needed
to obtain a sufficient number of head capsules. These results indicate that, in cold lakes (mean July/August air temperature
≤11°C), large proportions of head capsules are <150 μm, and sieving the samples in a 150 μm mesh leads to altered temperature
reconstructions. 相似文献
4.
Cotton blue was added to sediment samples at least 2 h before chironomid head capsules were picked under a binocular microscope
and mounted on slides for identification. The use of stain greatly increased the visibility of chironomid head capsules during
picking and enhanced the contrast of various parts of the head capsules (pores, ventromental plates, striations on ventromental
plates), which could aid identification. In the seven samples studied, there was no significant difference between the percentages
of taxa found in stained and unstained samples. The number of taxa were also similar in stained and unstained samples. This
method allowed samples to be picked faster. 相似文献
5.
Several techniques are available to examine the isotopic composition of historic lake waters, providing data that can subsequently
be used to examine environmental changes. A recently-developed technique is the stable oxygen isotope analysis of subfossil
chironomid (Diptera: Chironomidae) head capsules (mostly chitin) preserved in lake sediments. This technique involves a high
Temperature Conversion Elemental Analyzer (TC/EA), which has been a relatively recent addition to the suite of online peripherals
for analyzing the stable isotopic composition of organic samples. The highly precise and accurate 18O/16O and D/H measurements obtainable using the TC/EA with samples in the microgram range make this instrumentation suitable for
studying geochemical and biological processes. Preparation of organic samples for isotopic analysis typically requires first
weighing each sample into silver/tin capsules. These capsules can introduce oxygen and hydrogen contamination (a “blank effect”),
which is especially problematic for analysis of small organic samples (e.g. less than 100 μg). Here we tested tin and silver
capsules from two manufacturers and a range of sizes to assess contamination to small organic samples on the TC/EA. We also
assessed how a method for cleaning silver capsules affected our analysis of commercial chitin. In general, capsules made of
silver have less detectible oxygen than those made of tin, and capsules from the two manufacturers varied in their detectible
oxygen. There was no detectable H contamination from silver capsules. In addition to our empirical findings, we present a
model demonstrating the influence that contaminant oxygen can have on the δ18O of small organic samples. Sample mass becomes an important issue for such analyses. In light of our findings, we recommend
a minimum sample mass ≥50 μg (approximately 120 whole chironomid head capsules) on a TC/EA-IRMS (Deltaplus XP system). Finally, we present a detailed protocol for preparing and transferring chironomid head capsules into silver capsules
that minimizes the influence of contaminant oxygen. This protocol provides the paleo-community with another potential method
for reconstructing paleoenvironments. 相似文献
6.
Barbara Lang Alan P. Bedford Nigel Richardson Stephen J. Brooks 《Journal of Paleolimnology》2003,30(4):451-460
Initial investigations of Holocene carbonate sediment from Hawes Water, Northwest England, yielded lower numbers of chironomid head capsules than anticipated. Standard techniques used to prepare sediment for chironomid analysis were ineffective in breaking up the coarse crystalline sediment structure sufficiently. This led to large amounts of sediment being retained and increased sample processing times. The low yield of head capsules also meant that more sediment was needed to produce adequate numbers of head capsules for analysis. The use of ultra-sound as part of the sediment processing was investigated. This technique reduced the amount of sediment left for sorting and yielded significantly more head capsules which were of equivalent structural condition and cleaner than those produced by conventional methods. The technique was extended to clay samples where similar results were obtained although shorter treatment times are recommended. The proportion of Tanytarsini and Tanypodinae heads increased significantly in carbonate and clay samples, respectively; both sediment types showed a significant decline in the proportion of Chironomini. The results indicate that ultra-sonic preparation of samples will yield a more accurate representation of chironomid assemblages in sediments leading to greater sensitivity and reliability in analysing past environmental conditions. 相似文献
7.
F. Verbruggen O. Heiri G.-J. Reichart J. W. De Leeuw K. G. J. Nierop A. F. Lotter 《Journal of Paleolimnology》2010,43(4):857-872
Stable oxygen isotope measurements on fossil chironomid head capsules from lake sediments show that these chitinous remains
can be used to reconstruct past lake water δ18O and, indirectly, past climate change. We examined the impact of chemical pretreatment procedures on the chemical and stable
oxygen isotope composition, and morphology of chironomid cuticles. Use of alkali, acids, and sodium chlorite alters the chemical
composition and the morphological structure of chironomid cuticles by selective removal of chitin or proteins. Gas chromatograms
of pyrolyzates show that NaClO2 causes deproteination, whereas the combined use of HCl and HF results in partial chitin removal. Head capsules pretreated
with KOH contained both chitin- and protein-derived moieties, although the concentration of protein was reduced, especially
after KOH treatment at high concentration (28%) and temperature (100°C). Scanning electron microscopy confirmed that a proteinaceous
matrix is still present in modern and fossil head capsules after KOH treatment. This matrix, however, is largely absent in
head capsules pretreated with NaClO2. A change in the proportion of chitin and proteins in our samples was associated with differences in chironomid δ18O values. Our results suggest that deproteination results in a relative increase of chironomid δ18O, whereas removal of chitin leads to decreased δ18O values. We therefore discourage the use of acids or prolonged (≥1 h) exposure to hot alkali (70°C) prior to chironomid δ18O analysis. Chitin purification by sodium chlorite causes significant weight loss, which may preclude down-core chironomid
δ18O measurements. Caution and standardization are required when pretreating samples for chironomid δ18O analysis to ensure reliable, comparable, and reproducible results. 相似文献
8.
Short sediment cores from two gulfs, Monche Bay and Kunchast Bay, of Lake Imandra (Kola Peninsula, northern Russia) were analysed for sediment chemistry and chironomid head capsule remains. Monche Bay has been receiving metals from the Severonikel copper-nickel smelter since the late 1930's. Kunchast Bay was selected in the remotest lake basin as an internal reference site. There were no pronounced changes in the chironomid assemblages with the beginning of slight metal contamination of Kunchast Bay. Based on the reconstructed environmental variables and chironomid assemblages, three developmental stages were distinguished from the chironomid fauna history of Monche Bay: (1) A natural development stage; (2) the early warning stage; and (3) the developing crises stage. During the first period, the changes in the chironomid fauna reflect an anthropogenically undisturbed assemblage, with Micropsectra insignilobus dominating (17–23%). The changes during the second period reflect the initial phase of anthropogenic succession associated with the beginning of metal pollution. The main species showed opposite distributional patterns in this period: the abundance of M. insignilobus decreased, whereas the abundance of Chironomus, Procladius and Sergentia coracina increased. At the same time, maximal numbers were attained for species richness (45) and Shannon-Weaver diversity (4.85) of chironomid assemblages, and the highest head capsule concentration (75 head capsules · g–1 of dry sediment). The third period was characterized by a major shift in the faunal assemblages, from M. insignilobus to other dominant species, including Chironomus (22–44%), Procladius (10–30 %) and S. coracina (15–18%). Besides fauna changes, assemblages of the third period are distinguished by the occurrence of mouthpart deformities in Chironomus head capsules. 相似文献
9.
Tomi P. Luoto 《Journal of Paleolimnology》2012,47(1):141-157
Surface sediment samples from Lake Moaralmsee in the Austrian Alps were examined for fossil remains of aquatic insects and
mites. This study investigated the influence of water depth on the fauna, to explore the possibility of using such fossil
remains in sediment cores to reconstruct past water level changes. In addition, instar-specific patterns of chironomid (Diptera:
Chironomidae) head capsule accumulation were examined to evaluate whether the smaller, lighter-weight early instars are more
easily transported within the lake basin, creating a potential source of error for paleolimnological inferences. Results showed
that intra-lake distribution of these zoological remains is closely related to water depth and suggested that the fossils
accumulate near each species’ habitat. In addition, the ratio between exoskeletons of oribatid mites (Acari: Oribatida) and
chironomid head capsules was strongly related to water depth. Examination of instar-specific accumulation patterns of all
chironomid remains showed no significant relationship between specific instars and water depth, though littoral samples consisted
only of the 3rd and 4th instars. A taxon-specific examination revealed that the early instars of Paracladius are significantly focused to the deeper parts of the basin. Because most taxa displayed significant relations with water
depth, a transfer function was developed, relating fossil chironomids to water depth. This model has a high coefficient of
determination and a low estimate of prediction error. In this study, Paracladius was found to prefer shallow and intermediate water depths, hence enhanced offshore transport of early instar head capsules
may weaken model performance statistics. Results indicate that intra-lake calibration sets of invertebrate remains have great
potential in paleolimnological research, though there is a possible risk of spatial autocorrelation. Such datasets also contribute
to the understanding of the modern ecology of the fauna because fossil assemblages in surface deposits provide habitat-specific
autecological information. More effort should be directed at evaluating how remains of different instars are transported within
other lake basins, because selective offshore transport of head capsules of different larval stages can potentially cause
bias in environmental reconstructions. 相似文献
10.
A multiple stable isotope record of Late Quaternary limnological changes and chironomid paleoecology from northeastern Iceland 总被引:1,自引:0,他引:1
We present results from multiple stable isotope analyses (δ18O of chironomid larval head capsules, chironomid adult thoraxes and other insect remains and δD, δ13C, δ15N of total organic matter—TOM) of a lake sediment core (04-SVID-03) taken from Stora Vidarvatn in northeastern Iceland to
reconstruct past environmental, limnological and δ18O of past lake water changes during the Holocene. Core 04-SVID-03 represents a ∼12,000 cal. yrs BP to present record. Large
magnitude changes in δ18O occurred during the Holocene at the site. Downcore shifts in δ18O of chironomids did not correlate with measurements of the δ13C and δ15N of chironomid head capsules, implying that the δ18O changes were not primarily driven by changes in chironomid diet during the Holocene. The δD of TOM provided a proxy of relative
lake-water δD changes at the site and also showed large magnitude changes during the record. This approach was supported by
analyses of a modern training set where δDTOM analyses were conducted using surface sediments from a suite of freshwater lakes over a large latitudinal gradient. The magnitude
of changes in both the δ18O and δD and the relatively negative δ18O values throughout much of the core suggest that the proxies represent more paleoenvironmental information than solely temperature.
Additional possible influences on lake-water isotopic composition are discussed, including changes in the seasonality of precipitation,
in the patterns of air masses supplying precipitation to Iceland and in the dominant mode of the North Atlantic Oscillation. 相似文献
11.
Within-lake variability of subfossil chironomid assemblages in shallow Norwegian lakes 总被引:3,自引:5,他引:3
Oliver Heiri 《Journal of Paleolimnology》2004,32(1):67-84
Subfossil chironomids in the surface sediments of five small and shallow Norwegian lakes were studied to determine the within-lake variability of fossil assemblages, changes in chironomid assemblages with respect to water depth, and the representativeness of single samples for the entire chironomid fauna of a lake. In each of the lakes studied, six short sediment cores in the deepest part of the lake basin and two littoral to deep-water transects of seven cores each were obtained using a gravity corer, and chironomid assemblages in the uppermost centimetre of sediment were analysed. In three of the five lakes, chironomid concentrations were highest in the deepest parts of the lake basins. In the remaining two lakes, concentrations were either very variable or, in a lake with clear indications of anoxia in the bottom waters, highest at intermediate water depth. Chironomid assemblages tended to be dominated by the same taxa within a lake basin. However, in each of the lakes studied there was a clear and statistically significant shift in chironomid assemblages with respect to water depth. The organic content of the sediments was statistically significant in explaining the variance in the chironomid assemblages only in lakes where organic matter content was closely related to water depth. Only a few chironomid taxa were restricted to the shallowest parts of the lake basins, whereas a number of chironomids were found exclusively in deep-water sediments. Chironomid head capsules of running water taxa and simuliid remains were generally found in sediments close to lake tributaries and in the deepest parts of the lake basins. Although any individual sample contained only a part of the total subfossil chironomid fauna (21–63% of the total taxa per lake), chironomids dominant in any section of the study lakes were found in most of the transect and mid-lake samples. 相似文献
12.
Katherine Griffiths Neal Michelutti Jules M. Blais Lynda E. Kimpe John P. Smol 《Journal of Paleolimnology》2010,44(2):405-412
The mass transport of nutrients by migratory animals can markedly alter the biogeochemistry and ecology of recipient ecosystems,
particularly in nutrient-poor regions such as the Arctic. However, the role of biovectors in the global cycling of nutrients
is often overlooked. Here we investigate nitrogen dynamics in two seabird-affected ponds in the Canadian High Arctic. The
ponds lie at the base of a large seabird colony and have been greatly enriched in nutrients due to the input of guano and
other wastes. Using sediment cores that span the last ~200 years, we measured stable isotopes of nitrogen (δ15N) in bulk sediments as well from the subfossil remains of chironomid (Diptera) head capsules and Daphnia ephippia. The bulk-sediment samples from our seabird-affected ponds had elevated δ15N values relative to seabird-free sites elsewhere in the Arctic. In general, the chironomid δ15N profiles roughly paralleled those of bulk sediments in both study ponds, while the Daphnia profile remained relatively stable in contrast to the considerable variation recorded in the bulk sediments and chironomids.
Interestingly, no apparent pattern emerged among δ15N values recorded in the bulk sediments, chironomids, and Daphnia between the two study ponds. The stability recorded in the δ15N profiles from bulk sediments relative to the more variable invertebrate profiles point towards the complexity of nitrogen
uptake by chironomids and Daphnia at these sites. These data suggest that the bulk sediments are integrating the different fractions of the overall δ15N pool and thus may be most appropriate for reconstructing overall trends in lake trophic status. 相似文献
13.
A suite of surface sediment samples from three Icelandic lakes was analysed for subfossil chironomid head capsules, and a
quantitative July air temperature inference model was applied to the data to investigate whether there was significant variability
among samples taken from a lake. Ordination and simple regression methods were used to analyse the relationships between environmental
and sedimentological variables and the chironomid assemblages and inferred temperature data. Substrate was the most important
influence on the chironomid assemblages and inferred temperatures, while water depth at the sampling location had no relationship
with the chironomid-inferred temperatures. Within-lake variability of the chironomid assemblages and their inferred temperatures,
however, were not significant statistically, suggesting that in lakes of western and northwest Iceland within-lake sampling
location has no effect on the data obtained, and therefore on training set samples. 相似文献
14.
Spatial variability of chironomid death assemblages in the surface sediments of a fluctuating tropical lake (Lake Naivasha,Kenya) 总被引:1,自引:0,他引:1
Studies addressing within-lake variability of fossil chironomid assemblages are very few, and all deal with hydrologically
stable temperate lakes where the question of spatial integration mostly relates to the mixing of faunal assemblages associated
with shallow, warm-water habitat and those associated with deeper, cold-water habitat. Here we study within-lake variability
of surface-sediment chironomid assemblages in the fairly large (∼100–170 km2 since 1983) and shallow (Z
max = 5–8 m) fluctuating tropical lake basin of Lake Naivasha, Kenya, and compare the patterns observed with those in two smaller
adjacent basins, one similarly shallow (Lake Oloidien, 5.1–5.7 km2, 5–8 m), the other deep and stratified (Crescent Island
Crater, 1.9 km2, 14–17 m). Chironomid assemblages were analysed in core-top samples and surface sediments along inshore to offshore transects,
and how well individual samples represented the total (basin-wide mean) subfossil assemblage was considered both in terms
of taxon richness and taxon percent composition. Within-lake variability of subfossil chironomid concentrations (with generally
higher absolute values in nearshore samples) could be explained by effects of sediment winnowing and focusing, whereas between-lake
variability reflected their relative susceptibility to wind-driven sediment disturbance or bottom anoxia. In all study lakes,
but most significantly in lakes Naivasha and Oloidien, species distribution in the subfossil chironomid assemblages showed
a strong nearshore to offshore gradient, which in these shallow lakes, reflects the dominant control of substrate and food
quality on species distribution in the living community. Particularly in the larger basins, nearshore samples better represented
the total lake assemblage than offshore samples, because the former always contained a component of mud-dwelling species whereas
the latter often lacked a component of macrophyte-dwelling species. Our results show that although sedimentation dynamics
in the shallow, wind-stressed Lake Naivasha is dominated by frequent resuspension and random sediment redistribution, the
near- to offshore gradient in chironomid habitat remains imprinted on subfossil assemblages. We conclude that also in shallow
fluctuating lakes, given sufficient size, incomplete pre-burial spatial integration of habitat-specific chironomid assemblages
can be exploited for within-lake calibration of environmental gradients. 相似文献
15.
Testate amoebae are informative about palaeoecological conditions, but the methods generally used for their analyses in lake
sediments differ from those used for their analyses in peats, making comparisons difficult. This study examines how filter
mesh size and total number of individuals counted affect species richness, Shannon diversity, equitability, density and assemblage
structure. We analysed the complete testate amoeba contents of six sediment samples from Lake Lautrey, France. The abundance
of testate amoebae was high (1,403–10,870 shells cm−3), and species smaller than 63 μm in both length and width represented up to 89% of total abundance and 43% of species richness.
A simulation showed that using 47- or 63-μm mesh-size filters reduced inter-sample differences and changed the patterns of
abundance, species richness and assemblage structure, causing loss of information and leading to potential erroneous palaeoecological
interpretation. Rarefaction analyses suggest that although 170 shells are sufficient to assess the general structure of assemblages,
such small sample sizes can underestimate species richness by overlooking taxa with relative abundances <4%. Total counts
of 400 shells yield better estimates of assemblage structure and recover at least 50% of total species richness, although
species with absolute frequencies below 2% may still be missed. Higher counts are required to obtain reliable estimates of
species richness and assemblage structure in samples that have high testate amoeba densities but are dominated by a few small
taxa. Further studies should determine the bioindicator value and functional roles of small and/or rare species in lakes and
thus to what extent overlooking them affects palaeoecological interpretations. 相似文献
16.
We examined the effects of sieving with different mesh sizes on the efficiency of processing fossil chironomids from lake
sediments for isotope analyses. Results obtained for three different sediments indicate that each of the studied sieve fractions
(100–150, 150–200, 200–250, 250–300, >300 μm) contain a similar proportion of the overall mass of chironomid fossils in a
sample. However, the sorting time needed to separate chironomids from other sieve residue is disproportionately large for
smaller mesh sizes. Employing sieves with a 200-μm rather than the 100-μm mesh commonly used for standard palaeoecological
analyses of fossil chironomids decreased processing time for a given mass of fossils by 30–58% in our study. For optimizing
the efficiency of chironomid sample processing for stable isotope and radiocarbon analysis we therefore recommend a 200-μm
mesh size sieve, although the sorting of all >100-μm fractions may be necessary in sediments with low chironomid abundances.
Excluding certain small taxa from isotope analysis, may structurally bias isotope values of samples. Therefore, further studies
on taxon-specific isotope analysis are required to quantify these effects. 相似文献
17.
Random distributions for a wide range (1–100,000) of chironomid head capsules (HC) were simulated on a 1-m2 surface. The number of HC found in circular surfaces equivalent to standard core diameters (90 and 63 mm) was estimated 1000 times, over the range of tested densities. For each number of HC found in the samples, the range of simulated densities was estimated using a threshold probability (p > 0.95). This enabled us to develop equations to infer HC density from sample counts. Because of the threshold probability for comparable sample counts, the equations yield higher estimated densities under a random distribution than for a regular distribution. The probability of sampling at least one HC was >0.95 for densities of 900 HC m?2 for the 90-mm core and 1400 HC m?2 for the 63-mm core. For a specific sample count, the range of actual densities was ~10 times higher for the 63-mm core than the 90-mm core. Comparison with field larval densities revealed that most densities were too low to be suitable for annually resolved reconstruction of a quantitative signal, using current corer sizes, although a large number of populations can support sub-decadal analyses. Nonetheless, some lakes exhibit population sizes large enough to reconstruct robust quantitative estimates of past chironomid abundances. This work provides guidance to reconstruct species dynamics and fine-scale time series analyses in paleoecology. 相似文献
18.
Isabelle Larocque Martin Grosjean Oliver Heiri Christian Bigler Alex Blass 《Journal of Paleolimnology》2009,41(2):329-342
Inferred temperatures from chironomids preserved in the varved sediment of Lake Silvaplana in the Eastern Swiss Alps were
compared with instrumental data obtained from a meteorological station in Sils-Maria, on the shore of Lake Silvaplana, for
the time interval 1850–2001. At near-annual resolution, the general patterns of chironomid-inferred temperature changes followed
the meteorological record over the last ∼150 years (r
Pearson = 0.65, P = 0.01) and 87% of the inferences had deviations from the instrumental data below the root-mean-square error of prediction
(RMSEP). When the inferences were compared with a 2-year running mean in the meteorological data, 94% of the inferences had
differences with the instrumental data below the RMSEP, indicating that more than half of the inaccurate inferences may have
been due to errors in varve counting. Larger deviations from the instrumental data were also obtained from samples with low
percentages of fossil taxa represented in the training set used for temperature reconstruction and/or assemblages with poor
fit to temperature. Changes in total phosphorus (TP, as inferred by diatoms) and/or greater precipitation were possible factors
affecting the accuracy of the temperature reconstruction. Although these factors might affect the quantitative estimates,
obtaining >80% accurate temperature inferences suggests that chironomid analysis is a reliable tool for reconstructing mean
July air temperature quantitatively over the last ∼150 years in Lake Silvaplana. 相似文献
19.
Stephen J. Brooks Vivienne J. Jones Richard J. Telford Peter G. Appleby Emily Watson Suzanne McGowan Stuart Benn 《Journal of Paleolimnology》2012,47(4):631-644
Loch Ruthven holds the largest British population of the rare water-bird Podiceps auritus, the Slavonian or horned grebe. The breeding success of this bird has fluctuated annually since records began in 1970. To
investigate whether these trends are linked to the abundance of chironomid midges, which are an important food-source for
the grebe chicks, we analysed a sediment core from the lake, which was sliced at 2.5-mm intervals and provided near-annual
sampling resolution. We also analysed diatoms and algal pigments in the lake sediments and inferred changes in total phosphorus
from the diatom assemblage to determine whether changes in lake productivity have influenced the abundance of chironomids.
Trends in grebe productivity, chironomid abundance and algal assemblages were compared against climate data to determine whether
climate, specifically, the North Atlantic Oscillation, was the ultimate driver of the trends we recorded. Our results show
that grebe breeding success is positively correlated with chironomid abundance and chironomid abundance is positively correlated
with diatom-inferred total phosphorus. Lake productivity and chironomid abundance began to rise early in the twentieth century
and continued to rise on a steeper trajectory from the mid-twentieth century to the present. Since the mid-1960s, chironomid
abundance began to fluctuate erratically and since 1970 was in phase with grebe productivity, with the grebe trends most plausibly
lagging by 1 year. These trends appear to correlate with inter-annual fluctuations in diatom-inferred total phosphorus. No
correlation was found between grebe productivity or chironomid abundance and climate variables, suggesting that the size of
the chironomid population and breeding success of Podiceps auritus at Loch Ruthven is resource-linked. 相似文献
20.
Larisa Nazarova Ulrike Herzschuh Sebastian Wetterich Thomas Kumke Ludmila Pestryakova 《Journal of Paleolimnology》2011,45(1):57-71
We investigated the subfossil chironomid fauna of 150 lakes situated in Yakutia, northeastern Russia. The objective of this
study was to assess the relationship between chironomid assemblage composition and the environment and to develop chironomid
inference models for quantifying past regional climate and environmental changes in this poorly investigated area of northern
Russia. The environmental data and sediment samples for chironomid analysis were collected in 5 consecutive years, 2003–2007,
from several regions of Yakutia. The lakes spanned wide latitudinal and longitudinal ranges and were distributed through several
environmental zones (arctic tundra, typical tundra, steppe-tundra, boreal coniferous forest), but all were situated within
the zone of continuous permafrost. Mean July temperature (TJuly) varied from 3.4°C in the Laptev Sea region to 18.8°C in central Yakutia near Yakutsk. Water depth (WD) varied from 0.1 to
17.1 m. TJuly and WD were identified as the strongest predictor variables explaining the chironomid communitiy composition and distribution
of the taxa in our data set. Quantitative transfer functions were developed using two unimodal regression calibration techniques:
simple weighted averaging (WA) and weighted averaging partial least squares (WA-PLS). The two-component TJuly WA-PLS model had the best performance. It produced a strong coefficient of determination (r
2
boot = 0.87), root mean square error of prediction (RMSEP = 1.93), and max bias (max biasboot = 2.17). For WD, the one-component WA-PLS model had the best performance (r
2
boot = 0.62, RMSEP = 0.35, max biasboot = 0.47). 相似文献