ABSTRACT: Sacrower See is a eutrophic lake with annually laminated sediments extending back to A.D. 1868. Analysis of annual layers
revealed multi-decadal periods of distinct diatom assemblages at A.D. 1868–1875, 1876–1940, 1941–1978, and 1979–2000. Detrended
correspondence analysis performed on individual seasonal sediment layers showed decadal-scale patterns of turnover in the
diatom flora. The spring–summer layers showed higher sample scores until the early 1960s, after which the differences with
the autumn–winter layers became smaller. Rates-of-change analysis revealed that the seasonal variability in diatom assemblages
was higher than the annual changes. Summer diatom rates of change over the period A.D. 1894–1960 was on average higher than
for winter, whereas between the 1960s and 1970s the winter rates of change became higher than the summer ones. Redundancy
Analyses showed that seasonal temperatures and wind strength were significant explanatory variables for diatom assemblages
in both annual and seasonal layers. These results suggest that meteorological changes indirectly affected diatom assemblages
via the mixing regime of the lake. A comparison of the diatom rates of change with the amplitude of inter-annual climate change
shows a statistically significant correlation for the spring-summer layers in the period of A.D. 1963–2000, showing that the
sensitivity of diatom assemblages to meteorological changes has varied over the past century, with a stronger effect on diatoms
registered during the past 40years.
KeywordsAnnually laminated sediments–Varves–Diatoms–Climate
Aquatic Sciences 04/2012; 73(2):201-210. · 2.11 Impact Factor
ABSTRACT: The distribution of benthic invertebrates and their subfossil remains was examined within the basin of De Waay, a dimictic,
eutrophic lake in the Netherlands. We focused on Chironomidae, but also report the abundances of 11 invertebrate groups that
potentially produce chitinous remains that are preserved in the fossil record, although their remains could only be identified
at a coarser taxonomic resolution. Most living invertebrates sampled in different seasons were constrained to the littoral
zone, with the exception of a few taxa (Ceratopogonidae, Chaoborus flavicans, and Chironomus) that are adapted to low oxygen conditions in the seasonally anoxic profundal zone. In contrast, assemblages of invertebrate
remains in lake surface sediments were similar in the entire lake basin, suggesting that considerable numbers of invertebrate
remains are transported and redeposited off-shore in Lake De Waay, due to its steep bathymetry. These results indicate that
a single sediment sample obtained from the centre of this lake contains subfossil invertebrate remains originating from the
entire lake basin. In Lake De Waay, the majority of taxa found in the living assemblages were identified as remains in lake
surface sediments, at least for the Chironomidae that could be identified at a similar taxonomic level in living and subfossil
assemblages. Of the total 44 chironomid taxa found in Lake De Waay, 35 taxa occurred in the living assemblages and 34 taxa
occurred in the subfossil assemblages. Thirty chironomid taxa occurred both as living and subfossil specimens, and on average
these 30 taxa represent 94% of the specimens encountered in a sediment sample. Five rare chironomid taxa present as living
larvae were not detected in the subfossil assemblages. Conversely, eight rare and four common chironomid taxa were found in
subfossil remains, but not in living assemblages. Our results indicate that subfossil assemblages in surface sediment samples
provide spatially integrated and representative samples of the living assemblage. However, a combined approach examining both
the living benthic invertebrate fauna and invertebrate remains in lake surface sediments will potentially give a more complete
and detailed overview of benthic invertebrates in a lake ecosystem than an approach based exclusively on one of these groups.
Aquatic Sciences 04/2012; 73(2):247-259. · 2.11 Impact Factor
ABSTRACT: We studied the trophic development of the past 30–100years in eight moderately deep Dutch lakes based on their sedimentary
fossil diatom assemblages. The dominant diatoms indicating meso- to eutrophic conditions were Aulacoseira subarctica, Cyclotella ocellata, C. cyclopuncta, C. meneghiniana, Puncticulata bodanica, Aulacoseira granulata, Cyclostephanos dubius, C. invisitatus, Stephanodiscus hantzschii, S. medius, and S. parvus. Ordination of diatom data separated the lakes into four groups according to their total phosphorus concentrations (TP),
water supply, water management, and origin. The first group consists of dike-breach lakes, which were in stable eutrophic
to hypertrophic conditions throughout the past century with diatom-inferred TP (DI-TP) concentrations of between 70 and 300μgl−1. The main factors influencing these dike-breach lakes are river management, ground water supply of riverine origin, and local
land use. The second group are artificial lakes of fluctuating oligo- to mesotrophic conditions and DI-TP concentrations of
10–30μgl−1. Only one of the artificial lakes showed a DI-TP increase due to changes in catchment agricultural practice. A third group
includes an artificial moat and an inland dike-breach lake with DI-TP concentrations of 50–100μgl−1. The fourth group contains an individual dike-breach lake with stable mesotrophic conditions of 50μgl−1 throughout the past century. Rather than showing a regional pattern, the studied lakes behave very individualistically with
regard to their trophic history, reflecting changes in the local hydrology and in their nutrient sources.
Hydrobiologia 04/2012; 637(1):157-171. · 1.78 Impact Factor
ABSTRACT: 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 (≥1h) 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.
KeywordsFossil chironomids-Stable oxygen isotope composition-Pyrolysis-GC/MS-TC-EA/IRMS-Chitin-Insect cuticle
Journal of Paleolimnology 04/2012; 43(4):857-872. · 1.90 Impact Factor
Quaternary Science Reviews 01/2012; 33:87-99. · 3.97 Impact Factor
Quaternary Science Reviews 01/2012; 36:50-58. · 3.97 Impact Factor
ABSTRACT: Summary1. Methanogenic carbon can be incorporated by methane-oxidising bacteria, leading to a 13C-depleted stable carbon isotopic composition (δ13C) of chironomids that feed on these microorganisms. This has been shown for the chironomid tribe Chironomini, but very little information is available about the δ13C of other abundant chironomid groups and the relationship between chironomid δ13C and methane production in lakes.2. Methane flux was measured at the water surface of seven lakes in Sweden. Furthermore, fluxes from the sediments to the water column were measured in transects in two of the lakes. Methane fluxes were then compared with δ13C of chitinous chironomid remains isolated from the lake surface sediments. Several different chironomid groups were examined (Chironomini, Orthocladiinae, Tanypodinae and Tanytarsini).3. Remains of Orthocladiinae in the seven study lakes had the highest δ13C values (−31.3 to −27.0‰), most likely reflecting δ13C of algae and other plant-derived organic matter. Remains of Chironomini and Tanypodinae had lower δ13C values (−33.2 to −27.6‰ and −33.6 to −28.0‰, respectively). A significant negative correlation was observed between methane fluxes at the lake surface and δ13C of Chironomini (r = −0.90, P = 0.006). Methane release from the sediments was also negatively correlated with δ13C of Chironomini (r = −0.67, P = 0.025) in the transect samples obtained from two of the lakes. The remains of other chironomid taxa were only weakly or not correlated with methane fluxes measured in our study lakes (P > 0.05).4. Selective incorporation of methane-derived carbon can explain the observed correlations between methane fluxes and δ13C values of Chironomini. Remains of this group might therefore have the potential to provide information about past changes in methane availability in lakes using sediment records. However, differences in productivity, algal δ13C composition and the importance of allochthonous organic matter input between the studied lakes may also have influenced Chironomini δ13C. More detailed studies with a higher number of analysed samples and detailed measurement of δ13C of different ecosystem components (e.g. methane, dissolved inorganic carbon) will be necessary to further resolve the relative contribution of different carbon sources to δ13C of chironomid remains.
Freshwater Biology 12/2011; 57(1):166 - 177. · 3.29 Impact Factor
ABSTRACT: A pollen-inferred vegetation shift, from pioneer birch–pine woodland to mixed pine–summergreen oak forests, in the southern Alpine forelands, is commonly attributed to a centennial-scale warming that occurred between the Gerzensee Oscillation (GO) and the Younger Dryas. Two microtephra layers bracketing the Younger Dryas onset (the Laacher See Tephra and the Vedde Ash) improve the chronology at Lago Piccolo di Avigliana (northern Italy) and allowed accurate correlation with Central European records where the GO is clearly detected. We used pollen percentages, pollen accumulation rates (PARs) and plant macrofossils to assess the population dynamics of Quercus, and leaf-cuticle analysis for a better taxonomic identification of Quercus. Our results indicate that the species that was locally present was probably Quercus robur. PARs suggest that the population expansion started as early as the Bølling and followed an exponential increase through time. We attribute this gradual shift to increasing summer temperatures and longer growing seasons which contrast with a gradually decreasing temperature trend as recorded in Greenland ice cores and in Central Europe. Breaks or set-backs in the PAR record may indicate the biotic response to minor Lateglacial cooling events of different life-history stages in the Quercus population. Copyright © 2011 John Wiley & Sons, Ltd.
Journal of Quaternary Science 09/2011; 26(7):694 - 702. · 2.31 Impact Factor
ABSTRACT: Summary1. The distributions of subfossil remains of chironomid larvae in 28 large, deep and stratified lakes in Europe were examined in surface sediments along a latitudinal transect ranging from northern Sweden to southern Italy.2. Canonical correspondence analysis (CCA) showed that summer surface water and July air temperature, as well as total phosphorus (TP) concentrations, hypolimnetic oxygen availability and conductivity were statistically significant (P < 0.05) explanatory variables explaining between 11 and 14% of the variance in the chironomid data.3. Owing to the spatial scale covered by our study, many environmental variables were covarying. Temperature, TP concentration and oxygen availability were positively or negatively correlated with the first axis of a detrended correspondence analysis (DCA) of chironomid assemblages, suggesting that climatic and trophic conditions influenced profundal chironomid assemblages either in a direct (food and oxygen) or in an indirect (temperature) way. Parameters related to local environmental conditions, lake morphology and bedrock geology, such as organic matter content of the sediment, maximum lake depth, Secchi depth and pH, were not significant in explaining the distribution of chironomid assemblages in our study lakes.4. The strong relationship between chironomid assemblages and summer temperature may be related to the covariation of temperature with parameters, such as nutrient and oxygen availability, known to affect chironomid assemblages in deep, stratified lakes. However, summer temperature explained a statistically significant proportion of the variance in the chironomid assemblages even when effects of oxygen availability and TP concentrations were partialled out. This suggests that summer temperature has an effect on chironomid assemblages in deep lakes, which is not related to its covariation with trophic state.5. The potential of fossil chironomid analysis for quantitatively reconstructing past nutrient conditions in deep, stratified lakes was examined by calculating the Benthic Quality Index (BQI) based on subfossil chironomids and by comparing BQI values with observed TP concentrations. BQI was linearly related to log-transformed TP. Applying this relationship to fossil chironomid assemblages from Lake Päijänne (Finland) produced a TP reconstruction in agreement with measured TP during the period 1970–1990, demonstrating that this approach can provide quantitative estimates of past nutrient concentrations in deep, stratified lakes.
Freshwater Biology 02/2011; 56(3):407 - 423. · 3.29 Impact Factor
Limnlogy and Oceanography. 01/2011; 56:2071–2079.
Aquatic Sciences. 01/2011; 73:247-259.
Freshwater Biology. 01/2011; doi:10.1111/j.1365-2427.2011.02710.x.
ABSTRACT: To unravel the short-term climate variability dur-ing Marine Isotope Stage (MIS) 11, which represents a close analogue to the Holocene with regard to orbital bound-ary conditions, we performed microfacies and time series analyses on a ∼3200-yr-long record of annually laminated Holsteinian lake sediments from Dethlingen, northern Ger-many. These biogenic varves comprise two sub-layers: a light sub-layer, which is controlled by spring/summer diatom blooms, and a dark sub-layer consisting mainly of amor-phous organic matter and fragmented diatom frustules de-posited during autumn/winter. Time series analyses were performed on the thickness of the light and dark sub-layers. Signals exceeding the 95 % and 99 % confidence levels occur at periods that are near-identical to those known from mod-ern instrumental data and Holocene palaeoclimatic records. Spectral peaks at periods of 90, 25, and 10.5 yr are likely associated with the 88-, 22-and 11-yr solar cycles, respec-tively. This variability is mainly expressed in the light sub-layer spectra, suggesting solar influence on the palaeopro-ductivity of the lake. Significant signals at periods between 3 and 5 yr and at ∼6 yr are strongest expressed in the dark sub-layer spectra and may reflect an influence of the El Niño-Correspondence to: A. Koutsodendris (email@example.com) Southern Oscillation (ENSO) and the North Atlantic Oscil-lation (NAO) during autumn/winter. Our results suggest that solar forcing and ENSO/NAO-like variability influenced cen-tral European climate during MIS 11 similarly to the present interglacial, thus demonstrating the comparability of the two interglacial periods at sub-decadal to decadal timescales.
Climate of the Past 01/2011; 7:987-999. · 3.51 Impact Factor
ABSTRACT: A pollen-inferred vegetation shift from boreal Betula/Pinus forests to mixed Pinus/summergreen Quercus forests in the southern Alpine forelands is commonly attributed to a centennial-scale prominent warming that occurred in the Alpine region between the Gerzensee Oscillations (GO) and the Younger Dryas. Two microtephra layers bracketing the Younger Dryas onset (the Laacher See Tephra and the Vedde Ash)
Journal of Quaternary Science 01/2011; 26:694-702. doi: 10.1002/jqs.1493. · 2.31 Impact Factor
Quaternary Science Reviews. 01/2010; 29:2271-2279.
Journal of Paleolimnology. 01/2010; 43:857–872.
ABSTRACT: Enormous quantities of the free-floating freshwater fern Azolla grew and reproduced in situ in the Arctic Ocean during the middle Eocene, as was demonstrated by microscopic analysis of microlaminated sediments recovered from the Lomonosov Ridge during Integrated Ocean Drilling Program (IODP) Expedition 302. The timing of the Azolla phase (approximately 48.5 Ma) coincides with the earliest signs of onset of the transition from a greenhouse towards the modern icehouse Earth. The sustained growth of Azolla, currently ranking among the fastest growing plants on Earth, in a major anoxic oceanic basin may have contributed to decreasing atmospheric pCO2 levels via burial of Azolla-derived organic matter. The consequences of these enormous Azolla blooms for regional and global nutrient and carbon cycles are still largely unknown. Cultivation experiments have been set up to investigate the influence of elevated pCO2 on Azolla growth, showing a marked increase in Azolla productivity under elevated (760 and 1910 ppm) pCO2 conditions. The combined results of organic carbon, sulphur, nitrogen content and 15N and 13C measurements of sediments from the Azolla interval illustrate the potential contribution of nitrogen fixation in a euxinic stratified Eocene Arctic. Flux calculations were used to quantitatively reconstruct the potential storage of carbon (0.9-3.5 10(18) gC) in the Arctic during the Azolla interval. It is estimated that storing 0.9 10(18) to 3.5 10(18) g carbon would result in a 55 to 470 ppm drawdown of pCO2 under Eocene conditions, indicating that the Arctic Azolla blooms may have had a significant effect on global atmospheric pCO2 levels through enhanced burial of organic matter.
Geobiology 04/2009; 7(2):155-70. · 4.11 Impact Factor
ABSTRACT: Nutrient enrichment and the ecology of surface waters have been
intensively studied in lowland regions. However, detailed
palaeolimnological reconstructions of the trophic and flooding history
of floodplain lakes are still rare. In the Netherlands dike-breaches
caused by high floods of the river Rhine formed a new type of lake since
the Middle Ages. These dike-breach lakes were strongly impacted by the
development of channel systems in their catchment, agriculture, and
repeated flooding events. Here we present a multiproxy
palaeolimnological study of past nutrient loading and ecology of the
dike-breach lake De Waay which is located on the Rhine-Meuse delta (The
Netherlands). The lake was created in A.D. 1496 as a result of damage
done to a dike by floating ice and the subsequent dike-breach due to a
flooding event. A sediment core of 11.5 m was recovered from Lake De
Waay and diatoms, Cladocera, and geochemistry were analyzed in the
sediment. From the beginning of the lake's existence to the end of the
18th century diatom-inferred total phosphorus (TP) concentrations were
above 300 µg/l, suggesting hypertrophic conditions. Cladoceran
assemblages reflect the lake's pioneer stage and suggest a lack of
rooted aquatic macrophytes resulting from low water-transparency,
possibly caused by frequent floods. Until the late 18th century floods
occurred regularly in the area, as shown by the elevated Ti values in
the sediments, indicative of high erosion from the floodplain and runoff
from the surrounding agricultural catchment. This caused the
exceptionally high sedimentation rates and elevated nutrient contents of
the lake waters. Since the beginning of the 19th century sewage input
and flooding frequency were strongly reduced by the construction of new
ditches, canals, and dikes. The improved sewage and dike systems are
reflected by decreased TP concentrations of 40-150 µg/l. The
increased stability of littoral habitats led to an increased diversity
in the Cladocera assemblages. The phase with the lowest inferred TP
concentrations lasted from the end of the 19th to the mid-20th century.
During this period direct nutrient sources were no longer connected to
the lake and TP concentrations consequently decreased to 40 µg/l.
Dike construction was highly developed and flooding events no longer
affected this region. However, a renewed eutrophication with TP values
reaching 100 µg/l was registered in the sediment record since the
mid-20th century. The increased TP concentrations are most likely
related to increased agricultural activity in the vicinity of the lake.
Our results show that Lake De Waay was eutrophic to hypertrophic during
much of its history. The lake was formed as a consequence of human
activity and never existed in an undisturbed state. Restoration of lakes
to an "undisturbed" natural state, as required by the European Water
Framework Directive, can therefore not be recommended for strongly
modified lowland lakes such as De Waay.