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1.
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
2.
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
3.
Laurent Millet Charline Giguet-Covex Valérie Verneaux Jean-Claude Druart Thierry Adatte Fabien Arnaud 《Journal of Paleolimnology》2010,44(4):963-978
This paper presents the recent history of a large prealpine lake (Lake Bourget) using chironomids, diatoms and organic matter
analysis, and deals with the ability of paleolimnological approach to define an ecological reference state for the lake in
the sense of the European Framework Directive. The study at low resolution of subfossil chironomids in a 4-m-long core shows
the remarkable stability over the last 2.5 kyrs of the profundal community dominated by a Micropsectra-association until the beginning of the twentieth century, when oxyphilous taxa disappeared. Focusing on this key recent period,
a high resolution and multiproxy study of two short cores reveals a progressive evolution of the lake’s ecological state.
Until AD 1880, Lake Bourget showed low organic matter content in the deep sediments (TOC less than 1%) and a well-oxygenated
hypolimnion that allowed the development of a profundal oxyphilous chironomid fauna (Micropsectra-association). Diatom communities were characteristic of oligotrophic conditions. Around AD 1880, a slight increase in the
TOC was the first sign of changes in lake conditions. This was followed by a first limited decline in oligotrophic diatom
taxa and the disappearance of two oxyphilous chironomid taxa at the beginning of the twentieth century. The 1940s were a major
turning point in recent lake history. Diatom assemblages and accumulation of well preserved planktonic organic matter in the
sediment provide evidence of strong eutrophication. The absence of profundal chironomid communities reveals permanent hypolimnetic
anoxia. From AD 1995 to 2006, the diatom assemblages suggest a reduction in nutrients, and a return to mesotrophic conditions,
a result of improved wastewater management. However, no change in hypolimnion benthic conditions has been shown by either
the organic matter or the subfossil chironomid profundal community. Our results emphasize the relevance of the paleolimnological
approach for the assessment of reference conditions for modern lakes. Before AD 1900, the profundal Micropsectra-association and the Cyclotella dominated diatom community can be considered as the Lake Bourget reference community, which reflects the reference ecological
state of the lake. 相似文献
4.
Donna R. Francis 《Journal of Paleolimnology》1997,17(3):255-261
Statoblast valves produced by the freshwater bryozoan Plumatella nitens were recovered in three sediment cores from Douglas Lake, Michigan. Douglas Lake is a multi-depression lake of glacial origin. The region was heavily logged from 1880 to 1920. Sediment cores were taken from three of the seven depressions, and dated using 210Pb isotopes and pollen. Sedimentation rates were very low in the Grapevine Point core as compared to the other two cores. Concentrations of statoblasts ranged from three to 140 ml-1 of wet sediment. Profiles of statoblast concentrations and accumulation rates indicate a sharp decline in Plumatella populations corresponding to the time the Douglas Lake watershed was being clear-cut. It appears that logging and the resulting increase in erosion had adverse effects on bryozoan populations, and possibly on the entire littoral zone of the lake. High sediment loads to the lake could have caused mortality in Plumatella by interfering with the feeding of these animals, or by decreasing numbers of macrophytes which are frequently used as substrate. Populations of Plumatella have not recovered to pre-disturbance levels. 相似文献
5.
Victor Frossard Laurent Millet Valérie Verneaux Jean-Philippe Jenny Fabien Arnaud Michel Magny Jérôme Poulenard Marie-Elodie Perga 《Journal of Paleolimnology》2013,50(3):257-273
We sampled modern chironomids at multiple water depths in Lake Annecy, France, before reconstructing changes in chironomid assemblages at sub-decadal resolution in sediment cores spanning the last 150 years. The lake is a large, deep (zmax = 65 m), subalpine waterbody that has recently returned to an oligotrophic state. Comparison between the water-depth distributions of living chironomid larvae and subfossil head capsules (HC) along three surface-sediment transects indicated spatial differences in the influence of external forcings on HC deposition (e.g. tributary effects). The transect with the lowest littoral influence and the best-preserved, depth-specific chironomid community characteristics was used for paleolimnological reconstructions at various water depths. At the beginning of the twentieth century, oxygen-rich conditions prevailed in the lake, as inferred from M. contracta-type and Procladius sp. at deep-water sites (i.e. cores from 56 to 65 m) and Paracladius sp. and H. grimshawi-type in the core from 30 m depth. Over time, chironomid assemblages in cores from all three water depths converged toward the dominance of S. coracina-type, indicating enhanced hypoxia. The initial change in chironomid assemblages from the deep-water cores occurred in the 1930s, at the same time that an increase in lake trophic state is inferred from an increase in total organic carbon (TOC) concentration in the sediment. In the 1950s, an assemblage change in the core from 30 m water depth reflects the rapid expansion of the hypoxic layer into the shallower region of the lake. Lake Annecy recovered its oligotrophic state in the 1990s. Chironomid assemblages, however, still indicate hypoxic conditions, suggesting that modern chironomid assemblages in Lake Annecy are decoupled from the lake trophic state. Recent increases in both TOC and the hydrogen index indicate that changes in pelagic functioning have had a strong indirect influence on the composition of the chironomid assemblage. Finally, the dramatic decrease in HC accumulation rate over time suggests that hypoxic conditions are maintained through a feedback loop, wherein the accumulation of (un-consumed) organic matter and subsequent bacterial respiration prevent chironomid re-colonization. We recommend study of sediment cores from multiple water depths, as opposed to investigation of only a single core from the deepest part of the lake, to assess the details of past ecological changes in large deep lakes. 相似文献
6.
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
7.
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
8.
A chironomid‐based model for inferring late‐summer hypolimnetic oxygen in southeastern Ontario lakes
Hypolimnetic oxygen depletion has been accelerated in many lakes due to cultural eutrophication. However, the extent and magnitude of environmental change is difficult to ascertain due to the lack of historical records. Larval Chironomidae (Diptera) are useful proxy indicators of oxygen, as they show a wide range of tolerances to oxygen conditions and their chitinous head capsules preserve well in lake sediments. Using paleolimnological techniques, chironomid assemblages from the surface sediments of 42 southeastern Ontario lakes were related to environmental conditions. Hypolimnetic oxygen conditions, measured as the average endofsummer hypolimnetic dissolved oxygen (AvgDO(Summ)), explained the most variation in the chironomid assemblages, whereas dissolved inorganic carbon, the Anoxic Factor, max. depth and total phosphorus concentrations were also correlated with assemblage composition. Based on the relative abundances of 45 chironomid taxa, a robust, partial least squares (PLS) regression transfer function for AvgDO(Summ) was constructed (r2 = 0.74, r2
(jack) = 0.58, n = 40). This new transfer function should allow paleolimnologists to directly track past trends in hypolimnetic oxygen levels. 相似文献
9.
Emily M. Stewart Neal Michelutti Jules M. Blais Mark L. Mallory Marianne S. V. Douglas John P. Smol 《Journal of Paleolimnology》2013,49(2):205-219
Nutrients from the waste products of large seabird colonies can enter freshwater ecosystems, markedly altering water quality and biotic assemblages, especially in nutrient-poor regions like the Canadian High Arctic. Here, we investigate the influence of nutrient-rich seabird wastes on freshwater larval chironomid assemblages from two distinct seabird colonies. The study sites include four ponds dominated by northern fulmars (Fulmarus glacialis) at Cape Vera, Devon Island, as well as one pond near a large group of common eider ducks (Somateria mollissima borealis) on Tern Island (unofficial name) near Cornwallis Island, Nunavut. The rare combination of nutrient-enriched and well-oxygenated waters allowed us to contrast the effects of nutrients, oxygen, and temperature on chironomid community structure in shallow Arctic ponds using sediment cores. Despite highly elevated nutrient levels, the subfossil assemblages were dominated by cold stenotherms typical of oligotrophic waters. Although nutrient inputs appear to have increased chironomid head capsule numbers due to enhanced food availability, the fertilization had little direct effect on assemblage composition, at least at the taxonomic level achievable based on fossil material. The presence of low abundances of eutrophic/anoxic taxa, such as Chironomus plumosus-type, suggests that biogeographic barriers to dispersal are not influencing the assemblages. These data demonstrate that, in the presence of high concentrations of dissolved oxygen, nutrient enrichment had little direct effect on chironomid community composition in shallow Arctic ponds. 相似文献
10.
A high resolution multi-proxy record of pronounced recent environmental change at Baker Lake,Nunavut
A. S. Medeiros C. E. Friel S. A. Finkelstein R. Quinlan 《Journal of Paleolimnology》2012,47(4):661-676
Arctic aquatic systems are considered to be especially sensitive to anthropogenic disturbance, which can have cascading effects
on biological communities as aquatic food-web structure is altered. Bio-indicators that respond to major limnological changes
can be used to detect and infer major environmental change, such as climate warming, with the use of paleolimnological techniques.
A multi-proxy approach was used to quantify recent environmental changes at Baker Lake, Nunavut, Arctic Canada. Analyses of
fossilized remains of chironomids and diatoms were conducted on a sediment core of 20 cm in length sampled at 0.5-cm intervals.
A new surface sediment training set of subfossil chironomid assemblages from 65 lakes across the eastern Canadian Arctic generated
a robust (r
jack2 = 0.79) surface water paleotemperature transfer function. The transfer function was applied to stratigraphic intervals from
the Baker Lake sediment core to generate a paleotemperature reconstruction of sub-decadal resolution. The surface water temperature
reconstruction inferred a 2°C increase in mid-summer surface water temperature for Baker Lake over the last 60 years, which
was corroborated by the local instrumental record spanning the period of 1950–2007 AD. The chironomid record shows a recent
decline of several cold-water taxa and appearance of warm-water indicators. This shift in community structure began circa
1906 AD, and intensified after 1940 AD. The corresponding fossil diatom record showed an increase in small planktonic Cyclotella taxa over the past 60 years, intensifying in the last 5 years, which also suggests a warmer climate and longer ice-free periods.
The shifts in the diatom assemblages began later than the shifts in the chironomid assemblages, and were of lower magnitude,
reflecting differences in the mechanisms in which these two indicators respond to environmental change. 相似文献
11.
Dirk Verschuren 《Journal of Paleolimnology》1994,10(3):253-263
Aquatic invertebrates are intrinsically capable of rapid and sensitive response to changes in their lacustrine habitat. Fossil invertebrate assemblages preserved in the sediments of a climate-sensitive lake can thus produce high-resolution proxy records of past climate. In shallow lakes, however, a potential conflict exists between the sensitivity of biota to frequent habitat change in their fluctuating environment and the increased probability of disturbance of selected proxy records by bioturbation and physical mixing of sediments. I investigated this problem with tropical-African aquatic invertebrate faunas in a paleolimnological sensitivity study that incorporates both the response of biota to short-term habitat change and the taphonomic integrity of fossil assemblages in a small, shallow, and hydrologically closed lacustrine basin. Analysis of chironomid, cladoceran, and ostracode remains in a210Pb-dated short core from Lake Oloidien (Kenya) indicates that habitat changes accompanying the late 19th- and 20th-century fluctuations in lake level (Z
max
range: 3 to 18 m) and salinity (conductivity range:c. 400 toc. 2000–4000 µS cm–1) were sufficient to drastically alter the composition of local benthic and planktonic invertebrate faunas. This response remained relatively unaffected by taphonomic phenomena during its incorporation into the sediment record. Results indicate that tropical-African aquatic invertebrate faunas in suitable climate-sensitive lakes are a valuable tool to resolve paleoclimatic fluctuations on a timescale of decades.This paper was presented at the VI Palaeolimnology Symposium, held at Canberra in April 1993. Dr. Mark Brenner guest edited this contribution. 相似文献
12.
Sediments from Tugulnuit Lake in the Okanagan Valley of British Columbia, Canada, were examined for chironomid assemblages. The chironomid stratigraphy obtained encompasses the last 4000 to 5000 years and suggests a warm and fairly stable climate typical for a temperate lake at low- to mid-elevation. This is indicated by the even distribution of warm-water taxa, such as Cladopelma, Dicrotendipes, Polypedilum, Pentaneurini, Stempellina, Stempellinella/Zavrelia and Pseudochironomus throughout the core. Very few cold-water taxa occurred in the sediments. However, stream inputs have had a major impact on Tugulnuit Lake. Sandy sediments and the appearance of Simuliidae and stream-inhabiting chironomid taxa (e.g., Brillia/Euryhapsis, Eukiefferiella/Tvetenia, Rheocricotopus) indicate that a stream intruded into the current lake's basin ca. 3800 yr Before Present (BP). Sediments deposited prior to, and after, the stream's intrusion show a distinctly different chironomid assemblage exhibiting chironomid taxa more typical for lentic habitats. This result indicates that chironomids can serve to detect past stream influences on lake environments. Thus, rheophilic chironomids preserved in lake cores provide a new alternative for reconstructing stream palaeoenvironmental records. 相似文献
13.
The freshwater Zippel Bay (Minnesota, USA), from its headwaters to its outlet on Lake of the Woods, a larger lake, was identified
as a degraded system because of augmented nutrient and sediment loads, and for low oxygen affecting aquatic life. Anthropogenic
impacts were purportedly from stressors including agriculture, urban development and hydrologic modifications, so paleolimnology
using multiple indicators was employed in the bay and its two primary tributaries to characterize long-term trends since European
settlement of the region. Isotope analyses of the sediment cores indicated notable shifts in sedimentation rates in response
to human activities, and the application of a new diatom-based nutrient model to fossil diatom assemblages indicated that
phosphorus levels have approximately doubled over the last ∼150 years. While Zippel Bay appears to be naturally eutrophic,
increased nutrient loads have resulted in significant algal blooms, particularly during late summer. The multiple-core approach
revealed that anthropogenic activities upgradient of the two tributaries varied in their contributions to aquatic degradation
in Zippel Bay, and that despite the close proximity of the cores, there has been notable spatial variation in water quality.
This research also further validates the application of traditional freshwater paleolimnological methods to lotic systems
with sufficient sedimentary regimes. This study has important implications for Zippel Bay as it quantifies the extent of limnological
impacts and underlines the need for remediation. 相似文献
14.
Mirko Dreßler Thomas Hübener Solvig Görs Petra Werner Uwe Selig 《Journal of Paleolimnology》2007,37(2):205-219
During monthly investigations from 1996 to 2000, a hypolimnetic layer of phototrophic sulphur bacteria (Chromatium spp.) were observed in Lake Dudinghausen, a small dimictic lake in northern Germany. This paleolimnological study was initiated
to detect if the occurrence of sulphur bacteria was related to cultural eutrophication or reflected natural conditions. Therefore,
diatoms, algal pigments, okenone, geochemical proxies, and 210Pb and 137Cs were used in four sediment cores to investigate historical changes in trophic development, hypolimnetic redox conditions,
anoxia and phototrophic sulphur bacteria abundances. Fossil diatoms, pigments, the ratio of chlorophyll derivatives to total
carotenoids and the ratio of chlorophyll a to its derivatives suggest two phases of eutrophication coupled with hypolimnetic anoxia over the last ~80 years: a first
phase from about 1923–1932 and a second from 1952 to 1982. In the first phase the ratios of Fe–Mn as well as Fe–Ca increased,
suggesting seasonal anoxia. However, hypolimnetic anoxia was only weak because low levels of okenone suggest no mass development
of sulphur bacteria. In contrast, sulphur bacteria increased during the early stages of the second eutrophication phase, suggesting
increased temporal and spatial hypolimnetic anoxia. Surprisingly, the ratios of Fe–Mn as well as Fe–Ca decreased during this
time. Possibly Fe, Mn and Ca were equally reduced through the intense anoxia. In the final stage, sulphur bacteria decreased
again. As these bacteria need both anoxic conditions and a certain amount of light, the increased nutrient load probably led
to low Secchi depth and therefore insufficient light conditions. In more recent years, diatoms and pigments suggest a decrease
in nutrient levels. A second mass development of sulphur bacteria occurred, probably due to improved light conditions and
continued anoxia in the upper hypolimnion. We conclude that the recent development of phototrophic sulphur bacteria do not
represent natural conditions in Lake Dudinghausen. Furthermore, the upper sediments contain a completely new diatom flora
that never occurred in older sediments of Lake Dudinghausen. Therefore, nutrient levels may eventually reach natural conditions,
however they may not represent biological background reference conditions. 相似文献
15.
Paleolimnological analyses were used to infer limnological changes during the past ~ 300 yrs in the west basin of Peninsula Lake, a small (853 ha) Precambrian Shield lake in Ontario, Canada, that has been subjected to moderate cultural disturbances (forest clearance, cottage and resort development). This study represents a pioneering attempt to use sedimentary chironomid assemblages and weighted-averaging models to quantify past hypolimnetic anoxia (expressed as the anoxic factor, AF). Impacts of forest clearance and human land-use on deepwater oxygen availability and surface water quality were assessed by comparing chironomid-inferred AF and diatom-inferred total phosphorus concentration ([TP]) to changes in terrestrial pollen and historical data. This study also discusses the ability of chironomids to quantitatively infer changes in AF.Pre-disturbance chironomid assemblages were stable and dominated by taxa indicative of oxygen-rich hypolimnetic conditions (e.g., Protanypus, Heterotrissocladius, Micropsectra type), while diatoms indicated oligotrophic lake status (diatom inferred [TP] = 5-7 g·l-1). Chironomids characteristic of lower oxygen availability (e.g., Chironomus, Procladius) increased following land-clearance, road construction, establishment of a grist mill and lakeshore development beginning ca. 1870. Increased abundances of Tanytarsus s. lat., a multigeneric group of mainly littoral chironomids, since 1900, indicated that littoral chironomids may have comprised a greater proportion of fossil assemblages during periods of eutrophication and prolonged anoxia. Abundances of meso-eutrophic diatom taxa (e.g., Fragilaria crotonensis, Asterionella formosa, Aulacoseira ambigua, A. subarctica) increased concurrent with European settlement (ca. 1870) and diatom-inferred [TP] doubled (~ 6-12 g·l-1), further indicating that naturally-oligotrophic Precambrian Shield lakes were extremely sensitive to initial land-clearance activities.Recent increases in oligotrophic diatom taxa (e.g., Cyclotella stelligera) indicate a shift to more oligotrophic conditions since ca. mid-1960s, with greatest changes since ca. 1980. The chironomids Heterotrissocladius and Micropsectra type also increased at this time suggesting greater deepwater oxygen availability. These recent water-quality improvements, possibly in response to enhanced nutrient removal from detergents and sewage, climate-related reductions in external phosphorus loads, and catchment (but not lake) acidification and reforestation, suggest that habitat for commercially-valuable cold-water fishes has improved in recent decades despite greater recreational lake-use.Paleolimnological assessment of trophic status changes in Peninsula Lake using fossil diatom and chironomid assemblages were in good agreement. Diatom inferences of [TP] and chironomid inferences of AF both suggest that Peninsula Lake was historically oligotrophic, became oligo-mesotrophic after European settlement, and returned to oligotrophy in recent yrs. Chironomid inferences of [TP] consistently underestimated the trophic status of Peninsula Lake, possibly due to its relatively large hypolimnion. These results suggest that AF represents a useful tool for quantitatively reconstructing the past trophic status of deeper, stratified lakes. 相似文献
16.
R. Niloshini Sinnatamby Yi Yi Michael A. Sokal Kenneth P. Clogg-Wright Taro Asada Sheila R. Vardy Tammy L. Karst-Riddoch William M. Last John W. Johnston Roland I. Hall Brent B. Wolfe Thomas W. D. Edwards 《Journal of Paleolimnology》2010,43(4):705-717
A multi-proxy paleolimnological record obtained from a small, lowland closed-drainage basin located in the Peace-Athabasca Delta (Alberta, Canada), 10 km northwest of the present-day shore of Lake Athabasca, captures evidence of pronounced hydroecological changes over the past ~400 years. Consistent with historical maps produced by early European explorers of western Canada, paleolimnological data support the existence of a Lake Athabasca highstand during the Little Ice Age (LIA), c. 1600–1900 Common Era (CE). This contrasts with interpretations from previous analyses on sediment cores from an upland closed-drainage basin located centrally within the Peace sector of the delta that indicate low water levels during this interval. The different paleohydrological records at these two basins reflect the relative influence of different controls on the lake water balances. During the LIA, the lowland site was influenced by high levels in Lake Athabasca, whereas the elevated basin was outside the range of water-level rise in the lake and its distributaries, and was instead controlled by dry atmospheric conditions that led to evaporative drawdown. Integration of paleolimnological records and historical sources demonstrates that the ecosystem has undergone marked climate-driven hydroecological change over the past century, which is important information for effective management. 相似文献
17.
Combining ordination techniques and geostatistics to determine the patterns of diatom distributions at Lake Lama, Central Siberia 总被引:4,自引:0,他引:4
The patterns of spatial variation of diatom assemblages from surface sediments in Lake Lama were quantified using a combined approach of ordination and geostatistics. The aims were (i) to estimate the amount of variation between diatom assemblages within the lake, (ii) to model the spatial variability of the diatom assemblages and their diversity, and (iii) to map the diatom distributions in the lake. A correspondence analysis (CA) separated the diatom assemblages into a planktonic and a periphytic group. Rheophilic taxa were found within the periphytic group. Variogram analysis showed that only the sample scores of the first CA axis and the Shannon diversity index were spatially structured. The range of spatial correlation was estimated to be 55 km for both variables. The diversity and, to a lesser extent, the sample scores had considerable small-scale variability of about 20 and 3%, respectively. Estimates of the first component of the CA and the Shannon index were derived using block-kriging. The maps of the estimates provided a basis for partitioning Lake Lama according to the spatial structures into an eastern and a western basin, a north–south connection between the basins, and a north–south directed tip at the far eastern end. It was shown that variation in diatom assemblages is mainly spatially structured at the catchment scale and that there is a considerable amount of variation at smaller scales. According to the modeled spatial distribution, the assemblages are most likely affected by the lake size, morphology, and the water and nutrient input introduced by rivers. This has to be taken into account when paleolimnological interpretations are drawn from records of complex lake systems like Lake Lama. 相似文献
18.
Elizabeth E. Alexson Euan D. Reavie Richard P. Axler Sergiy V. Yemets Pavel A. Krasutsky Mark B. Edlund Robert W. Pillsbury Diane Desotelle 《Journal of Paleolimnology》2018,59(3):373-395
The St. Louis River Estuary (SLRE), a freshwater estuary bordering Duluth, Minnesota, Superior, Wisconsin, and the most western point of Lake Superior (46.74°, ? 92.13°), has a long history of human development since Euro-American settlement ~ 200 years ago. Due to degradation from logging, hydrologic modification, industrial practices, and untreated sewage, the SLRE was designated an Area of Concern in 1987. Action has been taken to restore water quality including the installation of the Western Lake Superior Sanitary District in 1978 to help remove beneficial use impairments. A better understanding of historical impacts and remediation is necessary to help document progress and knowledge gaps related to water quality, so a paleolimnological study of the SLRE was initiated. Various paleolimnological indicators (pigments, diatom communities, and diatom-inferred phosphorus) were analyzed from six cores taken throughout the SLRE and another from western Lake Superior. Reductions in eutrophic diatom taxa such as Cyclotella meneghiniana and Stephanodiscus after 1970 in certain cores suggest an improvement in water quality over the last 40 years. However, in cores taken from estuarine bay environments, persistence of eutrophic taxa such as Cyclostephanos dubius and Stephanodiscus binderanus indicate ongoing nutrient problems. Sedimentary pigments also indicate cyanobacteria increases in bays over the last two decades. Diatom model-inferred phosphorus and contemporary monitoring data suggest some of the problems associated with excess nutrient loads have been remediated, but modern conditions (internal phosphorus loading, changing climate) may be contributing to ongoing water quality impairments in some locations. The integrated record of biological, chemical, and physical indicators preserved in the sediments will aid state and federal agencies in determining where to target their resources. 相似文献
19.
Chaoborid and chironomid (Diptera) fossils were examined in sediment cores form nine Ontario Precambrian Shield lakes that were fishless in 1979. An abundance of Chaoborus americamus (intolerant of predation by fish) throughout cores from four lakes indicated that they were fishless historically. Occurrence of Chaoborus punctipennis and C. flavicans and absence of C. americanus in cores, except near the surface in two cases, indicated that four other lakes were inhabited by fish historically. One of these was probably periodically fishless as suggested by fluctuations among these Chaoborus species. The ninth lake was not suitable for Chaoborus; only one specimen of C. trivittatus was found in this core. Chironomid fossil associations were substantially different in historically fishless and inhabited lakes. Fishless lakes had chironomids typical of eutrophic conditions indicating that seasonal oxygen depletion likely was inimical to fish. Chironomid associations of oligotrophic waters occurred in lakes historically inhabited by fish. Both good water quality and accessibility were required for long-term habitation by fish. Partial recovery of alkalinity and rise in pH were accompanied by substantial re-invasion by fish in two lakes which had been inhabited historically by fish. Diptera associations provide valuable information on the historical suitability of lakes for fish and the presence/absence of fish in regions where acidification of surface waters has occurred. 相似文献
20.
Brenda Moraska Lafrancois Suzanne Magdalene D. Kent Johnson 《Journal of Paleolimnology》2009,41(4):603-622
Long-term water quality monitoring data from two riverine lakes in the Upper Mississippi River basin, Lakes St. Croix and
Pepin, were analyzed to compare the long-term average water quality conditions and land use distributions, water quality trends
and loads at lake inlets and outlets, trends from long-term versus short-term monitoring records, and the ability of paleolimnological
cores to accurately infer lake water quality conditions. During the 1976–2004 period, the long-term average concentrations
of nutrients, suspended solids, and chlorophyll-a were consistently lower at the Lake St. Croix inlet versus the Lake Pepin inlet, which drains a greater proportion of urban
and agricultural runoff. Despite these differences, nutrient trends were similar at the inlets to both lakes; reductions in
total phosphorus and ammonium concentrations were attributed to improvements in point source technologies, whereas increasing
nitrate concentrations were attributed to both point source changes and nonpoint source increases. Despite improvements in
several water quality variables, nitrate concentrations are increasing in both lakes, sediment trends indicate persistent
nonpoint source inputs to Lake Pepin, and current total phosphorus concentrations remain well above pre-1950s levels in both
lakes. Since urban development and agriculture are increasing in the Lake St. Croix and Lake Pepin Watersheds, continued point
source regulation and additional nonpoint source control efforts will be needed to further improve water quality in these
lakes. The 1976–2004 trends for most water quality variables were similar at inlet versus outlet sites on Lake St. Croix.
Trends at Lake Pepin inlet versus outlet sites were less similar, but data availability limited the comparison to the 1993–2003
period. While the truncated data record highlighted short-term trends in both lakes, the full data record was most useful
for exploring general patterns in water quality. Length of monitoring record affected our ability to detect trends at the
inlets to both lakes, and altered the magnitude of detected trends. During the two decades of the 1980s and 1990s, paleolimnological
estimates of retained phosphorus loads were similar to those estimated from recent water quality monitoring. These similarities
support the use of paleolimnological approaches to infer past water quality conditions in Lakes St. Croix and Pepin.
This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this
special issue of the Journal of Paleolimnology. D. R. Engstrom served as guest editor of the special issue. 相似文献