Diatomaceous sedimentation in late Neogene lacustrine basins of western Macedonia, Greece

Several lacustrine basins were formed by late Miocene tectonic processes in western Macedonia, Greece. These were occupied by a series of lakes and wetland swamps during the late Miocene and early Pliocene giving rise to diatomaceous claystones, siltstones and diatom-bearing tufa deposits. Diatoms are rare or fragmentary in sandstones and chemical sediments, and are absent in conglomerates. The Fe²⁺-rich phosphate minerals anapaite and vivianite are present in parts of the diatomaceous siltstones. Six major diatom groups were identified using cluster and correspondence analyses, each of which tends to be associated with a particular lithofacies. The floras are indicative of mildly acidic to alkaline water of varying depths. The dominant taxa include Aulacoseira ambigua, A. distans, Cyclotella iris and several of its varieties, C. aegeae, C. castracanei, C. elymaea, C. ocellata, and two unidentified Cyclotella. Fragilariaceae are common, consisting mainly of Fragilaria bituminosa, Pseudostaurosira brevistriata, P. zeilleri, Staurosira construens, Staurosirella leptostauron, and S. pinnata. Locally, chysophycean stomatocysts are common, suggesting more oligotrophic conditions. Nine diatom stages are recognized in the Lower Neogene Series at Kariditsa (Kozani basin), reflecting shallow swamps, small alkaline lakes, and terrestrial settings. The Upper Neogene Series rocks are characterized by Mg-rich carbonates such as hydromagnesite, huntite and magnesite. A detailed stratigraphy was developed for Mio-Pliocene deposits in the Florina basin at Klidi. Parts of this sequence show clear cyclicity in both the sediments and the diatom floras, with shallow-water diatoms repeatedly giving way to taxa indicative of deeper conditions. Larger-scale, shallow-deep cycles are also present and may be related to precession- and eccentricity-forced climate change.     

Late Quaternary stratigraphy,sedimentology and geochemistry of an underfilled lake basin in the Puna plateau (northwest Argentina)

Depositional models of ancient lakes in thin‐skinned retroarc foreland basins rarely benefit from appropriate Quaternary analogues. To address this, we present new stratigraphic, sedimentological and geochemical analyses of four radiocarbon‐dated sediment cores from the Pozuelos Basin (PB; northwest Argentina) that capture the evolution of this low‐accommodation Puna basin over the past ca. 43 cal kyr. Strata from the PB are interpreted as accumulations of a highly variable, underfilled lake system represented by lake‐plain/littoral, profundal, palustrine, saline lake and playa facies associations. The vertical stacking of facies is asymmetric, with transgressive and thin organic‐rich highstand deposits underlying thicker, organic‐poor regressive deposits. The major controls on depositional architecture and basin palaeogeography are tectonics and climate. Accommodation space was derived from piggyback basin‐forming flexural subsidence and Miocene‐Quaternary normal faulting associated with incorporation of the basin into the Andean hinterland. Sediment and water supply was modulated by variability in the South American summer monsoon, and perennial lake deposits correlate in time with several well‐known late Pleistocene wet periods on the Altiplano/Puna plateau. Our results shed new light on lake expansion–contraction dynamics in the PB in particular and provide a deeper understanding of Puna basin lakes in general.     

The macrobenthic fauna of a former perennial and now episodically filled mexican saline lake

Totolcingo (El Carmen), a large and now episodically filled playa lake in the east-ernmost portion of the Mexican Plateau, filled with water in 1993. Water persisted for just one month (May). Alkaline (pH 10), saline (K₂₅ up to 30,000S/cm) waters, dominated by NaHCO₃ and Na₂CO₃, characterized the lake. The fauna was depauperate. The components of the fauna wereEphydra (Hydropyrus)hians Say (ephydrid),Limnodrilus hoffmeisteri Claparède (tubificid), andBerosus sp. (Coleoptera). The species in the lake were widely dispersed and typical inhabitants of saline lakes. Possible reasons for the depauperate fauna include (a) overall physical and chemical conditions, (b) unpredictable hydrology, and (c) the short (one month) inundation period prevented colonization.     

Diatom and thecamoebian signatures of Red River (Manitoba and North Dakota) floods: Data collected from the 1997 and 1999 spring freshets

Overbank deposits that aggraded during the severe and moderate Red River, Manitoba and North Dakota floods of 1997 and 1999 were examined to characterize the typical diatom and thecamoebian flood assemblages. The deposits contain diatom assemblages dominated by Nitzschia spp., Stephanodiscus spp. and Navicula spp. as well as large quantities of Hantzschia amphioxys, Luticola imbricata and L. mutica and lesser amounts of Aulacoseira italica, A. granulata, A. ambigua, Cyclotella meneghiniana, Amphora montana and Synedra ulna. Samples collected from the Red River in late summer are dominated by the plankton Cyclotella atomus, species of Stephanodiscus, Cyclostephanos sp. 1 (cf. delicatus), Cyclotella meneghiniana, Nitzschia reversa and Nitzschia acicularis. Late summer, floodplain lake plankton are dominated by Fragilaria capucina, Cocconeis placentula, Stephanodiscus parvus/minutulus and Cyclotella atomus. Red River thecamoebian flood assemblages are dominated by Cyclopyxis spp., with lesser amounts of Centropyxis aculeata and Arcella vulgaris. Late summer water samples from the Red River contain very few thecamoebian remains. The majority of the taxa present are Centropyxis aculeata, Arcella vulgaris and Cyclopyxis spp. Floodplain lakes are dominated by benthic thecamoebians, especially Difflugia oblonga and Cucurbitella tricuspis, a eutrophic indicator. The results of this baseline study suggest that diatom and thecamoebian assemblages can characterize flood deposits, within floodplain lake basins, during both very high and moderately high flood years, and that these assemblages are inherently different from those typically found in lakes along the Red River.     

Climatic control on Lower Cretaceous sedimentation in a playa-lake system of a tectonically active basin (Huérteles Alloformation,Eastern Cameros Basin,North-Central Spain)

The Berriasian Huérteles Alloformation is the fourth alloformation in which the Tithonian-Berriasian Depositional Sequence is divided in Eastern Cameros Basin. This depositional sequence can be recognized in several basins East of The Iberian Plate. Huérteles Afm. was deposited in a trough with a NW-SE orientation and strong subsidence. In this trough the sedimentary record exceeds 1000 m in thickness for this alloformation. The Basin shows a marked asymmetry, with the highly subsident trough displaced to the NE.The sedimentary system consists of a playa complex, in which several subenvironments can be distinguished. The proximal or bajada environments were located to the west. The terrigenous materials, that constitute the sediments of these areas, come from the erosion of materials previously deposited in the Basin. To the East the environments were mainly saline lakes, that received siliciclastic materials from the Northeast, where the main border fault system was situated.The vertical sequence in the central part of the Basin (where a perennial saline lake was located) shows a marked cyclicity, with primary sequences about 10 m thick. These consist of laminated limestones in their lower part, and carbonate breccias at the top. These primary sequences represent the filling of a lake, with relatively dilute waters at first, passing gradually into a saline lake. This reflects a transition from humid to arid climatic periods.Additionally there is another cyclicity of a higher rank indicated by sequences about 300 m thick These major sequences are formed by primary sequences. The minor primary sequences are mainly composed of laminated limestones in the lower part of the major sequences, and the carbonate breccias dominate in the upper part of the major sequences. These major sequences may indicate longer periods of climatic variation, that varied from a relatively humid to an arid climate. This sequential arrangement was accentuated by the strong tectonic activity during sedimentation, that produced large slump structures where evaporites were more abundant.This is the sixth paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.     

Diatom,pollen, and geochemical evidence for the palaeosalinity of Medicine Lake,S. Dakota,during the late-Wisconsin and early Holocene

Medicine Lake is a highly saline meromictic lake in eastern South Dakota. A lithostratigraphic and biostratigraphic study of the late-glacial and early post-glacial sediments shows that it was a relatively deep dilute freshwater lake during the period of the Picea pollen zone. When spruce forest changed to a Betula and then to a Quercus/Ulmus woodland in the early post-glacial period, the lake water became more concentrated but remained fresh. However, during the subsequent rapid transition to prairie in the early Holocene, when Gramineae, Ambrosia, and Artemisia dominated dry-land vegetation, the freshwater diatom flora was progressively replaced by a saline assemblage characterized by Cyclotella quillensis, Chaetoceros, and eventually Cyclotella caspia. The lake became permanently saline at about 9000 yr BP. A comparison of the fossil diatom assemblages with surface-sediment samples from a range of lakes in the Dakotas indicates that the change involved an increase in conductivity from about 500 S cm^–1 in the late-glacial period to > 10 000 S cm^–1 in the early Holocene. This rapid change is also marked by an abrupt increase in sulphate concentration in the sediment, the first appearance of bands of gypsum crystals, and the beginning of a well-laminated core sequence that continues through the remaining sediment record. Conditions of high salinity have prevailed to the present day.Contribution 299, Limnological Research Center.     

Lake-Sediment Records of Recent Environmental Change on Svalbard: Results of Diatom Analysis

Surface sediments from 23 lakes on Svalbard were analysed for diatoms. About 182 taxa were found but samples generally have a low richness, with the majority of sites dominated by benthic genera such as Fragilaria, Navicula, and Achnanthes. Centric Cyclotella species occur at only three sites. Modern relationships between diatom abundance and water chemistry and other environmental variables were explored numerically and a preliminary transfer function for pH was developed. Lakes fell into three groups on the basis of their diatom assemblages: (1) high pH, high cation, high conductivity sites characterised by Amphora libyca, (2) shallow sites with relatively high nutrient values characterised by Fragilaria species, and (3) more acid and dilute sites with high amounts of snow cover in the catchments characterised by small Achnanthes species and Navicula digitulus. Five sediment cores representing the recent past were also analysed for diatoms. Three shallow sites were dominated by Fragilaria species throughout the period represented by the cores and no shifts in inferred pH were found. At two deeper sites (Arresjøen, Birgervatnet) major assemblage shifts are found which are unrelated to independent evidence for atmospheric contamination. Early (ca. 1200 AD) changes found at both sites are possibly related to the onset of the ‘Little Ice Age’. Later changes are neither synchronous nor similar in nature and might be best explained as individual responses to the recovery from the ‘Little Ice Age’ and subsequent climatic warming.     

Aeolian dust in a saline playa environment, Nevada, U.S.A.

Saline playas in north-western Nevada, U.S.A., remnants of pluvial periods of the Pleistocene, represent a tremendous source of unconsolidated sediments available for aeolian transport. This study investigated the transport of aqueous-soluble solutes in dust from July 1994 through June 1996 along a transect from a barren salt-encrusted playa surface (elevation=1224 m), to a former pluvial lake beach (elevation=1228 m), to a dune-mantled upland (elevation=1248 m). The content of aqueous-soluble solutes in aeolian dust showed a significant (p≤0·05) interaction with dust trap location (playa, beach, dune) and time of collection. Dust collectors on the playa surface generally contained significantly more aqueous-soluble solutes and had greater total flux of solutes than either the beach or the dune locations. The solute content of aeolian dust was usually higher, in some cases several orders of magnitude, than that in the surface 5 cm of soil. Recent changes in playa hydrology may explain this result. Pulses of nitrate-rich dust, synchronous with spring emergence, and other nutrient additions via aeolian dust may have stimulated invasion of dune-mantled uplands by the weedSalsola paulsenii (barb-wire Russian thistle).     

The postglacial environmental development of Raffles Sø, East Greenland: inferences from a 10,000 year diatom record

A 341 cm long sediment sequence was recovered from the unofficially named Raffles Sø on Raffles Ø, outer Scoresby Sund region, East Greenland. The sediment sequence consists in the upper part (0–230 cm) of a stratified gyttja enriched in organic carbon and biogenic silica whereas the lower core part (235–341 cm) is composed of terrigenous, consolidated glacio-limnic sediments. ¹⁴C-AMS measurements indicate that the sediment sequence represents the entire Holocene lake history from 10,030 calibrated radiocarbon years.The geochemical parameters (opal, total organic carbon (TOC), total nitrogen (TN)) and the total diatom concentration show similar developments during the Holocene, and reflect changes in biological production and nutrient input into the lake. These records clearly reveal a broad Holocene TOC-opal-maximum interval between 5200 and 1800 cal. yrs BP.The diatom flora consisted of 66 taxa representing 20 genera but only seven taxa were abundant and, sometimes, these were monospecifically dominant during the Holocene. In the sediment core from Raffles Sø four successive stratigraphical zones can be distinguished. Accumulation of diatom valves began at 9900 cal. yrs BP with a Stephanodiscus minutulus (Kütz.) Cleve and Möller dominated assemblage (stratigraphic zone 1) followed by a diatom flora dominated by Cyclotella pseudostelligera Hustedt and, less frequently, by Diatoma tenuis Agardh (9400 until 5900 cal. yrs BP, zone 2). Cyclotella sp. A, a taxon which belongs to the Cyclotella rossii-comensis-tripartita-complex, was the dominant floral element between 5200 and 1800 cal. yrs BP (zone 3). From 1800 cal. yrs BP, the periphytic taxa Fragilaria capucina var. gracilis (Østr.) Hustedt and F. capucina var. rumpens (Kütz.) Lange-Bertalot attained highest relative abundances, also almost monospecifically (zone 4).The distribution and composition of the diatom assemblages in the sediment record from Raffles Sø probably reflect past variations in the extent of the lake-ice cover during the growing season. More or less ice-free conditions during summer may have prevailed during the early Holocene until ca. 1800 cal. yrs BP, which allowed growth of planktonic diatoms (Cyclotella taxa) in the pelagic lake region. From 1800 cal. yrs BP, colder conditions lead to a perennial lake-ice cover with a small ice-free moat in summer which favored the growth of periphytic, littoral species (Fragilaria capucina varieties).     

Late Wisconsinan and Holocene diatom stratigraphy from Amarok Lake,Baffin Island,N.W.T., Canada

Diatom analyses from the longest continuous record of lacustrine sedimentation in the eastern Canadian Arctic indicate four phases of lake development during the past 20000 years. PlanktonicAulacoseira taxa are dominant between 20 and 10 ka and during the Neoglacial. The earliest Holocene is characterized byFragilaria, whereas benthic acidophils (e.g.Frustulia, Brachysira & Eunotia spp.) dominate sediments of early to mid Holocene age. Ordination by correspondence analysis illustrates stratigraphic changes in diatom life form and pH tolerances, and these are related to both regional paleoclimatic conditions and local edaphic factors. The occurrences of planktonic floras during the cold Late Foxe and Neoglacial periods suggests that, even at these times, the lake became ice free during summer. The interplay of increased runoff as a mechanism of ice disintegration and enhanced silicon supply by erosional processes (corroborated by the more clastic nature of the sediments during these periods) likely enabledAulacoseira to flourish. Early and mid Holocene limnological regimes were more strongly controlled by lake authigenic processes.This paper was presented at the VI Palaeolimnology Symposium, held at Canberra in April 1993. Dr. Mark Brenner guest edited this contribution.     

Lake Issyk-kul,Kirgizia

The main limnological features of Lake Issyk-kul are described. The lake is a large (6,236 km²), deep (z_m, 668 m), closed lake in eastern Kirgizia. It lies at ∼1,607 m above sea level, but water-levels have been dropping since the last century. It is slightly saline (salinity, ∼6g L⁻¹), with Na⁺, Mg²⁺, Cl⁻ and SO ₄ ²⁻ the dominant ions. Nutrient levels are low and the lake is considered ultra-oligotrophic. Characeae dominate the macrophytes. About 300 and 117 taxa of, respectively, phytoplankton and zooplankton have been identified, withArctodiaptomus salinus the most numerous in the zooplankton. Chironomids dominate the benthos. Several endemic taxa of fish occur, of whichLeuciscus bergi was dominant until the 1970s. The fish fauna has been supplemented by many introduced species. Three mysids were introduced in 1965–8 and are now a significant part of the ecosystem. The present annual fish catch permitted is 320 t. The most important value of the lake is as a recreational resource. To promote and sustain this value requires careful, ongoing management. The most significant threats to the lake are local pollution, visitor pressure, and declining water-levels.     

A Holocene paleosalinity diatom record from southwestern Saskatchewan, Canada: Harris Lake revisited

Fossil diatoms were analysed from a 10.3 m core from Harris Lake, Cypress Hills, Saskatchewan, and a diatom-salinity transfer function was used to construct a history of Holocene salinity changes for the lake. The diatom paleosalinity record indicates that Harris Lake remained fresh <0.5 g l-¹ throughout the Holocene, with only slight increases in salinity between approximately 6500 and 5200 years BP. This interval corresponds to the only period in the lake's history when planktonic diatoms were abundant; benthic Fragilaria taxa, mainly F. pinnata, F. construens and F. brevistriata were dominant throughout most of the Holocene. The shift from a benthic to a planktonic diatom flora between 6500 and 5200 years BP may be an indirect response to a warmer climate that reduced forest cover in the watershed and allowed greater rates of inorganic sedimentation. The small salinity increase that accompanies the floristic change is probably not the result of lower lake levels; in fact the lake was probably deeper at this point than in the later Holocene. This paleosalinity record indicates that Harris Lake did not experience episodes of hypersalinity during the mid-Holocene, as suggested by a previous study, and that the lake may have been fresh during the early Holocene as well.     

Late Quaternary paleolimnology of Walker Lake,Nevada

Diatoms, crustaceans, and pollen from sediment cores, in conjunction with dated shoreline tufas provide evidence for lake level and environmental fluctuations of Walker Lake in the late Quaternary. Large and rapid changes of lake chemistry and level apparently resulted from variations in the course and discharge of the Walker River. Paleolimnological evidence suggests that the basin contained a relatively deep and slightly saline to freshwater lake before ca. 30 000 years B.P. During the subsequent drawdown, the Walker River apparently shifted its course and flowed northward into the Carson Sink. As a result, Walker Lake shallowed and became saline. During the full glacial, cooler climates with more effective moisture supported a shallow brine lake in the basin even without the Walker River. As glacial climates waned after 15 000 years ago, Walker Lake became a playa. The Walker River returned to its basin 4700 years ago, filling it with fresh water in a few decades. Thereafter, salinity and depth increased as evaporation concentrated inflowing water, until by 3000 years ago Walker Lake was nearly 90 m deep, according to dated shoreline tufas. Lake levels fluctuated throughout this interval in response to variations in Sierra Nevada precipitation and local evaporation. A drought in the Sierras between 2400 and 2000 years ago reduced Walker Lake to a shallow, brine lake. Climate-controlled refilling of the lake beginning 2000 years ago required about one millennium to bring Walker lake near its historic level.Through time, lake basins in the complex Lake Lahontan system, fill and desiccate in response to climatic, tectonic and geomorphic events. Detailed, multidisciplinary paleolimnologic records from related subbasins are required to separate these processes before lake level history can be reliably used to interpret paleoclimatology.This is the fifth of a series of papers to be published by this journal that was presented in the paleolimnology sessions organized by R. B. Davis and H. Löffler for the XIIth Congress of the International Union for Quaternary Research (INQUA), which took place in Ottawa, Canada in August 1987. Drs. Davis and Löffler are serving as guest editors of this series.     

Biomonitoring past salinity changes in an athalassic subarctic lake

A short sediment core was taken from a small saline lake located on an intermontane plateau in the central Yukon Territory, Canada. In July 1990, chemical analyses indicated that, although the lake was shallow (Z_max=1.1 m), it was also chemically stratified, with hyposaline (9.9 to 10.0 g L⁻¹) surface waters and slightly mesosaline (22.0 g L⁻¹) deeper waters. The surface water was dominated by Na⁺ and HCO ₃ ⁻ . To our knowledge, this is the northernmost athalassic saline lake yet recorded. Quantification of algal (diatom, chrysophyte, and pigment) and invertebrate (chironomid, ceratopogonid, andChaoborus) fossils at four stratigraphic levels indicated that the lake sediments preserved numerous biological indicators that could be used to infer recent lake development. Many of the taxa are found in other athalassic salt lakes. The most striking stratigraphic change was a remarkable drop in the species richness of diatoms and invertebrates in the recent sediments, which parallels the elimination of species characteristic of less saline conditions. Halophilous taxa dominate the most recent sediments, indicating the development of more saline conditions. At the same time, a significant shift in chrysophyte cyst composition was observed. Fossil carotenoids and chlorophylls indicated a decrease in total algal abundance in recent sediments, as green and blue-green algae replaced diatoms and chrysophytes. Together, these paleolimnological data suggest a recent shift to drier conditions or increased evaporation in the central Yukon Territory.     

A reference typology of low alkalinity lakes in the UK based on pre-acidification diatom assemblages from lake sediment cores

This paper has two aims: (1) to show for the first time how a natural typology can be established using palaeoecological methods; and (2) to show how it can be used in lake restoration studies with respect to the definition of recovery targets for acidified lakes. By defining the characteristic reference assemblages for low alkalinity site types rather than for a specific site it allows success to be measured more broadly, unconstrained by the specific composition of the pre-acidification flora. We analyse statistically the pre-acidification diatom assemblages of sediment cores from 121 low alkalinity lakes in the UK in order to assess whether a reference typology for such lakes can be defined on the basis of their diatom floras. We use samples dating to ~1850 AD to represent pre-acidification conditions. The results show that three main clusters can be identified, two dominated by benthic taxa (Clusters 1 and 3) and one dominated by planktonic taxa (Cluster 2). Cluster 1 is characterised by taxa such as Brachysira vitrea, Cymbella microcephala and Fragilaria spp., Cluster 2 by Cyclotella comensis, C. radiosa, Asterionella formosa, Aulacoseira subarctica and Achnanthes minutissima and Cluster 3 by Eunotia incisa, Frustulia rhomboides var. saxonica, Fragilaria virescens var. exigua, and Cymbella perpusilla. Although environmental data for 1850 AD are not available it is apparent from the contemporary distribution of the taxa in the different clusters that Cluster 2 represents the most alkaline pre-acidification conditions. Some sites in this cluster have been acidified, but some, especially the larger, deeper lakes have been enriched. Cluster 1 includes sites that contain diatoms with relatively high pH optima (pH 6.4–7.4) whereas Cluster 3 sites contain diatoms with the lowest pre-acidification pH conditions in the data-set. Sites in this cluster also have the lowest base cation concentrations at the present day and include the sites in the UK that have been most affected by acid deposition.     

Microfossils of Polynesian cultigens in lake sediment cores from Rano Kau, Easter Island

Previous wetland vegetation records from Easter Island showing deforestation and Polynesian agriculture are limited to cores that rely on pollen, with a single cultigen pollen type identified: Urticaceae/Moraceae, possibly Broussonetia payrifera (paper mulberry). Here we redress this by also using phytolith and starch analyses on four lake sediment cores on a ~350-m transect along the southwest edge of Rano Kau, focusing on in-washed basal clayey layers. We also use a new method, Fourier transform infrared spectroscopy, to positively identify degraded starch collected from sedimentary deposits. The cores are the first samples recovered from an area in the lake that (a) lies below the relict village of Orongo, (b) is near a section of the crater believed to be most accessible from the Pacific coast, and (c) is far from the northern crater rim and receives high solar radiation, a likely benefit for crops of tropical origin. Pollen and phytoliths are abundant in the clayey layers and sparse in overlying layers of organic lake detritus and living rhizomes. Mixing of core deposits as a result of human activity has disordered the radiocarbon sequence, precluding development of an reliable chronology. Containing microfossils of several introduced cultigens, the clayey layers represent gardened terraces that have slumped into the lake. The data indicate large-scale deforestation and a mixed-crop production system including Broussonetia papyrifera, Colocasia esculenta (taro), Dioscorea alata (greater yam), Ipomoea batatas (sweet potato), Lagenaria siceraria (bottle gourd) and Musa (banana) sp. The data show (a) the potential for using the combined analyses to provide direct evidence of Polynesian horticulture on Easter Island and (b) that the island’s wetlands potentially hold extensive horticultural records. The study highlights the concept of ‘transported landscapes,’ whereby colonising people replace indigenous forests with artificial, imported agricultural landscapes.     

The post-glacial diatom history of Splan Lake,New Brunswick

The first account is given of the postglacial history of a lake in eastern Canada. Splan Lake is a 4 ha lake situated in a hollow in Palaeozoic metasedimentary rock in southern New Brunswick. Diatoms were identified and counted in a 6.98 m core, from which five developmental phases were recognized. Initially Splan Lake supported a pioneer Fragilaria assemblage comparable to that in modern arctic and glacial moraine lakes. This is believed to represent growth in the moat of a partially ice covered lake. An embryonic limnic flora consisting of Cyclotella bodanica and C. stelligera appeared ca. 11 300 y.B.P., which was terminated by the younger Dryas cool interval — ca. 11 000–10 000 y.B.P. There appeared to be no autochthonous production in Splan Lake during this latter episode. Subsequently, a C. bodanica: C. Stelligera: Navicula community developed. From ca. 8 800–5 500 y.B.P. Asterionella ralfsii v. americana, Tabellaria spp. and large numbers of chrysophyte scales occurred together with Cyclotella spp. The recent phase is dominated by Tabellaria, Frustulia, Fragilaria, Eunotia and Navicula. The lake evolved from alkaline to slightly acid, and from oligotrophic to mesotrophic following the younger Dryas. The flora developed from benthic/littoral to a predominantly littoral/limnic community over the same period, and with continued sedimentation, into a littoral/benthic diatom community.     

Paleolimnological evidence of mining and demographic impacts on Lac Dauriat, Schefferville (subarctic Québec, Canada)

Qualitative and quantitative analysis of fossil diatoms and geochemical signals preserved in the sediments of Lac Dauriat (subarctic Quebec) were performed to evaluate the impacts of nearby mining activity and the expansion of the town of Schefferville on the water quality of the lake, and to reconstruct the changes of its trophic status. The presence of taxa typical of nutrient-enriched environments (e.g., Cyclostephanos invisitatus, Nitzschia gracilis, Nitzschia perminuta) and the low percentages of chrysophytes were indicative of the advanced state of eutrophication of the lake during the peak of mining activity, and were evidence of the negative impacts of municipal waste on the water quality of Lac Dauriat. Sedimentary analysis of metals, notably lead, mercury, cadmium, bismuth, cobalt, copper and zinc, showed maximum concentrations between 1940 and 1960 with mining era to pre-development enrichment factors ranging from 4.5 to 7.9. The changes seen in recent sediments reflected 3 distinct stages in the recent history of this ecosystem: (a) the non-perturbed, pre-mining (1882–1939), (b) the perturbed, mining period (1939–1977) with accelerated eutrophication, and (c) the post-mining period (1977–1999) with indications of natural recovery of the system after the installation of a water treatment plant in 1975, the closing of the mine in 1983, and the subsequent exodus of the town’s population. Despite the trajectory towards a return to the lake’s natural conditions, water resource managers and (paleo-)limnologists should be alarmed that the impacts of past human disturbance are still in evidence more than 20 years after the closure of the mines, and that Lac Dauriat has yet to reach its natural state of the period preceding extreme anthropogenic impact.     

Late Holocene climate and environment of the SE Pampa grasslands,Argentina, inferred from biological indicators in shallow,freshwater Lake Nahuel Rucá

We analyzed pollen, non-pollen palynomorphs (NPPs), calcareous microfossils, plant macrofossils, diatoms, chrysophyte cysts, opal phytoliths and organic matter content in a 123-cm sediment sequence from Nahuel Rucá Lake, a shallow, freshwater system in the southeastern Pampa grasslands, Argentina. Three stages in the lake evolution were identified. Before 3,680 cal year BP, only pollen, NPPs (dinoflagellate cysts and acritarchs) and ostracods were recovered, suggesting brackish/saline conditions in the lake and nearby areas. Freshwater conditions are, however, indicated by Myriophyllum, Pediastrum and Zygnemataceae. The brackish/saline conditions could have been caused by marine influence during a Holocene sea level high stand that affected the area ca. 6,000 year BP. Between 3,680 and 390 cal year BP, macrophyte pollen and plant macrofossils indicate increasingly freshwater conditions in the lake and the adjacent area. Diatom and ostracod assemblages, however, suggest brackish and oligotrophic conditions, giving way to freshwater and meso-eutrophic conditions toward the end of this period. The relationship between submersed macrophytes (Myriophyllum, Potamogeton, Ceratophyllum, Chara) and planktonic algae (Chlorophyta and diatoms), suggests a shift in the lake from a clear to a turbid state. This turbid state is more evident after 390 cal year BP. High values of Pediastrum, Scenedesmus and diatoms (Cyclotella meneghiniana, Aulacoseira granulata, A. muzzanensis) observed during this stage could have reduced light penetration, with consequent loss of submersed plants. Pollen and plant macrofossils in the uppermost 20 cm indicate a shallow, freshwater lake similar to present, though an increase in brackish/freshwater diatoms suggests an increase in salinity, perhaps related to periodic droughts. Opal phytoliths yield a regional paleoclimatic reconstruction that agrees closely with inferences made using pollen, mammals and sediment characteristics.     

Paleoenvironmental evolution of the Early Pleistocene lacustrine sequence at Barranco León archeological site (Orce,Baza Basin,Southern Spain) from stable isotopes and Sr and Mg chemistry of ostracod shells

Stable isotope and trace element contents of Cyprideis torosa valves from the Lower Pleistocene marginal lacustrine sequence of Barranco León, Baza Basin (Southern Spain), allow us to reconstruct the geochemical record of environmental change in this marginal area of the basin and to compare these data with the environmental changes inferred from the faunal associations. Hydrochemical features of the Baza Lake system have been influenced by changes in water source, solute composition, and water level during the past. Three water types may have been involved in a complex mixing in the marginal area during the studied intervals (1) waters of the Baza lacustrine system that underwent large P/E changes, (2) dilute, meteoric water inputs (surface and shallow groundwaters), (3) saline groundwater inputs of meteoric origin that acquired their salinity by halite and gypsum dissolution. Four stages in the Pleistocene paleoenvironmental evolution of the Barranco León area have been differentiated: stage I records a high lake level (highstand) of the saline closed-lake system. Stage II corresponds to very shallow, palustrine conditions. Stage III records the varying influence of the three water types under changing water level in a closed-lake. Stage IV corresponds to a through-flowing, open lacustrine environment mainly fed by meteoric saline groundwaters with minor inputs of stream waters. This small through-flowing lake was connected to a larger, inner saline closed-lake system. The BL 5 mammal site with lithic tools of an early human occupation phase in Western Europe corresponds to a particular episode within this stage of the environmental evolution in the marginal zone of the Baza Lake. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.