Lake Marl Research Articles

Identification and quantitative estimates of groundwater transfers to formerly charophyte dominated marl lakes with radon-222

Interaction with groundwater determines many processes in marl lakes. Net transfer of inorganic carbon helps define their chemical characteristics and determines their unique benthic flora. Nutrient enrichment weakens the biogeochemical buffering mechanisms which help maintain a clear-water state and many small, shallow marl lakes are prone to siltation. Despite hydrological processes being recognised as important for the complex interactions between plants, nutrient availability and physical sediment properties which shape marl lake ecology, groundwater discharge to many of these lakes has never been quantified. The aim of this study was to locate and quantify groundwater transfers to degraded marl lakes in a Special Area of Conservation on the island of Ireland. A RAD7 radon detector identified and measured elevated concentrations of 222Rn in three lakes for quantifying their groundwater influx with a 222Rn mass-balance equation. Conservative estimates of mean daily groundwater discharge to Kilroosky Lough, Drumacrittin Lough, and Dummy's Lough were 143 m3, 502 m3, and 269 m3 respectively. With extrapolation to the entire hydrological year, annual groundwater recharge contributed approximately 47 %, 155 %, and 50 % of the respective lake volumes. The areas within the lakes which were found to have the highest groundwater influence also closely matched the locations where substantial charophyte communities persist suggesting that the two are linked. These findings underline the importance of groundwater transfers for the water budget in small marl lakes and will inform management efforts to mitigate their eutrophication.

The response of ostracod faunal assemblages to hydrology, lake level, and carbon cycling in a Jamaican marl lake: a palaeolimnological investigation

Abstract. Ostracod taxa from shallow freshwater lakes are sensitive to a range of limnological factors including temperature, hydrological habitat, lake level, and the distribution of aquatic plants. Ostracod assemblages preserved in Quaternary lake sediments can be used to reconstruct limnological change and are therefore potentially valuable palaeoenvironmental proxies. However, lack of autecological information about some taxa may limit the validity of such reconstructions. We use fossil ostracod assemblages recovered from radiocarbon-dated late Holocene sediments from Wallywash Great Pond, a small, shallow freshwater lake in southwestern Jamaica, to reconstruct limnological change over the past ∼ 1800 years. We circumvent ongoing taxonomic and ecological uncertainties associated with the identification of fossil ostracod taxa by drawing on observations of the ecology of ostracods found living in Jamaican water bodies. By combining this information with limnological data from the extant lake, and with sedimentological and isotopic data from the lake sediments, we show that a published interpretation of ostracod assemblages for the late Quaternary of Wallywash Great Pond is simplistic, at least for the late Holocene section of the sediment record. We conclude that changes in ostracod assemblages are linked to variations in the input of undersaturated groundwater to the northern part of the lake from which the core was recovered. These variations, which were driven by changes in the precipitation / evaporation ratio (effective moisture), also controlled sedimentation, with reduced effective moisture and a decline in undersaturated groundwater input favouring marl precipitation, whereas organic sediments are linked to increased effective moisture and enhanced groundwater input. Our findings suggest that the dramatic shifts in ostracod assemblages at this site are a complex response to changes in hydrology, sedimentology, and carbonate saturation rather than being a simple indicator of lake-level change. Combining ostracod assemblage data with the results of other palaeolimnological analyses also allows more detailed reconstructions to be made for this lake, and such a multiproxy approach is recommended for similar lakes elsewhere.

Spatial interpretation of high‐resolution environmental proxy data of the Middle Pleistocene Palaeolithic faunal kill site Schöningen 13 II‐4, Germany

To spatially characterize the palaeolakeshore environment at the archaeological kill site Schöningen 13 II‐4 of the Middle Pleistocene Reinsdorf sequence, in‐depth palynological, geochemical, aquatic microfossil and archaeological analyses were undertaken on sediment sections with an average thickness of about 15 cm, concordantly overlain by faunal remains, dominated by horse, from the unique ‘Spear Horizon’ layers of the 1995 excavation campaign. The data reveal a distinctive lake level drop, documented by the change from a carbonate‐rich lake marl to a carbonate‐free organic mud with increased carbon content and decreasing C/N, Si/Al, Si/K and Fe/Al ratios, indicating a higher pedogenic supply of organic matter and drier conditions at the site. Compared with older, similar transitional phases of lake level changes occurring within the Reinsdorf sequence, it is important that these youngest sediments are undisturbed, indicating continuous development. Ostracod and diatom analyses indicate a lowering water level with higher salinities and rich aquatic vegetation. Mesorheophilic ostracod species along with tychoplanktic diatom taxa point to flowing waters and turbulence at the lakeshore, presumably related to spring‐fed streams originating from nearby highlands. Palynological results reveal a very diverse zonal vegetation pattern around the palaeolakeshore considering an area of investigation of approximately 50 × 75 m and a tessellated type of regional vegetation during the formation of the archaeological horizons. On topographically lower elevated areas, birch groves and taxa favouring wet, marshy conditions such as Cyperaceae, indicative of terrestrialization, were predominating, while other stands of this transitional phase reveal a very dry, grass‐dominated steppe woodland favouring a rich wildlife with a striking number of megaherbivores. Our results suggest that the lithological differences of the ‘Spear Horizon’ layers containing the archaeological finds were due to their respective topographical situation and that the layers were deposited almost simultaneously during the beginning of the lake level drop. Human activities seem to have concentrated in sparsely vegetated areas along the palaeolakeshore, rather than in areas of adjacent denser birch swamp forest stands.

A Fluctuating Environment: Micromorphological and Archaeobotanical Investigations of the Early Iron Age Lakeshore Settlement at Traunkirchen (Upper Austria)

ABSTRACT Since its discovery in 1981, the site at Traunkirchen has remained among the very few Iron Age lakeshore settlements in the Circum-Alpine region. Micromorphological and archaeobotanical analyses of drilled cores from the lake bottom help to reconstruct the taphonomy of the Early Iron Age cultural layers and past environmental conditions. Our study also reveals that the water level of Lake Traunsee dropped twice by ca. 2.5/3 m within approximately 100–150 years during the Early Iron Age. The accumulation of well-preserved organic debris indicates the presence of building features in a shallow-water area, protected by a thick layer of lake marl. Carpological remains also provide insights into the local plant diet and land use based on cereals, legumes, edible fruits and nuts, all commonly used during the Iron Age. Our observations contribute to understanding Traunkirchen as an Iron Age key site, which was presumably involved in the distribution of salt from the mine at Hallstatt, down the Traun River and across Lake Traunsee.

An 1800-year oxygen-isotope record of short- and long-term hydroclimate variability in the northern neotropics from a Jamaican marl lake

Hydroclimate variability on multi-decadal timescales has been a prominent feature of the circum-Caribbean region over the common era, with marked dry intervals noted in particular for the period 800–950 CE coinciding with the Terminal Classic Period (the so-called Terminal Classic Drought: TCD) in Mesoamerica, and with the Little Ice Age from about 1500 to 1800 CE, linked to complex ocean-atmosphere interactions. Previous compilations of palaeoclimate reconstructions have revealed a clear precipitation dipole between northern and southern Mesoamerica over the common era, which is consistent with meteorological data and modelling experiments. However, patterns of variability elsewhere within the region are less well understood, although palaeoclimate records do point to spatial complexity. Here, we present a ∼sub-decadal-scale lake-sediment hydroclimate reconstruction based on ostracod-shell stable isotopes from Wallywash Great Pond, Jamaica, covering the past ∼1800 years, which fills a spatial gap in records for the region. Variations in δ18O values at this site are a proxy for changes in effective moisture and they reveal a marked wet phase over the Terminal Classic Period (TCP), suggesting that the precipitation dipole over northern and southern Mesoamerica may have an east to west component. This is supported by some previous studies, although additional sites are required from strategic localities within the region to confirm this. The Little Ice Age interval at Wallywash is drier than the TCP, although the signal is less clear than at some sites within the wider region, suggesting that regional complexity in hydroclimate has characterised this interval as well.

High resolution Late Miocene sediment accommodation rates and subsidence history in the Austrian part of the Vienna Basin

We present the first detailed intra-basin correlation of Upper Miocene deposits in the Austrian part of the Vienna Basin (VB) integrating the most important hydrocarbon fields. Herein, we use a high resolution dataset by separating the Pannonian (= Tortonian) stack into 20 lithostratigraphic units, which allow calculating regional differences in sedimentation rates over a time span of ∼1.6 Ma. During this time span we recognize an initial phase of high lateral variability in thicknesses, reflecting the influence of paleo-topography on deposition during the early Pannonian. The relief difference of about 300 m was rapidly filled by lake marls and delta lobes of the Paleo-Danube. Subsequently, lateral variability in sediment thicknesses declined strongly around 11.0 Ma. At that point the relief was largely sealed, and subsidence became the controlling factor. Our data document a shift of high subsidence rates from the southern VB to the northern VB into three steps, initiated by increased activity of the Steinberg Fault around 10.5–10.4 Ma. Sedimentation rates have been declining during the early Pannonian but reveal a strong pulse in subsidence during the middle Pannonian. The still high sedimentation rates during the late Pannonian indicate persisting extensional tectonics in the VB throughout the Late Miocene and question the prevailing tectonic model of a compressional regime for this time. The lack of uppermost Pannonian deposits in most wells documents a post-Pannonian erosion of about 400 m in large parts of the VB.

Late Quaternary paleoclimatic and paleoenvironmental changes in the Konya Closed Basin (Konya, Turkey) recorded by geochemical proxies from lacustrine sediments

The Konya Closed Basin is an important basin in central Turkey, in terms of its geographic position, Quaternary infills, and well-preserved archeological sites. It comprises Quaternary lake marls and other, mainly fine grained, sediments with locally in excess of 400 m. Geochemical data for samples taken from the 7-m-deep Adakale trench from the late Quaternary lacustrine sediments in the Konya Closed Basin are presented and have been used as proxies to elucidate the past climatic changes, weathering regime, redox conditions, and productivity. Climate changes observed in the studied samples for last 50,000 years were represented by oscillations in weathering processes, detrital input, redox conditions, water levels, and paleoproductivity. Geochemical data show that three periods of high detrital input (high Si+Al+K+Ti+Fe, high Ti/Al, Rb/Sr, low Ca and low Si/Ti), four periods of anoxic conditions (low Mn and Th/U and high Ni/Co, Mo/Al and V/Cr), and four periods of higher productivity (high Cu/Al, Ni/Al, Ca/Al, Ba/Al Si/Ti and Ca/Ti) were effective in the study area. These periods are corresponding to climatic changes during last glacial periods, the warm climate of Dansgaard-Oeschger (D/O) events (D/O 2-12) and the cold climate of Heinrich events (H 2-5).

Biological and geochemical indicators of climatic oscillations during the Last Glacial Termination, the Kaniewo palaeolake (Central Poland)

• Bølling-Allerød complex shows climatic heterogeneity and includes cold events. • Deglaciation passed 3 cold (GS-2a, GI-1d, GS-1) and 2 warm periods (GI-1e, GI-1a-c) • Traces of cold oscillation (GI-1b) within the Allerød were found. This study presents the results and interpretations of biological (floral and faunal) and geochemical (isotopic and chemical element composition) investigations of the Late Glacial and Holocene sediment accumulated in the Kaniewo palaeolake. These data allowed us to determine the indicators of environmental changes in this lake ecosystem, such as zooplankton and vegetation development, trophic state, water temperature, and water level. We documented the three cold periods (Oldest, Older, and Younger Dryas) separated by two warm periods (Bølling, Allerød). Additionally, we found traces of cold oscillations within the Allerød, lasting approximately 150 years, probably the Intra-Allerød-Gerzensee oscillation, recorded in western and southern Europe. Our data show that sediment accumulation began at the end of the Oldest Dryas period before ca. 13,900 yr cal BP. The top of the studied sediments represented the transition from the Late Glacial to the early Holocene (Preboreal period, ca.10,500 yr cal BP). The lithology of the sediments changed from silty sands at the bottom, then calcareous detritus gyttja partially interbedded by lake marl to peat at the top. Organic matter occurring in the deposits reflects algae and terrestrial sources. In the cold periods, small number of both Cladocera individuals and species (e.g. Bosmina (E.) longispina , Chydorus sphaericus , Alona affinis ), corroborate the unfavourable conditions for the development of zooplankton. Cladocera species indicated the initial oligotrophic status of the lake and the subsequent increase in trophic status. Plant and animal macrofossils indicate initial shallow lake ecosystem. Chara meadow developed at the bottom of the lake with a belt of vascular plants ( Carex sp., Hippuris vulgaris , Scirpus sp . ) in the littoral zone of the lake. Rich shallow vegetation was accompanied by animals, such as Mollusca (e.g. Valvata piscinalis, Pisidium obtusale, Bithynia tentaculata ) and Oribatidae sp., Cristatella mucedo , and Plumatella type.

Mössbauerite; polytypes in Tatkul Lake (Russia) marls and evidence in a Murray River reservoir (Australia)

Mossbauer spectroscopy characterizes “Green rust related minerals” of the fougerite group within the hydrotalcite supergroup (Mills et al. Mineral. Mag. 76(5), 1289–1336, 2012) in locations on Earth quite different from the original studies done in a temperate climate such as Brittany- France, Western Europe. Two examples are described, the gley at the bottom of Tatkul Lake in South Urals (Russia), which is representative of permafrost conditions, and a gley at the bottom of Yanga Lake, a reservoir in the Murray River catchment (NSW-Australia), which is representative of warm and desert conditions. Complementary information is obtained from XRD patterns.

Toward a tephrostratigraphic framework for the British Isles: A Last Glacial to Interglacial Transition (LGIT c. 16-8 ka) case study from Crudale Meadow, Orkney

Abstract Our understanding of the timing and phasing of abrupt climatic oscillations during the Last Glacial to Interglacial Transition (c. 16-8 ka) in terrestrial sequences is limited by a lack of high-resolution, sensitive proxy records with precise chronological data. Lacustrine carbonate records provide an excellent opportunity to address this issue with frequently high depositional rates, and the ability to extract biological and chemical proxy data related to palaeoclimate variations. However, these archives are also some of the most difficult to date due to associated problems with radiocarbon sample contamination. We present the tephrochronological findings from Crudale Meadow, Orkney, one of the most northerly former marl lakes in the British Isles. Thirteen intervals containing tephra are chemically characterised, of which six may be correlated to known eruptions. The results provide a tephrochronological framework from which it is possible to refine the age estimates of less securely dated cryptotephras, and also provide a basis from which to frame ongoing climate reconstructions using state-of-the-art proxy methods. The results presented here demonstrate that Crudale Meadow is a key record in the development of a regional tephrostratigraphic framework, and an important site in developing a refined network of well-dated high-resolution palaeoclimatic records across northern Europe.

Chara spp. exhibit highly heterogeneous light adaptation, calcite encrustation and epiphyton patterns in a marl lake

The aim of this work was to determine the relationships between calcite encrustation, photosynthetic pigments and the epiphyton community of upper and lower thallus parts of Chara spp. from different depths of a marl lake (Lake Prošće, NP Plitvice Lakes, Croatia). Samples were taken from two Chara species, spread across three lake depths (Chara subspinosa at 1 and 5 m, and Chara globularis at 10 m), and analysed spectrophotometrically for photosynthetic pigment (chlorophyll a, chlorophyll b and total carotenoids) composition, and gravimetrically for organic matter and calcite encrustation contents within the macroalgal species. Epiphytic (i.e., epialgal) protozoa and micro-metazoa were determined on live material. The amounts of calcite deposits on Chara were two times higher at the depths of 1 and 5 m, compared to 10 m – most likely due to water chemistry (i.e., pH, temperature and calcium concentrations), light availability and photosynthesis patterns as well as Chara species morphology differences. Photosynthetic pigments exhibited complex patterns, differing both between upper and lower charophyte thallus parts, and among depths, likely reflecting adaptations of the macroalgae and epiphytes to light conditions. Protozoans and micro-metazoans exhibited various assemblages at different depths, with C. subspinosa supporting highest diversity (42 taxa at 5 m) and C. globularis exhibiting highest abundance (up to 9000 ind/gDW). Peritrich ciliates and rotifers preferred Chara thalli with less extensive calcite encrustations and more complex structure.

Late Pleistocene and early Holocene drainage events in the eastern Fehmarn Belt and Mecklenburg Bight, SW Baltic Sea

The Fehmarn Belt is a key area for the Late Pleistocene and Holocene development of the Baltic Sea as it was a passage for marine and fresh water during its different stages. The pre‐Holocene geological development of this area is presented based on the analysis of seismic profiles and sedimentary gravity cores. Late Pleistocene varve sediments of the initial Baltic Ice Lake were identified. An exceptionally thick varve layer, overlain by a section of thinner varves with convolute bedding in turn covered by undisturbed varves with decreasing thicknesses is found in the Fehmarn Belt. This succession, along with a change in varve geochemistry, represents a rapid ice‐sheet withdrawal and increasingly distal sedimentation in front of the ice margin. Two erosional unconformities are observed in the eastern Mecklenburg Bight, one marking the top of the initial Baltic Ice Lake deposits and the second one indicating the end of the final Baltic Ice Lake. These unconformities join in Fehmarn Belt, where deposits of the final Baltic Ice Lake are missing due to an erosional hiatus related to a lake‐level drop during its final drainage. After this lake‐level drop, a lowstand environment represented by river deposits developed. These deposits are covered by lake marls of Yoldia age. Tilting of the early glacial lake sediments indicates a period of vertical movements prior to the onset of the Holocene. Deposits of the earliest stages of the Baltic Sea have been exposed by ongoing erosion in the Fehmarn Belt at the transition to the Mecklenburg Bight.

Paleomagnetic Constraints on the Middle Miocene‐Early Pliocene Stratigraphy in the Xining Basin, NE Tibetan Plateau, and the Geologic Implications

AbstractThe Xining Basin lies in the transitional zone between the arid Asian interior and the East Asian monsoon region. The continuous Cenozoic sediments in the basin provide a unique archive recording the uplift of the Tibetan Plateau and its environmental effects on central Asian aridification and Asian monsoon evolution. However, sediments deposited since the middle Middle Miocene have not been precisely dated, hindering our ability to address these issues. Here we dated a 336 m‐thick section containing many Late Miocene fossil mammals from the eastern basin. High‐resolution paleomagnetism revealed 16 normal and 16 reversed zones that correlate well with chrons 3n to 5Ar.1r of the Geomagnetic Polarity Time Scale, constraining the section to ∼12.7–4.8 Ma. The changes in lithofacies from floodplain to braided river at ∼8.6 Ma and to thick alluvial fan at ∼6.3 Ma with predominantly southerly paleocurrent directions occur simultaneously with an increase in the sedimentation rates, representing two periods of rapid uplift in the eastern Qilian Shan to the north. Our results provide a robust oldest age constraint (<4.8 Ma) on the ancient Huang Shui and Yellow River terraces on the basin sediments and eolian deposits on the terraces. The presence of well‐developed floodplain paleosols, shallow lake marls, and many large mammals in the lower section suggests that the monsoon climate in the late Middle Miocene to Late Miocene was more humid and stronger than that at present.

Ecological sensitivity of marl lakes to nutrient enrichment: evidence from Hawes Water, UK

Summary Highly calcareous (marl) lakes are infrequent but important freshwater ecosystems, protected under the EU Habitats and Species Directive. Chara lakes have been considered resistant to eutrophication owing to the self‐stabilising properties of charophyte meadows. However, the opposite is suggested by the large‐scale biodiversity declines in marl lake taxa in Europe, and evidence of charophyte sensitivity to eutrophication. We combined contemporary, palaeolimnological and archival methods to investigate the eutrophication of Hawes Water, a shallow marl lake in north‐west England (U.K.). Changes in aquatic macrophyte and invertebrate communities were reconstructed through the analysis of historical macrophyte surveys and sedimentary plant and animal macrofossils in two dated sediment cores from the littoral and deep zones of the lake. In addition, chlorophyll and carotenoid pigments were analysed to track changes in primary production from benthic and pelagic areas. Substantial changes in macrophyte communities were detected over centennial timescales, suggesting high ecosystem sensitivity considering the presently moderate phosphorus concentrations in Hawes Water (mean annual total phosphorus 20 μg L−1). Two apparent periods of threshold‐like change were identified from the sediment record: (i) changes in cyanobacteria (aphanizophyll + myxoxanthophyll to canthaxanthin + zeaxanthin) and potentially in nutrient stoichiometry, reductions in the maximum macrophyte colonisation depth and water clarity, reduced charophyte and Potamogeton diversity, and increases in Nymphaeaceae; and (ii) severe reductions in light availability inferred from subdecadal doubling in phytoplankton abundance, substantial increases in Daphnia abundance and the extinction of charophytes from higher water depths. Further, change in both the littoral and deeper water has confined key marl lake taxa to smaller niches. In the littoral, increasing siltation and reed and Nymphaeaceae densities caused extinction of Littorella uniflora in the early 1900s and have reduced the evenness of Characeae with suspected imminent extinction of two highly localised Chara spp. In the deeper water, upslope creep of maximum colonisation depth has reduced habitat for intermediate‐depth marl lake taxa leading to the loss of four Potamogeton and one Chara species, and replacement of these taxa by Nuphar lutea. The large changes in macrophyte community composition and increased incidences of turbid water have reduced the distinctive and valued marl lake features of Hawes Water, indicating that marl lakes can, as a habitat type, be highly sensitive to eutrophication. The persistence of abundant generalist macrophyte species at considerable water depth may be a feature of high‐alkalinity lakes in clearwater, macrophyte‐dominated states, but is a distinct eutrophication response in marl lakes rather than an indication of resistance to eutrophication.

The coming and going of a marl lake: multi-indicator palaeolimnology reveals abrupt ecological change and alternative views of reference conditions

Eutrophication is the most pressing threat to highly calcareous (marl) lakes in Europe. Despite their unique chemistry and biology, comprehensive studies into their unimpacted conditions and eutrophication responses are underrepresented in conservation literature. A multi-indicator palaeolimnological study spanning ca 1260 to 2009 was undertaken at Cunswick Tarn (UK), a small, presently eutrophic marl lake, in order to capture centennial timescales of impact. Specific aims were to 1) establish temporal patterns of change (gradual/abrupt) across biological groups, thereby testing theories of resistance of marl lake benthic communities to enrichment, and 2) compare the core record of reference condition with prevailing descriptions of high ecological status. Analyses of sediment calcium (Ca), phosphorus (P), pigments, diatoms, testate amoebae, cladocerans, and macrofossils, revealed three abrupt changes in ecosystem structure. The first (1900s), with biomass increases in charophytes and other benthic nutrient-poor indicators, supported ideas of resistance to eutrophication in Chara lakes. The second transition (1930s), from charophyte to angiosperm dominance, occurred alongside reductions in macrophyte cover, increases in eutrophic indicators, and a breakdown in marling, in support of ideas of threshold responses to enrichment. Core P increased consistently into the 1990s when rapid transitions into pelagic shallow lake ecology occurred and Cunswick Tarn became biologically unidentifiable as a marl lake. The moderate total P at which these changes occurred suggests high sensitivity of marl lakes to eutrophication. Further, the early record challenges ideas of correlation between ecological condition, charophyte biomass and sediment Ca. Instead, low benthic production, macrophyte cover, and Ca sedimentation, was inferred. Management measures must focus on reducing external nutrient and sediment loads at early stages of impact in order to preserve marl lakes.

What is a litre of sediment? Testing volume measurement techniques for wet sediment and their implications in archaeobotanical analyses at the Late Neolithic lake-dwelling site of Parkhaus Opéra (Zürich, Switzerland)

Volume measurements in archaeobotany are not performed uniformly. The goal of this paper therefore is to test the different known methods and to define the obtained differences, in order to make the density values (remains per litre of sediment) for plant macroremains in the samples comparable between sites. Three methods of volume measurement were tested for a large number of samples of different sizes coming from two late Neolithic layers of the lakeshore site of Parkhaus Opéra (Zürich, Switzerland). The sampled layers were preserved in waterlogged conditions and there were samples rich in sand, loam, lake marl but mostly consisting of organic remains, including uncharred subfossil plant macroremains. In general, the classical volume (that is the upper limit of the sediment in water) measured before and after freezing as pre-treatment gave similar results. But a systematic difference was found between the classical volume measured after freezing and the displacement volume. This difference could be described by a proportionality factor of 1.5. This proportionality factor could be used to make data obtained with different methods of volume measurement comparable, although more evaluations are needed from other sites in order to test the generality of the factor proposed.

Assessing the status of marl lakes under the European Union Water Framework Directive – insights from contemporary and palaeolimnological studies of three English lakes

Methods for ecological status assessment of high-alkalinity lakes under the Water Framework Directive (WFD) differ between continental Europe and the UK. In the UK, marl lakes, i.e. carbonate-precipitating lakes, are placed in a separate category in which metrics account for the naturally low phosphorus content and sensitive macrophyte communities found therein. If this separation is appropriate, the UK method, which applies a correction factor for stricter assessment of marl lakes, should assess ecological status more effectively. Using contemporary macrophyte and chlorophyll-a data, this supposition was assessed for three English lakes by calculating ecological status with and without the correction factor. The veracity of the results was assessed using palaeolimnological and historical surveys. Further, the potential of macrophyte maximum colonisation depth (Cmax) as an additional metric was investigated. For two lakes, the status suggested by historical-palaeolimnological data was poorer (Moder- ate) than that suggested by WFD classification, both with and without the correction factor (Good and/or High). This has important implications as restoration is required only for water bodies classed below Good. For the third lake, for which high chlorophyll-a resulted in Poor status in agreement with historical-palaeolimnological data, the discrepancy between the macrophyte metrics with and without the correction factor was considerable (Poor, Moderate, respectively). The results suggest that a separate marl lake category is warranted and may be advisable for other Member States in continental Europe. Importantly, status was higher than recommended for the two lakes close to the Good/Moderate boundary even with the correction factor. This leads us to recommend more studies be undertaken on eutrophication responses of marl lakes. In lakes where macrophyte species composition varies with water depth, eutrophication is apparent through reductions in Cmax especially of Characeae and Potamogetonaceae. Cmax is simple to measure and may much improve the reliability of marl lake assessment.

Environment and agriculture of the transitional period from the Late Bronze to early Iron Age in the eastern Baltic: an archaeobotanical case study of the lakeshore settlement Luokesa 1, Lithuania

Prehistoric agriculture and vegetation in Lithuania have so far been reconstructed largely using palynological data. This paper reports the archaeobotanical investigation of macroremains from the Late Bronze-early Iron Age (LBA–EIA) lakeside settlement Luokesa 1 (L1) in eastern Lithuania, with the aim of elucidating the settlement’s history and crop diversity. The single phase settlement was fortified with an onshore palisade and is dated between 625 and 535 cal. bc. Samples were taken along a land to lake transect, and in the centre of L1. The stratigraphy consisted of three distinct layers: lake marl, cultural deposit and sandy limnic sediment on top. The plant spectrum shows that L1 was constructed on an exposed morainic shoal. It was surrounded by woodland, meadows, fields/gardens, ruderal habitats and riverine vegetation. Accumulated cultural deposits consisted mainly of manure (litter, fodder and dung of sheep/goat), with rubbish, sweepings from the houses or remains of the on-site vegetation. The crops were Panicum miliaceum, Triticum spelta, T. dicoccon, Hordeum vulgare s.l., Pisum sativum and Camelina sativa, the latter being the first prehistoric evidence in Lithuania. The trophic state of the lake increased during the occupation period. After the abandonment of the settlement the ruins decayed until the lake flooded the site. The results are discussed in a broader context of the LBA/EIA cultures in northern Central Europe.

The potential of micromorphology for interpreting sedimentation processes in wetland sites: a case study of a Late Bronze–early Iron Age lakeshore settlement at Lake Luokesa (Lithuania)

Lake Luokesa lies in the eastern part of Lithuania and is part of a region of lakes formed by the Scandinavian ice-sheet and its melt waters during the last glaciation. During the Late Bronze–Early Iron Age transition, between 625 and 535 cal BC, a lakeside settlement with an onshore palisade was built on the platform of a carbonate bank. A total of five profiles, each comprising an organic occupation layer and lake sediments at its bottom and top, were examined micromorphologically. In this paper, natural and anthropogenic processes that led to the formation of the individual layers are presented; their possible origins are reconstructed and then discussed and compared to lakeside settlements of the circum-alpine region. This includes the emergence of lake marl, accumulation of organic layers in the settlement area as well as their decomposition, erosion and trampling features and inwash of sand through runoff from the hinterland. Due to the accumulation of the up to 60 cm thick culture layers in waterlogged environments, indications of seasonal deposition cycles could be identified.

Palynological investigations at the Late Bronze–Early Iron Age lakeshore settlement of Luokesa 1 (Moletai District, Lithuania): a contribution to the Middle-Late Holocene vegetation history of the south-eastern Baltic regions

Today, the settlement site of Luokesa 1 (L1) lies under water at the northern edge of Lake Luokesa in the Baltic Uplands, south-eastern Lithuania. Its 60 cm-thick Late Bronze–Early Iron Age cultural layer lies on top of lake marl. During excavations in 2008 and 2009, core samples at L1 were taken for the purpose of multidisciplinary investigations. From this material, five on-site pollen diagrams were created in parallel with geo-archaeological investigations and the examination of the botanical macro-remains. Two of these cores mainly comprised the cultural layer, another two consisted largely of the underlying lake marl and the fifth contained primarily the transition from the lake marl to the cultural layer. The chronological sequence was established through 11 AMS dates. The woodland history, starting from the Late Atlantic period, was recorded. The Quercetum mixtum values are quite low in the Subboreal, with the coniferous forest consisting mainly of Pinus and, though significantly less, Picea. At the transition to the cultural layer (Subatlantic) the pollen curves are highly variable, showing peaks in the curves for Betula and Alnus. Pollen from aquatic plants is also present. Changes in riparian vegetation and turbulent sedimentation conditions are to be expected and can be explained by a drop in the water level. As L1 was located on damp ground at that time, water influxes alternating with dry episodes were observed. In the area around L1 the sedge belt was less pronounced, and riparian woodland extended all the way to the shores of the lake. Pollen analyses of four sheep/goat dung samples provide information on the grazing season and pasture location of these domestic animals. The paper also discusses layer formation processes such as water level fluctuations and hiatuses.