Late Glacial to Holocene climate change and human impact in the Mediterranean: The last ca. 17ka diatom record of Lake Prespa (Macedonia/Albania/Greece)

Lake Prespa (Macedonia/Albania/Greece) occupies an important location between Mediterranean and central European climate zones. Although previous multi-proxy research on the Late Glacial to Holocene sequence, core Co1215 (320 cm; ca. 17 cal ka BP to present), has demonstrated its great value as an archive of Quaternary palaeoclimate data, some uncertainty remains in the interpretation of climate change. With the exception of oxygen stable isotope data, previous palaeolimnological interpretation has relied largely on proxies for productivity. Here, existing interpretation is strengthened by the addition of diatom data. Results demonstrate that shifts in diatom assemblage composition are driven primarily by lake-level changes and thus permit more confident interpretation of shifts in moisture availability over time, while corroborating previous interpretation of catchment- and climate-induced productivity shifts. An inferred cold, arid shallow lake phase between ca. 17.1 and 15.7 cal ka BP is not only followed by a high-productivity phase from ca. 15.7 cal ka BP with Late Glacial warming, but also is the first evidence for a gradual increase in lake level, in line with other regional records. Clear evidence for a Younger Dryas climate reversal between ca. 13.1 and 12.3 cal ka BP is followed by an unusually gradual transition to the Holocene and deeper, oligotrophic–mesotrophic lake conditions are reached by ca. 11.0 cal ka BP. In contrast to the arid episode from ca. 10.0 to 8.0 ka inferred from positive 18δOcalcite values, rapid diatom-inferred lake-level increase after the start of the Holocene suggests high moisture availability, in line with palynological evidence, but with only very subtle evidence for the impact of an 8.2 ka cold event. The maintenance of high lake levels until 1.9 cal ka BP, and the peak of inferred humidity from ca. 7.9 to 6.0 cal ka BP, matches the oxygen stable isotope profile and confirms that the latter is driven primarily by evaporative concentration rather than reflecting regional shifts in precipitation sources over time. During the Late Holocene progressive eutrophication is inferred between 1.9 and present. Two shallow phases at ca. 1.0 cal ka BP and at ca. 100 years ago probably represent an aridity response which is added to increase human impact in the catchment. Overall, the study is important in confirming previous tentative inferences that Late Glacial to Holocene moisture availability has strong affinity with other sites in the Eastern Mediterranean. It also tracks the pattern of North Atlantic forcing

Cyclotella paleo-ocellata, a new centric diatom (Bacillariophyta) from Lake Kinneret (Israel)

© Czech Phycological Society (2015). Large, subfossil populations of an unknown centric, planktonic diatom were observed in a lake sediment core from Lake Kinneret (Israel), which is here described as Cyclotella paleo–ocellata sp. nov. The new taxon, which belongs to the Cyclotella ocellata species complex, is described and separated from other similar taxa (e.g., Cyclotella ocellata, Cyclotella kuetzingiana, Cyclotella polymorpha, Cyclotella paraocellata) based on a combination of the following morphological characters: valve diameter, number of orbiculi depressi (circular depressions), number of striae/10 μm, stria length, number and position of rimoportulae and the number of central and marginal fultoportulae. Cyclotella paleo–ocellata can be distinguished mainly by two prominent characteristics: (1) the number and the arrangement of the orbiculi depressi (4–8) which increase with the valve diameter and (2) the marginal fultoportulae, situated on each, every second or third costa. Since Cyclotella paleo–ocellata is at present only known from the subfossil bottom sediments of Lake Kinneret, its ecological preferences are inferred simply from the associated diatom flora

Spatial patterns of diatom diversity and community structure in ancient Lake Ohrid

[EN] The extraordinary diversity in long-lived lakes is largely driven by distinct eco-evolutionary processes. With their unique biota and numerous endemic taxa, these lakes are key settings for fundamental studies related to ecology, diversity, and evolution. Here, we test how the environment shapes diatom diversity and community patterns over space in ancient Lake Ohrid. By applying Bray–Curtis similarity analyses of diatom community data, including widespread and endemic taxa, we identified two major zones: littoral and sublittoral. The latter one is being characterized with higher endemic diversity. The a and b diatom diversity and community distribution in the northern and eastern part of the lake are influenced by the presence of vertical (bathymetrical) and horizontal barriers. The zonation of the diatom communities appears driven by two large-scale factors: (i) water depth, and (ii) water chemistry, primarily, the concentration of total phosphorus, nitrogen ammonia, and conductivity. Both drivers appear to equally influence diatom diversity and community patterns. We present initial data on diatom–environment relations, where the results support earlier ecological studies emphasizing the relevance of ongoing human-induced eutrophication in the northern lake area. This study provides background information on the role of the environment in structuring contemporary diatom diversity. However, future research needs to focus on the biotic component including species competition in order to reveal the mechanisms driving spatial community dynamics in Lake OhridSIThe presented study would not have been possible without the support of the Western Balkan Environmental Network project (www.newenproject.org

Observations of the genus muelleria (bacillariophyceae) from the Republic of north Macedonia

Background and aims – An increased interest in the diatom flora from subaerial habitats in the Republic of North Macedonia has revealed the presence of a large number of interesting and often unknown, species. During a recent biodiversity survey, seven Muelleria species were recorded, several of which could not be identified based on the available literature. Methods – Using both Light Microscopy and Scanning Electron Microscopy techniques, the morphology of several Muelleria species has been analysed. The morphology of all taxa is described, illustrated and compared with other possible similar Muelleria taxa, known worldwide. Key results – Four already documented Muelleria species, M. gibbula, M. islandica, M. terrestris and M. undulata (= Navicula gibbula f. undulata) were identified, while two distinct species are described as new. These new species belong to the M. gibbula complex, and can be differentiated by valve size, stria density, shape of the proximal raphe ends and the shape of external areola foramina. The identity of one taxon remains uncertain due to a low number of observed specimens in the samples. As their ultrastructure is almost entirely unknown, they are briefly discussed. Conclusions – The diversity of Muelleria in Europe and the North Hemisphere is most likely underestimated and some of the previous records of M. gibbula belong to other species. Observations of diatoms from “extreme” habitats such as intermittent ponds, wet mosses and soils can reveal the existence of interesting and new species

Drivers of phytoplankton community structure change with ecosystem ontogeny during the Quaternary

Freshwater species are particularly sensitive to climate fluctuations, but little is known of their response to the large-scale environmental change that took place during the Quaternary. This is partly due to the scarcity of continuously preserved freshwater sedimentary records with orbital chronology. We use a 1.363 Ma high-resolution fossil record of planktonic diatoms from ancient Lake Ohrid to evaluate the role of global and regional versus local-scale environmental change in driving temporal community dynamics. By using a Bayesian joint species distribution model, we found that communities were mostly driven by the local-scale environment. Its effects decreased over time, becoming less important than global and regional environment at the onset of the penultimate glacial, 0.183 Ma. Global and regional control over the environment became important with successive deepening of the lake at around 1.0 Ma, and its influence remained persistent until the present. Our high-resolution data demonstrate the critical role of lake depth and its thermal dynamics in determining phytoplankton response to environmental change by influencing lake mixing, nutrient and light availability. With this study we demonstrate the relative impact of various environmental factors and their scale dependant effect on the phytoplankton communities during the Quaternary, emphasizing the importance of not only considering climate fluctuations in driving their structure and temporal dynamics but also the local environment. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

The Lake Ohrid SCOPSCO project

The ICDP SCOPSCO project at Lake Ohrid in Macedonia and Albania was one of the most successful lake drilling campaigns worldwide. Drilling took place from April to June 2013 and yielded more than 2000 m of sediments from four different sites in the lake. The maximum penetration was 569 m below lake floor and the overall recovery at all drill sites was > 95 %. Almost two years after the drilling operation, core opening and processing as well as biological and geological analyses are still ongoing

Environmental filtering drives assembly of diatom communities over evolutionary time‐scales

Aim Ecological communities are structured through the interplay of deterministic assembly processes such as competition and environmental filtering. Whereas the drivers of spatial community structure are frequently studied in extant communities, little is known about the relative importance of assembly processes in response to environmental factors over evolutionary time-scales. Here, we use an integrative framework to unravel community assembly processes since the inception of a long-lived lake ecosystem. Location Lake Ohrid. Time period From lake formation 1.36 million years ago to the present. Major taxa studied Planktonic diatoms. Methods We constructed a dated phylogeny of extant and extinct diatoms and collected trait data for 380 fossil communities to quantify phylogenetic community structure and functional richness and to determine the relative importance of deterministic assembly processes over time. We then used regression analysis to correlate the phylogenetic community structure with palaeoenvironmental and intrinsic biological predictors and to identify primary drivers of assembly processes. Results Our results suggest a dense packing of niche space with higher species richness and co-occurrence of closely related species. There are only two short episodes in the very recent past dominated by distantly related taxa. We found distinct changes in phylogenetic community structure upon speciation or extinction events and an increase in mean community relatedness over time. Main conclusions Our finding of closely related co-occurring species implies environmental filtering as the primary assembly mechanism, with a minor but increasingly important role of competition towards the present, driven by evolutionary dynamics. Such an increase in the relative contribution of competition to the assembly of communities in relation to the aging of an insular ecosystem, together with a denser packing of morphospace in the early phase of system ontogeny is compatible with ecological predictions according to the theory of island biogeography

The geodynamic and limnological evolution of Balkan Lake Ohrid, possibly the oldest extant lake in Europe

Studies of the upper 447 m of the DEEP site sediment succession from central Lake Ohrid, Balkan Peninsula, North Macedonia and Albania provided important insights into the regional climate history and evolutionary dynamics since permanent lacustrine conditions established at 1.36 million years ago (Ma). This paper focuses on the entire 584-m-long DEEP sediment succession and a comparison to a 197-m-long sediment succession from the Pestani site ~5 km to the east in the lake, where drilling ended close to the bedrock, to unravel the earliest history of Lake Ohrid and its basin development. 26Al/10Be dating of clasts from the base of the DEEP sediment succession implies that the sedimentation in the modern basin started at c. 2 Ma. Geophysical, sedimentological and micropalaeontological data allow for chronological information to be transposed from the DEEP to the Pestani succession. Fluvial conditions, slack water conditions, peat formation and/or complete desiccation prevailed at the DEEP and Pestani sites until 1.36 and 1.21 Ma, respectively, before a larger lake extended over both sites. Activation of karst aquifers to the east probably by tectonic activity and a potential existence of neighbouring Lake Prespa supported filling of Lake Ohrid. The lake deepened gradually, with a relatively constant vertical displacement rate of ~0.2 mm a−1 between the central and the eastern lateral basin and with greater water depth presumably during interglacial periods. Although the dynamic environment characterized by local processes and the fragmentary chronology of the basal sediment successions from both sites hamper palaeoclimatic significance prior to the existence of a larger lake, the new data provide an unprecedented and detailed picture of the geodynamic evolution of the basin and lake that is Europe’s presumed oldest extant freshwater lake

Anthropogenic activities in the páramo trigger ecological shifts in Tropical Andean lakes

A robust understanding of the impact of anthropogenic activities on high-altitude tropical aquatic ecosystems is key for the conservation and protection of the Tropical Andean biodiversity hot spot. We present the results of a multiproxy study of lake sediments from the high Andean páramo of El Cajas National Park, a UNESCO biosphere reserve in Ecuador. The main site, Laguna Pallcacocha, is well known for recording El Niño-driven clastic flood layers that are triggered by high-intensity rainfall anomalies from the eastern Pacific. The second site, Laguna El Ocho, does not contain clastic laminations, providing a control. The records show abrupt shifts in diatom assemblages ca. AD 1991 in both high-elevation Andean lakes accompanied by local changes in páramo composition that suggest a sudden nutrient enrichment of the environment. The diatom assemblages from Laguna Pallcacocha, in relation to the clastic input events, are remarkably stable and do not show evident El Niño signals at the analysed resolution. Based on comparison with the nonlaminated El Ocho record, we deduce the main source of this nutrient enrichment to be the construction of a heavily transited road that runs through the park, while climate warming played secondary role by amplifying its effects