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

Morphological variation within the Placoneis elginensis (W.Gregory) E.J.Cox species complex

Freshwater diatom species Placoneis elginensis (W.Gregory) E.J.Cox was originally described in 1856 as Pinnularia elginensis W.Gregory. Because it is often confused with other species, its distribution requires closer investigation. The Placoneis elginensis species complex includes taxa with elliptic-lanceolate to linear-lanceolate valve shapes and capitate to rostrate apices. At present, six taxa are known from this complex: P. elginensis, P. paraelginensis Lange-Bertalot, P. abiskoensis (Hustedt) Lange-Bertalot & Metzeltin, P. ignorata (Schimanski) Lange-Bertalot, P. rostrata (A.Mayer) E.J.Cox and P. undulata (Østrup) Lange-Bertalot. Most of these taxa are widely distributed and rarely found in high numbers. They can occur in habitats with different environmental conditions, but mostly, they prefer mesotrophic to eutrophic waters with medium electrolyte content. During observations of different habitats (lakes, ponds, streams, wetlands, peat bogs) throughout North Macedonia seven species were recorded. In Taor cannel (near the city of Skopje), on mud, one new species from this complex was observed. It is characterized by elliptic-lanceolate valves with distinctly capitate apices, broad central area and distantly spaced striae (10–12 in 10 µm). All seven species are illustrated with LM and SEM and their morphological features are compared. Additionally, shape analyses of all species have been performed using software DiaOutline. For visualization and statistical evaluations, Principal Component Analyses (PCA), and Linear Discriminant Analyses (LDA) were used. Results showed that all analyzed species are significantly different with respect to the valve shape. Important separating features for the identification of species from this complex include valve shape, valve margin, shape of the valve apices and stria density.12th Central European Diatom meeting, Belvaux, Luxembourg, 26-27 March 201

Complexity of diatom response to Lateglacial and Holocene climate and environmental change in ancient, deep and oligotrophic Lake Ohrid (Macedonia and Albania)

© Author(s) 2016. Lake Ohrid (Macedonia and Albania) is a rare example of a deep, ancient Mediterranean lake and is a key site for palaeoclimate research in the northeastern Mediterranean region. This study conducts the analysis of diatoms as a proxy for Lateglacial and Holocene climate and environmental change in Lake Ohrid at a higher resolution than in previous studies. While Lake Ohrid has the potential to be sensitive to water temperature change, the data demonstrate a highly complex diatom response, probably comprising a direct response to temperature-induced lake productivity in some phases and an indirect response to temperaturerelated lake stratification or mixing and epilimnetic nutrient availability in others. The data also demonstrate the possible influence of physical limnological (e.g. the influence of wind stress on stratification or mixing) and chemical processes (e.g. the influence of catchment dynamics on nutrient input) in mediating the complex response of diatoms. During the Lateglacial (ca. 12 300-11 800 cal yr BP), the low-diversity dominance of hypolimnetic Cyclotella fottii indicates low lake productivity, linked to low water temperature. Although the subsequent slight increase in small, epilimnetic C. minuscula during the earliest Holocene (ca. 11 800-10 600 cal yr BP) suggests climate warming and enhanced stratification, diatom concentration remains as low as during the Lateglacial, suggesting that water temperature increase was muted across this major transition. The early Holocene (ca. 10 600-8200 cal yr BP) is characterised by a sustained increase in epilimnetic taxa, with mesotrophic C. ocellata indicating high water-temperature-induced productivity between ca. 10 600-10 200 cal yr BP and between ca. 9500-8200 cal yr BP and with C. minuscula in response to low nutrient availability in the epilimnion between ca. 10 200-9500 cal yr BP. During the middle Holocene (ca. 8200-2600 cal yr BP), when sedimentological and geochemical proxies provide evidence for maximum Holocene water temperature, anomalously low C. ocellata abundance is probably a response to epilimnetic nutrient limitation, almost mimicking the Lateglacial flora apart from the occurrence of mesotrophic Stephanodiscus transylvanicus in the hypolimnion. During the late Holocene (ca. 2600 cal yr BP-present), high abundance and fluctuating composition of epilimnetic taxa are probably a response more to enhanced anthropogenic nutrient input, particularly nitrogen enrichment, than to climate. Overall, the data indicate that previous assumptions concerning the linearity of diatom response in this deep, ancient lake are invalid, and multi-proxy analysis is essential to improve understanding of palaeolimnological dynamics in future research on the long, Quaternary sequence

New Amphora and Halamphora (Bacillariophyta) species from springs in the northern Apennines (Emilia-Romagna, Italy)

Background and aims – The detailed analysis of algae and cyanoprokaryotes in a heterogeneous group of spring habitats (including all the different typologies) of the northern Apennines (Emilia-Romagna Region, Italy) revealed a new Amphora species in a small mountain flowing spring with low conductivity, and a new Halamphora species in a large, inland-saline (Triassic gypsum), fast flowing spring (Poiano spring). The present study aims to describe in detail these two new species found in contrasting spring types.Methods – This study is based on light microscopy (both fresh –for plastids – and prepared materials) and scanning electron microscopy observations, as well as a thorough morphological, physical, chemical, and biological characterization of the habitats.Key results – Amphora eileencoxiae sp. nov. is most similar to A. vetula (and allied taxa), and is characterized by the outline with acutely rounded, moderately ventrally bent ends, by the dimensions, and by the well-defined, semi-elliptic dorsal area. Halamphora poianensis sp. nov. is most similar to H. gasseae but differs by the higher stria density, the clearly ventrally bent ends, and the strongly developed dorsal raphe ledge.Conclusions – This is a contribution to the knowledge of the genera Amphora and Halamphora in mountain springs in understudied geographic areas and inland-saline springs, the species communities of which are likely insufficiently explored

Complexity of diatom response to Lateglacial and Holocene climate and environmental change in ancient, deep and oligotrophic Lake Ohrid (Macedonia and Albania)

Lake Ohrid (Macedonia and Albania) is a rare example of a deep, ancient Mediterranean lake and is a key site for palaeoclimate research in the northeastern Mediterranean region. This study conducts the analysis of diatoms as a proxy for Lateglacial and Holocene climate and environmental change in Lake Ohrid at a higher resolution than in previous studies. While Lake Ohrid has the potential to be sensitive to water temperature change, the data demonstrate a highly complex diatom response, probably comprising a direct response to temperature-induced lake productivity in some phases and an indirect response to temperature-related lake stratification or mixing and epilimnetic nutrient availability in others. The data also demonstrate the possible influence of physical limnological (e.g. the influence of wind stress on stratification or mixing) and chemical processes (e.g. the influence of catchment dynamics on nutrient input) in mediating the complex response of diatoms. During the Lateglacial (ca. 12 300-11 800 cal yr BP), the low-diversity dominance of hypolimnetic Cyclotella fottii indicates low lake productivity, linked to low water temperature. Although the subsequent slight increase in small, epilimnetic C. minuscula during the earliest Holocene (ca. 11 800-10 600 cal yr BP) suggests climate warming and enhanced stratification, diatom concentration remains as low as during the Lateglacial, suggesting that water temperature increase was muted across this major transition. The early Holocene (ca. 10 600-8200 cal yr BP) is characterised by a sustained increase in epilimnetic taxa, with mesotrophic C. ocellata indicating high water-temperature-induced productivity between ca. 10 600-10 200 cal yr BP and between ca. 9500-8200 cal yr BP and with C. minuscula in response to low nutrient availability in the epilimnion between ca. 10 200-9500 cal yr BP. During the middle Holocene (ca. 8200-2600 cal yr BP), when sedimentological and geochemical proxies provide evidence for maximum Holocene water temperature, anomalously low C. ocellata abundance is probably a response to epilimnetic nutrient limitation, almost mimicking the Lateglacial flora apart from the occurrence of mesotrophic Stephanodiscus transylvanicus in the hypolimnion. During the late Holocene (ca. 2600 cal yr BP-present), high abundance and fluctuating composition of epilimnetic taxa are probably a response more to enhanced anthropogenic nutrient input, particularly nitrogen enrichment, than to climate. Overall, the data indicate that previous assumptions concerning the linearity of diatom response in this deep, ancient lake are invalid, and multi-proxy analysis is essential to improve understanding of palaeolimnological dynamics in future research on the long, Quaternary sequence

From commercial sand digging to diatoms “hotspot“

The artificial sandpit lake “Peskara“ is located between the two saline lakes, Lake Velika Rusanda and Lake Mala Rusanda, in the protected zone of Rusanda Nature Park (Vojvodina, Serbia). The lake was created by human activity for the exploitation of sand. The depression (on average 4.4 m deep, around 205 m long, and 107 m wide) was filled with water that can be classified into sodium bicarbonate chemical type. Over time a stable diatom community developed. During observations of the samples collected from the sand and reed during 2019 and 2020, 111 diatom taxa belonging to 37 genera were recorded. 14 diatom taxa and one genus (Seminavis) were noted for the first time for the diatom flora of Serbia. Fresh alkaline waters with elevated concentrations of electrolytes (1860–1950 μS/cm) enabled the development of freshwater diatoms (e.g. Achnanthidium minutissimum, Gomphonema parvulum) but also diatoms characteristic for brackish and coastal waters, such as Bacillaria paxillifera, Entomoneis costata, Haslea duerrenbergiana, Pleurosigma salinarum, Staurophora brantii, Seminavis strigosa, etc. Many of these species have not been found in saline lakes and ponds in the Vojvodina province, which makes “Peskara“ a significant “hotspot” from the aspect of diatom biodiversity. This artificial sandpit lake requires more detailed research in order to obtain a certain degree of legal protection and to prevent possible backfilling and habitat loss for many diatom species.12th International Phycological Congress - IPC2021, 22-26 March 2021, Virtual forma

Metabarcoding and morphological data of Mayamaea species from soda pans in Serbia

Soda pans located in the northern part of Serbia are alkaline and very shallow water habitats influenced by seasonal drying. Due to the rareness, vulnerability, and specific biota, these saline habitats have high conservation priority according to the EU Habitats Directive (92/43/EC). Since 2017, ten soda pans have been intensively studied with the aim to determine the diatom biodiversity and to evaluate ecological conditions. Diatom samples were collected from mud and reed, and samples for molecular analyses were additionally collected in 2021. The diatom community is mostly composed of species that prefer alkaline conditions and high conductivity. Some of the most dominant genera are Nitzschia and Navicula. Among the recorded diatoms, Mayamaea permitis and one unknown Mayamaea species were recorded in two soda pans (Okanj bara and Bela bara). The unknown Mayamaea can easily be distinguished from similar species by the valve outline and shape of the central area using light and scanning electron microscopy. In a metabarcoding (partial 18S rRNA gene sequence) data set from the same sample, we could identify two amplicon sequence variants showing affinities to the genus Mayamaea, one of them matching published sequences from M. permitis, the other without exact matches in the Diat.barcode and NCBI databases. We conclude that the latter probably belongs to the new Mayamaea species observed by microscopy, which indicates that the unknown Mayamaea species is closely related to but different from Mayamaea terrestris. Based on morphological features and molecular analyses, we consider the unknown Mayamaea species as a species new to science. Bearing in mind the vulnerability of soda pans due to anthropogenic threats and climate change, knowing which species inhabit these habitats is the first step in preserving these unique ecosystems

How do newly-described diatom species affect biomonitoring? – An example of Gomphonema paratergestinum vs. G. tergestinum

Over the past decade a great number of new diatom taxa was described, as well as re-definitions and delimitations of taxa from different species complexes have been performed. The reasons for the constant increase in the number of described diatom taxa are numerous: unexplored habitats, improved light microscope resolution and digital cameras with accompanying softwares, scanning electron microscopy, molecular studies. For most of the newly-described species only morphological characteristics are known. What about their ecological preferences? OMNIDIA is a widely used software for evaluation of ecological status of water bodies based on diatoms. The database from the first version of the software up to today has grown from 2035 to more than 23.000 diatom taxa. However, for the most newly-described taxa there are no indicator values. In our study we evaluated the ecological status at six sites in lakes Ohrid and Prespa, respectively, based on different biological quality elements (diatoms, macrozoobenthos and macrophytes) as well as water chemistry. In two out of six sites in lake Ohrid, and five out of six sites in lake Prespa, Gomphonema paratergestinum was a dominant or subdominant species (33.5-69.66 % in Ohrid Lake and 9.95-65.34 % in Prespa Lake). In the OMNIDIA software, there currently are no indicator values for G. paratergestinum. However, the very similar species G. tergestinum has well known indictor values. G. paratergestinum resembles G. tergestinum with respect to some morphological characteristics (e.g. valve outline), but can be differentiated by the stria density. Both species were present in lakes Ohrid and Prespa, however, with dominance of G. paratergestinum. Based on the diatoms recorded at a site, OMNIDIA calculates diatom index values. How could G. paratergestinum with abundances up to 69.66 % influence diatom indices? If we “experiment” and substitute G. paratergestinum with G. tergestinum, the obtained diatom index values indicated a completely different ecological quality class. Every newly-described species is important since it increases our knowledge about diversity, biogeography and distribution of diatoms. However, there still is a gap between taxonomy and biomonitoring. How can we overcome this problem? According to the Botanical Nomenclature Code for algae, fungi, and plants no note or suggestion regarding ecology or ecological preferences of a species is required for description. Maybe, a possible solution could be that in the description of the species ecological data, such as pH, conductivity, total phosphorus, concentrations of different anions etc. should be included. Scientists today join forces to review material and species collected by Kützing, Ehrenberg, Grunow, Van Heurck, Cleve etc... In the same way ecological data of newly-described species could be assembled and their indicator values calculated

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

Lateglacial and Holocene climate and environmental change in the northeastern Mediterranean region: Diatom evidence from Lake Dojran (Republic of Macedonia/Greece)

The juncture between the west-east and north-south contrasting Holocene climatic domains across the Mediterranean is complex and poorly understood. Diatom analysis of Lake Dojran (Republic of Macedonia/Greece) provides a new insight into lake levels and trophic status during the Lateglacial and Holocene periods in the northeastern Mediterranean. Following a very shallow or even desiccated state at the core base at ca. 12,500 cal yr BP, indicated by sedimentological and hydro-acoustic data, diatoms indicate lake infilling, from a shallow state with abundant benthos to a plankton-dominated relatively high lake level and eutrophic state thereafter. Diatom-inferred shallowing between ca. 12,400 - 12,000 cal yr BP and a very low lake level and eutrophic, oligosaline state between ca. 12,000 - 11,500 cal yr BP provide strong evidence for Younger Dryas aridity. The earliest Holocene (ca. 11,500 - 10,700 cal yr BP) was characterised by a high lake level, followed by a lake-level reduction and increased trophic level between ca. 10,700-8,500 cal yr BP. The lake was relatively deep and exhibited peak Holocene trophic level between ca. 8,500-3,000 cal yr BP, becoming shallow thereafter. The diatom data provide more robust evidence and strengthen previous lake-level interpretation based on sedimentological and geochemical data during the earliest, mid and late Holocene, and also clarify previous uncertainty in interpretation of Lateglacial and early-Holocene lake-level change. Our results are also important in disentangling regional climate effects from local catchment dynamics during the Holocene, and to this end we exploit extant regional palynological evidence for vegetation change in the highlands and lowlands. The importance of seasonality in driving Holocene climate change is assessed by reference to the summer and winter latitudinal temperature gradient (LTG) model of Davis and Brewer (2009). We suggest that increased precipitation drove the high lake level during the earliest Holocene. The early- Holocene low lake level and relatively high trophic state may result climatically from high seasonality of precipitation and locally from limited, nutrient-rich catchment runoff. We argue that the mid- Holocene relatively deep and eutrophic state was driven mainly by local vegetation succession and associated changes in catchment processes, rather than showing a close relationship to climate change. The late-Holocene shallow state may have been influenced by a temperature-induced increase in evaporative concentration, but was coupled with clear evidence for intensified human impact. This study improves understanding of Lateglacial and Holocene climate change in the northeastern Mediterranean, suggests the important role of the LTG on moisture availability during the Holocene, and clarifies the influence of catchment processes on palaeohydrology