Lake Ohrid Research Articles

OCCURRENCE OF LAMPROGLENA PULCHELLA (NORDMANN, 1832) (COPEPODA: LERNAEIDAE) IN SOME CYPRINID FISH FROM OHRID LAKE (MACEDONIA)

The representatives of the class Copepoda are of great importance in fish pathology. Lamproglena pulchella (Nordmann, 1832) (Copepoda: Lernaeidae) is an ectoparasite of many cyprinid fish, widespread in Europe up to the Aral Sea. During the long-term investigations of 12 species of cyprinid fish from the Lake Ohrid, a total of 7 specimens of Lamproglena pulchella was found in 5 fish from 4 fish species: Rutilus ohridanus, Squalius squalus, Scardinius knezevici and Chondrostoma ohridanus. Only fresh fish were subjected to routine parasitological examinations, dissection, and observation methods. Parasite identification was performed morphologically, based on the character of their maxilla, maxilliped, antennae, legs and uropods, using a referent key for determination. The 3 parasite specimens were found in two samples of Rutilus ohridanus, followed by 2 parasite specimens in Squalius squalus and one specimen in Scardinius knezevici and Chondrostoma ohridanus, each. These parasites attach to gills and general body surfaces by their maxilla and maxilliped, causing wounds that become the spots of secondary infection by microbes. The damage caused by this parasite is more pronounced in aquaculture systems. We did not find many parasites, but considering the potential danger that Lamproglena pulchella poses to the fish health, we point out the need to monitor infestations with this parasite and take preventive measures so that the parasite does not spread massively among fish in Lake Ohrid and to prevent its introduction into other waters in Macedonia. The record of Lamproglena pulchella in all four cyprinid fish in the present study is considered as the first from the Ohrid Lake. At the same time, Rutilus ohridanus, Scardinius knezevici and Chondrostoma ohridanus represent new hosts for this parasite, worldwide.

Unraveling the Secrets of Lake Ohrid, Europe’s Oldest Lake

Lake Ohrid is located on the border of Albania and North Macedonia. It is believed to be the oldest and most biodiverse lake in Europe. Several hundred meters of sediments have built-up on the lake bottom since its formation. These sediments are a record of what happened both within the lake and in its environment in the past. Therefore, Lake Ohrid is a unique place to learn more about Earth’s history. Drilling down into the lake bottom to get samples of sediment layers allowed us to unravel the secrets of the lake’s history. The sediments revealed that the lake formed between 1.9 and 1.4 million years ago. They showed past environmental and climate changes in the Mediterranean region. Tiny fossils showed the evolution of the lake’s biodiversity in the past, which benefitted from the lake’s long and stable existence. The stability of Lake Ohrid’s ecosystem is now threatened by increasing human impacts. Protecting this unique place is needed.

Autecology of the extant ostracod fauna of Lake Ohrid and adjacent waters - a key to paleoenvironmental reconstruction

Understanding the ecology of bioindicators such as ostracods is essential in order to reconstruct past environmental and climate change from analysis of fossil assemblages preserved in lake sediment cores. Knowledge of the ecology of ancient Lake Ohrid’s ostracod fauna is very limited and open to debate. In advance of the Ohrid ICDP-Drilling project, which has potential to generate high-resolution long-term paleoenvironmental data of global importance in paleoclimate research, we sampled Lake Ohrid and a wide range of habitat types in its surroundings to assess 1) the composition of ostracod assemblages in lakes, springs, streams, and short-lived seasonal water bodies, 2) the geographical distribution of ostracods, and 3) the ecological characteristics of individual ostracod species. In total, 40 species were collected alive, and seven species were preserved as valves and empty carapaces. Of the 40 ostracod species, twelve were endemic to Lake Ohrid. The most common genus in the lake was Candona, represented by 13 living species, followed by Paralimnocythere, represented by five living species. The most frequent species was Cypria obliqua. Species with distinct distributions included Heterocypris incongruens, Candonopsis kingsleii, and Cypria lacustris. The most common species in shallow, flooded areas was H. incongruens, and the most prominent species in ditches was C. kingsleii. C. lacustris was widely distributed in channels, springs, lakes, and rivers. Statistical analyses were performed on a “Lake Ohrid” dataset, comprising the subset of samples from Lake Ohrid alone, and an “entire” dataset comprising all samples collected. The unweighted pair group mean average (UPGMA) clustering was mainly controlled by species-specific depth preferences. Canonical Correspondence Analysis (CCA) with forward selection identified water depth, water temperature, and pH as variables that best explained the ostracod distribution in Lake Ohrid. The lack of significance of conductivity and dissolved oxygen in CCA of Ohrid data highlight the uniformity across the lake of the well-mixed waters. In the entire area, CCA revealed that ostracod distribution was best explained by water depth, salinity, conductivity, pH, and dissolved oxygen. Salinity was probably selected by CCA due to the presence of Eucypris virens and Bradleystrandesia reticulata in short-lived seasonal water bodies. Water depth is an important, although indirect, influence on ostracod species distribution, which is probably associated with other factors such as sediment texture and food supply. Some species appeared to be indicators for multiple environmental variables, such as lake level and water temperature.

Distribution, diversity and diversification from DNA barcoding perspective: The case of Gammarus radiation in the ancient Lake Ohrid

AbstractAimA detailed, comparative DNA‐barcoding and morphospecies‐based overview of the vertical and horizontal distribution of Lake Ohrid's endemic Gammarus species flock is provided. Re‐evaluation of the time frame for the onset of the species flock and identification of events that putatively influenced diversification processes.LocationLake Ohrid, Balkan Peninsula, Europe.TaxonGammarus species flock (Amphipoda, Crustacea).MethodsExtensive sampling and DNA barcoding of 600 individuals was carried out. DNA sequences were analysed using species delimitation methods, haplotype network reconstructions, Bayesian molecular dating and demographic analyses. The COI‐based species delimitation results were validated with nuclear 28S RNA data.ResultsThe species flock distribution has a weak horizontal but clear vertical structure. The diversity along bathymetric gradients correlates with temperature and salinity; and the highest diversity is observed in sublittoral and springs on the lake's shore. Two new molecular units representing putatively new species are revealed and supported also by the nuclear marker. The onset of flock radiation overlaps with the time of lake formation. The COI gene shows signs of positive selection and an acceleration in substitution rate. The demographic changes within the flock happened during the last thousands years.Main ConclusionsDistribution of the Gammarus species flock is vertically structured, reflecting habitat zonation. Parapatric speciation is one of the possible mechanisms behind the flock's diversification. Detection of new MOTUs suggests that the flock's diversity is still not fully revealed. Simultaneously, failure to collect three previously known MOTUs suggests a loss of gammarid diversity in the lake. This represents, together with the current threats to the lake ecosystem (i.e. climate changes, development of tourism), a clear call for conservation efforts. The speciation events and demographic changes within the flock relate presumably to glacial and postglacial water level changes and to the colonisation of new depth ranges and the associated springs.

Mercury records covering the past 90 000 years from lakes Prespa and Ohrid, SE Europe

Abstract. The element mercury (Hg) is a key pollutant, and much insight has been gained by studying the present-day Hg cycle. However, many important processes within this cycle operate on timescales responsive to centennial- to millennial-scale environmental variability, highlighting the importance of also investigating the longer-term Hg records in sedimentary archives. To this end, we here explore the timing, magnitude, and expression of Hg signals retained in sediments over the past ∼ 90 kyr from two lakes, linked by a subterranean karst system: Lake Prespa (Greece, North Macedonia, and Albania) and Lake Ohrid (North Macedonia and Albania). Results suggest that Hg fluctuations are largely independent of variability in common host phases in each lake, and the recorded sedimentary Hg signals show distinct differences first during the Late Pleistocene (Marine Isotope Stages 2–5). The Hg signals in Lake Prespa sediments highlight an abrupt, short-lived peak in Hg accumulation coinciding with local deglaciation. In contrast, Lake Ohrid shows a broader interval with enhanced Hg accumulation and, superimposed, a series of low-amplitude oscillations in Hg concentration peaking during the Last Glacial Maximum, which may result from elevated clastic inputs. Divergent Hg signals are also recorded during the Early and Middle Holocene (Marine Isotope Stage 1). Here, Lake Prespa sediments show a series of large Hg peaks, while Lake Ohrid sediments show a progression to lower Hg values. Since ∼ 3 ka, anthropogenic influences overwhelm local fluxes in both lakes. The lack of coherence in Hg accumulation between the two lakes suggests that, in the absence of an exceptional perturbation, local differences in sediment composition, lake structure, Hg sources, and water balance all influence the local Hg cycle and determine the extent to which Hg signals reflect local- or global-scale environmental changes.

Ancient Endemic or Recent Invader? Phylogenetic Position and the Probable Origin of the Ccladoceran Diaphanosoma macedonicum (Diplostraca, Sididae) from the Ancient Lakes in the Balkans.

Ancient lakes contain unique and very vulnerable fauna. Determining and understanding the origin of such biodiversity is a key factor in promoting conservation and management actions in some of the most singular ecosystems on the planet. Lake Ohrid in the Balkans is known as a natural laboratory for speciation, containing a high number of endemic species. However, the identity and origin of the planktonic cladoceran Diaphanosoma is uncertain. Representatives of the genus were long considered to have invaded the lake, but recent morphological studies have suggested that they belonged to the endemic taxon in the Balkans, D. macedonicum. Here, phylogenetic methods based on two mitochondrial gene fragments (COI and 16S) were used to identify Diaphanosoma specimens from the ancient Lake Ohrid and Lake Prespa in the Balkans and compare them with other species in Europe, including those living in nearby water bodies. Molecular evidence showed that D. macedonicum was constrained to the ancient lakes Ohrid, Prespa, and Mikri Prespa, which suggests reproductive isolation within the lakes. Phylogenetic analyses supported previous morphological assessments and situated D. macedonicum within the D. mongolianum species group, which contains three sibling species (D. mongolianum, D. lacustris, and D. macedonicum). Nuclear markers are needed to study intraspecific gene flow in these organisms and discard a potential formation of hybrids.

Fish Population in the Belčišta Wetland – Risk Assessment, Prevention and Management

Abstract Belčišta wetland is the largest wetland habitat in R. of North Macedonia, located 20 km distance from Ohrid Lake and it is a relict remnant of the ancient Desaret Lake, which existed in this area since the Pliocene. This region hosts an endemic freshwater species of the Balcan Penninsula, Pelasgus minutus, which is threatened by habitat loss. There are intentions of artificial introduction of salmonid fishes in Belčišta wetland to develop the recreative fishery and tourism in this area. Introduction and spread of salmonids is a great risk factor to the survival of the ohrid minnows (Pelasgus minutus).

An Upper Pleistocene and Holocene Black Carbon‐Related Fire Record From the SW Balkans

AbstractLake sediments are unique archives of human environment interactions. Lake Prespa is one of the oldest lakes in Europe, lying in the southwestern Balkans and thus on a possible dispersal route of anatomically modern humans from Africa. In this study, we investigated the effects of climate, vegetation and human activity on fire over the last 92,000 years in this region. Sediment samples were taken from Lake Prespa, and nearby Lake Ohrid for comparison of the regional relevance, and analyzed for benzene polycarboxylic acids as markers for burned organic carbon residues (black carbon, BC). Peaking contents of BC (up to 1 g BC kg−1 sediment) coincided with warm and humid phases, when forests expanded at marine isotope stages (MIS) 5 and 1. During the colder and more arid climates of MIS 4 and 2, BC contents were lowered by a factor of 10, with a distinct minimum during the Last Glacial Maximum (0.07 g BC kg−1). The ratio of pentacarboxylic acid to mellitic acid (B5CA/B6CA) declined from 1.2 at MIS 5 to values of 0.3 at MIS 2, confirming a change in fire regime. Overall, BC contents peaked at cycles of solar radiation, vegetation composition and fuel availability, and thus correspond to the BC signal of other environmental archives. However, in the Late Holocene and as a result of human sedentary settlement, BC production increased, independent of decreasing insolation forcing.

Vegetation dynamics and land-use change at the Neolithic lakeshore settlement site of Ploča Mičov Grad, Lake Ohrid, North Macedonia

Detailed knowledge about the interactions between vegetation, climate and land use during the Mesolithic and Neolithic, at the transition from foraging to farming, is still scarce in the Balkans. Here we present a palaeoecological study combining pollen, spores and charcoal found in sedimentary cores from Lake Ohrid, Ploča Mičov Grad, North Macedonia, with a particular focus on the vegetation dynamics during the Late Glacial-Holocene and the Mesolithic-Neolithic transitions. Our record begins at ca. 13,500 cal bp (11,550 cal bc) when partially open vegetation, consisting mainly of Pinus, Abies and deciduous Quercus tree stands grew on the hilly flanks of the bay of Ploča. From 12,650 cal bp (cal 10,700 bc), herbs dominated the record until the onset of the Holocene (ca. 11,700 cal bp; 9750 cal bc), when increasing temperatures led to the establishment of pine-deciduous oak forests including Alnus, Fraxinus ornus, Tilia, Ulmus and Abies. These forests persisted until 7,500 cal bp (cal 5550 bc), when deforestation started due to Neolithic land use. This first phase of Neolithic activities in the Ploča Mičov Grad area precedes the earliest archaeological structures so far recorded by almost 1,000 years. Our data suggest two phases of human land use between 7,500 and 6,300 cal bp (5550–4350 cal bc), when high values of Cerealia type pollen and other cultural indicators indicate intense arable and pastoral farming activities. Once human activities decreased, forests were able to re-establish quickly (within 100–250 years), although the composition changed with disturbance-adapted Ostrya type (mostly Ostrya carpinifolia) and Fagus becoming more important. We conclude that forests were resilient to early human disturbance, despite intensive land use and logging activities gradually leading to forest composition changes. Many of these composition changes can still be seen today, suggesting the legacy of Neolithic farmers is still present in today’s landscape.

A new Ancylus and a new genus of Hydrobiidae from the Ohrid Lake basin (Mollusca: Gastropoda)

Two new gastropod species recently collected in the St. Naum springs situated near the southeastern edge of Lake Ohrid in North Macedonia are described. Ancylus naumiensis n. sp. molecularly belong to “Ancylus sp. D” of Albrecht et al. (2006) previously recorded for St. Naum springs in Macedonia and Tusemista spring in Albania. A​ new genus, Ohridonaumia n. gen., was created to include a new species, Ohridonaumia trajanovski n. sp.

A new perspective on the molecular dating of the brown trout complex with an extended phylogeographic information on the species in Serbia

Abstract To elucidate the historical biogeography of a species, the patterns of population divergence must be understood, and the evolutionary history of the species must be accurately known. For brown trout (Salmo trutta complex), estimating divergence times remains a challenge due to the lack of well-defined time calibration points and insufficient phylogeographic coverage in previous studies. The present work aims to improve molecular dating of mitochondrial control region sequences by using a multicalibration framework based on the latest paleogeological evidence for dating the origin of Lake Ohrid and two available Salmo fossils, including the overlooked Salmo immigratus. Our results clearly show that, contrary to common belief, the major divisions within the brown trout occurred in the Late Pliocene, not the Pleistocene. The Pliocene origin suggests that the brown trout lineages did not form because of geo(hydro)morphological changes during glaciation cycles but may be the result of orogeny and drainage evolution. In addition, increased sampling, particularly in Serbia, led to the identification of a new haplogroup (da-int) occupying an intermediate position with respect to da-es and da-bs haplogroups. While the control region can delineate brown trout lineages, its phylogenetic resolution is limited, so even extensive sampling could not further resolve the lineage level polytomies.

Dendroarchaeology at Lake Ohrid: 5th and 2nd millennia BCE tree-ring chronologies from the waterlogged site of Ploča Mičov Grad, North Macedonia

On the prehistoric site of Ploča Mičov Grad (Ohrid, North Macedonia) on the eastern shore of Lake Ohrid a total of 799 wooden elements were recorded from a systematically excavated area of nearly 100 square metres. Most of them are pile remains made of round wood with diameters up to almost 40 cm. A comprehensive dendrochronological analysis allows the construction of numerous well-replicated tree-ring chronologies for different species. High agreements between the chronologies prove that oak, pine, juniper, ash and hop-hornbeam can be crossdated. The chronologies are dated by means of radiocarbon dates and modelling using wiggle matching. An intensive settlement phase is attested for the middle of the 5th millennium BCE. Further phases follow towards the end of the 5th millennium BCE and in the 2nd millennium around 1800, 1400 and 1300 BCE. Furthermore, the exact, relative felling dates allow first insights into the minimum duration of the settlement phases, which lie between 17 and 87 years. The multi-centennial chronologies presented in this study can be used as a first robust dating basis for future research in the numerous not yet dated prehistoric lake shore settlements of the region with excellently preserved wooden remains.

A preliminary study of chemical parameters of water in the Albanian part of Lake Ohrid at the end of the spring season

The transboundary lake of Ohrid, which lies between North Macedonia and Albania, is one of the deepest lakes in the Balkan Peninsula. The study was conducted in Albanian part of lake in order to make an overall assessment of the water quality of Lake Ohrid in terms of phosphorus, phosphates, nitrogen and nitrites at the end of the spring season which is characterized by a high frequency of tourism. The research was carried out in June of 2016 at three selected points of the lake (at the entrance of the city of Pogradec, at the point that was a few meters away from the former iron-nickel mine and at the exit of the village Lin). Water samples were collected from the surface and the chemical parameters were measured by the spectrophotometric method. The results showed that points 2 and 3 had the highest values of total P (0.187 mg/l and 0.177 mg/l) and total N (0.296 mg/l and 0.268 mg/l). In terms of nitrites there were no major differences between the points and the values were low. The high values of phosphates in point 1 can be justified by the high intensity of tourism in the city of Pogradec in the spring-summer season. According to the Regulation on the Quality of Drinking Water in Albania dated 25.5.16, the waters of Lake Ohrid in terms of total N enter the class A, while according to the UNECE 1994 recommendation for surface waters, in terms of total phosphorus, the waters of Lake Ohrid belong to the fourth class.

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.

Environmental changes in southeastern Europe over the last 450 ka: Magnetic and pedologic study of a loess-paleosol profile from Kaolinovo (Bulgaria)

Magnetic properties are sensitive paleoenvironmental proxies frequently used in studies of loess paleosol profiles. Understanding precisely the magnetic recording of soil responses to environmental and climatic changes needs combining pedologic data and geophysical proxies. Here we present a new high-resolution study of a 450 ka old loess-paleosol profile from low Danube loess area at Kaolinovo (NE Bulgaria). The profile consists of Holocene soil S0 on top, three paleosol units (S1, S2, S3–S4) and the intercalated loess horizons L1 to L4. Mineral magnetic and rock magnetic data together with pedological parameters (particle size distribution, total, crystalline and amorphous iron, soil organic carbon, total nitrogen, cation exchange capacity, carbonate content) show systematic variations in response to environmental changes. Principal component analyses carried out separately on magnetic mineralogy, rock magnetic and pedological variables reveal the complex response of loess – paleosol sediments to changes in source material and climate. The observed sharp shift in coercivity of mineral magnetic carriers at depth of the third loess L3 marks the change from low-coercivity mineral assemblages in older units to higher coercivity in the last three loess paleosol couplets (L1-S0, L2-S1, L3 – S2). This boundary is related to both dust source change and increased climate aridity. The observed spikes in concentration-dependent magnetic parameters in the lowermost part of the profile and particular magnetic and pedologic signature of the oldest deposits (S3–S4 pedocomplex) suggest that it may result from tephra additions in the studied loess-paleosol sequence, tentatively correlated to cryptotephra layers in other terrestrial archives in the region like Tenaghi Philippon and lake Ohrid sedimentary sequences. This work demonstrated that using PCA tool for studying the significance and objective inter-relationships of multiple mineralogical, mineral magnetic and pedological characteristics along depth of loess – paleosol profiles is an exemplary approach for revealing the underlying sedimentary and environmental processes.

Signposts of Saint Nicholai Velimirovich

Abstract: Thanks to the communique of the Holy Assembly of Bishops of the Serbian Orthodox Church, issued after their last year’s regular meeting, we were able to recall that in 2021 three anniversaries connected with the saintly image of Nicholai of Ohrid and Žiča were celebrated. One hundred and forty years have passed since his birth in the village of Lelić in the middle of Podgorina, a village which became famous precisely because of him. Just as Nazianz is known after St. Gregory the Theologian, Lelić became famous after Nicholai. It has also been sixty-five years have passed since Nicholai’s blessed death, as well as thirty years since the transfer of his miraculous relics. It seems that “everything” has been said about St. Nicholai of Ohrid and Žiča, however, our need for a word in the Glory of God and the Saint’s honor is motivated by the desire that this beloved of God could be seen again and again on the basis of his imperishable deeds. Nicholai’s legacy, in this way, becomes the lens of our recognition in the hagiological reflection of his mystical presence among us until today. The very complex topic of his achievements, which postulates numerous researches, will be reffered to in the upcoming presentation, focused on the text of the Troparion from the Service to the Saint. The backbone of the presentation on the announced topic is an empirical experiment with the aim of pointing out the significance of the works of St. Nicholai of Ohrid and Žiča. With the deep conviction that many Orthodox Christians share such experiences in an immediate way, the author’s reflections on the mentioned topic are conveyed. At the same time, the acquired knowledge indicates a high degree of analogy with the content of the Troparion from the service to St. Nicholai of Ohrid and Žiča. Key words: Saint Nicholai Velimirovich of Ohrid and Žiča, Lake Ohrid, Lelić, Bialystok, Petar II Petrović Njegoš.

Changes in the Parasitism Rate and Parasitoid Community Structure of the Horse Chestnut Leafminer, Cameraria ohridella (Lepidoptera: Gracillariidae), in the Czech Republic

The horse chestnut leafminer, Cameraria ohridella, Deschka and Dimić, is a moth that has invaded most of Europe since it was first recorded in Macedonia near Lake Ohrid in 1985. It attacks horse chestnut trees and causes aesthetic and vitality problems. The parasitism rate, other mortality rates, and parasitoid structure were studied during a five-year survey at six sites in the Czech Republic. The results showed that the total parasitism rates varied from 1.9% to 20.5%, with an average of 7.2%, similar to other those published studies. The parasitism rate was significantly related to year, the developmental stage of C. ohridella, latitude, and greenery maintenance but not to C. ohridella population density, altitude, or area size. In contrast, the total other mortality rates varied from 13.7% to 59.5%, with an average of 31%, but overall temporal changes in the values indicated a declining trend. The parasitoid complex was predominantly polyphagous parasitoids of the family Eulophidae, similar to that found previously in south-eastern Europe. The results further revealed that the most abundant parasitoid species, Minotetrastichus frontalis (Nees), was gradually replaced by Pediobius saulius (Walker). The increasing abundance of P. saulius is thus an interesting adaptation of an autochthonous parasitoid to a new host.

OHRİ GÖLÜ’NÜN SOSYAL VE EKONOMİK HAYATA ETKİSİ (1853-1903)

Lake Ohrid is within the borders of North Macedonia and Albania today. Being an important fishing center in Rumelia, the lake came to the fore with some problems related to flooding and fishing during the Ottoman period. There are important cities and towns called Ohrid, Ustruga (Struga) and Istarova on the lake shore. This study has two main aims. The first one is to find the answer to the question, “What kind of method has been followed to prevent the floods to which the people living around Lake Ohrid are exposed?”; the other is to determine the reaction of the people to the iltizam system applied in the collection of taxes collected from fishing, which is the main source of income of the local people, and the problems that arise. We can add to these the potential of fishing revenues in Lake Ohrid. The local people are not satisfied with the iltizam system regarding the collection of fishing taxes. The wish of the people is that fishing is free in exchange for 1/5 of the revenue. The fish tax obtained from Lake Ohrid in 1891 constituted approximately 5.60% of the total fish income in the country. In our study, Ottoman archival documents were used to a large extent. In addition, other sources were also consulted.

Diatom community responses to environmental change in Lake Ohrid (Balkan Peninsula) during the mid-Pleistocene Transition

The Quaternary is characterized by a series of glacial-interglacial cycles and a shift in the Earth's climate state known as the mid-Pleistocene Transition (MPT, ca. 1200 ka to 720 ka). The progressive increase in glacial cycle length from approximately 41 ka to on average 100 ka affected marine and terrestrial life, but how it affected freshwater communities is far less known. Here, diatom and paleoenvironmental data between 1050 ka and 815 ka from a sediment succession of ancient Lake Ohrid are used to understand how the freshwater communities responded to environmental changes during key-periods of glacial intensification associated with the MPT. Based on stratigraphically constrained incremental sum of squares cluster (CONISS), a distinct diatom community turnover in Lake Ohrid was identified during the study period. The first community existed between 1050 and 955 ka MIS (Marine Isotope Stages) 30–25 and was mostly influenced by environmental parameters related to nutrient supply, mixing processes and primary productivity in the lake. The second community existed between 955 and 815 ka (MIS 25–21) and was largely driven by ontogenetic processes related to the ongoing deepening of the lake, changes in bottom water redox conditions and changes in mixing processes in the lake. The increased severity and duration of cold, glacial stages during the MPT shows only a weak impact on the diatom community in Lake Ohrid. Shifts in species phenotypes, abundance and composition are found in both communities, likely as adaptation in response to the changing environmental conditions. This study shows that the diatom communities were only weakly affected by the progressive intensification of the glacial intensity during the MPT, emphasizing the role of local environmental changes in regulating freshwater communities.

Half-precession signals in Lake Ohrid (Balkan) and their spatio-temporal relations to climate records from the European realm

The nature of half-precession (HP) cycles (∼9000–12,000 years), although identified in numerous records, is still poorly understood. Here we focus on HP signals in Lake Ohrid and in a variety of different marine and terrestrial proxy records from Europe and the Northern Atlantic region. Our study examines the temporal evolution of the HP signal from the early/middle Pleistocene to the present, discusses the results across the latitudes of the Mediterranean and Europe, and assesses the potential of the HP to reflect the connectivity of climate systems over time.We apply filters on the datasets that remove the classical orbital cycles (eccentricity, obliquity, precession) and high frequency signals to focus exclusively on the bandwidth of the HP signal. Evolutionary wavelet spectra and correlation techniques are used to study the evolution of frequencies through the different records.Next to a connection of HP cycles to interglacials, we see a more pronounced HP signal in the younger part of several proxy records. Although the HP signal is present in all of the investigated sites, we observe a more pronounced HP signal in the southeast compared to records from the north. The latter is consistent with the assumption that HP is an equatorial signal and can be transmitted northward via various pathways. The appearance of HP signals in mid- and high-latitude records can thus be an indicator for the intensity of the mechanisms driving these pathways. The African Monsoon probably plays a major role in this context, as its magnitude directly influences the climate systems of the Mediterranean and Southern Europe.