Search Results (26)

Long-term data on the phytoplankton of the Bulgarian Black Sea (BBS) coast describe three states for the ecosystem: a “pristine” reference phase (1954–1970 years); an intensive anthropogenic eutrophication (1970–1992 years) phase; and a post-eutrophication phase after the early 1990s of the 20th century. The eutrophication period is characterised by ecosystem degradation and intense phytoplankton blooms, some of which were formed by the potentially toxic species Lingulodinium polyedra. This warm-water species is a red tide former that is associated with fish and shellfish mortality events. In the 1980s, L. polyedra reached the highest biomass of 84.4 g·m⁻³ in Varna Bay, BBS. The aim of this study (1992–2022) was to provide an overview of the development of L. polyedra in the phytoplankton biocenosis in the Bulgarian part of the Black Sea, taking into account the influence of anthropogenic stress and the climatic variables NAO and SST on the development of the species population. An analysis of the distribution of the dinoflagellate L. polyedra is based on a total of 5126 phytoplankton samples collected during the period between 1992 and 2022 under projects led by the Institute of Fish Resources, Varna. The samples were analyzed using standard methods validated for the Black Sea, and phytoplankton abundance and biomass were determined. The species are most abundant in summer in the coastal marine areas exposed to anthropogenic influence. During the analyzed period, a decrease in the abundance and biomass of L. polyedra in Bulgarian Black Sea waters were observed. It was found that the influence of climatic factors such as NAO and SST on the species population is from weak to moderate, and the correlation with NAO cycles is better expressed. Full article

Rewetting of drained wetlands is practiced as a method to enhance biodiversity, improve water and nutrient retention, and counteract climate change. While rewetting efforts are most commonly directed toward various types of wetlands, there are relatively few reports on the restoration of lakes drained in the past. The Olsztyn Lake District is a region where extensive, organized drainage works were carried out in the 19th century, leading to the disappearance of numerous lakes. This paper examines the changes that have occurred since the early 19th century in a group of 143 lakes identified as the complete set of fully drained lakes in the region. An analysis of cartographic materials revealed that the total area of these lakes, originally about 3000 hectares, was reduced to nearly zero by the early 20th century. However, a gradual restoration of the former lakes is now being observed, primarily as a result of spontaneous processes but also through planned interventions. The study of water quality and trophic status in 25 fully restored lakes revealed that such water bodies typically exhibit unfavorable conditions, primarily due to excessive phosphorus levels. A similar state was observed in 14 examined wetlands, which were partially rewetted. In the absence of organized restoration programs in the study region, the slow trend of passive rewetting of such water bodies is expected to continue. However, this process may be hindered by adverse hydroclimatic changes associated with ongoing climate warming. Full article

The aim of this work is to investigate drought variability in Padua, northern Italy, over a nearly 300-year period, from 1725 to 2023. Two well-established and widely used indices are calculated, the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI). They are compatible with a data series starting in the early instrumental period, as both can be estimated using only temperature and precipitation data. The Padua daily precipitation and temperature series from the early 18th century, which were recovered and homogenized with current observations, are used as datasets. The standard approach to estimate SPI and SPEI based on gamma and log-logistic probability distribution functions, respectively, is questioned, assessing the fitting performance of different distributions applied to monthly precipitation data. The best-performing distributions are identified for each index and accumulation period at annual and monthly scales, and their normality is evaluated. In general, they detect more extreme drought events than the standard functions. Moreover, the main statistical values of SPI are very similar, regardless of the approach type, as opposed to SPEI. The difference between SPI and SPEI time series calculated with the best-fit approach has increased since the mid-20th century, in particular in spring and summer, and can be related to ongoing global warming, which SPEI takes into account. The innovative trend analysis applied to SPEI12 indicates a general increasing trend in droughts, while for SPI12, it is significant only for severe events. Summer and fall are the most affected seasons. The critical drought intensity–duration–frequency curves provide an easily understandable relationship between the intensity, duration and frequency of the most severe droughts and allow for the calculation of return periods for the critical events of a certain duration. Moreover, the longest and most severe droughts over the 1725–2023 period are identified. Full article

We show for the first time the results of a study into the spatial distribution of birds in forests at the eastern edge of Europe (Republic of Tatarstan, Russia) and changes from early to late winter. A transect method was used to census randomly selected plots spread over a large geographical area in the winters 2018/9–2022/3. We used regression and ordination methods to assess the influence of key environmental factors on species richness, total density of birds, biological diversity, and the probabilities of occurrence of individual species. The most abundant bird species in early winter was the Willow Tit, and in the late winter was the Common Redpoll. Compared with the end of the 20th century, the number of wintering bird species has increased in the study area, likely due to climate warming. Species richness, total density, and the Shannon Index of diversity were higher in early winter than in late winter. Species richness and the Shannon Index were also higher at low elevations and in the west of the study region. Our research shows strong ecological-geographical differences in the preferences of individual bird species in the studied forests. However, almost without exception, birds had a higher probability of occurrence at lower elevation and toward the west. Full article

Forests of the Carpathians are of increasing research interest, as they cover a large area (>9 Mha) within European forests and are influenced by diverse environmental conditions and contrasting historical developments. We reviewed 251 papers dealing with Carpathian forests, their history, and future perspectives. Over 70% of articles and reviews appeared in the last ten years, and 80% refer to the Western and Eastern Carpathians, while the Serbian Carpathians remain a gap in this research field. Forest expansion and species changes have occurred since Holocene deglaciation, influenced by timber use, settlements, cropland development, and, since the Bronze Age, pasture activities. At higher elevations, early conifer successors have been increasingly replaced by Norway spruce (Picea abies), silver fir (Abies alba), European beech (Fagus sylvatica), and hornbeam (Carpinus betulus), while oaks have been present in the Carpathian foothills throughout the whole of history. In the 19th and 20th centuries, Norway spruce afforestation was favored, and timber use peaked. Recent transitions from agriculture to forest land use have led to a further increase in forest cover (+1 to +14% in different countries), though past forest management practices and recent environmental changes have impaired forest vitality in many regions; climate warming already causes shifts in treelines and species distributions, and it triggers pest outbreaks and diseases and affects tree–water relations. The risk of forest damage is the highest in monodominant Norway spruce forests, which often experience dieback after cascade disturbances. European beech forests are more resilient unless affected by summer droughts. In the future, increasing dominance of broadleaves within Carpathian forests and forest management based on a mix of intensive management and ecological silviculture are expected. Maintenance and promotion of silver fir and mixed European beech forests should be encouraged with respect to forest stability, biodiversity, and economic sustainability. As supported by the Carpathian Convention and related institutions and initiatives, connectivity, management, and stakeholder cooperation across administrative borders will be crucial for the future adaptive potential of Carpathian forests. Full article

Most species arriving from a donor to a recipient area do not succeed in establishing long-lasting self-sustaining populations. However, successful introductions are far better documented than those that failed, especially those occurring before or near the advent of the Linnaean binomial nomenclature. We report here an introduction from the mid-18th century (possibly in 1750 or 1751) of an exotic mussel transported as fouling on ship hulls from the western coast of Morocco (Atlantic Ocean) to the port of Marseilles (Mediterranean Sea). The exotic mussel, which survived several years, has been identified as probably being the brown mussel, Perna perna, a species with warm-water affinities, which much later became invasive in several areas of the world ocean. The documents of the 18th and early 19th century, which mentioned the event, held ‘the curious’ and ‘amateurs’, who harvested the mussels, responsible for its extirpation. More realistically, it is hypothesised that the mussel population did not survive the return of severe cold weather conditions, after a few relatively mild decades, in the context of the Little Ice Age (LIA). These conclusions were deduced from historical data and are therefore open to discussion. Full article

Ongoing climate warming poses significant threats to forest ecosystems, particularly in drylands. Here, we assess the intricate responses of tree growth to climate change across two warming phases (1910–1940 and 1970–2000) of the 20th century in the Loess Plateau of China. To achieve this, we analyzed a dataset encompassing 53 ring-width chronologies extracted from 13 diverse tree species, enabling us to discern and characterize the prevailing trends in tree growth over these warming phases. The difference in the primary contributors over two warming phases was compared to investigate the association of tree growth with climatic drivers. We found that the first warming phase exerted a stimulating effect on tree growth, with climate warming correlating to heightened growth rates. However, a contrasting pattern emerged in the second phase as accelerated drought conditions emerged as a predominant limiting factor, dampening tree growth rates. The response of tree growth to climate changed markedly during the two warming phases. Initially, temperature assumed a dominant role in driving the tree growth of growth season during the first warming phase. Instead, precipitation and drought stress became the main factors affecting tree growth in the second phase. This drought stress manifested predominantly during the early and late growing seasons. Our findings confirm the discernible transition of warming-induced tree growth in water-limited regions and highlight the vulnerability of dryland forests to the escalating dual challenges of heightened warming and drying. If the warming trend continues unabated in the Loess Plateau, further deterioration in tree growth and heightened mortality rates are foreseeable outcomes. Some adaptive forest managements should be encouraged to sustain the integrity and resilience of these vital ecosystems in the Loess Plateau and similar regions. Full article

We examined the influence of significant 21st century warming on the radial growth patterns of shortleaf pine growing on adjacent north/northeast- and south/southwest-facing slopes (hereafter NS and SS), in the Uwharrie Mountains of North Carolina, USA. Using two chronologies developed from old-growth trees dating to the 1700s, we compared raw radial growth rates (hereafter radial growth) associated with earlywood, latewood, and totalwood during 1935–2020. Both chronologies exhibited similar (r = 0.951, p < 0.001) age-related growth decreases through the 20th century. However, both chronologies experienced abrupt increases in radial growth with less fidelity (r = 0.86, p < 0.001), correlating with the onset of warming mean annual temperatures (r = 0.58, p < 0.01) and warming winter temperatures (r = 0.55, p < 0.05) in 2002. These results show that shortleaf pine growing on both NS and SS have experienced significant radial growth increases since the early 21st century, but that aspect affected growth rates. During 2002–2020, NS radial growth increased significantly (p < 0.05) more than SS earlywood, latewood, and totalwood, indicating that the effects of warming were greater for NS trees. We conclude that old-growth shortleaf pine trees retain climatic sensitivity to significant environmental changes associated with a warming climate and can reverse age-related growth declines. Full article

A study of the climatic characteristics and annual runoff of the Volga and Severnaya Dvina rivers demonstrates that, on the East European Plain (EEP), Early Twentieth Century Warming (ETCW) manifested in a multiyear drought between 1934 and 1940; this drought has no analogues in this region in terms of intensity and duration according to Palmer’s classification, and caused extreme hydrological events. The circulation conditions during this event were characterized by an extensive anticyclone over Eastern Europe, combined with a cyclonic anomaly in the circumpolar region. An analysis of the spatial features of sea surface temperature (SST) anomalies indicate that the surface air temperature (SAT) anomalies in July on the EEP during ETCW were related not only to the North Atlantic (NA) warming and positive AMO phase, but also to a certain spatial pattern of SST anomalies characteristic of the 1920–1950 period. The difference between the SST anomalies of the opposite sign in the different NA zones, used as the indicator of the obtained spatial pattern, shows the quite close relations between the July SAT anomalies on the EEP and the atmospheric circulation patterns responsible for them. The positive phase of the Atlantic Multidecadal Oscillation (AMO) and the expansion of the subtropical high-pressure belt to the north and to the east can be considered as global-scale drivers of this phenomenon. The AMO also impacts the sea ice cover in the Barents–Kara Sea region, which, in turn, could have led to specific atmospheric circulation patterns and contributed to droughts on the EEP in the 1930s. Full article

The sharp increase in soybean (Glycine max (L.) Merrill) acreage in the late 20th century and early 21st century is due to the demand for edible oil and feed protein. However, a limiting factor in the extent of soybean cultivation is its high heat requirements and response to photoperiod. Most varieties are short-day plants and are generally the best-yielding genotypes. At higher latitudes (longer day length), there is a delay in the occurrence of subsequent developmental stages and problems with plant maturation before the onset of autumn frost. Global warming allows the cultivation range of warm-season species (including soya) to be shifted; however, periodic droughts and very high temperatures limit crop production. Adverse weather events result in a reduction in soybean seed yield of around 30%. Environmental stresses related to day length, high and low temperatures and water shortage or excess have the greatest impact on soybean yields, as we have no influence on them and can only, to a very limited extent, offset their negative effects. This paper reviews the recent world literature on how soybean responds to these stress factors. The results of our own research were also used. Full article

Discoglossus pictus is a North African amphibian that was introduced in southern France early the 20th century and has spread south and north along the Mediterranean coastal plains up to 170 km. In order to disentangle the conservation implications of the spread of D. pictus for sensitive native species, we examined the impact of long-term climate warming on the basis of niche overlap analysis, taking into account abiotic factors. The study area covered the distribution ranges of all genus Discoglossus species in northwestern Africa (659,784 km²), Sicily (27,711 km²), the Iberian Peninsula, and southern France (699,546 km²). Niche overlap was measured from species environmental spaces extracted via PCA, including climate and relief environmental variables. Current and future climatic suitability for each species was assessed in an ensemble-forecasting framework of species distribution models, built using contemporary species data and climate predictors and projected to 2070′s climatic conditions. Our results show a strong climatic niche overlap between D. pictus and native and endemic species in the Iberian Peninsula. In this context, all species will experience an increase in climatic suitability over the next decades, with the only exception being Pelodytes punctatus, which could be negatively affected by synergies between global warming and cohabitation with D. pictus. Full article

A study was undertaken to investigate the structure and condition of urban permafrost in the city of Yakutsk. The response of permafrost to recent climate change was assessed for a Shergin Shaft site in a cryogenic landscape. The results indicate that the thickness of the active layer which consists of anthropogenic soils experienced no change during the second half of the 20th century and the early 21st century. However, the thermal state of the underlying alluvial sediments has changed significantly in response to the warming of the climate. The permafrost temperatures at a depth of 10 m increased by about 3 °C between 1934 and 2015. Full article

Analysis of climatic characteristics, Palmer Drought Severity Index, and large-scale river runoff based on observational data (CRUTEM.5, GISSTEMP v4, CRU TS4.05, CRU-scPDSI) and 20th century reanalysis (ERA20C, CERA20C) shows that the early 20th century warming period, in particular the 1930s, on the East-European Plain was marked by the strong long-lasting drought that has no analogues during the observation period. The atmospheric circulation patterns and drivers of this phenomena, as well as the associated reduction in the sea ice extent of the Kara Sea, are studied. Full article

This article aims to reconstruct the invasion of the ear-shaped pond snail, Radix auricularia (Linnaeus, 1758), to Lake Baikal, East Siberia. This species is widely distributed in the Palaearctic and Northern America, and since the early 20th century has formed abundant and sustained populations in Lake Baikal. The data provided on the morphological and genetic variability of R. auricularia help to better describe and delineate the species. With an integrative approach involving morphological and molecular data, we improved the knowledge of the intraspecific variability of R. auricularia in the most important characteristics used for its determination. Molecular sequences of nuclear spacer fragment ITS-2 and mitochondrial gene fragment cyt–b were obtained from 32 individuals of Radix (including seven outgroup Radix species) collected from various parts of Lake Baikal and adjacent waterbodies and compared with sequences of 32 individuals of R. auricularia from different regions of the Palaearctic as well as with individuals determinated as R. intercisa from Lake Baikal, R. iturupica from the Kurile Islands, R. ussuriensis from the Khabarovsk region, R. narzykulovi from Tajikistan, and R. schubinae from the Amur region. Molecular genetic analyses revealed that all specimens collected from Lake Baikal belong to R. auricularia. There are no genetically distinct groups of snails that would correspond to two morphospecies previously recorded in Lake Baikal (e.g., R. auricularia s. str. and R. intercisa). Variability of the characteristics that are commonly used for species identification (shell morphology, mantle pigmentation, shape and position of the bursa copulatrix, length and position of the bursa duct, length ratio of preputium to penial sheath) were found in individuals analysed with molecular genetics to be broader than recognised in the current literature. Some shells of R. auricularia collected from Lake Baikal resemble shells of another lymnaeid species, R. balthica, and without molecular assessment can be confused with the latter. Geometric morphometric analysis of more than 250 shells revealed no observed hiatus between Baikalian and non-Baikalian R. auricularia. The probable stages and pathways of R. auricularia invasion to Lake Baikal’s ecosystem are outlined and discussed. Factors such as global climate warming and human activity stimulated and facilitated the ongoing dispersal of ear pond snails within Lake Baikal. Full article

The circum-Mediterranean region is the cradle of ancient civilizations that had their roots in the Holocene. Climate change has been considered a key element that contributed to their rise or fall. The Roman Warm Period (RWP), 200 B.C. to 400 A.D., was the warmest period in Europe during the last two thousand years. Hydroclimatic change at the end of the RWP has been suggested as a possible influence on the stability of the Roman political regime and the eventual collapse of the Roman Empire in 476 A.D. A lack of precise proxy records hampers our understanding of hydroclimatic variability over the RWP. Here we present a stalagmite-based climate record from 550 ± 10 B.C. to 950 ± 7 A.D. (2σ) from northern Italy, which reveals a climatic trend of warming and increased humidity throughout the RWP. By comparison with other proxy records in Europe and the circum-Mediterranean region, we argue that the warm, humid climate in southern Europe could be linked to the multi-centennial warming of the Mediterranean Sea. Our record further suggests a century-long rapid drying trend from the early-4th to early-5th century, followed by a 100-year-long drought event, which could have influenced the fall of the Roman Empire. Full article