The indirect response of an aquatic ecosystem to long-term climate-driven terrestrial vegetation in a subalpine temperate lake

Aim: To assess whether climate directly influences aquatic ecosystem dynamics in the temperate landscape of Tasmania or whether the effects of long-term climatic change are mediated through the terrestrial environment (indirect climate influence). Location: Paddy’s Lake is located at 1065 m a.s.l. in temperate north-west Tasmania, a continental island south-east of mainland Australia (41°15–43°250 S; 145°00– 148°150 E). Methods: We developed a new 13,400 year (13.4 kyr) palaeoecological dataset of lake sediment subfossil cladocerans (aquatic grazers), bulk organic sediment carbon (C%) and nitrogen (N%) and d13C and d15N stable isotopes. Comparison of this new data was made with a recently published pollen, geochemistry and charcoal records from Paddy’s Lake. Results: Low cladoceran diversity at Paddy’s Lake is consistent with other temperate Southern Hemisphere lakes. The bulk sediment d15N values demonstrate a significant lagged negative response to pollen accumulation rate (pollen AR). Compositional shifts of dominant cladoceran taxa (Bosmina meridionalis and Alona guttata) occur following changes in both pollen AR and pollen (vegetation) composition throughout the 13.4 kyr record at Paddy’s Lake. The d15N values demonstrate a significant positive lagged relationship to the oligotrophic:eutrophic cladoceran ratio. Main conclusions: Long-term changes in cladoceran composition lag changes in both pollen AR and terrestrial vegetation composition. We interpret pollen AR as reflecting climate-driven changes in terrestrial vegetation productivity and conclude that climate-driven shifts in vegetation are the principal driver of the cladoceran community during the last ca. 13.4 kyr. The significant negative lagged relationship between pollen AR and d15N reflects the primary control of vegetation productivity over within-lake nutrient status. Thus, we conclude that the effects of long-term climate change on aquatic ecosystem dynamics at our site are indirect and mediated by the terrestrial environment. Vegetation productivity controls organic soil development and has a direct influence over lake trophic status via changes in the delivery of terrestrial organic matter into the lake

Effects of long term nutrient and climate variability of subfossil Cladocera in Lake Garda (northern Italy)

Although Cladocera remains are considered to be a reliable proxy for tracking historical lake development they have scarcely been studied, in large and deep lakes. In order to reconstruct Cladocera species distribution and abundances in the two basins of the largest and deep italian lake (Lake Garda) during the last few centuries, a first sediment core was collected from the largest subbasin (Brenzone, 350 m deep), while other two cores were retrieved from the profundal and the littoral zones of the smaller sub-basin (Bardolino, 80 and 40 m deep, respectively). The long-term differences in Cladocera assemblage were analyzed and related to historical limnological and climatic variability, and were compared with chnges in other biological proxies, such as diatoms, pigments and Pediastrum remains, in order to discriminate the lake’s response to nutrient enrichment and climate change. Although the three cores studied showed some minor differences related to the different morphological and hydrological features of the two basins , they outlined highly coherent temporal changes in the Cladocera assemblages. The profundal layers of the three cores were characterized by species sensitive to water temperature, suggesting a response of the lake at the major climatic events, such as the Medieval Climatic Anomaly and the Little Ice Age. On the other hand a common and evident change in Cladocera assemblage occurred during the 1960s, when planktonic taxa, such as Daphnia spp. and Bosmina spp., dominated at the expense of littoral taxa. A nonmetric multidimensional scaling (NMDS) revealed a clear response of Cladocera to climate variability before the 1960s, i.e. during periods of low lake nutrient levels, which is in contrast with. the scarce response of diatoms to climate variability during the same period. On the other hand, Cladocera and diatoms exhibited concomitant changes in assemblage composition after the 1960s, which have been related to increased nutrient concentrations . During this period of lake’s nutrient enrichment, the response of Cladocera to climate variations seemed to be overridden by changing nutrient levels. This study highlights the value of a multi-proxy approach for disentangling the biological responses to multiple environmental stressors in large and deep lakes

A multi-proxy sediment study to assess long-term effects of nutrients and climate variability on the ecological dynamics of the largest Italian lake (Lake Garda)

The study of lake sediments allows to place limnological investigations within a secular temporal perspective, providing a longer time-span compared to monitoring data. A multi-site and multi-proxy paleoecological approach was applied to Lake Garda, the largest Italian lake, in order to disentangle the effects of local anthropogenic forcings, such as nutrients, and climate variability on the lake ecosystem during the last few centuries.Short sediment cores were collected from the deepest point of the two lake basins: Brenzone (350 m depth) and Bardolino (81 m depth). Biological indicators(diatoms and Cladocera) were used to reconstruct changes in the aquatic food web and to define the lake reference conditions, while sediment geochemistry, analyzed by wavelength-dispersive X-ray fluorescence spectroscopy (WD-XRF), was investigated to obtain information on different physical or chemical processes affecting the lake and its catchment. The selected biological proxies suggested stable oligotrophic conditions of Lake Garda until the 1960s, while the following lake nutrient enrichmentled to a drastic change in the phytoplankton community. The major climatic anomalies,i.e. the Medieval Climatic Anomaly and the Little Ice Age, did not apparently affect planktonic diatom taxonomic composition, while Cladocera showed changes in total abundance and speciescompositions. On the other hand, diatoms showed an indirect response to climate variabilitysince the beginning of the nutrient enrichment phase in the 1960s, while Cladocera revealed a weaker climate-response during this nutrient-driven period. This different response to nutrients and climate was put in relation with the thermal dynamics of large and deep lakes. In fact, climate variability regulates magnitude and frequency of thermal circulationin large and deep lakes, which in its turn controlthe degree of nutrient fertilization of the entire water column and the related phytoplankton growth. Geochemical data showed a pronounced change in elemental composition since the middle of the 20th century, when major elements and lithogenic tracers started to decrease, while elements related to redox conditions and contamination (trace elements) increased. The general trends agreed with the biological records. However, some differences recorded in the two different basins of Lake Garda reflected the effects of local hydrological and sedimentation patterns

Environmental changes during the last millennium recorded in subfossil Cladocera, diatoms and sediment geochemistry from Lake El Sol (Central Mexico)

High-altitude lakes, which are very sensitive ecosystems and respond rapidly to climatic changes, are one of the best targets for palaeolimnological studies. Here, we present the record of environmental changes over the last millennium that are recorded in the sediments of El Sol, a tropical, high-altitude, volcanic crater lake on the Nevado de Toluca, Central Mexico. Palaeolimnological reconstructions are based on subfossil Cladocera, diatoms, magnetic susceptibility and chemical analysis of the sediments. In general, Cladocera occurring in tropical regions, and especially at high altitude, have been studied very little. Our data indicate that in the sequence studied, the species diversity of subfossil Cladocera is very low. Only four species were recorded, and the assemblage is dominated by littoral species. Two Cladocera taxa, Alona manueli and Ilyocryptus, found at Lake El Sol are endemic. Cladocera, diatoms and the sediment chemistry show changes in Lake El Sol which are mostly related to climate. The most pronounced climatic signal was obtained for the early Little Ice Age (1350–1625 AD). This cold episode was expressed by a reduction in the frequency of zooplankton (individuals/cm2/yr) and diatoms (valves/g of dry sediment) and by changes in the organic carbon content in the sediment. Our results show that human activity was very limited throughout the study period. According to historical data the presence of humans at the lake shore was mostly occasional, usually for ceremonial and ritual purposes, and humans did not have an important influence on the lake ecosystem. Only one period was identified when human activity was important. This period corresponds to the introduction of fish into the lake at the beginning of the 20th century

Religion and attitudes towards abortion and euthanasia among young people in Poland and Norway

This article compares attitudes towards abortion and euthanasia in two countries with different Christian traditions. Poland is a former communist country with a strong Catholic tradition. Norway is a highly secularized Scandinavian country with a dominating Lutheran Church. The two countries have different legal frameworks regarding abortion and euthanasia. We aim here to investigate the connection between religion and attitudes towards abortion and euthanasia. Our methodological approach is "most different systems design". If one finds similar patterns in countries with different religious and political cultures, there is reason to believe that the findings will also apply to other countries. Though the two countries differ with respect to political and religious culture, we find interesting similarities between them. In both countries, religiosity has a negative impact on attitudes towards abortion and euthanasia; this means that the most religious people also have the most negative attitudes regarding these issues. Views regarding the role religion should perform in society are also strong predictors of attitudes. In both countries, those who think that church and religion should actively influence society have negative attitudes towards abortion and euthanasia while those who think church and religion should adapt to trends in society support both abortion and euthanasia as a right