Multi-proxy palaeoecological responses to water-level fluctuations in three shallow Turkish lakes

Natural or human-induced water-level fluctuations influence the structure and function of shallow lakes, especially in semi-arid to arid climate regions. In order to reliably interpret the effect of water-level changes from sedimentary remains in the absence of historical data, it is crucial to understand the variation in sedimentary proxies in relation to water level measurements. Here, we took advantage of existing water surface elevation data on three large shallow lakes in Turkey to elucidate the impact of lake-level changes on benthic-pelagic primary production over the last 50-100 years. Sub-fossil cladocerans, diatoms, plant remains and pigments were investigated as biological variables; X-ray fluorescence (XRF) and loss on ignition (LOI) analyses were conducted as geochemical-physical variables on a set of Pb-210 and Cs-137 dated cores. Dating of the cores were robust, with the exception of uncertainties in Lake Marmara littoral core due to low unsupported 210Pb activities and high counting errors. Results indicated that Lake Marmara was dominated by benthic species throughout the sediment record, while Lakes Beysehir and Uluabat shifted from a littoral-dominated system to one with increased pelagic species abundance. In all cores there was a stronger response to longer-term (decadal) and pronounced water-level changes than to short-term (annual-biennial) and subtle changes. It was also noted that degree of alteration in proxies differed between lakes, through time and among pelagic-littoral areas, likely emphasising differences in depositional environments and/or resolution of sampling and effects of other stressors such as eutrophication. Our results highlight lake-specific changes associated with water-level fluctuations, difficulties of conducting studies at required resolution in lakes with rather mixed sediment records and complexity of palaeolimnological studies covering recent periods where multiple drivers are in force. They further emphasise the need to include instrumental records when interpreting effects of recent water-level changes from sediment core data in large shallow lakes

Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins

Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.Peer reviewe

Türkiye sığ göllerinin yakın geçmiş zamandaki durumlarının diatom fosilleri kullanılarak belirlenmesi.

Current study provides information about the factors that influence the diatom composition of shallow lakes in Turkey. Thirty two shallow lakes were sampled with snap-shot sampling. Moreover, short cores from four small shallow lakes and three large lakes were retrieved. The study showed that conductivity had a significant impact on shaping the fossil diatom composition in surface sediment samples and the effect of eutrophication was captured in short core samples especially after 1970s for altering the past status of Turkish shallow lakes. The complex interactions of biological remains and environmental variables were also revealed.The comparison of instrumental waterlevel data (40-100 years) with fossil diatom samples showed the reflection of short term water level changes in sediment cores was rather poor but the negative impact of eutrophication was hinted especially for Lake Uluabat and Lake Marmara. vi The current study suggested that diatom fossils are good indicators for capturing the environmental variations and can be used in the absence of historical data for tracking the historical changes of shallow lakes in Turkey. However, to achieve clear signs of the composition alteration, a long-term perspective is needed and the complexity of multiple drivers for shaping the community structure of the diatom flora should be considered. In addition, the significant influence of conductivity and nutrients emphasizes the expected impacts of climate change on Mediterranean region.Ph.D. - Doctoral Progra

Çoklu stres faktörlerinin Daphnia Pulex'in hayatta kalma oranı ve yaşama döngüsü üzerindeki etkileri.

As Daphnia have an important role in freshwater food webs, it is important to understand how environmental stressors affect their survival and life history traits. Daphnia pulex were first acutely exposed to a combination of NaCl salinities (0.00-10.0 g/L) and fish-exuded kairomone. The 24 and 48 hour LC50 values were 0.401 and 0.159 g/L in kairomone-absence and 1.962 and 1.007 g/L in kairomone-presence. Hence, survival decreased with increasing salinity, while the kairomone enhanced daphnid resistance to salinity below 2 g/L. During the chronic exposure to salinity (0.00-1.5 g/L) combined with the fish-exuded kairomone, impacts of temperature and food were also investigated. Survival decreased significantly with increased salinity, while the kairomone had a positive impact on survival at intermediate salinity levels, suggesting an antagonistic relationship. Temperature alone had a significant negative impact on survival and its combined effect with salinity and fish kairomone was synergistic. However, the impact of food limitation was insignificant. Life history parameters were affected by both salinity and the fish-exuded kairomone, the combination of which significantly decreased the body length: width ratio. Egg number/individual decreased with salinity and increased in the presence of the fish kairomone. In conclusion, the combined impact of salinity and fish-exuded kairomone significantly affected daphnid survival and life history traits in a non-linear manner, such that fish kairomone enhanced daphnid resistance to intermediate salinity levels. Moreover, the combined effect of salinity, temperature and fish kairomone on daphnid survival was also significant.M.S. - Master of Scienc

DİATOM FOSİLLERİ KULLANARAK YAKIN GEÇMİŞTEN GÜNÜMÜZE SIĞ GÖLLERDE ÖTROFİKASYONUN BELİRLENMESİ

DİATOM FOSİLLERİ KULLANARAK YAKIN GEÇMİŞTEN GÜNÜMÜZE SIĞ GÖLLERDE ÖTROFİKASYONUN BELİRLENMES

FEN BİLİMLERİ ENSTİTÜSÜ/LİSANSÜSTÜ TEZ PROJESİ

DİATOM FOSİLLERİ KULLANARAK YAKIN GEÇMİŞTEN GÜNÜMÜZE SIĞ GÖLLERDE ÖTROFİKASYONUN BELİRLENMES

Impact of pesticide Cypermethrin and fish kairomone on the life history traits of Daphnia pulex

In freshwaters Daphnia, which help increasing water clarity due to its high grazing pressure and water filtration capacity, are fundamental for the conservation of aquatic biodiversity. In lake ecosystems, predation pressure and exposure to agricultural pesticides are among the most important factors affecting the Daphnia population. Therefore, the investigation of the adaptations of Daphnia under the combined influence of fish predation pressure and insecticides provides a new and more realistic ecological approach to the traditional toxicological approach because pesticides shown to disturb natural chemical communication significantly and thus pose an ecological risk. One of the commonly used pesticides in recent years in Turkey is the synthetic pyrethroid insecticide cypermethrin. The survival of the Daphnia pulex individuals exposed to cypermethrin levels between 0.01-5.00µg L-1 in the acute toxicity experiment indicated that these species might be more sensitive to cypermethrin in the presence of the fish kairomone, which was mimicked by fish kairomone. The chronic toxicity experiments, which were carried out at very low doses (ng L-1), suggested that there might be a trade-off between survival and reproduction, especially in the presence of fish predation pressure. These effects of cypermethrin in the presence and absence of fish predation pressure on Daphnia are discussed from an ecological perspective

Comparison Of Recent Past And Present States Of Turkish Shallow Lakes By Using Cladocera Sub Fossil Remainings

Order Cladocera (small crustaceans) has an important place in lake ecosystems as they are both consumers of primary producers and prey for larger predator species. As a result, their abundance is a strong indicator of ecological conditions in a lake at a certain time. Cladocera body parts, such as headshields, shells, etc.) are largely silica based and can be preserved inside the lake sediment for long periods of time. Sedimentary sub-fossil records of Cladocera remains allow us to understand past and more recent conditions. Our aim is to determine changes in lake ecological status over time by using abundances of Cladocera sub-fossils at top (present) and bottom(recent past) centimeters of the sediment cores taken from 28 shallow lakes of Turkey. Comparison of the recent past and present states were carried out using Similarity/Dissimilarity Analysis. Furthermore the results were assesed exploring the changes took place in a specific lake through time