Turkish Lakes Research Articles

Size‐based interactions across trophic levels in food webs of shallow Mediterranean lakes

Abstract Body size is a key trait of an organism which determines the dynamics of predator–prey interactions. Most empirical studies on the individual size distribution of the aquatic community have focused on the variations in body size of a single trophic level as a response to certain environmental variables or biotic factors. Few studies, however, have evaluated how individual size structure is altered simultaneously across interacting trophic levels and locations. Such comparative examinations of the size distribution in predator and prey communities may bring insight into the strength of the interactions between adjacent trophic levels. We assessed the potential predation effect of size‐structured predators (i.e. predation by individuals of different sizes) on prey size structure using data from 30 shallow Turkish lakes spanning over five latitudinal degrees. We correlated size diversity and size evenness of predator and prey assemblages across the planktonic food web after accounting for the confounding effects of temperature and resource availability which may also affect size structure. We expected to find a negative relationship between size diversity of predators and prey due to the enhanced strength of top‐down control with increasing predator size diversity. We also hypothesised that competitive interactions for resources in less productive systems would promote a higher size diversity. We further expected a shift towards reduced size diversity and evenness at high temperatures. In contrast to our hypothesis, we found a positive correlation between size structures of two interacting trophic levels of the planktonic food web; thus, highly size‐diverse fish assemblages were associated with highly size‐diverse zooplankton assemblages. The size evenness of fish and phytoplankton assemblages was negatively and positively related to temperature, respectively. Phytoplankton size diversity was only weakly predicted by the resource availability. Our results suggest that size structure within a trophic group may be controlled by the size structure at adjacent trophic levels, as well as by temperature and resource availability. The positive relationship between the size diversity of fish and zooplankton suggests that higher diversity of the resources drives a higher size diversity of consumers or vice versa, and these effects are beyond those mediated by taxonomic diversity. In contrast, the size diversity and size evenness of phytoplankton are mainly influenced by physical factors in this region and perhaps in warm shallow lakes in general.

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 50–100years. 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 210Pb and 137Cs 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 Beyşehir 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.

Spatiotemporal Change Detection Analysis of Turkish Lake Water Surface Area in Response to Anthropogenic Ecosystem Disturbances Using Long-Term Landsat TM/ETM+ Data

The provision of diverse ecosystem goods and services by lakes is vital to ecosystem health and economic well-being of nations or regions. Securing ecologically safe lake water quality and quantity through sustainable uses and management practices concerns both present and future generations. The present study quantifies long-term impacts of human-induced disturbances including climate change on water surface areas of the 18 largest Turkish lakes. Spatiotemporal change detection analysis was carried out using long-term Landsat time series data between 1973 and 2014 with the aid of geographical information systems (GIS). Supervised and unsupervised classification techniques were combined to temporally differentiate and spatially delineate lake water surface areas using ancillary data. Over the period of about 40 years, lake surface area decreased for 15 lakes at a mean annual rate of 0.96 km2 but increased for three lakes at a mean annual rate of 0.17 km2. These spatiotemporal changes may be attributed to such human-induced pressures as drought, sectoral water uses/withdrawals, draining, and landfilling. These changes in turn lead to losses of or damages to both marketable and non-marketable ecosystem benefits that the lakes provide with humans at the local-to-regional spatial scales in the long-to-short-term temporal scales. The integration of remote sensing and GIS techniques adopted in this study allows for dynamic monitoring of not only lake water quality and quantity but also other natural resources, thus facilitating a timely and effective development of preventive and mitigative measures.

Inferring past environmental changes in three Turkish lakes from sub-fossil Cladocera

Cladocerans are increasingly used in palaeolimnological studies as their community composition is sensitive to both anthropogenic and natural forces in lakes. We present the results of a palaeolimnological investigation of three Turkish shallow lakes located in cold dry steppe and semi-dry Mediterranean climatic regions. The aim was to elucidate historical changes in environmental conditions by analysing sub-fossil cladocerans in 210Pb-dated sediment cores. Sub-fossil cladoceran remains from the surface sediment of 40 Turkish lakes were analysed to examine the environmental factors that most correlated with variation in the cladoceran assemblage. Redundancy analysis showed that salinity, macrophyte abundance, fish density, depth and total phosphorus were the most correlated with change in cladoceran assemblage composition with eigenvalues for the first and the second axes being λ1 = 0.312 and λ2 = 0.061, respectively. Sedimentary cladoceran assemblages from three cores were placed passively within the framework of the surface sediment ordination. The results reveal a prevalent impact of salinity, fish abundance and water level changes from the past to present. Thus, using cladoceran-based inferences, we traced key environmental changes related to variation in climate change, restoration and water level regulation over the last century.

Relatedness between contemporary and subfossil cladoceran assemblages in Turkish lakes

Cladocerans are valuable indicators of environmental change in lakes. Their fossils provide information on past changes in lake environments. However, few studies have quantitatively examined the relationships between contemporary and sub-fossil cladoceran assemblages and no investigations are available from Mediterranean lakes where salinity, eutrophication and top-down control of large-bodied cladocerans are known to be important. Here we compared contemporary Cladocera assemblages, sampled in summer, from both littoral and pelagic zones, with their sub-fossil remains from surface sediment samples from 40 Turkish, mainly shallow, lakes. A total of 20 and 27 taxa were recorded in the contemporary and surface sediment samples, respectively. Procrustes rotation was applied to both the principal components analysis (PCA) and redundancy analysis (RDA) ordinations in order to explore the relationship between the cladoceran community and the environmental variables. Procrustes rotation analysis based on PCA showed a significant accord between both littoral and combined pelagic–littoral contemporary and sedimentary assemblages. RDA ordinations indicated that a similar proportion of variance was explained by environmental variation for the contemporary and fossil Cladocera data. Total phosphorus and salinity were significant explanatory variables for the contemporary assemblage, whereas salinity emerged as the only significant variable for the sedimentary assemblage. The residuals from the Procrustes rotation identified a number of lakes with a high degree of dissimilarity between modern and sub-fossil assemblages. Analysis showed that high salinity, deep water and high macrophyte abundance were linked to a lower accord between contemporary and sedimentary assemblages. This low accord was, generally the result of poor representation of some salinity tolerant, pelagic and macrophyte-associated taxa in the contemporary samples. This study provides further confirmation that there is a robust relationship between samples of modern cladoceran assemblages and their sedimentary remains. Thus, sub-fossil cladoceran assemblages from sediment cores can be used with confidence to track long-term changes in this environmentally sensitive group and in Mediterranean lakes, subjected to large inter-annual variation in water level, salinity and nutrients.

Survey of Turkey's endemic amphibians for chytrid fungus Batrachochytrium dendrobatidis.

We report a new survey for Batrachochytrium dendrobatidis (Bd) in Turkey. We swabbed 228 individuals of 7 amphibian species (from 5 families) living in 2 locations (26-August National Park and the Turkish Lakes District) in the southwestern Anatolian region. The infection intensity of all the samples was determined using quantitative PCR. All 4 amphibian breeding sites and 4 amphibian species in 26-August National Park were infected by Bd, with the prevalence at each site ranging from 8 to 29%. Only 1 species was sampled from Beysehir Lake near the conservation area Beysehir Natural Park, but these samples were notable for their high detection rates (prevalence of 32.11%). This study reports the first records of Bd infecting wild Pelophylax ridibundus, Hyla orientalis, Pseudepidalea variabilis, and endemic Beysehir frogs Pelophylax caralitanus.

Water level and fish-mediated cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra- and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish.

Recovering Turkish narrow clawed crayfish (Astacus leptodactylus) populations carryAphanomyces astaci

Crayfish stocks collapsed in Turkey in mid 1980’s due to crayfish plague epidemics, with up to 25% survival in some cases. The collapsed stocks have then recovered slowly and commercial crayfish fishery was reinitiated gradually within a decade. We examined the prevalence of Aphanomyces astaci DNA in the narrow clawed crayfish (Astacus leptodactylus) collected from two Turkish lakes, Lake Iznik and Hirfanli Dam (N = 40 from both sites). The qPCR results, verified by conventional PCR and sequencing, indicated that nearly all sampled crayfish were A. astaci carries with some of them showing gross symptoms of infection, such as tissue erosion and melanisation, while some did not show any visible symptoms. The prevalence of A. astaci DNA was high in both stocks, being on the average 95% in both Lake Iznik and Hirfanli Dam. Our results show that these stocks are carries of A. astaci , but capable of forming productive stocks which indicates past and contemporary partial resistance adaptation in the host or virulence evolution in the A. astaci .

North Atlantic Oscillation influences on Turkish lake levels

AbstractThe North Atlantic Oscillation (NAO) is a large‐scale mode of natural climate variability governing the path of Atlantic mid‐latitude storm tracks and precipitation regimes in the Atlantic and Mediterranean sectors. The primary focus of this study is to investigate the variability of lake levels in seven lakes scattered across Turkey using the method of continuous wavelet transforms and global spectra. The long winter (December, January, February and March) lake‐level series and the NAO index (NAOI) series were subjected to wavelet transform. The global wavelet spectrum (energy spectrum of periodicities) of lake levels and winter NAOI anomalies, in most cases, revealed a significant correlation. It was shown that the Tuz, Sapanca, and Uluabat lakes reflect much stronger influences of the NAO than the other four lakes. In contrast, weak correlations were found in the coastal areas of the Mediterranean and eastern Turkey. The periodic structures of Turkish lake levels in relation to the NAO revealed a spectrum between the 1‐year and 10‐year scale level. Although the periodicities of more than 10‐year scale levels were detected, explaining significant relations between the NAO and these long‐term periodicities remains a challenging task. The results of this study are consistent with the earlier studies concerning the teleconnection between the NAO and climate variables in Turkey. Copyright © 2009 John Wiley & Sons, Ltd.

Effects of water quality and hydrologic drivers on periphyton colonization on Sparganium erectum in two Turkish lakes with different mixing regimes

The aim of this paper is to determine and compare the environmental factors controlling vertical colonisation of periphyton on Sparganium erectum in a shallow eutrophic turbid lake, Manyas Lake, and an oligo-mesotrophic deep lake, Sapanca Lake, Turkey during the July 1997--November 1998. To investigate the effect of the environmental factors on periphyton colonization on S. erectum, the stem was cut above the rhizomes and subdivided into three equal sections. Multivariate statistical analyses have been applied to clarify relationships between environmental variables and periphyton colonization on S. erectum. Results indicated that physical disturbance and trophic level of the lakes influenced the colonization of the periphyton. Among the measured parameters, low light intensity, total suspended solids, temperature and water level fluctuation were observed as driving factors in Manyas Lake whereas nutrient deficiency was found as key factor in Sapanca Lake. The zonation of the periphyton, density, composition and dominant/subdominant taxa were significantly different in these lakes. However, Oedogonium sp., Mougeotia sp., Cylindrocapsa sp., Cladophora glomerata (Linn.), Aulacoseira italica (Ehr.) Simonsen, Melosira varians C. Agardh, Navicula tripunctata (O.F. Müller) Bory and Fragilaria ulna (Nitzsch) Lange-Bertalot were found as dominant species at all sections of S. erectum both in Manyas Lake and Sapanca Lake. It can be thought that these species have a broad range of tolerance to several physical, chemical and hydrologic disturbances. This is the first study to introduce how much the water quality and hydrologic drivers have affected vertical colonization of periphyton on S. erectum in two lakes with different mixing regimes.

The influence of environmental conditions on the morphological variability of phytoplankton in an oligo-mesotrophic Turkish lake

2Phytoplankton dynamics and morphological plasticity were studied in an oligo-mesotrophic lake from late spring to early autumn in 2004 on a weekly to bi-weekly basis. This study aimed to evaluate the effect of environmental constraints on morphological plasticity and size structure of dominant species through the stratified period of the lake. While centric diatoms developed mainly in the epilimnion, Fragilaria crotonensis, Synedra sp. and Synedra acus were very well distributed through the whole water column, as was the cryptophyte Plagioselmis nannoplanctica. A filamentous cyanobacterium, Planktothrix rubescens, was stratified in the metalimnion throughout the sampling period, while Mougeotia sp. was entrained through the whole water column during the early autumn. Surface area / volume (S/V) ratios were calculated for the dominant species on each sampling date. The minimum S/V ratio was found with centric diatoms, while maximal values measured were for Synedra sp. and Asterionella formosa. The S/V ratio of the only dominant cryptophyte, Plagioselmis nannoplanctica was also high; variations were negatively correlated with NO3-N and PO4-P (-0.62 and -0.61, respectively) and positively correlated with euphotic depth (r=0.57) and temperature (r=0.82). On the other hand, the S/V ratios of Fragilaria crotonensis and Cyclotella ocellata each showed strong negative correlation with silica concentrations (-0.55 and -0.62, respectively). It is concluded that allometric relationships showed significant differences among species according to depth and season.

Catastrophic-like shifts in shallow Turkish lakes: a modeling approach

A generalized logistic model (GLM) was developed to determine occurrence of submerged macrophytes in shallow Lake Eymir, and the model was tested independently on the upstream shallow Lake Mogan using the data collected fortnightly from both lakes during 1997–2002. The independent variables included concentrations of chlorophyll-a (chl-a), suspended solids (SS) and total phosphorus (TP), Secchi disc transparency and z-scores of water levels. The dependent variable was the binary index of submerged plant occurrence. We used bootstrapping to determine the maximum number of epochs to train the model and to execute training when the corrected average cross entropy ( c-index) leveled off. The model predicted that SS concentration, z-scores of water levels and TP concentration were the most important variables for determining occurrence of submerged plants. Sensitivity analyses showed that the probability of submerged plant occurrence followed a strong hysterisis response to varying water levels and the concentrations of SS and TP, with the break points being ±50 cm, 12–17 mg l −1 and 200–300 μg l −1, respectively. This observed sensitivity was in accordance with the alternative stable states hypothesis of shallow lakes. For occurrence of submerged plants, chlorophyll-a concentration and Secchi disc transparency had low significance. This was in concert with both relevances of input variables and the field results. The model gave a good definition of the system since the c-index and corrected c-index on the training data were high (0.970 and 0.963, respectively). Testing the model on Lake Mogan produced a c-index of 0.815 with around 80% of the cases being correctly classified. This showed that the model had a high ability to generalize over a spatially independent test set; therefore, it had a great reliability as well. In addition, the predictive power of the model was indeed very high. Consequently, the model captured the relationships between the input and output variables successfully and consistently with alternative stable states hypothesis.

Are fish introductions a threat to endemic freshwater fishes in the northern Mediterranean region?

Seventy species of exotic or transplanted fish species have been introduced into this region, 60% of them in the last 40 years. The effects of these introductions on endemic species have rarely been described. The few exceptions are: hybridization of Salmo marmoratus with Salmo trutta; the extinction of three endemic species of Phoxinellus in a Turkish lake owing to the introduction of Stizostedion lucioperca; and the spatial displacement of Aphanius in sites where Gambusia affinis occurs. A further phenomenon possibly attributable to the introduction of exotic fish is the increased turbidity in Lake Mikri Prespa following the introduction of Carassius auratus. Because of the paucity of information, the effects of introductions on endemic species remain controversial. It is therefore essential to initiate conservation action plans, for each catchment in wetland areas rich in endemic fish. An awareness campaign directed at land managers and decision-makers on the role and importance of fish in the functioning of aquatic ecosystems must also be undertaken very soon.

International and Domestic Maritime Trade in the Ottoman Empire during the 18th Century

A glance at a map shows what an important role the sea played in the vast empire of the Ottomans in the 18th century, linking as it did the three continents of Europe, Asia, and Africa that made up the Old World. The Ottoman Empire dominated not only the eastern Mediterranean but also the major part of the southern shore of the western Mediterranean, the Black Sea—a “Turkish lake” until the 1780s—the Red Sea, and part of the Arab/Persian Gulf.Geography gave the sea a decisive role in the trade that took place in the Ottoman Empire both internationally and domestically.

Recent Inorganic Nonmarine Carbonate Environments: ABSTRACT

Compared with modern carbonate environments associated with or derived from the marine milieu, the study of nonmarine carbonate depositional environments has been neglected, although these offer a much wider range of conditions under which carbonate formation and diagenesis can occur. During the past years I have studied the following environments: (1) lakes and ponds, (2) springs and rivers, (3) caves (speleothems), (4) soils (especially caliche, and (5) technical incrustations (scale). My investigations clearly reveal that the formation of primary carbonate minerals (calcite, high-magnesium calcite, aragonite, hydrous magnesium carbonates) and of secondary carbonates (dolomite, huntite, and magnesite) in these various environments having different hydrochemistry, salinity, climatic conditions, etc., is mainly dependent on the Mg/Ca ratio of the solution in which the formation or transformation occurs. By loss or extraction of carbon dioxide, evaporation concentration or mixing of different water bodies, calcite, high-magnesium calcite, aragonite, and hydrous magnesium carbonates precipitate in an order of increasing Mg/Ca ratios. Dolomite formation takes place only at elevated Mg/Ca ratios (> 7) if high-magnesium calcite is available. The reactions leading to the formation of huntite and magnesite at very high (> 30) Mg/Ca ratios are not fully understood; from observations in Turkish lakes, it seems evident that dolomite is the precursor of huntite and huntite is the precursor of magnesite. A comparison between inorganic carbonate minerals deposited in the marine and nonmarine environments shows that the only significant difference in carbonate mineralogy is that (low-magnesium) calcite does not form under marine (or marine-derived) conditions. The explanation is that the high Mg/Ca ratio of the seawater (about 5) does not allow the formation of (low-magnesium) calcite. End_of_Article - Last_Page 1844------------