Lake Eymir Research Articles

Planning Process of Mogan Lake Environment

İklimsel ögelerin yanı sıra yerkürenin yapısını oluşturan dağlar, denizler, ormanlar ve göller doğal çevrenin cansız ögeleri olarak bilinir. Yerküredeki insanlar, bitki örtüsü, hayvan toplulukları ve mikro organizmalar ise çevrenin canlı ögeleridir. Mogan Gölü de cansız bir doğal varlık olarak, canlıların doğal ortamda yaşamalarını ve ekolojik dengenin sürekliliğini sağlamaktadır. Kıyısı boyunca rekreaktif etkinliklerin yoğun olarak yer aldığı Mogan Gölü’nün çevresindeki yapılaşma 1920 yılından başlamış ve artarak günümüze kadar gelmiştir. Aynı zamanda, gölün konumlandığı Gölbaşı ilçesi de 1950li yıllardan itibaren giderek artan bir göç ve hızlı nüfus artışına maruz kalmıştır. İlçedeki planlama çalışmaları ise çeşitli dönemlerde yapılmış fakat uygulanamamıştır. Buradaki plansız yapılaşma, Gölbaşı ve çevresinin Özel Çevre Koruma Bölgesi ilan edilene kadar devam etmiştir. Birbirine yakın ve aynı bölge içinde konumlanmasına rağmen, eski planlarda birbirinden ayrı değerlendirilen Eymir ve Mogan Gölleri, ilk defa Özel Çevre Koruma Kurumu’nun hazırladığı Çevre Planında bir arada gösterilip ele alınmıştır. Dolayısıyla, bu makalede Ankara’nın önemli doğal kaynaklarından biri olan Mogan Gölü ve çevresinin planlama süreci ele alınmış, böylece aynı havzada bulunan Mogan ve Eymir Göllerinin korunması amacı ile yapılacak olan planlama çalışmalarına bir veri oluşturulması sağlanmaya çalışılmıştır.

Response of the Mogan and Eymir lakes (Ankara, Central Anatolia) to global warming: Extreme events in the last 100 years

Mogan and Eymir lakes are shallow wetlands which are potentially susceptible to global warming. Previous geological studies demonstrated several complete desiccation and shrinkage events in Lake Mogan since the 1800s. Archival records show at least three desiccation events in 1910, 1934 and 1938, and many severe shrinkages later. Here, the significance of climatic and anthropogenic drivers is still a subject of curiosity. The back-analysis of the hydrological data during the regulator intervention indicates that Lake Mogan would have dried out in 1974, and would have shrunk considerably in the years 2007/2008 and 2017/2018 if human intervention was not involved. Our lake budget analysis shows that, assuming no human intervention and stream recharge, the water level of both lakes would have dropped below the threshold level in less than a week by natural downstream discharge, and the remaining volume of the lakes would evaporate in less than two years. This fact indicates the benefits of regulators for the protection of the lakes. The meteorological and lake budget data suggest that the underlying climatic threat over the studied lakes is high frequency (sub-decadal) rainfall scarcity coupled with long-term (several decades) insolation increase but not slow, steady deterioration of the climatic parameters.

Trend Analyses of Meteorological Variables and Lake Levels for Two Shallow Lakes in Central Turkey

Trend analyses of meteorological variables play an important role in assessing the long-term changes in water levels for sustainable management of shallow lakes that are extremely vulnerable to climatic variations. Lake Mogan and Lake Eymir are shallow lakes offering aesthetic, recreational, and ecological resources. Trend analyses of monthly water levels and meteorological variables affecting lake levels were done by the Mann-Kendall (MK), Modified Mann-Kendall (MMK), Sen Trend (ST), and Linear trend (LT) methods. Trend analyses of monthly lake levels for both lakes revealed an increasing trend with the Mann-Kendall, Linear, and Sen Trend tests. The Modified Mann-Kendall test results were statistically significant with an increasing trend for Eymir lake levels, but they were insignificant for Mogan lake due to the presence of autocorrelation. While trend analyses of meteorological variables by Sen Test were significant at all tested variables and confidence levels, Mann-Kendall, Modified Mann-Kendall, and Linear trend provided significant trends for only humidity and wind speed. The trend analyses of Sen Test gave increasing trends for temperature, wind speed, cloud cover, and precipitation; and decreasing trends for humidity, sunshine duration, and pan evaporation. These results show that increasing precipitation and decreasing pan evaporation resulted in increasing lake levels. The results further demonstrated an inverse relationship between the trends of air temperature and pan evaporation, pointing to an apparent “Evaporation Paradox”, also observed in other locations. However, the increased cloud cover happens to offset the effects of increased temperature and decreased humidity on pan evaporation. Thus, all relevant factors affecting pan evaporation should be considered to explain seemingly paradoxical observations.

Development planning approach for children with orthopaedic disabilities; example of Eymir Lake (Ankara)

DOI : 10.26650/forestist.2019.362135 Calismanin amaci, Ankara kenti yakin cevresinde bulunan Eymir Golu’nun dogal cevre degerlerinin paydaslarin katilimi ve ortopedik engelli cocuklarin kullanici kesimler olarak gozlemlenmesi dogrultusunda yeniden planlanmasini saglamaktir. Arastirmada kullanim Surecinde Degerlendirme Metodu (POE) uygulanmistir. Bu kapsamda anket olusturma, gozlem yapma ve ilgili uzmanlarla gorusme teknikleri kullanilmistir. Gozlem sonucunda cografi bilgi sistemi kullanilarak deneklerin yapmis olduklari etkinliklerin gosterildigi davranis haritalari olusturulmustur. Basta cevredeki insanlarin rahatsiz edici tavirlari, ulasim olanagi kisitliligi ve mevcut ekonomik sorunlar, bu engelli cocuklarin acik yesil alanlara gitmesini engellemektedir. Eymir golu ve cevresinin, ortopedik engelli cocuklara yonelik gelistirilen etkinliklere uygun olmasi ve bu kapsamda erisilebilirligin saglandigi uygun gecis yollarinin yeniden duzenlenmesi onerilmektedir.

Positive Health Effects Of The Natural Environment On Children With Disability

ABSTRACT It is seen that nature have healing and treating features for the disabled children with natural environment values (vegetation, water resources, birds, and other living creatures) that they possess. Getting information about what these features are and what kind of improvement does the presence of the disabled children in these natural areas provide is the starting point of this study. The goal of the study is to determine the effect of the natural environment values of the Lake Eymir located in the immediate environment of Ankara city on the children with Cerebral Palsy. In order to define the healing and treating effects of the natural environment values of Lake Eymir-Mogan on the children with Cerebral Palsy, natural factors of the area of Lake Eymir the study was conducted step-by-step: 1. Systematically Observation 2. Development Observation Forms 3. Survey and interview. In the study, observation method was implemented on children with Cerebral Palsy chosen from Dogan Caglar Special Education Primary School (DCSEPS) in the Lake Eymir and its surroundings. After providing disabled children to join the trip and conduct different activities in the area of Lake Eymir and its surroundings for 6 days, development form was prepared in order to evaluate the effects of this kind of natural areas on the children subjected the study. This form was given to teachers working in DCSEPS and they were asked to observe the four students taking part in the study during lessons and in the classrooms. To obtain information about the level of performance of the natural areas in Ankara and their adequacy and compliance level, and also to better understand the problems of these children, survey studies were conducted on parents with disabeled childeren. In addition, the interview was conducted face to face with the psychologist working in the Center of Education and Rehabilitation of the Cerebral Palsy and also in DCSEPS. In this study, it was seen that spending time in natural areas created a positive effect on the children with Cerebral Palsy and the activities conducted in this area improved motor, language, social and sentimental development as well as their self-maintenance skills.

Assessment of Toxic, Essential, and Other Metal Levels by ICP-MS in Lake Eymir and Mogan in Ankara, Turkey: An Environmental Application

Assessment of Toxic, Essential, and Other Metal Levels by ICP-MS in Lake Eymir and Mogan in Ankara, Turkey: An Environmental Application

Restoration of Eutrophic Lakes with Fluctuating Water Levels: A 20-Year Monitoring Study of Two Inter-Connected Lakes

Eutrophication continues to be the most important problem preventing a favorable environmental state and detrimentally impacting the ecosystem services of lakes. The current study describes the results of analyses of 20 year monitoring data from two interconnected Anatolian lakes, Lakes Mogan and Eymir, receiving sewage effluents and undergoing restoration. The first step of restoration in both lakes was sewage effluent diversion. Additionally, in hypertrophic Lake Eymir, biomanipulation was conducted, involving removal of benthi-planktivorous fish and prohibition of pike fishing. The monitoring period included high (H) and low (L) water levels (WL) enabling elucidation of the effects of hydrological changes on lake restoration. In shallower Lake Mogan, macrophyte abundance increased after the sewage effluent diversion in periods with low water levels even at turbid water. In comparatively deeper Lake Eymir, the first biomanipulation led to a clear water state with abundant macrophyte coverage. However, shortly after biomanipulation, the water clarity declined, coinciding with low water level (LWL) periods during which nutrient concentrations increased. A second biomanipulation was conducted, mostly during high water level (HWL) period, resulting in a major decrease in nutrient concentrations and clearer water, but without an expansion of macrophytes. We conclude that repetitive fish removal may induce recovery but its success may be confounded by high availability of nutrients and adverse hydrological conditions.

Positive Matrix Factorization dynamics in fingerprinting: A comparative study of PMF2 and EPA-PMF3 for source apportionment of sediment polychlorinated biphenyls

Receptor models were typically used in air pollution studies and few publications are available for Positive Matrix Factorization (PMF) that consider the details of parameters and procedures in evaluating the trace organic pollutants in sediments. In this study, environmental fate and source composition of Lake Eymir sediments contaminated by polychlorinated biphenyls (PCBs) were explored by applying two PMF models, Paatero's PMF2 and United States Environmental Protection Agency's (US EPA) EPA-PMF3. PMF2 and EPA-PMF3 rely on different algorithms; Paatero's algorithm and multilinear engine algorithm, respectively. Here, the approaches of two PMF models were compared for the identification of PCB patterns taking into consideration the effects of various uncertainty matrices, residual matrices and goodness-of fit parameters. As a result of the study, it was understood that both models resolved five factors and indicated Clophen A60 as the source of PCBs. These results were consistent with the results resolved by Chemical Mass Balance model applied to the same data set in a previous study. However, source contributions identified by two models differed in quantity, but with similar patterns. This study indicates a way in understanding behavior, fate and global source of persistent organic pollutants in sediment by applying and comparing with a special data including high percentage of below detected value (38.2%) to understand the dynamics of PMF model parameters.

Impact of alternating wet and dry periods on long-term seasonal phosphorus and nitrogen budgets of two shallow Mediterranean lakes

The water balance, with large seasonal and annual water level fluctuations, has a critical influence on the nitrogen and phosphorus dynamics of shallow lakes in the semi-arid climate zone. We constructed seasonal water and nutrient budgets for two connected shallow lakes, Lakes Mogan and Eymir, located in Central Anatolia, Turkey. The study period covered 20years with alternations between dry and wet years as well as restoration efforts including sewage effluent diversion and biomanipulations in Lake Eymir. Both lakes experienced a 1–2m water level drop during a drought period and a subsequent increase during the wet period, with seasonal water level fluctuations of 0.60 to 0.70m. During wet years with high water levels, small seasonal differences were observed with a nutrient peak in spring caused by external loading and nutrient loss via retention during summer. During years with low water levels, nutrient concentrations increased due to internal and external loading, exacerbated by evaporative water loss. In Lake Eymir, a shift to eutrophic conditions with turbid water occurred under low water level conditions and consequent internal loading of P from the sediment, causing high nutrient concentrations in summer. Our results indicate a threat of lakes drying out in the semi-arid climate zone if evaporation increases and precipitation decreases as anticipated from the global climate change predictions. In addition, our results show the influence of the water balance on the eutrophication of shallow lakes in the Mediterranean climate zone and highlight the ultimate consequences for lake management.

Comparison of undrained shear strength by pressuremeter and other tests, and numerical assessment of the effect of finite probe length in pressuremeter tests

There is a wide body of research reported in the literature which compare the undrained shear strength determined from various field and laboratory tests. The pressuremeter testing equipment and the related design techniques have been continuously refined. However, the undrained shear strength (S u) determined from the pressuremeter test (PMT) is generally higher than that obtained from other field or laboratory tests. In this study, numerical methods to consider the effects of length to diameter ratio (L/D) of the pressuremeter probe, and the procedural implications of soil disturbance and testing depth on the undrained shear strength determined from the PMT were investigated and possible correction factors depending on L/D ratio were established. In addition, in order to compare the variations in undrained shear strength of a clayey material with depth and testing method, a lightly overconsolidated and highly plastic clay, called “Eymir Lake clay” near Ankara (Turkey), was selected as the material of the study, and its values of undrained shear strength (S u), which were determined by PMT, field vane shear (FVT), conic penetration test (CPT), and laboratory tests, were compared. Based on the numerical analysis results, the correction factors depending on the L/D ratio of the conventional probes were suggested. The correction factors ranged from 0.83 to 0.96 for L/D ratios of 5.3 to 11, respectively, and they were determined to be independent of the rigidity values ranging from 25 to 200. It was also shown that overestimation of S u is independent of depth. In addition, due to very low permeability values of the Eymir Lake clay, it is concluded that for soils with coefficients of permeability lower than 10−10 m/s, partial drainage around the pressuremeter probe is unlikely. Based on the comparison among the results from laboratory and different field tests, the values of S u determined from the theoretical Palmer’s solution are higher than those from CPT, FVT, and CU tests. If the correction for L/D ratio is applied to the values of S u determined from the Palmer’s solution, S u from pressuremeter approaches S u obtained from FVT; however, there is still a slight overestimation in S u obtained from PMT. This overestimation is probably due to the differences in the mode of failure and the presence of a disturbed zone around the pressuremeter probe. However, S u determined from the PMT by empirical methods is close to those determined from CPT, FVT, and CU tests.

Generation of the bathymetry of a eutrophic shallow lake using WorldView-2 imagery

In this study, water depth distribution (bathymetric map) in a eutrophic shallow lake was determined using a WorldView-2 multispectral satellite image. Lake Eymir in Ankara (Turkey) was the study site. In order to generate the bathymetric map of the lake, image and data processing, and modelling were applied. First, the bands that would be used in depth prediction models were determined through statistical and multicollinearity analyses. Then, data screening was performed based on the standard deviation of standardized residuals (SD_SR) of depth values determined through preliminary linear regression models. This analysis indicated the sampling points utilized in depth modelling. Finally, linear and non-linear regression models were developed to predict the depths in Lake Eymir based on remotely sensed data. The non-linear regression model performed slightly better compared to the linear one in predicting the depths in Lake Eymir. Coefficients of determination (R2) up to 0.90 were achieved. In general, the bathymetric map was in agreement with observations except at re-suspension areas. Yet, regression models were successful in defining the shallow depths at shore, as well as at the inlet and outlet of the lake. Moreover, deeper locations were successfully identified.

Levels, Distribution, and Sources of Polychlorinated Biphenyls in Sediments of Lake Eymir, Turkey

Little information is available on the occurrence and fate of persistent organic pollutants in lakes of Turkey. The present study was performed as a first step to assess the occurrence, spatial distribution, and potential sources of polychlorinated biphenyls (PCBs) in surface sediments of Lake Eymir located in a special protection area. Σ41PCB concentrations range from 1.09 to 2.33 ng g(-1) in 62 sediment samples collected from the lake. The spatial homogeneity of the PCBs along the whole lake suggests the resuspension or redistribution of historic PCB contamination. A chemical mass balance (CMB) receptor model was used to identify the possible sources of PCBs, for which a limited number of congeners are available for modeling purposes. Results indicated Clophen A60 to be the major PCB source in lake sediments. CMB analysis also showed the importance of a number of compounds used for the assessment of source contributions.

The influence of water level on macrophyte growth and trophic interactions in eutrophic Mediterranean shallow lakes: a mesocosm experiment with and without fish

Summary1. Water‐level fluctuations are typical of lakes located in the semi‐arid Mediterranean region, which is characterised by warm rainy winters and hot dry summers. Ongoing climate change may exacerbate fluctuations and lead to more severe episodes of drought, so information on the effects of water level on the functioning of lake ecosystems in such regions is crucial.2. In eutrophic Lake Eymir, Turkey, we conducted a 4‐month (summer) field experiment using cylindrical 0.8‐m‐ (low‐water‐level) and 1.6‐m‐deep (high‐water‐level) mesocosms (kept open to the sediment and atmosphere). Fish (tench, Tinca tinca, and bleak, Alburnus escherichii) were added to half of the mesocosms, while the rest were kept fishless. Ten shoots of Potamogeton pectinatus were transplanted to each mesocosm.3. Sampling for physicochemical variables, chlorophyll a (chl‐a), zooplankton and per cent plant volume inhabited (PVI%) by macrophytes was conducted weekly during the first 5 weeks, and subsequently biweekly. Macrophytes were harvested on the last sampling date. During the course of the experiment, the water level decreased by 0.41 ± 0.06 m.4. Throughout the experiment, fish affected zooplankton abundance (−), nutrient concentrations (+), chl‐a (+) and water clarity (−) most strongly in the low‐water‐level mesocosms and the zooplankton community shifted towards dominance of small‐sized forms. The fishless mesocosms had a higher zooplankton/phytoplankton ratio, suggesting higher grazing.5. Greatest macrophyte growth was observed in the low‐water‐level fishless mesocosms. However, despite high nutrient concentrations and low water clarity, macrophytes were also abundant in the fish mesocosms and particularly increased following a water‐level decrease from midsummer onwards. Macrophyte growth was poor in the high‐water‐level mesocosms, even in the fishless ones with high water clarity. This was ascribed to extensive periphyton development reducing light availability for the macrophytes.6. Our results indicate that a reduction in water level during summer may help maintain the growth of macrophytes in Mediterranean eutrophic shallow lakes, despite a strong negative effect of fish predation on water clarity. It is therefore probable that an expected negative effect of global climate change on water clarity because of eutrophication and enhanced top‐down control of fish may be, at least partly, counteracted by reduced water level, provided that physical disturbance is not severe.

Assessing the impact of climate change on Mogan and Eymir Lakes’ levels in Central Turkey

Global warming is likely to have significant effect on the hydrological cycle. Some parts of the world may see significant reductions in precipitation or major alterations in the timing of wet and dry seasons. Climate change is one of the serious pressures facing water resources and their management over the next few years and decades. As part of the southern belt of Mediterranean Europe, Turkey is highly vulnerable to anticipated climate change impacts. The changes in global climate will seriously affect inland freshwater ecosystems and coastal lakes. Mogan and Eymir Lakes located in Central Turkey are shallow lakes that may be impacted significantly by climate change. The interaction between the lakes and groundwater system has been modelled in order to analyse the response of lake levels to climate change over a planning period of 96 years, beginning from October 2004 and ending in September 2100. The impacts of the emission scenarios of A2 and B1 of the Intergovernmental Panel on Climate Change (IPCC) on lake levels have been analyzed with the help of the lake-aquifer simulation model. The fluctuations in lake levels due to climate change scenarios are compared with the results of a scenario generated by the assumption of the continuation of the average recharge and discharge conditions observed for 1999 and 2004. The results show that very small, but long-term changes to precipitation and temperature have the potential to cause significant declines in lake levels and temporary drying of the lakes in the long-term. The impact of climate change on lake levels will depend on how these water resources are managed in the future.

Determination of Secchi Disc depths in Lake Eymir using remotely sensed data

Abstract In this study Secchi disk depths (SDD) are determined in an eutrophic Eymir Lake in Ankara using the multi-spectral image obtained from the Quickbird satellite. For this purpose, empirical models given in literature and artificial neural networks (ANN) are used. SDDs at 17 sampling points in Eymir Lake are measured via field studies. In the satellite image, pixel values at the sampling points are determined using ERDAS Imagine. Results indicate very low correlations between the SDD values calculated using the empirical models and the ones measured in-situ. Correlation of determination values (R2) up to 0.92 are achieved when ANN modeling is applied. In ANN models developed, Levenberg-Marquardt (LM) and gradient decent algorithm (GDA) are the training algorithms that provided the best results. This study indicates that ANN is an important tool in obtaining information from the remotely sensed data.

Batch and column experiments to support heavy metals (Cu, Zn and Mn) in alluvial sediments

Laboratory batch sorption and column transport experiments were performed on heterogeneous alluvial soils with a wide range of physical characteristics from wells that are located in the region between Mogan Lake and Eymir Lake, Golbs1, Ankara. The mean values for the K(subscript d) of Cu were found to be highest in clay (32550.350 L/kg) and lowest in loamy sand (18170.76 L/kg). The minimum and maximum sorption capacity values (mean values) for Zn were found to be in clay (10985.148 mg/kg) and in silty loam (8597.14 mg/kg) units, respectively. Similarly, the minimum and maximum values for Mn were found in loamy sand (4908.695 mg/kg) and clay (7587.39 1 mg/kg) units. The non-linear least-squares optimization code ”CXTFIT” was used to determine transport parameter values by curve-fitting. The results of the column experiments demonstrate dispersivity values within the range of 0.024-1.13 cm for soil samples.

Batch and Column Experiments to Support Heavy Metals (Cu, Zn, and Mn) Transport Modeling in Alluvial Sediments Between the Mogan Lake and the Eymir Lake, Gölbaşı, Ankara

This article describes laboratory batch sorption and column transport experiments that were conducted using heterogeneous alluvial sediments with a wide physical characteristic from wells, located between Lake Mogan and Lake Eymir, Gölbaşı, Ankara. The batch sorption experiment was conducted in two separate systems, that is, single and multicomponents. Single batch experiment was performed to determine equilibrium condition between the heavy metal ions and the soil adsorption sites. The sorption isotherms data from multibatch experiments were used to calculate the sorption parameters. Single batch experiment indicated that equilibrium was attained within 9 days from the start of the sorption test. As a result of multicomponents batch experiments, for Zn and Mn, the sorption process was well described by the Freundlich or Langmuir isotherm model, whereas sorption of Cu was better described by the linear isotherm model. The Kd of Cu were found to be highest in soil 1 (32550.350 L kg−1) and lowest in soil 5 (18170.76 L kg−1). The maximum and minimum sorption capacity values for Zn were found to be in soil 1 (10985.148 mg kg−1) and in soil 2 (8597.14 mg kg−1) units, respectively. [Correction added after online publication 15 July, 2010: In the preceding sentence, the words “minimum” and “maximum” were initially switched.] Similarly, soil 1 (7587.391 mg kg−1) and soil 5 (4908.695 mg kg−1) units provided the maximum and minimum values for Mn. In the column experiments, flow and tracer transport was studied under saturated conditions using conservative tracer to determine the transport parameters. Transport parameter values were obtained by curve‐fitting using the nonlinear least‐squares optimization code CXTFIT. Results of the column experiments indicated that the dispersivity values obtained for soil samples were in the range of 0.024 to 1.13 cm.

Water quality trend analysis in Eymir Lake, Ankara

In this study, trends in selected water quality parameters in Eymir Lake over a period of 10 years are analyzed using the Mann–Kendall test. Analyzed water quality parameters are dissolved oxygen (DO), total phosphorus (TP), total suspended solids (TSS), and secchi depth (SD). In addition, trends in the yearly averages of precipitation, lake volume, and ambient temperature are examined. According to Mann–Kendall test results, precipitation, volume and ambient temperature values exhibit decreasing trends in 1998–2008. DO and TSS exhibit increasing trends while TP and SD have decreasing trends in Eymir Lake. The change in the volume of the lake has a significant impact on the trends of DO, TSS, and SD. These results indicate that, besides eutrophic conditions, water balance and drought conditions significantly impact the water quality of Eymir Lake.

Restoration of a shallow Mediterranean lake by biomanipulation complicated by drought

Whether fish biomanipulation is an efficient restoration technique in eutrophic warm sub/tropical lakes has been subject to recent debate. Our investigations undertaken in warm Lake Eymir, Turkey show that fish re- moval increased water clarity during a five-year period. Rapid re-colonisation of submerged plants, Potamogeton pectinatus and Ceratophyllum demersum, occurred. This recovery was achieved at higher total phosphorus (TP) levels than the suggested threshold for stability, probably owing to the nitrogen-limited condition of the lake. Re- establishment of vegetation coincided with significantly reduced concentrations of TP and dissolved inorganic nitrogen (DIN). Abundance of the large-bodied Daphnia pulex was low and it later disappeared completely from the zooplankton community, probably due to increased fish predation. A severe drought, occurring two years after the fish removal, significantly lowered the water level, increased the hydraulic residence time and caused an expan- sion of the vegetation. The drought was also associated with a significant increase in salinity, conductivity, nutrient concentrations (TP and DIN) and in the abundance of Arctodiaptomus bacillifer. The in-lake nutrient amounts became more dependent on internal processes rather than on the external loading, which was very low during the drought period. When the water level rose to normal values, the concentrations of TP and soluble reactive phosphate (SRP) decreased. However, the DIN concentration significantly increased due to slowed denitrification processes in consequence of the low availability of dissolved oxygen. This increase in ammonium concentrations may have contributed to the instability of clear-water conditions by releasing the lake from its former nitrogen-limited state, since the TP levels in the lake had already surpassed critical levels. Along with this, tench (Tinca tinca ) biomass in- creased to pre-biomanipulation levels and the pike (Esox lucius) to planktivorous fish ratio decreased with increased chlorophyll-a concentrations, largely by inedible cyanobacteria, which led to a decline in summer water clarity but not to disappearance of submerged plants. The early growth of plants was probably controlled by the spring water clarity, which remained high, and the lake maintained its macrophyte-dominated state, despite the relatively turbid conditions prevailing in summer. The highly positive effect of the Lake Eymir restoration effort contradicts the experiences from other subtropical lakes. This could be due to the fact that warm Lake Eymir being at high latitude with a strong presence of predatory fish and limited abundance of planktivorous fish species, as opposed to low altitude warm lakes. However, drought as an inherent feature of the arid region may be even more important in the future as drier conditions are predicted for the Mediterranean region in consequence of the global climate change.

Sustainable management of Mogan and Eymir Lakes in Central Turkey

Mogan and Eymir Lakes, located 20km south of Ankara in Central Turkey, are important aesthetic, recreational, and ecological resources. Dikilitas and Ikizce reservoirs, constructed on upstream surface waters, are two man-made structures in the basin encompassing an area of 985km2. The purpose of this study is to quantify groundwater components in lakes’ budgets and to assess the potential impacts of upstream reservoirs on lake levels for sustainable management of the system. Available data have been used to develop a conceptual model of the system. A three-dimensional groundwater model, incorporating a lake component, has been developed for the system. The model has been calibrated successfully under transient conditions over a period of 6years using monthly periods. The results show that groundwater inflows and outflows have the lowest contribution to the overall lakes’ budget. The model has been subsequently used to evaluate the impacts of upstream reservoirs. The results show that these reservoirs have a significant effect on lake stages but not on groundwater levels. A trade-off curve between the quantum of water released and the average stage in Lake Mogan has been developed to enhance decision makers’ ability for sustainable management of the system in the long term.