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 mu g 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.


Hysteresis in vegetation shift - Lake Mogan prognoses
Zhang, JJ; Jorgensen, SE; Beklioğlu, Meryem; Ince, O (Elsevier BV, 2003-06-15)
A structurally dynamic model developed [Ecol. Model. (in press)] for Lake Mogan was applied to set up prognosis for the response of the lake to the increased phosphorus input. It was found that a shift to a turbid water state takes place at phosphorus concentration between 0.16 and 0.25 mg TP l(-1) resulting in a significant decrease in the submerged plants. Consequently, above the threshold P level, the submerged plants abruptly disappeared, while phytoplankton became dominant. The model simulated the reco...
A structurally dynamic modelling - Lake Mogan, Turkey as a case study
Zhang, JJ; Jorgensen, SE; Tan, CO; Beklioğlu, Meryem (Elsevier BV, 2003-06-15)
A structurally dynamic model based on phosphorus nutrient limitation has been developed for Lake Mogan located nearby Ankara, Turkey. This eutrophication model, which includes very dense submerged plants, was calibrated using a standard procedure described by Jorgensen and Bendoriccho [Fundamentals of Ecological Modelling, 3rd ed. Elsevier, Amsterdam, 20 pp.]. Furthermore, exergy was applied as a goal function to consider the dynamic adaptation and the seasonality of plankton species (e.g. size shifts). Thi...
Modeling complex nonlinear responses of shallow lakes to fish and hydrology using artificial neural networks
Tan, Can Ozan; Beklioğlu, Meryem (Elsevier BV, 2006-07-10)
Mathematical abstractions may be useful in providing insight that is otherwise very difficult to obtain due to complex interactions in the ecosystems. The difficulty associated with the nonlinearity and complexity of ecological processes and interactions can be avoided with artificial neural networks (ANN) and generalized logistic models (GLMs) which are practically ANNs without hidden layer. An ANN and a GLM were developed to determine the probability of submerged plant occurrence in five shallow Anatolian...
Climatic controls on biophysical interactions in the Black Sea under present day conditions and a potential future (A1B) climate scenario
Cannaby, Heather; Fach Salihoğlu, Bettina Andrea; Arkin, Sinan S.; Salihoğlu, Barış (2015-01-01)
A dynamical downscaling approach has been applied to investigate climatic controls on biophysical interactions and lower trophic level dynamics in the Black Sea. Simulations were performed under present day conditions (1980-1999) and a potential future (2080-2099) climate scenario, based on the Intergovernmental Panel for Climate Change A1B greenhouse gas emission scenario. Simulations project a 3.7 degrees C increase in SST, a 25% increase in the stability of the seasonal thermocline and a 37 day increase ...
Lacustrine mineral facies and implications for estimation of palaeoenvironmental parameters: Neogene intervolcanic Pelitcik basin (Galatean Volcanic Province), Turkey
Süzen, Mehmet Lütfi (2000-06-01)
The mineralogy of the Neogene lacustrine facies of Pelitcik basin was investigated for the purpose of deriving the palaeoenvironmental parameters of this intervolcanic basin. The laboratory studies indicate that dolomite and K-feldspar are the major non-clay minerals in the study area, where plagioclase, analcime, fibrous zeolite and quartz are the minor constituents. Dolomites are found to be non-stoichiometric in chemistry. The clay fraction of the lacustrine facies is composed mainly of dioctahedral smec...
Citation Formats
C. Tan and M. Beklioğlu, “Catastrophic-like shifts in shallow Turkish lakes: a modeling approach,” ECOLOGICAL MODELLING, pp. 425–434, 2005, Accessed: 00, 2020. [Online]. Available: