Ecological Modelling 189 (2005) 436–446 Fuzzy logic modeling of the dissolved oxygen fluctuations in Golden Horn Abd¨ usselam Altunkaynak a , Mehmet ¨ Ozger a , Mehmet C ¸ akmakcı b,∗ a Istanbul Technical University, Faculty of Civil Engineering, Hydraulics Division, Maslak 34469, Istanbul, Turkey b Istanbul Technical University, Faculty of Civil Engineering, Environmental Engineering Department, Maslak, Istanbul 34469, Turkey Received 27 August 2004; received in revised form 9 February 2005; accepted 29 March 2005 Available online 2 June 2005 Abstract The modern modeling techniques show a significant progress in recent years. Fuzzy logic approach is one of these methods that can be used for forecasting purposes and identification of complex systems. In this study, it is aimed to model monthly dissolved oxygen (DO) amount variations. Firstly, regression technique is used to remove the trend from the actual dissolved oxygen time series. Detrended time series is then modeled with Takagi–Sugeno Fuzzy logic approach. The monthly historical records of DO as considered in this paper provide a fundamental data exhibiting persistence. It is this dependence that gives opportunity for the serial modeling of the data sequence concerned. These models are the prime and sole means to derive the future likely excedences over the historical values and hence provide a chance for the future planner with decision variables such as the minimum DO amounts and their persistence for some duration. In the scope of this study, DO concentration changes in the two stations located in Golden Horn at the 0.5 m (upper layer) depth were modeled. As a result of the study, it is seen that one can forecast the next month’s DO amount from antecedent measurements within an acceptable relative error limits. © 2005 Elsevier B.V. All rights reserved. Keywords: Concentration dissolved oxygen; Forecast; Fuzzy logic; Golden Horn 1. Introduction Dissolved oxygen (DO) is a vital element for the survival of the living beings in the estuarine ecosys- tems. DO concentration has also traditionally been ∗ Corresponding author. Tel.: +90 2122853792; fax: +90 2122853781. E-mail addresses: altunkay@itu.edu.tr (A. Altunkaynak), cakmakci@itu.edu.tr (M. C ¸ akmakcı). used as a variable of water quality. The relationship be- tween DO concentration decrease and the appearance in the water column of non-desirable effects should be observed (Garcia et al., 2002). Imported sediments are often enriched with nutrients and organic matter. Lake depth and water storage capacity are reduced by deposition of sediments. The distribution of DO concentration and other vital water quality parameters are affected by the deposition. Fish assemblage com- position and other biotic community can be influenced 0304-3800/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2005.03.007