Process-based simulation library SALMO-OO for lake ecosystems. Part 2: Multi-objective parameter optimization by evolutionary algorithms Hongqing Cao ⁎ , Friedrich Recknagel, Lydia Cetin, Byron Zhang School of Earth and Environmental Sciences, University of Adelaide, 5005, Australia ARTICLE INFO ABSTRACT Article history: Received 29 November 2006 Received in revised form 15 January 2008 Accepted 8 February 2008 SALMO-OO represents an object-oriented simulation library for lake ecosystems that allows to determine generic model structures for certain lake categories. It is based on complex ordinary differential equations that can be assembled by alternative process equations for algal growth and grazing as well as zooplankton growth and mortality. It requires 128 constant parameters that are causally related to the metabolic, chemical and transport processes in lakes either estimated from laboratory and field experiments or adopted from the literature. An evolutionary algorithm (EA) was integrated into SALMO-OO in order to facilitate multi- objective optimization for selected parameters and to substitute them by optimum temperature and phosphate functions. The parameters were related to photosynthesis, respiration and grazing of the three algal groups diatoms, green algae and blue-green algae. The EA determined specific temperature and phosphate functions for same parameters for 3 lake categories that were validated by ecological data of six lakes from Germany and South Africa. The results of this study have demonstrated that: (1) the hybridization of ordinary differential equations by EA provide a sophisticated approach to fine-tune crucial parameters of complex ecological models, and (2) the multi-objective parameter optimization of SALMO-OO by EA has significantly improved the accuracy of simulation results for three different lake categories. © 2008 Elsevier B.V. All rights reserved. Keywords: Multi-objective parameter optimization SALMO-OO Lake categories Evolutionary algorithms Genetic programming 1. Introduction Over the past three decades numerous lake ecosystem models incorporating pelagic food webs and nutrient cycles have been developed based on complex ordinary differential equations (ODE) (e.g. Parker, 1968; Park et al., 1974; Radtke and Straškraba, 1980; Benndorf and Recknagel, 1982; Hongping and Jianyi, 2002; Arhonditsis and Brett, 2005a). Those ODE usually consist of several state and driving variables as well as numerous process equations and parameters which allow to simulate seasonal dynamics of food webs and nutrient cycles. A typical example is the lake simulation library SALMO-OO (Recknagel et al., 2008; Recknagel et al., submitted for publication) that represents an object-oriented implementation of the ODE of the model SALMO (Benndorf and Recknagel, 1982) and alternative process repre- sentations for algal growth and grazing as well as zooplank- ton growth and mortality adopted from (Park et al., 1974), Arhonditsis and Brett (2005a) and Hongping and Jianyi (2002) (see http://ecolinfo.ees.adelaide.edu.au:8080/SALMO-OO/index. html). ECOLOGICAL INFORMATICS 3 (2008) 181 – 190 ⁎ Corresponding author. E-mail address: hxc@cs.nott.ac.uk (H. Cao). 1574-9541/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoinf.2008.02.001 available at www.sciencedirect.com www.elsevier.com/locate/ecolinf