Journal of Environmental Sciences 21(2009) 319–327 A vertically integrated eutrophication model and its application to a river-style reservoir – Fuchunjiang, China WU Tingfeng 1,2 , LUO Liancong 1 , QIN Boqiang 1, ∗ , CUI Guangbai 2 , YU Zuoming 3 , YAO Zhiming 4 1. State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences, Nanjing 210008, China. E-mail: tfwu@ niglas.ac.cn 2. College of Hydrology and Water Resources, Hohai University, Nanjing 210098, China 3. Hangzhou Research Institute of Environmental Sciences, Hangzhou 310014, China 4. Administrative Division of Qingshan Reservoir, Hangzhou 311305, China Received 27 March 2008; revised 28 July 2008; accepted 15 August 2008 Abstract Based on a 2-D hydrodynamic model, a vertically integrated eutrophication model was developed. The physical sub-model can be used for calculation of water density at different depths, and the water quality sub-model was used for calculation of algal growth. The cohesive and non-cohesive sediments were simulated separately with different methods. The light extinction coefficient used in the underwater light regime sub-model was linearly related to the sum of sediment and phytoplankton biomass. Some components less important to the model were simplified to improve practicability and calculation efficiency. Using field data from Fuchunjiang Reservoir, we calculated the sensitivity of ecological parameters included in this model and validated the model. The results of sensitivity analysis showed that the parameters strongly influenced the phytoplankton biomass, including phytoplankton maximum growth rate, respiration rate, non-predatory mortality rate, settling rate, zooplankton maximum filtration rate, specific extinction coefficient for suspended solids and sediment oxygen demand rate. The model was calibrated by adjusting these parameters. Total chlorophyll a (chl-a) concentrations at different layers in the water column were reproduced very well by the model simulations. The simulated chl-a values were positively correlated to the measured values with Pearson correlation coefficient of 0.92. The mean difference between measured and simulated chl-a concentrations was 12% of the measured chl-a concentration. Measured and simulated DO concentrations were also positively correlated (r = 0.74) and the mean difference was 4% of measured DO concentrations. The successful validation of model indicated that it would be very useful in water quality management and algal bloom prediction in Fuchunjiang Reservoir and a good tool for water quality regulation of other river-style reservoirs. Key words: river-style; reservoir; eutrophication; numerical model; Fuchunjiang Reservoir DOI: 10.1016/S1001-0742(08)62271-8 Introduction River-style reservoirs are normally formed with dam construction for water storage at the lower reaches of river. They are characterized by a narrow, deep shape, with short water residence time and often seasonal stratification due to stable water body and meteorological conditions. They have features of both reservoirs and rivers, which results in much more complexity of numerical simulation of water quality. Fuchunjiang Reservoir is a typical river-style reservoir locating at the lower reaches of Qiantang River. Its water storage is controlled by a dam and therefore, the water storage change can impact the currents in whole river and play an important role in the whole river ecosystem. In 2004, an algal bloom was formed in Fuchunjiang Reservoir which then received much attention from local environ- mental authorities and research scientists to understand the * Corresponding author. E-mail: qinbq@niglas.ac.cn algal bloom mechanism. In order to provide insight into how it was formed, we developed an eutrophication model for reproducing the algal bloom in 2004 and predicting further events for water quality management. Eutrophication models originally developed for reser- voirs or rivers do not work well with river-style reservoirs (Liu and Yang, 2004). It is difficult to reflect the spatial variation in hydrodynamics and water quality in river- style reservoirs using 1-D models, whereas 3-D models require long computation time and sometimes difficult for calibration and validation. For simulating river-style reservoir ecosystem, a laterally averaged mode (2-D mod- el) is supposed to be the ideal tool since the simulation results can provide information about vertical variation of water quality (Bowie et al., 1985). There has been a degree of worldwide scientific concern about eutrophica- tion models, however, most of them were designed for shallow lakes (Rao et al., 2003). In this study, we introduce