School of Computer Science and Engineering, Seoul National University, Seoul, 151-721, South Korea
Department of Biological Science, Pusan National University, Busan, 609-735, South Korea
In the regulated Nakdong River, algal proliferations are annually observed in some seasons, with
cyanobacteria (Microcystis aeruginosa) appearing in summer and diatom blooms (Stephanodiscus hantzschii) in winter. This study aims to develop two ecological models forecasting future chlorophyll a at two time-steps (one-week and one-year forecasts), using recurrent neural networks tuned by genetic algorithm (GA-RNN). A moving average (MA) method pre-processes the data for both short- and long-term forecasting to evaluate the effect of noise downscaling on model predictability and to estimate its usefulness and trend prediction for management purposes. Twenty-five physicochemical and biological components (e.g. water temperature,
DO, pH, dams discharge, river flow, rainfall, zooplankton abundance, nutrient concentration, etc. from 1994 to 2006) are used as input variables to predict chlorophyll a. GA-RNN models show a satisfactory level of performance for both predictions. Using genetic operations in the network training enables us to avoid numerous trial-and-error model constructions. MA-smoothed data improves the predictivity of models by removing residuals in the data prediction and enhancing the trend of time-series patterns. The results demonstrate efficient development of ecological models through selecting appropriate network structures. Data pre-processing with MA helps in forecasting long-term seasonality and trend of chlorophyll a, an important outcome for
decision makers because it provides more reaction time to establish and control management strategies.