Remedial strategy of algal proliferation in a regulated river system by integrated hydrological control: an evolutionary modelling framework

Abstract

We simulated water-quality measures in a regulated river system (the lower Nakdong River) under simultaneous discharge control at upriver dams and an estuarine barrage with the goal of reducing phytoplankton biomass (chlorophyll a concentration). We used genetic programming (GP) to create a rule-set-based predictive model for the chlorophyll a concentration based on 16 years (1994–2009) of meteorological, hydrological, and limnological data. The rule-set model used eight variables, including water temperature, dam and estuarine barrage discharge, phosphate and silica concentrations, and accurately predicted the phytoplankton biomass (determination coefficients, r2, for training and test data were 0.52 and 0.45, respectively). According to sensitivity and scenario analyses, a larger water volume resulting from increased discharge from upriver dams and decreased discharge from an estuarine barrage would reduce chlorophyll a concentrations at the study site. This result provided ample evidence that simultaneous manipulation of dam and estuarine discharge rates could effectively increase river flow and flush aggregated algal populations downstream. Additionally, we considered that even small increases in river flow could play a role in diluting phytoplankton biomass during the dry winter season when estuarine discharge remains low. These two hydrological mechanisms could be used as selective strategies for water-resource management.

Response of Microcystis and Stephanodiscus to Alternative Flow Regimes of the Regulated River Nakdong (South Korea) Quantified By Model Ensembles Based on the Hybrid Evolutionary Algorithm (HEA)

“…Data for the year 2002 were incomplete and have been excluded from this study. Scenarios have been based on the suggestion, 350 m 3 s À1 is the flow threshold above which Chl-a concentrations decline significantly (Hong et al, 2014). Accordingly, the scenario 1 assumes a two-fold increase and scenario 2 a three-fold increase of flow that is below the threshold, whereby flow rates exceeding 700 m 3 s À1 (≈83rd percentile of the river flow) have been halved (Figure 1).…”

“…Seasonally altered river flow by optimum water release from dams appears as viable option for algal bloom control (e.g. Jeong et al, ; Hong et al, ), which can be determined by modelling techniques.…”

Limnological assessment of the meteo-hydrological and physicochemical factors for summer cyanobacterial blooms in a regulated river system

“…Lake Taihu in China (Duan et al, 2012;Zhang et al, 2012), Lakes Suwa (Yokoyama and Park, 2002) and Kasumigaura (Islam et al, 2012) in Japan, and Han and Nakdong Rivers and Daechung Reservoir in South Korea are representatives of cyanobacterial bloom ecosystems. The Nakdong River is a regulated river system with dams and an estuarine barrage for water resource management during the monsoon season (Jeong et al, 2011;Kim et al, 2012;Hong et al, 2014). This river had a severe cyanobacterial bloom problem in the 1990s (Ha et al, 1998(Ha et al, , 1999.…”

“…The hydrological changes and rainfall variability in the Nakdong River due to global climate change have been hypothesized to promote cyanobacterial bloom outbreaks (Seo et al, 2012;Hur et al, 2013). For almost 20 years, long-term ecological research (LTER) data have provided considerably more complex and variable information about the Nakdong River (Jeong et al, 2011;Kim et al, 2012;Hong et al, 2014), and comparison of cyanobacterial bloom trends based on LTER data combined with monsoon climate data (e.g., summer monsoon rainfall) might lead to the identification of more complex inter-annual variability of bloom formation.…”