Abstract
Following the installation of 16 weirs in South Korea’s major rivers through the Four Rivers Project (2010–2012), the water residence time increased significantly. Accordingly, cyanobacterial blooms have occurred frequently, raising concerns regarding water use and the aquatic ecosystem health. This study analyzed the environmental factors associated with cyanobacterial dominance at four weirs on the Nakdong River through field measurements, and parametric and non-parametric data mining methods. The environmental factors related to cyanobacterial dominance were the seven-day cumulative rainfall (APRCP7), seven-day averaged flow (Q7day), water temperature (Temp), stratification strength (ΔT), electrical conductivity (EC), dissolved oxygen (DO), pH, and NO3–N, NH3–N, total nitrogen (TN), total phosphorous (TP), PO4–P, chlorophyll–a, Fe, total organic carbon (TOC), and SiO2 content, along with biological and chemical oxygen demands. The results indicate that site-specific environmental factors contributed to the cyanobacterial dominance for each weir. In general, the physical characteristics of EC, APRCP7, Q7day, Temp, and ΔT were the most important factors influencing cyanobacterial dominance. The EC was strongly associated with cyanobacterial dominance at the weirs because high EC indicated persistent low flow conditions. A minor correlation was obtained between nutrients and cyanobacterial dominance in all but one of the weirs. The results provide valuable information regarding the effective countermeasures against cyanobacterial overgrowth in rivers.
Highlights
Abnormal overgrowth of cyanobacteria in rivers and lakes adversely affects the biodiversity in freshwater ecosystems [1] and affects water usage by generating taste and odor compounds in drinking water [2,3]
The weather, flow, water quality, and algae measurement data collected at four weirs (GGW, Dalseong weir (DSW), Hapcheon Changnyeong weir (HCW), and Changnyeong Haman weir (CHW)) installed on the Nakdong River from May 16, 2017, to November 23, 2018, were analyzed using data mining techniques
The important variables related to cyanobacterial dominance were extracted for each weir and the causes of algal bloom were analyzed in an integrated manner
Summary
Abnormal overgrowth of cyanobacteria (hereinafter referred to as “algal blooms”) in rivers and lakes adversely affects the biodiversity in freshwater ecosystems [1] and affects water usage by generating taste and odor compounds in drinking water [2,3]. Algal blooms in South Korea have caused sporadic problems in stagnant waters such as those of dam reservoirs and estuary lakes. Since 16 weirs were installed on major rivers as part of the Four Rivers Project (2010–2012), the algal blooms have been occurring widely in large rivers such as the Nakdong, Geum, and Yeongsan Rivers, causing a major socio-environmental issue [6]. There are various opinions on the cause of the algal blooms that frequently occur at weirs installed on major rivers [7,8]. Intensive studies have been performed in the lowland rivers of south-eastern
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