Abstract
Flow regulation is one of the most common anthropogenic factors affecting rivers worldwide. In Korea, 16 weirs were constructed along four major rivers from 2009 to 2012. This study aimed to elucidate initial changes in physical, chemical, and biological variables after the construction of consecutive weirs on the Nakdong River, a major large river system. Water quality variables and phytoplankton cell densities were investigated at eight representative sites and compared with the data recorded before the weir construction. There were spatial and temporal changes in the hydraulic retention time (HRT), total phosphorus (TP), and chlorophyll a concentrations among the eight weir sections. HRT increased after the weir construction, while TP and chlorophyll a tended to decrease from the middle to lower section of the Nakdong River. Furthermore, differences were observed in the phytoplankton community composition between 2006–2007 and 2013. There was a marginal decrease in the duration of centric diatom (Stephanodiscus hantzschii) blooms after weir construction. However, Microcystis aeruginosa proliferated more extensively during summer and autumn than it did before the weir construction. Our results suggest that changes in hydrological factors, in response to consecutive weir construction, may contribute to greater physical, chemical, and ecological variability.
Highlights
The ecological effects of hydrological changes, including the water level, river flow, water velocity, and hydraulic retention time (HRT), on aquatic ecosystems have often been studied
The mean monthly air temperatures in the Nakdong River weir section ranged from −1.5 to
St. 8, the annual mean BOD5 concentration was 2.4 mg·L−1, which was lower than that before the construction, but there were no statistically significant differences (p > 0.05). These results showed that the organic pollution levels were different in each stretch of the Nakdong River after the weir construction (Table 2)
Summary
The ecological effects of hydrological changes, including the water level, river flow, water velocity, and hydraulic retention time (HRT), on aquatic ecosystems have often been studied. Phytoplankton is a source of food and energy for organisms at higher trophic levels within an aquatic ecosystem [7,8], and phytoplankton composition usually changes with seasonal fluctuations in water temperature [9]. The phytoplankton species composition and biomass depend, in a complex manner, on various environmental factors, including the concentration of nutrients (nitrogen and phosphorus) derived from watersheds, light, water temperature, flow, turbidity, and HRT [10,11,12,13,14,15,16]. Public Health 2018, 15, 2348; doi:10.3390/ijerph15112348 www.mdpi.com/journal/ijerph
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