Hydrological management strategies for the control of algal blooms in regulated lowland rivers

Abstract

Reservoirs of lowland floodplain rivers with eutrophic backgrounds cause variations in the hydrological and hydraulic conditions of estuaries and low‐dam reservoir areas, which can promote planktonic algae to proliferate and algal bloom outbreaks. Understanding the ecological effects of variations in hydrological and hydraulic processes in lowland rivers is important for algal bloom control. In this study, the middle and lower reaches of the Han River, China, a typical regulated lowland river with a eutrophic background, are selected. Based on the effect of hydrological and hydraulic variability on algal blooms, a hydrological management strategy for river algal bloom control is proposed. The results showed that (a) differences in river morphology and background nutrient levels cause significant differences in the critical threshold flow velocities for algal bloom outbreaks between natural river and low‐dam reservoir sections; there is no uniform threshold flow velocity for algal bloom control. (b) There are significant differences in the river hydrological/hydraulic conditions between years with and without algal blooms. The average river flow, water level and velocity in years with algal blooms are significantly lower than those in years without algal blooms. (c) For different river sections where algal blooms occur and to meet the threshold flow velocities, the joint operation of cascade reservoirs and diversion projects is an effective method to prevent and control algal blooms in regulated lowland rivers. This study is expected to deepen our understanding of the ecological significance of special hydrological processes and guide algal bloom management in regulated lowland rivers.

Causality Analysis and Prediction of Riverine Algal Blooms by Combining Empirical Dynamic Modeling and Machine Learning Techniques

“…In the context of algal blooms in the Han River, the average air temperature during the 1998 bloom period was 12.5°C. However, as the air temperature dropped below 5°C in mid‐to‐late March, the water temperature in the Han River rapidly dropped, leading to a swift decline in algal blooms (Li et al., 2021). To sum up, the water temperature in the Han River stands as a crucial factor influencing the occurrence of algal blooms in the area.…”

Environmental flow mechanism and management for river–lake‐marsh systems

“…Hu et al (2021) built a two‐dimensional model to obtain the fitting curves between fish's Weighted Usable Area (WUA) and water levels, and then identified suitable water levels in different periods. To control algal bloom in the middle and lower reaches of Han River, Li, Yin, et al (2021) established a hydrological management framework and determined the threshold flow velocities. The results indicated that differences in river morphology and background nutrient levels could cause significant differences in the critical threshold flow velocities for algal bloom outbreaks.…”

Algal proliferation risk assessment using Vine Copula-based coupling methods in the South-to-North Water Diversion Project of China

“…Abnormal algal proliferation, which marks the precursor of eutrophication, has been widely studied in low-flow velocity, highdepth water column bodies such as lakes and reservoirs (Zou et al, 2020;Li et al, 2021). A series of achievements have been reported regarding key limiting nutrient factors and ecological control measures in algal proliferation (Cheng et al, 2019;Brookfield et al, 2021).…”