Key nutrients and their transportation processes influencing algal growth in a dam-controlled river

Abstract

A dam-controlled river refers to a river where flow and water levels are regulated through hydraulic engineering structures, such as dams and sluices. This research focuses on controlling eutrophication in dam-controlled rivers, with particular attention to the Huaidian Dam on China's Shaying River. The primary objective of this research was to identify the key nutrients and their transportation processes affecting algal growth during the non-flood season. To achieve this, we analyzed algal density, species diversity, and the distribution of key nutrients, including ammonia nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N), and total phosphorus (TP) across dissolved, suspended, and sediment phases in both the hyporheic zone and surface water. The results reveal that diatoms dominate the algal community, comprising 66.91 % of the total composition and displaying higher cell density and biomass. Nutrient concentrations were mainly observed downstream of the dam, with NH₄⁺-N predominantly detected in sediments (2.92–9.23 mg/kg) and pore water (1.1–13.5 mg/L), NO₃⁻-N in sediment (2.5–12 mg/kg), and TP mainly in sediments (50–70 mg/kg). Redundancy analysis demonstrated that NO₃⁻-N in overlying water, sediment, and pore water were critical for algal growth, contributing 78.9 %, 77.5 %, and 75 %, respectively. Our findings suggest that the interaction between NO₃⁻-N transport and transformation within sediments and pore water is a significant factor influencing algal growth during non-flood seasons. This study highlights the influence of nutrient transport and transformation at the water-sediment interface for algal growth and recommends targeted measures to mitigate eutrophication risks in dam-controlled rivers.