Unraveling the complex dynamics of benthic algae in the Red River Basin: A comparative study

Benthic algae, as critical primary producers in fluvial ecosystems, exhibit distinct responses to environmental gradients across heterogeneous river systems. This comparative study analyzed three tributaries in the Red River Basin—Lixian River (LXR, pristine), Yuanjiang River (YR, anthropogenically disturbed), and Panlong River (PLR, karst-influenced)—to identify key drivers of algal community structure. Results revealed nitrogen (NH₄ + -N) as the primary density regulator in LXR, while substrate heterogeneity and hydrological stability governed diversity (H′) and evenness (J'). In nutrient-enriched YR, total phosphorus (TP) dominated algal density, with diversity suppressed by eutrophication indicators (TP, Chl-a) and physical factors (depth, DO). PLR's calcium-rich karst environment promoted filamentous algal dominance, where density correlated with NH₄ + -N and current velocity, serving as a proxy for benthic diversity (H′-J': R 2 > 0.75). Basin-wide analysis demonstrated nitrogen's outsized influence over phosphorus, with geochemical factors (e.g., Ca 2+ ) emerging as critical modulators of algal resilience in karst systems. These findings highlight the spatial variability of algal-environment interactions, emphasizing the need for basin-specific management strategies that account for both anthropogenic pressures and geomorphic contexts. • Nitrogen (NH₄ + -N) is the primary driver of benthic algae density in pristine rivers. • Total phosphorus (TP) dominates algae density in nutrient-enriched, human-impacted rivers. • Calcium-rich karst environments promote filamentous algae dominance and diversity. • Hydrological stability and substrate heterogeneity enhance algae diversity and evenness. • Basin-specific management is crucial due to varying algal responses to environmental factors.