Effects of microhabitat construction on water-ecosystem coupling in Urban Rivers: integrated assessment of water quality and biodiversity responses in Beijing, China

Graphical abstract summarizing the integrated assessment of water quality and biodiversity responses to microhabitat construction in Beijing's five river basins. The figure shows water quality improvement (reduced BOD5, COD) but increased phytoplankton at basin scale, contrasted with a demonstration site where restoration led to 80.5% phytoplankton reduction, increased water transparency, and expanded submerged vegetation. Urban river restoration requires understanding water-ecosystem coupling. This study investigated microhabitat construction effects across five Beijing river basins and a demonstration site. At 47 basin-wide monitoring sites (2024–2025), BOD5 and CODmn decreased (p < 0.01), while phytoplankton increased (p < 0.001), reflecting persistent eutrophication. TN was the strongest predictor of biodiversity (r = −0.773, p < 0.0001). PCA showed PC1 and PC2 explained 73.88% of total variance (PC1: 40.24%, PC2: 33.64%). At the Jinghe River demonstration site, integrated restoration was associated with 80.5% phytoplankton reduction (t = −4.690, p = 0.0001), transparency improved from 40–50 cm to 70–100 cm, and submerged vegetation exceeded 40%. Due to the observational design without control sites, causal attribution cannot be established; the results demonstrate associations between integrated restoration (∼200 yuan/m2) and improved ecological conditions, offering a cost-effective nature-based solution for water-scarce megacities.