Colonization Requirements of Submerged Macrophytes Based on Underwater Light Environment
The underwater light environment is a critical limiting factor for the colonization of submerged macrophytes and the ecological restoration of shallow lakes. Previous studies rarely quantified the contribution of aquatic environmental factors to the water quality–underwater light–macrophyte relationship, nor did they comprehensively consider factor correlations or establish thresholds for macrophyte colonization. This study, conducted in a typical national wetland nature reserve (Hongze Lake), measured photosynthetically active radiation, light attenuation coefficient (Kd), euphotic depth (Zeu), water transparency (SD), total suspended solids (TSS), chlorophyll-a (Chl-a), total nitrogen (TN), and total phosphorus (TP). A simulation model for Kd was developed, spatial distributions of environmental factors were analyzed, and contribution rates to light attenuation were quantified. Results showed that the mean Kd was 10.31±3.76 m⁻¹, and the mean Zeu (0.53±0.24 m) was lower than the mean water depth (0.94±0.29 m), with a spatial pattern of shallower Zeu in the west and deeper in the east. TSS and Chl-a were the primary direct influencing factors, while TN acted mainly indirectly. To achieve effective macrophyte colonization under average water depth conditions, thresholds were determined: Zeu ≥ 0.94 m, SD ≥ 0.41 m, Kd ≤ 4.95 m⁻¹, and Chl-a ≤ 3.8 μg/L. These findings provide quantitative guidance for lake restoration and water quality management.