This study examined how C–N–P cycling and eutrophication-related processes regulate the distribution and transport of polycyclic aromatic hydrocarbons (PAHs) among different environmental compartments in lake systems. PAH partitioning between suspended particulate matter (SPM) and the dissolved phase was associated with DOM composition, nutrient levels, and water physicochemical conditions. In the overlying water, the C2 and C3 fluorescent components of DOM were positively associated with the transfer of PAHs from SPM to the dissolved phase, whereas the biological index (BIX) was positively associated with PAH retention in SPM. Dissolved oxygen (DO), pH, NH₄⁺, dissolved total nitrogen (DTN), dissolved total phosphorus (DTP), and particulate phosphorus (PP) were also significantly related to PAH partitioning toward the dissolved phase.
Within the sediment-overlying water system, refractory organic carbon (ROC), labile organic carbon (LOC), nitrogen fractions (CF-N and NTN), and phosphorus fractions (BD-P, Fe/Al-P, Ca-P, and OP) were positively associated with PAH accumulation in sediments. By contrast, phytoplankton-derived organic matter (PH), representing an autochthonous source, significantly promoted the release of PAHs from sediments to the overlying water (p < 0.01). This relationship suggests that the production and subsequent transformation of autochthonous organic matter may enhance PAH remobilization at the sediment–water interface.
The PLS-SEM results further showed that PAH partitioning between SPM and the dissolved phase was jointly controlled by nutrient conditions and DOM characteristics. Sedimentary phosphorus (SP; 0.225, p < 0.05), sedimentary nitrogen (SN; 0.393, p < 0.05), and organic matter characteristics (OM; 0.476, p < 0.01) exerted significant positive effects on PAH accumulation in SPM. These results indicate that N and P enrichment, together with changes in DOM composition, favored the association of PAHs with suspended particles. SN (0.456, p < 0.001) and SP (0.312, p < 0.05) also had significant positive effects on OM, indicating that nutrient cycling indirectly regulated PAH phase partitioning by altering DOM sources and composition. In the sediment-overlying water system, PAH partitioning was governed primarily by sedimentary organic matter composition. The ROC/LOC ratio exerted a significant positive effect on the sediment-to-overlying-water PAH concentration ratio (0.495, p < 0.001), demonstrating that a greater relative abundance of refractory organic carbon enhanced the sorption and long-term preservation of PAHs in sediments.

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