Selective mobilization of particulate phosphorus via lacustrine groundwater discharge: a hidden pathway in lake...

In wetland ecosystems, the discharge of groundwater enriched in nutrients represents an important component of lake nutrient budgets. However, current frameworks largely focus on solutes and may overlook potential contributions of particulate transport. Here, we identify a previously underappreciated pathway of particulate phosphorus (P) input associated with groundwater discharge at lakeshore springs, supported by elevated turbidity and particulate P signatures. Continuous monitoring of pressure-flow dynamics, combined with statistical analysis, reveals two distinct particle-mobilization regimes: a preferential channel erosion mode under thick surficial clay cover and a surface-exposed aquifer discharge system with localized convergence. The quantitative results show that the P flux carried by fine particles is comparable to or exceeds the dissolved P input (0.3-8.2 times). Geochemical analysis and physical calculations further indicate that these particles are selectively mobilized from weakly bound fine fractions, likely through shear-driven erosion of the upper aquitard and interfacial detachment from clay lenses. The released particles are enriched in Fe-Mn oxides and clay minerals, and their potentially bioavailable P (OP + NaOH-P) is 34.04-212.77 mg/kg higher than that of the source sediments. Importantly, sensitivity analysis indicates that this physically constrained release mechanism can operate across heterogeneous aquifer systems with a wide range of permeabilities, and particulate transport, being less affected by concentration-gradient effects during groundwater-lake water mixing than solute transport, may represent a persistent source of P to groundwater-fed lakes. These findings suggest that particulate transport with groundwater should be explicitly incorporated into nutrient budget assessments and eutrophication management strategies.