Species-specific benthic bioturbation mechanisms regulating heavy metal release in lake sediments

Benthic bioturbation exerts species-specific control over heavy metals mobilization in sediments, though mechanistic drivers remain poor understood. Using sediment-water microcosms colonized by three functionally distinct benthos (Limnodrilus hoffmeisteri (LH), Cipangopaludina cahayensis (CC), Corbicula fluminea (CF)), this study explored the metal distribution in overlying water. Release flux, cumulative release, and kinetic modeling elucidated mobilization mechanisms, while benthos-sediment accumulation factors (BSAFs) quantified bioaccumulation. The concentrations of target heavy metals were determined using inductively coupled plasma-mass spectrometry (Cu, Cr, As, Zn, Ni), DMA-80 direct Hg analyzer (sediments and benthos Hg), and two-step gold amalgam-cold atomic fluorescence spectrometry (water Hg). The results indicated that: (1) Short-term disturbances enhanced all the heavy metal release by LH, which reduced release of Cr and As by CC and of Cr by CF. (2) Heavy metals release by LH was mainly in particulate form (p < 0.05), while CC and CF predominantly released dissolved Cu and As. (3) Initial release intensities were species-specific and metal-dependent. LH displayed higher Hg and Zn but lower Cu, As, and Cr release than CC and CF (p < 0.05). (4) Kinetic analyses indicated pore diffusion dominated for LH, versus chemisorption for CC and CF. (5) CF bioaccumulated Hg, Zn, and As (BSAFs=0.94, 0.43 and 0.27) at 2.4-fold higher levels than CC, while CC retained more Cu (BSAFs=0.67). These species-dependent mechanisms provided a scientific basis for lake management strategies targeting benthic-mediated contaminant flux, particularly LH-driven Cu, Ni, and Zn and CF-mediated As mobilization.