Interactions between Lanthanum-Modified Bentonite (LMB) and Benthic Macroinvertebrates with Varied Bioturbation Modes

Lanthanum-Modified Bentonite (LMB) is widely used to mitigate endogenous phosphorus (P) in eutrophic lakes. Benthic macroinvertebrates coexisting with LMB may potentially impact its distribution and P removal efficiency; however, research on the interaction between LMB and macroinvertebrates, especially with different bioturbation patterns, is limited. Accordingly, three prevalent benthic macroinvertebrate species-Branchiura sowerbyi (BS), Chironomus flaviplumus (CF), and Radix swinhoei (RS), were selected for microcosm incubation experiments. Our findings indicate no substantial impact of macroinvertebrates on the overall P removal efficiency of LMB, although its vertical redistribution was species-specific with BS > CF > RS. Although substantial BS bioturbation may reduce LMB's efficacy in removing P at the sediment-water interface (SWI), it may enhance P retention capacity in deeper sediments. In contrast, CF constructed transient holes and corridors in the surficial sediments, compromising the integrity of the LMB capping layer, while RS only occupied the SWI with minimal bioturbation of the LMB. As CF and RS primarily occupied the SWI, there was minimal impact on LMB's P removal but with higher La concentrations in the overlying water compared to BS. Crucially, LMB appeared to inhibit the growth and reproduction of both RS and CF and increased mortality. Although La bioaccumulation was highest in BS, which also had the greatest ability to disrupt the LMB capping layer, there was no significant adverse effect on its growth and survival.