The reaction of the macroinvertebrate Gammarus pulex to lanthanum-modified bentonite (LMB)

Recently, lanthanum-modified bentonite (LMB) has been widely used for internal phosphorus control in eutrophication management. Generally, LMB application results in the formation of LMB layer, which can affect the surface sediment environment and may affect organisms living on the sediment surface. To explore it, we studied the effects of LMB on the macroinvertebrate Gammarus pulex. In a 3-day habitat choice trial, compared with the pebbles covered with sand, bentonite or LMB, G. pulex preferred the uncovered pebbles. In a 4-day acute toxicity trial, one death was found in the 500, 1000 and 2000 g m^-2 LMB treatments, respectively. In a 7-day feeding trial, the feeding rate of G. pulex in the Low, Middle and High-LMB treatments was lower than that in the control by 19 %, 59 % and 55 %, respectively. In a 21-day survival trial, the survival rate of G. pulex in the control was significantly higher than in Low, Middle and High-LMB treatments regardless of the presence of sediment. Our results show that G. pulex preferred a substrate environment with gap and shelter. There was no acute toxicity of LMB to G. pulex, but LMB covered the leaves, thus reducing its feeding rate on leaves. In addition, with food restrictions and unwelcome changes in the environment by LMB, intraspecific competition and cannibalism of G. pulex might be enhanced, resulting in a reduced survival rate of G. pulex under LMB application. Hence, our study indicates that extended experimental studies and in situ monitoring of macroinvertebrates after LMB applications are needed.