The Effect Of Invertebrate Bioturbation On Nutrient Release And Permeability Of Streambed Sediment

Quantifying and qualifying the influences of bioturbation from the sediments on the contamination in hyporheic zone is significant in maintaining the heath of a river ecosystem. Benthic disturbance can change the physical and chemical properties of sediments and affect the sediment redistribution, at the same time, the sediment movement will strongly affect ecological processes and water exchange in hyporheic zone. The bioturbation processes of different invertebrates, collected sample from Weihe River including Chironomid larvae and Limnodrilus hoffmeiteri, have been investigated in laboratory to explore their impacts on the release of ammonia, total nitrogen and total phosphate from sediments, and the influences to the concentration of dissolved oxygen in overlying water. In order to investigate the effects of bioturbation on hydraulic conductivity of hyporheic streambed sediments through indoor simulation, dominant species including Chironomid larvae, Limnodrilus hoffineiteri, and Physa acuta were sampled from the lintong section of Weihe River in Shaanxi for study. The actual density ratio of three creatures is 7:98:10.The results show that (1)the activities of both Chironomid larvae and Limnodrilus hoffineiteri certainly enhanced the release amount of ammonia,total nitrogen and total phosphate from sediments. For the group only including Chironomid larvae, the average net increasing amount of the ammonia, total nitrogen and total phosphate are 2.32 mg·L-1,0.787 mg·L-1,0.105 mg·L-1 respectively, and the average net increasing amount of these parameters are the highest in the mixing experimental group. The influences to the release rate of ammonia and total nitrogen from sediments to overlying water caused by Chironomid larvae is strongest among all experimental group. (2) In mixing group, with the increase of the number of Chironomid larvae, the ammonia and total nitrogen concentration in overlying water increase. It demonstrates that the Chironomid larvae played leading role in release process of the ammonia and total nitrogen, what's more, the mixing interactions (23 Chironomid larvae,47 Limnodrilus hoffmeiteri) would lead to the decrease of the release of total nitrogen and ammonia from sediments into the overlying water. (3).Dissolved oxygen concentration in overlying water of experimental group is less than that of blank group, and the average daily dissolved oxygen concentration in overlying water decreases along with the amount of Limnodrilus hoffmeiteri increase, which shows that oxygen consumption of bioturbation of Chironomid larvae is more than that of Limnodrilus hoffineiteri. Limnodrilus hoffmeiteriare so sensitive to environmental changes that the variation of dissolved oxygen concentration can enhance the effect of bioturbation of them. The results of experiment on permeability of sediment showed that the bioturbation process of Chironomid larvae can reduce fine sand content on sediment surface, which can increase the permeability of sediment.On the contrary, activity of Limnodrilus hoffmeiteri can increase fine sand content in the sediment, which can decrease the permeability of sediment. The influence of particle size distribution and permeability of sediment caused by Physa acuta is not obvious;The mixing activity of Chironomid larvae and Physa acuta made the permeability enhanced most obviously.