Bioturbation effects of Chironomid Larvae on nitrogen release and ammonia-oxidizing bacteria abundance in sediments

Abstract

The purpose of this work was to reveal the Chironomid larvae bioturbation impact on N release and to find the mechanism of bioturbation to N conversion at the SWI (sediment-water interface). Sampling at four points during a 35-day incubation experiment was conducted. Two in situ techniques (microelectrode and Peeper) were used to capture more realistic and accurate microenvironment information around U-shaped corridors. The results demonstrate that the concentrations of ammonia nitrogen (NH4+) and nitrate nitrogen (NO3-) decreased by 21.26% and 19.50% in sediment and increased by 8.65% and 49.82% in the overlying water compared to the control treatment, respectively. An inverse relationship was observed between NH4+ and NO3- concentrations in pore water in Chironomid larvae treatment, and they were significantly negatively/positively correlated with AOB (ammonia-oxidizing bacteria) abundance, respectively. This study confirmed that the Chironomid larvae bioturbation promoted the N (NH4+ and NO3-) release from sediment by in situ techniques, and a part of NH4+ converted into NO3- during their flow into the overlying water through the nitrification affected by AOB. Furthermore, the main depth of bioturbation influence is approximately 12 cm below the SWI and the most significant bioturbation effect was observed from days 15 to 25.