Interactions between iron mineral and low-molecular-weight organic acids accelerated nitrogen conversion and release...

Endogenous nitrogen (N) release from lake sediments is one of main causes affecting water quality, which can be affected by the presence of iron (Fe) minerals and organic matter, especially low-molecular-weight organic acids (LMWOAs). Although these substances always coexist in sediments, their interaction effect on N fate is not yet clear. In this study, the role and mechanisms of the coexistence of iron mineral (ferrihydrite, Fh) and LMWOAs, i.e. citric acid (CA) and galacturonic acid (GA) on the release and transformation of N in lake sediments were systematically evaluated via microcosm cultivation for 45 d Results showed that the addition of Fh+LMWOAs significantly accelerated N mineralization and conversion in lake sediments, accompanied by increasing ferrous iron content and decreasing redox potential. Biotic pathways played more critical roles than abiotic oxidation pathways during this process, and Fh+LMWOAs strengthened cooperation among microbial species by forming complex topologies and higher positive correlations. Correspondingly, cellular functions, iron respiration, and N metabolism modules were increased. CA with high carboxyl content showed greater total nitrogen removal and metabolic abundance. The present findings facilitate understanding the synergies of iron minerals and organic matter on N fate and N biogeochemical cycling in lake sediments.