Biogeochemical Impacts of Typhoon Disturbance in Polluted Aquatic Ecosystems and the Role of the Feammox Process in Contaminated Riparian Zones

Abstract

The ecosystem response to increasingly frequent and severe tropical cylone disturbance was investigated in three systems that experience high levels of industrial and/or agricultural pollution: the Pearl River and Zhanjiang Estuaries in Guangdong Province, China, and the Neuse River Watershed in North Carolina, USA. In all three systems, there is an observed shift in the geochemical factors and microbial communities of both the sediment and water column due to storm disturbance, with significant correlations identified between the chemical and microbial response. The recovery process following storm events varies greatly between the three systems, with discrepancies attributed to differences between the ecosystems studied and the frequency of storm disturbance.

Analysis of the impact of storm events on the microbially-mediated nitrogen (N)-cycle shows significant shifts in the microbial community composition and the abundance of key functional genes. The Feammox process, conducted by Acidimicrobium sp. A6 (referred to as A6), contributes to ammonium (NH4+) oxidation under anaerobic and iron-reducing conditions. Results from field surveys of all studied systems show that major storm disturbance can result in increased ferric iron concentration in sediments, which may enhance Feammox activity. Laboratory incubations of Neuse River sediment samples demonstrate that the Feammox process is capable of oxidizing comparable levels of NH4+ to aerobic microbial processes. Incubations also assessed the ability of the Feammox process to reduce toxic selenium (Se) oxyanions in addition to other known compounds, such as Uranium(VI), perfluorooctanoic acid and perfluorooctane sulfonate. There was no observed microbial reduction of selenate, however there was a toxic effect of both selenate and selenite on A6 activity and limited Se oxyanion bioavailability due to significant sorption by Ferrihydrite.

This is the first study showing that in aquatic systems such as the Neuse River, which has ideal conditions for the Feammox process due to its acidic pH and high iron and NH4+ content, there is equal potential for aerobic and anaerobic NH4+ oxidation. Furthermore, the observed increase in ferric iron concentration in aquatic sediments following storm disturbance may lead to environmental conditions that invigorate the Feammox process.