Regulation of nitrogen dynamics at the sediment-water interface during HAB degradation and subsequent reoccurrence.

Weiping Sima,Manyu Zhou,Yitao Lv,Yixi Qiu,Hainan Ai,Lichun Dai,Meijuan Hu,Tao Zhou,Qiang He,Hong Li,Hao Zhan,Qingwei Shao

doi:10.1039/c9ra10673a

Abstract

The effects of harmful algal blooms (HABs) on nutrient dynamics have been extensively studied; however, the response of nitrogen to continuous HAB degradation and subsequent reoccurrence is not well understood. Here, a small-scale experiment was conducted to assess how nitrogen in the sediment–water interface (SWI) responds to HAB degradation and subsequent reoccurrence at different initial algal densities. The results showed that during the algae decomposition stage, the NH4+–N flux of the SWI remained positive but decreased with the increase in algal density from 3.5 × 107 to 2.3 × 108 cells per L, indicating that the sediment was the source of NH4+–N. In contrast, the deposit was a sink of NO3−–N. However, during the reoccurrence of HAB, the distribution of NH4+–N and NO3−–N fluxes was completely converted. Nitrogen flux analysis throughout algae decomposition and reoccurrence indicated that although the sediment acted as a sink of nitrogen, the flux was dependent on the initial algal density. Our results confirmed that algae decomposition and reoccurrence would greatly affect the nitrogen cycle of the SWI, during which dissolved oxygen (DO) and initial algal density dominated. This study is the first to show that the regulation of nitrogen flux and migration changes during continuous HAB decomposition and subsequent reoccurrence.

Highlights

As a global environmental problem, eutrophication, which is responsible for harmful algal blooms (HABs), has attracted increasing attention.[1]
When the maximum bloom developed, 40% of the lake area was covered with dense patches of the bloom, and a large amount of nitrogen was released when the algae bloom decayed in Lake Atitlan.[8]
We explored the nitrogen dynamics of the sediment– water interface (SWI) and the underlying mechanisms at different initial cyanobacterial densities

Summary

Introduction

As a global environmental problem, eutrophication, which is responsible for harmful algal blooms (HABs), has attracted increasing attention.[1] Severe HABs can cause a variety of ecological and environmental problems, including serious threats to biodiversity, resulting in hypoxia during the decomposition phase and the release of toxic metabolites.[2,3]. Contrary to the nutrients of active phytoplankton species, the decomposition of algae cells can release large amounts of inorganic and organic nutrients that constitute an important pool of nutrients in the water and become a source of endogenous contamination of sediments.[11]

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