Laboratory simulation of dissolved oxygen reduction and ammonia nitrogen generation in the decay stage of harmful algae bloom

To evaluate how the decay of bloom-forming algae affect the coastal dissolved oxygen, a laboratory simulation was conducted in terms of three typical harmful algae, Alexandrium catenella, Prorocentrum donghaiense, and Skeletonema costatum. Algae of same biomass (55 mu g/mL) were conducted in lightproof columns, and the cell density, dissolved oxygen (DO), and ammonia nitrogen of different layers were monitored at certain time series. Results show that the decomposition of algae significantly decreased the DO, and increased the ammonia nitrogen in all layers; and significant deference between different species was observed. The A. catenella treatment showed the lowest DO (average concentration of 3.4 mg/L) and the highest ammonia nitrogen (average concentration of 0.98 mg/L) at the end of test, followed by P. donghaiense; and the S. costatum showed relatively high DO and low ammonia nitrogen due to slow decay rate. Results indicate that decomposition of harmful bloom algae, especially dinoflagellate, would cause significantly DO depletion and toxic ammonia nitrogen increase, which will detrimentally affect both pelagic and benthic ecosystem.

Automated summary

The decomposition of harmful bloom algae, especially dinoflagellate, leads to significant depletion of dissolved oxygen and increase in toxic ammonia nitrogen. Different species of algae exhibit varying levels of impact, with Alexandrium catenella showing the lowest dissolved oxygen and highest ammonia nitrogen, while Skeletonema costatum has slower decay rate resulting in higher dissolved oxygen and lower ammonia nitrogen.