Effects of organic nitrogen components from terrestrial input on the phytoplankton community in Jiaozhou Bay

Dissolved organic nitrogen (DON) from terrestrial input exacerbates eutrophication and induces harmful algal blooms. We investigated the effects of hydrophilic (Hic) and low molecular weight (LMW) DON on the phytoplankton community in Jiaozhou Bay during autumn (October 2017) and spring (May 2018). Our results showed DON additions significantly increased algal growth while decreasing community biodiversity and provide a competitive advantage for Skeletonema costatum. These situations were further intensified by increasing temperature in autumn. Additionally, Hic DON had a higher bioavailability than LMW DON. Based on emission-excitation matrix spectra, we identified protein-like components as the main components of Hic DON whereas humus-like components were the principal components of LMW. Correlation analysis confirmed a positive correlation between DON bioavailability and protein-like components. Therefore, our results indicate DON from terrestrial input disrupts the structural stability of the phytoplankton community and increases the risk of harmful algal blooms, which in turn threaten coastal ecosystems.

Automated summary

The study reveals that dissolved organic nitrogen (DON) from terrestrial input exacerbates eutrophication and induces harmful algal blooms in Jiaozhou Bay. The addition of hydrophilic (Hic) and low molecular weight (LMW) DON significantly increases algal growth, reduces community biodiversity, and provides a competitive advantage for Skeletonema costatum. These effects are further intensified in autumn with increasing temperature. Hic DON has higher bioavailability than LMW DON.