Terrestrial input of herbicides has significant impacts on phytoplankton and bacterioplankton communities in coastal waters

Abstract Herbicide use has increased very rapidly worldwide in recent decades, and some of these herbicides eventually enter the ocean. At present, herbicide pollution in the ocean has become a global environmental problem. Here, in a field investigation of 22 commonly used herbicide residues (triazine, phenylurea, and amide) in the Bohai Sea and the Yellow Sea, we found that the detection rate of herbicide residues within 100 km from shore was 100%. Notably, triazine herbicides have reached concentrations (up to 12.07 nmol L −1 ) that can significantly disturb phytoplankton and bacterioplankton communities in microcosm experiments. Under exposure to triazine herbicides at close to their total in situ concentrations, the photosynthesis of the phytoplankton community was significantly inhibited, which was reflected by the significant decrease of F v / F m (28.7–63.8%) of the phytoplankton community and dissolved oxygen content (18.1–32.2%) in seawater. Concurrently, the phytoplankton community structure underwent significant changes with the dominant group shifting from diatoms to dinoflagellates, due to the higher atrazine sensitivity of diatoms compared to facultative dinoflagellates. Triazine herbicide also significantly altered the bacterioplankton community structure and inhibited their metabolism of many carbon sources including carbohydrates, amino acids, and carboxylic acids. As phytoplankton and bacterioplankton are closely related, the impact of herbicide on the bacterioplankton community was clearly aggravated by the phytoplankton community. In view of the significance of phytoplankton and bacterioplankton communities in supporting marine food webs and biogeochemical cycles, a continuous increase in herbicide input in the future may seriously affect the stability of coastal oceans.