Was Dissolved Nitrogen Regime Driving Diatom to Dinoflagellate Shift in the Bohai Sea? Evidences From Microcosm Experiment and Modeling Reproduction

Abstract

The shift of diatom dominance to combination of diatom and dinoflagellate dominance in the Bohai Sea (BS), China might be associated with the change of dissolved nitrogen (DN). This study combines field investigation, ship‐based microcosm experiments, a nitrogen biogeochemical model, and statistical analysis to reveal the impact of DN loading on the dominance of diatoms and dinoflagellates in the BS, considering the quantitative relationship between the algal growth/death and nitrogen migration/transformation processes. The diatom to diatom‐dinoflagellate shift was significantly associated with the DN regime shift of oxidized nitrogen (NO3‐N) to reduced nitrogen (NH4‐N and dissolved organic nitrogen [DON]) since the mid‐1990s. This phenomenon was supported by microcosm and numerical experiments: (a) Gonyaulax verior as a dominant dinoflagellate in the BS efficiently absorbed/assimilated NH4‐N, and it can also utilize DON derived from centric diatoms; Chaetoceros densus as dominant centric diatoms in the BS was able to absorb/assimilate NO3‐N, and it can also utilize DON derived from the Xiaoqing River; (b) The change in dinoflagellates/diatoms ratios was reproduced with the change in DN regime from the 1980s to the 2010s by the proposed nitrogen biogeochemical model based on localized parameters in the BS. Moreover, mixotrophism and stronger survival stability, associated with the faster NH4‐N and DONalgal uptake and slower decomposition of G. verior, also supported the shift from diatoms to diatoms–dinoflagellates during high variations in nutrient supply. This study infers the phytoplankton regime shift mechanism associated with the DN structure in coastal waters, providing a credible scientific basis for the shift from water quality‐based to ecosystem‐based environmental management.

Nitrogen from agriculture and temperature as the major drivers of deoxygenation in the central Bohai Sea

“…This imbalanced nutrient availability caused a gradual shift from a diatom-dominated to a diatom-dinoflagellate dominated or dinoflagellate-dominated system in the BS (Fig. 7b), consistent with previous studies (Chen et al, 2022a;Wang et al, 2019a;Xin et al, 2019).…”

Plankton Community Changes and Nutrient Dynamics Associated with Blooms of the Pelagic Cyanobacterium Trichodesmium in the Gulf of Mexico and the Great Barrier Reef

“…Lenes et al [118] noted a three-fold enrichment in DON in June and July of 1999 in west Florida Shelf waters, co-incident with increased Trichodesmium abundance. These impacts of Trichodesmium blooms on community structure, including the promotion of potentially harmful dinoflagellate species, are likely to increase in area and duration due to climate change effects in the tropical and subtropical regions where they proliferate [33,69,[119][120][121]. Notes: * The enrichment values shown are the range of daily differences observed between nutrient concentrations inside and outside the bloom over the entire study.…”

Human-driven long-term disconnect of nutrient inputs to the Yellow River basin and river export to the Bohai Sea

“…Flagellates (Alexandrium tamarense, Chattonela marina and H. akashiwo) in the BS, grew well in the presence of DOP (Wang et al, 2011). DON is known to drive the shift from diatom to dinoflagellate in the Bohai Sea (Chen et al, 2022).…”