Responses of Primary Productivity and Phytoplankton Community to the Atmospheric Nutrient Deposition in the East China Sea

Qingwei Ma,Fanghui Wang,Ying Chen,Haowen Li

doi:10.3390/atmos12020210

Abstract

Atmospheric deposition of nutrients to the surface seawater may significantly affect marine phytoplankton growth. Two in situ bioassay experiments were performed in the East China Sea (ECS) by adding nutrients (N, P, and Si) and atmospheric aerosols into the surface seawater. Chlorophyll a (Chl a) concentrations were largely enhanced by simultaneous input of N and P with the maximal increase of 0.68–0.78 μg Chl a per μmol N addition. This Chl a increment was significantly lower (0.19–0.47 μg) in aerosol treatments as a result of initial N-replete condition (N/P ratio ~50) and extremely high N/P ratio in aerosols (>300). Among the multiple influencing factors, atmospheric dry flux of NH4+ + NO3− (AN) was found to be an effective predictor for springtime Chl a in the ECS with a time lag of three days and were strongly correlated with Chl a concentrations on day 3 (r = 0.81, p < 0.001), which might be partly explained by the asynchronous supplies of N (atmospheric deposition) and P (subsurface water). Although dinoflagellates dominated the phytoplankton community in both initial seawaters, additions of P and N + P + Si profoundly enhanced the cell densities and dominance of diatom species Thalassiosira sp. and Nitzschia closterium in the 2012 and 2014 bioassay experiments, respectively. Moreover, the percentage of dinoflagellates were promoted by adding higher NH4+/NO3− ratio (6/4 vs. 1/9) when silicate was at a low concentration (~2 μmol L−1). Atmospheric deposition is likely to be an important N source supporting the high primary production in the ECS and its supply of excess N relative to P may influence dominant phytoplankton groups.

Highlights

Marine primary productivity is influenced by multiple factors such as irradiance, temperature, salinity and grazing, but nutrients availability is probably the most important one [1,2]
The maximal Chlorophyll a (Chl a) concentrations were considerably higher in N + P treatments (8.41, 7.37 and 8.48 μg L−1 for T3, T4 and T6, respectively, Figure 3b) compared to T2 (2.47 μg L−1), implying that initial N concentration (2.91–5.35 μmol L−1) in seawater may not be sufficient to support the phytoplankton growth induced by 0.6 μmol L−1 P addition and PN co-limiting seemed to occur
Elevated N/P ratio in the Eastern China Sea has been reported in the past decades [31,33,34,90], and the soluble phosphate concentration in most parts of the YS and Nutrient structure is one of the most important factors controlling marine primary productivity

Summary

Introduction

Marine primary productivity is influenced by multiple factors such as irradiance, temperature, salinity and grazing, but nutrients availability is probably the most important one [1,2]. The East China Sea (ECS) is one of the largest marginal seas of the western North Pacific (WNP) and has a high primary productivity of ~145 g C m−2 y−1 [3], which plays vital roles in the biogeochemical cycles of carbon and other elements [4]. Diatoms are considered to be more efficient than dinoflagellates in carbon export to the deep water due to its relatively large size and siliceous structures [10]. The reduction of diatoms was Atmosphere 2021, 12, 210 considered to be more efficient than dinoflagellates in carbon export to the deep water due to its relatively large size and siliceous structures [10].

Methods

Results

Conclusion