Spatiotemporal Dissolved Silicate Variation, Sources, and Behavior in the Eutrophic Zhanjiang Bay, China

Peng Zhang,Jia-Lei Xu,Jian-Xu Li,Xin-Qi Luo,Yi Li,Ji-Biao Zhang,Yan-Chan Zhang

doi:10.3390/w12123586

Abstract

Dissolved silicate (DSi) is an important nutrient in coastal water, which is used by planktonic diatoms for cell division and growth. In this study, surface water samples were collected in the eutrophic Zhanjiang Bay (ZJB) in 2019, covering a seasonal variation of coastal water and land-based source water discharge. The spatiotemporal DSi distribution, land-based sources flux input and behaviors in ZJB were studied and discussed. The results show that the DSi concentration had significant differences in spatiotemporal scale. The average concentration of DSi in ZJB was 38.00 ± 9.48 μmol·L−1 in spring, 20.23 ± 11.27 μmol·L−1 in summer, 12.48 ± 1.42 μmol·L−1 in autumn and 11.96 ± 4.85 μmol·L−1 in winter. The spatiotemporal DSi distribution showed a decreasing gradient from the top to the mouth of ZJB, which was affected by land source inputs and hydrodynamics. The land-based sources’ input concentration of DSi in ZJB ranged from 0.021 to 0.46 mol·L−1, with an average of 0.14 mol·L−1, and the total annual flux of DSi was 1.06 × 109 mol, comprising up to 8.28%, 41.55% and 50.17% in dry, normal, and wet seasons, respectively. The Suixi River contributed the highest DSi flux proportion in all seasons. The DSi in land-based source water was mainly affected by water flow discharge, diatom uptake and impacts from anthropogenic activities. Compared with dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP), the DSi was the limitation nutrient in ZJB. Additionally, the DSi concentration in the coastal water was negatively correlated with salinity. The seasonal DSi/DIN and DSi/DIP ratios in land-based sources discharge water was significantly higher than that in coastal water (p < 0.05). Land-based sources of DSi input played an important role in nutrients composition that sustained diatoms as the dominant species in ZJB.

Highlights

Silicon is the second most abundant element in the Earth’s crust and is one of the major constituents in seawater, where it is present in both dissolved and particulate form [1]
This study provides the first assessment of how spatiotemporal Dissolved silicate (DSi) dynamics in coastal water respond to increased land-based sources’ input in Zhanjiang Bay (ZJB) and understand the DSi behavior in aquatic systems
The annual DSi flux discharged into ZJB was 1.06 × 109 mol, of which 8.28% was in dry season, 41.55% in the normal season and 50.17% in the wet season

Summary

Introduction

Silicon is the second most abundant element in the Earth’s crust and is one of the major constituents in seawater, where it is present in both dissolved and particulate form [1]. Dissolved silicate (DSi) is a vital nutrient required by diatoms for growth in coastal water [2,3,4]. The availability of DSi and its relative abundance compared to the other nutrients can influence the composition of the phytoplankton community, which can subsequently affect the ecological functioning of the ecosystem [9,11,13,14]. It controls N and P nutrient ratios and planktonic blooms in the aquatic ecosystem [12,15]. As it is closely related to the ocean carbon cycle and biological pumps, the research on the biogeochemical behavior of silicon has attracted people’s attention during recent years [2,12,16,17,18,19]

Objectives

Methods

Conclusion