Nutrient Pollution and Its Dynamic Source-Sink Pattern in the Pearl River Estuary (South China)

Wei Tao,Tao Fu,Yanhong Dong,Quansheng Lou,Lixia Niu

doi:10.3389/fmars.2021.713907

Abstract

Nutrient enrichment and its quantitative cause-effect chains of the biogeochemical processes have scarcely been documented in the Pearl River Estuary (South China). Field investigations of nutrient samples taken between 1996 and 2018 showed significant differences in nitrogen and phosphorus with times and sites. The concentrations of DIN and DIP gradually increased over the past two decades, with good fitted linear curves (R2 = 0.31 for DIN, R2 = 0.92 for DIP); while the temporal variation in DSi was non-significant. Higher levels of nitrogen and silicate mainly appeared in the upper estuary because of the riverine influence. The phosphorus pollution was accumulated in the northeast (e.g., Shenzhen bay). The aquatic environment was highly sensitive to nutrient pollution and eutrophication risk, which accordingly corresponded to high phytoplankton production and biodiversity. Phosphorus was the limiting factor of phytoplankton growth in this estuary, and more frequently caused the eutrophication risks and blooms. The nutrient pollution was largely influenced by riverine inputs, quantified by PCA-generation, and the contributions of coastal emission and atmospheric deposition were followed. The two-end member mixing model differentiated the physical alterations from the biological activity and identified the dynamic source-sink patterns of nutrient species. Nitrogen and silicate had relatively conservative behaviors in the estuary and phosphate showed an active pattern.

Highlights

The aquatic environment in the estuary has been negatively affected by eutrophication risks and phytoplankton blooms, and the fundamental forcing is the accumulation of nutrient pollution in the water column from the river to the sea (Bianchi et al, 2010; Guo et al, 2020; Potter et al, 2021)
The Pearl River Estuary was enriched in nutrients during the high inflows
The observed Dissolved inorganic nitrogen (DIN) and Dissolved phosphorus (DIP) during summer showed a gradual increase between 1996 and 2018, while the annual trend of Dissolved silicate (DSi) was non-significant during that period

Summary

Introduction

The aquatic environment in the estuary has been negatively affected by eutrophication risks and phytoplankton blooms, and the fundamental forcing is the accumulation of nutrient pollution (especially N and P) in the water column from the river to the sea (Bianchi et al, 2010; Guo et al, 2020; Potter et al, 2021). The biogeochemical properties of various nutrients vary spatially and temporally, related to the estuarine processes (Gan et al, 2014; Borges et al, 2020; Wang et al, 2021) These environmental factors and estuarine processes that influence the nutrient fluxes distribute over a large time-and-space scale. Drastic increases in nutrients have posed a big threat to the Nutrient and Source-Sink Pattern ecological stability of the marine environment (Kim et al, 2014; Yuan et al, 2021), for instance, eutrophication, red tides, and dead fishes caused by hypoxia These environmental pressures are closely correlated with the biogeochemical characteristics of nutrient source-sink patterns (Han et al, 2012; Li et al, 2017). The roles of nutrient enrichment and estuarine processes have raised the necessity to understand the biological responses (Farrow et al, 2019; Mathew et al, 2021)

Methods

Results

Conclusion