Implications of Nutrient Enrichment and Related Environmental Impacts in the Pearl River Estuary, China: Characterizing the Seasonal Influence of Riverine Input

Abstract

The Pearl River estuary is an ecologically dynamic region located in southern China that experiences strong gradients in its biogeochemical properties. This study examined the seasonality of nutrient dynamics, identified related environmental responses, and evaluated how river discharge regulated nutrient sink and source. The field investigation showed significant differences of dissolved nutrients with seasons and three zones of the estuary regarding the estuarine characteristics. Spatially, nutrients exhibited a clear decreasing trend along the salinity gradient; temporally, their levels were obviously higher in summer than other seasons. The aquatic environment was overall eutrophic, as a result of increased fluxes of nitrogen and silicate. This estuary was thus highly sensitive to nutrient enrichment and related pollution of eutrophication. River discharge, oceanic current, and atmospheric deposition distinctly influenced the nutrient status. These factors accordingly may influence phytoplankton that are of importance in coastal ecosystems. Phytoplankton (in terms of chlorophyll) was potentially phosphate limited, which then more frequently resulted in nutrient pollution and blooms. Additionally, the nutrient sources were implied according to the cause–effect chains between nutrients, hydrology, and chlorophyll, identified by the PCA-generated quantification. Nitrogen was constrained by marine-riverine waters and their mutual increase-decline trend, and a new source was supplemented along the transport from river to sea, while a different source of terrestrial emission from coastal cities contributed to phosphate greatly.

Spatio-Temporal Patterns and the Fluxes of Regional Nutrient Pollution in the Pearl River Basin, China

“…These point sources of pollution were related to the dense urban agglomeration downstream of the Pearl River. In the Pearl River Delta region, the total amount of sewage ranged from 12,000 to 18,000 t/a in 2008-2017 [35], and the sewage discharge was the first contributor to TP in the Pearl River [36].…”

Terrestrial and Biological Activities Shaped the Fate of Dissolved Organic Nitrogen in a Subtropical River‐Dominated Estuary and Adjacent Coastal Area

“…Continuous freshwater discharge during the rainy season (generally April to October in the Lingdingyang Estuary) plays an important role in facilitating the cross‐boundary transportation of nutrients between terrestrial and marine environments (Niu et al., 2020; M. Wu et al., 2016; Ye et al., 2018). Nitrogen from allochthonous sources transported during these “hot moments” has the potential to significantly subsidize ecosystem metabolism (Z. Lu et al., 2018).…”

Advances in phytoplankton population ecology in the Pearl river estuary

“…Spatially, nitrogen and phosphorus pollution trends are more prominent in the east but inconspicuous in the west. Dissolved inorganic nitrogen (DIN) in the PRE indicated that upstream of the mouth is dominated by NH 4 -N, and the concentration of NO 3 -N was the highest at the mouth, accounting for 51.2%-80.4% (Niu et al, 2020b;Li et al, 2022). Generally, the level of nitrogen and phosphorus nutrients is one of the key drivers of red tides in the PRE.…”

“…The vertical exchange of nutrients is hindered, limiting the growth of phytoplankton in the PRE. Niu et al (2020b) showed that the annual average sediment load in the PRE was mainly carried by runoff during 1974-2016. Moreover, they found that a large amount of suspended matter affected the growth of phytoplankton by influencing their photosynthesis.…”