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

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3245
Author(s):  
Lixia Niu ◽  
Pieter van Gelder ◽  
Xiangxin Luo ◽  
Huayang Cai ◽  
Tao Zhang ◽  
...  
Keyword(s):  
Nutrient Enrichment ◽  
River Discharge ◽  
Nutrient Dynamics ◽  
Southern China ◽  
Salinity Gradient ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Pearl River ◽  
The Pearl River Estuary ◽  
The Pearl River

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.

scholarly journals Mid-Holocene variability of the East Asian monsoon based on bulk organic δ13C and C/N records from the Pearl River estuary, southern China

The Holocene ◽  
2011 ◽  
Vol 22 (6) ◽  
pp. 705-715 ◽  
Author(s):  
Fengling Yu ◽  
Yongqiang Zong ◽  
Jeremy M Lloyd ◽  
Melanie J Leng ◽  
Adam D Switzer ◽  
...  
Keyword(s):  
Asian Monsoon ◽  
East Asian Monsoon ◽  
Southern China ◽  
East Asian ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Pearl River ◽  
The Pearl River Estuary ◽  
The Pearl River

scholarly journals Effects of Physical Forcing on Summertime Hypoxia and Oxygen Dynamics in the Pearl River Estuary

Water ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 2080 ◽  
Author(s):  
Huang ◽  
Hu ◽  
Li ◽  
Wang ◽  
Xu ◽  
...  
Keyword(s):  
River Discharge ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Pearl River ◽  
Vertical Diffusion ◽  
Physical Forcing ◽  
The Pearl River Estuary ◽  
Hypoxic Area ◽  
Water Stratification ◽  
The Pearl River

A validated hydrodynamic-biogeochemical model was applied to investigate the effects of physical forcing (i.e., river discharge, winds, and tides) on the summertime dissolved oxygen (DO) dynamics and hypoxia (DO < 3 mg L−1) in the Pearl River estuary (PRE), based on a suite of model sensitivity experiments. Compared with the base model run in 2006 (a wet year), the simulated hypoxic area in the moderate year (with 75% of river discharge of the base run) and the dry year scenario (with 50% of river discharge of the base run) was reduced by ~30% and ~60%, respectively. This is because under the lower river discharge levels, less particulate organic matter was delivered to the estuary that subsequently alleviated the oxygen demand at the water–sediment interface, and in the meantime, the water stratification strength was decreased, which facilitated the vertical diffusion of DO. Regarding the effect of winds, the highly varying and intermittent strong winds had a significant impact on the replenishment of bottom DO by disrupting water stratification and thus inhibiting the development of hypoxia. Sensitivity experiments showed that the hypoxic area and volume were both remarkably increased in the low wind scenario (with a bottom hypoxic zone extending from the Modaomen sub-estuary to the western shoal in Lingdingyang Bay), whereas hypoxia was almost absent in the strong wind scenario. The DO budget indicated that winds altered the bottom DO mostly by affecting the DO flux due to vertical diffusion and horizontal advection, and had a limited influence on the DO consumption processes. Moreover, the DO concentration exhibited remarkable fluctuations over the spring-neap tidal cycles due to the significant differences in vertical diffusion. The results of a tide-sensitivity experiment indicated that without tide forcing, most of the shallow areas (average water depth < 5 m) in the PRE experienced severe and persistent hypoxia. The tides mainly enhanced mixing in the shallow areas, which led to higher vertical diffusion and enhanced replenishment of bottom DO.

scholarly journals Distribution and Activity of Ammonia-Oxidizers on the Size-Fractionated Particles in the Pearl River Estuary

2021 ◽  
Vol 8 ◽  
Author(s):  
Li Ma ◽  
Shangjin Tan ◽  
Hongbin Liu ◽  
Shuh-Ji Kao ◽  
Minhan Dai ◽  
...  
Keyword(s):  
Transcriptional Activity ◽  
Ammonia Oxidation ◽  
Salinity Gradient ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Pearl River ◽  
Ammonia Oxidizing Bacteria ◽  
The Pearl River Estuary ◽  
Large Particles ◽  
The Pearl River

To distinguish between the distribution and activity of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in the Pearl River estuary (PRE), we investigated the DNA- and cDNA-based β-proteobacterial and archaeal amoA genes on three size-fractionated particles of &gt;3.0 μm, 0.45–3.0 μm, and 0.22–0.45 μm. Results showed that AOB were more abundant in the freshwater with high concentrations of ammonium (NH4+) and low dissolved oxygen, whereas AOA were dominant in the NH4+-depleted seawater and sensitive to temperature. Obvious shifts in ammonia-oxidizing communities were found along the salinity gradient in the PRE. AOB clearly presented a particle-associated nature, as evidenced by higher relative abundance of amoA genes attached to the large particles (&gt;3.0 μm) and their transcripts exclusively detected on this fraction. Moreover, higher transcriptional activity (indicated by the cDNA/DNA ratio) of AOB on the large particles, suggesting AOB were actively involved in ammonia oxidation despite their lower abundance in the mid- and lower estuarine regions. In contrast, AOA exhibited higher transcriptional activity on the 0.45–3.0 μm and 0.22–0.45 μm particles, implying the free-living strategy of these microbes. Together, these findings from field observations provide useful information on the ecological strategies of ammonia-oxidizing communities in response to different environmental conditions.

Distribution Characteristics and Environmental Impacts of Nutrients in the Dry Season of the Pearl River Estuary in 2016

2020 ◽  
Author(s):  
Danna Zeng ◽  
Lixia Niu ◽  
Qingshu Yang
Keyword(s):  
Chlorophyll A ◽  
River Discharge ◽  
Spring Tide ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Dry Season ◽  
Pearl River ◽  
The Pearl River Estuary ◽  
Significant Difference ◽  
The Pearl River

&lt;p&gt;Based on the field efforts in 2016 during a dry season (30 Nov-6 Dec) in the Pearl River Estuary (PRE)&amp;#65292;south China, this study aimed to investigate the tidal changes of phytoplankton variability (in terms of chlorophyll a) and their responses to multiple environmental factors.Time series analysis&amp;#65292;principal component analysis (PCA)&amp;#65292;Pearson correlation analysis, and Delft3D model were carried out. A significant difference was found in the tidal variations of dissolved nutrients, covering both a spring tide and neap tide . Moderate differences in salinity and suspended sediment played different roles in the nitrogen and phosphate. The negative correlations of salinity and nitrogen ecologically implied a stronger diluting-mixing effect than that of phosphate, which has a large impact on the water quality. The adsorption of phosphorus by sediment particles was stronger than that of nitrogen. Nitrogen was mainly contributed by river discharge. DIN was constrained by tide-river dynamics and their mutual increase-decline trend, and a new source was supplemented along the transport from river to sea. The weak correlation between PO&lt;sub&gt;4&lt;/sub&gt;&amp;#160;and salinity suggested a different source contribution of the terrestrial emission from coastal cities; the contribution of river discharge was less compared with nitrogen.&amp;#160;Over site, P-limitation&amp;#160;was detected and was more frequently resulted in eutrophication and even bloom events.&amp;#160;Characterizing the relationships among chlorophyll a, nutrients, and hydrological factors enables us to develop effective ecosystem management strategies, and to design studies more focused on ecological health and function.&lt;/p&gt;

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