Dynamics of phytoplankton blooms and nutrient limitation in the Pearl River (Zhujiang) estuarine coastal waters

China has a long coastline. Only for the continental part of China, the length of coastline amounts to 18,000 km and, when including the coastline of more than 6,400 islands, an overall length of more than 32,000 km may be counted. As far as the geographical features are concerned, China is characterized by the prevalence of plateau in the west, such as plateau of Tibet and Sinkiang regions and plateau of Yunnan and Kweichow provinces. There are nearly a hundred rivers, the most prominent of which are: the Yangtze River, the Yellow River, the Pearl River etc., flowing from west to east into the Pacific, and carrying about 2,000 million tons of sediment each year to the sea. As a result, silty coasts prevail in the vicinity of estuaries while sandy coasts emerge from a distance away. Generally speaking, the depth of coastal waters is comparatively small, especially along the silty coasts, where the beach profile presents a very gentle slope, varying from 1/50 to 1/500, and in some extreme cases even to 1/2000. Hence the maintenance of water depth in coastal harbours and estuaries has become one of salient problems of coastal engineering in our country.

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Influence of seasonal monsoons on net community production and CO<sub>2</sub> in subtropical Hong Kong coastal waters

Biogeosciences ◽

10.5194/bg-8-289-2011 ◽

2011 ◽

Vol 8 (2) ◽

pp. 289-300 ◽

Cited By ~ 20

Author(s):

X.-C. Yuan ◽

K. Yin ◽

W.-J. Cai ◽

A. Y. Ho ◽

J. Xu ◽

...

Keyword(s):

Hong Kong ◽

Coastal Waters ◽

River Estuary ◽

Pearl River Estuary ◽

Pearl River ◽

Wet Season ◽

Net Community Production ◽

The Pearl River ◽

Hong Kong Coastal Waters ◽

Community Production

Abstract. Data from seven cruises in three different environments including the Pearl River estuary, sewage discharge outfall, and eastern coastal/shelf waters were used to examine the seasonal variations in net community production (NCP) and the biologically active gases O2 and CO2. In the winter dry season, when monsoon-induced downwelling was dominant, NCP was negative (−84 ± 50 mmol C m−2 d−1) in all three regions. The negative NCP corresponded to O2 influxes of 100 ± 50 mmol O2 m−2 d−1 and CO2 effluxes of 24 ± 10 mmol C m−2 d−1. In the summer wet season, when upwelling brought the deep oceanic waters to the coast due to the southwest monsoonal winds, there was a 2 to 15-fold increase in integrated primary production (IPP) compared to winter. The increase in IPP was likely due to the favorable conditions such as stratification and the nutrient inputs from upwelled waters and the Pearl River estuary. NCP in the mixed layer reached up to 110 ± 48 mmol C m−2 d−1 in the wet season. However, accompanying the high positive NCP, we observed an O2 influx of 100 ± 60 mmol O2 m−2 d−1 and CO2 efflux of 21 ± 15 mmol C m−2 d−1. The contradictory observation of positive NCP and CO2 release and O2 uptake in the mixed layer could be explained by the influence of the southwest monsoon-induced upwelling along with the influence of the Pearl River, as the upwelling brought cold, low dissolved oxygen (DO, 160 ± 30 μM) and high dissolved inorganic carbon (DIC, 1960 ± 100 μatm) water to the surface in the wet season. Hence, the subtropical Hong Kong coastal waters are generally a CO2 source due to the monsoonal influence during both the dry-heterotrophic and wet-autotrophic seasons.

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