Temporal and spatial distribution of dissolved oxygen in the Pearl River Estuary and adjacent coastal waters

Abstract

The Pearl River is one of the large rivers in the world and it discharges to the northern part of the South China Sea. There has been a concern about the deterioration of dissolved oxygen conditions in the Pearl River estuary and adjacent coastal waters. In this study, historical data on dissolved oxygen (DO) from 1980, recent data from a summer cruise in 1999, and a 10-year time series in DO for 1990-2000 were used to examine spatial and temporal distribution of DO in the Pearl River estuary and adjacent coastal waters near Hong Kong. In the adjacent coastal waters, low oxygen waters <4 mg l -1 occurred in large areas during the summer of 1981, but DO rarely dropped to <3 mg l -1 . In the Pearl River estuary, DO was 3.5-4 mg l -1 in the eastern part, but was >4 mg l -1 in the western part in August 1984. In July 1999, DO was < 4 mg l -1 in a near bottom 2 m layer in a large area of the estuary and was Furthermore, the spatial distribution of DO in the bottom layer was parallel to the topography of the bottom, indicating the importance of benthic consumption of DO in the sediment and the subsequent flux of low DO waters from the sediment-water interface resuspended by physical mixing. Relative to the high loading of nitrogen from the Pearl River, the present PO 4 concentration is still low. It is possible that the lack of large areas of hypoxia in the region may be linked to phosphorus limitation as shown in the previous study. Phosphorus may also be a limiting factor for bacterial decomposition which has a strong control on total oxygen consumption in the water column and sediments.

Natural and human-induced hypoxia and consequences for coastal areas: synthesis and future development

“…Hypoxia that develops in coastal areas off the river mouths, notably the Mississippi River, Changjiang (Yangtze River), Pearl River (Zhujiang), Danube River, and Susquehanna River (Zaitsev, 1992;Turner and Rabalais, 1994;Li et al, 2002;Rabalais et al, 2002;Yin et al, 2004;Hagy et al, 2004;Black Sea Commission, 2008), usually has been related to anthropogenic activities in the catchment areas on land. In particular, changes in land-use and agriculture (e.g.…”

A trophic model of the Pearl River Delta coastal ecosystem

“…the Pearl River discharge, the oceanic waters from the South China Sea and the coastal waters from the South China Coastal Current [24]. The resultant nutrient-enriched waters provide large biol ogical productivity and sustain the most important commercial fisheries [25,26].…”

Influence of seasonal monsoons on net community production and CO&lt;sub&gt;2&lt;/sub&gt; in subtropical Hong Kong coastal waters

“…Coupled with the monsoonal influence, the seasonal freshwater discharge from the Pearl River further complicates the hydrodynamics and biochemical processes. Previous studies suggested that the anthropogenic inputs of nutrients and organic matter in the Pearl River estuary have led to a decrease in oxygen and an increase in CO 2 , especially in the upper estuary (Yin et al, 2004;Cai et al, 2004;Dai et al, 2006). Zhai et al (2005a) have reported that aerobic respiration is the most important process in maintaining a high pCO 2 level (>3000 µatm) in the upstream section of the Pearl River estuary.…”