Temporal and spatial variations in nutrient stoichiometry and regulation of phytoplankton biomass in Hong Kong waters: Influence of the Pearl River outflow and sewage inputs

Abstract

In 2001, the Hong Kong government implemented the Harbor Area Treatment Scheme (HATS) under which 70% of the sewage that had been formerly discharged into Victoria Harbor is now collected and sent to Stonecutters Island Sewage Works where it receives chemically enhanced primary treatment (CEPT), and is then discharged into waters west of the Harbor. The relocation of the sewage discharge will possibly change the nutrient dynamics and phytoplankton biomass in this area. Therefore, there is a need to examine the factors that regulate phytoplankton growth in Hong Kong waters in order to understand future impacts. Based on a historic nutrient data set (1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001), a comparison of ambient nutrient ratios with the Redfield ratio (N:P:Si=16:1:16) showed clear spatial variations in the factors that regulate phytoplankton biomass along a west (estuary) to east (coastal/oceanic) transect through Hong Kong waters. Algal biomass was constrained by a combination of low light conditions, a rapid change in salinity, and strong turbulent mixing in western waters throughout the year. Potential stoichiometric Si limitation (up to 94% of the cases in winter) occurred in Victoria Harbor due to the contribution of sewage effluent with high N and P enrichment all year, except for summer when the frequency of stoichiometric Si limitation (48%) was the same as P, owing to the influence of the high Si in the Pearl River discharge. In the eastern waters, potential N limitation and N and P co-limitation occurred in autumn and winter respectively, because of the dominance of coastal/oceanic water with low nutrients and low N:P ratios. In contrast, potential Si limitation occurred in spring and a switch to potential N, P and Si limitation occurred in eastern waters in summer. In southern waters, there was a shift from P limitation (80%) in summer due to the influence of the N-rich Pearl River discharge, to N limitation (68%) in autumn, and to N and P co-limitation in winter due HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript to the dominance of N-poor oceanic water from the oligotrophic South China Sea. Our results show clear temporal and spatial variations in the nutrient stoichiometry which indicates potential regulation of phytoplankton biomass in HK waters due to the combination of the seasonal exchange of the Pearl River discharge and oceanic water, sewage effluent inputs, and strong hydrodynamic mixing from SW monsoon winds in summer and the NE monsoon winds in winter.

Hydrochemistry, ostracods and diatoms in a deep, tropical, crater lake in Western Mexico

“…Alchichica; Ardiles et al, 2011); Manantiales, Los Tuxtlas (Vázquez and Caballero, 2013). Si:SRP and Si:DIN ratios were always above the limiting values for diatom growth (Si:P<16, Si:N<1; Xu et al, 2008), indicating that silica availability is not a limiting factor in this lake (Fig. 5b).…”

“…The Agua Caliente bay community also included Tryblionella granulata and Hippodonta lunemburgensis. This last one is a mesohalobous, benthic species (Lange-Bertalot, 2001) that can survive in this shallower area (~12 m) because during stratification it lies within Reynolds (1999)]; b) nutrient molar ratios showing areas of Si, N or P limitation according to Xu et al (2008). Tryblionella granulata is a littoral, marine species (Gasse, 1986;Moreno et al, 1996) and its presence in this lake was surprising; this report extends its ecological range to fresh waters, albeit with relatively high [Cl -].…”

Basic limnology of 30 continental waterbodies of the Transmexican Volcanic Belt across climatic and environmental gradients

“…Most of the lakes had also high concentrations of SiO 2 (SiO 2 :P-PO 4 < 16:1 and SiO 2 :DIN < 1:1, Xu et al, 2008, Figure 4B). Following these primary productivity nutrient limitation criteria (Redfield, 1958;Reynolds, 1999;Xu et al, 2008) 13 lakes could have some kind of primary productivity nutrient limitation at the time of sampling. Phosphorus limitation was the most frequent (8 lakes), followed by nitrogen (6) and silica (5); some of these lakes were co-limited by more than one of these nutrients: one lake was co-limited by nitrogen, phosphorus and silica (Zirahuén); two by phosphorus and nitrogen (Alberca de Tacámbaro and El Sol) and one by nitrogen and silica (Alchichica) (Figure 4).…”

Phytoplankton Biomass and Production in Subtropical Hong Kong Waters: Influence of the Pearl River Outflow

“…Hong Kong waters are subjected to seasonal exchange between the Pearl River discharge in the wet season and coastal/oceanic water in the dry season induced by the seasonal alteration between southwest monsoon wind in summer and northeast monsoon wind in winter (Yin 2002;Xu et al 2008). Biological processes are strongly coupled with physical processes The seasonal mean chl-specific photosynthetic rate for all light levels (100%, 55%, 30%, 10%, and 1% surface irradiance) for two phytoplankton size fractions in four regions.…”