A comparison of eutrophication impacts in two harbours in Hong Kong with different hydrodynamics

Abstract

27Eutrophication impacts may vary spatially and temporally due to different 28 physical processes. Using a 22-year time series data set , a comparison of 29 eutrophication impacts between two eutrophic harbors, Victoria and Tolo Harbours, in 30 Hong Kong with very different hydrodynamic conditions was conducted. In the 31 highly-flushed Victoria Harbour (Victoria), the highest Chl a (13 μg L -1 ) occurred due 32 to stratification in summer as a result of the input of the eutrophic Pearl River 33 discharge, but the high flushing rate restricted nutrient utilization and the further 34 accumulation of algal biomass. In other seasons, vertical mixing induced light 35 limitation and horizontal dilution led to low Chl a (< 2 μg L -1 ) and no spring bloom. 36 Few hypoxic events (DO < 2 mg L -1 ) occurred due to strong tidal mixing. Therefore, 37 Victoria is resilient to nutrient enrichment. In contrast, in the weakly-flushed Tolo 38 Harbour (Tolo), year long stratification, the long residence times and weak tidal 39 currents favored algal growth, resulting in a spring diatom bloom and high Chl a (up 40 to 30 μg L -1 ) all year and frequent hypoxic events in summer. Hence, Tolo is 41 susceptible to nutrient enrichment and it responded to nutrient reduction since sewage 42 treatment resulted in a 32-38% decrease in algal biomass in Tolo, but not in Victoria. 43 A significant (11-22%) reduction in bottom DO in the both harbors after sewage 44 treatment was due to a decrease in the organic loading from sewage treatment or the 45 diversion.46

Occurrence of Halogenated Flame Retardants in Sediment off an Urbanized Coastal Zone: Association with Urbanization and Industrialization

“…Although Tolo Harbour was grossly polluted from the 1970s to early 1990s by large amounts of sewage effluent discharged as a result of rapid population growth during the development of a new town in Shatin, 35 Victoria Harbour since 1997 has resulted in a great improvement in water quality. 36 The eastern and southern sites contained relatively lower concentrations of HFRs, apparently because their adjacent areas are less populated and lower urbanized and there are relatively limited marine traffics in these areas.…”

Global diversity of two widespread, colony‐forming diatoms of the marine plankton, Chaetoceros socialis (syn. C. radians) and Chaetoceros gelidus sp. nov.

“…The material from warm water agreed well with C. radians as described by Sch€ utt (1895) from the Baltic, whereas the cold-water material was different. However, the original description of C. socialis being from warm water led us to search for information on the seawater temperature in Hong Kong, which has been 1138 reported to be no lower than 15°C-17°C in winter (Yin 2002, Xu et al 2010. Considering that the material separated into two phylogenetic clades which correlated with different temperatures, it became likely that the cold-water material was different from C. socialis.…”

Differential utility of the Bacteroidales DNA and RNA markers in the tiered approach for microbial source tracking in subtropical seawater

“…The relative persistence of Bacteroidales gene markers and the standard FIB in hypoxic seawater is scarcely known. The hypoxic seawater with light irradiation tested in this study is common for the shallow coastal line of Hong Kong (Xu et al 2010). Our results suggest that the use of the DNA of the Bacteriodales gene markers together with E. coli in the tiered approach is not affected by hypoxia when light is present.…”