Diatom-based palaeoecology of Kowloon Bay, Hong Kong
DIATOM-BASED PALAEOECOLOGY OF KOWLOON BAY, HONG KONG
Thomas L. Glemvright
for the degree of Doctor of Philosophy at The University of Hong Kong in March 2000
Hong Kong phytoplankton communities are dominated by the diatoms.
Diatoms are effective biological indicators of eutrophication because their ecological responses are strongly mediated by nutrient availability. Over time, their decayresistant siliceous fmstules and resting spores are deposited and incorporated into bottom sediments. Sediment profiles from Kowloon Bay were retrieved in three replicate core samples in 1995. 210Pb and 137Cs radionuclide dating techniques were employed on the longest core 5 cm). Magnetic susceptibility readings were used to con'elate between cores. These measurements established a chronostratigraphy dating back to ca. 1898 in the relatively undisturbed sediments. The diatom biostratigraphy from these sediments were used to deduce an otherwise unavailable 100 year record of ecological change in Victoria Harbour.
Common diatom species in the sediments were moderately or heavily silicified fon11S. These were over-represented compared to their abundance in the phytoplankton due to differential dissolution. An assessment of the relative preservation of diatom assemblages between cores and depths revealed only minor differences. Downcore diatom shifts were mediated by ecological factors not preservation differences. Major changes in the observed characteristics of sub-fossil diatom assemblages were linked to nutrient loading derived from sewage contamination and habitat loss through land reclamation.
Diatom assemblages deposited between ca. 1898 and ca. 1950 were characterised by low abundance of the nutrient indicator species Thalassionema nitzschioides. Diatom standing crop (indicated by diatom and diatom fragment abundance) was low. The impact of nutrient enrichment through increasing sewage discharge as Hong Kong's population grew was minimal prior to ca. 1950. Diatom assemblages deposited before ca. 1950 contained the highest content (10-15%) of
allochthonous benthic fOnTIs. This indicated less turbid waters and the greater expanse of natural littoral and shallow subtidal habitats before extensive shoreline land reclamation.
The period ca. 1950 to ca. 1978 was characterised as a period of transition ..
Diatom standing crop increased significantly. Thalassionema nitzschioides increases were most dramatic between ca. 1968 and ca. 1978. This reflected mounting nutrient enrichment of Victoria Harbour caused by substantial increases in human population numbers. The abundance of the common meroplanktonic species Cyclotella striata, Cyclotella stylorum and Paralia sulcata peaked during this period. These species require benthic contact for their development as part of their life cycle. Benthic species also declined. By the mid-1960's, the fringes of Victoria Harbour were reclaimed urban sea front.
Between ca. 1978 and ca. 1994, Thalassionema nitzschioides dominated diatom assemblages (25-30%). This period was also marked by the highest levels of diatom standing crop. The size distribution of the Paralia sulcata component of diatom assemblages was significantly lower in these youngest sediments. Smaller Paralia sulcata frustule sizes indicated high diatom productivity conditions. The diatom evidence was interpreted as indicative of the impacts of the mounting levels of sewage-derived nutrients entering Victoria Harbour.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:diatoms china hong kong paleoecology kowloon bay
Date of Publication:01/01/2000