Abstract:
Purpose The geochemical compositions of sediments from
three sectors in Trincomalee Bay (Koddiyar Bay, Thambalagam
Bay and the Inner Harbour) in Sri Lanka were examined to
determine fluvial and marine contributions and the effects of
sorting and heavy mineral concentration. The present environmental status of the bay was also assessed.
Materials and methods Forty-nine sediment samples were
collected from Trincomalee Bay and analysed by X-ray fluorescence, yielding data for the major elements and 17 trace
elements. Mean grain size and sorting were also measured.
Data were compared with the compositions of sediments from
the lower Mahaweli River, which supplies most of the clastic
detritus to Trincomalee Bay.
Results and discussion Sediments in the three sectors differ
significantly in chemical composition, according to position
relative to the Mahaweli River delta source, depositional envi ronment, heavy mineral concentration and marine influences.
According to accepted sediment quality guidelines, some As
contamination may have occurred in the Inner Harbour and
Thambalagam Bay and Cr contamination in all three sectors.
Conclusions Proximal Koddiyar Bay sediments compare
closely with Mahaweli River bedload. Although the clastic
component in the more distal Thambalagam Bay and the Inner
Harbour is also derived from the Mahaweli River, compositions are modified significantly by marine contributions. High
concentrations of elements including Ti, Zr, Ce, Nb and Y in
NW Koddiyar Bay are consistent with heavy mineral concentration by winnowing in high-energy zones. Some decoupling
of Fe–Ti- and Zr-bearing heavy mineral assemblages may
occur within the bay. Al-normalized metal enrichment factors
and contour maps show that apparent contamination by As
and Cr is spurious and is caused by locally high background
levels from Mahaweli River detritus. This illustrates the importance of establishing local background levels of elements
during environmental studies.
