Songkhla Lake, a tropical estuarine lagoon system in southern
Thailand, is located between latitudes 7°08′ and 7°50′ N
and longitudes 100°07′ and 100°37′ E. The system has four
interconnected water bodies, namely Thale Noi, Inner Lake, Middle Lake and
Outer Lake, ranging from fresh to saline water. The system receives runoff,
wastewater and sediments from surrounding watershed and drains into the Gulf of
Thailand. Seventy-four surface sediment samples from the whole lake system were
determined for As, Cr, Hg, Fe, Mn, Al, organic carbon and textural
characteristics. Total concentration of As in Thale Noi, Inner & Middle
Lake, and Outer Lake are 8.2 ± 1.7 (5.7–10.8), 5.9 ±; 1.5
(3.7–10.8) and 10.7 ± 5.5 (5.1–25.7) mg
kg
$^{-1}$
, respectively. Total concentration of Cr in Thale
Noi, Inner & Middle Lake, and Outer Lake are 45.2 ± 5.0
(36.0–55.2), 36.6 ± 9.2 (23.7–73.3) and 29.6 ± 9.2
(7.9–48.2) mg kg
$^{-1}$
, respectively. Total
concentration of Hg in Thale Noi, Inner & Middle Lake, and Outer Lake are
89.1 ± 14.9 (63.4–113.1), 38.4 ± 11.1 (24.3–68.0) and
49.3 ± 15.2 (26.6–110.3) μg kg
$^{-1}$
,
respectively. In most part of the lake, As and Cr concentrations are at or near
natural levels, except at station 57. The concentration of Hg may be natural or
influenced to some degree by anthropogenic sources. Thale Noi, the most natural
part of the lake system which contains high organic content, has the highest
concentrations of Cr and Hg. Diagenetic processes involving iron oxides and
aluminosilicate appear to be the most important factor controlling the
behaviour of As, Cr and Hg in sediments. Organic matter and clay size particles
seem to have less direct influence on the geochemistry of the metals.
