Macrobenthic fauna community in the Middle Songkhla Lake, Southern Thailand

A bimonthly investigation of macrobenthic fauna at the area from Ban Pak Khat to Ban Leam Chong Thanon in the Inner Songkhla Lake from February 1998 to February 1999 was undertaken to determine the species richness and abundance. A total of 7 phyla and 161 species were identified. Annelida (58 species), Arthropoda (64 species) and Mollusca (23 species) were the major phyla while Nemertea (1 species), Platyhelminthes (1 species), Cnidaria (4 species) and Chordata (10 species) were the minor. Fifty-seven speciesof Polychaete annelids were found. The highest species richness (14 species) was in the Nereididae Family, of which Ceratonereis burmensis and Namalycastis indica were predominant. Nephtys sp. and Heteromastus sp. were not so highly abundant but appeared at almost all stations through every sampling month, while Prionospio cirrifera and Pseudopolydora kempi were found in higher densities but with narrower distribution. Ficopomatus sp. and unidentified Terebellidae were not commonly found, but occasionally reached a high density. Amphipods gave the highest species richness (22 species), with Photis longicaudata distributed widely and in all months. Five species of Tanaidaceans were found with Apseudes sapensis the second most dominant (max. 5044 individuals m-2 in February) in the overall fauna. Isopoda were not as densely found as tanaidaceans but there were many species (18 species). Cyathura sp.1 was the most dominant isopod. Brachidontes arcuatulus was the most dominant bivalve (max. 29449 individuals m-2 in April), especially at stations with a sand-gravel substrate. The mean density of total macrobenthic fauna among stations ranged from 920 to 10620 ind. m-2 while the monthly densities ranged from 1520 to 6160 ind.m-2. The mean density of macrobenthic fauna was highest in the dry season (April). The species richness among stations ranged from65 to 105 species while varying from 81 to 112 species during the different months. The highest species richness was in the SW monsoon season (light rain, June-August). Polychaetes and molluscs tended to decrease in the NE monsoon season with heavy rain from December-February, while crustaceans increased during this time. The best fitting of the environmental variables to explain the macrobenthic fauna community pattern of the Inner Songkhla Lake was an 8-variable combination of %clay, %silt, %organic carbon, soil pH, depth, dissolved oxygen, total suspended solid and temperature (harmonic rank correlation coefficient, ρw = 0.84)

Distribution of macrobenthic fauna in Phawong and U-Taphao canals flowing into a lagoonal lake, Songkhla, Thailand

The macrobenthic fauna of two discharge ecosystems, Phawong Canal and U-Taphao Canal flowing into Songkhla Lake in Thailand, were studied from August 1994 to August 1995. The salinity of Phawong Canal and U-Taphao Canal ranged from 0.1 to 27.8 and 0.1 to 17.0 practical salinity units (PSU), respectively. The biochemical oxygen demand (BOD) of Phawong Canal ranged from 2.5 to 33.0mg L21, while that of U-Taphao Canal ranged from 1.1 to 12.6mgL21. Temporal changes in the number of species and individuals were determined throughout a year. During the season of heavy rains (November-December), the density and number of most species decreased markedly. Only chironomid larvae increased and these were distributed in the uppermost reaches of the canals during this period. Sixty-two and 52 species of macrobenthic fauna were found in Phawong Canal and U-Taphao Canal, respectively; however, the abundance and number of species collected at each sampling was very low in the upper reaches of the canals. The most numerous benthic fauna in the Phawong Canal were polychaetes, followed by amphipods. Pelecypods and gastropods were the dominant groups in U-Taphao Canal. A distribution pattern of macrobenthic fauna associated with pollution gradients (BOD) was observed only at Phawong Canal. In addition, species diversity according to the Shannon-Wiener index only was not applicable to the assessment of benthic environmental health when the few individuals found were evenly distributed among the few species present at U-Taphao Canal. It is recommended that a coastal care project be established by the appropriate government agencies in the study areas

Distribution of trace elements in sediments and biota of Songkhla Lake, Southern Thailand

The concentrations of Co, Ni, Cu, Zn, Cd, Pb, As, Fe, Mn, and Al were determined in sediments and biota of Songkhla Lake, a shallow coastal lagoon located in southern Thailand. In June 2006, surface sediments were sampled in 44 stations in the three sections of the lake (inner-, middle-, and outer sections). Sediment cores were also sampled in 13 stations in three cross-sections of the lake. In surface sediments, trace and major elements, organic matter, sediment grain size analysis, and sulfides were determined, and in the sediment cores, redox profiles were made. Soil samples were also collected at garbage dumping sites in the vicinity of the lake. In addition, the metal accumulation in two catfish species (Arius maculatus and Osteogeneiosus militaris) and the crustacean (Apseudes sapensis) was also investigated. Trace element concentrations in sediments of Songkhla Lake show that, especially the Outer section of the lake, in particular the sediments at the mouths of the Phawong, U-Taphao, and Samrong Canals are significantly enriched with trace elements due to municipal, agricultural, and industrial discharges entering the lake through the canals. Aluminum-normalized enrichment factors throughout the lake vary from 0.4 to 1.7 for Ni, 0.3 to 3.3 for Cu, 0.2 to 7 for Zn, 0.1 to 14 for As, 1 to 24 for Cd, 0.7 to 6.8 for Pb, and 0.1 to 7.8 for Mn. Correlations between the elements and sediment characteristics show that Cu, Zn, Cd, and Pb are essentially associated with the sulfide fraction; that Ni and Co are predominantly bound to the clay minerals and iron oxy-hydroxides, and that As is principally bound to iron oxy-hydroxides. The accumulation of trace elements between muscle tissue and liver and eggs of A. maculatus and O. militaris is element-specific, but concentrations of trace elements in fish muscle tissue are well within the limits for human consumption