Abstract:
Sea grasses are submerged flowering plants in shallow coastal waters and play a
significant role in the near shore dynamics including nutrient cycling,
remineralization and act as a sink for pollutants in coastal environment. The
occurrence of Thalassia hemperichii in South East Asia has been reported to be
associated with the presence of other dominant seagrass species. Heavy metals in
the coastal areas have been resulted from significant discharge of effluents from
boat construction and painting sites and various metal using industries. Sea grasses
are capable of uptaking metals from both water through leaf surfaces, sediment and
interstitial water through their roots. Therefore, the filtering ability of selected
heavy metals is studied by Thalassia hemperichii at selected coastal sites. Water,
sea grass and sediments were collected from Dondra and Weligama reef lagoons.
Concentration of metals (Cu, Pb) in water, sea grass and sediment were analyzed
using Atomic Absorption Spectrometer. The highest concentrations of copper in
water at Weligama and Dondra sites were 0.284 and 0.123ppm respectively. The
highest lead concentrations in water of Weligama and Dondra sites were 0.41 ppm
and 0.34ppm respectively. According to independent t test, there was no significant
difference of copper concentrations in sediment between Dondra and Weligama
areas. But, significant difference of copper concentrations in sediment between
Dondra and Weligama areas was observed (P<0.05). The highest copper
concentrations in sediment of Weligama and Dondra sites were 5pgg'] and 174 pgg'
1 dw, respectively. The highest lead concentrations in sediment of Weligama and
Dondra area were 202 pgg'1 and 424 pgg'1 respectively. The highest copper and lead
concentrations in the sea grass at Dondra reef lagoon were 149 and 467 pgg-'dw
respectively. The highest copper and lead concentrations in sea grass at Weligama
site were 204 and 1750 pgg-'dw, respectively. A significant difference in metal
concentrations was found in water between the sea grass present sites and the sea
grass absent sites in Dondra (p<0.05). Also, the variation depends on the abundance
of sea grass and metal concentrations at sampling sites. The results of the laboratory
experiment showed a significant positive correlation between metal uptake rate by
the seagrass and metal concentrations in the water. Therefore, this study shows
clearly the ability of the sea grass for accumulating metals from the ambient and the
potential of use as a natural, low cost biofilter for reducing metals in the coastal
environment.
