Seagrass interaction with heavy metals at Pulai River Estuary

Abstract

Environmentalists have raised their concerns that pollution from development along Pulai River Estuary will have an impact on marine ecosystem. In 1994 eleven seagrass species were found in the area. However, when this study were conducted in 2011 only seven seagrass species were identified at the area, namely Enhalus acoroides, Halophila minor, Halophila spinulosa, Halophila ovalis, Thalassia hemprichii, Halodule uninervis and Cymodocea serrulata. The seagrass can uptake metals and therefore plays the role as bioindicator. Field work was conducted between July 2011 and April 2014 where seagrass, water and sediment were collected for analysis. The samples were analysed using Perkin Elmer Atomic Absorption Spectrophotometer Model AAnalyst 400 for copper (Cu), cadmium (Cd), and lead (Pb). Flow Injection Mercury System Perkin Elmer model FIMS 100 was used for mercury (Hg) and arsenic (As) analysis. Analysis of variance and Pearson’s correlation coefficients of metal concentrations were carried out using Statistical Package for the Social Science (SPSS) for seagrass tissues, seawater and sediment. Esri ArcGIS software was used to determine the metals distribution. The seagrass percent covers on the seagrass bed were determined by transect method. The study shows that Halophila minor was the most abundant species covering Pulai seagrass bed at 27% followed by Halophila ovalis (18%), Halophila spinulosa (8.8%), Enhalus acoroides (6.4%), Thallasia hemprichii (5.3%), Cymodocea serrulata (1%), and Halophila uninervis (0.3%). Among the seven seagrass species found, Halophila ovalis have the highest accumulation of metal and indicates positive significant correlation to translocation of metal in seagrass tissues, hence it meets the criteria to be selected as a bioindicator. Mapping using Esri ArcGIS, shows the metals distribution originated from land use. Monitoring conducted on 4th of April, 2014 indicated that land reclamation for Forest City has changed the condition of seagrass bed hydrodynamic and trophic state from upper-mesotrophic to light-eutrophic. Quantitative water, sediment and seagrass fugacity/equivalance mass balanced model was developed to describe the movement pattern of metals that ends up in the seagrass bed. Estimation rates of As, Cu, Cd, Hg and Pb concentration in seawater are at 3.18 µg/L, 32.35 µg/L, 39.94 µg/L, 4.99 µg/L and 99.86 µg/L, respectively for 1 day.