Spatial distribution of heavy metals in surface sediments of a mangrove creek and its adjacent seagrass bed (Cordova, Mactan Island, central Philippines)

The sediment heavy metal concentrations of two sections (upstream and midstream stations) of a mangrove creek and its adjacent seagrass bed were compared. Eight heavy metals (Pb, Zn, Cd, Cu, Cr, Ni, Mn and Fe) were analyzed using atomic absorption spectrometry (AAS). Six (i.e., Cd, Cu, Fe, Mn, Pb and Zn) of the eight heavy metals showed significant differences among stations. In Fe, Mn and Cu, both the upstream and midstream stations were significantly higher than the seagrass bed. There were no significant differences among stations for Ni and Cr. In Zn and Pb, the midstream station was significantly higher than the seagrass bed, while in Cd the midstream station was significantly lower than both the upstream station and the seagrass bed. The relative order of heavy metal concentration for the upstream station is Fe > Mn > Cu > Ni > Zn > Cr > Cd > Pb. For the midstream station it is Fe > Mn > Ni > Cu > Zn > Pb > Cr > Cd, and for the seagrass station it is Fe > Ni > Mn > Cu > Cr > Cd > Zn > Pb. The heavy metal concentrations in the sediments at Solod-Tunggan River are below the values that could significantly affect the mangrove stands. The heavy metal concentrations in the sediments at the upstream and midstream part of the Solod-Tunggan River, Cordova, Mactan Island, central Philippines were relatively lower compared to other mangrove swamp sediments in other parts of the world due to the absence of major industrial facilities in the area.