A study on the composition of size-fractionated suspended particulate matter in shallow coastal waters of Chabahar Bay

Abstract In the present study, sampling and analysis of size-fractionated suspended particulate matter (SPM) in coastal waters of Chabahar Bay have been done for the first time. Sampling has been conducted on December 25 of 2018 from 5 stations in different locations of the Bay in order to evaluate the effects of natural and human activities on SPM mass and composition. With an overall average of 2.44 and 2.37 mg/L for small size (0.4-25 μm) and large size (>25 μm) fraction, concentrations of SPM ranged from less than 1.16 mg/L in the north of the Bay to a maximum of 3.96  mg/L near the urbanized area (Konarak harbor)  in the west of the Bay, respectively. The bulk composition of SPM was mostly of lithogenic materials and particulate organic matter with low contribution from biogenic CaCO3 and even lower biogenic silica, widely varied over stations. Leaching with HCl shows that most of the particulate Fe (>60%), Mn and P (>80%) were labile, while for lithogenic elements, such as Al and Ti the acid-leachable fraction was lower than 10%.  Me/Al ratio for heavy metals of Mn, Fe, Cr, Zn, Ni, and Cu was compared with local sediment and rocks. The ratio was higher in larger size fraction except for Cu.  Enrichment factor relative to reference sediment for Mn, Fe, and Cr was usually lower than 1.0, while for the other three elements the EF values higher than 1.5 indicates a significant contribution from non-crustal sources.