Ecological impact of Mahshahr petrochemical activities on abundance and diversity of macrobenthic fauna in Zangi Creek (Persian Gulf)

The Moosa Creek extends from its opening into the Persian Gulf, with some sub narrow creeksleading to it. Zangi creek is one of the main branches of Moosa creek. The creek containsnumerous sources of organic pollution, including sewage outlet flows and boat waste. Afterestablishing the Petrochemical special Economic Zone (PETZONE) in 1997 near to the ZangiCreek, the pipelines, streets and railway made it distinct from eastern and western parts of thiscreek. Industrial activities have released sludge and effluents in this creek along these years. Asurvey of the Zangi creek was performed, assessing water properties, organic pollution, and thepopulation density, distribution and diversity of macrobenthic fauna through bi-monthlysampling from July 2006 to September 2007.Samples were collected from water near the bottom and sediment at 7 stations include 2 stationsinside the distinct Zangi creek and 4 stations along a transect with 1 km distances between themin eastern free part and one reference station located at the Persian Gulf entrance to the Moosacreek. The environmental parameters such as temperature, salinity, pH, dissolved oxygen, COD,turbidity, EC and heavy metals include Hg, Cd, Pb, Ni as well as percentage silt-clay and totalorganic matter of the sediment were measured. The faunal population density and theirdistribution are discussed in relation to the environmental changes.Results showed spatial heterogeneity in faunal distribution of the Zangi creek. Nine groups ofmacrofauna were identified out of distinct zangi creek. Polychaets formed the dominant group(48%) followed by bivalves (13%), gastropods (10%), Decapods (2%), Tanaids (5%), and allother groups (22%). The distinct creek was heavily polluted without any macrofaunacommunities probably as a consequence of the high pH, COD, low salinity and heavy metalscontamination specially Cd and Pb. The other stations near to the disposal site were found withmacrofauna communities commonly tolerant to organic pollution, At 3 km east of the disposalsite, macrofauna is comparable to the surrounded creek, whereas macrofauna still indicateenvironmental degradation. Farther a way, faunal density decreases and equilibrium taxagradually replace opportunistic species, while the other stations were far from polluted areacontained lower pollution and relatively healthy macrofauna.The mean biomass of macrobenthic fauna were estimated for the whole studied area. The resultsare considered in Minimum density and biomass in surrounded creek and maximum density andbiomass in 3 km of surrounded area. Biodiversity Indices were low in surrounded creek. TheShanon-weaver information index was used to describe the spatially variations in diversity.Macrofauna density, shanon and simpson index were significantly variable between surroundedand free parts of Zangi creek (p<0.05). The numerical abundance of macrobenthose varied from221. m-2 in polluted area to 4346 m-2 in free part of Zangi creek. The Shanon-weaver informationindex varied from 0.4 in distinct area to 2.9 in reference station.The physico- chemical changes between distinct and free creeks showed significant variationssuch as pH, salinity and EC. Salinity and EC were significantly positive correlate to macrofaunadensity, whereas pH and TOM percentage indicated significantly negative correlation to density.Heavy metals concentrations in sediments were higher than water samples. Concentration patternof heavy metals in sediments and water samples were Ni>Pb>Cd>Hg. Salinity and pHwere significantly correlated to metals in sediments (p<0.01).No significant correlation were found between Macrofauna density and heavy metals (p<0.05).

PhD

Advisors: Alireza Nikoyan Counsellors: A. Keyvan, T. Valinasab