Use of Macrobenthos Biodiversity in Assessing the Ecological Status of Zangi Estuary about Heavy Metal Contamination

In the present study, the possibility of using macrobenthos as a biological indicator to assess the level of contamination of the rust estuary with heavy metals has been investigated.

Sampling was performed in 2016 from 4 stations in Zangi estuary at full tide.Sediment was harvested from each station using Van Wen (with a cross section of 0.025 m2) to identify benthos, determine heavy metals in sediment, determine organic matter and granulate sediments. In all 4 stations, clay particles formed the main part of the sediments.

The range of organic matter was 6.90-6.98%, with station 3 having the highest percentage and station 4 having the lowest percentage of organic matter. The identified macrobenthos in Zangi estuary were divided into five categories: Bivalvia, Gastopoda, Polychaeta, Crustacea and Fish and 26 genera and species. Station 1 with 13 species had the highest number of species and Station 2 had the highest number of macrobenthos per square meter and the highest Shannon diversity and uniformity index. Species of Hydroides sp. Polychaeta with 25.97% had the highest frequency in the population of Zangi estuary macrobenthos. Accordingly, Polychaeta with 49.1% and Bivalvia with 37.21% had the most abundant category and fish with 0.86% had the lowest frequency. Polychaeta class in stations 1 and 4 with 63.26 and 56.1% and Bivalvia class in stations 2 and 3 with 44 and 33.06%, respectively, had the highest percentage. Zinc, nickel and chromium had the highest concentrations with averages of 32.41, 23.13 and 19.16 mg/kg.Selenium had the lowest concentration in all 4 stations. The mean concentrations of heavy metals in stations 2 and 3 were significantly less polluted with stations 1 and 4 (p <0.05). Calculation of the degree of pollution in 4 stations of Zangi estuary showed the degree of severely polluted for these stations. Based on the contamination factor, except for vanadium at all stations and lead metal at station 2, which is in the highly contaminated range, other metals were in the low to high contamination range. Thus, the concentration of all metals in the bell ring was in the alarming state.

The results of the present study showed that the first and most important factor influencing the distribution of estuarine macrobenthos was the percentage of bed clay particles, heavy metals such as cadmium, lead, nickel, vanadium, chromium and zinc and then the organic matter in the bed. Also, copper metal had the least effect and correlation with the number of macrobenthos among the studied metals.