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Determination of the biological health status of Mahshahr petrochemical salt extraction ponds using macrobenthos
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Farahnaz Kianersi   1, Najmeh Jahani , Mehrnaz Shirmohammadi , Hossein Hooshmand , Mohsen Mazraavi , Jamil Bani Torfizadegan , Fereidoon Owfi , Siroos Naserian , Seyed Mehdi Babaeinejad |
| 1- the Institute of Fisheries Research of the Country |
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Abstract: (47 Views) |
Introduction
Mahshahr port is considered to be a strategic and economically important port among the ports of Iran, which is connected to Musi Creek and then the Persian Gulf through the tributaries of the Creek (Jafarian Moghadam et al., 2018). The salt ponds of the petrochemical complex, designed for salt extraction from seawater, inadvertently allow a variety of aquatic animals in their larval stages from Creeks to enter during the dewatering process. These creatures face challenging and stressful living conditions characterized by high salinity, intense evaporation, and insufficient water flow. The relationships between macrobenthos and natural environmental factors can be used to describe natural and artificial habitats and create basic knowledge that enables the detection of their spatial and temporal changes (Sule et al., 2024). There was limited information regarding the biotic and abiotic characteristics of salt ponds and Odleh Creek (Dehghan Madiseh et al., 2009; Heydari et al., 2021). To gain a more thorough and ongoing understanding of the region's condition, a detailed study was deemed necessary to assess biological parameters. This research aims to evaluate the health status of the community structure in salt extraction ponds and Odleh Creek, which serves as the sole source of water supply.
Methodology
Seven stations were selected in the Odleh Creek and salt extraction ponds No. 1 and 2. Sampling at the selected stations was conducted seasonally from May 2023 to April 2024. Sediment samples were gathered for macrobenthos identification, grain size analysis (GSA), and total organic matter (TOM) assessment, utilizing a van Veen grab with a coverage area of 0.0625 square meters. The total organic matter was determined using the combustion method, and sediment granularity was evaluated using the wet sieving technique (Buchanan, 1984). This study utilized the identification and counting of macrobenthos to evaluate the biological health of the target area, along with ecological indicators such as Shannon diversity, Margalef richness, Simpson's dominance, and AMBI index.
Results
As one moves away from the Creek and toward pond number 2, there was a noticeable increase in the levels of organic matter and silicate-clay. This study involved the isolation and identification of 50,908 individuals from three macrobenthic groups across four sampling seasons at seven designated stations in the Odleh Creek and Mahshahr salt ponds. The polychaetes were the most prevalent, comprising 17,600 individuals, while the mollusks were the least abundant, with only 2,552 individuals identified. Stations 1 and 2 showed the greatest density of crustaceans. At station 6, mollusks were the most abundant group, whereas station 7 was primarily dominated by insects. In the other stations, polychaetes were the most common. The total abundance of macrobenthos at different stations revealed that station 1 had the highest levels in the summer, whereas stations 4, 5, and 6 recorded the lowest levels during the winter.
The results of this study showed that from Odleh Creek station to the stations located in the salt extraction ponds, the abundance of macrobenthos, and the indices of diversity and richness of species exhibited a decreasing trend, while the dominance index exhibited an increasing trend. Station 2 showed the highest Shannon diversity index and species richness, whereas station 7 had the lowest values. Conversely, the dominance index peaked at station 7. AMBI biological index values in the studied stations during the sampling period ranged from 0 to 4.18. In the analysis of the AMBI index at the Odleh Creek stations, station 3 exhibited a moderate level of pollution, while the other stations demonstrated low pollution levels. The calculation of this index was not possible at stations 6 and 7 due to the extremely low diversity of macrobenthic groups. Consequently, severe pollution conditions are anticipated at these stations based on this index.
Discussion and conclusion
The findings of this research, along with the examined biological indicators, indicate that the benthic communities at the stations prior to the ponds exhibit low to moderate levels of pollution. In contrast, the stations within the ponds demonstrate moderate to severe pollution. The rise in organic materials in the sediment, along with a decline in the density and diversity of benthic organisms at the stations within the salt pond, can be attributed to the unique characteristics of the salt pond's structure. Factors such as high salinity, reduced water levels due to evaporation, lack of water currents for oxygen exchange, and the accumulation of decomposing animals and plankton are more pronounced in these areas compared to the Odleh Creek stations. In line with this research, the studies conducted by Dehghan Madiseh et al. (2009) in the Odleh estuary found that the levels of indicators were comparable to those observed in the current study, indicating a low level of pollution. However, the abundance of benthic organisms was greater than what was reported in the present study (Dehghan Madiseh., 2009).
Overall, the variations in the diversity and density of macrobenthos in artificial salt ponds appear to be linked to elevated salinity levels and the presence of organic matter in the sediment. Both factors play a significant role in influencing benthos. Implementing effective management strategies, such as drying the pond beds, establishing water channels, and dredging can help eliminate the remains of deceased animals and plants in the ponds. This will enhance the living conditions for the aquatic life inhabiting these salt ponds.
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| Keywords: Benthos, Petrochemical salt pond, Odleh Creek, heavy metals, AMBI index |
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Full-Text [PDF 655 kb]
(25 Downloads)
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Type of Study: Research |
Subject:
اكولوژي محيطهاي آبي
Received: 2024/10/21 | Accepted: 2024/12/30
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