محسن مزرعاوی

Phytoplankton are the primary producers at the base of food webs in aquatic ecosystems. Marine zooplankton are the secondary producers of the marine food web. The distribution of zooplankton affects the growth potential of fish in the area, especially their larvae. The sensitivity of plankton to slight changes in the environment has made them suitable biological indicators that reflect the health conditions of the aquatic ecosystem. In the Mahshahr salt ponds, during the dewatering stage, shrimp and fish larvae are introduced into the ponds through pumping from Odleh Creek, which is the only source of water supply to the ponds, where they grow in harsh conditions. As a result, regular assessment is necessary to protect the inhabitants of this aquatic ecosystem. The purpose of this study was to investigate the biological health of the Mahshahr salt ponds and Odleh Creek ecosystem using the Water Quality Score (WQS) and ecological indicators based on the planktonic communities of this ecosystem.

Sampling was conducted at seven stations, from Odleh Creek to Salt Ponds 1 and 2. Water samples for the investigation of phytoplankton and zooplankton were collected using a plankton net across four seasons, from May 2023 to April 2024. Physical and chemical factors, including dissolved oxygen, pH, total phosphate, total nitrogen, and biochemical oxygen demand, were measured to evaluate the WQS index. Some physicochemical factors such as pH, temperature, and dissolved oxygen were measured at the sampling site using a portable multi-parameter device, and salinity was measured using a salinometer. The remaining parameters were measured using standard experimental methods.

During this research, moving away from the estuary and towards the ponds showed an increasing trend in the abundance of phytoplankton, salinity, nitrate and dominance index, while the abundance of zooplankton, phosphate, diversity index, species richness, and biological balance exhibited a decreasing trend. A winter peak was observed for phytoplankton density, followed by a spring peak for zooplankton density. In this study, 51 species from 6 phytoplankton groups and 17 species and 4 larvae from 2 zooplankton groups were identified. The average abundance of phytoplankton was 4,229 cells per liter, while that of zooplankton was 10,395 cells per liter. The Bacillariaceae and Paracalanidae families, as well as the larval stages (Nauplius and Copepoda), were the dominant groups in the region. According to the evaluation of the WQS index, a rank of 2.6 was determined for the estuary stations and salt pond No. 1, while a rank of 3.4 was determined for the stations inside pond No. 2. According to the WQS index, the values of pH and dissolved oxygen during the sampling period received a score of 5 (good quality), while total nitrogen, total phosphorus, and BOD5 during the study period received a score of 1 (low quality). Overall, the stations at Odleh Creek and the beginning of pond No. 1 have low quality, whereas the stations at the end of pond No. 1 and inside pond No. 2 have poor quality in terms of water quality. A positive correlation was observed between phytoplankton abundance and salinity and nitrate levels, while zooplankton showed an inverse relationship with these two parameters.

According to the study, as salinity and nitrate increased in the ponds, the abundance of phytoplankton increased, while zooplankton decreased. This was probably due to the sensitivity of zooplankton to salinity and the creation of osmotic pressure beyond their capacity. Following this, with the reduction of predators and the availability of nitrate as a food source for phytoplankton, we witnessed greater growth of phytoplankton. Also, as we moved towards the ponds, species diversity decreased due to intense evaporation and high salinity, and resistant species formed the dominant population. On the other hand, according to the results of the WQS index, the water quality of the area was low, which can be attributed to stressful conditions such as intense evaporation. Therefore, in the ponds, it is necessary to conduct continuous monitoring and identify and eliminate stressful factors to improve the living conditions of aquatic animals in this area.

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.

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.

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. 

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.

Continuous monitoring and evaluation of surface water quality is necessary to protect the global ecosystem and human health. One of the most critical ways to estimate water quality is the WQI method. In order to check the water quality of the Maroon Dam lake located in Khuzestan province (15 km from Behbahan city), five sampling stations were selected at the inlet, outlet and inside of the lake. Sampling to measure the water temperature factor (with intervals of five meters by five meters from the surface to the bottom of the lake) and other factors such as dissolved oxygen, pH, biochemical oxygen demand, total phosphorus, total nitrogen monthly and from the surface to a depth of 60 meters (with distances of 20 meters by 20 meters) were carried out from October 2014 to September 2019 and finally the WQI index was calculated using qualitative parameters. The results of this study showed that the trend of changes in WQI index in different months of sampling in different stations in the quality class was medium to relatively good and the range of changes of this index was calculated between 49 in June to 66 in October. The depth measurement of temperature showed that in the lake behind the dam thermal stratification was created in spring (0 to 20 meters), summer and autumn (0 to 40 meters), but in winter, there is no such difference between surface and depth. According to the evaluation of the WQI index values of the reservoir water, it is suitable for all kinds of drinking purposes for domestic animals, agricultural purposes and raising resistant species of fish.

In this study, a comprehensive assessment of the occurrence and spatial distribution of heavy metals including Nickel, Lead, Zinc, Copper, Cadmium and Chromium, as well as, TPHs in the surface sediments of the coastal areas and far from the coast of the Persian Gulf in Bushehr and Khuzestan provinces were performed to identify the possible sources of sediment contamination and determining the degree of pollution. Eight pollution indices were used to evaluate the quality of sediments in terms of heavy metal and TPH pollution. The investigated areas could be distinguished by a significant degree of heavy metal pollution of Nickel, Cadmium and Zinc. High concentrations of Nickel and Zinc were observed in stations around Nakhiloo, Bushehr. The comparison of average pollution indices between regions showed that both Bushehr and Khuzestan provinces, respectively, with the average of contamination degree (CD) (20.25 and 22.11), modified contamination degree (MCD) (3.38 and 3.69), pollution load index (PLI) (31.17 and 57.57), potential ecological risk index (PERI) (353.54 and 349.39) have a significant degree and risk of Nickel and Cadmium pollution, especially in Nakhiloo area, Bushehr. Investigating the spatial fluctuations of the concentration of TPHs in two provinces showed an increasing trend from Bushehr to Khuzestan. However, areas were located in no pollution or low pollution zonation and were safe from the adverse biological effects of TPHs. Comprehensive and impressive strategies to control and reduce these pollutions, especially in polluted areas, should be considered, so that the sources of these pollutions be managed.

In this study, due to the importance of Doiraj Dam Lake, which supplies an important part of agricultural water of Dehloran and Mosian, the assessment of the lake water was carried out in order to develop aquaculture activities and investigate the possibility of fish farming in the lake behind the dam. For this, 4 stations selected, the entrance, before and ater the lake and sampling were done in three seasons by using Van veen grab with with 0.0625 m2. The results of this study were determined based on the biological indicators. In benthic indices, the quality of water was evaluated by determining the species composition and biological value of different species using Shannon-Wiener diversity indices and Hilsenhoff Family Biotic Index (HFBI). The HFBI index in the studied stations ranged from 3.07 to 6.07. In general, based on the biological indicators, in most of the stations and seasons, moderate pollution was observed, which was more evident in the stations before the dam due to its without move nature than the entry and after stations.

The object of this study was to investigate the status of physicochemical parameters and nutrients in demersal fishing grounds in the Iranian waters of the Persian Gulf from the Hormozgan province to Khuzestan province, from autumn and winter of 2017 to 2020. The local data of physical and chemical parameters of water were recorded and analyzed, by using a CTD (Conductivity, Temperature, and Depth)  device, during 2017, 2018 and 2020 years. Also, the sea surface temperature and chlorophyll-a were recorded from the MODIS (Moderate Resolution Imaging Spectroradiometer) satellite, aqua sensor, in 2018 and 2019 years. The average of remote sensing data of sea surface temperature and chlorophyll-a were 22.83 C° and 1.80 mg.m-3, respectively in the studied area, from 2018 to 2020. The average of local data of water temperature, chlorophyll-a, salinity and pH were 21.53 °C, 0.84 mg.m-3, 39.53 ppt and 8.28, respectively in the studied area during the years 2017, 2018 until 2021 winter. The average of concentrations of nitrate, phosphate and silicate were 0.034, 0.008 and 0.517 mg/L, respectively, in the present study. Based on the results, the amount of chlorophyll in the Persian Gulf has a relationship with the sea surface temperature and silicate. By increasing the sea surface temperature and concentration of silicate, the chlorophyll-a increases in the studied area. Changes in the concentrations of nitrate and phosphate had no significant effect on the concentration of chlorophyll-a in the studied area. The average of sea surface temperature and the concentrations of phosphate and silicate increased, but the concentration of chlorophyll-a and nitrite decreased from 2018 autumn to 2020 winter.