Effects of nutrients on the primary production and determination of the restricting factors in primary production in the international wetland of Choghakhor (Iran)

Limitations in nutrients and physicochemical parameters play a key role in aquatic ecosystems. The present study aimed to determine the influential physicochemical factors in the chlorophyll-a content for wetland management by identifying the restricting factors in primary production. Sampling was conducted during March 2017-February 2018. Factors such as water salinity, temperature, pH, nitrate and phosphate concentrations, biochemical oxygen demand, total dissolved solids, electrical conductivity, total suspended solids, and dissolved oxygen were measured in triplicate at each station. In addition, the trophic state index (TSI) was used to determine the trophic state of the wetland. No significant difference was observed in chlorophyll-a contents in different seasons (P>0.05), with the highest values reported in spring and autumn, and the lowest values reported in summer. The maximum and minimum chlorophyll-a content were observed in stations A and C, respectively. Station A had a significantly higher value compared to the other stations (P<0.05). In addition, no significant differences were observed in the water physicochemical parameters in different seasons (P>0.05). The highest (5.9 mg/l) and lowest water nitrate levels (4.1 mg/l) were observed in spring and autumn, respectively (mean nitrate level: 4.84 mg/l). The highest (2.1 mg/l) and lowest water phosphate levels (0.47 mg/l) were observed in spring and autumn, respectively (mean nitrate level: 1.04 mg/l). Moreover, TSI indicated that the wetland is oligotrophic in spring and winter, while it is mesotrophic in summer and autumn. Overall, the nitrate level in water was the main restricting factor in the management of Choghakhor wetland.