A Study on the effects of Monsoon phenomenon on physicochemical parameters, nutrients and Chl. a in Chabahar Bay

Chabahar Bay is a semi-closed environment in the southeastern coast of Iran, with two important ports of Konarak and Chabahar in its margins. The connection of this Bay to the Indian Ocean through the Oman Sea causes this region to be affected by the Monsoon phenomenon, especially the southwest Monsoon, in the late spring to late summer. On the other hand, with the expansion of various industries and increasing marginal population, it is expected that aquatic environment and, as a result, sensitive ecosystems such as coral habitats and mangroves, as well as water desalination plants affected by human activities. In this research, the effects of the Monsoon phenomenon on physicochemical parameters, nutrient concentration and Chl a will be studied. Also, the possibility of the effect of loading nutrients through the ports of Konarak and Tiss will be examined by comparing the results from these ports with the adjacent stations in the Bay.

Sampling from 4 stations in the Bay in two depths (0.5 m beneath the surface and 1 m above the bottom) was performed using five liters Niskin bottle in three replicates. Physicochemical parameters were measured by relevant portable probes at the sampling site. In the laboratory, the reagents were prepared for colorimetric detection according to the instructions (MOOPAM, 1999), and the amount of nutrients were measured by spectrophotometer in a quartz cell with a path length of 2 cm. Statistical analysis were performed using PRIMER 6 and STATISTICA 10 software.

According to the acquired results, the concentration of phosphate, nitrite and nitrate, as well as chlorophyll a, are higher in the post-monsoon period and are in the order of post-monosoon > pre-monsoon> monsooon. In the case of silicates, this trend is different and is as pre-monsoon> monsoon≈post-monsoon. Comparison of inter-annual results shows that the phosphate, nitrate and nitrite values in year 2017 were more than the corresponding values in 2013-2014. Chlorophyll a indicates a positive correlation with the nutrient concentration, which indicates that the primary production is controledl by the nutrients availablity. The pH and DO values have a positive correlation and both are generally less in the pre-monsoon than the post-monsoon in both sampling periods of 2013-2014 and 2017.

Comparison of the results between 2013-2014 and 2017 shows that there is a difference in nutrients and physicochemical parameters due to differences in the intensity and duration of the monsoon in different years. High concentrations of nitrate, phosphate and nitrite in the post-monsoon season are due to the monsoon-induced upwelling and the emergence of nutrient-rich waters. Lower silicates in the post-monsoon season than the pre-monsoon and post-monsoon seasons seems to be the result of the silicate depletion by diatoms that blooms during this period, as the Chl a in the post-monsoon is greater than the preceding seasons. Finally, the comparison of nutrients in two marginal seaports with adjacent stations in the Bay shows that the amounts are significantly higher. However, they are still not at the stage to intensely elevate the nutrients levels in the Bay.