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

Document Type : Original Article


Iranian National Institute for Oceanography and Atmospheric Sciences, Chabahar, Iran


Introduction: Chabahar Bay is a semi-enclosed marine environment in the southeastern coast of Iran, with
two important ports i.e., Konarak and Chabahar in its margins. The connection of this Bay to the Indian Ocean
through the Gulf of Oman causes this region to be affected by the monsoon phenomenon, especially the
southwest monsoon, from late spring to late summer. Due to the expansion of various industries and increasing
marginal population, aquatic environments are expected to be severely affected by human activities. Sensitive
ecosystems such as coral reef habitats and mangrove forests are vulnerable to these changes. In this research,
the effects of the monsoon phenomenon on physicochemical parameters, nutrient concentration, and
chlorophyll-a (Chl-a) were studied. The possibility of nutrient loading through the ports of Konarak and Tiss
was examined by comparing the results from these ports with the adjacent stations in the Bay.
Material and methods: Sampling from two depths (0.5 m beneath the surface and 1 m above the bottom) at
4 stations was performed using 5l Niskin bottle in three replicates during five seasons. 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 standard instructions, and the amount of nutrients were
measured by spectrophotometer in a quartz cell with a path length of 2 cm. Statistical analyses were performed
using PRIMER 6 and STATISTICA 10 software.
Results and discussion: According to the acquired results, the concentration of phosphate, nitrite, and nitrate,
as well as Chl-a, were higher in the post-monsoon period and were in the order of post-monosoon > pre- monsoon> monsooon. In the case of silicate, its trend was different and showed a decreasing trend in the order of pre-monsoon> monsoon≈post-monsoon. Comparison of inter-annual results showed that the phosphate, nitrate, and nitrite values recorded in 2017 were higher than the corresponding values in 2013-2014. Chl-a showed a positive correlation with the nutrient concentration, which indicated that the primary production was controled by the nutrient availablity. The pH and dissolved oxygen values had a positive correlation and both were generally low in the pre-monsoon than the post-monsoon in both sampling periods of 2013-2014 and 2017.
Conclusion: Comparison of the results between 2013-2014 and 2017 showed that there were differences in nutrient concentrations and physicochemical parameters due to variations in the intensity and duration of the monsoon in different years. High concentrations of nitrate, phosphate, and nitrite in the post-monsoon season occurred due to the monsoon-induced upwelling and the emergence of nutrient-rich waters. Lower silicates in the post-monsoon than the pre-monsoon and monsoon seasons seems to be the result of the silicate depletion by diatoms that show outbreaks during this period, as the Chl-a in the post-monsoon was greater than the preceding seasons. Finally, the amount of nutrients was significantly higher in two marginal ports compared to adjacent stations in the Bay. However, they are still not at the stage to intensely elevate the nutrients levels throughout the Bay.


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