A Spatial and Seasonal Pattern of Water Quality in the Sundarbans River Systems of Bangladesh

Abstract

Rahaman, S.M.B.; Rahaman, M.S.; Ghosh, A.K.; Gain, D.; Biswas, S.K.; Sarder, L.; Islam, S.S., and Sayeed, A.B., 2015. A spatial and seasonal pattern of water quality in the Sundarbans river systems of Bangladesh. Journal of Coastal Research, 31(2), 390-397. Coconut Creek (Florida), ISSN 0749-0208.Comprehensive field measurements were made in three major river systems (RSs) of the Sundarbans during October 2010 to August 2011 under post-monsoon, dry winter, and monsoon seasons to assess the pollution status. Fifteen experimental sites were set for collection of water samples from discrete layers under different tidal conditions. Salinity, temperature, pH, and dissolved oxygen (DO) were determined in situ and chemical oxygen demand (COD), biological oxygen demand (BOD), total nitrogen (TN), total phosphorus (TP), nitrate, phosphate, and ammonium were measured through laboratory analysis. Mean DO was recorded between 3.93 and 7.37 mg/L with an average 5.44 mg/L. Highest average DO was noticed at Rupsha-Passur RS during post-monsoon, whereas the lowest was in Kholpetua-Arpangashia RS during monsoon. Mean BOD ranges between 0.3 and 4.1 mg O 2 /L, with an average of 2.04 mg O 2 /L, where maximum and minimum concentrations were measured at Kholpetua-Arpangashia RS in monsoon and dry winter respectively. Mean COD was found to vary from 20 to 240 mg O 2 /L, with an average 121.33 mg O 2 /L, exceeding the permissible range of 4-8 mg O 2 /L. Rupsha-Passur RS shows lowest average COD during post-monsoon, whereas Kholpetua-Arpangashia RS indicated highest COD in winter. Measured COD was higher in the dry season than in the wet season because of precipitation that causes dilution in the RSs. The study indicates the existence of organic pollution, though the DO concentration was within the permissible limit. Analyzed water samples showed nitrate, phosphate, and ammonium values in the range of 0.083 6 0.03 to 0.627 6 0.42 mg/L, 0.011 6 0.005 to 0.449 6 0.26 mg/L, and 0.038 6 0.018 to 0.176 6 0.16 mg/L respectively. TN and TP concentrations were not high enough in most cases, as there is a chance of eutrophication due to algal pollution. Study results will help identify factors responsible for affecting the biodiversity of the Sundarbans intertidal mangrove forest.ADDITIONAL INDEX WORDS: Sundarbans, BOD, COD, nutrients, mangrove forest, aquatic ecosystem, organic pollution.

Modelling spatial biodiversity in the world’s largest mangrove ecosystem—The Bangladesh Sundarbans: A baseline for conservation

“…The average soil salinity has already increased by 60% since 1980 (Aziz & Paul, ). Opportunistic harvesting of trees and heavy siltation in the internal channels are ongoing (Rahaman et al, ). Therefore, our findings lead us to conclude that additional harvesting, siltation, cuts in freshwater supply and range expansions of the generalists under projected sea level rise (Karim & Mimura, ) may convert the whole Sundarbans into a species‐poor homogeneous ecosystem.…”

Assessment of coastal surface water quality for irrigation purpose

“…The coastal belt of the country is facing enormous challenges in meeting freshwater demand due to limited water supply from the groundwater and surface water sources as they are affected by the various degrees of salinity and other water quality problems (Chowdhury et al 2014). Reports showed that about 53% of the coastal watersheds of Bangladesh are affected by various degrees of salinity (Minar et al 2013;Rahman et al 2015). The problem becomes intensified due to some climate change-associated hazards like sea-level rise, riverbank erosion, land accretion, insufficient and irregular rainfall, cyclones, tidal surges, and so on.…”

“…Therefore, the irrigated waters can affect plant growth through toxicity, nutrient deficiency, or altering plant availability of nutrients (Ayers & Westcot 1985). A few studies have revealed that Kalapara is one of the vulnerable mid-coastal watersheds of Bangladesh with high to moderate degrees of salinity (Rahman et al 2015). These studies mainly focused on seasonal variations of salinity, the impact of salinity on agriculture, fisheries, land uses, crop production, and so on.…”

Assessment of Temporal Variation of Water Quality Parameters and the Trophic State Index in a Subtropical Water Reservoir of Bangladesh

“…Sirajul Islam, Yousuf Ali, M. Humayun Kabir, Rofi M. Zubaer, Nowara Tamanna Meghla, Mausumi Rehnuma, Mir M. Mozammal Hoque (Islam et al, 2017;Islam et al, 2019). Thus, the nutrient concentration must be within suitable limit for a good aquatic environment and for better production of aquatic organisms (Rahaman et al, 2015). In the past decades, limnologists have developed many methods to assess the trophic status, including the character method (Rao, 1956), parameter method, the biotic indices method (Alba-Tercedor, 1996), the phosphorus budget model method (Dillon and Rigler, 1974) and the trophic state index method (Carlson, 1977).…”