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Impact of Rainfall on Spatio-temporal Distribution of Sediment Organic Matter Along the Chittagong Coast, Bangladesh

Avijit Talukder
Department of Marine Bio-resources Science, Chittagong Veterinary and Animal Sciences University, Chittagong 4225, Bangladesh.

Debbrota Mallick
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong 4331, Bangladesh.

Shamindra Nath Mandal
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong 4331, Bangladesh.

Ishrat Zahan Anka
Department of Aquaculture, Chittagong Veterinary and Animal Sciences University, Chittagong 4225, Bangladesh.

Milan Kumar Shiuli
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong 4331, Bangladesh.

Tasnuba Hasin
Department of Fisheries Resources Management, Faculty of Fisheries,, Chittagong Veterinary and Animal Sciences University, Chittagong 4225, Bangladesh.

Shubha Sarker
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong 4331, Bangladesh.

Abstract/ Executive Summary:

Sediment organic matter regulates the coastal biogeochemical cycle which is influenced by rainfall pattern and has potential relationship with organic carbon as well as mud characteristics. The objective of present research was to identify the impact of precipitation on the spatio- temporal variation inorganic features of intertidal mudflats. Three locations were selected in freshwater zone; two were in brackish water region and last three locations situated in marine waters from Halda to Salimpur coast. Two sites from each location were designated as the highest high tide level (onshore) and lowest low tide level (offshore) of the intertidal zone during winter (December to February) and monsoon (June to August) spanning between 2013 and 2014. Sediment organic matter and carbon were measured by combustion and Walkey-Black wet oxidation in turn. Average organic matter content in monsoon were found 4.5±0.03, 2.3±0.01 and 2.4 in freshwater, brackish and marine locations whereas 5.2±0.6, 3.9±0.14 and 5.4±0.04% investigated during winter. Precipitation pattern varies from different seasons and locations that have impact on land runoff, freshwater inflow, mixing and circulation. Mud dominated coastal intertidal zones represented high organic matter content than sand dominated coast. Furthermore, depositional pattern, transport, erosion-accretion processes, tidal action, wave characteristics and seasonal inconstancy control the organic matter characteristics in the coastal sediment. This research suggests the necessity of periodic observation of rainfall pattern and organic matter distribution to assess the intertidal deposits which support the stabilization of local geomorphology and biogeochemistry in Chittagong coastal region.

Keywords: Biogeochemistry, Organic matter, Precipitation, Spatio-temporal variation

Location: Chittagong coastal region.

Start Date: 00-00-2013

End Date: 00-00-2014

Program Area: Crop-Soil-Water Management

Non-commodity: Rainfall

Objectives:

To identify the impact of precipitation on the spatio- temporal variation inorganic features of intertidal mudflats.

Methodology:

Eight distinct locations were selected to conduct the research. Three freshwater locations Halda (22°25'59"N, 91°52'20"E), Karnafully (22°25'50"N, 91°53'13"E) and Chaktai (22°19'42"N, 91°51'11"E) were designated due to inland runoff and freshwater inflow. Besides, two brackish water locations Saderghat (22°19'32"N, 91°50'12"E) and 15 No. Ghat (22°14'31"N, 91°49'12"E) were selected having moderately saline zone, intertidal mudflat and marsh communities. Two brackish water locations were in the Karnafully river estuary and selected due to disposal characteristics of sediment along the river bank. Three marine locations Patenga (22°13'49"N, 91°47'40"E), Khejurthalighat (22°21'05"N, 91°45'18"E) and Salimpur (22°24'00"N, 91°44'24"E) were chosen. Patenga sea beach is characterized with more extended sand dominated beach without any prominent vegetation. Khejurthalighat characterized with salt marsh, mangrove plant communities was selected for mixed sediment type beach and long intertidal zone characteristics. In contrast, last location Salimpur was designed on account of extended thick sediment bed, creek networking, mangrove and salt marsh communities. Replication of sample was collected from two sites of each location during low tide of monsoon and winter season. Samples were taken at schedule basis during the new moon phase of hydrological year 2013 to 2014. Sediment corer used to collect sediment sample having the diameter of 10 cm and 20 cm in length. Collected sediment samples were kept into polythene container (500 g). Later they were spread on sheet of trays and dried in air at laboratory. Larger aggregates were broke preferably in a wooden mortar and pestle and passed through a 0.5mm sieve. Processed sediment sample were preserved in low temperature (>25°C) in the plastic pack for further analysis. Sediment organic matter was measured by combustion process and other sediment quality parameters also measured by standard methods (APHA, 2005). Organic carbon was determined by Walkey and Black wet oxidation method modified. Precipitation data of the respective year along the Chittagong coast was recorded from Patenga station and collected from Bangladesh Meteorological Department. Data were analyzed by IBM SPSS 22.00 software for statistical analysis, such as seasonal variation, Two Way ANOVA, bivariate analysis; box and whisker plot. Analysis of variance test established relationship among precipitation trends with various seasons and locations; also showed impact of rainfall on sedimentological characteristics. Bivariate analysis demonstrated significant relationship among various sedimentological parameters. Box and whisker plot was used to demonstrate the variation in characteristics of sediment organic matter and organic carbon from mean value.

Source of Information: Res. Agric. Livest. Fish., Vol. 3, No. 1, April 2016: 175-186

Article Link (Online Journal): DOI: http://dx.doi.org/10.3329/ralf.v3i1.27876

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The findings indicated that the variability of organic matter occur due to anomalous characteristics of rainfall pattern except the Patenga. Patenga sea beach was highly fine sand dominated with ignorable fraction of clay and silt. Contrariwise, fine grained dominated locations revealed more organic matter and carbon content than other locations. In the 15 No.Ghat, the concentration were in moderate level due to less clay and silt dominancy than Salimpur and Khejurthali location. The results of this study imply that, coastal sediment trapped in continental shelf margin during low energy season and washed away partially at high energy season. Surface sediment from all locations washed away due to land drainage and heavy precipitation rate which decreased the rate of organic matter and carbon during monsoon. Huge amount of sediment accumulate during winter season which is crucial for organic matter and carbon accumulation processes. Therefore, much attention should be paid to the intertidal surficial sediment for monitoring biogeochemical processes of the Bay of Bengal.

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