Modeling spatio-temporal variability of suspended matter and its relation with hydrodynamic parameters in the northern B
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ORIGINAL ARTICLE
Modeling spatio‑temporal variability of suspended matter and its relation with hydrodynamic parameters in the northern Bay of Bengal Md. Masud‑Ul‑Alam1 · Md. Ashif Imam Khan1 · Md. Nazrul Islam2 · S. M. Mustafizur Rahman1 Received: 12 October 2020 / Accepted: 10 November 2020 © Springer Nature Switzerland AG 2020
Abstract Variation of the non-algal suspended particulate matter (SM) was assessed, both on a spatial and temporal scale using satellite datasets. Located on one of the biggest deltas around the world, enormous rivers, and sediment discharge make this region’s suspended matters more prone to variations. Noticeable latitudinal transformations were found in SM as it ceased to exist after 21.5° N, with discrete seasonal changes that included summer SM concentration as high as 90–95 g/m3, while in winter it was 70–75 g/m3 on average near the river mouth. Such contrasting values are because of the variation in input from the nearby major rivers including Ganges–Brahmaputra, which in terms brings suspended load, particulate matters, nutrients, and other material fluxes along with it. However, other regions had a seasonally averaged concentration of 36 g/ m3. Temporal analysis of SM revealed that it consisted of an increasing pattern between 2004 and 2010, but it gradually altered to decreasing trends from 2012 to 2018. Secchi depth, chlorophyll-a, nitrate, phosphate, silicate, sea level anomaly, current speed, temperature, and salinity are the hydrodynamic parameters those are considered in this article to find which one is well correlated with SM. Nitrate and silicate proved a significant positive correlation with SM, whereas chlorophyll-a, salinity, and Secchi depths were negatively correlated over the whole period. Eventually, further wavelet analysis gave rise to an interesting sign of the SM on chlorophyll-a for specific regimes of the time. Keywords Suspended particulate matter · Spatio-temporal variability · Chlorophyll-a · Wavelet analysis · Bay of Bengal
Introduction Situated at the northernmost part of the Indian Ocean, the Bay of Bengal (BoB) encompasses one of the largest deltas in the world, which is interweaved with convoluted systems of rivers and several tidal channels. These rivers, and channels transport large quantities of sediments downstream that exceed annual loads of approximately 1.7 billion tonnes (Chowdhury and Zafar 2018). Coastal northern Bay of Bengal (NBoB) receives a seasonal freshwater influx of * Md. Masud‑Ul‑Alam [email protected] Md. Nazrul Islam [email protected] 1
Department of Oceanography and Hydrography, Bangabandhu Sheikh Mujibur Rahman Maritime University, Plot# 14/06‑14/23, Pallabi Mirpur‑12, Dhaka 1216, Bangladesh
Department of Geography and Environment, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh
2
1.625 × 1012 m3/year (Subramanian 1993), mainly through Himalayan-originated rivers. One of those rivers, the Ganges–Brahmaputra (GB) system single-handedly brings 0.6 × 1012 organic carbon per year (Galy et al. 2007).
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