Spatio-temporal variability in soil and water salinity in the south-central coast of Bangladesh.

[Display omitted] • Salinity varied with time, space, topography and land use activities. • Salinity decreased with increasing distance from the coastline of the Bay of Bengal. • Polder restricts direct salinization of coastal soils. • Landsat imagery based salinity indexes can reliably predict soil salinity. • A large coastal area turned into saline in the last few decades. Salinity in soils and water of coastal tracts in Bangladesh, one of the major challenges for agriculture, varies significantly due to multiple stressors, including the consequences of rapid changes in the climate pattern. However, their dynamics has not been studied in detail accentuating its importance for the management of agriculture. Here, we examined such changes along zones - defined by spatial proximity from the seafront towards inland in the south-central coast of Bangladesh. Samples of soil and water were collected at single-month intervals between November 2020 and June 2021. In April, a comprehensive soil sampling was conducted to examine spatial variability in relation to soil type and land use. Moreover, Landsat imagery-based salinity index was calculated. Our results showed that soil and water salinity gradually increased from January onwards and peaked during May. It decreased gradually from the seafront to inland, suggesting direct and indirect intrusion of salinity from the sea. A significant non-linear relationship was found between Landsat imagery-based salinity index and measures values (r2 = 0.79, p < 0.01), indicating the Landsat imagery- based estimate could potentially be used for agriculture. Our observation also showed that salinity to soil and water was significantly low in highlands, croplands, and interior of polders as compared respectively to that of low land, fallow land, and exterior of polders. Our estimation of salinity in soil and water of the south-central coast of Bangladesh was significantly higher than that of historical records. This study, thus, would contribute to contemporary policy issues on cropland management along coastal Bangladesh. [ABSTRACT FROM AUTHOR]