Abstract
Despite its complexity and importance in managing water resources in populous deltas, especially in tidal areas, literatures on tidal rivers and their land use linkage in connection to water quality and pollution are rare. Such information is of prior need for Integrated Water Resource Management in water scarce and climate change vulnerable regions, such as the southwestern coast of Bangladesh. Using water quality indices and multivariate analysis, we present here the land use signatures of a dying tidal river due to anthropogenic perturbation. Correlation matrix, hierarchical cluster analysis, factor analysis, and bio-geo-chemical fingerprints were used to quantify the hydro-chemical and anthropogenic processes and identify factors influencing the ionic concentrations. The results show remarkable spatial and temporal variations (p < 0.05) in water quality parameters. The lowest solute concentrations are observed at the mid reach of the stream where the agricultural and urban wastewater mix. Agricultural sites show higher concentration of DO, Na+ and K+ reflecting the effects of tidal spill-over and shrimp wastewater effluents nearby. Higher level of Salinity, EC, Cl−, HCO3−, NO3−, PO43− and TSS characterize the urban sites indicating a signature of land use dominated by direct discharge of household organic waste into the waters. The spatial variation in overall water quality suggests a periodic enhancement of quality especially for irrigation and non-drinking purposes during monsoon and post-monsoon, indicating significant influence of amount of rainfall in the basin. We recommend that, given the recent trend of increasing precipitation and ground water table decrease, such dying tidal river basins may serve as excellent surface water reservoir to supplement quality water supply to the region.
Highlights
River water chemistry is controlled by many natural and anthropogenic factors
Weathering effects are weak in the stream, effects of soil leaching and runoff are evident
Hierarchical cluster analysis (HCA) and factor analysis (FA) performed on the river water samples depicted three distinct water groups based on major ion composition; urban wastewater, agricultural runoff and mixed water
Summary
River water chemistry is controlled by many natural and anthropogenic factors Anthropogenic factors such as land use is well known as one of the major influences on the hydrochemistry of the rivers (e.g., Rothwell et al 2010; Pratt and Chang 2012; Huang et al 2013a, b, etc.). Quantifying the major ion composition of stream waters has broad implications, i.e., water type, hydrogeology characteristics, weathering processes and rainfall chemistry. These researches featured in scientific literatures over 50 years (e.g., Gibbs 1970; Brennan and Lowenstein 2002; Nordstrom 2011). Understanding how land use and land cover change influence the flow and water quality of rivers is of utmost importance for river management and restoration (e.g., Barbosa et al 2012; Huang et al 2013a, b)
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