Environmental Study on a Coastal River of Bangladesh with Reference to Irrigation Water Quality Assessment: A Case Study on Shailmari River, Khulna
2016
Water quality is the critical environmental determinant that influences the
agricultural production and therefore, the economy that solely depends on its
agricultural productions. Batiaghata Upazilla is one of the major crop
productive areas of Khulna region and the agricultural production here largely
depends on the natural water of the Shailmari River system around it. The
present study was conducted to assess the suitability of this coastal river
water for irrigational use. 66 water samples were collected during this study
in three consecutive agricultural seasons, viz., pre-monsoon (22), monsoon (22)
and post-monsoon (22) from 11 sampling stations within the river system considering
the high (11) and ebb (11) tides for each station. Standard methods were followed
throughout the study period for the collection of the samples and analysis of
major physicochemical parameters (pH, EC, TDS, salinity, Na, K, Ca, Mg, Cl, HCO3,
SO4, NO3 and PO4). Hydrocehmical characterization
using Piper trilinear diagram shows that the water of the river system is Na-Cl
dominated saline water type in pre-monsoon, whilst most of the samples of the
river and the connected channel are characterized as fresh water of Ca-Mg-Na-HCO3 and Ca-Na-Mg-HCO3 types in monsoon and post-monsoon respectively. The
calculated values of chemical indices like SAR, %Na, KI, PI and MH using the
results of the analysed parameters indicate that the river water is chemically
unsuitable for use in irrigation during pre-monsoon, while in the monsoon and
post-monsoon the river water is within good to permissible limit for the use in
the agricultural fields. However, high %Na, KI and MH values with high salinity
of the channel water limit its use in agricultural applications in monsoon and
post-monsoon. The USSL (United States Salinity Laboratory) diagram depicts that
the river water is C4-S4 type with very high salinity and sodium content in
pre-monsoon, while in other seasons the water is mostly C1-S1, C2-S1 or C2-S2 types
(low to moderate salinity and sodium) in the river. Wilcox diagram shows that
the river water is “suitable” for irrigation during monsoon and post-monsoon as
the most of the samples range within “Excellent to Good” and “Good to
permissible” categories, while it is “unsuitable” for crop irrigation during
pre-monsoon when SAR (Sodium Adsorption Ratio) and EC (Electrical Conductivity)
values of the water reach to their peaks.
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