Evaluation of simple algorithms for spatial interpolation of salinity hazard parameter in natural waters.

Aggressive cultivation practised across the Indian subcontinent to meet the growing food demands results in the groundwater at many places being severely affected by salinity, and this is a recognised hazard of agricultural belts. Evaluating spatial variations of salinity hazards is important for managing agricultural activity and implementing suitable and timely remedial measures. A precise representation of spatial variations of groundwater salinity using electrical conductivity (EC) can help identify potential sources and evaluate their severity and spatial impact. Simple spatial interpolation schemes, viz., inverse distance weighted (IDW) and trend surface analysis (TSA) are evaluated with over 250 EC measurements in groundwater during two seasons from saline-impacted regions of northwest India. Considering the three performance metrics, namely, correlation coefficient, root mean square error and mean absolute error, IDW scheme was adjudged better than TSA for both seasons. Interpolation by TSA and contour plot using OriginLab^® software resulted in unrealistic (negative) values of EC, whereas IDW was free from such limitations. Errors associated with IDW-based interpolated EC values for this site would be 320–415 μS/cm for pre-monsoon and 630–800 μS/cm during post-monsoon seasons. Refined EC map generated using seasonal IDW interpolation scheme would facilitate timely and cost-effective remediation of salinity hazard, impact assessment of point and non-point sources on salinity hazard. Research highlights: Simple algorithms were examined for spatial interpolation of groundwater EC; IDW was adjudged better over TSA. Seasonal influence on interpolation parameters for EC was highlighted. IDW parameters ascertained from systematic search in this study are different from reported default values in commercially available software. Whereas TSA or default interpolation with OriginLab® resulted in negative(unrealistic) EC values, IDW results were consistent. Refined EC map generated using seasonal IDW interpolation scheme would facilitate: timely and cost-effective remediation of salinity hazard; impact assessment of point and non-point sources on salinity hazard. [ABSTRACT FROM AUTHOR]