Evaluation of Groundwater Electrical Conductivity Regarding Rice Cultivation in Guilan Province, Iran

Considering Sefidrud River discharge decrease in the last decade in Guilan province in the north of Iran, groundwater and surface water resources can meet the water demand of rice cultivation in this area. It is evident that irrigation water quality should be considered in rice cultivation. Electrical conductivity (EC) is one of the essential parameters of assessing the quality of groundwater. The purpose of this research is to identify areas at risk of groundwater EC decrease for rice cultivation. For this purpose, zoning and probabilistic maps were prepared by ArcGIS software. The models were evaluated using ME, RMSE, MSE, RMSSE, and ASE statistical indices. The accuracy of the models was very good; the RMSE values for ordinary kriging were between 0.2674 and 0.4172 dS/m, and for indicator kriging, they ranged from 0.2841 and 0.4087 dS/m. The zoning and probabilistic maps showed an increase in EC of more than 1 dS/m from 2002 to 2015. In addition, the highest EC in Guilan province was in the central and eastern parts of the province, including Rasht, Astaneh, and Lahijan cities. More than 30% of groundwater resources were exposed to excessive salinity exceeding rice's tolerance level. Therefore, to prevent the quality mitigation of groundwater resources in the province and prevent yield penalty related to irrigation water salinity, the regional water companies should take appropriate management measures such as a ban on digging new wells or reducing groundwater extraction in hazardous areas.