Consequence of Seawater Intrusion on Soil Properties in Agricultural Areas of Nonthaburi Province, Thailand

Seawater intrusion associated with climate change and sea level rise (SLR) has been postulated for the last decade that causes negative impact on worldwide environmental resources. In Thailand, however; the pertaining information to its effect on soil properties in agricultural areas has not been clearly reported yet. Hence, this study aimed to investigate the seawater intrusion effect on soil properties in agricultural areas of Nonthaburi Province, Thailand. Five study locations, which anticipated to be affected by seawater intrusion, were selected based on the different distances from the Chao Phraya River. Soil morphological properties at depth of 0-15 and 15-30 cm were recorded, besides disturbed soil samples at depth of 0-15, 15-30, 30-60, 60-90 and 90-120 cm were collected to determine the soil physical and chemical properties. Additionally, the soil electrical conductivity (ECe) and sodium adsorption ratio (SAR) analyses demonstrating soil salinity and sodicity were monthly conducted from March 2018 to February 2019 and their annual average values were calculated. The results revealed that all soils were deep to very deep, consisted of silty clay, clay textures, and its field soil pH varied from 6.0-8.0. Soil saturated hydraulic conductivity rating exhibited that it was very slow to moderate. ECe and SAR values of these soils ranged from 0.21-4.38 dS m-1 and 8.29-41.89 consecutively, which trended to increase from its annual average during March and April 2019 as well as July and August 2019. These results suggested that seawater intrusion could be presumptively regarded as a co-factor affecting the variability of soil salinity and sodicity occurring at the interval of insufficient freshwater content for forcing seawater. The implementation strategies for freshwater management and planning are required to prevent future potential seawater intrusion.