Assessing the impact of agricultural practices on water quality in the Arenal-Tempisque Irrigation District, Costa Rica

This study assessed water quality in Costa Rica’s Arenal Tempisque Irrigation District (ATID) from 2017 to 2023, focusing on its agricultural importance and water resource challenges. Analyses of physicochemical parameters and 83 pesticides in dams, waterways, and wells revealed exceedances of national water quality standards for irrigation and consumption, particularly for biochemical oxygen demand, dissolved oxygen, ammonium, nitrate, and boron. Additionally, 22 pesticides, including herbicides (terbutryn, ametryn) and fungicides (carbendazim, tebuconazole), were detected, with some surpassing international guidelines. While the Dutch Index suggested water quality ranged from good to very poor, it was insufficient for a comprehensive evaluation. The lack of event-based sampling limited the assessment of precipitation impacts on pollutant transport. Future studies should incorporate event-driven sampling during and after heavy rains to better understand water quality dynamics, particularly under extreme weather conditions expected to intensify with climate change.