Irrigation‐induced evaporative water loss in a glacially derived soil site

Abstract

Worldwide, significant agricultural activities take place where groundwater is used for irrigation and water losses occur due to evaporation. Water loss through evaporation is affected by the soil type, local climate and most likely crop type. Previous studies from arid regions demonstrated the utility of oxygen and hydrogen isotopes in estimating evaporative water loss during return flow back to an aquifer. This study examined the region around Kalamazoo, Michigan, United States, where the soil is formed from glacial sediments and the region experiences a temperate climate. The present study is applicable to agricultural practices in many parts of the world that are in a temperate climate zone. The study area primarily uses centre‐pivot systems supplied by wells. Water samples were taken periodically from wells close to centre‐pivot irrigation systems. Knowledge of isotope ratios in precipitation, the primary source of groundwater recharge is a prerequisite for this study. The distribution of oxygen and hydrogen in local precipitation, the so‐called Local Meteoric Water Line, is available based on several years of measurements. An evaporative model of the isotope data indicates water loss from evaporation to be in the range of 14% and 6%. This is less than what was estimated for arid region zones and is perhaps also due to the well‐drained nature of the regional soil which promotes rapid infiltration lowering evaporation. Evaporative loss was greater at wells near cornfields than at wells that supplied other crop types. Little expected correlation between the groundwater isotope data and chloride concentration is attributable to an external input of chloride from road salt used in winter months.