Agricultural Irrigation Induced Evaporative Water Loss in a Temperate
Climate Study Site: a Stable Isotope Approach
Abstract
Worldwide, significant agricultural activities take place in temperate
climate zones In regions where groundwater is used for irrigation, water
losses take place due to evaporation. Previous studies demonstrated the
utility of stable oxygen and hydrogen isotopes in estimating evaporative
water loss experienced during return flow back to an aquifer. Unlike
arid regions where the other studies took place, this study examined the
region around Kalamazoo, Michigan, the United States, which experiences
a more temperate climate.. Irrigation in the Kalamazoo area primarily
uses center-pivot systems supplied by wells, unlike flood irrigation in
previous study areas. Water samples were taken periodically from wells
close to center-pivot irrigation systems. Water losses due to
evaporation were estimated using stable oxygen and hydrogen isotopes,
which are effective tracers for water. This approach was possible in the
Kalamazoo area since the distribution of oxygen and hydrogen isotopes in
local precipitation, which is the source of groundwater recharge, is
known based on years of measurements. The link between agriculture and
meteorology is thus clear. Isotope analyses during the irrigation season
suggest water loss due to evaporation is in the range of 9.1% and
14.3%. This is less than what was estimated by previous studies in arid
climate zones. Evaporative water loss was greater at wells near
cornfields than at wells that supplied other crop types. There was
little expected correlation between the groundwater’s isotope ratio
values and the change in chloride concentration. This is likely due to
an external input of chloride from road salt used in winter months.