Abstract
We measured water quality, oxygen, and hydrogen stable isotopes and tritium concentrations in river water, irrigation water, and groundwater in irrigated areas of the middle basin of the Heihe River Basin, located in a semiarid region, in September 2008. Geochemical data clarified groundwater recharge and flow processes, including effects of human activity.
Similarities in inorganic solute concentrations and stable isotopes show that irrigation using river water of the Heihe River main stream recharges groundwater in the upper reaches. In middle reaches, groundwater samples showed similar geochemical composition and lower stable isotopic ratio than the river water. Lower isotopes in groundwater suggest that groundwater in the middle reaches is recharged by river water and by other sources. Branches such as the Liyuanhe River, which have lower isotopic ratios because of lower isotopic precipitation on the northeast side of Qilian Mountains, are possible groundwater sources in irrigated areas. Lower isotopic groundwater tends to have longer residence time, as inferred from low tritium concentrations. Results suggest that groundwater recharging in the middle reaches has two important origins: river water with short residence time via irrigation water and groundwater with long residence time recharged by branches on the northeast side of the Qilian Mountains.
