LANZHOU－Wang Hansheng, a shepherd-turned-ranger, patrols a wetland nature reserve where he used to herd sheep. Over the past decade, he has witnessed the area's transformation from a salinized riverbed to a restored wetland ideal for wintering birds.

Wang, 57, works at the Heihe Wetland National Nature Reserve in Zhangye city, Gansu province, in the arid region of northwestern China. The reserve covers more than 40,000 hectares at the middle stretches of the Heihe River, China's second-largest inland river.

Before taking up the role of wetland ranger in 2010, Wang, like many other local farmers, had been grazing sheep on the dry riverbed of the river.

Back then, the river was no more than a few small streams flowing in a 350-meter-wide channel due to serious water shortages caused by excessive water use upstream, Wang recalled.