Is groundwater sufficient to support sustainable irrigation agriculture in a reclaimed wetland region?

Abstract. Water resources management is the key to sustainable agriculture and wetlands ecosystems. Understanding whether agriculture with groundwater-dominated irrigation is sustainable is sometimes difficult due to complex hydrological conditions, e.g. in the case of a wetland region. To investigate this issue we have chosen a wetland and rice paddy fields co-existing area with a groundwater-dominated irrigation scheme in the Sanjiang Plain, NE China, which has been reclaimed from lake-swamp type of natural wetlands since the 1950s. Using a multi-tracer approach involving water chemistry and isotopes (²H, ¹⁸O, ³H, ¹³C, ¹⁴C), integrated with data on groundwater regime, we demonstrate that it is possible to delineate the mechanism of hydraulic interactions between groundwater and river, ponds and rice paddy fields in the wetlands terrain. Regional variations in hydrogeology have been found to be the main factors controlling groundwater recharge and regime. Groundwater in the confined Quaternary aquifer with ages over 50 years and evidenced by depleted heavy isotopes is recharged by lateral flow from nearby mountains. The groundwater is in general not affected by surface activities, however, its yield is limited. Groundwater alone is not sufficient to support sustainable irrigation agriculture. On the contrary, the unconfined Quaternary aquifer is recharged by rainfall or riverbank infiltration, especially at localities near the rivers. It is more likely for the groundwater to be affected by agricultural activities, though its yield is rather abundant. This paper also indicates that utilization and planning of water resources for reclaimed agriculture can be improved through hydrological studies using environmental tracers.