Sources of monsoon precipitation and dew assessed in a semiarid area via stable isotopes

Precipitation is usually the primary source of water for the hydrological cycle in a semi-arid area. However, dew occurs frequently and affects water circulation dramatically in the west of Jilin Province in China. Measurements of the amount of dew formed and precipitation were carried out from July 2012 to October 2013 in the Momoge Natural Reserve. The results indicated that moisture from primary precipitation in the summer originated from the East Asian Monsoon and was affected by the atmospheric circulation in the middle and high latitudes of Eurasia in the winter. The dew amount was approximately 19.44 mm (approximately 5% of the total rainfall amount), consisting of the evapotranspiration in the local area and atmospheric moisture. Dew also supplies nutrients to the local vegetation. The maximum contribution of total nitrogen (TN), total phosphorus (TP) and potassium (K) in unit corn area could reach 288.60 mg/m2, 27.46 mg/m2 and 291.63 mg/m2 in half a month, respectively. The wind speed, relative humidity and lowest temperature were the primary factors that dramatically affected dew formation and amount. As an additional source of fresh water, dew not only had a positive impact on the ecosystem in arid and semi-arid zones but also played an important role in the local water cycle and other ecological processes. This research has important implications for water circulation and land use management.