Assessment of the Impact of Reclaimed Lands for Rice Fields on Water Budget and Quality for Sustainable Agriculture in Northeast China: Using Isotopic Tracers

摘要

The Sanjiang Plain in Northeast China is one of the main grain production areas in the country and is supporting a rich biological diversity. However, the wetlands and forest lands have shrunk to one Ih of their original size in the last five decadesbecause of increasing population and land reclamation for agriculture. A major part of the reclaimed land has been used for rice production (rice wetlands). Sustainable management of these rice wetlands is important to protect water resources. Isotopic signatures of oxygen-18 (delta 0-18,6180) and hydrogen-2 (62H), water chemistry and depth of groundwater were monitored on three farms, namely, Honghe (HH), Qianfeng (QF) and Qianshao (QS). Results showed that the 6180 for groundwaters in all three farmsvaried from -8.8 per 1000 (expressed as mil, %o) to -13.8% with an average of -12.4%. However, 6180 for groundwater from a single farm showed large variations, suggesting a complex source and mixing in the groundwater. Groundwater nitrate (NO3") levels underneath these rice wetlands were less than baseline values (6 mg N037L) suggesting that NO3" contamination of groundwater under the Sanjiang Plain wetlands is not a major environmental issue. The groundwater 6180 in HH (-12.9%) and Qf(-13.0%o) farms showed that lateral groundwater flow probably dominates the groundwater recharge. However, the groundwater on the QS farm is uniformly enriched with an average 6180 of -12.2&. This suggests that the aquifer on the QS farm is probably influenced by the vertical infiltration, and there exists a strong groundwater-surface water interaction. The results have important implications for wetland reclamation and agricultural production on the Sanjiang Plain.