Large Scale Evaluation of Water Conservation Zones for Water Quality Improvements and Biomass Production in Northern Iran

摘要

Water scarcity and uneven distribution of rainfall are the most mportant limiting factors for the development of agriculture in Iran, order to assess water quality, quantity and characterize seasonal variation in isotopic signatures of oxyge-18 (6180)and hydrogen-2 (6D), a study was conducted during 2010 to 2011 in 30 different ponds in the north of Iran (Ab-bandans). Water samples were collected in winter, spring and summer of 2010 and 2011 and analysed for chemical and isotopic compositions. Datashowed that highest 80and 6D were recorded in summer (-1.15%o and -12.11%o for 6,80 and 6D) and the lowest 6180 and 6D were recorded in winter (-7.50% and -47.32% for 6180 and 6D), respectively. The 6180 and 6D signatures showed that the water at the Ab-bandons were enriched from spring (-3.57 and -27.72%) to summer (-1.15 and -12.12%), respectively. The relationship between 6180 and 5D for pond water and local/global precipitation showed that rainfall and snowmelt can be a major source of water for these Ab-bandans. Water and nutrient balance based on input, output and storage showed that on average 7.6 million cubic meters of water along with 86 tonnes of nitrogen (N) and 17 tonnes of phosphorus (P) were captured and stored by these ponds and are available for irrigating downstream rice crops. Flood irrigation of this water at a rate of 10 000 m3/ha over the growing season (April to September) was able to produce rice in an area of 730 ha with a yield of 3.5 t/ha. However, changing the irrigation method from flood to an eight-day irrigation interval was able to cultivate 1500 ha with similar yield and significantly increased water use efficiency by 53%. The results of the study are useful to identify the sources of water in the pond and to improveland and water management practices to optimize the capture and storage of water and nutrients for downstream irrigation.