题　  目：Comparison of Irrigated Agriculture in the US High Plains and North China Plain

报 告 人： Dr. Bridget R.Scanlon

时 间：2010年7月15日（周四）下午 13:30

地 点：地理科学馆411会议室

Present Position:

Senior Research Scientist, Bureau of Economic Geology, The University of Texas at Austin

Academic Background:

• 　　 B.S. Geology, Trinity College, Dublin, Ireland, 1980
• 　　 M.S. Geology, University of Alabama, 1983
• 　　 Ph.D. Geology, University of Kentucky, 1985

Areas of Expertise:

• 　　 Evaluation of the impact of climate variability and land use change on groundwater resources.
• 　　 Application of numerical models for simulating variably saturated flow and transport.
• 　　 Assessment of natural and anthropogenic contamination of aquifers, including arsenic and nitrate.

Abstract:

Irrigation is widespread in the US High Plains and the North China Plain (NCP) with large scale depletion of groundwater resources during the past few decades. Comparison of these two regions can provide insights into controls on water quantity and quality issues related to irrigation practices and paths toward sustainable irrigation management. Irrigation in both regions consumes up to 90 – 95% of the water supply. Irrigation in the NCP was primarily supplied by surface water originally in the late 1950s and early 1960s. Groundwater-fed irrigation has been expanding since the 1960s and currently supplies up to 80% of irrigation water in some regions. Groundwater level declines ≤ 0.7 m/yr were recorded in many regions, resulting in stream channels drying up. Irrigation in the US High Plains is derived primarily from groundwater with water table declines ≤1.4 m/yr in areas of intense irrigation where the aquifer was originally thick. Soil water salinity in the NCP is generally low and is attributed to relatively high quality irrigation water and application of sufficient water to flush salts. Irrigation water is applied in the winter to wheat whereas most precipitation occurs during the summer monsoon; therefore, precipitation can also flush salts that accumulate from irrigation.

In contrast, irrigation water in the southern High Plains, the area of most intense groundwater depletion has relatively high salt load and large salt bulges (Cl, ClO4, SO4) are accumulating in the soil profile. These salt bulges are building up faster, at decadal timescales, than the rate of salt accumulation under natural ecosystems, at millennial timescales. The accumulation of salts is attributed to poor quality irrigation water, deficit irrigation, and lack of flushing from precipitation which is coincident with crop growth and irrigation in the summer. Both the NCP and the High Plains record large accumulations of nitrate in the soil profile, which are attributed to over application of fertilizers and failure to account for nitrate in irrigation water. Both systems are evolving from initially open systems with discharge to rivers to more closed systems with declining water tables and reduction in groundwater discharge to rivers and springs. Groundwater quality is projected to degrade much more in the future with mobilization of salts and nutrients that are currently measured in the soil profile into the underlying aquifer. Declining groundwater tables will reduce the assimilative capacity of the aquifer, further exacerbating water quality problems. Groundwater quantity and quality issues will have to be considered when developing more sustainable irrigation practices in the future.

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