March 2009, Vol. 21, No.3

Waterline

Plants Accumulate Nanoparticles

Researchers at the University of Delaware (Newark) have found that plants can take up and accumulate nanoparticles in their tissues. The study identified a possible pathway for nanoparticles to enter the food chain and reveals a new approach for studying nanoparticles and their potential impacts, according to the Dec. 17 edition of UDaily, the university’s online news service. The study was led by Yan Jin, professor of soil physics, and John Xiao, professor of physics and astronomy.

Pumpkins were grown hydroponically in a medium containing nanoparticles of iron oxide or magnetite, a magnetic form of iron ore, according to the article. Pumpkins were chosen because they are easy to grow and take in a lot of water, Jin explained.

In preliminary screenings, no magnetic signals were detected in lima bean plants, compared to strong signals detected in the pumpkin plants. This finding suggests that different plants have varied responses to nanoparticles, the article says. In addition, the researchers tested plants grown in sand containing the nanoparticles. There was little uptake of the nanoparticles in the plants grown in sand and no uptake of the nanoparticles in the plants grown in soil, Jin said. 

“Our study was a worst-case scenario in order to test the feasibility of our approach in being able to detect the particle,” Xiao said. “It really provides a new technique for doing this kind of research.”

Jin and Xiao recently were awarded a STAR grant by the U.S. Environmental Protection Agency to examine the transport of engineered nanoparticles in porous media, including soil and groundwater. 
 

Drip Irrigation Responsible for Water Depletion

Drip irrigation has been found to consume more water than flood irrigation, according to researchers at New Mexico State University (NMSU; Albuquerque). Even though more water is applied to the land by flood irrigation, more water is captured and stored by the plants with drip irrigation, NMSU professor Frank Ward explained.

“We’ve discovered that one irrigator’s sloppy management can be another’s water supply,” Ward said.

Drip irrigation applies water at optimal times and in plant root zones to increase crop water consumption and crop yields. While many policy measures encourage adoption of water-conserving irrigation methods, such as drip irrigation, these methods reduce the return flows and limit aquifer recharge, Ward said.

NMSU researchers recently completed a study of the Upper Rio Grande Basin, examining the net amount of water conserved by irrigation methods at different levels of public subsidies.

By increasing public subsidies for drip irrigation, the amount of water applied to farmlands decreases, but the overall amount of water in the basin also decreases with subsidies. An additional net water depletion of 45,269,450 m3 (36,700 ac-ft) per year results from a 100% subsidy, according to the study. Each subsidy level resulted in the use of more water than the original irrigation techniques.

According to the study, the net economic benefits from subsidies show an increase in revenue for the farm and the basin area but a decrease in economic benefits for the nation, when taking into consideration the taxpayers’ contribution. The study points out a need for public policy to determine whether the increase in net farm income compensates for the decrease in local water supply.

Suggestions made in the study for achieving real water savings include accurate accounting of watershed water use, reducing or converting nonbeneficial evaporation from soil or supply sources to beneficial evapotranspiration, restricting acreage or water use expansion, and switching to lower-water-consuming crops or irrigating current crops at a deficit.


©2009 Water Environment Federation. All rights reserved.