March 2011, Vol. 23, No.3

Research Notes

Finding the right balance of sediment in the Missouri River

The Missouri River doesn’t carry enough sediment anymore for some native birds and fish. According to a report by the U.S. National Research Council (NRC), current efforts to restore habitats along sandbars and shallow waters in the Missouri River cannot substantially re-establish historic volumes of sediment that were transported downstream to the Mississippi Delta in Louisiana.

Construction of dams and riverbank stabilization structures during the 20th century cut the amount of sediment that travels down the river. This is changing the river’s natural habitat and contributing to declines of the pallid sturgeon, the least tern, and the piping plover, according to a news release from the National Academies.

The U.S. Army Corps of Engineers (Washington, D.C.) in the early 2000s began projects to restore sediment levels in the river, but these were met with concern about water quality and violations of pollution control laws — particularly increasing the “dead zone” in the Gulf of Mexico.

In response, the Army Corps requested the NRC study, which found that the projects are not significantly changing the size of the dead zone but also were not making a large contribution to volumes of sediment, when compared to historic volumes, the news release says.

NRC found that sediment concentration and deposition are as important as the quantity and flow of water for many river processes, but current means for collecting and evaluating sediment data are fragmented and not well organized.

The report recommends creating a centralized system for evaluating, archiving, and retrieving Missouri River sediment for better river and sediment management decisions. Other recommendations include establishing ecological performance objectives, developing conceptual models to evaluate environmental variables and their influences on endangered species, determining alternative actions for species recovery, and developing a “sediment budget” for the entire river that can be updated. The report also states that sediment discharge activities should be monitored to ensure compliance with water quality criteria.

The current restoration projects could release enough sediment to increase supply to the Mississippi Delta by 10% to 20% — roughly 31 million Mg/yr (34 million ton/yr) — for at least the next 15 years, but there is little potential in the near future to re-establish volumes of sediment transported downstream to levels seen before dams and stabilization structures were constructed, the release says.


Crops irrigated with river water show no signs of microconstituent uptake, study finds

Crops irrigated with water from the Colorado River do not show signs of taking up pharmaceuticals and other microconstituents that can be detected at trace levels in the river, according to a recent research report. However, direct irrigation using wastewater effluent found the potential, “albeit very low,” for microconstituent uptake, the report says.

Macrolide antibiotics, pseudoephedrine, and illicit drugs have been found in municipal wastewater streams that discharge into the Colorado River. Research chemist Tammy Jones–Lepp and her colleagues from the U.S. Environmental Protection Agency partnered with University of Arizona (Tucson) scientists to examine the potential for food-chain transfer when microconstituent-containing waters are used for irrigation, according to the report, “Method Development and Application To Determine Potential Plant Uptake of Antibiotics and Other Drugs in Irrigated Crop Production Systems,” which appeared in the November 2010 issue of the Journal of Agricultural Food and Chemistry.

According to the report, to measure microconstituent uptake, researchers irrigated greenhouse-grown crops with water spiked with three antibiotics. Crops tested in the greenhouse included lettuce, spinach, and carrots.

Researchers also conducted field experiments at two different sites where plants were irrigated with wastewater effluent containing microconstituents, Colorado River water containing trace levels of microconstituents, and microconstituent-free well water. Crops tested in the field studies included bell peppers, Bermuda grass, cantaloupe, carrots, spinach, and watermelon.

The results of the greenhouse studies show the potential for uptake of one or more of the antibiotics at very low, parts-per-trillion, levels. In the food crops irrigated directly with wastewater effluent, only an industrial flavoring agent (N,N’-dimethylphenethylamine) was found consistently, the report says.

Most notably, none of the evaluated contaminants was found in crops irrigated with Colorado River water, the report says.

The data indicate that irrigation with river water is unlikely to be a major source of antibiotic accumulation in crops. Other avenues of crop contamination, such as application of animal manure and composts — which are used on both feed and food crops in irrigated desert production systems — could be a possible source, but further research is needed to confirm this, the report says.


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