Hurricane Rita's storm surge contaminates Louisiana soils

Hurricane Rita struck the coast of southwestern Louisiana and southeastern Texas on Sept. 23-24, 2005, as a Category 4 storm on the Saffir-Simpson Hurricane Scale. In the days following landfall of Hurricane Rita, an unprecedented storm surge inundated the coastal parishes of southwestern Louisiana, including parts of Calcasieu, Cameron, Jefferson Davis, Vermilion, and Iberia parishes.

The storm surge covered approximately 2,900 square miles with water containing varying levels of soluble salt. Some flooded areas were covered with freshwater from lakes and bayous pushed out of these bodies by the force of brackish saltwater from coastal marshes and the Gulf of Mexico. Other areas, however, were covered by concentrated saltwater from the Gulf of Mexico. Agricultural fields in some areas were flooded as long as three weeks.

The storm surge affected a myriad of agricultural lands, but a majority of the impacted areas are located in the rice-growing region of southwestern Louisiana. These extraordinary circumstances made clear definition of the effects of the storm surge extremely difficult. The levels of soluble salts remaining after the floodwater receded are cause for major concern and have left the productivity of large tracts of rice soils in serious question for the 2006 crop year.

Efforts are under way to define the extent and severity of salt contamination, to interpret results of soil tests revealing levels of salt contamination, and to offer recommendations for remediation of the contaminated soils.

In a cooperative endeavor between Louisiana State University AgCenter personnel and private industry, soil samples were collected on 1-mile grids in the impacted areas. Soil test results indicated that soluble salt levels in a 12-inch layer of surface soil ranged from 20 to 13,500 parts per million (ppm); therefore, some areas were much more severely affected than others.

Greenhouse research is ongoing at the LSU AgCenter Rice Research Station in Crowley, La., to address rice production issues associated with the storm surge. Soil from seven sites in Vermilion Parish was collected for greenhouse research. Laboratory soil tests determined that soluble salt levels in these soils were 590 to 8,270 ppm.

A greenhouse bioassay showed that rice emergence and plant dry weight 21 days after rice planting were not affected in soils with soluble salt levels less than 980 ppm, whereas seedling emergence was reduced at least 76 percent in soils with greater than 6,430 ppm soluble salts.

Unfortunately, the impact on rice development of season-long exposure to these soluble salt levels is not clear. Furthermore, the negative effects of salt contamination have been more pronounced when rice is water-seeded than when it is dry-seeded.

Soil test results have shown, however, that soluble salt levels at the seven sites tested in greenhouse research decreased 40 percent to 60 percent from Oct. 25 to Dec. 12, 2005. More rainfall through the remainder of the winter months will be required for severely impacted fields to be productive in 2006.

Jason Bond is a rice agronomist with the LSU AgCenter's Rice Research Station in Crowley, La.

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