Barataria-Terrebonne water-quality study, March-August 1999

Background

• Herbicides from the mid-continent arrive in Louisiana approx. May-July
• Distributaries allow for east-west interbasin flow
• Atrazine is widely used on Sugarcane and Corn in La., but applied Feb.-March

Issues

• Drinking-water exceedences for atrazine in southern Louisiana
• Interbasin flow from the Mississippi and Atchafalaya Rivers makes routing studies difficult
• Effects on environmental health of freshwater marshes are poorly known

Objectives of Study

1. Determine the occurrence, distribution, and transport of nutrients and pesticides in the Bayou Grosse Tete/Verret system
2. Distinguish local use from mid-continent sources

Sites

• Bayou Grosse Tete at Frisco
• Cancienne Canal at Hwy 400
• B. Grosse Tete at Rosedale
• Grassy Lake at Simon Pass
• Bayou Boeuf at Amelia
• Belle River at Hwy 70
• Bayou Pierre Part at Hwy 70
• GIWW at Jack Miller Landing
• Bayou Chevreuil nr. Kraemer
• Choctaw B. nr. Brusley
• Bayou Lafourche at Thibodaux

Constituents Sampled

• Major inorganic ions
• Nutrients
• Pesticides
• DOC/SOC
• Chlorophyll a & b

Atrazine levels in the Verret Basin, Spring 1999

• March Atrazine levels
• May Atrazine levels
• June Atrazine levels
• August Atrazine levels

Atrazine, Alachlor, and Metalochlor

Mississippi R. nr. St. Francisville

Cancienne Canal

Bayou Lafourche at Thibodaux

Bayou Pierre Part

Conclusions

• Atrazine concs. from local sources peak before mid-continent sources
• The specific mix of pesticides and date can strongly indicate sources
• Southern Louisiana therefore is exposed to low-level but long-term concs. of atrazine
• for more information, visit the Barataria-Terrebonne Study page.