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NONPIINT SOURCE SUCCESS STURY
Implementing a Suite of Best Management Practices Results in
Removal of Bayou Mallet s Dissolved Oxygen Impairment
Waterbody Improved
Pollution from agricultural runoff entering Louisiana's Bayou
Mallet caused dissolved oxygen levels to fall below water quality
standards, which impaired the bayou's fish and wildlife propagation (FWP) designated use. As a result,
Bayou Mallet was listed on the 2002 modified court-ordered Clean Water Act (CWA) section 303(d)
list of impaired waters. Since 2005, local landowners have implemented agricultural best management
practices (BMPs) within the watershed to reduce runoff of sediment and fertilizer. Dissolved oxygen
levels have improved, prompting the Louisiana Department of Environmental Quality (LDEQ) to
remove the dissolved oxygen impairment from the CWA section 303(d) list in 2010. Dissolved oxygen
levels continue to trend upward.
Problem
The Bayou Mallet watershed (LDEQsubsegment
050103) is in Acadia, Evangeline, and St. Landry par-
ishes in Louisiana; it covers approximately 141 square
miles (Figure 1). Primary agricultural land uses in
the watershed are soybeans (22 percent), pasture
(19 percent) and rice (17 percent). Producers typically
add fertilizer to fields in this watershed to enhance
crop production. Nutrients in the fertilizer are primar-
ily nitrogen and phosphorus.
Louisiana's water quality criteria for dissolved oxygen
in Bayou Mallet are seasonal. From March through
November (summer), dissolved oxygen must remain
above 3.0 milligrams per liter (mg/L); from December
through February (winter), dissolved oxygen levels must
remain above 5.0 mg/L. To meet the FWP designated
use, no more than 10 percent of measurements taken
over a 12-month period may fall below the seasonal
criteria. In 1998, three of 12 ambient dissolved oxygen
samples (25 percent) failed to meet seasonal criteria:
2.2, 2.95 and 1.73 mg/L. In 2003, two of 11 ambient
dissolved oxygen samples (18 percent) did not meet
criteria: 2.94 and 2.95 mg/L. Sampling in both years
showed that the bayou failed to meet the 10 percent
exceedance threshold for dissolved oxygen.
The suspected source of impairment was runoff
from crop production that transported sediment and
Bayou Mallet
Subsegment050103
Land Use
0 075 1.5 3 4.5 6Miles
Figure 1. The Bayou Mallet watershed is in central Louisiana.
nutrients to the watershed, threatening fish and wildlife.
High nutrient loading facilitates algal growth and oxygen
depletion as the algae die off and decompose, resulting
in low levels of dissolved oxygen. Due to these condi-
tions, Bayou Mallet was listed for dissolved oxygen
impairment on the modified court-ordered CWA section
303(d) list of impaired waters in 2002.
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•= Dissolved Oxygen Criteria Exceedance Rates (1998-2013)
1998
2003
2005
Year(s)
2008-2009
2012-2013
Figure 2. Annual exceedance rates of dissolved oxygen criteria
in Bayou Mallet (ambient sampling cycles, 1998-2013).
Project Highlights
A total maximum daily load was developed in 2002,
which indicated that nonpoint source pollution loads
should be reduced by 12.5 percent from March
through November to meet the dissolved oxygen crite-
ria; no load reductions were necessary from December
through February. Beginning in 2005, the Louisiana
Department of Agriculture and Forestry (LDAF) and the
U.S. Department of Agriculture's Natural Resources
Conservation Service (NRCS) worked with local
landowners to implement several agricultural BMPs,
including nutrient management (1,911 acres), irrigation
land leveling (14,271 acres), conservation crop rotation
(5,285 acres), grade stabilization structures (222 units),
wetland wildlife management (15,672 acres), and field
borders (142,050 feet). From 2010 to 2013 additional
BMPs were implemented with 319 funds in the water-
shed which included conservation crop rotation, resi-
due and tillage management (no-till/direct seeding),
grade stabilization structure, irrigation land leveling,
irrigation water management, nutrient management
and pest management.
Results
Dissolved oxygen concentrations improved in Bayou
Mallet as a result of the BMP implementation. In the
2008-2009 monitoring period, one sample was below
3 mg/L in the summer season. In the 2012-2013
monitoring period, one sample was below 5 mg/L in
the winter season. These results translate to a less
Figure 3. Bayou Mallet below Louisiana Highway 95 in 2015,
after restoration efforts improved dissolved oxygen levels and
restored the FWP designated use.
than 10 percent annual exceedance rate of the sea-
sonal dissolved oxygen criteria in the 2008-2009 and
2012-2013 sampling seasons (Figure 2), both of which
meet water quality criteria. Due to these improve-
ments, LDEQ removed Bayou Mallet from the state
impaired waters list for dissolved oxygen impairment
in 2010 (Figure 3).
Partners and Funding
LDAF provided $152,352 in CWA section 319 funding,
along with landowner in-kind match of $146,782 for
a total of $299,134 from FY2010-2013. NRCS also
provided approximately $3,909,310 in federal funding
along with landowner in-kind match of $3,658,475
from FY2005-2012.
yss
Ill
o
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-16-001G
May 2016
For additional information contact:
Faran Dietz, Office of Soil and Water Conservation, Louisiana
Department of Agriculture and Forestry
fdietz@ldaf.state.la.us • 337-893-5664 Ext. 3
Karen Vidrine, Nonpoint Source Pollution Unit, Louisiana
Department of Environmental Quality
Karen.Vidrine@la.gov • 225-219-1208
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