,'qN Section 319
Vs*2/ NONPIINT SOURCE PRIGUM SUCCESS STORY
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Partners Cooperate to Improve Water Quality in Lake Arthur and Lower
Mermentau River
\A/ t h H I	H In 1999 the Louisiana Department of Environmental Quality (LDEQ)
3 6T 0 y mprove added the Lake Arthur and Lower Mermentau River assessment unit
(AU) to the state's court-ordered Clean Water Act (CWA) section 303(d) list of impaired waters for not
meeting the fish and wildlife propagation (FWP) designated use. Suspected causes of impairment
included low dissolved oxygen (DO) and high levels of total suspended solids (TSS), nutrients, turbidity,
oil and grease, and ammonia from point and nonpoint sources of pollution. Landowners implemented
agricultural best management practices (BMPs) to reduce pollutant loading within the watershed.
Water quality improved, prompting LDEQ to remove the Lower Mermentau River and Lake Arthur AU
from the state's list of impaired waters in 2010 for sediment/siltation, TSS, turbidity, and ammonia, and
in 2012 for DO, nitrate/nitrite, and total phosphorus (TP).
Problem
The Lower Mermentau River flows through Lake
Arthur before entering Grand Lake in southern
Louisiana. LDEQ classifies the tidally dominated
estuarine waters of the Lake Arthur and Lower
Mermentau River AU as basin subsegment 050402
(Figure 1). The predominant land uses in the AU's
29,200-acre watershed are rice crop (32 per-
cent), water (20 percent), and pasture/hay fields
(19.8 percent); the remaining uses are freshwater
marsh, low- to medium-density development, and
forests.
In the late 1990s, LDEQ's ambient water quality data
indicated high concentrations of TSS, turbidity, and
nutrients and low DO concentrations in the Lower
Mermentau River and Lake Arthur. The DO criterion
for the Lower Mermentau River is that no more
than 10 percent of monthly samples may fall below
5.0 milligrams per liter (mg/L). In 1998 DO values
remained below the state's criterion of 5.0 mg/L
for seven months of the year; the lowest value,
2.37 mg/L, occurred in August. Although Louisiana
does not currently have a numeric criterion for TSS,
the U.S. Environmental Protection Agency (EPA)
recommends a maximum TSS guideline of 29 mg/L
to ensure support of the FWP use. LDEQ's ambient
water quality data indicated that TSS values exceed-
ed the guideline during June and November of 1998.
Likewise, the state does not currently have numeric
criteria for nutrients; it does, however, provide narra-
tive criteria that require the naturally occurring range
of nitrogen and phosphorus to be maintained using
site-specific studies to establish limits for nutrients
Lake Arthur and Lower Mermentau River
LDEQ Basin Subsegment 050402
peci
SIS CENTER
Biscuit Isla
- Area between the ICWW and Grand Lake
0 12 3 4
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^ 050402 \

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Mermentau Basin
Figure 1. The Lake Arthur and Lower Mermentau River Basin
Subsegment is in southern Louisiana.
to avoid aquatic growth that creates a public nui-
sance or interferes with designated water uses.
On the basis of these data and assessments, LDEQ
added the Lake Arthur and Lower Mermentau River
AU to the 1999 CWA section 303(d) list for failing to
support its FWP designated use due to low DO and
high TSS, nutrients, turbidity, oil and grease, and
ammonia. The suspected sources of impairment
included minor municipal point sources, crop produc-
tion, petroleum activities, individual septic tanks, and
flow alterations/modifications.

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Concentration of DO in Lower Mermentau River
at Lacassine National Wildlife Reguge
7
H1998
H2003
lJ2007
B2010/2011
Figure 2. Dissolved oxygen concentrations in the lower
Mermentau River have improved.
In 2001 EPA completed a total maximum daily
load (TMDL) for turbidity, TSS, and siltation for the
Mermentau River Basin, including the Lake Arthur
and Lower Mermentau River AU. The TMDL identi-
fied fluvial erosion processes as the dominant con-
tributor to high turbidity, TSS, and siltation levels. In
2002 EPA completed a TMDL for DO, nutrients, and
ammonia in portions of the Lower Mermentau River
Basin. This TMDL indicated that a 40 percent reduc-
tion in oxygen-demanding substances was neces-
sary to meet the state's DO water quality standard.
The TMDL indicated that DO would likely improve if
nutrient concentrations were reduced.
Project Highlights
From 2002 through 2011, the U.S. Department
of Agriculture's (USDA's) Natural Resources
Conservation Service (NRCS) partnered with
watershed landowners to develop comprehen-
sive resource management systems—plans that
included sets of approved conservation practices
necessary to achieve conservation goals. The prac-
tices included irrigation water management, residue
and nutrient management, conservation crop
rotation, grade stabilization structures, and wetland
wildlife habitat management. Through USDA's rank-
ing criteria, lands that drain directly to the Lower
Mermentau River and Lake Arthur were prioritized
for cost-share and technical assistance.
NRCS partnered with the Gulf Coast Soil and Water
Conservation District (SWCD), Vermilion SWCD, and
Jefferson Davis SWCD to provide technical and/or
cost-share assistance to help Lower Mermentau/
Lake Arthur watershed landowners implement
BMPs on approximately 2,645 acres: 1,551 acres
on rice fields, 742 acres on crawfish operations,
193 acres on soybean fields, and 158 acres on
pastures. The BMPs included residue management
(seasonal) on approximately 1,307 acres, conserva-
tion crop rotation on 1,242 acres, irrigation water
management on 1,711 acres, integrated pest man-
agement on 1,265 acres, nutrient management on
1,006 acres, wetland wildlife habitat on 884 acres,
and prescribed grazing on 125 acres. Landowners
often applied multiple BMPs on the same acreage.
Contracts with landowners will remain in place
through 2018, so water quality should continue to
improve. A watershed coordinator is working with
stakeholders on a watershed implementation plan
to continue activities and programs to improve
water quality.
Results
LDEQ collected water quality data in the Lower
Mermentau River at Lake Arthur during four sam-
pling periods: 1998, 2003, 2007, and 2010/2011.
Between the 1998 and 2010/2011 sampling periods,
average annual DO concentrations increased from
4.7 mg/L to 7.8 mg/L. In all but one month, DO levels
during the 2010/2011 sampling period remained
above 5.0 mg/L, thereby meeting the DO criterion
necessary to fully support the Lower Mermentau
River's FWP designated use (Figure 2). TSS values
exceeded EPA's guideline maximum of 29 mg/L
during June and November 1998, but they have
remained below this level in all sampling periods
since that time. Average annual TSS concentrations
declined from 27.48 mg/L in 1998 to 12.29 mg/L in
2010/2011. In addition, monitoring data collected
since 1998 show that average annual TP concentra-
tions decreased from 0.27 mg/L in 1998 to 0.13 mg/L
in 2010/2011. Based on these monitoring data, LDEQ
removed the Lower Mermentau River and Lake
Arthur AU from the state's list of impaired waters
in 2010 for sediment/siltation, TSS, turbidity, and
ammonia, and in 2012 for DO, nitrate/nitrite, and TP.
Partners and Funding
NRCS, Gulf Coast SWCD, Jefferson Davis SWCD,
Vermilion SWCD, and 23 landowners partnered to
implement practices. NRCS provided approximately
$264,158 in USDA Farm Bill funds to implement
both agricultural and pastureland BMPs. Louisiana
Department of Agriculture and Forestry staff helped
landowners implement practices. Partners applied
$85,800 in EPA CWA section 319 funds towards
projects in this watershed.
* A
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U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA EPA 841-F-14-001W
May 2014
For additional information contact:
Gwendolyn Berthelot
Louisiana Department of Environmental Quality
225-219-0879
gwendolyn.berthelot@la.gov

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