NONPOINT SOURCE SUCCESS STORY
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State and Federal Efforts Help Reduce Turbidity in Lake St. Joseph
Waterbody Improved
Runoff from agricultural fields in the Lake St. Joseph watershed caused a high
sediment influx into the lake, resulting in the lake not meeting its designated
use for fish and wildlife propagation (FWP). As a result, the Louisiana Department of Environmental Quality (LDEQ)
added Lake St. Joseph to the state's 2002 Clean Water Act (CWA) section 303(d) list of impaired waters for turbidity.
LDEQ and the Louisiana Department of Agriculture and Forestry (LDAF) began an initiative in 2006 assisting
landowners in implementing best management practices (BMPs) to decrease sediment runoff primarily from corn,
soybean and cotton fields. Water quality sampling verifies that the lake now meets the standard for turbidity;
therefore, LDEQ is proposing to remove this parameter from the state's 2016 list of impaired waters.
Problem
The 14,000-acre Lake St. Joseph watershed is in
Tensas Parish. The lake lies within an agricultural row
crop area. Cotton, corn, wheat and soybeans are typi-
cally grown in close proximity to the lake (Figure 1).
Production of these types of crops disturbs topsoil,
transporting sediments via runoff during rainfall
events into the lake. Increased agricultural activity
around Lake St. Joseph over the past century has
greatly accelerated its natural succession. The lake
bottom consists of a deep layer of silt, with a depth at
pool stage less than 3 feet in much of the lake.
Before construction of a water-control structure in
Clark Bayou, the lake levels fluctuated naturally with
backwater from spring floods flowing freely into the
lake. However, the construction of the water-control
structure eventually led to increased accumulation of
sediments and an associated decrease in lake depth.
The lake's physical condition is now conducive to
high summertime water temperatures and turbid-
ity (planktonic and suspended sediments). The
conditions limit the dissolved oxygen content in the
water, causing most fish species to become stressed.
Numerous fish kills have been attributed to these
factors.
Turbidity is a standard measurement of suspended
sediments in a stream. Louisiana's water quality
standard for FWP for turbidity in Lake St. Joseph is 25
nephelometric turbidity units (NTU). The FWP criteria
for turbidity requires that no more than 30 percent
of samples collected on a monthly or near-monthly
basis can exceed 25 NTU. All 12 ambient samples
collected in 1999 indicated that the standard for
Lake St. Joseph
Subsegment 081202
Land Use Map
Figure 1. Lake St. Joseph watershed land use, eastern Louisiana.
turbidity was exceeded, prompting LDEQ to add Lake
St. Joseph (LA081202_00) to the state's 2002 CWA
section 303(d) list of impaired waters. The suspected
sources of impairment were listed as natural condi-
tions and an unknown source.
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Turbidity
I Linear (Turbidity)
Turbidity
Figure 2. Turbidity concentrations in Lake St. Joseph have trended downward over time,
thanks to long-term restoration efforts by multiple stakeholders.
Project Highlights
LDEQ developed a watershed implementation
plan (WIP) in 2004. Beginning in 2006, the U.S.
Department of Agriculture's Natural Resources
Conservation Service (USDA-NRCS) provided cost
share through the Farm Bill, helping landowners
implement BMPs through the Environmental Quality
Incentives Program. In 2012 LDEQ revised the WIP
with additional available information.
LDEQ, LDAF and USDA-NRCS began a project in fiscal
year 2012 using both CWA section 319 and Farm Bill
funds in a focused effort to reduce nutrients and
sediments. LDEQ provided funds to collect hydrologic
and water quality baseline data for 1 year (February
2012-January 2013) to better understand the pollu-
tion sources and identify the substantial pathways
for the pollutant load to the lake. The data gathered
were used to determine critical areas for BMP
implementation. LDAF and USDA-NRCS helped local
landowners implement multiple agricultural BMPs,
including conservation cover, conservation crop
rotation, cover crops and irrigation water manage-
ment on approximately 5,100 acres of the watershed.
LDEQ continued sampling for an additional 2 years
during implementation to monitor for water quality
improvement.
Results
Turbidity concentrations improved in Lake St. Joseph
as a result of the BMP implementation (Figure 2).
Average turbidity concentrations declined from 68.9
NTU in 1999 to 23.5 NTU for the 2013-2014 ambient
sampling cycle. Only two of the 12 samples collected
exceeded 25 NTU (a 16.7 percent exceedance rate),
which meets the water quality standard. Therefore,
Louisiana is proposing to remove the turbidity impair-
ment for Lake St. Joseph's FWP designated use from
the state's 2016 list of impaired waters.
Partners and Funding
LDEQ and LDAF provided $467,141 in CWA section
319 funds to the Louisiana State University AgCenter
to support monitoring efforts and to help agriculture
producers and landowners implement BMPs. A total
of $374,183 was obtained in matching funds. USDA-
NRCS also provided $691,444 in Farm Bill funds from
2006 to 2014. The Tensas-Concordia Soil and Water
Conservation District has been a significant partner in
the restoration effort.
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-16-001K
June 2016
For additional information contact:
Michael Schooler, LDAF
318-435-6743 Ext. 122 » mschooler(5)ldaf.state.la.us
Karen Vidrine, LDEQ
225-219-1208 • karen.vidrine(5)la.gov
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