MERCURY SAMPLING SURVEYS OF
SARDIS, ENID AND GRENADA RESERVOIRS
SARDIS LAKE
S'
MARSHALL CO.
LAFAYETTE CO.
S-3-3
S-3-1
S-2-4
S-3-4
S-3-2
S-2-5
S-2-3
T6S
T7S
S-2-6
SARDIS RESERVOIR
Abbeville
S-1-5
S-2-2
S-2-7
S-1-6
7
S-1-4
S-2-1
S-1-7
S-1-3
S-1-2
S-1-8
T7S
T8S
S-4-1
S-4-5
S-1-1
S-1-9
S
S-4-3
S-4-2
S-4-4
35
LAFAYETTE CO.
PANOLA CO.
R6W
30
Oxford
R5W
R5W
R7W R6W
6
R4W
R6W R5W
R4W
R3W
R3W
R5W R4W
315
LEGEND
VE
R
ENID LAKE
YO
CO
NA
RI
H 2 O CHEMICAL ANALYSIS
H 2 O & SEDIMENT CHEMICAL
ANALYSIS
PANOLA CO.
LAFAYETTE CO.
YALOBUSHA CO.
E'
OPEN WATER
5-1
2-2.4
2-2.5
2-2 2-2.1
2-2.2
1-1
1-2
3-1
8-2
8-4
8-3
8-6
8-5
8-7
8-1
5-3
7-10
T 11 S
2-2.3
6-2
7-12
8-8
YALOBUSHA CO.
HIGH WATER AREAS
GEOLOGIC CONTROL POINTS WELLS, SURFACE OUTCROPS
T 10 S
2-1
PANOLA CO.
R2W
REFERENCE POINT
ENID RESERVOIR
7-5
2-3
7-6
7-7
R
7-9
7-8
R' GEOLOGIC CROSS-SECTION
7-1
E
3-3
2-4
N
32
4-3
2-5
51
SARDIS
55
ENID
T
26
N
GRENADA
R
4E
32
LOCATION IN
NORTH MISSISSIPPI
GRENADA LAKE
22
G3-7
25
23
G3-5
24
G3-6
G3-4
21
G3-3
7
G3-2
YALOBUSHA CO.
T 24 N
T 23 N
20
GRENADA CO.
19
YALOBUSHA CO.
GRENADA CO.
CALHOUN CO.
G3-1
G1-1
1
2
G1-2
G
G1-3
G'
14
8
G1-8
G2-6
GRENADA RESERVOIR
3
10
G2-4
12
G2-2
11
G2-3
7
9
G1-7
G2-1
13
G2-8
G1-6
G1-5
T 23 N
T 22 N
G2-5
G2-7
6
G2-10
18
16
G2-9
17
5
15
G1-4
4
Grenada
8
R5E
R6E
R6E
R7E
R7E
R8E
0
0
1
1
2 Miles
2
3 Km
INVESTIGATIONS INTO THE PROBLEM OF MERCURY IN FISH TISSUES,
ENID LAKE, MISSISSIPPI
Beginning with consideration of fish tissue data collected by the Mississippi Department of Environmental Quality (MDEQ), in 1994, the
MMRI has been investigating the problem of mercury levels in excess of the state (.75ppm) and federal (1.00ppm) guidelines in fish taken
from Enid Lake in North Mississippi. Included in the MDEQ's 1996 fish consumption advisories, Enid stands out as the only locale in the
northern, sparsely populated, non-industrialized, part of the state. Data collected by the MDEQ in 1995 and in subsequent years indicate a
problem that is persistent and, likely, worsening, statewide.
In 1996, the MMRI began a series of field investigations designed to isolate the source of the mercury in this remote, recreational, inland
water, constructed by the US Army Corps of Engineers (COE) in the 1950's for flood control. Water and sediment samples were collected
and analyzed for mercury content. Water parameters affecting methylation (conversion to an organic form capable of being incorporated by
organisms) of mercury, including depth, temperature, dissolved oxygen, total dissolved solids, oxygen reduction potential, pH, and
conductance, were measured at the surface and at total depth at each sample site. No obvious source of mercury was discovered, though
it was found that, when compared with the other COE lakes in North Mississippi, Enid is more acidic, a condition which promotes
methylation of mercury.
The following year, the study was expanded to include the COE lakes to the north (Sardis) and to the south (Grenada) of Enid. The
geological investigation of the area including these three lakes, conducted by the Mississippi Office of Geology in 1999-2000, was
incorporated into the MMRI study. Analyses of fish data collected by the USDA Sedimentation Laboratory for the MMRI in 1998 were also
included in the investigation. All results point to a problem not evident in the water or substrate, persisting nevertheless, and consistently
producing levels of mercury in the fish tissues that make them unacceptable for consumption by humans. While mercury concentrations in
the tissues of fish taken from Enid remain consistently high - 1.3ppm average for 18 specimens of five species taken for MMRI sampling in
1998 - those of fish taken from Sardis and Grenada appear to have increased from 1994 through 1997. Very few specimens analyzed from
elsewhere in the Yazoo River drainage basin exhibit concentrations of mercury that are out of range by either state or federal standards.
In the US EPA Mercury Study Report to Congress (P3-33 of Volume I, the Executive Summary), of 374 surface water bodies tested,
"Mercury levels above 1ppm were found in at least one fish at 2 percent of the sites and above 0.5 ppm in at least one fish at 15 percent of
the sites." No sites from North Mississippi were included in the EPA study.
GEOLOGIC CROSS-SECTIONS
SARDIS LAKE
MEAN SEA LEVEL (IN FEET)
S
S'
300
300
200
200
100
100
0
0
MEAN SEA LEVEL (IN FEET)
E
ENID LAKE
E'
300
300
200
200
100
100
0
0
Group
200
G'
300
Winona Formation
Tallahatta - Neshoba Sand member
Tallahatta - Basic City Shale member
Meridian Sand
200
Wilcox Undifferentiated
Wilcox
MEAN SEA LEVEL (IN FEET)
300
100
Hatchetigbee
Tuscahoma
100
1
0
Formation
Zilpha Formation
Claiborne
G
GRENADA LAKE
Map Unit
0
80
Approximate Vertical Exaggeration