3.6
Cape
Fear River Subbasin 03-06-19
Includes the Black River, Six Runs Creek and Great Coharie Creek
Municipalities: Town of Clinton
LCFRP Station Codes (DWQ #): LCO
(64), GCO (63), 6RC(65)
DWQ/UNCW ambient monitoring site(s): none
Waterbody: Little Coharie Creek,
Great Coharie Creek and Six Runs Creek, all flow to the Black River
Location: Sampson
County
Lat/Lon: N
34.91857 W
78.38873 (GCO)
N 34.79357
W 78.31192
(6RC)
|
Use Support Ratings, from
NCDENR, DWQ (Cape
Fear River Basinwide Water Quality Plan, July 2000):
Freshwater Streams
Fully Supporting:
452.1 mi.
Partially Supporting:
15.0 mi.
Not Supporting:
0.0 mi.
Not Rated:
40.2 mi.
This
subbasin is located in the coastal plain within Sampson County.
Land adjacent to the Black River is primarily undisturbed forest.
There is a very high concentration of hog farms within these watersheds.
There are 7 permitted dischargers, the largest of which is the Town of
Clinton. (NCDENR, DWQ Cape Fear
River Basinwide Water Quality Plan, July 2000)
Stewarts Creek (15.0 miles from source to Six Runs Creek) is currently partially
supporting (PS) due to an impaired biological community.
The Town of Magnolia discharges into a tributary, which eventually flows
to Stewarts Creek downstream of Warsaw. The
Magnolia WWTP has had problems with effluent toxicity and has been fined monthly
since November 1999. Stewarts Creek
is the only stream in the subbasin that is impaired and on the state’s year
2000 303(d) list. (NCDENR, DWQ Cape Fear River Basinwide Water Quality Plan,
July 2000)
Portions of Great Coharie Creek, Little Coharie Creek, Six Runs Creek and Crane
Creek were impacted during Hurricane Fran in 1996.
These steams were also subject to massive desnagging operations after the
storm. Benthic monitoring is
recommended to determine the impacts of de-snagging operations that remove
important habitat in these waters (NCDENR, DWQ Cape Fear River Basinwide Water
Quality Plan, July 2000).
UNC-Wilmington
– Center for Marine Science, LCFRP
Station Names: LCO, GCO, 6RC
Data collection: February 1996 to
present
Sampling relevance: Concentrated
animal operations (CAOs) within
the watershed, reference areas for point and nonpoint source pollution
GCO - blackwater stream, drains
riparian wetlands in an area with
concentrated animal operations
Little Coharie Creek (LCO)
and Six Runs Creek (6RC) were found to be good quality for dissolved oxygen (DO)
concentrations, falling below the NC State Standard of 5.0 mg/L only once in
July 2002. Great Coharie Creek (GCO)
was rated as poor quality for dissolved oxygen concentrations, not meeting the
standard of 5.0 mg/L in 50% of sampled months.
When reevaluated using the swampwater standard of 4.0 mg/L, GCO was rated
as fair quality, with only 2 samples below the 4.0 mg/L swampwater standard.
The lowest values for DO at GCO were in July 2002, measuring 2.6 mg/L,
and September 2002, measuring 0.8 mg/L. The
dissolved oxygen concentration values for GCO are represented graphically in
Figure 3.6.1.
All sites within this
subbasin were found to be good quality for chlorophyll a concentrations,
fecal coliform bacteria concentrations and turbidity concentrations.
Nutrient loading,
especially total phosphorus (TP) was a problem at GCO (Figures 3.6.2).
In September of 2002 TP levels were 1,400 mg/L,
and average concentrations for the sampling period were 373 mg/L.
These levels were far above the concentrations known to lead to ATP
increases, bacterial increases and increased biochemical oxygen demand (BOD) in
blackwater streams (Mallin et al. 2001, Mallin et al. 2002).
Figure 3.6.1 Dissolved
oxygen concentrations (mg/L) for GCO during the
2002-2003 monitoring period.
The line shows the NC State Standard for
dissolved oxygen of 5.0 mg/L,
and the dashed line shows the NC State
Standard for swampwater of 4.0 mg/L.
Figure 3.6.2
Total phosphorus concentrations (mg/L)
for GCO during the
2002-2003 monitoring period.