ENVIRONMENTAL ASSESSMENT OF THE LOWER CAPE FEAR RIVER SYSTEM, 2002-2003
by
Michael A. Mallin, Matthew R.
McIver, Heather A. Wells,
Michael S. Williams, Thomas E. Lankford, and James F. Merritt
CMS Report Number 03-03
Center for Marine Science
University of North Carolina at Wilmington
Wilmington, N.C. 28409
October 2003
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Executive
Summary
Multiparameter water sampling for the Lower Cape Fear River Program (LCFRP) has
been ongoing since June 1995. Scientists
from the University of North Carolina at Wilmington (UNCW) perform the sampling
effort. The LCFRP currently
encompasses 35 water sampling stations throughout the Cape Fear, Black, and
Northeast Cape Fear River watersheds. The
LCFRP sampling program includes physical, chemical, and biological water quality
measurements, analyses of the benthic and epibenthic macroinvertebrate
communities, and assessment of the fish communities.
Principal conclusions of the UNCW researchers conducting these analyses
are presented below, with emphasis on the period July 2002-June 2003.
The opinions expressed are those of UNCW scientists and do not
necessarily reflect viewpoints of individual contributors to the Lower Cape Fear
River Program.
The mainstem lower Cape Fear River is characterized by reasonably turbid water
containing moderate to high levels of inorganic nutrients.
It is fed by two large blackwater rivers (the Black and Northeast Cape
Fear Rivers) that have low levels of turbidity, but highly colored water, with
less inorganic nutrient content than the mainstem.
While nutrients are reasonably high in the river channels, algal blooms
are rare because light is attenuated by water color or turbidity, and flushing
is high. Periodic algal blooms are
seen in the tributary stream stations, some of which are impacted by point
source discharges. Below some point
sources, nutrient loading can be high and fecal coliform contamination occurs.
Other stream stations drain blackwater swamps or agricultural areas, some
of which periodically show elevated pollutant loads or effects.
During the 2002-2003 sampling period, a prolonged drought that had been in
effect for over two years ended. The
summer of 2002 had been characterized by high salinity in the estuary and main
river channel; low salinities were found in these locations in spring and early
summer 2003. Whereas annual
turbidity means remained below the long-term average in the river and estuary,
the ending of the drought did lead to increasing turbidities in the upper
estuary. Low dissolved oxygen
remained a major problem in the LCFR basin, with a summer sag in the lower river
and upper estuary, and some stream stations (ANC, NC403, and SR) were impacted
severely. Algal blooms were largely
absent in the larger streams but several occurred in smaller, nutrient-impacted
streams. Several stream stations,
particularly BCRR, BC117, LRC, BRN and HAM showed high fecal coliform counts on
a number of occasions. Chronic or
periodic high nutrient levels were found at a number of stations, including ANC,
BC117, BCRR, LRC, NC403, PB and SAR. Rockfish
Creek (ROC) is showing increasing trends (and sporadic high levels) of
phosphorus and nitrate over the past several years and is a station of
increasing concern. Water column
metals concentrations were not problematic during the period 2002-2003.
This report includes an in-depth look at use support ratings for each subbasin,
comparing the results of the North Carolina Division of Water Quality's 2000
Basinwide Management Plan with the UNCW-LCFRP's assessments of the 2001-2002
sampling year. The UNCW-LCFRP
utilized definitions for use support that consider a water body to be of poor
quality if the water quality standard for a given parameter is in violation >
25% of the time, of fair quality if the standard is in violation between 11 and
25% of the time, and good quality if the standard is violated no more than 10%
of the time. UNCW also considerers
nutrient loading in water quality assessments, based on published experimental
and field scientific findings. UNCW
found that 97% of the stations sampled showed good water quality in terms of
turbidity and chlorophyll a. However,
33% of the stations had either fair or poor water quality in terms of fecal
coliform bacterial contamination, and 60% of the stations were fair to poor in
terms of dissolved oxygen concentrations. In
addition, UNCW considered 20% of the stations to be negatively impacted by
excessive nutrient loading.
The
UNCW-LCFRP conducted an examination of river and stream biochemical oxygen
demand (BOD) over a five-year period in the lower Cape Fear River system, in
coastal North Carolina. Median BOD5
was approximately 1.0 mg/L in the Piedmont-derived sixth order Cape Fear River
and slightly lower in the two fifth order blackwater tributaries, the Black and
Northeast Cape Fear Rivers. BOD in
the Cape Fear River was most strongly correlated with chlorophyll a,
whereas in the two blackwater tributaries BOD was most strongly correlated with
phosphorus concentrations and fecal coliform bacterial counts.
This relationship may be a result of nutrient induced increases in
heterotrophy, as previous experimental studies have shown that phosphorus
additions to blackwater streams lead directly to increased bacterial counts and
BOD concentrations. BOD load as lbs
BOD/day was correlated much more strongly with river discharge than BOD
concentration in all three rivers, with discharge alone able to explain from
40-80% of BOD load variability, depending upon the system.
A set of second-to-third order rural streams in the Black River basin was
also examined. Median BOD5
concentrations ranged from 0.9-1.2 mg/L in all six tributaries, regardless of
land use and watershed size. BOD
load varied directly with stream flow. In
contrast, BOD5 and BOD20 concentrations in three urban streams in Wilmington,
N.C. were approximately double those of the rural streams, with much higher
storm event maxima in the urban situations.
The reintroduction of electroshocking data from this years survey has given us
the ability to closely monitor fish species richness and disease incidence.
Species richness in samples collected by this gear has shown declines
that give cause for concern. Trend
line analysis shows over a 23% drop and this is excluding a seven-month and a
nine-month data gap that would likely have lowered the trend line further due to
the time of year in which they occurred. Although
the drought had little, if any effect on overall fish community structure,
non-native percentages, or disease incidence, species richness reached record
levels in the trawling surveys. This
suggests the drought created a more estuarine environment in our sampling area
and more estuarine dependant species were therefore captured. The catches of
estuarine dependent species further reinforces the important role the Cape Fear
River system plays as habitat for not only resident species but estuarine and
marine species. Drops in disease
percentages in the electroshocking and gillnets surveys were mostly driven by
the drops in the disease percentage of bowfin.
Although most of the trend analysis showed no discernible patterns in a
positive or negative direction, a trend toward decreasing species richness and
catch-per-unit-effort in the electroshocking surveys may be developing and
should be closely monitored in future surveys.
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**Any tables or figures not included on this site are available in hard copy
from the Center for Marine
Science at the University of North Carolina at Wilmington**