Hurricane Effects on Water Quality and Benthos in the Cape Fear Basin
5.1 Introduction
During the summer of 1996 the Cape Fear region of southeastern North
Carolina sustained two hurricanes. On July 12, Hurricane Bertha made landfall near the
City of Wilmington and proceeded north along the coast, crossing the Neuse River at New
Bern. Although some coastal areas suffered damage, there was comparatively little
structural damage in the middle and upper Cape Fear watershed. However, heavy rainfall
followed the hurricane and persisted for about two weeks. On September 5, Hurricane Fran
made landfall near Wilmington and proceeded up the Cape Fear basin to the Raleigh area in
the North Carolina Piedmont, causing considerable damage to homes, businesses,
automobiles, and power lines. Many areas were without power for several days. Heavy rains
followed this hurricane as well, especially in the upper region of the Cape Fear
watershed, with large volumes of swamp water flooding into the main channels.
Hurricane Fran and its aftermath caused devastating environmental
impacts to the Cape Fear River and Estuary. Power failures caused numerous municipalities
to divert large volumes of raw and partially-treated sewage and stormwater runoff into the
Cape Fear River (NCDEHNR 1996b). Additionally, during the week following the hurricane at
least four hog waste lagoons ruptured, overtopped, or were inundated, releasing millions
of liters of raw or partially-treated animal waste into the Northeast Cape Fear River
(NECF), a major tributary of the Cape Fear Estuary (NCDEHNR 1996). A large fish kill
followed, with State environmental personnel reporting thousands of carcasses including
hogchokers, catfishes, carp, bass, sunfish, pickerel, shad and eels, with deaths
attributed to low dissolved oxygen conditions (NCDWQ 1997, North Carolina Division of
Water Quality field records).
In this report we describe the physical, chemical, and biological
environmental effects caused by both hurricanes, compare the two events, and interpret the
role of anthropogenic and natural factors associated with Hurricane Fran in water quality
degradation to the lower Cape Fear watershed. We also discuss how altered environmental
management practices could have reduced the water quality impacts to the system.
5.2 Sampling Locations
We maintain 16 sampling stations along the estuary and lower rivers,
and include data herein from several key freshwater and brackish stations noted on Figure
5.1. NC11 is on the mainstem Cape Fear River and represents inputs to the lower watershed.
AC is located about 15 km downstream of NC11, and about 5 km downstream of a pulp and
paper mill discharge. B210 represents inputs from the Black River to the lower watershed,
while BBT is affected by both the Black and mainstem Cape Fear Rivers. NCF117 represents
inputs from the upper Northeast Cape Fear watershed to the lower watershed. All of the
above stations are freshwater. Upper estuarine stations included NCF6, an oligohaline site
located in the lower Northeast Cape Fear River about 10 km upstream of Wilmington, and
NAV, another oligohaline station located 10 km downstream of where the Black River enters
the mainstem Cape Fear River. M35 is located at Channel Marker 35 in the mesohaline
estuary.
The benthic community was sampled at four oligohaline to mesohaline
stations, including NAV, NCF6, and Channel Marker 31 (M31), located about 3.4 km
downstream of M35. An additional station, Channel Marker 54 (M54), was sampled because of
its location at the approximate turbidity maximum zone (Mallin et al. 1997a), an important
transitional region for benthic community composition. At each station, samples were taken
in approximately 2.5 m water depth.
5.3 Methods
Rainfall data were obtained from the North Carolina Climate Office
at North Carolina State University, and river flow data was obtained from the U.S.
Geological Survey, Raleigh, N.C. Salinity and dissolved oxygen (DO) values were collected
on a weekly to biweekly basis at 14 stations by obtaining vertical profiles using a
Solomat 803PS Multiparameter Water Quality Probe displayed on a Solomat 803 datalogger.
Light attenuation coefficients k were obtained monthly at 0.5 m intervals by collecting
vertical PAR data with a LiCor -1000 Datalogger coupled to a spherical sensor and applying
the data to standard formulas (Raymont 1980). Five-day biochemical oxygen demand (BOD5)
data was obtained following Standard Methods (APHA 1995). BOD5 data was collected monthly
from stations NC11, AC, B210, BBT, and NCF117 (Fig. 5.1). Nutrients were analyzed from
surface water samples collected monthly from the surface at all stations. Orthophosphate
was analyzed from filtered samples using a Technicon AutoAnalyzer. Ammonia,
nitrate+nitrite, total phosphorus (TP) and total Kjeldahl nitrogen (TKN) were analyzed
using Standard Methods (APHA 1995). Organic phosphorus was computed as the difference
between total phosphorus and orthophosphate, and total nitrogen (TN) was computed as the
sum of TKN plus nitrate.
Benthic samples were taken on six occasions at the M31 and M54
stations: December 11, 1995, March 28, August 19, October 1, October 31, and December 17,
1996. At NAV, samples were taken December 11, 1995, March 28, August 19, October 31, and
December 17, 1996. At NCF6 samples were taken December 11, 1995, March 28, October 31, and
December 11, 1996. Sampling in the upper stations immediately after Hurricane Fran was
attempted but valid samples were not obtained due to the high amount of debris in those
areas at that time. All samples were taken with a Petite Ponar grab, 15 cm x 15 cm
opening, 15 cm depth. Five grab samples were taken at each station on each sampling date
(grabs were kept only if the grab was full in order to standardize volume sampled).
Samples were sieved through a 0.5 mm mesh screen, preserved in 10% formalin, and
subsequently transferred to 70% ethanol for later identifications. Differences in infaunal
abundances were compared among sampling dates for common taxa (comprising at least 3% of
the individuals at a site) and higher taxonomic groups using Analysis of Variance on
log-transformed abundances. Because of differences in faunal composition at the 4 sites
(reflecting salinity and other riverine gradients), comparisons between dates were
conducted separately for each site.
Rainfall
The Cape Fear River Basin experienced broad rainfall extremes in the
summer of 1996. Wilmington rainfall for July was 31.8 cm, 9.9 cm higher than the 1985-1994
average. The month of August was drier than normal, with Wilmington rainfall measured at
5.9 cm, which was 15.3 cm below the ten-year average (N.C. Climatologist Office records).
Hurricane Bertha, which made landfall along the southeast coast of North Carolina on July
12, accounted for much of the July rainfall in the Wilmington area. However, Bertha
produced little or no rainfall for the middle and upper regions of the Cape Fear River
Basin.
A few days prior to Hurricane Fran making landfall on September 5 near
Southport (Fig. 5.1), the entire Cape Fear River Basin received heavy rainfall from a
continental weather system. Rainfall amounts along the basin for the period September 1-4
were 14.2 cm in Greensboro, 1.5 cm in Fayetteville, and 8.4 cm in Wilmington (Bales and
Childress 1996). As Fran passed through North Carolina on September 5-6, the Cape Fear
River Basin experienced precipitation amounts ranging from 5-20 cm. Following the
hurricane from September 9-12, continental storm systems unrelated to the hurricane
deposited 7-20 cm of additional rain throughout the region (Bales and Childress 1996).
Total rainfall amounts for the month of September typically average
10-15 cm in the Cape Fear Basin. For 1996, Greensboro (26.7 cm), Fayetteville (26.9 cm),
Elizabethtown (33.3 cm), and Wilmington (30.7 cm) substantially exceeded those averages
(N.C. Climatologist Office records). At each of these cities, most of the September
precipitation occurred within the first two weeks of the month.
River discharge is recorded daily by the US Geological Survey at
gauging stations along the Cape Fear, Northeast Cape Fear, and Black Rivers. All of these
rivers experienced substantial peaks in water flow during September 1996 (Table 5.1; Fig.
5.2).
Water flow at Lock and Dam #1 on the Cape Fear River near Kelly, NC,
peaked at 1,262 m3/s on September 13. For the month, the mean flow rate was 588
m3/s. Data for September 11 and 12 were unavailable and were not included in
the monthly mean. September discharges for the period 1982-1996 at Lock and Dam #1
averaged approximately 105 m3/s. The previously recorded monthly maximum for
those years was 570 m3/s, which occurred during February 1989. River flow in
North Carolina is generally much lower in the summer months because of the substantial
increase in evapotranspiration resulting from warm air temperatures.
On the Northeast Cape Fear River near Chinquapin, approximately 100 km
upstream of Wilmington, the peak flow was 268 m3/s measured on September 8.
Data was unavailable for September 9, 11-12, and 15-20. The September 1996 mean discharge
at this site was 110 m3/s, but would likely have been higher had more data been
available. Since 1940 when data collection began, the maximum mean monthly flow was 135 m3/s
recorded during September 1955. The average flow for September for the years 1940-1996 was
approximately 14.2 m3/s (U.S.Geological Survey records), considerably less than
what was experienced in 1996.
A gauging station near Tomahawk, about 65 km upstream of Wilmington,
reported a peak flow of 393 m3/s for the Black River on September 10, its
highest daily peak since 495 m3/s was recorded in 1984 (Bales and Childress
1996). For the month of September 1996, river discharge averaged 136 m3/s. The
greatest previous monthly mean flow had been 94 m3/s (September 1955). Typical
September flows average approximately 15.5 m3/s (1952-present), comparable to
discharges measured on the Northeast Cape Fear River (U.S. Geological Survey records).
The Cape Fear River experienced long-term hypoxic and anoxic events
during 1996. Weekly or biweekly DO data was available from several sites (Fig. 5.3). Just prior to Hurricane Bertha, dissolved
oxygen levels at these sites averaged approximately 4-7 mg/L. After the passage of Bertha,
dissolved oxygen levels dropped substantially at stations NAV (oligohaline site on the
mainstem Cape Fear River), NCF6 (oligohaline site on the Northeast Cape Fear River), and
M35 (mesohaline site in the Cape Fear Estuary). The hypoxic conditions at these three
sites resulted from the heavy rains and subsequent flooding of low dissolved oxygen swamp
waters into the Cape Fear and Northeast Cape Fear Rivers. However, dissolved oxygen levels
at NC11, an upstream riverine site, remained relatively constant after Bertha. As
mentioned above, heavy precipitation from this storm primarily affected the coast and did
not significantly affect the Cape Fear River Basin upstream of NC11. Dissolved oxygen
concentrations gradually returned to pre-Bertha levels at the estuarine stations by late
August.
When Hurricane Fran struck North Carolina in early September, the Cape
Fear and Northeast Cape Fear Rivers exhibited typical summertime dissolved oxygen
conditions, ranging from 3.4 mg/L at NCF6 to 7.7 mg/L at NC11 (Fig.5.3). After Fran and
the subsequent period of heavy rains which followed the hurricane, dissolved oxygen levels
at all sites in the Cape Fear River Basin plummeted to 0-2 mg/L. Anoxic conditions (0-0.2
mg/L) in the Northeast Cape Fear River at NCF6 and hypoxic conditions at NAV and M35
(<3 mg/L) persisted until early October (Fig.5.3). Surface and bottom DO concentrations
at the benthic sampling location M54 were 0.5 and 0.4 mg/L on Sept. 16, 1.1 and 0.8 mg/L
on Sept. 24, and 4.0 and 3.8 mg/L on Oct. 14, respectively. At the mainstem site NC11
dissolved oxygen concentrations had increased to 5.6 mg/L by the last week of September (Table 5.1).
The Black River, with a swampy watershed and average river flows
similar to the Northeast Cape Fear, experienced hypoxic conditions following Hurricane
Fran. Approximately 2 weeks after the September 5 storm, dissolved oxygen was 2.0 mg/L at
B210 and 0.4 mg/L at BBT. During the same period along the Northeast Cape Fear River, DO
at NCF117 was 0.4 mg/L and DO at NCF6 was 0.1 mg/L. By the second week in October, about 6
weeks after Fran, DO levels in the Black River had recovered to 5.4 mg/L at B210 and 4.1
mg/L at BBT, while DO in the Northeast Cape Fear river was 4.5 mg/L at NCF117 and 3.1 mg/L
at NCF6 (Table 5.1). The North Carolina water quality standard is 5.0 mg/L in most
situations, and may be lowered to 4.0 mg/L for swamp waters (NCDEHNR 1994). Intermediate
dissolved oxygen data between the September and October samples was not collected for
B210, BBT, and NCF117.
With two exceptions, 5-day BOD was low (<2.2 mg/L) at all five sites during each month in 1996 (Fig. 4). Station AC showed a BOD5 of 2.4 mg/L in July prior to Hurricane Bertha. There was no unusual BOD5 measured at any station during August 1996, approximately four weeks after Hurricane Bertha. In September 1996, the BOD5 concentration at NCF117 was measured at greater than 8.2 mg/L (sample exhausted >8.2 mg/L dissolved oxygen prior to end of five days). This sample was collected 12 days after Hurricane Fran during a period when the Northeast Cape Fear River experienced near-anoxic conditions. The Black River and mainstem Cape Fear River data exhibited no similar maxima in BOD5 after the hurricane (Table 5.1; Fig. 5.4). The contrast between B210 and NCF117 (two similar blackwater environments) should be noted and will be examined in the Discussion.
Monthly 1996 light attenuation coefficient (k) data are
available for the entire Cape Fear River system with the exception of the estuarine
stations for July (Fig. 5.5). The average
light attenuation coefficient of 15 lower Cape Fear sites, representing the riverine and
estuarine CFR, NECF, and Black Rivers, was 3.51/m during 1996. July (pre-Bertha, k =
3.67/m) and August (post-Bertha, k = 3.72/m) data were nearly equivalent suggesting
little long-term effects on water color from Hurricane Bertha. The data do depict a
substantial peak in light attenuation (k = 5.27/m) for the entire Cape Fear River
during September following Hurricane Fran and the subsequent heavy rains. The average
light attenuation at all Cape Fear River sites was still high in October, averaging
3.96/m, the second greatest monthly mean during 1996.
Attenuation values at NC11 (mainstem CFR upriver site) averaged
approximately 3.03/m for 1996, but were usually less than 2.60/m (Fig. 5.5). Pre-Bertha
and post-Bertha k values showed a slight decrease (2.40/m and 2.02/m, respectively),
suggesting minimal effects from that hurricane on light attenuation. After Hurricane Fran
(September), however, the high, sediment-laden river flow increased k to 4.35/m. Light
attenuation remained high during October 1996 (k = 3.81/m).
At BBT, the 1996 mean k value was 3.44/m (Fig. 5.5). The strongest
light attenuation (k = 6.20/m) occurred at this station during September, following
Hurricane Fran. Light attenuation remained substantially higher than the yearly mean
during October (k = 4.37/m). This section of the Black River experienced
significant flooding from surrounding swamps in addition to turbidity loading from the
Cape Fear River. Blackwater systems have naturally higher light attenuation than similarly
turbid non-blackwater systems because of the magnitude of dissolved organic matter in
swamp water. As with the other stations, July (k = 3.65/m) and August (k =
3.49/m) data were nearly equivalent and no direct affects from Bertha were observed.
The Northeast Cape Fear River, a predominantly blackwater system,
experienced little fluctuation in light attenuation during 1996 as opposed to the other
selected sites (Fig. 5.5). K values averaged 3.86/m during 1996 with a maximum of
4.91/m in November 1996. Unlike the other Cape Fear sites, this station did not experience
a significant increase in light attenuation immediately following Hurricane Fran. This
site is heavily influenced by swamp waters throughout the year so that the substantial
flooding of streamside swamps did not alter k values following the storm. No direct
effects from Bertha could be detected at this site either.
During 1996, the mean light attenuation k value at the estuarine
station M35 averaged 3.15/m (Fig. 5.5). There was a substantial peak in light attenuation
(k = 6.65/m) at M35 following Hurricane Fran, resulting from high turbidities and
increased dissolved organic matter influxes from the blackwater tributaries. Light
attenuation also remained higher than average during October (k = 4.28/m).
Unfortunately, no July data was available for M35 and comparisons with Hurricane Bertha
are not possible.
Our data revealed no discernible effects from Hurricane Bertha on
nutrient levels in the Cape Fear River in August (Figs.
5.6 and 5.7). However, samples were not
collected until nearly three weeks after the storm had passed, and July samples were
collected prior to Bertha’s arrival. If Bertha-driven nutrient loading to the system
occurred, it was localized and ephemeral, because effects of that storm were mainly
limited to the coastal region and river flows upstream were not increased by Bertha (Fig. 5.2).
There were no stations in the mainstem Cape Fear River or Estuary that
exhibited significant increases in total nitrogen concentrations following Hurricane Fran
relative to 1996 mean values. However, at stations located in the Black (B210) and
especially in the Northeast Cape Fear Rivers (NCF6 and NCF117), total nitrogen peaks in
September were substantially above the 1996 averages (Table 5.1). At B210, the measured TN concentration
in September was 1,750 ug/L (1996 mean = 1,326 ug/L). At the NECF stations, the peaks were
more substantial. NCF6 had a September TN concentration of 2,100 ug/L (1996 mean = 1,415
ug/L) and NCF117 a September concentration of 2,360 ug/L (1996 mean = 1,487 ug/L).
Nitrate+nitrite levels were extremely low throughout the Cape Fear
system following Hurricane Fran. Since dissolved oxygen levels approached or reached
anoxic conditions at virtually all stations, most of the inorganic nitrogen existed in its
reduced form as ammonia. However, the mainstem Cape Fear River and Estuary exhibited
relatively low concentrations of ammonia as well. In contrast, stations along the
Northeast Cape Fear and Black Rivers exhibited uncharacteristically high ammonia levels (Table 5.1; Fig.
5.6). The Black River site B210 had a 1996 peak during September of 80 ug/L. At
NCF117, ammonia levels were even greater and measured 140 ug/L (also a yearly maximum).
Mean 1996 ammonia levels at these two blackwater stations were 28 ug/L at B210 and 54 ug/L
at NCF117. Overall, the data collected at NCF117 and B210 clearly indicate that organic
species and ammonia dominated nitrogen composition following the Hurricane Fran at these
blackwater sites.
As with nitrogen, the mainstem Cape Fear River and Estuary exhibited no
distinct September peak in phosphorus following Hurricane Fran. However, both NCF117 and
B210 displayed significant peaks in organic phosphorus and total phosphorus (Table 5.1; Fig.
5.7) in September. At NCF117, organic P concentrations measured 292 ug/L following
Hurricane Fran, 3.7 times the 1996 mean of 79 ug/L, while TP measured 380 ug/L, 3 times
the 1996 mean of 124 ug/L. At B210, there was a peak in organic phosphorus measured at 116
ug/L, twice the 1996 average of 58 ug/L, and TP measured 200 ug/L, compared with the 1996
mean of 88 ug/L.
There was considerable variability in infaunal distribution patterns
over the year of sampling, as is common in oligohaline estuarine areas (Holland 1985,
Nichols 1985, Holland et al. 1987, Posey et al. 1993). At the NCF6 station in the
Northeast Cape Fear River, there was a significant decline in total faunal abundance after
Hurricane Fran relative to all other sampling periods (Table 5.2). This decline primarily reflected the
absence of amphipods and low numbers of insect larvae at this site following the
hurricane. Recovery occurred during fall and winter with numbers returning to
pre-hurricane levels by mid December. Four other taxa, Cyathura sp., Gammarus
palustris, Procladius sp. and Maranzellaria virdis, displayed
temporal variability in numbers independent of Hurricane Fran effects. In contrast to the
NCF6 site, the NAV station in the mainstem Cape Fear River was not characterized by
statistically significant declines in infaunal abundances after the hurricane (Table 5.2).
The NAV station had no amphipods or polychaetes present in the first sample collection
after Hurricane Fran (in contrast to other sampling periods) and had 50% lower total
infaunal abundances at that time compared to either prior or following sampling periods.
However, the high variability in faunal counts made statistical determination of patterns
difficult. Procladius sp., Polypedilum sp., and Maranzellaria
exhibited significant temporal variability at this site independent of the hurricane
effect.
M54 represented a mid-estuary site that was located near the turbidity
maximum zone. Several benthic groups, including isopods, polychaetes, and total infauna
exhibited lower abundances in the sampling periods after Hurricane Fran. Recovery of these
taxa groups was slower than at the other sites, with total infaunal abundances in December
1996 not significantly different from October 1, 1996 samples, but significantly lower
than observed in the previous December (Table 5.2). Total amphipod abundances at M54
exhibited an overall decline after Hurricane Bertha (August samples), with numbers
dropping to zero after Hurricane Fran. However, the lack of data from the previous year
makes assessment of Bertha effects difficult. Monoculodes sp., oligochaeta, Maranzellaria
virdis and Mediomastus sp. exhibited significant temporal variability in
numbers at M54. M31 was the furthest downstream site and fauna in this region showed a
mixed response. The polychaete Mediomastus had higher abundances after Hurricane
Fran compared to pre-storm samples. Only amphipods displayed a statistically significant
decline in numbers after Hurricane Fran at M31.
5.5 Discussion
Increased light attenuation through loading of darkly-stained swamp
water to the rivers can be considered a natural environmental effect of the
hurricane’s aftermath. One likely effect of increased water color and particulate
matter on the lower estuary and nearshore ocean would be to decrease phytoplankton and
benthic algal primary production (Alpine and Cloern 1988, Mallin and Paerl 1992). There
are no productivity rates available, but phytoplankton chlorophyll a biomass in the
lower estuary during September and October 1996 was 3.2 and 3.4 ug/L, respectively,
compared with 13.6 and 12.8 ug/L in those same months during 1995 (Mallin et al. 1996).
September light attenuation coefficients were the highest systemwide since data collection
began in July 1994. However, runoff incidents have caused severe light attenuation on
other occasions as well, either due to turbidity pulses along the mainstem Cape Fear River
or heavy rain in the blackwater tributaries (Mallin et al. 1997a). Light attenuation has
been cited as a periodic limiting factor to phytoplankton productivity in the Cape Fear
Estuary, mainly during winter months (Mallin et al. 1997a). The heavy flooding and
increased light attenuation following the hurricanes likely caused coastal ocean light
limitation as well during fall of 1996.
The Black and Northeast Cape Fear Rivers make excellent comparative
systems because they drain similar-sized watersheds, are both blackwater systems, and have
similar land-use patterns. Along the lower rivers are extensive riparian swamp forests,
and among the tributary streams are numerous large-scale swine and poultry farming
facilities (NCDEHNR 1996), variously known as intensive livestock operations (ILO’s)
or concentrated animal operations (CAO’s), and feature a system in which thousands of
swine or fowl are raised in long, shed-like structures, with their liquid and solid waste
rinsed into nearby open lagoons. The waste material undergoes sludge settling and receives
some anaerobic breakdown in the lagoons, and when lagoon levels rise enough the liquid
effluent is normally sprayed onto nearby fields with a grass covering, usually
Bermudagrass (Westerman et al. 1985).
Both the Black and Northeast Cape Fear watersheds suffered from heavy
September rainfall, judging from their relatively similar river flow rates following
Hurricane Fran (Table 5.1; Fig. 5.2), and both rivers suffered from decreased DO
following the hurricanes (Table 5.1). Swamp
water is naturally low in dissolved oxygen, and inputs into blackwater rivers from
flooding will lower river DO concentrations (Meyer 1992). However, swamp-derived organic
materials in blackwater rivers are largely composed of refractory or recalcitrant carbon
compounds, with a low BOD5 (Meyer 1990, Meyer 1992). Following Hurricane Fran, BOD5 was 6X
higher and dissolved oxygen concentrations 80% lower in the Northeast Cape Fear River at
NCF117 than in the Black River at B210 (Table 5.1). The major difference in impacts was
probably anthropogenic, caused in part by at least four swine waste lagoons breaching,
overtopping, or being inundated on the Northeast Cape Fear floodplain, allowing large
quantities of raw and partially treated swine urine and feces to enter the river. Another
lagoon was reported to have overtopped and discharged into the Black River watershed
(NCDEHNR 1996). Authors of another study reported that swine waste lagoon liquid from five
tested lagoons had an average COD of 1,839 mg/L, with a range of 970 to 2,255 mg/L
(Westerman et al. 1990). Lagoon sludge was reported to have an average COD of 67,430 mg/L
(J. Barker, NCSU, unpublished data); thus, these concentrated and highly-labile effluents
are likely to exert a major oxygen demand on already oxygen-poor waters. A previous
incident demonstrated this effect: in July 1995 a poultry waste lagoon in the upper
Northeast Cape Fear watershed ruptured, releasing 32.6 million L of waste into tributary
creeks which subsequently entered the river (Mallin et al. 1997b). This created a
dissolved oxygen sag which reached its minimum of 1.0 mg/L at NCF117, 90 km downstream of
the spill area 17 days after the rupture. Until the aftermath of Hurricane Fran this DO
reading was the lowest on record (27 yrs) at this station.
In addition to outright waste release incidents, lagoon operators
sprayed unknown amounts of liquid wastes on already-saturated fields to prevent other
lagoons from overtopping in the rains following Hurricane Fran (NCDEHNR 1996b; WMS 1996).
Another anthropogenic source which may have contributed to BOD loading was an unknown
number of septic systems flooded by heavy rainfall along the floodplain. Finally, at least
five of the aforementioned publicly-owned treatment facilities malfunctioned along the
Northeast Cape Fear River, releasing approximately 1.0 million gallons of human waste in
various stages of treatment to the watershed. Treatment plant and pump station failures
diverted about 4.7 million gallons of human sewage into the Black River watershed. The
majority of the human sewage diversions (approximately 70 million gallons) occurred along
the mainstem Cape Fear River basin (NCDEHNR 1996b). Human sewage has an average BOD of
approximately 200 mg/L (Clark et al. 1977); however, the diverted liquid ranged from
concentrated sewage to waste heavily diluted by stormwater runoff, so quantification of
the BOD load would be very speculative. Regardless, the mainstem received a sizable BOD
load from human sewage but its greater flow (Table
5.1; Fig. 5.2) and subsequent flushing and
dilution of BOD allowed DO levels to increase to acceptable levels more quickly than those
of the Northeast Cape Fear (Fig. 3) or the Black
River. Additionally, blackwater rivers are already more oxygen-stressed than Piedmont
rivers in summer (Meyer 1990, Meyer 1992, Mallin et al. 1996), further lengthening
recovery time from BOD pollution incidents.
Ammonia and phosphorus are nutrients which, in elevated concentrations,
are characteristic of human and animal wastewater (Clark et al. 1977, Donham et al. 1985,
Westerman et al. 1990). With available background monitoring data it is possible to
utilize pulses of these nutrients as evidence of anthropogenic inputs to a water body.
Thus, in 1995 we attributed a water column "spike" in ammonia in the lower
Northeast Cape Fear River to an upstream poultry waste lagoon rupture ten days earlier
(Mallin et al. 1997b). Following Hurricane Fran both ammonia and phosphorus reached
notable peaks (Table 5.1; Figs. 5.6 and 5.7);
a check of North Carolina Department of Environment, Health and Natural Resources records
indicated that total phosphorus concentrations in the Northeast Cape Fear River at NCF117
following Hurricane Fran were the highest recorded in 27 years of available data. These
nutrient concentrations were over 50% higher than those in the Black River and the
mainstem Cape Fear River, and we conclude that anthropogenic loading, primarily
concentrated animal waste, was largely responsible for these burdens.
Benthos represent an important group of consumers and prey items in the
Cape Fear system. Because of their trophic position and relatively sedentary lifestyle,
benthos can provide an approximation of the degree and longevity of environmental effects
on animals in the system. Benthos at several sites exhibited significant declines in
abundance after the passage of Hurricane Fran relative to previous time periods,
especially in the Northeast Cape Fear site and the mid-estuary site M54. A major event
such as Hurricane Fran may impact benthos through a variety of mechanisms, including
increased sedimentation, introduction of contaminants, short-term changes in salinity,
changes in DO, and disturbance from increased flow. Sediment deposition may have affected
certain species, but observations of grabs taken after the hurricane did not indicate
dramatic changes in sediment composition or provide evidence of significant deposition.
Both NCF6 and M54 had higher concentrations of N and P associated with storm runoff.
Although chronic nutrient loading may affect benthic communities (Beukema 1991), there is
less evidence to suspect significant effects from short-term increases. Significant
declines in freshwater taxa, such as oligochaetes and insect larvae, suggest that salinity
decline was not the primary factor driving post-hurricane faunal changes.
Low DO was likely the most important environmental change associated
with the passage of Hurricane Fran, causing general declines among a variety of benthos.
Both NCF6 and M54 had substandard surface and bottom DO concentrations for an extensive
period. Low DO associated with organic enrichment has been well-demonstrated to reduce
abundances of several infaunal groups (Dauer 1984, Aschan and Skullerud 1990, Tsutsumi
1990, Weston 1990). Storm-associated low DO has been suggested to cause declines in
abundance of several of the taxa observed in our samples, including certain amphipods
(e.g. Cyathura, Corophium, Leptocheirus and Gammarus: Boesch
et al. 1976; Whitehurst and Lindsey 1990), isopods and certain polychaetes (e.g. Streblospio,
Nereis, and Maranzellaria: Boesch et al. 1976; Dauer 1984). Taxa more
tolerant of low DO, such as the capitellid polychaete Mediomastus (Aschan and
Skullerud 1990) exhibited more variable responses and actually increased in abundance at
the lowest estuarine station M31. At M31 significant decreases were only detected for
amphipods. Decreased effects at M31 further suggest that low salinity was not the primary
mechanism for declines in abundance since the mesohaline species found at this station may
be expected to be most susceptible to dramatic salinity reductions. Decreased storm
effects may reflect adequate DO at this station after Fran, along with the influences of
tidally introduced oceanic waters. Significant hurricane effects were not demonstrated at
the oligohaline Cape Fear River site NAV, reflecting high background variability in this
region and possibly the relatively rapid recovery of bottom-water DO to 5.0 mg/L by
October 4.
There was recovery of benthic fauna within 2-4 months at some
locations, providing evidence to support the idea that the rapid reproduction and
opportunistic nature of many estuarine benthos will lead to high resiliency in benthic
community composition and abundances (Dauer 1984). However, recovery did not occur at
equal rates among all sites, possibly reflecting differences in the dominant taxa present.
NCF6 was dominated by amphipods and insect larvae, whose brooding reproductive strategies
or adult dispersal can allow rapid increases in population numbers after a disturbance.
Among the taxa most affected at M54 were polychaetes that must rely upon spring
recruitment for recovery.
5.6 Environmental Policy and Hurricane Effects
We contend that human activities, particularly those concerned with
waste treatment, significantly magnified the deleterious effects of Hurricane Fran on
water quality. Power outages caused diversions of over 75 million gallons of inadequately
treated human sewage into the Cape Fear River system; statewide approximately 210 million
gallons were diverted (NCDEHNR 1996b). Much of this diverted material could have been
properly treated had backup generating systems been mandated for publicly-owned waste
treatment facilities. In some situations, local industries offered the use of generators
to treatment facilities but these facilities were inadequately wired to utilize the
generators (H. Strickler, G.E. Corporation, pers. com.). Siting of animal waste lagoons
was also a major environmental hazard. Our analysis demonstrates that several lagoon
incidents contributed to serious water quality damage in the Northeast Cape Fear basin;
statewide there were at least 22 lagoon incidents attributed to Fran (NCDEHNR 1996b).
Lagoon breaches and other incidents have happened previously for a variety of reasons
(Burkholder et al. 1997, Mallin et al. 1997b). However, much of the post-hurricane animal
waste loading was a direct result of siting waste lagoons on river floodplains. In
addition to lagoon accidents, spraying of lagoon liquid on rain-saturated floodplains to
prevent further overtoppings probably caused more BOD and nutrient loading to nearby
streams. Finally, many private residences built on river floodplains suffered flooding and
problems with septic systems.
Treatment system backup generators can be retrofitted. Legislation was
introduced in the N.C. General Assembly in February 1997 to require on-site generators for
wastewater treatment plants which are permitted to discharge waste. Legislation to
prohibit construction of new animal waste lagoons and prohibit expansion of existing
facilities in locations subject to flooding by a one-hundred year flood was also
introduced in the N.C. General Assembly in February 1997. The legislation requiring
on-site generating systems did not make it out of committee during the 1997 session. As
part of a comprehensive clean water effort the General Assembly did pass legislation
barring future construction of hog houses and lagoons within the one- hundred year
floodplain, although land application sites (spray fields) are permitted. Regardless of
this legislation, however, lagoons already present on floodplains will remain potential
hazards until retired from use and pumped down. The siting of residences in flood-prone
areas is also likely to remain problematic, depending on land-use planning efforts (or
lack thereof). While Hurricane Fran in particular led to large-scale environmental damage,
the experiences garnered from this event have led to serious policy discussions and some
improved environmental policy efforts in hurricane-prone regions.
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