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<br />
<br />ether, ethyl tert-butyl ether (ETBE),
<br />ethyl benzene, toluene, xylene,
<br />methyl tert-butyl ether (MTBE),
<br />and methyl tert-pentyl ether. Three
<br />samples were collected from the
<br />Tar River at sites 14 (two samples)
<br />and 16. A sample also was collected
<br />at site 40 on the Cape Fear River.
<br />The only compound detected was
<br />MTBE at sites 16 (57,8 ng/L) and
<br />40 (36.3 ng/L). However, such lim-
<br />ited sampling, in terms of frequency
<br />and areal coverage, cannot provide
<br />an accurate assessment of the
<br />impact of fuel spills on floodwater
<br />quality.
<br />
<br />Nitrogen and Phosphorus
<br />Loads
<br />
<br />A load is an estimate of the total
<br />mass of a constituent passing a
<br />selected stream location during a
<br />given period of time. For example, a
<br />nitrogen load calculated for the Pam-
<br />lico River at Washington provides an
<br />estimate of the total pounds of nitro-
<br />gen entering the Pamlico River
<br />estuary during the period of interest.
<br />Loads from different size basins can
<br />be normalized by dividing the load
<br />by the basin area, providing a yield
<br />(in, for example, pounds per square
<br />mile per year), so that export from
<br />different basins can be compared.
<br />There is some uncertainty in the
<br />calculation of floodwater loads
<br />because of the small number of
<br />water-quality samples used in the
<br />calculation. However, as a result of
<br />the relatively small variation at a site
<br />in constituent concentrations during
<br />flooding, the calculated loads seem
<br />to provide reasonable estimates of
<br />basin export.
<br />Nitrogen and phosphorus loads
<br />were determined at selected loca-
<br />tions for September 15-0ctober 20,
<br />
<br />1999, by using calculations of mean
<br />daily discharge and periodic mea-
<br />surements of concentration. The
<br />
<br />(''''
<br />'.l ;,~:' .~:..
<br />: ._ ,~f' .:.~:.
<br />......"r,r.~ 'i
<br />.' ~';;.. :~ s'
<br />"
<br />
<br />~
<br />t
<br />
<br />. '1'(::.
<br />
<br />oj
<br />
<br />"
<br />
<br />mean discharge data were not
<br />available, an estimate of monthly
<br />mean discharge for September and
<br />October and the
<br />median of water-
<br />quality data from
<br />samples collected
<br />by the North
<br />Carolina Division
<br />of Water Quality
<br />during September
<br />and October
<br />(Larry Ausley,
<br />Division of Water
<br />Quality, written
<br />commun" Janu-
<br />ary 2000) were
<br />used to calculate
<br />the nitrogen and phosphorus yield for
<br />September and October.
<br />The cumulative load of nitrogen
<br />in Hurricane Floyd floodwaters
<br />ranged from 450 tons in the Lumber
<br />River (site 45) to 4,200 tons in the
<br />Neuse River near Fort Barnwell
<br />(site 32, fig. 15). At Kinston (site 28),
<br />a nitrogen load of about 1,700 tons,
<br />equivalent to half ofthe mean annual
<br />nitrogen (3,400 tons; Harned and
<br />others, 1995), was carried by
<br />
<br />__ ____,~;-.:,.r-~--
<br />
<br />'~'~~c;l
<br />
<br />1011
<br />1999
<br />
<br />Figure 15. Cumulative total nitrogen load at sites near the mouths of the Tar.
<br />Neuse. Cape Fear. Northeast Cape Fear. and Lumber Rivers,
<br />
<br />Black River near Tomahawk, N.C.
<br />
<br />36-day period used for the load
<br />calculations includes the rise, peak,
<br />and fall of floodwaters from Hurri-
<br />cane Floyd. At most sites, subse-
<br />quent rainfall from Hurricane Irene
<br />(October 17-18) caused secondary
<br />flooding (for example, figs. 8 and 10)
<br />that was not included in these load
<br />calculations because concentration
<br />data were not collected during this
<br />secondary rise. For the Pamlico
<br />River at Washington where daily
<br />
<br />4,500
<br />
<br />4,000
<br />
<br />~ 3,500
<br />a
<br />~
<br />z
<br />~- 3,000
<br />'"
<br />g
<br />aJ 2,500
<br />~
<br />a
<br />~
<br />~ 2,000
<br />w
<br />>
<br />~ 1.500
<br />~
<br />::;
<br />131,000
<br />
<br />
<br />500
<br />
<br />9119
<br />
<br />9123
<br />
<br />9127
<br />
<br />Two :'vlomhs of Flooding in Eastern North Carolina. September-October 1999
<br />
<br />
<br />-NeuseRivernear
<br />FtBarnwell
<br />
<br />Tar River at
<br />Greenvilll!
<br />
<br />Northeast Cape Fear River
<br />_ Cape Fear River at nearChinqllapin
<br />Lock 1 I
<br />
<br />Lumber River at Boardman/
<br />
<br />10/5
<br />
<br />10113 10/17
<br />
<br />10/9
<br />
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