20080868 Ver 2_Section III C Water Quality 2020 PCS Creeks Report_20210701

C. WATER QUALITY
(Section III. C. was prepared by Dr. Suelen Tullio, the laboratory manager in the
Environmental Research Laboratory of East Carolina University with assistance from Dr.
Siddhartha Mitra, Professor of Geological Sciences, East Carolina University, Greenville, NC).
1.0 History
Water quality monitoring sites on three creek systems were initially established in
1998 as follows: (1) two locations in Jacks Creek, (2) three locations on Tooley Creek, and (3)
four locations on Huddles Cut (Figures I-B3, I-B10, and I-B13). These stations were monitored
in accordance with the 1998 plan and continued under the final 2011 plan as outlined in Table I-
A1. By December 2011, two stations each in six additional creeks (three control creeks and
three creeks to be impacted) had been added such that ten creeks designated for water quality
monitoring were part of the regular program (no water quality samples have ever been collected
in Muddy Creek).
Water quality stations at two locations were added in the following creeks in
2011: Little Creek- LCWQ1 and LCWQ2, one at each of the salinity stations (Figure I-B5);
Jacobs Creek- JCBWQ1 near the upstream salinity station and JCBWQ2 near the old railroad
trestle (Figure I-B6). Project Area 2 (PA2) - PA2WQ1 at the upstream end of the main channel
and PA2WQ2 at the midstream salinity station (Figure I-B7). Drinkwater Creek- DWWQ1 at the
upstream well array and DWWQ2 near the upstream salinity station (Figure I-B8); Long Creek-
LOCWQ1 and LOCWQ2, one at each of the salinity stations (Figure I-B9); Porter Creek- one
downstream of the most upstream well array (PCWQ1) and PCWQ2 at the upstream salinity
station (Figure I-B14); and Duck Creek- DKCWQ1 at the upstream salinity monitor and
DKCWQ2 at the downstream salinity monitor (Figure I-B18). With the addition of two stations in
2013 on two small, unnamed tributaries (UTs) to Durham Creek, DCUT11 (DC11WQ1 . Figure I-
B16 and DCUT19 (DC19WQ1; Figure I-B17) all water quality stations designated in the study
plan north of NC Highway 33 were in place.
In 2018, two additional creeks were added to the study, Broomfield Swamp
Creek (Figure I-B1) and SCUT1, a tributary to South Creek as control (Figure I-B2); however,
the 2018 data record was incomplete for the year for all parameters and no data analysis was
performed. The data record for both Broomfield Swamp Creek and SCUT1 started being
included in the analysis for the water quality report in 2019.
a. Description of Analysis Techniques
Multivariate analysis was used to analyze all water quality data. Since
the 2015 report on data collected through 2014 (CZR 2015), the data have been divided into
two data sets. The first data set (Data Set 1) consists of data from 1999-2011 in Huddles Cut,
Jacks Creek, and Tooley Creek with no new data added; therefore, this data set has not been
repeated in any recent annual report. The second data set (Data Set 2) consists of all stations
with data from 2012-to present. The reason that these two data sets were separated was to
avoid bias from longer data sets on the principal components structure. For temporal and
spatial analysis of these creeks for the earlier years, please refer to the 2015 report (CZR 2015).
In each subsequent annual report, Data Set 2 has been updated with data from the current year
and analyzed for temporal and spatial variability. However, in analysis for this section of the
report, the entire data set (1999-current data collection year) was used to compare conditions in
pre -Mod Alt L and post -Mod Alt L years. Pre- and post -Mod Alt L data were compared at Jacks
Creek, Jacobs Creek, Drinkwater Creek, Tooley Creek, Huddles Cut, Porter Creek, and
DCUT11. The pre- and post -Mod Alt L divisions are shown in Table III-C1.
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Temporal variability at water quality stations across years was analyzed
via a Principal Components Analysis (PCA) to recombine all water quality variables into the
loading components that capture the intercorrelation between variables; in this context "loading"
is synonymous to "contributing". PCA has two primary uses: 1) to describe interrelationships
between a matrix of intercorrelated variables and 2) data reduction, (i.e., to reduce a large
matrix of intercorrelated variables into linear recombinations, or principal components [PC] of
the original variables). A missing value results in no PC values, thus, to decrease the number of
gaps in the data (missing values) when a variable was reported with a value below detection,
the detection value was used. Actual gaps in the PC interannual variability graph usually
indicate there was not enough water to collect a sample. The PCA plots all original variables in
multidimensional space (one dimension for each variable), and then fits a regression line
through these multiple dimensions. The principle of least squares is used to fit the regression
line and the resulting variance explained is recombined into a principal component that explains
a fraction of the total variation. This procedure is repeated, (i.e., a new regression line is fitted
to the remaining data), and a new principal component is calculated and generated, until all
variability is explained. The PCs themselves are uncorrelated to each other and therefore may
be used in further modeling without violation of regression assumptions. The PCs can be
related to the original variables by examination of the loadings on to each PC, and these values
represent the degree of correlation of each original variable to the new PC. To examine how
the PCs are related to one another, a loading plot is generated to show how the original
variables are related to the first two PCs. The resulting set of PC values represents new
variables, made from the original variables, but fewer in number and uncorrelated to each other.
Plotting the PC scores over the course of the years shows the temporal variability of multiple
variables, without the need to generate numerous plots. A PCA analysis was run for each water
quality station and the biplot, loadings, and PC time series are presented. Although it is
customary to examine all PCs until approximately 80 percent of the variance is explained, to
reduce the number of graphs in the report, only the first two PCs were graphically represented
(the ones that explain the majority of the variance).
Spatial variability among stations across all years was analyzed by
comparison of the yearly means of each water quality parameter at each monitoring station
using a cluster analysis, a multivariate technique that analyzes similarity or dissimilarity
computed from a data matrix. For example, a single water quality monitoring station may be
characterized by multiple water quality measurements. Thus, one might ask: how similar are
two water quality stations from two different creeks based on all of the water quality
measurements? While it is straightforward to compare salinity values between the two creeks,
the addition of more parameters makes the comparison more complex. This comparison of the
data matrix of water quality values was done by grouping by station while a dissimilarity matrix
was calculated, and a plot of the water quality values for each parameter in multivariate space
was built. Instead of fitting a regression line, as with PCA, the Euclidean distance is calculated
between the water quality values for each station. Values that are close to each other in space
have low dissimilarity and values that are far apart in space have high dissimilarity. Once the
dissimilarity matrix was computed, the dissimilarity values for each station were clustered and
displayed using a dendrogram (tree diagram). This analysis examines relationships between
stations and groups water quality monitoring stations with similar conditions. Doing this over
multiple years aims to demonstrate how relationships between stations might change over time.
The location of each station relative to the Pamlico River (upstream vs. downstream) was also
included in the spatial analysis to determine if distance from the river was a factor underlying
relationships between water quality monitoring stations. (As the data collection location figures
in Section I.B show, upstream water quality station locations are various distances from
downstream stations from creek to creek and some upstream stations in some creeks are
actually closer to the river than some downstream stations in other creeks; however, upstream
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stations are shallower than downstream stations). Water quality conditions for each group of
stations were then summarized graphically. Individual water quality values for all parameters by
group are also shown as means and standard deviation bar graphs to indicate the variability of
each parameter within each individual group or cluster.
Finally, to compare interannual variability in water quality parameters
pre- and post -Mod Alt L, the full time series of data from Jacks Creek, Jacobs Creek, Drinkwater
Creek, Tooley Creek, Huddles Cut, Porter Creek, and DCUT11 were used as shown in Table III-
C1. Pre- and post -mod Alt L conditions were compared using a one-way ANOVA, and t scores
and p-values were presented. Differences were considered significant if p-values were < 0.05.
It is important to note that the number of samples analyzed (N) has an effect on the ability to
detect differences pre- and post -impact. The greater the number of samples used to detect
changes in mean water quality parameter values pre- and post -impact, the greater the chance
that a change will be detected. It is also important to differentiate between statistical
significance versus practical (or in this case, ecological) significance (Amrhein et al., 2019;
Dushoff et al., 2019; Martinez-Abrain, 2008; Van Calster et al., 2018). The discussion around
null hypothesis significance testing (NHST) and ecological significance involves the ideas that
NHST does not provide important information, that is, the magnitude of an effect and the
precision of the estimate of the magnitude of that effect. NHST approaches informs the
probability of the observed data to test if the null hypothesis is true, conversely it lacks
information about the potential changes in ecosystem function and structure (Halsey, 2019;
Nakagawa and Cuthill, 2007; Wasserstein et al., 2019; White et al., 2013). The debate about
use of other metrics to assess potential changes continues, but for continuity with previous
reports this familiar metric will be used. Additionally, whether any changes in magnitude for the
water quality parameters might indicate ecological changes will continue to be assessed.
2.0 Results
Seventeen water quality parameters were analyzed for most creeks (Table III-
C2). Two of those parameters are considered biological (chlorophyll a and dissolved oxygen)
while the remainder are considered biochemical and are either conservative (e.g., salt and pH)
or non -conservative (e.g., nutrients). Locations of water quality sample stations are shown in
Figures I-B1-I-B3, Figures I-B5 - I-B10 and Figures I-B13 - I-B14, and Figures I-B16 — I-B18.
a. Temporal variability (2012-2020) in all creeks
Principal Components Analysis revealed significant interrelationships
between all water quality variables (Table III-C2) and showed the seasonal (Figure III-C1) and
interannual variability (Figure III-C2 through Figure III-C32). The biplot of the visual relationship
between the variables is shown in Figure III-C1. Variables with arrows pointing in the same
direction are positively correlated with each other, variables with arrows pointing the opposite
direction are negatively correlated with each other, and variables at right angles with each other
are not correlated. Each quadrant shows the prevailing conditions when PC1 and PC2 are
positive or negative and can be interpreted as seasonal changes in a clockwise manner. Upper
right quadrant corresponds to spring, lower right to summer, etc. During spring, turbidity,
ammonium, nitrate, total nitrogen, and dissolved organic carbon are highest indicating
freshwater inputs (Figure III-C1). As spring transitions to summer, total dissolved phosphorus,
and orthophosphate peak showing more estuarine inputs (Figure III-C1). Summer conditions
consist of peaks in temperature, particulate phosphorus, particulate nitrogen, chlorophyll a, and
dissolved Kjeldahl nitrogen (Figure III-C1). Fall conditions are characterized by peak salinity,
conductivity, and pH values for the year and depth values increase during the transition to
winter (Figure III-C1). Winter conditions have the highest values of dissolved oxygen (Figure III-
C1). This seasonal distribution of parameters has been observed since 2015 with the one
exception of nitrate in 2016 which peaked in summer. The individual time series for each
station in all creeks are discussed in the following subsections.
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i. Broomfield Swamp Creek water quality station BSCWQ1
This station is an upstream station with a clear seasonal pattern in
which PC2 values were higher in the first four months (Figure III-C2). However, the values for
PC1 were higher than PC2 on most samples until the final two months of the year.
ii. Broomfield Swamp Creek water quality station BSCWQ2
The seasonal trend for this station was almost identical to
BSCWQ1 with lower values in the second part of the year for PC2, but with some mixed values
for PC1 and PC2 (Figure III-C3). The main difference was clearer separation in values in the
last three months for PC2. The response of PC1 at this midstream station seems to indicate
more estuarine influence (low values on the PC1 axis represent higher conductivity and salinity
(Figure III-C1)).
Broomfield Swamp Creek water quality station BSCWQ3
The seasonal pattern detected for the previous two stations
continued with higher values for PC2 early and late in the year and PC1 value fluctuation
around 0 during fall and winter (Figure III-C4). The attenuation of values for PC1 compared to
the previous two stations suggests even more estuarine influence (station is located almost at
its confluence with South Creek).
iv. SCUT1 water quality station SC 1 WQ 1
The PC values for this upstream station clearly indicate higher
values for PC2 in the early and later part of the year with higher PC1 values during the spring,
summer, and early fall (Figure III-05). This seasonality in PC values was similar to the one
identified in Broomfield Swamp Creek.
v. SCUT1 water quality station SC 1 WQ2
The seasonal pattern for this station was, again, higher values for
PC2 during late fall and winter and high values for PC1 during spring, summer and early fall
(Figure III-C6). The initial response of PC1 in early summer was markedly stronger than on the
upstream station.
vi. SCUT1 water quality station SC 1 WQ3
The seasonal signal persisted in this downstream station. The response for PC1 and PC2 were
similar to the previous stations (Figure III-C7). The PC1 values followed the pattern indicated in
the other two SCUT1 stations in which spring and summer were higher, while the PC2 values
showed higher values for fall and winter.
vii. Jacks Creek water quality station JWQ 1
The seasonal trend for PC1 was mostly positive (freshwater influence) over the time series, with
most peak values in the summer (Figure III-C8). PC2 presents a similar annual cycle with lower
magnitude values overall and more negative values across the year with most of the peak
values in the summer (Figure III-C8). Both PC1 and PC2 fluctuated in magnitude over time, an
indicator of water quality variability at this station over the seasonal cycle. During 2020, the
PC1 and PC2 values return to the established separation pattern prior to 2019 indicating
separate responses to the 2020 environmental drivers.
vii. Jacks Creek water quality station JWQ2
The general seasonal trend for PC1 was negative during the
winter months (estuarine influence) and positive in the warmer months (Figure III-C9). PC2
showed an opposite annual cycle with peak values earlier in winter (Figure III-C9). Both PC1
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and PC2 presented a typical seasonal cycle for the 2020 year. Comparatively speaking, the
variability of both PCs for this year seems lessened when compared to previous years.
viii. Little Creek water quality station LC WQ 1
The seasonal trend showed positive peaks in magnitude in the
summer and negative values for PC1 during the winter when compared to PC2 values (Figure
III-C10). PC2 followed the opposite pattern and tended to peak earlier in the year with lower
values in the summer; however, it remained largely positive from terrestrial runoff influence
(Figure III-C10) as indicated by the parameters prevalent on the positive side of the PC2 axis in
Figure III-C1.
ix. Little Creek water quality station LCWQ2
The general seasonal trend for PC1 was negative throughout
2020 with peaks in positive magnitude in the summer, while PC2 values were positive with
peaks through the winter months (Figure III-C11) and minimal values during summer. Both PC1
and PC2 showed less fluctuations over time compared to LCWQ1; a typical indication of
environmental stability at this downstream creek station. The 2020 variability was typical for this
station and similar to previous years (with the exception of 2017).
x. Jacobs Creek water quality station JCB WQ 1
The 2020 seasonal trend for PC1 was positive in summer as in
previous years (max value of 2.099 on June 03, 2020; Figure III-C12). PC2 annual cycle was
similar to previous years with peak values typical in the winter (Figure III-C12). Although the
magnitude of variability in PC2 was higher in the pre -Mod Alt L years, PC2 water quality at this
station has become more stable within a typical seasonal cycle as evidenced by the smaller
variation in magnitude since 2014 and since 2018 for PC1.
xi. Jacobs Creek water quality station JCBWQ2
The 2020 seasonal trend for PC1 was similar to the previous year,
with near zero values in late summer, while PC2 varied around zero with higher values in late
fall to winter (Figure III-C13). Both PC1 and PC2 showed little fluctuation in magnitude over
time; water quality at this station was stable with a typical seasonal cycle with increased
estuarine influence in winter.
xii. PA2 water quality station PA2WQ 1
The seasonal trend for PC1 continued to be positive in summer
and negative in winter, while PC2 was opposite (Figure III-C14). The fluctuation in both PC1
and PC2 over time followed the typical seasonal pattern. Values for PC1 and PC2 in 2020 were
in line with the historical record (with exception of 2019 which showed more variability for both
PC1 and PC2 late in winter).
xiii. PA2 water quality station PA2WQ2
xix. PA2 water quality station PA2WQ2
This station shows a very clear general seasonal trend for both
PCs. PC1 was negative throughout the year with peak values in the late summer, early fall
while PC2 fluctuates between 0 and 2 (Figure III-C15). Both PC1 and PC2 vary over time in
minimal fashion with little overlap in values.
xiv. Drinkwater Creek water quality station DWWQ 1
The seasonal trend for PC1 is positive for most of 2020 with maximum values during the
summer (max value of 5.528 on August 26, 2020; Figure III-C16). PC2 values become negative
as the year progressed with some fluctuation during winter 2020 (Figure III-C16). Both PC1 and
PC2 values are within the observed historical record.
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xv. Drinkwater Creek water quality station DWWQ2
The seasonal trend showed PC1 became positive as summer
began (max value 4.796 on June 03, 2020) and then became negative from September through
the end of the 2020 (Figure III-C17). Although PC2 showed an opposite annual cycle or
behavior pattern to PC1, both PCs presented the most negative values on September 09, 2020
(PC1: -2.538 and PC2: -4.459; Figure III-C17). Both PC1 and PC2 show a muted fluctuation in
magnitude over time than the upstream station with a relatively stable seasonal cycle.
xvi. Long Creek water quality station LOCWQ 1
The seasonal trend for PC1 in 2020 and across the time series
was negative throughout most of the year, with peaks in magnitude in the summer and fall
(Figure III-C18). PC2 fluctuated around zero over the time series (Figure III-C18). Overall, PC1
showed increased fluctuation in magnitude in 2012, 2017, and 2018, an indicator of estuarine
influence at this station.
xvii. Long Creek water quality station LOCWQ2
The trend for PC1 was negative throughout the year, with the low
values during winter 2020 (Figure III-C19). PC2 fluctuated with mostly negative values but well
within the historical variation (Figure III-C19). With the exception of 2014-2016, summer values
for this station overlapped, and summer values over the entire time series showed little
fluctuation in magnitude; indicators that summer water quality seems most stable.
xvix. Tooley Creek water quality station TWQ 1
The general seasonal trend for PC1 was positive throughout the
year with peaks values in the summer (Figure III-C20). The only exception was late fall which
PC1 showed negative values. The 2020 PC2 values were negative in the middle of the year
and only became positive in winter (Figure III-C20). Both PC1 and PC2 showed increased
fluctuation over time.
xx. Tooley Creek water quality station TWQ2
Both PC1 and PC2 had considerable variability throughout 2020
(Figure III-C21). This site continues to periodically experience insufficient water levels for
sample collection throughout the year, thus the gaps in the data set. Due to the variability in
water level, it is not surprising that water quality values fluctuate (Figure III-C21). Despite the
gaps, the general trend for PC1 was positive while PC2 values were negative.
xxi. Tooley Creek water quality station TWQ3
The overall seasonal trend for PC1 was negative throughout 2020
and showed peak values in the summer (Figure III-C22). PC2 values showed minimal variability
over the time series although 2016 through early 2018 showed more positive values compared
to other years (Figure III-C22). Summer and fall of 2020 showed a convergence of values for
PC1 and PC2, a sign of stability (i.e., minimal water inputs/exchange).
xxii. Huddles Cut water quality station HWQ 1
The 2020 seasonal trend for PC1 was positive throughout the year
but showed fluctuations and higher values than the previous years (Figure III-C23). PC2
mirrored the PC1 annual cycle, as customary, with mostly negative values throughout 2020
(Figure III-C23) while low positive values occurred in winter 2018, 2019, and 2020.
xxiii. Huddles Cut water quality station HWQ2
The general seasonal trend for PC1 was largely positive with
peaks in the summer and lower values in the winter (Figure III-C24). PC2 peaked in the winter,
with most negative values in the summer (Figure III-C24). Both PC1 and PC2 showed large
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fluctuations throughout 2020.
xxiv. Huddles Cut water quality station HWQ3
The historical seasonal trend for PC1 remained positive
throughout the 2020 data record and increased over time (Figure III-C25). PC2 showed a
similar annual cycle, but fluctuated closer to zero throughout the year with few positive values;
no change in the historical trend was apparent (Figure III-C25). Both PC1 and PC2 fluctuated
throughout the year with values which followed the established pattern but were lower in
magnitude, with the exception of one value in May 2017, and one in July 2018 and July 2020.
xxv. Huddles Cut water quality station HWQ4
The 2020 seasonal trend for PC1 was similar to the historical
record (Figure III-C26). This station seems to have a rapid response to water level changes.
The variability of PC1 appeared to increase since 2016, and the magnitude of fluctuations
observed in 2020 were in line with the historical record. The years 2015 and 2016 remain the
only years when PC1 was positive all year, an indicator of more terrestrial runoff at this station.
The PC2 values were generally negative over the time series with a similar annual cycle to PC1;
however, it became more negative in late summer or fall (Figure III-C26).
xxvi. Porter Creek water quality station PCWQ1
The general seasonal trend for PC1 seemed to be positive in
summer and less positive or negative in winter (Figure III-C27). PC2 had a similar temporal
pattern of less apparent magnitude than previous years (Figure III-C27).
xxvii. Porter Creek water quality station PCWQ2
The 2020 seasonal trend showed the historical established trend
of PC1 positive values during the summer and less positive or negative during winter (Figure III-
C28). PC2 peaked in early spring and reached maxima negative values in late summer/early
fall (Figure III-C28).
xxviii. DCUT 11 water quality station DC 11 WQ 1
The general seasonal trend for PC1 was negative most of the year with high negative values in
late fall and winter (Figure III-C29). PC2 overlaps the PC1 pattern in the summers (Figure III-
C29). Both PC1 and PC2 showed fluctuations in magnitude over time opposite in trend with
each other. The year 2018 was the first post -Mod Alt L year, and 2019 and 2020 PC values
have a more muted response than 2018.
xxix. DCUT19 water quality station DC19WQ1
The historical seasonal trend for PC1 was positive in summer and
slightly positive, or negative in winter (Figure III-C30). For 2020, except for November and
December, PC2 values fluctuated near zero over the time series, and were of lesser variability
than previous years (Figure III-C30). The overall pattern for both PCs was similar to station
DC11WQ1 although the range of variability had less range in values.
xxx. Duck Creek water quality station DKCWQ 1
The general seasonal trend for PC1 was positive in summer and
slightly positive, or negative in winter. PC2 showed a similar annual cycle; however, most
peaks occurred in winter and spring (Figure III-C31). Both PC1 and PC2 continued to show a
reduction of fluctuations in magnitude over time and overlaps occurred in summer. Water
quality at this station seems more stable and with a typical seasonal cycle.
xxxi. Duck Creek water quality station DKCWQ2
The general seasonal trend for PC1 was largely negative
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throughout the year, with less negative or slightly positive values in summer (Figure III-C32).
PC2 shows a similar annual cycle, but fluctuated also near to zero but positive throughout much
of the years with peaks in spring and late winter (Figure III-C32). Both PC1 and PC2 showed
typical seasonal cycles; minimal fluctuation in magnitude over time and summer overlaps to
indicate that water quality was relatively stable.
b. Spatial variability (2012-2020) in all creeks
As in the previous four years, the cluster analysis revealed five distinct
groups of water quality station/years based on similarity or dissimilarity computed from the data
matrix of all water quality variables (Figure III-C33). A summary of all water quality conditions
across the five groups is shown in Table III-C3.
Group A had most of the station/years of all groups (95) and consisted
primarily of 49 upstream station/years from Duck Creek, Little Creek, Drinkwater Creek,
Huddles Cut, Jacks Creek, Porter Creek, Tooley Creek, and Broomfield Swamp Creek and 46
downstream station/years from Drinkwater Creek, DCUT11, DCUT19, Huddles Cut, and Porter
Creek. Drinkwater Creek represented about one third of the group (Figure III-C33). This group
had a mix of intermediate values for most water quality parameters compared to other groups,
although it also had the lowest average for temperature (Table III-C3). Group B was comprised
of nine upstream station/years in Little Creek, Broomfield Swamp Creek, and SCUT1 and ten
downstream station/years in Porter Creek, Broomfield Swamp Creek, and SCUT1 (Figure III-
C33). This group had the lowest average particulate nitrogen and chlorophyll a values but the
highest depth and nitrate values (Table III-C3). Group C consisted of 21 station/years from
Jacks Creek, Huddles Cut, Tooley Creek, and Porter Creek and three downstream station/years
from Huddles Cut. This group had highest average conductivity and particulate phosphorus
(Table III-C3). Group D was the smallest cluster with six station/years that consisted of only
Huddles Cut upstream west prong station in WQ1. This group had the lowest average depth,
salinity, conductivity, dissolved oxygen, and nitrate values, but the highest turbidity, ammonium,
DKN, particulate nitrogen, total dissolved nitrogen, orthophosphate, total dissolved phosphate,
chlorophyll a, and dissolved organic carbon. Group E was the second largest group (91
stations/years) and consisted primarily of upstream station/years from Jacobs Creek, Long
Creek, and PA2 which represented about 30 percent of the group, and downstream
station/years from Duck Creek, Jacobs Creek, Jacks Creek, Little Creek, Long Creek, PA2,
Tooley Creek, and DCUT19 comprised the remainder of this group (Figure III-C33). This group
had highest average salinity, temperature, dissolved oxygen, and pH, whereas it had the lowest
turbidity, ammonium, DKN, total dissolved nitrogen, orthophosphate, total dissolved phosphate,
particulate phosphate, and dissolved organic carbon concentrations (Table III-C3).
i. Depth
Depth (in) varied across the five groups. Groups B and E mean
depths were the highest while groups A, C and D had lower depths (Figure III-C34). Note that
groups B and E had a mixture of upstream and downstream stations, resulting in large standard
deviation values, indicating the different responses at these locations to variations in wind tide,
runoff, and/or catchment size. In contrast, group C and D members were mostly upstream but
consistent in depth.
ii. Temperature
Mean temperature (°C) showed small scale variability across three
of the five groups (Figure III-C35). Highest variability occurred in groups C and D with primarily
upstream stations and shallower depths.
Salinity
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Salinity showed substantial variability across the group means
(Figure III-C36) which were significantly different. Group E, comprised of predominantly
downstream station/years more subject to variations in river discharge, had the highest mean
salinity; group A, C and E had similar variability to each other.
Conductivity
Mean conductivity (mS) for group C was the highest while the rest
of the groups had similar values to each other (Figure III-C37). Group C also showed the
largest range in standard deviation, followed by groups A and E which followed the same
pattern identified in salinity.
iv. Turbidity
Turbidity (NTU) showed large standard deviations and some
variability across the means across the groups (Figure III-C38) with the broadest standard
deviation computed at group D. Group E had the lowest mean in spite of being the second
group with the most station/years.
v. Dissolved oxygen
Dissolved oxygen (mg L-1) showed some variability across group
means (Figure III-C39). Group D had the lowest mean dissolved oxygen value (Figure III-C39)
but overall, no biological conclusion can be drawn.
vi. pH
pH was similar across four group means (Figure III-C40) with the
group E having the highest average pH (7.20, almost neutral) and highest salinity (8.16) (Table
III-C3).
vii. NH4 (ammonium)
NH4 (mg L-1) showed large variability in means among the five
groups (Figure III-C41) with concomitant wide ranges in standard deviation. Differences among
groups were significant. Group E had the lowest mean, and the larger standard deviation was
computed for group D.
viii. NO3 (nitrate)
NO3 (mg L-1) concentration means were low among the A, C, D,
and E groups. Group B had the highest mean and standard deviation, and it was significantly
different from the other groups (Figure III-C42).
ix. DKN (dissolved Kjeldahl nitrogen)
DKN (mg L-1) varied in mean concentration values across all
groups. Groups C and D had slightly higher mean values and group D had the largest standard
deviation (Figure III-C43)
xi. PN (particulate nitrogen)
PN (mg L-1) mean concentrations (Figure III-C44) had a similar
pattern among the group means as DKN (Figure III-C43). Group D had highest mean
concentration value, albeit this group is only one station. The next highest mean value and the
largest standard deviation was group C.
xii. Total dissolved nitrogen
Total dissolved nitrogen (TDN mg L-1) showed some similarities
across all group means although D had a higher mean (Figure III-C45) with a distribution pattern
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of concentration means similar to both PN and DKN concentrations. Groups B and C had large
standard deviations when compared with the other groups.
xiii. PO4 (orthophosphate)
PO4 (mg L-1) also showed a similar pattern to PN and DKN mean
concentration values (Figure III-C43, Figure III-C44). Group D presented the highest mean
concentrations of orthophosphate and widest range (Figure III-C46). Overall, the values are
comparable to historic records in both the Pamlico (Hobbie, 1970; Taft and Taylor, 1975) and
the Neuse Rivers (Christian et al., 1991).
xiv. TDP (total dissolved phosphate)
TDP (mg L-1) mean concentration values (Figure III-C47) showed
the same trend among groups as was seen for PO4 (Figure III-C46), albeit with higher means,
as expected given that this parameter includes both dissolved organic and inorganic phosphate
species.
xv. PP (particulate phosphate)
PP (mg L-1) mean values (Figure III-C48) were similar among
groups; groups C and D had the highest mean values and the largest standard deviations. The
values presented a similar pattern as observed for the other phosphate species.
xvi. Chlorophyll a
Chlorophyll a (pg L-1) mean concentration values were also similar
in pattern to the phosphate -related concentrations across the groups (Figure III-C49). Groups
A, B, and E had lower chlorophyll a (pg L-1) mean values and reduced variability compared to
the higher chlorophyll a (pg L-1) mean values of groups C and D and the largest standard
deviation in group D.
xviii. DOC (Dissolved organic carbon)
DOC (mg L-1) showed variability across the five group means
(Figure III-050). The highest mean values and widest standard deviation were in group D
(Figure III-050).
c. Interannual Variability (Pre- and Post -Mod Alt L Creeks)
Comparisons among pre- and post -Mod Alt L water quality parameters
were made for Jacks Creek, Jacobs Creek, Drinkwater Creek, Tooley Creek, Huddles Cut,
Porter Creek, and DCUT11. To compare interannual variability among these seven creeks,
data from all stations for each parameter were classified as pre -Mod Alt L or post -Mod Alt L
(Table III-C1). Pre- and post -mod Alt-L conditions were compared using a one-way ANOVA
and t scores and p-values are presented in Table III-C4 — III-C10. Differences were considered
significant if p-values were < 0.05.
i. Jacks Creek
Jacks Creek showed significant differences for seven of the 17
parameters pre- and post -Mod Alt L; temperature and dissolved oxygen increased while depth,
pH, nitrate, particulate nitrogen, and chlorophyll a decreased, while most of the phosphorus
species increased slightly, but not significantly (Table III-C4). Chlorophyll a concentration post -
Mod Alt L mean continued to be less than half the pre -mean, an indication of fewer
phytoplankton.
ii. Jacobs Creek
Jacobs Creek showed statistically significant differences in six of
III-C-10

the 17 parameters pre- and post -Mod Alt L (Table III-05). Depth and turbidity increased, while
salinity, conductivity, pH, and particulate phosphate concentrations decreased. The nitrogen
species, orthophosphate, and total dissolved phosphate presented almost equally divided
among minimal increases and slight decreases, but were not significant.
Drinkwater Creek
Drinkwater Creek showed statistically significant differences for
nine of the 17 parameters (Table III-C6). Dissolved Kjeldahl nitrogen, orthophosphate, total
dissolved phosphate, particulate phosphate, chlorophyll a, and DOC decreased post -Mod Alt L
while turbidity, pH, and ammonium increased (Table III-C6). The rest of the parameters were
almost equally divided among slight increases and slight decreases, but were not significant.
iv. Tooley Creek
Tooley Creek showed statistically significant differences pre- and
post -Mod Alt L for seven of the 17 parameters (Table III-C7). Temperature, salinity,
conductivity, nitrate, and dissolved Kjeldahl nitrogen increased whereas turbidity and particulate
phosphate decreased. Ammonium, particulate nitrogen, orthophosphate, and total dissolved
phosphate increased, but not significantly. Total dissolved nitrogen and dissolved organic
carbon were not sampled in the pre -Mod AltL period for this creek.
v. Huddles Cut
Huddles Cut showed statistically significant differences in eight of
the 17 parameters pre- and post -Mod Alt L; turbidity and particulate phosphate decreased, while
temperature, salinity, dissolved oxygen, dissolved Kjeldahl nitrogen, orthophosphate, and total
dissolved phosphate increased post -Mod Alt L (Table III-C8). Ammonium and nitrate
concentrations decreased slightly, while chlorophyll a and particulate nitrogen increased slightly.
Total dissolved nitrogen and dissolved organic carbon were not sampled in the pre -Mod AltL
period for this creek.
vi. Porter Creek
Porter Creek showed statistically significantly increases in depth, turbidity, pH, ammonium,
DKN, particulate nitrogen, total dissolved nitrogen, orthophosphate, total dissolved phosphate,
particulate phosphate, chlorophyll a, and DOC. Among the other five abiotic parameters, the
distribution of increases and decreases was almost evenly distributed (Table III-C9).
vii. DCUT11
DCUT11 is on its third post -Mod Alt L year, and as such the
statistical power for any interpretation continues to be limited. Five parameters showed
significant differences: turbidity decreased, and depth, conductivity, pH, and DOC increased for
this comparison (Table III-C10).
3.0 Summary and Conclusions
a. Temporal variability
A Principal Components Analysis (PCA) indicated the continuation of the
relationships between the water quality parameters and the seasonal cycle of water quality
variability (Figure III-C1). The PC1 mean value for all stations per month of the historical record
presented two separate groups: negative values during the colder months (January, February,
March, April, November, and December) and positive values during the warmer months. The
mean PC2 values show the opposite pattern. This particular pattern shows stations responded
to biological (i.e., chlorophyll a and DO) and non -conservative biochemical concentrations (e.g.,
III-C-11

nutrient concentrations) during the warmer months when the phytoplankton community is most
active and, in contrast, during colder months responded mostly to conservative elements (e.g.,
salt and pH) as shown in the bi-plot (Figure III-C1).
b. Spatial variability
A cluster analysis revealed five distinct groups for the pre- and post -Mod
Alt L water quality station/years (Figure III-C33). Group A was the largest group with Duck
Creek, Little Creek, Drinkwater Creek, Huddles Cut, Jacks Creek, Porter Creek, Tooley Creek,
and Broomfield Swamp Creek upstream, and downstream stations in Drinkwater Creek,
DCUT11, DCUT19, Huddles Cut, and Porter Creek (red colored stations in Figure III-C33). This
group had a mix of intermediate values for most water quality parameters compared to other
groups, although it also had the lowest average for temperature (Table III-C3). Group B
consisted of upstream station/years in Little Creek, Broomfield Swamp Creek, and SCUT1 and
downstream station/years in Porter Creek, Broomfield Swamp Creek, and SCUT1 (Figure III-
C33 green colored group). This group had the lowest average particulate nitrogen and
chlorophyll a values, but the highest depth and nitrate values (Table III-C3). Group C included
mostly upstream stations from Jacks Creek, Huddles Cut, Tooley Creek, and Porter Creek
(Figure III-C33, blue colored group). This group had highest average conductivity and
particulate phosphorus (Table III-C3). Group D was the smallest group (only one station) that
had the lowest average depth, salinity, conductivity, dissolved oxygen, and nitrate values but the
highest turbidity, ammonium, DKN, particulate nitrogen, total dissolved nitrogen,
orthophosphate, total dissolved phosphorus, chlorophyll a, and dissolved organic carbon (Figure
III-C33; orange colored group). Group E was the second largest group with mostly downstream
stations (Figure III-C33. teal colored group). Group E presented the highest means for salinity,
temperature, dissolved oxygen, and pH, and the lowest means for turbidity, ammonium, DKN,
total dissolved nitrogen, orthophosphate, total dissolved phosphate, particulate phosphate, and
dissolved organic carbon (Table III-C3).
(End of material prepared by Dr. Suelen Tullio)
III-C-12

1.0
0.5
°
co
r
R3
C 0.0
Q1
0
C0
E
U
-0.5
-1.0
-1.0 -0.5 0.0 0.5
Component 1 (29.8 %)
1.0
Figure III-C1. Principal Components Analysis biplot of interrelationships among all water quality
variables. Water quality variables are: depth (DEP, in), temperature (TEMP, °C), salinity (SAL),
conductivity (COND, mS), turbidity (TURB, NTU), dissolved oxygen (DO, mg L-1), pH (pH),
ammonium (NHa, mg L-1), nitrate (NO3, mg L-1), dissolved Kjeldahl nitrogen (DKN, mg L-1),
particulate nitrogen (PN, mg L-1), total dissolved nitrogen (TN, mg L-1), orthophosphate (PO4, mg
L-1), total dissolved phosphate (TDP, mg L-1), particulate phosphate (PP, mg L-1), chlorophyll a
(CHL, pg L-1), and dissolved organic carbon (DOC, mg L-1).
III-C-13

a
a
Figure III-C2. Intra-annual variability of Principal Component
1 and Principal Component 2 over time at Broomfield Swamp
Creek Station BSCWQ1 (upstream). Data collection began
in 2019.
BSCWQ2
lan-20
Dale
Jan-21
Figure III-C3. Intra-annual variability of Principal Component
1 and Principal Component 2 over time at Broomfield Swamp
Creek Station BSCWQ2 (midstream). Data collection began
in 2019.
BSCWQ2
Figure III-C4. Intra-annual variability of Principal Component
1 and Principal Component 2 over time at Broomfield Swamp
Creek Station BSCWQ3 (downstream). Data collectin began
in 2019.
III-C-14

8
6-
4
-2 -
-6•
-8•
Ian-19
5C1WQ1
lan-20
Dale
Figure III-05. Interannual variability of Principal Component
1 and Principal Component 2 over time at SCUT1 station
SC1WQ1 (upstream). Data collection began in 2019.
5C1WQ2
`1� r
■
4 +6 N a+� r"•S 4
si 7
lan-2U
Dare -
Jan 21
Figure III-C6. Interannual variability of Principal Component
1 and Principal Component 2 over time at SCUT1 station
SC1WQ2 (midstream). Data collection began in 2019.
q
-2
.g
lan-20
Dare
lan-21
Figure III-C7. . Interannual variability of Principal Component
1 and Principal Component 2 over time at SCUT1 station
SC1WQ3 (downstream). Data collection began in 2019.
III-C-15

6
6
4
2
0
-2
-4
-6
Jan-12
Jan-13
Jan-14
lan 15
JWQ1
lark-16 lark-17
Date
,an-19
lan-20
lan 21
Figure III-C8. Interannual variability of Principal Component 1 and Principal Component 2
over time at Jacks Creek station JWQ1 (upstream). The value of the positive data point off
the scale is shown. Vertical line at 2015 separates pre- from post -Mod Alt L.
JWQ2
Jan-13 lan•14 lark-15 Jan-16 lan-17 lan-18 Jan-19 Jan•20 lan-21
Dare
Figure III-C9. Interannual variability of Principal Component 1 and Principal Component 2
over time at Jacks Creek station JWQ2 (downstream). Vertical line at 2015 separates pre -
from post- Mod Alt L.
III-C-16

—a— PC1
- ,- PC2
4
2
-6
-8
lan•12
r?
lar-14
ild
ry
1
rJ rp
ry rn,
■r�
fi
LCWQ1
r�
fi
Ian-I6 len-17
Date
rYI
r' 6, j1'' M1Ii ry II
ler' r'
i r
lan 18
Jar-=�
an-20
len-21
Figure III-C10. Interannual variability of Principal Component 1 and Principal Component 2
over time at Little Creek station LCWQ1 (upstream).
PCI
- jr PC2
an-13
Jan-14
fan-16 len-17 lan-18
Date
Jan-14
lan-20
len-21
Figure III-C11. Interannual variability of Principal Component 1 and Principal Component 2
over time at Little Creek station LCWQ2 (downstream).
III-C-17

JCBWQ1
Figure III-C12. Interannual variability of Principal Component 1 and Principal Component 2
over time at Jacobs Creek station JCBWQ1 (upstream). Vertical line at 2014 separates pre -
from post -Mod Alt L.
a
7 0
w
-2
-4
6
-a
!an-13
lan•11
JCBWC2
Jan-16 lark-17
Date
fan-18
an 17
fan•20
fan 21
Figure III-C13. Interannual variability of Principal Component 1 and Principal Component 2 over
time at Jacobs Creek station JCBWQ2 (downstream). Vertical line at 2014 separates pre- from
post -Mod Alt L
III-C-18

a
2
> 0
a
lar 12
Jan-13
Jan-14
lan-15
PA2WQ1
fan•15 Jen-17
Date
lan-18
lar--19
lan-26
Jen-21
Figure III-C14. Interannual variability of Principal Component 1 and Principal Component 2
over time at PA2 station PA2WQ1 (upstream).
a
5
0
-5
lan 12
Jan 13
lar:14
lan-15
PA2WQ2
tan-16 lan•17
Date
lan-16
ar:19
lan•26
lan-21
Figure III-C15. Interannual variability of Principal Component 1 and Principal Component 2
over time at PA2 station PA2WQ2 (downstream).
III-C-19

DWWR1
Figure III-C16. Interannual variability of Principal Component 1 and Principal Component 2
over time at Drinkwater Creek station DVVWQ1 (upstream). Vertical line at 2013 separates
pre- from post -Mod Alt L.
4
-2
-4
-6
lark-13
Jan-15
lark-16
Date
Jan-17
Jark-18
Ian-n
Figure III-C17. Interannual variability of Principal Component 1 and Principal Component 2
over time at Drinkwater Creek station DVVWQ2 (downstream). Vertical line at 2013 separates
pre- from post -Mod Alt L.
III-C-20

0
Jan-13
Jan-14
Jan -Li
LOCWQ1
fan.16 lan•17
Date
lan-18
lan-19
Jan•20
lan-21
Figure III-C18. Interannual variability of Principal Component 1 and Principal Component 2
over time at Long Creek station LOCWQ1 (upstream).
LOCWQ2
Figure III-C19. Interannual variability of Principal Component 1 and Principal Component 2
over time at Long Creek station LOCWQ2 (downstream).
III-C-21

6
2
.2
-4
-6
Ja -12
lan-13
len-14
lan-15
TWQ1
Jan-16 fan-17
n�1N
lan-18
Jan-19
1an-20
Ian 21
Figure III-C20. Interannual variability of Principal Component
1 and Principal Component 2 over time at Tooley Creek
station TWQ1 (upstream west prong). The Y axis separates
pre- from post -Mod Alt L.
Ja -12
Ja. .
1an.14
Jan-15
TWQ2
Jan-16 Jen-17
Date
1an-18
Jan-19
Jan-20
Figure III-C21. Interannual variability of Principal Component
1 and Principal Component 2 over time at Tooley Creek
station TWQ2 (upstream east prong). The Y axis separates
pre- from post -Mod Alt L.
Date
Figure III-C22. Interannual variability of Principal Component
1 and Principal Component 2 over time at Tooley Creek
station TWQ3 (downstream). The Y axis separates pre- from
post -Mod Alt L.
III-C-22

Jan-15
HWQ1
.ran-16 Jam17
Date
Figure III-C23. Interannual variability of Principal Component 1 and
Principal Component 2 over time at Huddles Cut station HWQ1
(upstream west prong). The value of the positive data point off the
scale is shown. Post -Mod Alt began in 2010.
6
-1
.4
HWQ3
■ . •
r •
f• T 0•611
+.. 4. :.
r 1` • 1,
y p J S.
I
i, /
p , t it .. :4s, f 4 ...4.. ' S 4 9„, ei i .
)46. +$' r4 11 ,•1y 9 i 5al4.
S" s a4 , y
,an-16 JM-1i
Date
Figure III-C25. Interannual variability of Principal Component 1
and Principal Component 2 over time at Huddles Cut station
HWQ3 (upstream main prong). The value of the positive data
point off the scale is shown. Post -Mod Alt began in 2010.
lan•12
lan-13
Jan•14
Jan•15
HWQ2
lan-16 Jan.0
Date
San-18
Jan-19
Jan•26
Jan•21
Figure III-C24. Interannual variability of Principal Component 1 and
Principal Component 2 over time at Huddles Cut station HWQ2
(downstream west prong). The value of the positive data point off
the scale is shown. Post -Mod Alt began in 2010.
fan-1,
„3
H V,144
aaa.t6
Date
Fan 71
Figure III-C26. Interannual variability of Principal Component 1
and Principal Component 2 over time at Huddles Cut station
HWQ4 (downstream main prong). The value of the positive data
point off the scale is shown. Post -Mod Alt began in 2010.
III-C-23

PCWQ1
Figure III-C27. Interannual variability of Principal Component 1 and Principal Component 2
over time at Porter Creek station PCWQ1 (upstream). The value of the positive data point off
the scale is shown. Vertical line at 2016 separates pre- from post -Mod Alt L.
- 4-
- 6-
-a
Jan-12
Jan-13
lan-14
Jan-15
PCWQ2
Jan-16 Jan 17
Date
Jan-18
Jen-19
Jan-20
tan-21
Figure III-C28. Interannual variability of Principal Component 1 and Principal Component 2
over time at Porter Creek station PCWQ2 (downstream). Vertical line at 2016 separates pre -
from post -Mod Alt L.
III-C-24

4
2
-4
PC!
- - PC2
Ian-13 ten-14
DC11WQ1
Ian-16 yan•17 lan-18 lan-19
Date
Ian-20 lan-21
Figure III-C29. Interannual variability of Principal Component 1 and Principal Component 2
over time at DCUT11 station DC11WQ1. Data collection began in 2013. Vertical line at 2018
separates pre- from post -Mod Alt L.
4
a
> 0
4
DC19WQ1
fan-16 fan•17
Date
1J, Ifi
an 21
Figure III-C30. Interannual variability of Principal Component 1 and Principal Component 2
over time at DCUT19 station DC19WQ1. Data collection began in 2013.
III-C-25

8
5
4
2
7 4
.2
Jun 13
San-14
Jan•15
DKCWQ1
Jan-26 Jan-17
Date
Jan-18
lan-19
Jan•20
Jan-21
Figure III-C31. Interannual variability of Principal Component 1 and Principal Component 2
over time at Duck Creek station DKCWQ1 (upstream).
4
2
7 0
-2
.4
Jan-12
Jan-13
Jan-14
Jan-15
DKCWQ2
Jan-16 Jan-17
Date
Jan-18
1an•19
Jan•20
Jan 21
Figure III-C32. Interannual variability of Principal Component 1 and Principal Component 2
over time at Duck Creek station DKCWQ2 (downstream).
III-C-26

B C
1_
ijh
Anm n
„ i„ kg lk„ R PRE1110.,1
11111011994
AAMA% AAAAAAARAAAAAAMAAAAAA EAAATARA %AAAAAAAAAAARAlTAAAAAAAAAAIAAAAA A AAAAA
�fl
D
1
1
r
1
E
Inggi' ;1:: 4141t5t “p
MATAAAAAAAAEATAIATAAA'AAAAAAAAAAAM
tat E
nyierilimiliiga Imp ;;;111
Figure III-C33. Agglomerative, hierarchical cluster analysis of annual means of each water quality parameter at each water quality station (2012-2020). Five distinct clusters of water quality stations were
revealed (A, B, C, D, E).
III-C-27

50
40 •
t
0
B
C D
Cluster
T
Figure III-C34. Comparison of mean depth (in) for each group of water quality stations
identified by cluster analysis. Error bar is 1 standard deviation from the mean.
20-
15-
5-
0
B
C
Cluster
D
Figure III-C35. Comparison of mean temperature (C) for each group of water quality
stations identified by cluster analysis. Error bar is 1 standard deviation from the mean.
III-C-28

10
8
6
4
2-
0
B
T
C D E
Cluster
Figure III-C36. Comparison of mean salinity for each group of water quality stations identified
by cluster analysis. Error bar is 1 standard deviation from the mean.
150
100-
Conductivity (mS)
50-
0-
-50 -
-100
s
A
Cluster
Figure III-C37. Comparison of mean conductivity (mS) for each group of water quality stations
identified by cluster analysis. Error bar is 1 standard deviation from the mean.
III-C-29

50
40-
10-
0 --
T
A
C
Cluster
Figure III-C38. Comparison of mean turbidity (NTU) for each group of water quality stations
identified by cluster analysis. Error bar is 1 standard deviation from the mean.
6
0
A B
Cluster
Figure III-C39. Comparison of mean dissolved oxygen (mg L-1) for each group of water quality
stations identified by cluster analysis. Error bar is 1 standard deviation from the mean.
III-C-30

8
7-
6-
5-
T s
Z T
A B C
Cluster
Figure III-C40. Comparison of mean pH for each group of water quality stations identified by
cluster analysis. Error bar is 1 standard deviation from the mean.
T
C
Cluster
Figure III-C41. Comparison of mean ammonium (NH4) (mg L-1) for each group of water quality
stations identified by cluster analysis. Error bar is 1 standard deviation from the mean.
III-C-31

0.8
a 0.6
m
O • 0.4
L
Z
0-2
0.0
B C
Cluster
Figure III-C42. Comparison of mean nitrate (NO3) (mg L-1) for each group of water quality
stations identified by cluster analysis. Error bar is 1 standard deviation from the mean.
J
2.5
E
✓
+a
'as
tti
7
0
0.5
C
0-0
A B C
Cluster
0
Figure III-C43. Comparison of mean dissolved Kjeldahl nitrogen (DKN) (mg L-1) for each group
of water quality stations identified by cluster analysis. Error bar is 1 standard deviation from
the mean.
III-C-32

1.2
1.0
as
E
• 0.8
a_
c
p 0.6
z
= ▪ 0.4
km
0.2
0.0
T
A c
Clu ster
Figure III-C44. Comparison of mean particulate nitrogen (PN) (mg L-1) for each group of
water quality stations identified by cluster analysis. Error bar is 1 standard deviation from the
mean.
J
Ca▪ !
L
2
G 1.5
as
0
1
Z 1.0
-a
m
7
0
0N
. 0.5 -
0
2.0•
0.0
A
Cluster
D E
Figure III-C45. Comparison of mean total dissolved nitrogen (TDN) (mg L-1) for each group
of water quality stations identified by cluster analysis. Error bar is 1 standard deviation from
the mean.
III-C-33

1.5
0.0
A
B
C
Cluster
Figure III-C46. Comparison of mean orthophosphate (PO4) (mg L-1) for each group of
water quality stations identified by cluster analysis. Error bar is 1 standard deviation from
the mean.
1.5
at
E
a
0
uN+ 0.5
io
0
A B C
Cluster
Figure III-C47. Comparison of mean total dissolved phosphate (TDP) (mg L-1) for each group
of water quality stations identified by cluster analysis. Error bar is 1 standard deviation from
the mean.
III-C-34

0.45 -
0.40-
J
0.35-
a ▪ 0.30-
= 0.15-
V
▪ 0.10-
0.05-
0.00
T
A
T
T
C
Cluster
Figure III-C48. Comparison of mean particulate phosphate (PP) (mg L-1) for each group of
water quality stations identified by cluster analysis. Error bar is 1 standard deviation from the
mean.
Chlorophyll a (ug/L)
100-
80-
60
40
20
C
A
Cluster
Figure III-C49. Comparison of mean chlorophyll a (Chl a) concentration (pg L-1) for each
group of water quality stations identified by cluster analysis. Error bar is 1 standard deviation
from the mean.
III-C-35

J
G
o;
o 25-
b.
u ▪ 20-
m
C • 15-
-a
10
0
5
0
T
T
A B
it
0 D E
Cluster
Figure III-050. Comparison of mean dissolved organic carbon (DOC) (mg L-1) for each group
of water quality stations identified by cluster analysis. Error bar is 1 standard deviation from
the mean.
III-C-36

Table III-C1. Water quality data record for all years for all study creeks.
Creek
Impact
Creek?
Pre -Mod Alt L Years
Post -Mod Alt L
Years
Broomfield
Swamp Creek
Y
2019-2020
DCUT11
Y
2013-2017
2018-2020
Drinkwater Creek
Y
2011a, 2012
2013-2020
Huddles Cut
y
1999a, 2000-2001, 2002a,
2007-2009
2010-2020
Jacks Creek
y
1999a, 2000-2005, 2011a,
2012-2014
2015-2020
Jacobs Creek
Y
2011a, 2012-2013
2014-2020
Porter Creek
Y
2011a, 2012-2015
2016-20209
Tooley Creek
Y
1999a, 2000-2001, 2002a,
2010-2011
2012-2020
DCUT19
N
2013-2020
Duck Creek
N
2011a, 2012-2020
Little Creek
N
2011a, 2012-2020
Long Creek
N
2011a, 2012-2020
PA2
N
2011a, 2012-2020
SCUT1
N
2019-2020
a These years have only partial data but included in the analysis.
III-C-37

Table III-C2. Loading for each water quality variable on each principal component. Positive
values indicate that the variable is positively correlated to the principal component. Negative
values indicate that the variable is negatively correlated to the principal component.
Water quality variable
Principal Component 1
Principal Component 2
Depth (in)
-0.4944
-0.1387
Temperature (°C)
0.2033
0.5525
Salinity
-0.5637
0.5467
Conductivity (mS)
-0.4359
0.6885
Turbidity (NTU)
0.5924
-0.2039
Dissolved oxygen (mg L-1)
-0.5199
-0.2507
pH
-0.4362
0.4303
Ammonium (NH4; mg L-1)
0.5037
-0.2854
Nitrate (NO3; mg L-1)
0.0958
-0.6279
Dissolved Kjeldahl nitrogen (DKN; mg L-1)
0.6623
0.2213
Particulate nitrogen (PN; mg L-1)
0.3593
0.6414
Total dissolved nitrogen (TN; mg L-1)
0.7482
-0.2007
Orthophosphate (PO4; mg L-1)
0.7221
0.1088
Total dissolved phosphate (TDP; mg L-1)
0.8021
0.1521
Particulate phosphate (PP; mg L-1)
0.5160
0.4414
Chlorophyll a (Chl; pg L-1)
0.2375
0.6614
Dissolved organic carbon (DOC; mg L-1)
0.7586
-0.0037
Table III-C3. Average of water quality parameters across the five groups identified by cluster
analysis on 2012-2020 data (Figure III-C33).
Parameter
Group A
Group B
Group C
Group D
Group E
Number of stations by Group
95
19
24
6
91
Depth (in)
12.16
33.29
7.30
7.28
21.21
Temperature (°C)
17.58
18.59
18.35
19.06
19.41
Salinity
4.53
2.45
3.16
2.02
8.16
Conductivity (mS)
7.01
4.04
28.58
3.41
12.41
Turbidity (NTU)
9.93
20.50
23.55
27.05
5.78
_1
Dissolved oxygen (mg L)
4.05
4.51
4.25
3.94
6.24
pH
6.55
6.55
6.66
6.65
7.20
Ammonium (NH4; mg L-1)
0.15
0.26
0.40
0.46
0.05
Nitrate (NO3; mg L-1)
0.07
0.58
0.04
0.01
0.04
Dissolved Kjeldahl nitrogen (DKN; mg L-1)
1.08
1.12
1.57
2.52
0.82
Particulate nitrogen (PN; mg L-1)
0.31
0.26
0.59
0.83
0.29
Total dissolved nitrogen (TN; mg L-1)
0.95
1.69
1.49
1.89
0.63
Orthophosphate (PO4; mg L-1)
0.21
0.09
0.28
1.39
0.05
Total dissolved phosphate (TDP; mg L-1)
0.26
0.13
0.34
1.36
0.08
Particulate phosphate (PP; mg L-1)
0.09
0.08
0.28
0.20
0.06
Chlorophyll a (Chl; pg L-1)
16.03
14.17
37.85
54.05
14.32
Dissolved organic carbon (DOC; mg L-1)
18.60
16.26
22.12
36.23
11.97
III-C-38

Table III-C4. Comparison of pre- and post -mod Alt-L conditions for Jacks Creek. Significant
comparisons in bold.
Parameter
Pre
Mean
Pre N
Post
Mean
Post N
t-ratio
p-value
Depth (in)
16.57
380
15.30
288
-2.67
0.01
Temperature (C)
16.97
380
18.45
283
-2.67
0.01
Salinity
4.77
380
4.53
283
0.78
0.44
Conductivity (mS)
7.17
380
7.25
283
-0.17
0.87
Turbidity (NTU)
14.17
367
12.58
283
0.83
0.41
Dissolved oxygen (mg L-1)
4.30
376
4.95
283
-2.53
0.01
pH
6.96
375
6.87
283
2.15
0.03
Ammonium (mg L-1)
0.18
375
0.12
277
1.79
0.07
Nitrate (mg L-1)
0.04
376
0.03
275
2.69
0.01
Dissolved Kjeldahl nitrogen (DKN; mg
L-V )
1.05
370
0.99
280
1.08
0.28
Particulate nitrogen (mg L-1)
0.39
373
0.30
283
2.74
0.01
Total dissolved nitrogen (mg L-1)
0.98
151
0.88
280
0.80
0.43
Orthophosphate (mg L-1)
0.09
376
0.11
283
-1.85
0.06
Total dissolved phosphate (mg L-1)
0.14
376
0.16
283
-1.75
0.08
Particulate phosphate (mg L-1)
0.24
376
0.24
281
0.13
0.89
Chlorophyll a (pg L-1)
32.42
363
13.98
283
3.10
0.002
Dissolved organic carbon (mg L-1)
16.17
151
16.25
280
-0.14
0.89
Table III-05. Comparison of pre- and post -mod Alt-L conditions for Jacobs Creek. Significant
comparisons in bold.
Parameter
Pre
Mean
Pre N
Post
Mean
Post N
t-ratio
p-value
Depth (in)
16.78
116
18.29
359
-2.17
0.03
Temperature (C)
18.51
116
19.86
359
-1.69
0.09
Salinity
11.35
116
7.38
359
11.41
<0.0001
Conductivity (mS)
16.66
116
11.43
359
10.90
<0.0001
Turbidity (NTU)
2.80
116
9.51
359
-3.86
0.0001
Dissolved oxygen (mg L-1)
5.90
116
6.30
359
-1.03
0.30
pH
7.24
116
7.13
359
2.17
0.03
Ammonium (mg L-1)
0.04
116
0.04
351
0.12
0.90
Nitrate (mg L-1)
0.03
116
0.02
349
0.96
0.34
Dissolved Kjeldahl nitrogen (DKN; mg
L-1)
0.90
112
0.85
351
1.70
0.09
Particulate nitrogen (mg L-1)
0.29
114
0.29
357
0.13
0.90
Total dissolved nitrogen (mg L-1)
0.62
106
0.63
357
-0.46
0.65
Orthophosphate (mg L-1)
0.05
116
0.06
357
-1.62
0.11
Total dissolved phosphate (mg L-1)
0.08
116
0.09
357
-1.70
0.09
Particulate phosphate (mg L-1)
0.08
116
0.06
355
3.33
0.001
Chlorophyll a (pg L-1)
15.84
116
14.53
353
0.65
0.51
Dissolved organic carbon (mg L-1)
12.24
106
12.62
357
-0.74
0.46
III-C-39

Table III-C6. Comparison of pre- and post -mod Alt-L conditions for Drinkwater Creek.
Significant comparisons in bold.
Parameter
Pre
Mean
Pre N
Post
Mean
Post N
t-ratio
p-value
Depth (in)
9.74
66
10.58
383
-1.45
0.15
Temperature (C)
17.42
66
17.60
381
-0.22
0.83
Salinity
5.37
66
4.12
381
1.82
0.07
Conductivity (mS)
7.88
66
6.28
381
1.67
0.10
Turbidity (NTU)
4.68
66
7.33
381
-3.08
0.002
Dissolved oxygen (mg L-1)
3.74
66
3.55
381
0.57
0.57
pH
6.40
66
6.54
381
-1.95
0.05
Ammonium (mg L-1)
0.07
66
0.11
373
-3.39
0.0008
Nitrate (mg L-1)
0.01
66
0.02
371
-0.33
0.74
Dissolved Kjeldahl nitrogen (DKN; mg
L-1)
1.22
64
1.07
373
2.93
0.004
Particulate nitrogen (mg L-1)
0.34
66
0.27
377
1.78
0.08
Total dissolved nitrogen (mg L-1)
0.89
50
0.88
378
0.03
0.98
Orthophosphate (mg L-1)
0.30
66
0.21
379
2.12
0.04
Total dissolved phosphate (mg L-1)
0.35
66
0.26
379
2.26
0.03
Particulate phosphate (mg L-1)
0.13
66
0.09
377
3.98
0.0001
Chlorophyll a (pg L-1)
26.85
65
14.54
377
2.65
0.01
Dissolved organic carbon (mg L-1)
28.01
50
19.80
378
3.17
0.003
Table III-C7. Comparison of pre- and post -mod Alt-L conditions for Tooley Creek. Significant
comparisons in bold.
Parameter
Pre
Mean
Pre
N
Post
Mean
Post N
t-ratio
p-value
Depth (in)
11.28
305
11.81
604
-0.88
0.38
Temperature (C)
16.61
307
17.75
596
-2.08
0.04
Salinity
5.52
307
6.49
597
-2.99
0.003
Conductivity (mS)
8.27
303
9.81
597
-3.20
0.002
Turbidity (NTU)
16.36
296
8.50
596
4.01
<0.0001
Dissolved oxygen (mg L-1)
4.43
301
4.72
594
-1.11
0.27
pH
7.02
298
6.80
597
1.28
0.20
Ammonium (mg L-1)
0.11
306
0.13
589
-1.34
0.18
Nitrate (mg L-1)
0.02
306
0.03
587
-1.96
0.05
Dissolved Kjeldahl nitrogen (DKN; mg
L-1)
1.09
305
1.18
585
-2.44
0.02
Particulate nitrogen (mg L-1)
0.32
302
0.33
592
-0.69
0.49
Total dissolved nitrogen (mg L-1)
No data
0
0.92
593
Orthophosphate (mg L-1)
0.24
306
0.27
597
-1.48
0.14
Total dissolved phosphate (mg L-1)
0.29
306
0.32
596
-1.50
0.13
Particulate phosphate (mg L-1)
0.28
306
0.12
591
12.52
<0.0001
Chlorophyll a (pg L-1)
18.30
295
15.33
590
1.71
0.09
Dissolved organic carbon (mg L-1)
No data
0
19.10
593
III-C-40

Table III-C8. Comparison of pre- and post -mod Alt-L conditions for Huddles Cut. Significant
comparisons in bold.
Parameter
Pre
Mean
Pre
N
Post
Mean
Post N
t-ratio
p-value
Depth (in)
6.51
507
6.87
993
-1.69
0.09
Temperature (C)
15.47
505
18.84
985
-7.30
<0.0001
Salinity
2.70
503
4.86
985
-12.60
<0.0001
Conductivity (mS)
4.09
502
18.49
982
-1.32
0.19
Turbidity (NTU)
28.16
489
18.71
991
3.60
0.0003
Dissolved oxygen (mg L-1)
3.40
488
4.15
985
-5.01
<0.0001
pH
6.76
490
6.73
984
0.96
0.34
Ammonium (mg L-1)
0.35
505
0.34
984
0.26
0.80
Nitrate (mg L-1)
0.02
505
0.01
976
1.85
0.07
Dissolved Kjeldahl nitrogen (DKN; mg
L-1)
1.49
503
1.67
975
-3.02
0.003
Particulate nitrogen (mg L-1)
0.54
503
0.58
986
-1.07
0.29
Total dissolved nitrogen (mg L-1)
No data
0
1.44
834
Orthophosphate (mg L-1)
0.41
505
0.53
990
-4.44
<0.0001
Total dissolved phosphate (mg L-1)
0.47
505
0.57
989
-3.53
0.0004
Particulate phosphate (mg L-1)
0.31
505
0.15
985
9.95
<0.0001
Chlorophyll a (pg L-1)
33.63
494
33.64
979
-0.002
1.00
Dissolved organic carbon (mg L-1)
No data
0
24.42
834
Table III-C9. Comparison of pre- and post -mod Alt-L conditions for Porter Creek. Significant
comparisons in bold.
Parameter
Pre
Mean
Pre N
Post
Mean
Post N
t-ratio
p-value
Depth (in)
18.10
209
22.00
244
-3.15
0.002
Temperature (C)
17.15
209
17.38
242
-0.33
0.75
Salinity
2.57
209
2.83
242
-0.73
0.47
Conductivity (mS)
4.72
209
4.53
242
0.25
0.80
Turbidity (NTU)
9.39
209
23.03
242
-5.40
<0.0001
Dissolved oxygen (mg L-1)
4.08
207
3.80
242
0.98
0.33
pH
6.24
209
6.55
242
-5.58
<0.0001
Ammonium (mg L-1)
0.14
201
0.25
240
-3.37
0.0008
Nitrate (mg L-1)
0.12
207
0.07
234
1.51
0.13
Dissolved Kjeldahl nitrogen (DKN; mg
L-1)
0.81
199
1.10
240
-5.66
<0.0001
Particulate nitrogen (mg L-1)
0.26
205
0.36
242
-2.71
0.007
Total dissolved nitrogen (mg L-1)
0.80
205
1.04
242
-4.50
<0.0001
Orthophosphate (mg L-1)
0.08
207
0.13
242
-5.63
<0.0001
Total dissolved phosphate (mg L-1)
0.14
207
0.18
242
-3.26
0.001
Particulate phosphate (mg L-1)
0.10
207
0.13
240
-2.19
0.03
Chlorophyll a (pg L-1)
13.66
203
20.29
243
-2.11
0.04
Dissolved organic carbon (mg L-1)
15.43
205
17.05
242
-2.59
0.01
III-C-41

Table III-C10. Comparison of pre- and post -mod Alt-L conditions for DCUT11. Significant
comparisons in bold.
Parameter
Pre
Mean
Pre N
Post
Mean
Post N
t-ratio
p-value
Depth (in)
18.53
129
20.35
78
-2.16
0.03
Temperature (C)
17.56
129
18.32
78
-0.61
0.54
Salinity
4.67
129
4.87
78
-0.37
0.71
Conductivity (mS)
18.53
129
20.35
78
-2.16
0.03
Turbidity (NTU)
7.77
129
4.99
78
3.28
0.001
Dissolved oxygen (mg L-1)
4.25
128
4.47
78
-0.52
0.61
pH
6.33
129
6.58
78
-3.81
0.0002
Ammonium (mg L-1)
0.06
124
0.04
78
1.90
0.06
Nitrate (mg L-1)
0.011
124
0.013
77
-0.54
0.59
Dissolved Kjeldahl nitrogen (DKN; mg L-
1)
0.74
123
0.76
78
-0.53
0.59
Particulate nitrogen (mg L-1)
0.22
127
0.18
78
1.92
0.06
Total dissolved nitrogen (mg L-1)
0.65
128
0.70
78
-1.28
0.20
Orthophosphate (mg L-1)
0.04
128
0.03
78
1.54
0.13
Total dissolved phosphate (mg L-1)
0.08
128
0.07
78
1.32
0.19
Particulate phosphate (mg L-1)
0.05
127
0.04
78
1.11
0.27
Chlorophyll a (pg L-1)
10.35
125
9.92
77
0.17
0.87
Dissolved organic carbon (mg L-1)
15.50
128
17.18
78
-2.08
0.004
III-C-42