Journal of Environmental Protection, 2011, 2, 255-270
doi:10.4236/jep.2011.23029 Published Online May 2011 (
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest
Arkansas, Downstream of a Municipal Wastewater
Treatment Plant
Brad W. Hufhines1, Kristofor R. Brye2, Brian E. Haggard3, Robert Morgan4
1Environmental Technician, Beaver Water District, Lowell, USA; 2Department of Crop, Soil, and Environmental Sciences; Univer-
sity of Arkansas, Fayetteville, USA; 3Department of Biological and Agricultural, Engineering, University of Arkansas, Fayetteville,
USA; 4Environmental Quality Manager, Beaver Water District, Lowell, USA.
Received November 18th, 2010; revised January 8th, 2011; accepted February 14th, 2011.
Wastewater treatment plays a crucial role in preserving water quality in receiving streams; however, continuous nutri-
ent enrichment can diminish the retention capacity of rivers. The objectives of this study were to evaluate the effects of
wastewater treatment plant effluent and river discharge on water chemistry and determine the retention efficiency of
nutrients add ed in the effluent along a 6.1-km reach of a 5th-order stream in the Ozark Highlands of northwest Arkan-
sas. From 2006 through 2007, effluent discharge increased river nitrite , soluble reactive P (SRP), and total organic C
(TOC) and conductivity. As river discharge increased, dissolved oxygen (DO) and turbidity increased, but water tem-
perature, conductivity, and TOC decreased. Net nutrient uptake lengths were inconsistent for NO3-N, NH4-N, and SRP.
Results indicated that the fluvial channel acted as both a sink and a source of NO3-N and SRP, but the channel always
acted as a sink for NH4-N with a significantly positive retention coefficient that indicated only 12% of added NH4-N
was retained in the study reach. The effluent discharge increased the concentrations of seven water quality parameters
and it appears the long-term enrichment has rendered the immediate-downstream reach ineffective as a nutrient sink.
Nutrients added in the effluent were generally transported with little to n o uptake or transformation, thus river chemical
concentra tions beyond the study reach have likely been influenced by this effluent discharge.
Keywords: Streamfl ow, Point-Source Pollution, Nutrient Spiraling, Source-Water Protection
1. Introduction
Water quality issues in the Ozark Highlands region of
northwest Arkansas, southwest Missouri, and northeast
Oklahoma include sedimentation and mineral and nutri-
ent enrichment. Numerous stream segments do not sup-
port the designated uses for aquatic life and/or as a mu-
nicipal and industrial water supply [1]. The causes of
these impairments include surface erosion, urban non-
point source pollution, and the effluent from municipal
wastewater treatment plants (WWTP) [1]. Even so, at
least the last two decades of water quality research in the
Ozark Highlands have focused primarily on nutrient
fluxes in surface runoff in response to animal manure
application [2-5]. A need exists to evaluate the impact of
treated wastewater on in-stream processes, focusing on
how effluent discharges influence stream nutrient reten-
In the 2000s, numerous studies evaluated the effects of
effluent discharges on nutrient dynamics within the
stream channel [6-9]. Impacts of the effluent discharge in
relatively small streams demonstrated the stream’s in-
ability to retain added phosphorous (P) and nitrogen (N);
added nutrients were traveling kilometer-scale distances
before being significantly retained. These streams pro-
vided short-term N storage through partial N cycling and
nitrification of ammonium (NH4-N) to nitrate-N (NO3-N).
However, NO3-N often showed a net increase in trans-
port downstream from the effluent discharge or traveled
long distances before retention within the fluvial chan-
Nutrient studies evaluating impacts of WWTP effluent
addition in other regions of the world have reported dif-
fering results. For example, a river near Berlin, Germany
was studied with a two-reach approach that showed little
to no effects on stream water chemistry from a mod-
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant
ern-day WWTP [10]. Gücker et al. [10] reported dimin-
ished rates of P and ammonium uptake, but increased
nitrate uptake efficiency downstream of the WWTP.
Gücker et al. [10] attributed the difference in their find-
ings, as compared to previous studies, to the modern ter-
tiary treatment of wastewater. Thus, it is clear that the
effects of effluent discharges on nutrient dynamics and
water chemistry vary with the treatment capacity of the
WWTPs. Treese et al. [11] even suggested that clogging
of the streambed may occur in effluent-dominated
streams due to increased physical, chemical, and bio-
logical processes from elevated nutrients to render the
stream unstable and result in a reduced capacity to re-
charge groundwater.
Most studies on the effects of effluent discharges on
stream nutrient retention have focused on smaller
streams, where the effluent discharge often has a pro-
found effect on physio-chemical properties and makes up
a large portion of discharge. Relatively few studies have
focused on large rivers, when the effluent discharge is
greatly diluted even during seasonal base-flow condi-
tions. The Chattahoochee River, a large urban river near
Atlanta, Georgia exhibited great variation in nutrient
patterns downstream of multiple effluent discharges due
to large fluctuations in river discharge and subsequent
dilution of the effluents [12]. Thus, the dilution of efflu-
ent discharges plays a large role in the impact on water
chemistry and nutrient transport downstream.
The objectives of this study were to evaluate the ef-
fects of WWTP effluent and river discharge on water
quality and determine the retention efficiency of nutri-
ents added in WWTP effluent in a 5th-order stream in
the Ozark Highlands of northwest Arkansas. It was hy-
pothesized that 1) there will be a no difference in water
quality upstream and downstream of the WWTP effluent
due to a large dilution effect, 2) dilution-corrected nutri-
ent concentration differences will not be observed among
downstream sample sites due to the relatively short study
reach, 3) nutrient retention coefficients would not differ
from zero indicating nutrient transport with no retention
nor export was occurring, and 4) retention coefficients
and net nutrient uptake lengths for N fractions would be
unrelated, but those for P fractions would be related to
certain water quality parameters, particularly turbidity.
2. Methods
2.1. The Study Area
The Ozark Highlands ecoregion covers parts of Kansas,
Missouri, Oklahoma, and Arkansas [13] and is charac-
terized by karst topography and high-gradient, riffle-pool,
clear-flowing streams. Stream base flows throughout the
dr summer months are maintained by springs and seeps. y
The ecoregion is known for its rich aquatic diversity.
Bedrock in the Ozark Highlands is typically limestone,
dolomite, and chert. Historically, land cover was oak
(Quercus spp.)—hickory (Carya spp.) forest with inter-
mittent tallgrass prairie. Most of the tallgrass prairie has
been converted to agriculture [14]. Approximately 20%
of the Ozark Highlands is used for pasture, 10% for
cropland, and 70% is forestland [15].
The Ozark Highlands is also an area of concentrated
poultry production [16]. Arkansas’ broiler production is
concentrated in the northwestern counties of Benton,
Washington, Carroll, and Madison, all of which are lo-
cated within the Ozark Highlands ecoregion. Poultry
litter is rich in N, P, and potassium (K) and is a
cost-effective way of fertilizing soils [17]. Between 1.3
million and 1.8 million Mg of litter is generated in Ar-
kansas annually. A large fraction of this litter is concen-
trated in northwest Arkansas [18]. This application of
litter has resulted in high soil-test P levels where pastures
have been fertilized long-term [19] and numerous surface
water quality issues throughout the region. Over the last
20 years, the northwest Arkansas portion of the Ozark
Highlands has experienced a high rate of urbanization.
From 2000 to 2007, the population within Washington
and Benton counties increased by 28% from 311,121 to
397,399 [20]. The increasing population has placed
greater demands on regional water resources, which re-
lies on Beaver Lake within the White River Basin
The White River in northwest Arkansas is the largest
tributary to Beaver Lake, and over 250,000 residents of
northwest Arkansas use water from Beaver Lake as their
source of drinking water. Three WWTPs discharge
treated wastewater within the Beaver Lake-White River
watershed. The Paul R. Noland WWTP in Fayetteville,
AR is the largest contributor of treated wastewater to
receiving waters within the watershed. The Paul R.
Noland WWTP discharges effluent into the White River,
which is classified as an impaired waterbody because of
the lack of support for aquatic life due to excessive silta-
tion and/or turbidity [1].
The White River is composed of three major branches:
the West Fork, the Middle Fork, and the main fork,
which is simply referred to as the White River (Figure 1).
The three branches of the White River originate in the
Boston Mountainss ecoregion and flow north to the
Ozark Highlands ecoregion. The Middle Fork of the
White River and the White River combine to form Lake
Sequoyah, a small, shallow reservoir. The outflow of
Lake Sequoyah combines with the West Fork of the
White River and eventually flows into Beaver Lake.
This study was performed on a 6.1 km reach of the
White River located between the confluence of the three
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant 257
Figure 1. Map of the major rivers within the Beaver Lake Watershed in Northwest Arkansas. The Paul R. Noland
municipal wastewater treatment plant (WWTP) discharges into the White River and was used as the nutrient input
source for this study. The study reach stretches 2.2 km upstream of the WWTP discharge to 3.9 km downstream of
the WWTP discharge.
forks of the White River and the headwaters of Beaver
Lake. The entire reach examined in this study was in the
Ozark Highlands. In 2004, the White River was desig-
nated to have an impaired ability to support aquatic life
due to siltation and/or turbidity, where the source was
likely from surface erosion. The causes of surface ero-
sion were agricultural activities, unpaved road surfaces,
and in-stream erosion mainly from unstable stream banks
[21]. The White River was categorized as a high-priority
for development of a total maximum daily load for the
indicated pollutants [1].
Six sites were selected for sampling during the study,
a United States Geological Survey (USGS) stream dis-
charge monitoring station was located in the study reach,
station 07084600 (Figure 2) at Wyman Bridge, just east
of Fayetteville, AR. one upstream (~2 km) of the Paul R.
Noland WWTP just south of Wyman Bridge and five
sites downstream were chosen at riffles, so that the water
column would be mixed by the turbulence of the water
moving over the shallow riffles. The only major water
inflow between Sites 1 and 2 was the effluent discharge
from the WWTP; there were no tributary inflows. The
sites downstream were from ~0.4 to ~4 km below the
WWTP discharge into the White River.
For the 30-year period from 1971 to 2000, Fayetteville,
AR experienced an average annual air temperature of
Copyright © 2011 SciRes. JEP
Health Risk Associated with Pesticide Contamination of Fish from the Densu River Basin in Ghana.
Figure 2. Map of the study reach with sampling sites and wastewater treatment plant (WWTP) discharge to the White river,
northwest AR.
14.2˚C and average annual precipitation of 117 cm [22].
During the study period of 2006 and 2007, annual pre-
cipitation at the USGS station 07048600 totaled 86 and
72 cm, 26% and 38%, respectively, below the 30-year
average [23]. The White River at Wyman Bridge has a
total drainage area of 1036 km2 [24] and is 74% forested,
15% pasture, and 4% developed or urban.
2.2. The Wastewater Treatment Plant
At the time of this study, the Paul R. Noland WWTP was
a Class IV, activated-sludge treatment plant with ul-
tra-violet disinfection. The WWTP’s National Pollution
Discharge Elimination System (NPDES) permit allowed
the WWTP to discharge a maximum of 27,710 m3
into the White River, and the effluent quality was regu-
lated by the Arkansas Department of Environmental
Quality (ADEQ). Daily to hourly discharge flow data
and effluent water quality records for days that sampling
occurred were obtained directly from the WWTP (per-
sonal communication, Tim Luther, Operations Manager,
CH2M HILL OMI). Effluent water quality data obtained
included: daily averages of temperature, dissolved oxy-
gen (DO), pH, total suspended solids (TSS), soluble re-
active phosphorous (SRP), total P (TP), and NH4-N.
Other forms of N (eg., NO3-N, NO2-N, and organic N)
were not routinely measured or reported for this effluent
discharge, thus were unavailable to use and report in this
2.3. Water Sample Collection, Processing, and
Water sampling was conducted monthly, excluding De-
cember and February, for two consecutive years from
January 2006 through 2007. Flow conditions in the
White River below the 40-year median flow of 10.5 m3·s1
were targeted as sampling dates, because higher flows
presented some personnel safety considerations. At each
of the six sampling sites, pH, electrical conductivity, DO,
and temperature were measured in-situ with a Thermo
Orion 5 Star portable meter (Beverly, MA) at three
points within the thalweg (i.e., left, middle, and right). A
1-L water sample was also collected at each of the three
points within the thalweg at each sampling site. In the
event of split flow resulting from channel morphological
changes, both channels were measured for discharge (see
below). If the secondary channel accounted for more
than 20% of the total discharge, one or more of the three
water samples were taken from its thalweg based on its
estimated contribution to discharge.
A cross section was surveyed with 11 equally spaced
survey points across the river channel for determining
river discharge (Q). The distance of the cross section was
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant 259
measured with a fiberglass measuring tape. Channel
depth was determined with a Marsh McBirney measuring
rod and flow velocity was measured electromagnetically
with a Flo-Mate 2000 (Marsh McBirney, Fredrick, MA).
River discharge was estimated using the product of the
water velocity (m·s–1) and cross-sectional area (m2) for
each area between survey points. The equal-interval dis-
charges were then summed to estimate total river dis-
charge at each sampling site.
Following collection, water samples were stored on
ice in a dark cooler. Within 24 hrs after collection, sam-
ple bottles were shaken and a well-mixed, 40-mL aliquot
was removed and preserved to a pH of ~ 2 with two
drops of concentrated HCl per 40 mL of solution for
subsequent total organic carbon (TOC) and total N (TN)
analyses. A 100-mL, well-mixed aliquot was then re-
moved from the 1-L bottle and preserved to a pH of ~ 2
with two drops of 12 N sulfuric acid per 100 mL of solu-
tion for subsequent TP analysis. Turbidity was measured
on a 20-mL aliquot using a HACH 2100N Turibidimeter
(Loveland, CO) according to the SM 2130 B method
[25]. Turbidity was reported in nephelometric turbidity
units (NTU). The remaining portion of the initial 1-L
sample was then vacuum-filtered through a 0.45-µm fil-
ter. The filtered aliquot was used for subsequent SRP,
nitrite (NO2-N), NO3-N, NH4-N, and chloride (Cl-)
Chloride concentrations were determined according to
the SM 4500-Cl- C mercuric-nitrate titration method [25].
Total organic carbon and TN were determined using a
Shimadzu TOC-VCSH TOC analyzer with an added
THM-1 TN measuring unit (Shimadzu, Kyoto, Japan)
using the SM 5310 B [25] and ASTM D 5176-91 meth-
ods [26], respectively. Determinations of NO3-N, NO2-N,
NH4-N, SRP, and TP were conducted using a HACH DR
4000 (HACH, Loveland, CO.) spectrophotometer. Ni-
trate was reduced to NO2-N using the SM 4500-NO3-E
cadmium-copper reduction method [25]. The resulting
reduced-sample was colormetrically analyzed for deter-
mination of the NO2-N concentration. The difference
between the reduced-sample NO2-N concentration and
the previously determined NO2-N concentration was
determined to be the NO3-N concentration [25]. Ammo-
nium was determined by the HACH Nessler method
8038 [27]. Nitrite was determined by the HACH Diazo-
tization method 8507 [27]. Soluble-reactive P was de-
termined by the HACH ascorbic acid method 8048 [27].
Preserved TP water samples were digested according to
the persulfate digestion method (SM 4500-P B) and de-
termined colormetrically by the HACH ascorbic acid
method [27]. All analyses were conducted before rec-
ommended holding times had expired [25].
2.4. Nutrient Retention, Export, or Net Uptake
Nutrients added to an aquatic system are retained in,
transported through, or exported from the system (i.e.,
added to the water column) [28]. The fraction of nutri-
ents retained within the study reach (i.e., the retention
coefficient (RC)) was calculated using the nutrient loads
from Sites 2 (S2) and 6 (S6) with Equation 1:
where N was the mean measured nutrient concentration
(mg·L–1) and Q was the measured river discharge (m3·s–1)
for the respective Site 2 (S2) or 6 (S6). Since NO2-N
made up such a small percentage of the inorganic N frac-
tion in the water column, the combined NO2-N + NO3-N
concentration was used in this analysis. Calculating nu-
trient export or retention in this way is a general ap-
proach that examines only reach-level inputs and outputs,
which rely on measured Q at the sites. Streams and rivers
in the Ozark Highlands often have relatively large sub-
surface Q flowing through the gravel alluvium within the
fluvial channel.
The WWTP effluent was used as the nutrient source
for determining net nutrient uptake length (SNET ). The
SNET approach evaluates longitudinal changes in nutri-
ent concentration throughout the entire study reach,
where SNET is a more quantitative approach to examin-
ing nutrient dynamics within a study reach than just ex-
amining nutrient inputs and outputs. The mean concen-
tration (based on three sub-samples) at each sampling
site was corrected for downstream of the effluent dis-
charge (Site 2) using Equation (2):
N N*ClClx
where ND was the dilution-corrected concentration
(mg·L–1) for the nutrient of choice, NX was the mean
nutrient concentration (mg·L–1) at sample site x, Cl0 was
the mean chloride concentration (mg·L–1) from Site 2 (i.e.,
the immediate downstream sample site of the WWTP),
and ClX was the mean chloride concentration (mg·L–1) at
sampling site x. The proportion of nutrient remaining in
the water column was then calculated using Equation (3):
where P was the proportion of the dilution-corrected nu-
trient (N) concentration remaining in the water column at
site (X). The proportion remaining in the water column
(P) was natural-log transformed, and the slope of the
linear relationship between the natural-log of the propor-
tion remaining in the water column and the distance from
S2 S2S6 S6S2 S2
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant
the WWTP discharge represented K. When K (i.e., the
slope) was significant (i.e., different from 0) at the p <
0.1, then SNET was calculated with Equation (4):
S1 K (4)
Net nutrient uptake length (SNET ) was expressed in
km and was calculated for SRP, NO3-N, and NH4-N
for each sampling date. Negative SNET values represented
net release of the nutrient through the study reach, while
positive distances demonstrate net retention with long
distance suggesting less efficient retention than shorter
distances (Newbold et al., 1981). An alpha value of 0.1
was used to judge significance due to the large scale (i.e.,
5th-order stream) of the White River [see also 12].
The net mass transfer coefficient (VF-NET) was calcu-
lated using SNET, Q, and the average wetted width of the
river (W) using Equation (5):
W (5)
and was expressed in m s–1. The VF-NET is the velocity
at which nutrients travel from the water column to the
stream substrate, and removes some hydrologic effects
for across site and date comparisons.
Net nutrient uptake rate (UNET ) was then calculated
by Equation 6:
U V*
C (6)
and was expressed in mg m2 s–1. This parameter con-
siders changes in concentrations downstream from the
effluent discharge to estimate net uptake rates.
2.5. Statistical Analyses
River discharge was graphically examined initially and,
due to large temporal variations, was divided into three
qualitative categories [i.e., Low (<2 m3·s–1), Medium (2 -
6 m3·s–1), and High (>6 m3·s–1)] based on the frequency
of sampling days with similar discharge rates (Figure 3).
Water quality parameters (i.e., TN, NO3-N, NO2-N,
NH 4 - N, TP, SRP, turbidity, TOC, Cl, pH, conductivity,
temperature, and DO) upstream of the municipal WWTP
discharge (Site 1) were compared to those at the first site
immediately downstream (Site 2) to evaluate the imme-
diate effect of WWTP effluent on water quality. This
was accomplished by conducting a two-factor analysis of
variance (ANOVA) using SAS (version 9.1, SAS Insti-
tute, Inc., Cary, NC) to evaluate the effect of site (up-
stream and downstream) and flow regime (i.e., low, me-
dium, and high) on water quality parameters. In addition,
paired t-tests were performed separately within each flow
regime comparing parameters upstream and downstream
to further evaluate the effect of the WWTP effluent dis-
charge on river water quality (Minitab 13.31, Minitab
Inc., State College, PA).
On dates in which SNET was significant, simple cor-
relation analyses using Minitab were performed to
evaluate the relationship between the SNET of individual
nutrients and other water quality parameters. An alpha
level of 0.1 was decided a priori to use to judge the sig-
nificance of SNET values due to the expected large spatial
variability with the measured parameters. An alpha level
of 0.05 was used to judge significance for all correlations
conducted. The parameters that were analyzed included:
Site 2 nutrient concentrations (SRP, NO3-N, NH4-N, TP,
and TN), TOC, turbidity, conductivity, temperature, pH,
DO, and the mean Q averaged across all six sites. Site 2
was chosen because the water quality parameters down-
stream would show how the effluent discharge might
influence nutrient dynamics. An average Q was calcu-
lated and used instead of Q measured at Site 2 because of
the fluctuations from site to site due to interflow within
the gravel streambed.
3. Results and Discussion
3.1. River and WWTP Discharge
White River discharge varied over the 20 sampling
months from 0.1 m3·s–1 in August 2006 to 14.3 m3·s–1 in
January 2007 in response to local precipitation (Figure
3). Average discharge was 4.2 m3·s–1 on days the river
was sampled. Based on the <2, 2 to 6, and >6 m3·s–1 dis-
charge thresholds, there were a total of 7, 7, and 6 sam-
pling dates that represented the low, medium and high
flow categories, respectively (Figure 3). The 42-year
(1964 to 2006) average river discharge for the study
reach was 15.3 m3 s–1 and included storm-flow as well as
base-flow discharge [29]. White River discharge was
below the 42-year average on all sample dates in this
study. Thus, the flow-regime categories that were as-
signed for this study do not represent the total variation
in White River discharge.
The WWTP discharge ranged from 0.1 m3·s–1 in Au-
gust 2006 and September 2007 to 0.6 m3·s–1 in March and
October 2007 (Figure 3), averaging 0.3 m3·s–1over the
20 sampling months. Effluent discharge was less variable
compared to river discharge on days sampled. The
WWTP discharge contribution to river discharge at Site
2 ranged from 2 to almost 100% of streamflow, average-
ing 19% of the total river discharge on the days sampled.
During August 2006, the low-flow conditions coupled
with gravel streambed material could explain the re-
ported WWTP discharge being larger than the measured
river discharge as flow through the gravel alluvium was
likely occurring. The variation in the degree to which
dilution occurred immediately after the WWTP effluent
discharge was part of the reason that river discharge was
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant 261
Figure 3. White River discharge throughout a 20-month sampling period from January 2006 to December 2007. Also plotted
are the wastewater treatment plant (WWTP) discharge into the White river and the 40-yr average White River discharge.
river dis charge was q uan titativel y divid ed in to th ree flo w regi mes (Lo w, Med ium, a nd High ). Horiz ontal li nes at 2 .0 and 6.0 m3
s1 indicate the thresholds separating the three flow regimes.
qualitatively categorized for purposes of this study.
3.2. Water Quality Upstream of the WWTP
Stream water quality was measured upstream of the
WWTP on all 20 sampling dates (Table 1). Turbidity
varied greatly across sampling dates ranging from 1.9 in
August 2006 to 45.2 NTU in March 2006. There was a
total maximum daily load (TMDL) present for turbidity
that was set by the ADEQ as required for impaired wa-
terbodies. Since no stream load data could be assessed
for turbidity (i.e., there is no concentration associated
with NTU because it is an optical measurement), total
suspended solids (TSS) was used as a surrogate to tur-
bidity to develop the TMDL. A target base-flow TSS
concentration of 11 mg·L–1 was reported to correspond
with a turbidity level of 10 NTU, while a storm-flow
TSS target of 12 mg·L–1 corresponded with a turbidity
level of 17 NTU [30]. Turbidity at Site 1 exceeded the
base-flow TMDL on 50% of the sample dates. All forms
of N measured (i.e., NO3-N, NO2-N, NH4-N, and TN)
had maximum concentrations < 1.0 mg·L–1 during the
sampling dates, and maximum SRP and TP concentra-
tions were 0.05 mg·L–1 (Table 1).
3.3. WWTP Effluent Characteristics
As was expected, some effluent characteristics varied
seasonally, while others did not. Effluent temperature
varied seasonally from a low of 13.0˚C in March 2007 to
a high of 27.2˚C in August 2007 and averaged 21.1˚C
across the study period. Similarly, effluent DO concen-
tration displayed a seasonal pattern varying from an av-
erage of 8.3 mg·L–1 in July and August to 13.2 mg·L–1 in
March and averaged 9.1 mg·L–1 across the study period.
Since oxygen solubility is known to be inversely related
to water temperature, this observed variation was ex-
pected. Effluent TSS concentrations also varied, but not
seasonally, ranging from a low of 0.5 mg·L–1 in Septem-
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant
ber 2007 to a high of 8.5 mg·L–1 in January 2007 and
averaging 2.7 mg·L–1 across the study period. Effluent
pH varied between pH 7 in January 2006 and 7.9 in Sep-
tember 2007.
Effluent SRP and TP concentrations were both < 0.4
mg·L–1, except for in April, May, and June 2006. Total P
and SRP were greatest in the effluent during May 2006,
1.9 and 1.4 mg·L–1, respectively. These concentrations
were much greater than any observed P concentrations
from the White River. Effluent ammonium concentra-
tions were <0.5 mg·L–1 on all sampling dates except in
the months of March and April 2006 and in April 2007.
April 2007 had the greatest observed NH4-N concentra-
tion (1.8 mg·L–1). The exact reason for the three months
of elevated SRP, TP, and NH4-N concentrations in the
effluent discharge is unknown.
When wastewater effluent NH4-N, SRP, and TP con-
centrations were compared with river concentrations at
Site 1 and 2, effluent nutrient concentrations were often
related to that observed downstream. Site 2 river SRP
(r = 0.67, p < 0.01) and NH4-N (r = 0.53, p < 0.05) con-
centrations were significantly positively correlated with
the WWTP effluent concentrations. These correlations
indicate that the WWTP effluent was a major factor in-
fluencing downstream dissolved P and NH4-N concen-
trations in the White River.
3.4. Upstream-Downstream Comparison
With the exception of NH4-N, pH, and temperature, all
other water quality parameters measured in this study
were affected by site (i.e., upstream or downstream),
flow regime (i.e., low, medium, or high), or both (Table
2). Based on the two-factor ANOVA, measured Cl, TN,
TP, and NO3-N concentrations were greater down-
stream than upstream of the WWTP discharge during
low-flow (p < 0.01), but did not differ between sites dur-
ing medium- or high-flow conditions (Figure 4). Meas-
ured Cl, TN, TP, and NO3-N concentrations at Site 2
ranged from 14 to 76 mg Cl·L–1, 0.9 to 10.6 mg TN·L–1,
0.04 to 0.16 mg TP·L–1, and 0.6 to 11.7 mg NO3-N·L–1
across sample dates during low-flow conditions. These
same sites ranged from 5 to 14 mg Cl·L–1, 0.3 to 2.7 mg
TN·L–1 , 0.01 to 0.13 mg TP·L–1 , and 0.2 to 2.4 mg
NO3-N·L –1 across sample dates during medium- and
high-flow conditions. During low-flow, the relatively
high concentrations of Cl, TN, TP, and NO3-N in the
WWTP effluent affected river water chemistry due to
less dilution in the river when compared to higher base
flows (i.e., medium and high flows in this study). This
supports the assumption that the degree of dilution, based
on river discharge, plays an important role in the nutrient
enrichment of the White River. Based on paired t-tests
that were conducted separately by flow regime, the con-
centrations of Cl and TP were always greater (p < 0.05)
downstream from the WWTP effluent discharge than
upstream, further indicating the significant impact that
the WWTP effluent discharge has on stream water
chemistry. Nitrate accounted for 91% of TN across both
sites and all sample dates; thus results for nitrate and TN
were similar. Nitrogen and Cl concentrations have been
shown to be elevated below a WWTP discharge in other
point-source-receiving streams in the Ozark Highlands
[6,7,32], therefore, it was not surprising that the WWTP
effluent affected downstream stream concentrations most
when diluting flows (i.e., high discharge flow rates) were
not present in the White River.
Nitrite, SRP, TOC, and conductivity were greater (p <
0.04) downstream than upstream when averaged across
all flow regimes (Table 2). The mean downstream
NO 2-N concentration was more than double that of the
upstream concentration (Table 3). Nitrite is an interme-
diate form of N during nitrification and is not stable in
the environment [33]. Soluble reactive P is biologically
important because it is often the limiting nutrient for
primary production in White River tributaries [34], but
concentrations were generally low (<0.1 mg SRP L–1) on
all sample dates throughout the study. The mean river
SRP concentration in the White River was four times
greater downstream than upstream of the WWTP when
averaged across flow regimes. The TOC concentration
was 35% greater downstream from the WWTP effluent
discharge compared to upstream (Table 3). Carbon
added from the WWTP effluent provides more substrate
for microorganisms in the river which can lead to more
heterotrophic production, which could influence micro-
bial processes and reach-level retention capacity. Stream
conductivity was always greater, on average 62% greater,
downstream than upstream of the WWTP effluent dis-
charge (Table 3) because of the added solutes in the ef-
Based on the ANOVA, turbidity and DO did not differ
between Site 1 and 2 (Tables 2 and 3). However, based
on a paired t-test within each flow regime, DO was
greater downstream than upstream of the WWTP effluent
discharge during low flow and was similar when flow
exceeded 2 m3·s–1. Conductivity, TOC, DO, and turbidity
varied among flow regimes (p < 0.015) when averaged
across sites (Table 2). Both TOC and conductivity were
greatest during low-flow conditions and did not differ
between medium and high-flow conditions (Table 4).
Conductivity during medium and high-flow conditions
was less than one half that observed during low-flow
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant
Copyright © 2011 SciRes. JEP
conditions (as defined in this study). Total organic car-
bon also experienced a similar decrease as that of con-
ductivity as the flow regime increased. Dilution of the
WWTP effluent was likely the mechanism responsible
for these changes when discharge exceeded 2 m3·s–1.
Dissolved oxygen varied among all three flow regimes
and increased as flow regime increased (Table 4). The
increased mixing and aeration from more turbulent flow
during increasingly greater discharge rates were likely
responsible for increasing DO concentrations. Though
water temperature was statistically unaffected by either
site or flow regime (Table 2), water temperature nu-
merically decreased from the low- to the high-flow re-
gime, while the DO concentration significantly increased
(Table 4), which was expected.
Similar to DO, turbidity was also greater during high-
than low-flow conditions, but turbidity during medium-
flow was similar to that during both low- and high-flow
conditions (Tab l e 4 ). The amount of suspended sediment
in the water column is typically directly proportional to
the water velocity, thus it was not surprising that turbid-
ity was greatest during high-flow conditions. However,
the relationship between exposure to and actual biologi-
cal impairment from suspended sediment, as character-
izes numerous streams in the Ozark Highlands, is poorly
understood [35].
Neither site nor flow regime affected (p > 0.05)
NH 4-N concentrations, water temperature, or pH based
on the ANOVA (Table 2). Averaged across sites and
flow regimes, mean ammonium concentration was 0.1
mg·L–1, mean pH was 7.3, and mean water temperature
was 18.6˚C. However, based on a paired t-test within
each flow regime, water temperature was slightly greater
downstream than upstream of the WWTP effluent dis-
charge when flows exceeded 6 m3·s–1.
3.5. Water Quality Downstream of the WWTP
White River water quality measured at the five sites
downstream of the WWTP effluent discharge varied
widely. Turbidity ranged from 5 to 50 NTU across all
downstream sample sites and dates during this study
(Table 5). The average turbidity for Sites 2 through 6
was above the TMDL NTU limit on 45% of the sampling
dates. The WWTP’s point-source-pollution effect was
apparent based on increased nutrient concentrations,
conductivity, and Cl. The mean NO3-N concentration
at Sites 2 through 6 averaged across sample dates was
3.2 mg·L–1, which was more than three times the mean
NO 3-N concentration at Site 1 upstream of the WWTP
discharge (Table 1). River TP averaged 0.10 mg TP L–1
across downstream sample locations and dates, but ex-
ceeded the EPA-recommended reference P concentration
for Ecoregion XI of 0.01 mg·L–1 [31] with a maximum
observed concentration 0.32 mg TP·L–1. Chloride con-
centrations ranged from 5 to 77 mg·L–1 and averaged 30
mg·L–1. The mean chloride concentration for Sites 2
through 6 was more than five times greater than Site 1
upstream of the WWTP (Table 1). Mean conductivity
for Sites 2 through 6 (330 μS·cm–1) was two times great-
Figure 4. Flow regime (i.e., Low, Medium, and High) and site location (i.e., upstream and downstream of the wastewater
treatment plant) effects on water quality parameters in the White River, Fayetteville, AR. Different letters above bars for the
same parameter are different at the 0.05 level.
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant
Table 1. Summary of water quality characteristics averaged acro ss all fl ow regimes in the White river upstr e a m (i.e., Site 1) of
the Paul R. Noland Wastewater Treatment Plant in Fayetteville, AR.
Water quality parameter Minimum Maximum Average
Nitrate (mg·L–1) < 0.01 0.87 0.26
Nitrite (mg·L–1) < 0.01 0.01 < 0.01
Ammonium (mg·L–1) 0.01 0.31 0.07
Total nitrogen (mg·L–1) 0.20 0.78 0.40
Soluble reactive phosphorus (mg·L–1) < 0.01 0.01 < 0.01
Total phosphorus (mg·L–1) < 0.01 0.05 0.03
Turbidity (NTU*) 1.9 45.2 13.1
Total organic carbon (mg·L–1) 0.8 4.1 2.3
Chloride (mg·L–1) 3.8 10.2 5.6
Dissolved oxygen (mg·L–1) 4.1 11.6 8.0
pH 6.6 7.7 7.3
Conductivity (μS·cm–1) 86 440 163
Temperature (˚C) 5.7 28.8 18.4
* Nephalometric turbidity units (NTU)
Table 2. Analysis of variance summary of the effects of site, flow regime, and their interaction on water quality parameters
measured upstream and downstream of the wastewater treatment plant effluent discharge i nto the White river in Fayetteville, AR.
Source of variation
Water quality parameter Site Flow regime Site x flow regime
Nitrate 0.003 0.011 0.004
Nitrite 0.015 0.347 0.382
Ammonium 0.424 0.217 0.863
Total nitrogen 0.002 0.004 0.003
Soluble reactive phosphorus 0.003 0.156 0.150
Total phosphorus < 0.001 0.002 0.009
Turbidity 0.969 0.015 0.999
Total organic carbon 0.027 < 0.001 0.072
Chloride < 0.001 < 0.001 0.001
Dissolved oxygen 0.898 < 0.001 0.717
pH 0.242 0.153 0.940
Conductivity 0.040 < 0.001 0.107
Temperature 0.878 0.081 0.992
Table 3. Summary of the effect of site averaged across flow regime, on water quality parameters measured upstream and
downstream of the wastewater treatment plant discharge into the White river in Fayetteville, AR. Mean values are reported
with standard errors in parentheses.
Water quality parameter Upstream Downstream LSD0.05
Nitrate (mg·L1) 0.3 (< 0.1) 2.2 (0.7)* 1.2††
Nitrite (mg·L1) < 0.01 (< 0.01) 0.02 (< 0.01)* 0.01
Ammonium (mg·L1) 0.07 (0.01) 0.09 (0.02) -
Total nitrogen (mg·L1) 0.4 (< 0.1) 2.3 (0.7)* 1.1††
Soluble reactive phosphorus (mg·L1) < 0.01 (< 0.01) 0.04 (0.01)* 0.02
Total phosphorus (mg·L1) 0.03 (< 0.01) 0.07 (0.01)* 0.02††
Turbidity (NTU) 13.0 (2.2) 13.1 (2.2) -
Total organic carbon (mg·L1) 2.3 (0.2) 3.1 (0.4)* 0.66
Chloride (mg·L1) 5.6 (0.3) 17.9 (4.3)* 6.5††
Dissolved oxygen (mg·L1) 8.0 (0.5) 8.0 (0.5) -
pH 7.3 (0.1) 7.4 (< 0.1) -
Conductivity (μS·cm1) 163 (19) 264 (54)* 92
Temperature (˚C) 18.4 (1.6) 18.8 (1.5) -
*Asterisks denote a significant difference between upstream and downstream mean values for the same water quality parameter; Least significant diference at the
0.05 level (LSD0.05 ); †† Parameter also had significant site x flow regime interaction.
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant
Copyright © 2011 SciRes. JEP
Table 4. Summary of the effect of flow regime (i.e., Low, Medium, and High), averaged across sites, on water quality pa-
rameters m easu red up stream a nd d ownstream of th e wa stewater treatm ent p lant discha rge in to the W hite rive r in F ayettev ille ,
AR. Mean values are reported with standard errors in parentheses.
Flow regime
Water quality parameter Low Medium High LSD0.05 ††
Nitrate (mg·L1) 2.5 (1.0)a 0.7 (0.2)b 0.4 (0.1)b 1.5
Nitrite (mg·L1) 0.01 (0.01) 0.01 (< 0.01) 0.01 (< 0.01) -
Ammonium (mg·L1) 0.1 (< 0.1) 0.1 (< 0.1) 0.1 (< 0.1) -
Total nitrogen (mg·L-1) 2.6 (1.0)a 0.8 (0.2)b 0.5 (0.1)b 1.32
Soluble reactive phosphorus (mg·L1) 0.03 (0.01) 0.01 (< 0.01) 0.02 (0.01) -
Total phosphorus (mg·L1) 0.07 (0.01)a 0.03 (0.01)b 0.04 (0.01)b 0.02
Turbidity (NTU) 7.2 (0.8)a 14.4 (2.3)ab 18.2 (3.7)b 7.3
Total organic carbon (mg·L1) 3.9 (0.4)a 2.3 (0.2)b 1.7 (0.2)b 0.8
Chloride (mg·L1) 21.3 (6.0)a 7.2 (0.7)b 5.9 (0.5)b 7.9
Dissolved oxygen (mg·L1) 6.1 (0.3)a 8.2 (0.4)b 10.0 (0.6)c 1.3
pH 7.4 (0.1) 7.2 (0.1) 7.3 (0.1) -
Conductivity (μS·cm1) 359 (69)a 156 (13)b 111 (4.6)b 113
Temperature (˚C) 21.8 (1.9) 17.7 (1.3) 15.9 (2.0) -
Flow regime categories are defined as follows: Low (< 2.0 m3 s–1), Medium (2.0 – 6.0 m3 s–1), and High (> 6.0 m3 s–1); †† Least significant difference at the
0.05 level (LSD0.05); Means followed by difference letters in the same row are different at the 0.05 level; Parameter also had significant site x flow regime
er than that of Site 1 (Table 1) and ranged from 95 to
1118 μS·cm–1.
3.6. Nutrient Retention, Export and Net Uptake
The White River showed variable retention or export of
nutrients across sampling dates and between constituents
when reach-level inputs and outputs were evaluated us-
ing the retention-coefficient approach. The various forms
of N showed retention coefficients ranging from a low of
–2.42 to a high of 0.96 for NH4-N, NO3-N + NO2-N, and
TN. Only NH4-N had an average retention coefficient
that was significantly different (i.e., greater) than zero (p
= 0.04), suggesting NH4-N was generally retained or
transformed through the study reach. The other forms of
N were, on average, just transported downstream without
retention or transformation. The retention coefficients for
NO3-N + NO2-N and TN were highly correlated (r = 0.99,
p < 0.001), which is not surprising since NO3-N made up
a large portion on the TN pool. However, NH4-N reten-
tion coefficients were not correlated (p > 0.10) with the
retention coefficients of other N forms within the White
Phosphorus retention coefficients within the study
reach were just as variable as N forms, ranging from
–1.19 to 0.94 for SRP and –0.92 to 0.94 for TP. On av-
erage, retention coefficients did not differ from zero,
suggesting that minimal retention was occurring. Reten-
tion coefficients for SRP and TP were significantly cor-
related (r = 0.64, p < 0.01), likely because SRP made up
a large portion of TP in the White River. Total N and P
retention coefficients were also correlated (r = 0.52, p =
0.02), suggesting that retention of these two nutrients
might be coupled within this study reach.
The calculations of net uptake lengths were not biased
by flow through alluvial gravel within the study reach, as
may have been the case for retention coefficients that
were based on reach-level inputs and outputs. Calculated
SNET values showed trends (increasing, decreasing, or
no significant change) in the downstream direction. Net
uptake lengths for SRP were significant (p < 0.10) on
five sample dates within the study period, ranging from
–8.7 to 7.9 km. Overall, little retention of SRP was oc-
curring within the fluvial channel of the White River,
suggesting that the study reach was not a consistent sink
for SRP. Across these five sampling dates, SRP SNET
was positively correlated to Site 2 SRP concentration (r
= 0.927, p = 0.02) suggesting that as the concentration of
SRP at Site 2 increased, SNET also increased. The study
reach acted as a source of SRP when the effects of the
effluent discharge were minimal and observed concen-
trations at Site 2 were 0.06 mg·L–1 or less. Net uptake
lengths for SRP were not correlated with any other phy-
sio-chemical property measured in the White River. Ta-
ble 6 summarizes VF-NET and UNET values for SRP
within the White River.
Net uptake lengths for NO3-N were significant on 10
sampling dates, ranging from –22.1 to 13.1 km. Similar
to SRP SNET, NO3-N SNET had some sampling dates
showing net retention within the study reach and others
suggesting net export from the study reach. The net ex-
port could be explained by nitrification of reduced N
forms within the fluvial channel, whereas the net retention
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant
Table 5. Summary of water quality characteristics averaged across all flow regimes and the five downstream study sites in the
White river downstream of the wastewater treatment plant discharge in Fayetteville, AR.
Water quality parameter Minimum Maximum Average
Nitrate (mg·L–1) 0.2 12.5 3.2
Nitrite (mg·L–1) < 0.01 0.14 0.04
Ammonium (mg·L–1) 0.01 0.88 0.19
Total nitrogen (mg·L–1) 0.3 11.0 3.1
Soluble reactive phosphorus (mg·L–1) < 0.01 0.32 0.07
Total phosphorus (mg·L–1) < 0.01 0.36 0.10
Turbidity (NTU*) 4.9 49.9 22.1
Total organic carbon (mg·L–1) 0.9 7.5 3.8
Chloride (mg·L–1) 4.8 76.7 30.4
Dissolved oxygen (mg·L–1) 5.1 13.8 8.8
pH 6.4 9.2 7.6
Conductivity (μS·cm–1) 95 1118 330
Temperature (˚C) 7.6 32.9 19.2
* Nephalometric turbidity units (NTU).
Table 6. Summary statistics for mass transfer coefficients (VF-NET ) and uptake rates (UNET ) for soluble reactive phosphorus
(SRP), ammonium-nitrogen (NH4-N), and nitrate-nitrogen (NO3-N) on sampling dates that demonstrated significant net
nutrient uptake or release in the study reach of the White River, AR downstream of the wastewater treatment plant.
Nutrient NPPPP Min Max Average Min Max Average
SRP 5 –7.3E–06 2.7E–05 6.9E–06 –4.4E–04 2.7E–03 7.7E–04
NH4-N 6 3.6E–06 4.0E–05 1.5E–05 2.5E–02 4.1E–01 1.6E–01
NO3-N 10 –1.1E–05 2.3E–05 5.8E–06 –1.9E00 19.4E00 2.6E00
The number of sampling dates in which nutrient uptake length (SNET) was significant at p < 0.1.
occurred when biological uptake and denitrification ex-
ceeded nitrification rates. Net uptake lengths for NO3-N
were only correlated with turbidity at Site 2 (r = 0.65, p =
0.04), whereas no other measured physio-chemical prop-
erty was related to NO3-N SNET. Table 6 summarizes
VF-NET and UNET values for NO3-N across the sampling
Net uptake lengths for NH4-N displayed less variation
than that for SRP or NO3-N SNET across the sampling
dates, ranging from 5.0 to 14.8 km. When SNET was
significant, uptake lengths were long, but positive, sug-
gesting that NH4-N was retained, albeit not efficiently,
within the White River downstream from the effluent
discharge. Net uptake lengths for NH4-N were not sig-
nificantly correlated to any physio-chemical property
measured downstream from the effluent discharge during
this study. Table 6 summarizes VF-NET and UNET values
for NH4-N across the sampling dates.
3.7. Comparison to Other Studies
Effluent chemistry often differs greatly from that in re-
ceiving aquatic systems [36], and the effluent discharge
at the White River near Fayetteville, Arkansas had a sig-
nificant influence on water chemistry and nutrient trans-
port. Despite the large size of the White River (i.e., 5th
order), this effluent discharge at times made up a sub-
stantial portion of flow within the study reach during
relatively dry summers. Overall, the influence of the ef-
fluent discharge on water chemistry was observable
across all flow regimes as defined in this study, but was
most profound during low-flow conditions (<2 m3·s–1).
Other studies have shown that effluent discharges influ-
ence stream water chemistry when the stream flow is
dominated by WWTP inputs [7-9,32].
Phosphorus generally travels long distances down-
stream from effluent discharges before significant reten-
tion occurs, and this observation is consistent across
streams receiving effluent discharge in the Ozark High-
lands [6,7,32] and others throughout the USA [12] and
the world [8,9]. When significant net retention occurs,
SNET distances can reach up to 85 km [12], but most
SNET SRP lengths is less than 20 km [6,7,12,32]. The
effects of effluent discharges on SRP concentrations and
transport likely vary with how much the effluent domi-
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant 267
nates a receiving stream and how much effluent changes
concentrations in the receiving stream. At the White
River, TP concentrations and transport were similar to
SRP, because TP was largely in the soluble-reactive
However, some consistencies occur across streams
that are effluent dominated to larger rivers where efflu-
ents are not a major proportion of discharge within the
fluvial channel. For example, both the White River (this
study) and other effluent-dominated streams [7,12,32]
showed net release of SRP from within the study reaches.
Haggard et al. [7] suggested that SRP release occurs
when effluent P concentrations are relatively low, and
the SRP concentration in the receiving stream is less than
that associated with the sediment equilibrium P concen-
trations (EPC0). Ekka et al. [32] showed that sediment
EPC0 are strongly influenced by effluent P inputs, and
that dramatic changes in EPC0 may occur with changes
in effluent P concentrations. It is likely that something
similar is happening within the White River downstream
of the WWTP input. However, sediment-P interactions
might be more complex in the White River because this
stream is more turbid relative to other Ozark streams.
Thus, dissolved inorganic P (i.e., SRP) transport, reten-
tion and release through the White River might be more
complex, for a variety of reasons, than that observed in
less turbid streams within the Ozark Highlands.
The White River was less efficient at NH4-N retention
compared to other smaller streams receiving effluent
discharge, because NH4-N SNET was 5 km or longer at
the White River compared to less than 1.5 km in smaller
systems (eg., Columbia Hollow; Figure 5) [7]. However,
the observation that these stream reaches were a sink for
NH4-N (i.e., SNET was positive on all sampling dates) was
consistent across small to large river systems. It is likely
that biological transformation (i.e., nitrification) was the
mechanism responsible for NH4-N retention, but sus-
pended and stream-bed sediments can also adsorb NH4-N
from the water column. In contrast, Gibson and Meyer
[12] showed that NH4-N release occurred within the
Chattahoochee River downstream from multiple effluent
discharges (Figure 5).
The transport of NO3-N downstream from effluent
discharges is complex, because nitrification of reduced N
forms within the effluent and the fluvial channel can re-
sult in increasing NO3-N concentrations with down-
stream distance [7,8]. In the White River, NO3-N was
significantly retained on half of the sampling dates, while
the other dates showed increases in dilution-corrected
NO3-N concentrations downstream. The observed
NO3-N dynamics in the White River match that observed
at many other streams receiving effluent discharge (Fig-
ure 5), where net NO3-N release occurs as often as net
Figure 5. Comparison of net nutrient uptake lengths (SNET)
for ammonium-nitrogen (NH4-N), nitrate-nitrogen (NO3-N),
and soluble reactive phosphorus (SRP) from two previous
studies examining wastewater treatment plant (WWTP)
effluent receiving streams to that from the current study.
Data are pr esent ed for Co lumb ia Holl ow (CH), Arkansas [7]
and the Chattahoochee River-upstream study reach
(CHAT-U) and downstream study reach (CHAT-D), Geor-
gia [12]. T he sta ndard error abo ut the me an and t he numb er
of observations (n) in each of the studies are also reported.
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant
NO3-N retention [8,12].
The observation that the White River downstream
from this effluent discharge does not efficiently retain
nutrients, either SRP or NO3-N, is important because the
end of this study reach is the headwaters of Beaver Lake.
Thus, this essentially means that nutrient inputs from this
WWTP travel kilometer-scale distances downstream to
the reservoir providing drinking water for northwest Ar-
kansas. The effluent discharge might actually be influ-
encing primary productivity in the headwaters of Beaver
Lake because sestonic chlorophyll-a concentrations gen-
erally increase with N and P supply [37]. However, the
WWTP effluent discharge contributes less than 10% of
the annual inputs of TN or TP to Beaver Lake from its
watershed [38]. Nutrient transport in streams down-
stream effluent discharges often depends on drought
conditions [39], and the relative contribution of annual
inputs from this WWTP to Beaver Lake will likely be
greater during years where annual discharge is less.
4. Conclusions
The WWTP discharge into the White River made up a
small fraction of the total river discharge, and the imme-
diate dilution of the effluent was apparent by the ob-
served changes in water quality during low river dis-
charge. This effluent discharge had a significant impact
on nutrient concentrations, despite its relatively low con-
tribution to river discharge. However, longitudinal pat-
terns in nutrient concentrations downstream from the
effluent discharge were not as consistent as reported pre-
viously for smaller-order rivers where the effluent made
up a relatively larger proportion of river discharge.
Nutrient retention coefficients were highly variable, and
suggested that NO3-N + NO2-N and SRP were, on aver-
age, not retained within the study reach. However,
NH4-N was significantly retained within the study, on
average, when evaluating reach level inputs and outputs.
Since little nutrient retention occurred in the White River
downstream from this effluent discharge, the headwaters
of Beaver Lake are likely directly influenced by the
WWTP evaluate in this study. The WWTP has relatively
low nutrient concentrations in its effluent discharge, but
its continual discharge of nutrients to the White River
has resulted in little retention within the study reach.
Thus, any changes to the effluent nutrient concentrations
or loading would likely influence the headwaters of
Beaver Lake.
5. Acknowledgements
Beaver Water District and staff are gratefully acknowl-
edged for providing the resources to conduct this study.
Mindi Crosswhite, Raymond Avery, and Rusty Tate pro-
vided invaluable field sampling support and expertise
and Cindy Harp assisted with timely laboratory analyses.
[1] Arkansas Department of Environmental Quality, “Ar-
kansas’s 2008 303(d) List (List of Impaired Waterbod-
ies),” 2008. Internet Available:
[2] D. R. Edwards and T. C. Daniel, “Effects of Poultry Lit-
ter Application Rate and Rainfall Intensity on Quality of
Runoff from Fescue Plots,” Journal of Environmental
Quality, Vol. 22, No. 2, 1993, pp. 361-365.
[3] D. R. Edwards, P. A. Moore, J. F. Murdoch and T. C.
Daniel, “Quality of Runoff from Four Northwest Arkan-
sas Pasture Fields Treated with Organic and Inorganic
Fertilizer,” Transactions of the ASAE, Vol. 39, No. 5,
1995, pp. 1689-1696.
[4] T. J. Sauer, P. A. Moore, G. L. Wheeler, C. P. West, T. C.
Daniel and D. J. Nichols, “Runoff Water Quality from
Poultry Litter-Treated Pasture and Forest Sites,” Journal
of Environmental Quality, Vol. 29, No. 2, 2000, pp.
515-521. doi:10.2134/jeq2000.00472425002900020020x
[5] B. C. Menjoulet, K. R. Brye, A. L. Pirani, B. E. Haggard
and E. E. Gbur, “Runoff Water Quality from Broi-
ler-Litter-Amended Tall Fescue in Response to Natural
Precipitation in the Ozark Highlands,” Journal of Envi-
ronmental Quality, Vol. 38, No. 3, 2009, pp. 1005-1017.
[6] B. E. Haggard, D. E. Storm and E. H. Stanley, “Effect of
a Point Source Input on Stream Nutrient Retention,”
Journal of the American Water Resources Association,
Vol. 37, No. 5, 2001, pp. 1291-1299.
[7] B. E. Haggard, E. H. Stanley and D. E. Storm, “Nutrient
Retention in a Point-Source-Enriched Stream,” Journal of
the North American Benthological Society, Vol. 24, No. 1,
2005, pp. 29-47.
[8] E. Marti, J. Autmatell, L. Godé, M. Poch and F. Sabater,
“Nutrient Retention Efficiency in Streams Receiving In-
puts from Wastewater Treatment Plants,” Journal of En-
vironmental Quality, Vol. 33, 2004, pp. 285-293.
[9] G. C. Merseberger, E. Martí and F. Sabater, “Net
Changes in Nutrient Concentrations below a Point Source
Input in Two Streams Draining Catchments with Con-
trasting Land Uses,” Science of the Total Environment,
Vol. 347, No. 1-3, 2005, pp. 217-229.
[10] B. Gücker, M. Brauns and M. T. Pusch, “Effects of
Wastewater Treatment Plant Discharge on Ecosystem
Structure and Function of Lowland Streams,” Journal of
the North American Benthological Society, Vol. 5, 2006,
pp. 313-329.
[11] S. Treese, T. Meixner and J. F. Hogan, “Clogging of an
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant 269
Effluent Dominated Semiarid River: A Conceptual Model
of Stream-Aquifer Interactions,” Journal of the American
Water Resources Association, Vol. 45, No. 4, 2010, pp.
1047-1062. doi:10.1111/j.1752-1688.2009.00346.x
[12] C. A. Gibson and J. L. Meyer, “Nutrient Uptake in a
Large Urban River,” Journal of the American Water Re-
sources Association, Vol. 43, No. 3, 2007, pp. 576-587.
[13] S. R. Femmer, “National Water-Quality Assessment Pro-
gram Ozark Plateaus Biology Study,” 1995. Internet
[14] K. R. Brye and C. P. West, “Grassland Management Ef-
fects on Soil Surface Properties in the Ozark Highlands,”
Soil Science, Vol. 170, 2005, pp. 63-73.
[15] H. D. Scott and L. B. Ward, “MLRA 116A Ozark High-
lands,” 2006. Internet Available:
[16] National Agricultural Statistics Service—United States
Department of Agriculture, “Poultry-Production and
Value, 2002 Summary,” 2003. Internet Available:
[17] T. J. T. Sims and D. C. Wolf, “Poultry Waste Manage-
ment: Agricultural and Environmental Issues,” Advances
in Agronomy, Vol. 52, 1994, pp. 1-83.
[18] University of Arkansas Cooperative Extension Service,
“Improving Poultry Litter Management and Carcass Dis-
posal,” 2002. Internet Available:
[19] N. A. Slaton, K. R. Brye, M. B. Daniels, T. C. Daniel, R.
J. Norman and D. M. Miller, “Nutrient Input and Re-
moval Trends for Agricultural Soils in Nine Geographic
regions in Arkansas,” Journal of Environmental Quality,
Vol. 33, No. 5, 2004, pp. 1606-1615.
[20] United States Census Bureau, “2007 Population Esti-
mates,” 2010. Internet Available:
[21] Arkansas Department of Environmental Quality, “West
Fork White River Watershed Data Inventory and Non-
point Source,” 2004. Internet Available:
[22] National Oceanic and Atmospheric Administration, “Wash-
ington County, Arkansas Climatology,” 2009. Internet
[23] United States Geological Survey, “Precipitation Data for
Site Number 07048600,” 2006. Internet Available:
[24] United States Geological Survey, “USGS 07048600
White River near Fayetteville, AR Site Information,”
2006. Internet Available:
[25] American Public Health Association—American Water
Works Association—Water Environment Federation,
“Standard Methods for the Examination of Water and
Wastewater,” 21st Edition, American Public Health Asso-
ciation, Washington DC, 2005.
[26] American Society for Testing and Materials, “Annual
Book of ASTM Standards,” Vol. 11, No. 1, ASTM, Phila-
delphia, 2004.
[27] HACH Company, “DR/4000 Spectrophotometer Hand-
book,” HACH, Loveland, 1996.
[28] J. D. Newbold, J. W. Elwood, R. V. O’Neill and A. L.
Sheldon, “Measuring Nutrient Spiraling in Streams,”
Canadian Journal of Fisheries and Aquatic Sciences, Vol.
38, No. 7, 1981, pp. 860-863. doi:10.1139/f81-114
[29] United States Geological Survey, “River Discharge Data
for Site Number 07048600,” 2006. Internet Available:
[30] FTN Associates, Ltd., “TMDLs for Turbidity for White
River and West Fork, AR,” 2006. Internet Available:
[31] Environmental Protection Agency, “Ambient Water
Quality Criteria Recommendations—Information Sup-
porting the Development of State and Tribal Nutrient
Criteria—Rivers and Streams in Nutrient Ecoregion XI,”
2000. Internet Available:
[32] S. A. Ekka, B. E. Haggard, M. D. Matlock and I. Chau-
bey, “Dissolved Phosphorus Concentrations and Sedi-
ment Interactions in Effluent-Dominated Streams,” Eco-
logical Engineering, Vol. 26, 2006, pp. 375-391.
[33] N. C. Brady and R. R. Weil, “The Nature and Properties
of Soils,” 13th Edition, Prentice Hall, Upper Saddle River,
New Jersey, 2002.
[34] A. L. Ludwig, “Periphytic Algae Nutrient Limitation in
Streams Draining the Beaver Reservoir Basin, Northwest
Arkansas, USA, 2005-2006,” Master’s Thesis, University
of Arkansas, Fayetteville, 2007.
[35] T. H. Diehl and W. J. Wolfe, “Suspended-Sediment Con-
centration Regimes for Two Biological Reference
Streams in Middle Tennessee,” Journal of the American
Water Resources Association, Vol. 46, No. 4, 2010, pp.
824-837. doi:10.1111/j.1752-1688.2010.00460.x
[36] R. O. Carey and K. W. Migliaccio, “Contribution of
Wastewater Treatment Plant Effluents to Nutrient Dy-
Copyright © 2011 SciRes. JEP
Net Nutrient Uptake in the White River, Northwest Arkansas, Downstream of a Municipal Wastewater Treatment Plant
Copyright © 2011 SciRes. JEP
namics in Aquatic Systems: A Review,” Environmental
Management, Vol. 44, No. 2, 2009, pp. 205-217.
[37] B. E. Haggard, T. P. A. Moore Jr., T. C. Daniel and D. R.
Edwards, “Trophic Conditions and Gradients of the
Headwater Reaches of Beaver Lake, Arkansas,” Pro-
ceedings of the Oklahoma Academy of Science, Vol. 79,
1999, pp. 73-84.
[38] B. E. Haggard, P. A. Moore Jr., I. Chaubey and E. H.
Stanley, “Nitrogen and Phosphorus Concentrations and
Export from an Ozark Plateau Catchment in the United
States,” Biosystems Engineering, Vol. 86, No. 1, 2003, pp.
75-85. doi:10.1016/S1537-5110(03)00100-4
[39] J. Hur, M. A. Schlautman, T. Karanfil, J. Smink, H. Song,
S. J. Klaine and J. C. Hayes, “Influence of Drought and
Municipal Sewage Effluents on the Baseflow Water
Chemistry of an Upper Piedmont River,” Environmental
Monitoring and Assessment, Vol. 132, No. 1-3, 2007, pp.
171-187. doi:10.1007/s10661-006-9513-1