Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
584
2017 SOUTHEASTERN NATURALIST 16(4):584–602
The Effect of Beaver Ponds on Water Quality in Rural
Coastal Plain Streams
Christopher W. Bason1,3,*, Daniel E. Kroes2, and Mark M. Brinson3,†
Abstract - We compared water-quality effects of 13 beaver ponds on adjacent free-flowing
control reaches in the Coastal Plain of rural North Carolina. We measured concentrations of
nitrate, ammonium, soluble reactive phosphorus (SRP), and suspended sediment (SS) upstream
and downstream of paired ponds and control reaches. Nitrate and SS concentrations
decreased, ammonium concentrations increased, and SRP concentrations were unaffected
downstream of the ponds and relative to the control reaches. The pond effect on nitrate
concentration was a reduction of 112 ± 55 μg-N/L (19%) compared to a control-reach–influenced
reduction of 28 ± 17 μg-N/L. The pond effect on ammonium concentration was an
increase of 9.47 ± 10.9 μg-N/L (59%) compared to the control-reach–influenced reduction
of 1.49 ± 1.37 μg-N/L. The pond effect on SS concentration was a decrease of 3.41 ± 1.68
mg/L (40%) compared to a control-reach–influenced increase of 0.56 ± 0.27 mg/L. Ponds
on lower-order streams reduced nitrate concentrations by greater amounts compared to
those in higher-order streams. Older ponds reduced SS concentrations by greater amounts
compared to younger ponds. The findings of this study indicate that beaver ponds provide
water-quality benefits to rural Coastal Plain streams by reducing concentrations of nitrate
and suspended sediment.
Introduction
Land-use practices and associated processes in agriculturally influenced rural
landscapes affect surface-water quality by contributing high levels of nutrients and
sediments to streams and estuaries. In the Coastal Plain of the southeastern US,
these practices and processes include fertilizer application, concentrated animal
operations, soil erosion, atmospheric deposition of nitrogen, use of domestic septic
systems, and extensive stream channelization (Correll et al. 1992, Duda 1982,
Glasgow and Burkholder 2000, Jordan et al. 1997, Mallin et al. 1997, Omernik
1976, Paerl 1995, Yarbro et al. 1984). Nutrient and sediment inputs can contribute
to ecosystem degradation and inability of waters to support their designated uses
(Carpenter et al. 1998, USEPA 2002). Advances in water-quality management
practices are being incorporated on agricultural lands (Correll 1997, Osmond et al.
2002), but expression of eutrophic conditions is expected to worsen in most south
Atlantic estuaries of the US (Bricker et al. 2007). Although inputs of both nitrogen
and phosphorous are high, estuaries in North Carolina are typically nitrogen limited
(Harned and Davenport 1990, Harned et al. 1995). Phosphorous concentrations are
1Delaware Center for the Inland Bays, 39375 Inlet Road, Rehoboth Beach, DE, 19971.
2US Geological Survey, Lower Mississippi-Gulf Water Science Center, Baton Rouge, LA,
70817. 3Department of Biology, East Carolina University, Greenville, NC 27858. †Deceased.
*Corresponding author - chrisbason@inlandbays.org.
Manuscript Editor: Robert Krenz
Southeastern Naturalist
585
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
naturally high in the waters of North Carolina due to geologic sources (Spruill et
al. 1998), and they are often augmented by inputs from croplands and effluent from
sewage-treatment facilities.
Castor canadensis (Kuhl) (Beaver) populations have reestablished throughout
much of the southeastern US (Arner and Hepp 1989, Butler 1991, Naiman 1988).
Reintroductions of Beaver to North Carolina began in 1939 (Woodward and Hazel
1991). By 1983, populations were present in 80 of 100 counties and affected a
minimum of 35,858 ha of bottomland (Woodward et al. 1985). Population growth
to such nuisance proportions was driven by abundant food resources, few natural
predators, and a weak fur market.
Beaver construct dams across stream channels and floodplains (Hair et al. 1978,
Pullen 1971). The ponds that form behind the dams decrease water velocities,
expand water–sediment interactions, and open forest canopies, thus increasing
aquatic primary production, facilitating sedimentation, and altering biogeochemical
transformations (Naiman et al. 1988). Beaver ponds have been shown to affect
water quality by reducing concentrations of nitrate and suspended sediments in
various regions of North America (Cirmo and Driscoll 1993, Correll et al. 2000,
Devito et al. 1989, Klotz 2010, Kroes and Bason 2015, Maret et al. 1987, Margolis
et al. 2001, Naiman et al. 1988). However, we are unaware of published research
documenting the effects of beaver ponds on stream-water quality in watersheds
with intensive agricultural land-use typical of the southeaster n Coastal Plain.
The purpose of this study was to explore variability in effects among different
beaver ponds on water quality in rural streams of the North Carolina Coastal Plain.
We used a paired study design to compare the differences in concentrations of
nitrate, ammonium, soluble reactive phosphorus (SRP), and suspended sediments
(SS) between paired upstream and downstream sampling locations in 13 Beaverimpounded
stream reaches and 13 upstream, free-flowing control reaches during
fall and winter, 2002–2003. We focused on the landscape scale to allow for inference
from a group of varied ponds, rather than concentrating our efforts on the
detailed biogeochemical dynamics of a single site using a mass balance approach,
as undertaken in the Maryland Coastal Plain by Correll et al. (2000). This approach
forgoes the resolution necessary to determine influences of season and streamflow
on the effects of 1 pond in exchange for the capacity to explore potentially influential
spatial and temporal factors, such as drainage-basin size and age, across
multiple ponds.
Study Area
The inner Coastal Plain of North Carolina is characterized by low elevations and
a muted relief that results in a poorly drained landscape (Hammond 1964). Streams
in that region typically have low gradients (less than 1% slope) that contribute to more
frequent (~5 times/year), and longer-lasting overbank flow than in higher-gradient
settings (Sweet and Geratz 2003). Floodplains without Beaver activity typically
support bottomland hardwood forests (Shafale and Weakley 1990). Stream-water
quality in the study area is typical of southeastern Coastal Plain blackwater streams
Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
586
(Smock and Gilinsky 1992), with moderately acidic to near neutral pH (min–max
= 4.94–6.74, median = 6.08) and generally low specific conductance (min–max =
63–225 μS/cm, median = 98 μS/cm), but often with high levels of nutrients depending
on watershed land-use and condition of the channel and riparian area (Yarbro
et al. 1984). The climate is warm temperate with an average annual temperature of
16.5 ºC and average annual precipitation of 126 cm (US Climate Data 2013). The
study area received 38 cm of precipitation during the study period (5 cm above
average) and the temperature was 5.5 ºC (1.1 ºC) below average (NOAA 2017a, b).
High summertime evapotranspiration can cause 1st- and 2nd-order streams (Strahler
1957) to become intermittent and large portions of beaver ponds to become dry.
Low wintertime temperatures can cause some ponds to periodically freeze, although
we did not observe this during our study .
Land use in the study area is dominated by agriculture and silviculture, and
confined animal feeding operations (CAFOs) are also common. These areas were
largely converted from deciduous forest with subsequent stream channelization, establishment
of field and roadside ditches, and development of roads and residential
areas (Cashin et al. 1992, Rheinhardt et al. 1999). Drainage efforts began as early
as the 1700s in North Carolina, and more than 40% of production cropland in North
Carolina requires drainage (Thomas et al. 1995). Field ditches typically connect to
1st- to 4th-order channelized streams. Channelization practices ended in the 1970s
following challenges by environmental groups (Coffey 1982). These practices
have affected most headwater streams and associated riparian areas on the Coastal
Plain. Such impairment contributes to high nutrient and sediment loads in receiving
streams, and ultimately, estuaries (Mallin et al. 1993).
Beaver activity in the study area was extensive. Beaver dams across low-gradient
stream channels and floodplains often created serial stair-step ponds (Kroes and
Bason 2015) that extended for several kilometers. Field assessments and study of
orthophotography led us to the conservative estimate that over one quarter of 2nd- to
5th-order stream length within the study area was impounded by Beaver. Associated
flood damage to timber and roads was substantial (Butler 1991, Woodward et al.
1985) and led to concerted population control ef forts.
Methods
Site selection
We studied orthophotography from 1998 to identify 60 potential site pairs
within an area of ~2500 km2 (Fig. 1). We selected 13 pairs of sites based on several
criteria: (1) site pairs occurred on 2nd- to 4th-order streams with a vegetated buffer
of at least 10 m in width on each side of the channel, (2) control reaches were
free-flowing and had no visible evidence of recent, sustained ponding from Beaver
activity, and (3) pond and control-reach pairs had comparable length, gradient, and
channelization status. We avoided road crossings, hydrologic inputs such as field
ditches, and sites in close proximity to CAFOs. At one site (#35), we discovered
a small hydrologic input with a nitrogen-rich discharge after the study began and
Southeastern Naturalist
587
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
eliminated this site from nitrogen analyses. In all cases, the study dam was the first
dam occurring downstream of the control reach.
Site factors
During the study period, dams were typically maintained so that pond-water
levels were at the top of the dam (full) or within centimeters of full. Some of these
Figure 1. (a) Study area on the inner Coastal Plain (ICP) of North Carolina with site locations
numbered. Inset shows approximate location relative to the Piedmont (PM) to the west
and the outer Coastal Plain (OCP) to the east. (b) Sampling locations at a typical study site;
PD = pond downstream, CD = channel downstream, CU = channel upstream.
Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
588
ponds were previously observed to experience summer drawdowns as precipitation
and groundwater inputs were reduced. All study sites had floodplains composed of
loam soils including loam, fine sandy loam, and sandy loam of the Bibb, Johnston,
Muckalee, and Rains complexes (NRCS 2016). We evaluated site pairs for stream
order, drainage-basin area, gradient, pond area, dam height, dam-maintenance condition,
channelization status, CAFO presence in the watershed, and pond age. We
estimated stream order and drainage-basin area upstream from each study dam from
digital US Geological Survey (USGS) topographic maps (1:24,000) in ArcView GIS
v3.2 (ESRI 1999). We recorded dam height as the mean of 3 measurements taken
from the top of the effective dam to the downstream floodplain surface, not as the
height of the dam in the stream channel. We classified dams as unmaintained if we
observed no evidence of upkeep, but they were still intact and impounding water. We
used GPS-derived point data of site perimeters in ArcView to calculate pond-surface
area at dam-full level. Longitudinal floodplain gradient (% slope) was derived from
pond length at dam-full condition and dam height. We calculated an estimate of damfull
pond volume as one half of the product of mean pond length, width, and dam
height. We estimated pond age as the number of years since evidence of ponding was
first detected in annual aerial photography plus 1 year to compensate for tree-canopy
thinning required for ponding to be detected. We determined presence or absence of
CAFOs from aerial photography. We considered sites channelized if we observed
spoil banks from channel excavation.
Water-quality sampling and analysis
We used a paired-study design to compare differences in nutrient and sediment
concentrations between upstream and downstream sampling locations in ponds
and in upstream, free-flowing control reaches. We established 3 sampling locations
within the hydrologically dominant channel at each site pair: pond downstream
(PD) was the compilation of major outflows ~2 m downstream of the study dam,
control downstream (CD) was just upstream of the backwater influence of the pond,
and control upstream (CU) was at a distance upstream from CD similar to the distance
from PD to CD. Renewed dam construction during the study raised water
levels at some sites and required that we move CD slightly upst ream (less than 15 m).
We collected grab samples on 4 to 6 dates per site pair from late October 2002 to
February 2003 while water flowed in streams and over dams. We did not collect samples
during warmer months because of highly intermittent flow. Analysis of USGS
National Water Quality Assessment Program samples taken near these sites from
January 2002 through December 2003 in the Neuse River at Kinston, NC (station #
02089500), showed samples from October 2002 from February 2003 to have a mean
filtered nitrate + nitrite concentration of 505 μg/l compared to 438 μg/l for all 2002–
2003. Filtered samples had a mean SRP concentration of 23 μg/l, compared to 36 μg/l
for all 2002–2003 sampling dates (USGS 2015). These concentrations indicate that
nitrogen concentrations sampled during our study were slightly elevated compared
to the rest of the year, whereas orthophosphate concentrations were seasonally low.
We sampled sites at a range of wadeable water levels to incorporate variation in water
residence times and to better approximate the range of biogeochemical conditions in
Southeastern Naturalist
589
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
stream systems during the study period. We stored our samples on ice before filtering
them in the laboratory within 24 h of collection.
We measured SS concentrations by filtering samples through pre-ashed,
pre-weighed glass microfiber filters (1.5-μm effective-pore size) within 24 h of
collection, drying at 105 °C for 24 h, and reweighing (APHA et al. 1995). Samples
used in determining dissolved inorganic nutrient concentrations were filtered as
above and stored frozen until analysis. We determined soluble reactive phosphorus
with the ascorbic acid method (APHA et al. 1995). We modified Solorzano’s (1969)
phenolhypochlorite method to determine ammonium: sample and reagent volumes
were halved and color developed for at least 2 h before measuring absorbance. We
employed the cadmium-reduction method (APHA et al. 1995) to determine total
oxidized nitrogen (NO3
-+NO2
--N), which we report as nitrate.
Data analysis
We determined reach effects on sediment and nutrient concentrations as differences
between concentrations at downstream (CD) and upstream (CU) locations for
the control reach and, for the pond reach, as differences between concentrations at
CD and locations below the dam (PD):
Control-reach Influence on Concentration = (CD - CU)
Pond-reach Influence on Concentration = (PD - CD).
This paired-sampling structure allowed determination of a single response variable
to estimate the effect of ponds adjusted for their control reaches:
Effect of pond on concentration adjusted for control = (PD - CD) - (CD - CU)
Proportional change (+, -) in concentration = (Effect/CD)(100)
We averaged influences for each water-quality variable by site. We employed
paired t-tests to determine significant differences between influence of control
reaches (CD - CU) and influence of ponds (PD - CD). Relationships between site
factors and the effect of ponds on concentrations as adjusted for their controls
were tested using Pearson’s correlation (r). We log10-transformed SS data to meet
test assumptions of normality. We also log10-transformed pond age to reduce the
undue influence of an outlier (16 y) on relationships. We examined associations
among site characteristics with Pearson’s correlation coefficients or Kendall’s
nonparametric coefficient of concordance (τ), as appropriate for the data distributions.
We employed t-tests (one-tailed, unequal variance) to compare differences
between nutrient concentrations of control streams in watersheds with and without
CAFOs and simple linear regressions to examine relationships between incoming
concentrations and reductions. We conducted all analyses in SPSS v. 11 (SPSS Inc,
Chicago, IL 2001).
Exceptionally high nitrate concentrations prevented inclusion of site 20 in parametric
statistical analyses of nitrate; all other water-quality variables at site 20 were
statistically analyzed. We excluded site 35 from nitrate and ammonium analyses
altogether due to nitrogen-rich discharge from an agricultural tributary that we
Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
590
discovered after the study began and whose influence confounded upstream–downstream
relationships (2–5 times other study reach concentrations).
Results
Site factors
Drainage-basin areas varied from ~1.67 km2 to 40.4 km2 (Table 1). Drainage areas
were inversely correlated to stream gradient, i.e., ponds with smaller drainage
areas had steeper gradients (r = -0.71, P = 0.004), and smaller pond surface-to-volume
ratios (r = 0.61, P = 0.014). Beaver dam height averaged 0.47 m, and 9 dams
(69%) were actively maintained during the study. We were unable to determine the
age of site 43 from aerial photographs and excluded it from age-related comparisons.
The mean pond age of the other ponds was 4.9 years; the single 16-year-old
pond was an outlier. Two sites (20 and 52) were channelized and another site (56)
was just downstream from a channelized reach. CAFOs were present in 42% of
study-site watersheds. Nutrient concentrations did not differ significantly between
streams in watersheds with and without CAFOs (nitrate: t = 1.23, P = 0.12; ammonium:
t = 0.00 P = 0.36; SRP: t = 0.6, P = 0.28).
Nitrate
Mean stream-nitrate concentrations spanned an order of magnitude from 151 μg
N/L at site 28 to 5114 μgN/L at site 20, and were significantly higher in channelized
streams (τ = 0.58, P = 0.009). Beaver ponds conveyed lower concentrations of
nitrate than controls (t = -3.7, P = 0.002, omitting site 35). Mean nitrate concentrations
showed greater reductions through the ponds (141 ± 48 μg N/L), than through
the control reaches (28 ± 17μgN/L; Fig. 2a). The effect of 11 of 12 ponds was to
Table 1. Characteristics of 13 Beaver ponds arranged by drainage-basin area. Dam maint. = whether
the dam was maintained. Chan. = was there channelization. CAFO indicates the presence or absence
of confined animal feeding operations within the watershed of the site (A = abandoned). n = 4–6,
depending on site.
Drainage Pond Dam Pond
Stream area Gradient area height volume Dam
Site order (km2) (%) (ha) (m) (m3) maint. Chan CAFO Age (y)
60 3 1.67 0.44 0.37 0.62 1150 Y N N 2
17 2 3.29 0.19 1.95 0.68 6350 Y N Y 7
35 2 3.94 0.52 0.17 0.42 392 N N Y 6
20 2 4.20 0.41 0.19 0.41 327 Y Y Y 7
52 3 4.54 0.20 0.60 0.28 735 Y Y N 1
32 2 4.71 0.27 1.00 0.93 4100 Y N N 5
50 2 8.47 0.21 1.97 0.55 6220 Y N N 6
56 3 18.67 0.13 0.97 0.27 1020 N N A 2
39 3 19.81 0.12 3.01 0.41 5410 N N Y 2
24 3 24.53 0.10 4.84 0.46 11,300 Y N N 3
36 4 28.93 0.10 3.53 0.46 7030 Y N Y 16
43 4 31.34 0.10 3.00 0.38 4890 Y N Y -
28 4 40.35 0.14 0.56 0.19 475 N N N 2
Southeastern Naturalist
591
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
decrease average concentrations. Reductions varied widely from 3 μgN/L to 753
μgN/L (Fig. 3a). Site 43 was the only pond that exhibited an increasing effect on
nitrate concentrations. High variation within site types may be attributed to small
sample size and inclusion of at least 1 high-discharge sample per site. Ponds that
had smaller drainage areas had higher stream gradients; both of these characteristics
were related to greater reductions in nitrate concentrations (r = -0.75, P = 0.007
and r = 0.72, P = 0.012, respectively; Table 2). Greater concentrations of nitrate
entering control streams correlated to greater reductions by ponds on concentrations
(r = 0.48, P < 0.001).
Figure 2. Distributions of control reach influence (CD–CU) and pond reach influence
(PD–CD) on concentrations of (a) nitrate, (b) ammonium, (c) soluble reactive phosphorus
(SRP), and (d) suspended sediment (SS). Dotted lines are means, solid lines are medians,
the bottom and top of each box are 25th and 75th percentiles, whiskers are the 10th and 90th
percentiles, and solid dots are outliers. Site 20 was omitted from (a) due to exceptionally
high nitrate concentrations.
Table 2. Pearson correlation coefficients between site factors and the effect of impoundments on
water-quality variables adjusted for control reaches. Dam maint. = dam maintenance; chan. = channelization..
*P < 0.05, **P < 0.01 and † indicates data were log 10 transformed
Stream Drainage Surface Dam Damfull Dam
Factor n order area Gradient area height volume maint. Chan. Age†
Nitrate 11 0.43 0.72* -0.75** 0.49 -0.20 0.33 -0.18 -0.33 0.51
Ammonium 12 -0.12 -0.29 0.29 -0.41 -0.16 -0.42 0.41 0.42 -0.12
SRP 13 -0.38 -0.08 0.48 -0.37 -0.10 -0.34 -0.29 0.13 0.10
SS† 13 -0.08 -0.04 -0.29 -0.12 -0.03 -0.06 -0.23 0.13 -0.71**
Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
592
Ammonium
Mean ammonium concentrations spanned an order of magnitude (10.9–209
μg N/L) and were significantly greater in streams associated with channelization
(τ = 0.62, P = 0.006). Beaver ponds conveyed significantly higher concentrations
of ammonium than control reaches (t = 3.007, P = 0.012; n = 12). On average,
Figure 3. Effect of
beaver ponds on
concentrations of
(a) nitrate and ammonium,
(b) soluble
reactive phosphorus
(SRP), and (c) suspended
sediment
(SS) as adjusted for
their free-flowing
control reaches, by
site. Bars are mean
(+ 1 SE). Sites arranged
by increasing
drainage area
from left to right.
Data were omitted
for site 35 in (a) as
explained in Methods.
Southeastern Naturalist
593
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
ammonium concentrations increased through the ponds (7.97 ± 11.7 μgN/L) and
decreased through the control reaches (1.49 ± 1.37 μgN/L; Fig. 2b). The effect of 9
of 12 ponds was to convey higher concentrations of ammonium (Fig. 3a). We found
no significant relationships between site factors and the effect of ponds (Table 2).
Higher concentrations of ammonium entering control streams was weakly correlated
to a greater effect of ponds on concentrations ( r = 0.28, P = 0.03).
Soluble reactive phosphorus
The variation of mean SRP concentrations in streams (3.0–46 μg P/L) was narrower
than for ammonium or nitrate, and the effect of ponds on SRP concentration
was not significant (t = -0.31, P = 0.76; n = 13). Ponds and control reaches exhibited
similar influences (1.15 μg P/L vs -0.82 μg P/L; Fig. 2c). Nine of 13 ponds had a
reducing effect on SRP concentrations, but about half of the sample-set differences
in concentrations fluctuated around zero (Fig. 3b). No significant relationships were
found between site factors and effect (Table 2). Higher concentrations of SRP entering
control streams correlated with greater pond effects on outgoing concentrations
(R2 = 0.68, P < 0.001).
Suspended sediment
The variation of mean SS concentrations entering ponds was over an order of
magnitude (1.3–19 mg/L). Ponds were better at trapping SS than the control reaches
(log10 transformed data, t = -4.75, P < 0.001; n = 13). Beaver ponds reduced SS
concentrations by 2.84 ± 1.48 mg/L. The control reaches acted as a source of sediment
(0.56 ± 0.27 mg/L; Fig. 2d). Eleven of 13 ponds had an effect of decreasing SS
concentrations, but 3 sites fluctuated around 0 (mg/L) difference. Mean reductions
ranged from 0.1 mg/L to 15 mg/L (Fig. 3c). The effect of ponds on SS concentrations
showed a significant negative relationship with pond age (log10 transformed
data: r = -0.71, P = 0.009; Table 2). The relationship between concentrations of
SS entering the control reach with the effect of the ponds was strong (r = 0.99, P less than
0.001) with high SS concentrations resulting in greater sedimen t trapping.
Discussion
The study was comprised of paired, adjacent reaches with and without effects
of beaver ponds to control for variation due to factors other than pond effect. This
restriction made it difficult to locate site pairs that lacked confounding hydrologic
inputs. After the study began, we discovered that 1 site (35) had a nitrogen-rich
input; thus, we eliminated it from nitrogen analyses. We could have employed a
mass-balance approach that measured all flows and nutrient loadings of a single
pond to overcome this problem, but that would not have met our study objectives.
Our objectives were to explore the variation in effects of beaver ponds on water
quality among a range of ponds and to examine the potential influence of factors,
such as watershed size and stream channelization, on those effects (Table 1). We
undertook fall and winter sampling because we assumed that stream-water nutrient
and suspended solids concentrations would be higher due to reduced vegetative and
Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
594
microbial assimilation and entrapment. In addition, extended lapses in flow from
Beaver impoundments due to high rates of evapotranspiration precluded sampling
from many sites during summer.
We observed high variability in water-quality parameter concentrations among
the sites. Ponds conveyed significantly lower nitrate concentrations (-19%) and significantly
higher ammonium concentrations (59%) relative to free-flowing stream
reaches (Fig. 2). A number of nitrogen transformations within beaver ponds may
be responsible for the effects we observed. Denitrification has been suggested as
the primary means of nitrogen removal for many riverine and riparian wetlands
(Brinson et al. 1984, Ettema et al. 1999, Klotz 2010, Willems et al. 1997), and was
likely responsible for the majority of nitrate concentration decreases in this study,
although we did not measure this directly. Beaver ponds provide excellent conditions
for denitrification because of the extended duration of water contact with pond
sediments rich in organic matter and the elevated nitrate concentrations of agriculturally
influenced stream flows entering ponds. In a study of 3 Rhode Island beaver
ponds, Lazar et al. (2015) found that denitrification dominated nitrogen transformations
and was negatively correlated with the dissolved-oxygen saturation of pond
water. Rates of assimilation of nitrogen into the organic nitrogen pool of these
ponds were lower than denitrification followed by rates of ammonium generation;
neither rate correlated with pond characteristics.
The variation in nitrate is of primary concern for water quality within beaver
ponds. Increases in ammonium concentrations below ponds may have been due to
the liberation of ammonium from anoxic pond sediments, mineralization, or from
dissimilatory nitrate reduction to ammonium. The fact that we did not measure oxygen
levels in the pond sediments limits our ability to speculate on the importance
of these potential transformations. We found that 2 sites conveyed exceptional
concentrations of nitrate or ammonium. Pond 43 conveyed nitrate concentrations
9.3% higher than its control reach, and samples from site 52 showed remarkably
high ammonium concentrations on several sampling dates. It is not clear why these
sites had elevated concentrations of nitrogen relative to other sites, and we could
not determine a specific source. It is possible that CAFOs or undetected conveyances
of nitrogen-rich water such as points of focused groundwater discharge in
the watershed of site 43 could have contributed, although this condition was not
observed in all other sites with CAFOs in the watershed.
The scale of the study did not allow determination of hydrographs for the sites or
how the effects of ponds on water quality varied between rising and falling stream
stage. Although we sampled each site at least once during elevated flow, we did not
determine if flow was rising or falling, which could influence nutrient and sediment
concentrations in streams (Lowrance and Leonard 1988, McDiffet et al. 1989). It
is notable that the collective ponds in this study reduced SRP concentrations and
SS concentrations to a greater degree at the highest flows compared to the lowest
flows (Wilcoxon signed-rank test: n = 13; SRP: z = -2.27, P = 0.023; SS: z = -1.85,
P = 0.064).
There was no significant effect on SRP concentrations in this study, and
only 3 site-pairs demonstrated a notable effect on concentrations: 2 site-pairs
Southeastern Naturalist
595
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
reduced concentrations and 1 increased concentrations (Fig. 3b). Other studies
have found inconsistent effects of beaver ponds on phosphorus with some ponds
augmenting and others reducing concentrations of SRP (Correll et al. 2000, Devito
and Dillon 1993, Klotz 1998, Maret et al. 1987). Higher SRP concentrations
discharged from ponds in New York were related to anoxic conditions during periods
of ice cover, a relatively rare phenomenon in the southeastern Coastal Plain
(C.W. Bason, pers. observ.).
Beaver ponds in this study acted as sediment traps, decreasing concentrations
of SS in waters entering ponds by 40% (3.41 mg/L) relative to the control-reach
influence (Fig. 2). The mechanism by which this decrease is accomplished is the
reduction in the velocity of water entering ponds. Beaver ponds in Maryland, Virginia,
North Carolina, and Wyoming caused decreases in stream SS concentrations
for at least part of the year (Correll et al. 2000, Kroes and Bason 2015, Maret et al.
1987). The Maryland stream conveyed total SS concentrations of 67.6 mg/L prior
to creation of a beaver pond and 49.3 mg/L after construction (Correll et al. 2000).
Decreases in SS concentrations in Virginia and North Carolina ponds varied from
-1.5 mg/L to -17 mg/L (Kroes and Bason 2015). Despite the regional differences
in sediment characteristics and concentrations, the SS proportional concentration
reductions were similar between these studies.
During high flows, deposition of sediment-associated nutrients in beaver ponds
could be an important mechanism for reducing total nutrient concentrations, as suggested
by Maret et al. (1987). Likewise, Correll et al. (2000) suggested that organic
phosphorus and organic nitrogen concentrations were reduced via sediment deposition.
Relative to larger ponds, the faster water-transit times in small ponds may
act to decrease total SS concentration by deposition of sands and coarse silts while
simultaneously increasing suspended fine silt and clay concentrations via bioturbation.
Interestingly, the 3 ponds exhibiting increases in SRP in our study (sites 20,
28, and 35) also had the smallest pond volumes and likely had higher bioturbation
by volume. Although we did not determine particle sizes of incoming and outgoing
SS, bioturbation of very fine sediment could have resulted in increases of SRP
because phosphorus is disproportionately adsorbed to clay.
Concentrations of SRP released from beaver ponds can also be influenced by the
differences in phosphorus concentrations between pond sediments and the overlying
water column (Klotz 1998). Sediments either act as sources or sinks of P to
the water column depending on the concentration gradient at the sediment–water
interface. We did not calculate sorption capacity in this study, but assumed that
pond sediments had higher sorption capacity than free flowing reaches due to their
finer grain size. Reductions in SRP concentrations attributable to ponds in this study
tended to be largest during the highest stream-flows and when SRP concentrations
upstream of the pond were high. This result suggests that the pond sediments had
high sorption capacity to reduce the elevated in solution P entering the ponds.
Sorbed P would likely be released during subsequent periods of low flow when we
would expect incoming SRP concentrations to be lower and pond sediments to be
in a more reduced state.
Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
596
Channel gradient and drainage area were the most influential site characteristics
on the reduction of nitrate concentrations in ponds. Both upstream position and
steeper gradients co-occur with higher nitrate concentrations because lower-order
streams on the NC Coastal Plain are surrounded by, and are in closer proximity to,
agricultural lands (Spruill et al. 1998). Where nitrate concentrations are higher, the
potential for greater removal of nitrogen via denitrification is also higher (Hanson
et al. 1994, Spieles and Mitsch 2000, Willems et al. 1997). Increasing drainage area
can also decrease water-retention time, reducing the capacity of wetlands to improve
water quality (Woltemade 2000). Estimates of retention time for a subset of
this study’s ponds indicated that sites with small drainage areas had average waterresidence
times over 4-fold longer than sites with large drainage areas. Our results
suggest that, like the smaller streams on which they are created (see Peterson et al.
2001), beaver ponds on smaller streams play a greater role in controlling nitrogen
concentrations in waters travelling to downstream estuaries.
Stream channelization alters biogeochemical functions by increasing and
sustaining groundwater-derived baseflow and decoupling channels from their
floodplain wetlands (Yarbro et al. 1984). Relative to an unchannelized stream, a
channelized stream typically has less heterogeneity that results from straightening
and removal of snags, low levels of particulate carbon in bed sediments, and shorter
hydraulic retention time. The net effect is lower retention of nitrate, total organic
nitrogen, particulate phosphorus, and sediments (Noe and Hupp 2005, Yarbro et al.
1984). Two of 3 channelized sites in this study (sites 20 and 56) were also located in
close proximity to active or abandoned CAFOs. Higher nitrate concentrations entering
our pond sites were not reduced to a greater degree than in ponds with lower
incoming concentrations. However, the greatest single reduction in nitrate occurred
with high incoming concentrations at 1 site. Beaver were found to hydraulically
reconnect floodplain wetlands with channelized streams in sites of this study and
those of Kroes and Bason (2015). In this study, recoupling of these floodplains in
the presence of a beaver pond had the ef fect of reducing nitrate concentrations.
Older ponds in this study reduced suspended sediment (SS) concentrations to
a greater degree than younger ponds. As ponds age, trees of floodplain forests die,
large, downed wood accumulates, and closed tree-canopies are replaced by dense
herbaceous vegetation. These structural changes reduce water velocities and create
complex microtopography in channels and on pond bottoms, thus facilitating
sedimentation in streams and floodplains (Harmon et al. 1986, Sand-Jensen 1998).
The process of sediment deposition changes and may be reduced as old ponds fill in
with sediments (Kroes and Bason 2015). However, we did not observe this change
in our study area perhaps due to generally low SS concentrations of Coastal Plain
streams and the recolonizing Beaver population. The lack of a significant relationship
between pond age and effects on nitrate suggests that the mere presence of a
beaver pond was important for nitrate reductions.
Inferences about the effects of pond age on study variables must be made in
context with the recolonizing population dynamics of Beaver in this region. Our
study design required free-flowing reaches upstream of ponds; thus, site selection
Southeastern Naturalist
597
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
was biased towards the most upstream point of Beaver recolonization within a
stream corridor, and consequently, younger ponds. Our results capture conditions
at 1 point in time during what is expected to be a cycle of colonization and recolonization
of Beaver populations as they respond to resource availability and
geomorphology over years to centuries (Johnston 2015, Johnston and Naiman
1990). The effects of Beaver on water quality may change dynamically over space
and time as populations and ponds age and are vacated due to declining resources
and trapping. However, it seems important that studies over time and regions
of North America have reported reductions in nitrate and sediment concentrations
due to beaver ponds. In more-developed landscapes such as the agricultural
coastal plain, human control of Beaver populations is likely to have a greater influence
on the water-quality effects of Beaver than the less-developed areas where
research on population dynamics has previously focused.
In addition to improving water quality, beaver ponds also diversify plant and
animal communities (Bason 2004, Feldmann 1995, Metts et al. 2001, Snodgrass
and Meffe 1998), provide valuable habitat (Menzel et al. 2000, Otis and Edwards
1999), and offer renewable harvest of Beaver and waterfowl (Hair et al. 1978).
In contrast to these ecological services, they create economic losses by flooding
timber, pastures, roads, and agricultural fields, and can facilitate invasive species
establishment (Perkins and Wilson 2005). Beaver populations are often managed
in response to individual nuisance complaints, and in some instances, are excluded
from potential habitat entirely. This form of control can reinforce the concept of
Beaver as problem animals (Halley and Rosell 2002) instead of as a keystone species
and ecosystem engineers in lotic ecosystems and riparian areas. Trade-offs
between ecosystem services and negative economic impacts should be considered
when managing Beaver populations. However, our results suggest that best management
of Beaver populations may be an option deserving of more consideration
as a water-quality improvement measure.
Conclusions
Our results indicate that beaver ponds may ameliorate some agricultural effects
on water quality of rural Coastal Plain streams by reducing nitrate concentrations
(19%) and sediment concentrations (40%). Ponds on lower-order streams reduced
nitrate concentrations by greater amounts. Older ponds reduced sediment concentrations
by greater amounts. In order to utilize the water-quality effects of beaver
ponds, resource agencies and landowners could consider (1) allowing expansion
of Beaver populations into impaired waters and, where appropriate, headwater
streams, (2) measured control of newly established populations to prevent rapid
population growth that can result in negative attitudes towards Beaver, (3) costshare
programs for trapping and water-level management structures and, 4) where
Beaver must be removed, leaving unmaintained dams to improve wa ter quality.
Nutrient runoff models like SPARROW (USGS 2016) could aid in identification
of watersheds that would most benefit from greater abundance of beaver ponds. The
basin-wide effects of beaver ponds have not been evaluated at a scale appropriate
Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
598
for quantifying a reduction in nutrient loading on estuarine water quality. However,
our conservative estimate that over ¼ of the 2nd- to 5th-order stream length within
the study area was impounded by Beaver suggests that non-point-source nitrogen
and sediment loading to North Carolina’s eutrophic and typically nitrogen-limited
estuaries was lower due to the presence of beaver ponds.
Acknowledgments
Unfortunately, Mark Brinson passed away prior to finalization of this paper. Wherever
he may be, we wish him the best. His friendship and guidance were essential to accomplishing
this research. We thank Chantal Bouchard, Bob Christian, Dennis Whigham,
Paul Vos, and David Beamer for their support, guidance, and field assistance. Although
research described in this article has been funded in part by the US Environmental Protection
Agency through cooperative agreement R-82868401 via a contract to East Carolina
University from Pennsylvania State University, it has not been subjected to the Agency’s
required peer and policy review, and therefore, does not necessarily reflect the views of
the Agency; no official endorsement should be inferred. Any use of trade, product, or firm
names in this publication is for descriptive purposes only and does not imply endorsement
by the US Government.
Literature Cited
American Public Health Association (APHA), American Water Works Association, and
Water Environment Federation. 1995. Standard methods for the examination of water
and wastewater. Washington, DC. 1100 pp.
Arner, D.H., and G.R. Hepp. 1989. Beaver pond wetlands: A southern perspective. Pp.
117–128, In L.M. Smith, R.L. Pederson, and R.M. Kaminski (Eds.). Habitat Management
for Migrating and Wintering Waterfowl in North America. Texas Tech University
Press Lubbock, TX. 574 pp.
Bason, C.W. 2004. Effects of beaver impoundments on stream-water quality and floodplain
vegetation in the inner coastal plain of North Carolina. M.Sc. Thesis. East Carolina
University, Greenville, NC. 147 pp.
Bricker, S., B. Longstaff, W. Dennison, A. Jones, K. Boicourt, C. Wicks, and J. Woerner.
2007. Effects of Nutrient Enrichment in the Nation’s Estuaries: A Decade of Change.
National Centers for Coastal Ocean Science, Silver Spring, MD. 32 pp.
Brinson, M.M., H.D. Bradshaw, and E.S. Kane. 1984. Nutrient assimilative capacity of an
alluvial floodplain swamp. Journal of Applied Ecology 21:1041–1057.
Butler, D.R. 1991. The reintroduction of the Beaver to the South. Southeastern Geographer
31:39–43.
Carpenter, S.R., N.F. Caraco, D.L. Correll, R.W. Howarth, A.N. Sharpley, and V.H. Smith.
1998. Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecological
Applications 8:559–569.
Cashin, G.E., J.R. Dorney, and C.J. Richardson. 1992. Wetland alteration trends on the
North Carolina Coastal Plain. Wetlands 12:63–71.
Cirmo, C.P., and C.T. Driscoll. 1993. Beaver pond biogeochemistry: Acid-neutralizing
capacity-generation in a headwater wetland. Wetlands 13:277–292.
Coffey, A. 1982. Stream improvement: The Chicod Creek episode. Journal of Soil and
Water Conservation 37:80–82.
Southeastern Naturalist
599
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
Correll, D.L. 1997. Buffer zones and water-quality protection: General principles. Pp. 7–20,
In N. Haycock, T. Burt, K. Goulding, and G. Pinay (Eds.). Buffer Zones: Their Processes
and Potential in Water Protection. The Proceedings of the International Conference on
Buffer Zones, September 1996. Quest Environmental Harpenden, Hertfordshire, UK.
326 pp.
Correll, D.L., T.E. Jordan, and D.E. Weller. 1992. Nutrient flux in a landscape: Effects of
coastal land- use and terrestrial community mosaic on nutrient transport to coastal waters.
Estuaries 15:431–442.
Correll, D.L., T.E. Jordan, and D.E. Weller. 2000. Beaver-pond biogeochemical effects in
the Maryland Coastal Plain. Biogeochemistry 49:217–239.
Devito, K.J., and P.J. Dillon. 1993. Importance of runoff and winter anoxia to the P and
N dynamics of a beaver pond. Canadian Journal of Fisheries and Aquatic Sciences
50:2222–2232.
Devito, K.J., P.J. Dillon, and B.D. Lazerte. 1989. Phosphorus and nitrogen retention in 5
Precambrian-shield wetlands. Biogeochemistry 8:185–204.
Duda, A.M. 1982. Municipal point-source and agricultural non-point–source contributions
to coastal eutrophication. Water Resources Bulletin 18:397–407.
Environmental Systems research Institute (ESRI) 1999. ArcView GIS v3.2. Redlands, CA.
Ettema, C.H., R. Lowrance, and D.C. Coleman. 1999. Riparian-soil response to surface
nitrogen input: Temporal changes in denitrification, labile and microbial C and N pools,
and bacterial and fungal respiration. Soil Biology and Biochemi stry 31:1609–1624.
Feldmann, A. 1995. The effects of Beaver (Castor canadensis) impoundment on plant
diversity and community composition in the Coastal Plain of South Carolina. M.Sc.
Thesis. University of Georgia, Athens, GA.
Glasgow, H.B., Jr., and J.M. Burkholder. 2000. Water-quality trends and management
implications from a 5-year study of a eutrophic estuary. Ecological Applications
10:1024–1046.
Hair, J.D., G.T. Hepp, L.M. Luckett, K.P. Reese, and D.K. Woodward. 1978. Beaver pond
ecosystems and their relationships to multi-use natural resource management. Pp.
80–92, In R.R. Johnson, and J.F. McCormick (Eds.). Strategy for Protection and Management
of Floodplain Wetlands and Other Riparian Ecosystems. US Forest Service,
General Technical Report. WO-12. 217 pp. Washington, DC.
Halley, D.J., and F. Rosell. 2002. The Beaver’s reconquest of Eurasia: Status, population
development, and management of a conservation success. Mammal Review 32:153–178.
Hammond, E.H. 1964. Classes of land-surface form in the 48 states, USA. Annals of the
Association of American Geographers 54(1):map supplement.
Hanson, G.C., P.M. Groffman, and A.J. Gold. 1994. Denitrification in riparian wetlands
receiving high and low groundwater nitrate inputs. Journal of Environmental Quality
23:917–922.
Harmon, M.E., J.F. Franklin, F.J. Swanson, P. Sollins, S.V. Gregory, J.D. Lattin, N.H. Anderson,
S.P. Cline, N.G. Aumen, J.R. Sedell, G.W. Lienkaemper, K. Cromack, and K.W.
Cummins. 1986. Ecology of coarse woody debris in temperate ecosystems. Advances in
Ecological Research 15:133–302.
Harned, D.A., and M.S. Davenport. 1990. Water-quality trends and basin activities and
characteristics for the Albemarle–Pamlico estuarine system, North Carolina and Virginia.
US Geological Survey Open-File Report 90-398. Reston, VA. 164 pp.
Harned, D.A., G. McMahon, T.B. Spruill, and M.D. Woodside. 1995. Water-quality assessment
of the Albemarle–Pamlico Drainage Basin, North Carolina and Virginia: Characterization
of suspended sediment, nutrients, and pesticides. US Geological Survey
Open-File Report 95-191. Reston, VA. 131 pp.
Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
600
Johnston, C.A. 2015. Fate of 150-year-old Beaver ponds in the Laurentian Great Lakes
Region. Wetlands 35:1013–1019.
Johnston, C.A., and R.J. Naiman. 1990. Aquatic-patch creation in relation to Beaver population
trends. Ecology 71:1617–1621.
Jordan, T.E., D.L. Correll, and D.E. Weller. 1997. Effects of agriculture on discharges of
nutrients from coastal plain watersheds of Chesapeake Bay. Journal of Environmental
Quality 26:836–848.
Klotz, R.L. 1998. Influence of Beaver ponds on the phosphorus concentration of stream
water. Canadian Journal of Fisheries and Aquatic Sciences 55:1228–1235.
Klotz, R.L. 2010. Reduction of high nitrate concentrations in a central New York state
stream impounded by Beaver. Northeastern Naturalist 17:349–356.
Kroes, D.E., and C.W. Bason. 2015. Sediment-trapping by Beaver ponds in streams of the
Mid-Atlantic Piedmont and Coastal Plain, USA. Southeastern Natu ralist 14:577–595.
Lazar, J.G., K. Addy, A.J. Gold, P.M. Groffman, R.A. McKinney, and D.Q. Kellogg. 2015.
Beaver ponds: Resurgent nitrogen sinks for rural watersheds in the northeastern United
States. Journal of Environmental Quality 44(5):1684–93.
Lowrance, R., and R. A. Leonard. 1988. Streamflow-nutrient dynamics on Coastal Plain
watersheds. Journal of Environmental Quality 17:734–740.
Mallin, M.A., H.W. Paerl, J. Rudek, and P.W. Bates. 1993. Regulation of estuarine primary-
production by watershed rainfall and river flow. Marine Ecology Progress Series
93:199–203.
Mallin, M.R., J.M. Burkholder, M.R. McIver, G.C. Shank, H.B. Glasgow Jr., B.W. Touchette,
and J. Springer. 1997. Comparative effects of poultry- and swine-waste lagoon
spills on the quality of receiving streamwaters. Journal of Environmental Quality
26:1622–1631.
Maret, T.J., M. Parker, and T.E. Fannin. 1987. The effect of Beaver ponds on the nonpointsource
water-quality of a stream in southwestern Wyoming. Water Research 21:263–268.
Margolis, B.E., M.S. Castro, and R.L. Raesly. 2001. The impact of Beaver impoundments
on the water chemistry of 2 Appalachian streams. Canadian Journal of Fisheries and
Aquatic Sciences 58:2271–2283.
McDiffet, W.F., A.W. Beidler, T.F. Dominick, and K.D. McCrea. 1989. Nutrient concentration–
stream-discharge relationships during storm events in a 1st-order stream. Hydrobiologia
179:97–102.
Menzel, M.A., C.T. Carter, W.M. Ford, and B.R. Chapman. 2000. Tree-roost characteristics
of subadult and female adult Evening Bats (Nycticeius humeralis) in the upper Coastal
Plain of South Carolina. American Midland Naturalist 145:112–119.
Metts, B.S., J.D. Lanham, and K.R. Russell. 2001. Evaluation of herpetofaunal communities
on upland streams and Beaver-impounded streams in the upper piedmont of South
Carolina. American Midland Naturalist 145:54–65.
Naiman, R.J., C.A. Johnston, and J.C. Kelly. 1988. Alteration of North American streams
by Beaver. Bioscience 38:753–762.
Natural Resource Conservation Service (NRCS). 2016. Web soil survey. Available online at:
http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx. Accessed 14 October 2016.
National Oceanic and Atmospheric Administration (NOAA). 2017a. Climate at a glance—
US time series: Precipitation. National Centers for Environmental Information. Available
online at: http://www.ncdc.noaa.gov/cag/. Accessed 7 February 2017.
NOAA. 2017b. Climate at a glance—US time series: Aveage temperature. National Centers
for Environmental Information. . Available online at: http://www.ncdc.noaa.gov/cag/.
Accessed 7 February 2017.
Southeastern Naturalist
601
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
Noe, G.B., and C.R. Hupp. 2005. Carbon, nitrogen, and phosphorus accumulations in floodplains
of Atlantic Coastal Plain rivers, USA. Ecological Applications 15:1178–1190.
Omernik, J.M. 1976. The influence of land use on stream-nutrient levels. Ecological research
series. US Environmental Protection Agency, Office of Research, Corvallis, OR.
106 pp.
Osmond, D.L., J.W. Gilliam, and R.O. Evans. 2002. Riparian buffers and controlled drainage
to reduce agricultural nonpoint-source pollution. North Carolina State University,
Raleigh, NC. 57 pp.
Otis, D.L., and N.T. Edwards. 1999. Avian communities and habitat relationships in South
Carolina Piedmont Beaver ponds. The American Midland Naturalist 141(1):158–171.
Paerl, H.W. 1995. Coastal eutrophication in relation to atmospheric nitrogen deposition:
Current perspectives. Ophelia 41:237–259.
Perkins, T.E., and M.V. Wilson. 2005. The impacts of Phalaris arundinacea (Reed Canarygrass)
invasion on wetland-plant richness in the Oregon Coast Range, USA depend
on Beavers. Biological Conservation 124:291–295.
Peterson, B.J., W.M. Wollheim, P.J. Mulholland, J.R. Webster, J.L. Meyer, J.L. Tank, E.
Marti, W.B. Bowden, H.M. Valett, A.E. Hershey, W.H. McDowell, W.K. Dodds, S.K.
Hamilton, S. Gregory, and D.D. Morrall. 2001. Control of nitrogen export from watersheds
by headwater streams. Science 292:86–90.
Pullen, T.M. 1971. Some effects of Beaver, Castor canadensis, and beaver-pond management
on the ecology and utilization of fish populations along warm-water streams in
Georgia and South Carolina. Ph.D. Dissertation. University of Georgia, Athens, GA.
84 pp.
Rheinhardt, R.D., M.C. Rheinhardt, M.M. Brinson, and K.E. Faser Jr. 1999. Application of
reference data for assessing and restoring headwater ecosystems. Restoration Ecology
7:241–251.
Sand-Jensen, K. 1998. Influence of submerged macrophytes in lowland streams. Freshwater
Biology 39:663–679.
Shafale, M.P., and A.S. Weakley. 1990. Classification of the natural communities of North
Carolina. 3rd approximation. North Carolina Natural Heritage Program, Division of
Parks and Recreation, NC Department of Environmental Health and Natural Resources,
Raleigh, NC. 325 pp.
Smock, L.A., and E. Gilinsky. 1992. Coastal-plain blackwater streams. Pp. 271–313, In
C.T. Hackney, M. Adams, and W. Martin (Eds.). Biodiversity of the Southeastern United
States. John Wiley and Sons, Inc. New York, NY. 779 pp.
Snodgrass, J.W., and G.W. Meffe. 1998. Influence of Beavers on stream-fish assemblages:
Effects of pond age and watershed position. Ecology 79:928–942.
Solorzano, L. 1969. Determination of ammonia in natural waters by the phenolhypocholrite
method. Limnology and Oceanography 14:799–801.
Spieles, D.J., and W.J. Mitsch. 2000. The effects of season and hydrologic and chemical
loading on nitrate retention in constructed wetlands: A comparison of low- and highnutrient
riverine systems. Ecological Engineering 14:77–91.
Spruill, T.B., D.A. Harned, P.M. Ruhl, J.L. Eimers, G. McMahon, K.E. Smith, D.R. Galeone,
and M.D. Woodside. 1998. Water-quality assessment of the Albemarle–Pamlico
drainage basin, North Carolina, and Virginia, 1992–95. United States Geological Survey,
Circular 1157, Raleigh, NC. 36 pp.
Strahler, A.N. 1957. Quantitative analysis of watershed geomorphology. American Geophysical
Union Transactions 38:913–920.
Southeastern Naturalist
C.W. Bason, D.E. Kroes, and M.M. Brinson
2017 Vol. 16, No. 4
602
Sweet, W.V., and J.W. Geratz. 2003. Bankfull hydraulic geometry relationships and recurrence
intervals for North Carolina’s Coastal Plain. Journal of the American Water Resources
Association 39:861–871.
Thomas, D.L., C.D. Perry, R.O. Evans, F.T. Izuno, K.C. Stone, and J. Wendell Gilliam.
1995. Agricultural drainage effects on water quality in southeastern US. Journal of Irrigation
and Drainage Engineering 121:277–282.
US Climate Data. 2013. Average annual temperature and precipitation. Available online at
http://www.usclimatedata.com/climate.php?location=USNC0281. Accessed 20 November
2013.
US Environmental Protection Agency (USEPA). 2002. 2000 National water-quality inventory.
Office of Water, Washington, DC. 207 pp.
US Geological Survey (USGS). 2015. Water-quality samples for the nation, USGS
02089500 Neuse River at Kinston, NC. Available online at http://nwis.waterdata.usgs.
gov/usa/nwis/qwdata. Accessed 27 August 2015.
USGS. 2016. SPARROW surface water-quality modeling. Available online at http://water.
usgs.gov/nawqa/sparrow/. Accessed 18 May 2016.
Willems, H.P.L., M.D. Rotelli, D.F. Berry, E.P. Smith, R.B. Reneau Jr., and S. Mostaghim.
1997. Nitrate removal in riparian wetland soils: Effects of flow rate, temperature, nitrate
concentration, and soil depth. Water Research 31:841–849.
Woltemade, C.J. 2000. Ability of restored wetlands to reduce nitrogen and phosphorus
concentrations in agricultural drainage water. Journal of Soil and Water Conservation
55:303–308.
Woodward, D.K., and R.B. Hazel. 1991. Beavers in North Carolina: Ecology, utilization,
and management. North Carolina Cooperative Extension Service, R aleigh, NC. 20 pp.
Woodward, D.K., R.B. Hazel, and B.P. Gaffney. 1985. Economic and environmental impacts
of Beavers in North Carolina. Pp. 89–96, In P.T. Bromley (Ed.). Proceedings of the
2nd eastern wildlife-damage control conference. Raleigh, NC. 281 pp .
Yarbro, L.A., E.J. Kuenzler, P.J. Mulholland, and R.P. Sniffen. 1984. Effects of stream
channelization on exports of nitrogen and phosphorus from North Carolina Coastal Plain
watersheds. Environmental Management 8:151–160.