Effects of Riparian Forestation on Water Quality in Urban Streams
Aana Taylor-Smith, UNCW Honors Student
Supervisor: Brian S. Arbogast, PhD.
UNCW Department of Biology and Marine Biology
Abstract
Several water quality parameters were tested to investigate the possible
correlation between riparian vegetation and water quality in urban streams. Water
temperature, conductivity, total dissolved solids (TDS), pH, dissolved oxygen (DO),
dissolved oxygen saturation, turbidity, and biological oxygen demand (BOD) were
monitored in deforested, reforested, and forested streams. A descriptive statistics
analysis was run on the water quality data and averages were compared between
stream types. Data were analyzed via MANOVA to determine whether change in
forestation influenced parameters. DO and BOD varied significantly with stream
type. Analyses of variance were also performed and compared between stream
types. Variance in temperature difference, turbidity, and water temperature
decreased with increased forestation when outliers in data were included, but
when outliers were removed, variance in temperature difference was not
significantly correlated with stream type. For both sets of data, variance in
conductivity increased significantly when forestation increased. Riparian vegetation
may not directly determine all parameters of water quality, but it may play a role in
stabilizing stream ecosystems by reducing fluctuation.
Objectives
The primary goal of this study was to investigate the correlation between degree of
riparian vegetation and water quality in urban streams through
• Descriptive statistics (mean, range, etc.) of water quality parameters
• MANOVA analysis for relatedness between parameters and forestation
• Variance within parameters
Another goal was to determine the usefulness of stream reforestation programs by
establishing a link between reforestation and improved water quality.
Study Area
The study was carried out in 12 streams across Greensboro, NC. Streams were
divided into 3 categories: deforested, reforested, and forested, according to the
level of riparian vegetation. The locations of those streams can be seen in Fig. 1.
Figs. 2-4 show examples of each stream type.
Fig. 2. Latham Park, a typical deforested stream
Friendship
Church Rd.
Summit Ave.
Cone Blvd.
Old Oak
Ridge Rd.
White St.
Latham Park
Arboretum
Lake Daniel
Lindley Park
Randleman Rd.
South ElmEugene St.
Fig. 1. Map showing locations of sampling sites in Greensboro, NC
Fig. 4. Friendship Church Rd., a typical forested stream
Methods
Results and Conclusions
Conductivity, DO, DO percent saturation, pH, temperature, and TDS were
measured in situ using a YSI 600QS multiprobe with a YSI 650MDS
datalogger. Turbidity was measured using a Hach 2100p turbidimeter. For
BOD, 300 mL glass BOD bottles were filled to the top to minimize trapped
air bubbles in the sample. Bottles were then stoppered with glass
stoppers, and kept in the dark at approximately 20-21oC for a period of
five days. At the end of the five day period, the DO in each sample was
tested with the YSI multiprobe and recorded. Final DO value was
subtracted from the original DO value obtained during in situ testing to
determine BOD. Each parameter was measured twice and averaged to
obtain a final value. This was performed to minimize error.
•
•
The YSI multiprobe was calibrated before and after each water quality
testing event, a total of twice per week, according to YSI standards. The
sonde was frequently washed with deionized water and kept in a moist
cup. The Hach 2100p turbidimeter was calibrated once per month, as it
requires less maintenance than the YSI multiprobe. After BOD was
obtained, bottles were washed with soap, then bathed with a 10% nitric
acid solution and thoroughly rinsed with deionized water.
Data were analyzed via descriptive statistics in Microsoft Excel, as well as
the MANOVA function in JMP 7.
Deforested
Muirfield
Fig. 3. Lake Daniel, a typical reforested stream
H2O Temp. Temp.
Cond.
TDS
pH
o
o
( C)
Diff. ( C) (µS/cm) (g/L)
Mean
24.37
3.02
0.179 0.117 7.57
Range
11.10
13.32
0.260 0.169 2.12
Minimum
19.63
-1.06
0.067 0.043 6.89
Maximum
30.73
12.26
0.327 0.212 9.01
Reforested
H2O Temp. Temp.
Cond.
TDS
pH
(oC)
Diff. (oC) (µS/cm) (g/L)
Mean
23.34
3.84
0.214 0.139 7.53
Range
11.65
9.61
0.243 0.158 1.42
Minimum
17.26
-1.46
0.083 0.054 6.90
Maximum
28.91
8.15
0.326 0.212 8.32
Forested
H2O Temp. Temp.
Cond.
TDS
pH
o
o
( C)
Diff. ( C) (µS/cm) (g/L)
Mean
23.82
3.65
0.177 0.115 7.55
Range
9.84
10.90
0.242 0.158 2.13
Minimum
17.62
-0.62
0.065 0.042 6.58
Maximum
27.46
10.28
0.307 0.200 8.71
DO
(mg/L)
9.92
11.77
6.96
18.73
DO Sat.
(%)
119.4
152.0
85.45
237.45
Turb.
(NTU)
11.52
76.53
2.23
78.75
BOD
(mg/L)
1.23
4.50
0.13
4.63
DO
(mg/L)
9.21
5.25
6.29
11.54
DO Sat.
(%)
108.7
71.6
73.0
144.6
Turb.
(NTU)
11.08
55.25
2.10
57.35
BOD
(mg/L)
0.71
2.03
0.10
2.13
DO
(mg/L)
9.03
9.70
5.59
15.29
DO Sat.
(%)
107.4
104.9
68.3
173.1
Turb.
(NTU)
7.17
35.88
1.62
37.50
BOD
(mg/L)
0.57
2.09
0.04
2.13
Fig. 5. Mean, range, minimum, and maximum for water quality data
Test
H2O Temp. (oC) F Test
Temp. Diff. (oC) F Test
Cond. (µS/cm) F Test
DO (mg/L)
F Test
Turb. (NTU) F Test
BOD (mg/L) F Test
Value
0.0068541
0.0115926
0.0001658
0.0401019
0.0207139
0.1597354
Exact F NumDF
0.8910
1
1.5070
1
0.0216
1
5.2133
1
2.6928
1
20.7656
1
DenDF
130
130
130
130
130
130
Prob>F
0.3469
0.2218
0.8835
0.0240
0.1032
<0.0001
•
•
Fig. 6. MANOVA results. DO and BOD were statistically significant.
H2O Temp. Temp.
(oC)
Diff. (oC)
Deforested 8.3945
4.1544
Reforested 7.6067
5.7118
Forested
6.0557
4.8199
Type
Cond.
(µS/cm)
0.0039
0.0045
0.0053
DO
(mg/L)
3.3985
1.4728
2.8022
Turb.
(NTU)
43.6284
33.7405
20.3492
BOD
(mg/L)
0.4783
0.2223
0.2486
Fig. 7. Variance values in water quality parameters
R² Value
H2O Temp.
(oC)
0.9657
Temp. Diff.
(oC)
0.1813
Cond.
(µS/cm)
0.9796
DO
(mg/L)
0.0915
Turb.
(NTU)
0.9925
BOD
(mg/L)
0.6652
Fig. 8. Correlation in variance between parameters and stream type.
Water temperature, conductivity, and turbidity were statistically
significant.
•
After correlation tests, TDS, pH, and DO saturation were
too closely related to other values to include in the data
set, and were removed prior to performing statistical tests
to minimize the number of variables.
See Fig. 5 for mean, range, minimum, and maximum for
each parameter.
• Average water temperature in reforested streams was
lower than that of both deforested streams and forested
streams.
• Difference between air temperature and water
temperature was greatest in reforested streams, which
may suggest that reforested streams were generally less
affected by air temperature than other stream types.
• Average conductivity in forested streams was slightly
lower than that of deforested streams. Conductivity in
reforested streams was higher than that of any other
stream type. TDS values followed the same pattern.
• Data did not indicate a significant change in average pH
values between the stream types.
• DO and DO saturation averages decreased as the degree
of riparian vegetation increased.
• Average turbidity was highest in deforested streams and
lowest in forested streams.
• BOD was also highest in deforested streams and lowest
in forested streams.
MANOVA results indicated that two variables, BOD and DO,
were significantly affected by changes in riparian
forestation (Fig. 6)
Variance in conductivity values was positively correlated to
stream type.
Variance in water temperature and turbidity values was
negatively correlated with stream type.
Acknowledgements
Drs. Brian Arbogast, Sean Lema, Frederick Scharf, Robert Buerger,
Larry Cahoon, and G. Brooks Avery; the City of Greensboro;
Rebecca Wells; Debbie Shoffner; Peter Schneider; Roy Graham;
David Phlegar; UNCW Honors Scholars Program; CSURF.