Water Air Soil Pollut (2014) 225:1955 DOI 10.1007/s11270-014-1955-4
The Impact of Wastewater Treatment Effluent on the Biogeochemistry of the Enoree River, South Carolina, During Drought Conditions C. Brannon Andersen & Gregory P. Lewis & Marylea Hart & John Pugh
Received: 20 August 2013 / Accepted: 3 April 2014 # Springer International Publishing Switzerland 2014
Abstract Drought conditions should magnify the effect of wastewater treatment plant (WWTP) effluent on river biogeochemistry. This study examined the impact of WWTP effluent on the Enoree River in the piedmont region of South Carolina during a period of significant drought. The Enoree River lacks impoundments, upstream agricultural runoff, and significant industrial point sources, so the single most important human influence on river chemistry is WWTP effluent. Water samples were collected from 28 locations on the Enoree River, 13 of its tributaries, and the effluent of four WWTPs. Effluent from the WWTP furthest upstream increased the salinity of the river and temporal variation and concentrations of most ions, especially nitrate, phosphate, sulfate, sodium, and chloride. The upstream WWTP set the downstream chemical composition of the river, with increasing proportions of chloride, sodium, C. B. Andersen (*) : M. Hart : J. Pugh Department of Earth and Environmental Sciences, Furman University, Greenville, SC 29613, USA e-mail:
[email protected] G. P. Lewis Department of Biology, Furman University, Greenville, SC 29613, USA Present Address: M. Hart 112 Tyra Lane, Townville, SC 29689, USA Present Address: J. Pugh Southern Company Services, 42 Inverness Center Pkwy, Birmingham, AL 35242, USA
and sulfate and decreasing proportions of dissolved silicon and bicarbonate. Downstream WWTPs had little or no impact on the chemical composition of the river. Mixing model results show that dilution was the dominant process of the downstream decrease in solute concentrations, but in-channel uptake mechanisms also contributed to declines in concentrations of nitrate, phosphate, and carbon dioxide. Despite dilution and uptake, the chemical signature of WWTP effluent was still evident 135 km downstream. These results lead to a better understanding of the effects of WWTP effluent on the biogeochemistry of rivers. Keywords Nitrate . Phosphate . River . Wastewater treatment effluent
1 Introduction The human impact on rivers has increased dramatically since the advent of industrialization. Globally, anthropogenic sources now contribute as much as 30 % of ions such as sodium, chloride, and sulfate in rivers (Meybeck 1980). This compositional change is the result of runoff from urban and agricultural land and discharge from both industrial and non-industrial sources (Meybeck 1998). Increases in nitrogen and phosphorus concentrations typically indicate anthropogenic input associated with discharge of effluent from wastewater treatment facilities (Moreau et al. 1998). Effluent impact, particularly on nitrogen in rivers, increases with increasing population density (Howarth et al. 1996).
1955, Page 2 of 21
In contrast to relatively pristine rivers such as the Amazon (e.g., Stallard and Edmond 1983) and the Clutha River in New Zealand (e.g., Kim et al. 1996), many rivers in Europe, the USA, and elsewhere have chemical compositions that are greatly affected by anthropogenic inputs. In Europe, for example, both agricultural runoff and discharge of communal effluent have greatly increased concentrations of phosphate, nitrate, and chloride in tributaries of both the Rhine and Seine Rivers (Goherman and Meyer 1985; Flintrop et al. 1996; Meybeck 1998; Roy et al. 1999). In China, degradation of water quality in the Pearl River is in large part the result of the discharge of sewage effluent (Zhu et al. 2002), and sewage effluent provides about 15 % of the nitrogen in the Changjiang River (Zhiliang et al. 2003). In the USA, phosphate concentrations increase dramatically in the Tennessee River after the river passes through areas with increased discharge of communal and industrial effluent (Johnson and Treece 1998), and carbon and nitrogen fluxes in the Mississippi River are increased by agricultural runoff and communal effluent discharge (e.g., Goolsby 2000; Raymond et al. 2008). Isolating the effect of communal, or wastewater treatment plant (WWTP), effluent on river chemistry can be difficult because of inputs of solutes from other sources. For example, in most of the previous studies of large rivers receiving WWTP effluent, the rivers drain catchments that consist, at least in part, of highly soluble minerals such as calcite. Second, most of those rivers also drain catchments that include upstream agricultural land cover and associated agricultural runoff. The result is that separating the effects of weathering, agricultural runoff, and industrial effluent from the discharge of WWTP effluent on the chemical composition of rivers is very difficult. In the Seine River, Roy et al. (1999) used inverse fuzzy modeling in order to separate the sources of solute inputs to the river. An alternative to understanding the impact of WWTP effluent on rivers is to focus on rivers where such effluent is the major anthropogenic input. The purpose of this study was to determine the impact of the discharge of WWTP effluent on the Enoree River in the piedmont region of the southeastern USA during drought conditions. In the upper half of the river basin, three major WWTPs discharged directly into the river, and one major WWTP discharged into a tributary. Two minor WWTPs also discharged into the lower half of the river. Our hypotheses were first that discharge of WWTP effluent would significantly change the
Water Air Soil Pollut (2014) 225:1955
chemical composition of the river and second that the major ion signature of WWTP effluent would be attenuated primarily by dilution where tributary discharge mixes with the main river channel, whereas nutrient ions would be attenuated by a combination of dilution and biological and sorption processes. The advantages of studying the Enoree River to determine the influence of WWTP effluent are four-fold. First, the river does not have significant industrial or agricultural inputs upstream of the WWTPs, which results in an unambiguous background chemical composition. Second, the river drains crystalline silicate rocks and therefore is characterized by low conductivity, so the signature of the effluent should be obvious. Third, agricultural runoff in the basin should be minimal because cropland cover is minimal (Muthukrishnan et al. 2007). Fourth, the impact of WWTP effluent on solute fluxes could be estimated because of the presence of four US Geological Survey (USGS) gaging stations, including one upstream of the WWTPs.
2 Study Area The Enoree River basin, a sixth-order tributary watershed (Strahler 1952) of the Broad River, is about 170 km long and drains 1,863 km2 of the piedmont region of South Carolina (Fig. 1). The geology of the region controls the background chemical composition of the Enoree River. The underlying bedrock is a structurally complex series of thrust sheets that can be divided into the Western and Central Piedmont and Charlotte Terranes (Butler and Secor 1991; Horton and McConnell 1991). The Western and Central Piedmont Terranes, which underlie the upper two thirds or more of the basin, are comprised primarily of felsic igneous and highgrade metamorphic rocks such as granites, biotite gneiss, sillimanite and muscovite schists, amphibolites, and rare diabase dikes. In contrast, the lower part of the basin is underlain by the Charlotte Terrane, which consists of a higher percentage of mafic rocks such as metagabbros and amphibolites, intermediate rocks such as metadiorites, and some possible ultramafic bodies, as well as granites, biotite gneisses, and schists. The weathering of these rocks has resulted in the formation of ultisols in most of the basin (e.g., Camp 1975). For nine tributary watersheds of the Enoree River, the chemical composition of streams as related to bedrock weathering is summarized in Andersen et al. (2001).
Water Air Soil Pollut (2014) 225:1955
Page 3 of 21, 1955
Fig. 1 Locations of sample localities, including US Geological Survey gaging stations, and wastewater treatment plants (WWTPs) in the Enoree River basin, South Carolina. Names of
the six WWTPs are indicated adjacent to symbols. Downstream distances for main channel localities and tributary confluences are listed in Table 1
The associated streams tend to be proportionally rich in dissolved silicon and have low conductivity (Andersen et al. 2001). The streams in the lower part of the basin have higher concentrations of total dissolved solids than streams in the upper part of the basin (Andersen et al. 2001). Land cover in the basin varied by location. The upper third of the basin consisted primarily of urban and residential land cover associated with the Greenville Metropolitan Area (population 560,000 in 2000), whereas the lower part of the basin was more rural and consisted primarily of pasture and forested land cover (Muthukrishnan et al. 2007). Assessment of satellite images and aerial photos of the Enoree River basin indicated that “agricultural” land cover was primarily pasture or abandoned fields rather than row crops (Muthukrishnan et al. 2007). Nitrate concentrations of the tributary streams were far below what is normally found associated with agricultural land cover in other regions (Muthukrishnan et al. 2007).
A total of six WWTP discharged effluent into the Enoree River or its tributaries during the period of our study. Of these six WWTPs, the four major WWTPs each served a population of about 20,000–30,000 residents of the Greenville Metropolitan Area. Monthly average discharges for each WWTP in June and July of 1999 and 2000 were obtained from the South Carolina Department of Health and Environmental Control. The Taylors and Pelham WWTP discharged effluent directly into the Enoree River in the upper third of the basin (Fig. 1; Table 1) at average rates of 0.13 and 0.22 m3 s−1 in 1999 and 0.14 and 0.21 m3 s−1 in 2000, respectively. The Gilder Creek WWTP discharged effluent into the river near the confluence with Gilder Creek at an average rate of 0.13 m3 s−1 in both 1999 and 2000. The Durbin Creek WWTP discharged effluent into Durbin Creek ~11 km upstream of its confluence with the Enoree River (Fig. 1) at an average rate of 0.05 m3 s−1 in both 1999 and 2000. Two additional minor WWTPs discharged effluents into tributaries of
ER20
ER19
ER18
ER17e
ER06
ER16
ER07
ER15
ER14
ER13
ER08c,d
ER09
ER10
ER11
ER12
Main channel
Locality
2000 (6)
1999 (NS)
2000 (6)
1999 (NS)
2000 (6)
1999 (5)
2000 (7)
1999 (5)
2000 (6)
1999 (5)
2000 (6)
1999 (6)
2000 (6)
1999 (7)
2000 (6)
1999 (6)
2000 (6)
1999 (3)
2000 (6)
1999 (6)
2000 (6)
1999 (7)
2000 (6)
1999 (NS)
2000 (6)
1999 (NS)
2000 (5)
1999 (NS)
2000 (5)
1999 (NS)
Year (n)a
48.4
41.0
35.1
29.0
26.1
23.0
21.1
19.0
16.4
15.9
15.3
6.6
3.7
2.6
1.5
kmb
25.7
25.6
25.6
22.8
23.6
24.2
24.6
23.2
24.2
22.9
23.9
22.5
24.2
23.1
23.9
22.7
24.0
22.2
23.4
22.1
22.7
23.0
23.0
22.6
T (°C)
6.93
6.99
7.11
6.82
6.96
7.47
6.93
6.80
6.84
6.66
6.78
6.56
6.87
6.61
6.85
6.58
6.89
6.63
6.69
7.05
6.70
6.78
6.84
6.65
pH
6.33
6.16
5.90
8.56
7.88
8.45
6.98
7.01
6.23
6.65
6.58
5.90
7.05
7.17
8.86
8.20
8.80
7.97
6.86
8.25
5.84
6.2
6.0
5.8
DO
113.4
108.9
113.4
103.9
136.3
128.3
180.5
131.6
197.8
88.7
155.5
119.3
234.5
110.2
45.3
46.2
43.9
41.1
41.1
94.2
43.6
39.6
44.2
42.9
Cond.
5.12
4.83
5.16
5.02
5.56
4.12
6.23
2.84
7.60
4.46
5.69
3.49
6.74
5.16
3.32
2.64
4.12
1.77
3.01
2.71
3.61
3.22
3.04
3.00
DOC
14.06
12.96
13.66
11.24
16.78
15.45
20.84
17.40
24.65
10.04
20.09
15.98
26.57
12.43
3.23
3.51
3.34
2.84
3.01
8.88
3.24
3.33
3.26
3.21
Na+
4.55
4.31
4.39
3.82
4.45
5.05
6.26
4.05
6.01
3.38
5.29
3.72
7.49
4.18
1.58
2.14
1.89
1.29
1.43
3.02
1.57
1.29
1.16
1.12
K+
4.74
5.05
4.97
4.64
5.57
5.85
9.75
3.49
10.30
3.25
8.24
3.61
11.56
3.61
2.89
2.64
3.04
2.65
2.79
5.35
3.17
3.22
3.29
3.31
Ca2+
1.41
1.46
1.38
1.40
1.51
1.36
2.89
1.90
3.41
1.40
2.64
1.84
3.78
1.52
1.16
0.93
1.18
1.01
1.10
1.87
1.23
1.30
1.28
1.41
Mg2+
5.35
5.41
5.64
5.85
5.99
5.91
6.48
6.38
6.62
6.02
6.59
6.43
6.78
5.92
6.25
5.68
6.31
5.78
6.07
8.44
6.84
7.69
7.60
7.55
Si4+
Table 1 Chemical composition of surface waters from the main channel, tributaries, and WWTPs of the Enoree River, South Carolina
22.69
21.30
21.03
16.38
24.22
24.42
28.47
22.68
31.32
17.69
27.65
23.16
35.86
18.69
15.13
13.10
15.63
13.50
14.27
28.85
16.06
16.15
16.43
16.48
HCO3−
13.93
12.75
13.71
10.70
17.71
14.49
23.65
19.01
28.20
10.53
21.78
17.90
32.80
9.91
3.52
3.77
3.67
2.98
3.01
7.37
3.61
3.18
3.29
3.24
Cl−
3.82
4.21
4.33
8.67
6.08
7.69
22.82
3.52
24.32
3.69
15.42
2.38
26.21
5.24
1.61
2.10
1.47
1.65
1.33
2.80
1.42
1.55
1.41
1.35
NO3−
8.68
8.45
9.02
7.22
10.90
8.26
13.77
9.32
14.82
5.64
10.52
9.30
16.26
7.84
1.50
1.66
1.55
1.49
1.27
5.54
1.14
0.95
0.95
0.93
SO42−
0.56
0.46
0.63
0.69
1.29
1.18
1.44
0.53
1.89
0.47
1.58
0.47
2.96
1.02
BD
BD
BD
BD
BD
0.15
BD
BD
BD
BD
H2PO4−
1955, Page 4 of 21 Water Air Soil Pollut (2014) 225:1955
MC01
BD01
UE14
Tributaries
ER01
ER28
ER02g
ER26
ER25
ER03
ER24
ER27
ER04f
ER23
ER22
ER21
Locality
2000 (6)
1999 (NS)
2000 (6)
1999 (NS)
2000 (4)
1999 (NS)
2000 (7)
1999 (2)
2000 (7)
1999 (NS)
2000 (7)
1999 (2)
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
2000 (7)
1999 (2)
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
2000 (7)
1999 (2)
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
Year (n)a
Table 1 (continued)
14.5
6.0
0.0
152.2
144.2
128.8
103.6
94.6
84.3
76.3
70.2
66.5
63.9
60.4
52.8
kmb
24.1
22.9
22.7
27.1
23.8
25.7
25.0
23.9
25.4
26.3
25.7
24.0
26.4
26.3
26.7
25.6
25.4
26.4
26.0
T (°C)
6.42
6.65
6.75
7.01
7.05
7.08
7.18
7.07
7.17
7.26
7.04
6.90
6.94
6.98
6.96
7.00
6.97
6.97
6.98
pH
5.14
5.99
5.96
6.61
8.25
6.63
5.81
8.45
6.95
6.93
6.16
8.10
7.16
7.15
6.88
8.45
5.80
7.70
7.07
DO
45.0
41.6
43.7
136.2
94.2
134.9
129.7
95.0
129.7
133.7
136.4
105.0
142.8
139.2
135.9
116.0
131.4
116.1
113.1
Cond.
3.69
2.96
2.72
5.13
2.71
4.72
4.44
2.12
4.35
6.36
4.68
4.21
4.93
4.92
5.30
5.30
5.37
5.47
5.31
DOC
3.34
3.30
3.16
14.02
8.88
13.88
14.69
9.71
15.46
15.67
17.05
11.89
17.55
17.71
16.83
12.64
16.20
13.78
14.53
Na+
1.85
1.35
1.09
4.42
3.02
4.66
3.97
2.95
4.38
4.44
4.63
3.15
4.79
4.86
4.52
4.35
4.78
4.21
4.29
K+
2.93
2.82
3.20
6.56
5.35
6.61
6.06
4.77
5.86
5.95
5.80
4.30
5.48
5.48
5.23
4.48
5.05
4.63
4.67
Ca2+
1.01
1.06
1.27
2.14
1.87
2.13
1.93
1.60
1.87
1.87
1.74
1.43
1.66
1.62
1.56
1.41
1.56
1.41
1.37
Mg2+
4.83
5.74
7.59
7.53
8.44
7.35
7.12
7.70
7.08
6.78
6.57
7.43
6.36
6.33
6.16
6.87
5.78
5.31
5.16
Si4+
15.58
13.74
15.97
36.35
28.85
35.41
33.54
25.06
31.60
30.24
29.99
25.88
29.51
28.86
28.14
22.28
28.14
25.70
24.59
HCO3−
2.83
3.69
3.26
13.28
7.37
13.84
15.40
8.35
15.49
16.51
17.68
8.48
18.25
18.49
17.56
13.63
16.09
13.05
13.44
Cl−
1.75
1.32
1.52
2.15
2.80
2.34
2.91
2.88
3.37
3.50
3.92
3.99
4.10
3.95
3.70
5.06
3.13
3.16
3.34
NO3−
1.76
1.24
0.90
7.29
5.54
7.48
7.77
6.00
7.96
8.48
9.03
6.88
9.00
8.94
9.11
7.77
9.44
7.96
8.63
SO42−
BD
BD
BD
0.09
0.19
0.10
0.16
0.25
0.23
0.28
0.37
0.29
0.53
0.45
0.56
0.57
0.61
0.62
0.58
H2PO4−
Water Air Soil Pollut (2014) 225:1955 Page 5 of 21, 1955
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
2000 (7)
1999 (NS)
2000 (6)
1999 (NS)
2000 (4)
1999 (NS)
2000 (7)
1999 (5)
2000 (7)
1999 (7)
2000 (7)
1999 (5)
2000 (9)
1999 (1)
2003 (1)
2003 (1)
TA
PL
WWTP effluents
SC01
UC01
KC01
IR01
DN01
DL01
DB01
GC01
AB01
DC01
RC01
BY01
AC01
1999 (7)
UT01
2000 (6)
Year (n)a
Locality
Table 1 (continued)
28.4
18.1
156.4
148.1
145.8
142.6
131.9
66.2
65.5
43.0
34.6
33.6
32.2
28.3
26.4
22.4
kmb
23.7
25.5
25.3
23.9
23.1
23.1
23.8
20.4
22.7
24.2
24.6
21.1
20.9
24.0
26.0
23.1
23.9
23.2
23.8
22.9
22.1
T (°C)
6.53
6.63
7.13
6.93
7.17
7.28
7.18
7.15
6.98
6.80
6.80
6.71
6.67
6.99
6.97
6.99
6.83
6.88
6.66
6.57
6.64
pH
6.91
6.19
7.82
7.09
7.29
5.45
5.65
6.96
6.63
6.20
6.47
7.68
8.78
7.41
7.76
7.14
8.16
6.65
3.60
6.46
7.90
DO
275.1
585.0
130.4
138.2
107.0
142.6
151.2
91.0
201.3
52.2
49.9
50.0
49.2
49.6
46.1
59.4
56.8
52.7
59.4
60.8
58.1
Cond.
13.83
13.24
5.93
3.74
6.87
8.15
4.66
2.62
4.20
4.69
4.00
3.95
2.09
4.01
3.15
3.60
3.89
3.64
2.23
3.53
2.12
DOC
37.07
76.95
9.53
11.06
8.94
9.66
12.30
7.36
27.62
3.69
3.93
3.58
3.48
3.48
3.24
4.24
3.73
3.75
3.82
4.87
4.69
Na+
8.91
14.07
1.60
1.70
2.05
2.01
15.19
2.24
4.00
2.48
2.41
1.92
1.66
2.16
1.95
2.26
2.72
2.31
2.23
1.98
1.75
K+
10.01
8.62
9.81
10.14
8.48
12.49
9.38
7.30
8.03
3.64
3.04
3.75
3.25
3.40
3.55
4.60
4.07
3.88
3.82
4.06
3.68
Ca2+
1.35
5.44
4.55
4.60
2.89
5.45
2.79
2.75
1.55
1.14
1.15
1.21
1.07
0.98
0.96
1.20
1.00
1.38
1.33
1.36
1.25
Mg2+
6.20
6.68
17.14
17.76
17.28
12.18
10.27
17.05
8.96
5.56
5.13
5.90
6.02
4.12
4.71
5.26
5.07
6.03
7.71
5.55
5.57
Si4+
46.96
49.41
65.57
68.14
54.05
78.39
66.52
42.26
30.51
16.74
14.16
14.93
13.66
14.12
13.65
19.96
16.69
17.09
18.34
17.86
16.00
HCO3−
28.41
76.27
3.86
4.93
3.61
4.78
9.34
3.65
31.59
3.62
4.38
4.50
4.58
3.60
3.45
3.85
3.64
3.87
3.45
3.82
3.45
Cl−
5.52
53.35
0.36
0.48
0.90
0.64
2.00
2.79
10.65
1.76
2.69
2.53
2.84
1.91
2.23
1.96
2.09
2.74
2.85
2.38
3.26
NO3−
20.58
36.51
2.86
3.30
1.66
2.33
12.84
1.60
7.13
2.38
1.86
1.92
1.70
2.93
2.88
2.99
2.75
2.03
1.76
4.49
4.75
SO42−
6.59
6.10
BD
BD
0.06
BD
0.03
0.18
0.51
BD
BD
0.71
BD
0.03
0.06
0.05
BD
BD
BD
BD
BD
H2PO4−
1955, Page 6 of 21 Water Air Soil Pollut (2014) 225:1955
US Geological Survey gaging station: Whitmire (02160700) g
US Geological Survey gaging station: Pelham (02160326)
US Geological Survey gaging station: Taylors (02160200)
US Geological Survey gaging station: Woodruff (02160390) f
e
d
Distance from uppermost tributary (UE14) to sampling locality on the main channel, to confluence with main channel for tributaries, or to discharge point or confluence with main channel for WWTPs
Averages of some parameters are anomalously high because of one sample collected on July 14, 1999 c
n represents the number of sampling events. Not all solutes were measured for every sample; in some cases, anion or cation analyses equal n−1
Page 7 of 21, 1955
b
a
WWTPs wastewater treatment plants, DO dissolved oxygen, DOC dissolved organic carbon, NS not sampled, BD below detection (
