Self-purification ability of a resurgence stream Roberta Vagnetti a , Paola Miana b , Mario Fabris b , Bruno Pavoni a, * a Dipartimento di Scienze Ambientali, Universit a Ca’Foscari di Venezia, Calle Larga S. Marta, 2137-30123 Venice, Italy b VESTA S.p.A., Venezia Servizi Territoriali Ambientali, Palazzo Bonfadini, Cannaregio 462-30121 Venezia, Italy Received 5 July 2002; received in revised form 10 April 2003; accepted 16 April 2003 Abstract The self-purification ability of a resurgence stream has been investigated by taking samples along the course of a channeled tract made up of a first part in beaten soil (3.3 km) and a second in concrete (7.2 km). The study has been conducted by statistically processing pre-existent data, acquired monthly by analyzing waters at the beginning and at the end of the whole canal for 6 years, from 1995 to 2000 (historic data), and by performing specific experiments (recent data) to evaluate differently the self-purification capacity of the beaten soil section and that in concrete. A significant abatement of concentrations has been observed from historic data for ammonium, phosphates, turbidity, heavy metals and bacteria. From the recent data, all these parameters seem to decrease in the beaten soil tract. Whereas significant further decreases in the concrete tract were observed only for ammonium, phosphates and bacteria. For other pa- rameters, e.g. pH, dissolved oxygen, chlorides, fluorides, sodium, and sulfates, a significant increase was observed from the historic data. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Self-purification; Resurgence stream; Nutrients; Metals; Turbidity; Bacteria 1. Introduction The water environment reacts to the input of pol- luting substances by means of a number of mechanisms aiming to restore its original conditions. This process, referred to as self-purification, actually consists of a re- cycling of materials (Vismara, 1998). More precise defi- nition for self-purification could be: ‘‘self-purification means the partial or complete restoration, by natural processes, of a stream pristine condition following the introduction (usually through the agency of man) of foreign matter sufficient in quality and quantity to cause a measurable change in physical, chemical and/or bio- logical characteristics of the stream’’ (Benoit, 1971). This transformation produces compounds having a less neg- ative impact than the starting ones. The natural self- purification process is therefore consisting of various complex phenomena involving numerous physical, chem- ical and biological factors acting and interacting more or less effectively. 1.1. Physical processes Dilution is an important component of self-purifica- tion, for it allows the achievement of suitable concen- trations for biological assimilation (Vismara, 1998). Adsorption is the binding of molecules and ions which are present in solution to solid particles. During the adsorption process other ions are displaced from the solid matrix into the solution (Benoit, 1971). Clays and other colloidal particles (e.g. oxides–hydroxides of Fe and Mn) can adsorb several organic and/or inorganic solutes. Furthermore the solid phase can be a proper support for bacterial degradation (Vismara, 1998). In Chemosphere 52 (2003) 1781–1795 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +39-41-234-8522; fax: +39-41- 2348582. E-mail address: [email protected](B. Pavoni). 0045-6535/03/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0045-6535(03)00445-4
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Chemosphere 52 (2003) 1781–1795
www.elsevier.com/locate/chemosphere
Self-purification ability of a resurgence stream
Roberta Vagnetti a, Paola Miana b, Mario Fabris b, Bruno Pavoni a,*
a Dipartimento di Scienze Ambientali, Universit�aa Ca’Foscari di Venezia, Calle Larga S. Marta, 2137-30123 Venice, Italyb VESTA S.p.A., Venezia Servizi Territoriali Ambientali, Palazzo Bonfadini, Cannaregio 462-30121 Venezia, Italy
Received 5 July 2002; received in revised form 10 April 2003; accepted 16 April 2003
Abstract
The self-purification ability of a resurgence stream has been investigated by taking samples along the course of a
channeled tract made up of a first part in beaten soil (3.3 km) and a second in concrete (7.2 km). The study has been
conducted by statistically processing pre-existent data, acquired monthly by analyzing waters at the beginning and at
the end of the whole canal for 6 years, from 1995 to 2000 (historic data), and by performing specific experiments (recent
data) to evaluate differently the self-purification capacity of the beaten soil section and that in concrete. A significant
abatement of concentrations has been observed from historic data for ammonium, phosphates, turbidity, heavy metals
and bacteria. From the recent data, all these parameters seem to decrease in the beaten soil tract. Whereas significant
further decreases in the concrete tract were observed only for ammonium, phosphates and bacteria. For other pa-
rameters, e.g. pH, dissolved oxygen, chlorides, fluorides, sodium, and sulfates, a significant increase was observed from
tetrachloroethylene, heterotrophic count at 22 and 36
�C, total and fecal coliforms, fecal streptococci, sulfite-
reducing clostridia spores. For some others (pH,
chlorides, fluorides, nitrites, sodium, and sulfates) a
significant increase was observed. Also dissolved oxygen
showed a significant increase with a 10% significance
level.
Statistical results are evident also in Fig. 3, which
shows the trends of pH (Fig. 3(a)), oxygen (Fig. 3(b)),
nitrates (Fig. 3(c)), nitrites (Fig. 3(d)) and phosphates
(Fig. 3(e)), from historic data (1995–2000). Dissolved
oxygen, nitrites concentration and pH were generally
higher at station 4 than at station 1 (particularly in
Box Whisker Plot o
-30
-20
-10
0
10
20
pH*1
0
Tur
bidi
ty
Am
mon
ium
Sod
ium
*10
Pot
assi
um*1
0
Oxy
gen
Flu
orid
e*10
0
Chl
orid
e*10
Nitr
ites*
100
Pho
spha
tes*
100
Sul
fate
s
Alu
min
um/1
0
Means+SDMeans-SD
Means+SEMeans-SE
Means
Fig. 2. Box Whisker Plot of differences for routinely acquired histori
Table 1 for units.
summer for nitrites). Phosphates were lower at station 4
than at station 1 and nitrates were also lower, but only
in summer. However for nitrates and nitrites a seasonal
trend was more evident.
Analytical results (recent data) are reported in Tables
2–4, and plotted in Figs. 4–6.
For ammonium, phosphates, turbidity, heavy metals
and bacteria a net abatement was observed from station
1 to station 2. Only ammonium, phosphates and bac-
teria decreased from station 2 to station 4. Whereas for
turbidity and heavy metals an increase was observed
from station 2 to station 4 and also from station 2 to
station 3 on 12th September. Concentration of nitrites
grew significantly from station 1 to station 4. Nitrates
and dissolved organic carbon did not show a particular
trend.
An estimation of the budget for all species of inor-
ganic nitrogen was attempted, in order to establish if
these species were simply transforming from one species
into another or if a total inorganic nitrogen decrease
also occurred. Concentrations of inorganic nitrogen for
historic data is reported in Table 5 and for recent data in
Table 6.
4. Discussion
4.1. Nitrogen
From historic data, a systematic decrease of total
inorganic nitrogen during the summer period (especially
f differences
Iron
/10
Man
gane
se
Cop
per
Zin
c
1,1,
1Tric
hlor
oet*
100
Tet
rach
loro
eth*
10
Het
erC
ount
22˚C
/100
0
Het
erC
ount
36˚C
/100
0
Tot
alC
olifo
rm/1
0000
Fec
alC
lifor
m/1
000
Fec
alS
trep
t./10
0
Clo
strid
iaS
pore
s
c data: negative difference¼ abatement; positive¼ increase. See
Fig. 3. Trends of pH (a), oxygen (b), nitrates (c), nitrites (d) and phosphates (e) from 1995 to 2000 (historic data obtained from
monthly analyses) at stations 1 and 4 (see Fig. 1, map of the canal).
R. Vagnetti et al. / Chemosphere 52 (2003) 1781–1795 1787
Table 3
Concentrations of selected parameters obtained by analyzing water samples during sampling session II (27th June), at stations 1 (Quarto d�Altino), 2 (End soil tract) and 4 (Favaro
Veneto) (recent data)
St. Turbidity (NTU) Ammonium (mg/dm3) Nitrites (mg/dm3) Nitrates (mg/dm3) Total phosphates (mg/dm3) DOC (mg/dm3)
1 9.4 0.19 0.15 18.99 0.13 1.9
2 7.4 0.08 0.19 16.92 0.11 1.8
4 14.4 0.08 0.18 17.05 0.09 1.7
Aluminum (lg/dm3) Iron (lg/dm3) Lead (lg/dm3) Manganese (lg/dm3) Copper (lg/dm3) Zinc (lg/dm3)
1 42.5 87.6 <0.1 9.9 2.8 6.6
2 48.8 98.1 <0.1 11.0 2.5 4.7
4 266.0 207.0 <0.1 11.8 3.1 7.6
Heterotrophic count
at 22 �C (CFU/cm3)
Heterotrophic count
at 36 �C (CFU/cm3)
Total coliforms
(CFU/100 cm3)
Fecal coliforms
(CFU/100 cm3)
Fecal streptococci
(CFU/100 cm3)
Clostridia spores
(CFU/100 cm3)
1 80 000 20 000 97 400 7560 400 30
2 40 000 4000 39 000 3960 44 22
4 20 000 3000 24 800 780 19 20
Table 2
Concentrations of selected parameters obtained by analyzing water samples during sampling session I (27th March), at stations 1 (Quarto d�Altino), 2 (End soil tract) and 4 (Favaro
Veneto) (recent data)
St. Turbidity (NTU) Ammonium (mg/dm3) Nitrites (mg/dm3) Nitrates (mg/dm3) Total phosphates (mg/dm3) DOC (mg/dm3)
1 7.4 0.26 0.10 15.6 0.27 2.20
2 2.8 0.12 0.20 15.5 0.30 2.32
4 8.0 0.07 0.19 15.5 0.24 2.16
Aluminum (lg/dm3) Iron (lg/dm3) Lead (lg/dm3) Manganese (lg/dm3) Copper (lg/dm3) Zinc (lg/dm3)
1 162 145.0 <0.1 10.1 2.5 14.8
2 111 53.0 <0.1 6.0 1.8 10.2
4 352 147.5 <0.1 9.4 7.4 11.4
Heterotrophic count
at 22 �C (CFU/cm3)
Heterotrophic count
at 36 �C (CFU/cm3)
Total coliforms
(CFU/100 cm3)
Fecal coliforms
(CFU/100 cm3)
Fecal streptococci
(CFU/100 cm3)
Clostridia spores
(CFU/100 cm3)
1 150 000 100 000 33 400 6000 246 42
2 17 300 11 900 4750 700 71 15
4 50 400 50 000 10 000 360 3 30
1788
R.Vagnetti
etal./Chem
osphere
52(2003)1781–1795
Table
4
Concentrationsofselected
para
metersobtained
by
analyzing
watersa
mplesduring
sampling
session
III(12th
Sep
tember),
atstations1
(Quarto
d�A
ltino),
2(E
nd
soil
tract),
3(S
iphon)and
4(F
avaro
Ven
eto)(recen
tdata)
St.
Turb
idity(N
TU)
Ammonium
(mg/dm
3)
Nitrites(m
g/dm
3)
Nitra
tes(m
g/dm
3)
Totalphosp
hates(m
g/dm
3)
DOC
(mg/dm
3)
16.0
0.16
0.13
17.6
0.14
1.9
23.3
0.07
0.17
17.5
0.13
1.8
36.2
0.07
0.18
17.6
0.13
1.8
49.7
0.06
0.17
17.5
0.12
1.8
Aluminum
(lg/dm
3)
Iron
(lg/dm
3)
Lea
d(l
g/dm
3)
Manganese(l
g/dm
3)
Copper
(lg/dm
3)
Zinc(l
g/dm
3)
1103
93
<0.1
7.7
1.0
6.7
2100
76
<0.1
5.5
0.6
3.1
3332
155
<0.1
7.7
0.7
4.9
4487
238
<0.1
10.5
2.9
7.9
Heterotrophic
countat
22�C
(CFU/cm
3)
Heterotrophic
countat
36�C
(CFU/cm
3)
Totalco
lifo
rms
(CFU/100cm
3)
Fecalco
lifo
rms
(CFU/100cm
3)
Fecalstrepto
cocci
(CFU/100cm
3)
Clostridia
spores
(CFU/100cm
3)
13760
13200
82600
6000
750
83
22000
2440
12000
2440
100
56
32320
4680
5900
780
300
26
41680
2100
5100
550
70
32
R. Vagnetti et al. / Chemosphere 52 (2003) 1781–1795 1789
in June) was observed. This phenomenon can last until
the early autumn depending on the particular year. This
is evident from the data reported in Table 5. During the
other periods of the year, the inorganic nitrogen budget
can be considered closed: in other words the concen-
tration of total inorganic nitrogen remains constant.
This trend has been confirmed by the results of the ex-
periments (Table 6). The only total inorganic nitrogen
decrease was monitored in the sampling session of 27th
June. In the other sampling sessions the concentration at
station 1 is not different from the concentration at sta-
tion 4. The summer abatement of nitrogen species was
observed by several investigators (Elosegui et al., 1995;
Bratli et al., 1999; Jing et al., 2001) and it can be rea-
sonably ascribed to a greater assimilation by living or-
ganisms, particularly plants. In fact, in this season the
most efficient nutrient and pollutant uptake occurs, be-
cause higher air and water temperatures and a more