ORIGINAL ARTICLE
Nutrient contents in bottom sediment samplesfrom a southern Brazilian microbasin
Marjore Antunes • Maısa Trevisan Antunes •
Andreia Neves Fernandes • Janaina da Silva Crespo •
Marcelo Giovanela
Received: 23 November 2011 / Accepted: 3 September 2012 / Published online: 15 September 2012
� Springer-Verlag 2012
Abstract The nutrients, carbon, nitrogen and phosphorus,
significantly affect the quality of aquatic environments,
especially when present at concentrations above natural
levels. In this context, the sedimentary column can act as
an environment for storage or accumulation of these
nutrients and for the reprocessing of such substances in the
water column and aquatic biota. In this context, this study
aimed to estimate the concentration of total organic carbon
(TOC), total nitrogen (TN), total phosphorus (TP), inor-
ganic phosphorus (IP) and organic phosphorus (OP) in
seven sediment samples that were collected from the
Marrecas Stream microbasin (Caxias do Sul, Rio Grande
do Sul State, Brazil). The relationships among the sediment
nutrient concentrations and the levels of organic matter
(OM), fine material (silt–clay) and the concentration of the
metal species, Al, Fe and Mn, as well as the possible
nutrient sources to the stream studied were also evaluated.
The data set suggest that the TOC and IP appear to have a
direct correlation with the vast riparian vegetation present
in areas adjacent to the sampling points and to the physico-
chemical properties of the water and sedimentary column.
Moreover, the results obtained for TN suggest that its
concentration possibly suffers interference from the tem-
perature of the water and its oxygenation, in addition to
other biological activities. On the other hand, one cannot
rule out human interference, mainly in the levels of OP,
possibly due to the inflow of domestic sewage to the
stream.
Keywords Sediments � Nutrients � Organic matter �Metal
species � Eutrophication
Abbreviations
IP Inorganic phosphorus
OM Organic matter
ON Organic nitrogen
OP Organic phosphorus
TN Total nitrogen
TOC Total organic carbon
TP Total phosphorus
Introduction
Water quantity and quality are factors that are directly or
indirectly influenced by population growth, regional eco-
nomic activities, irresponsible soil utilization and the indis-
criminate release of liquid and solid wastes into receiving
bodies (Froehner and Martins 2008; Souza et al. 2009). Many
chemical compounds, especially those containing carbon,
nitrogen and phosphorus, can influence the quality of a water
body. These elements are naturally present in aquatic eco-
systems, and their levels are influenced by their respective
biogeochemical cycles. Moreover, their concentrations can
vary depending on the temporal and spacial conditions. These
elements can be found in different forms in the environment
(i.e., organic, inorganic, dissolved or particulate) (Agemian
1997) and can therefore be present in both water and sediment.
Among the elements mentioned above, carbon is
undoubtedly the most abundant. According to Ouyang
M. Antunes � M. T. Antunes � J. da Silva Crespo �M. Giovanela (&)
Centro de Ciencias Exatas e Tecnologia, Universidade de Caxias
do Sul, Caxias do Sul, RS 95070-560, Brazil
e-mail: [email protected]
A. N. Fernandes
Instituto de Quımica, Universidade Federal do Rio Grande
do Sul, Porto Alegre, RS 91501-970, Brazil
123
Environ Earth Sci (2013) 69:959–968
DOI 10.1007/s12665-012-1980-9
(2003), the presence of this element may affect the avail-
ability of the others nutrients and control the solubility and
toxicity of contaminants. Nitrogen is normally encountered
in its organic form. The main natural sources of nitrogen-
ated compounds, which mainly include peptides and
polypeptides, are cell lysis, decay and excretion by phy-
toplankton and aquatic macrophytes (Esteves 1998).
Phosphorus, however, is predominant in its inorganic form
and originates naturally in combination with Fe, Al, Ca
and/or clay minerals from the chemical weathering of rocks
(Zhang et al. 2007, 2008).
In addition to the natural occurrence of nutrients in the
aquatic environment, some point and/or diffuse sources of
pollution, such as sewage, agricultural waste and industrial
effluents, can carry some of these substances to water
bodies, harming the homeostasis of the environment
(Roessink et al. 2008). An excess of these nutrients causes
an increase in the productivity of the aquatic ecosystem,
thus affecting its quality and biota through a process known
as artificial eutrophication (Nyenje et al. 2010).
The sedimentary column, in this context, can act as a
repository for the storage or accumulation of nutrients, the
reprocessing of these materials and the exchange of
chemical species with the water column and aquatic biota
(Mozeto and Soares 2006). These exchanges may occur
through biological, physicochemical, chemical and trans-
port processes and usually occur in the direction of greater
to lower concentrations, resulting in equilibrium between
the two compartments (Baumgarten et al. 2001). The
availability of nutrients in the aquatic environment can also
be influenced by the hydrodynamics of the water body,
causing an increase in the chemical exchanges between
water and sediment, especially in shallow environments
(Baumgarten et al. 2001; Roessink et al. 2008). Therefore,
many studies have assessed the composition of sediments
using the concentrations of carbon, nitrogen and phos-
phorus to investigate aquatic ecosystem quality (House and
Denison 2002; Spooner and Maher 2009; Grenz et al.
2010).
Within this context, the objectives of the present study
were: (1) to estimate the concentration of total organic
carbon (TOC), total nitrogen (TN), total phosphorus (TP),
inorganic phosphorus (IP) and organic phosphorus (OP) in
seven sediment samples collected from the Marrecas
Stream microbasin (Caxias do Sul, Rio Grande do Sul
State, Brazil); (2) to investigate the relationships among
nutrient concentrations and the levels of organic matter
(OM), fine material (silt–clay) and the concentration of the
metal species, Al, Fe and Mn; (3) to discuss the possible
sources of nutrients to the stream studied; and (4) to
compare the results obtained with the literature. This
microbasin was chosen as the study area because it will
contain the newest dam and surface water treatment
complex for the public supply of the local municipality. It
is important to highlight that this area of the basin is
influenced by various activities, including livestock pro-
duction (cattle, pigs, horses, sheep, poultry), agricultural
use (fruit production, horticulture, forestry) and industry
(slaughter of sheep), in addition to residences and five
recreational areas (camping) (Schneider et al. 2009).
Materials and methods
Study area
The Marrecas Stream microbasin (29�0303400S and
50�5703500W) lies within the Sao Marcos River basin, which
is one of the main tributaries of the Taquari-Antas hydro-
graphic basin. Located in a predominantly rural area, this
microbasin has an area of 55.12 km2 and borders the Faxinal
Stream basin and the Sao Francisco de Paula municipality.
The stream begins close to the locality of Apanhador in the
municipality of Caxias do Sul (Rio Grande do Sul State,
Brazil) and is approximately 15-km long (Antunes et al.
2008). The map in Fig. 1 shows its location in the regional
context and the detailing at a scale of 1:20,000, in addition to
the aerial view of the sampling points.
The natural vegetative cover in the region around the
microbasin is characterized as mixed ombrophilous forest
(Araucaria Forest). With regard to climate characterization,
the region is located in a temperate zone with a meso-
thermal climate. Annual temperatures, on average, are
between 14 and 22 �C, and the average annual rainfall
varies between 1,250 and 2,000 mm. With respect to relief,
the watershed is located in the Brazilian southern plateau
with rocks belonging to the Parana Sedimentary Basin,
being dominated by a sequence of basalts and basaltic
andesites at its base and by dacites, trachydacites and
rhyolites in the upper portion of the sequence. These
geological features give the water of the Marrecas Stream
microbasin an acidic characteristic, and the water has sig-
nificant concentrations of Fe and Al, which can later be
incorporated into the sedimentary column.
Sampling
In this study, seven sediment samples (named 1, 2, 3, 4, 5,
6 and 7) were collected directly from the bottom of the
stream using a Petersen sampling device. Fresh sediment
samples were used for granulometric analyses. For other
tests, the samples were first dried at 50 �C for 24 h, sub-
sequently ground and then fractionated in a 250-lm sieve
for determining the OM levels. For analysis of the con-
centrations of nutrients and the metal species, Al, Fe and
Mn, the dried samples were fractionated in a 63-lm sieve.
960 Environ Earth Sci (2013) 69:959–968
123
All laboratory glassware and plastic used in the sam-
pling and preservation of sediment samples were first
washed with tap water and then soaked in a 15 % (v/v)
solution of alkaline Extran for 24 h. Next, it was washed
thoroughly with tap water and left in a 50 % (v/v) solution
of HNO3 for 24 h. At the end of this procedure, all mate-
rials were rinsed with distilled water and dried at room
temperature.
Sediment analysis
The chemicals employed in the sediment analysis were all
of analytical grade. Hydrochloric, nitric and sulfuric acids
and hydrogen peroxide were obtained from Merck. The
salts of potassium dichromate, ammonium ferrous sulfate
hexahydrate, ammonium molybdate tetrahydrate and
anhydrous potassium phosphate monobasic were purchased
from Vetec. Ascorbic acid and potassium antimonyl tar-
trate trihydrate products were acquired from Synth, and the
solution of the indicator ferroin was acquired from Tec-
Lab. All aqueous solutions were prepared with deionized
water.
The TOC content of the sediment samples was deter-
mined by exothermic heating and oxidation according to
the Mebius method proposed by Rheinheimer et al. (2008).
The dry sediments (approximately 0.25 g) were initially
Fig. 1 Study area and aerial view of the sampling points
Environ Earth Sci (2013) 69:959–968 961
123
mixed with 10.0 mL of a 0.067 mol L-1 solution of
K2Cr2O7 and 15.0 mL of concentrated H2SO4. The sus-
pensions were then heated at 150 �C for 30 min in a
digestion block with a watch glass placed over the top of
the tube. After reaching room temperature, the contents
of these tubes were transferred to a beaker along with
80.0 mL of deionized water. The samples were finally
titrated with a 0.20 mol L-1 solution of Fe(NH4)2
(SO4)2 � 6H2O in the presence of the ferroin indicator until
the appearance of a violet color.
The determination of TN in the sediment samples, on
the other hand, was performed directly on a CARLO
ERBA 1110 elemental analyzer.
For the determination of TP, dry sediments (approxi-
mately 0.5 g) were initially ignited at 550 �C for 2 h to
convert the OP into orthophosphate, which is the main
form of phosphorus assimilated by aquatic biota (Aspila
et al. 1976; Esteves 1998; Zan et al. 2011). After ignition,
the residues were degraded at room temperature with a
solution of HCl (1.0 mol L-1) in an orbital shaker at
150 rpm for 16 h. The suspensions were then centrifuged
at 3,9299g for a 5-min period. At the end of this proce-
dure, 3.0 mL of the supernatant was removed and diluted
to a volume of 30.0 mL with deionized water (solution A).
The orthophosphate concentration was determined in a
MICRONAL B582 visual spectrophotometer (k =
885 nm), using the ‘‘working reagent’’ (a solution prepared
by combining sulfuric acid, ammonium molybdate, ascor-
bic acid and antimonyl tartrate) (solution B) (Agemian
1997). The absorbance of the samples was recorded 90 min
after the addition of 20.0 mL of solution B to solution A.
The IP content of the sediments was determined by
measuring the orthophosphate released when the dry,
unignited sediments were degraded by a solution of HCl
(1.0 mol L-1). It is important to highlight that this
extraction includes several inorganic subphases, which can
be further known by sequential extraction procedures
(Agemian 1997). The concentrations of TP and IP in the
samples were obtained using an analytical calibration curve
for orthophosphate (r = 0.9995). Finally, the OP content
was calculated from the difference between these mea-
surements (OP = TP - IP).
The determination of phosphorus in this extraction is
based on the reaction of ammonium molybdate with
orthophosphate to form molybdophosphoric acid, which is
then reduced by ascorbic acid to an intensely colored het-
eropoly molybdophosphoric acid complex. The intensity of
produced color is proportional to the orthophosphate con-
centration. The development of the color can be acceler-
ated by the addition of antimony potassium tartrate,
producing a more sensitive system with optimum sensi-
tivity at 885 nm (Agemian 1997).
Determination of the content of organic material,
fine material (silt–clay) and the metal species,
Al, Fe and Mn
Nutrient concentrations can be influenced by the physical
and chemical properties of the sediment and water column
and by the hydrodynamic characteristics of the water body,
which affect the granulometric distribution of sediments
(Svensson and Soderlund 1976; Agemian 1997; Esteves
1998). Thus, the present study also assessed the contents of
OM, fine material (silt–clay) and concentrations of the
metal species, Al, Fe, and Mn, in the sediment samples
studied.
The OM content was determined by ignition of 2.0 g of
sediment at 550 �C for 4 h. Grain size of sediments was
measured on a HORIBA LA-950 particle size distribution
analyzer using the water–quartz refractive index. The metal
species, Al, Fe and Mn, were quantified by flame atomic
absorption spectrometry in a VARIAN SPECTRAA 250
PLUS spectrometer after the sediment samples were diges-
ted in an acidic medium (a mixture of HNO3, H2O2 and HCl)
with heating, according to method 3050 B of the United
States Environmental Protection Agency (US EPA 1996).
Data quality
The quality assurance was controlled by certified reference
materials (CRMs). Blank samples were performed
throughout all the experiments. To evaluate the analytical
precision, all samples were determined in triplicate. The
accuracy of the total analysis was assured using the
E11035-A (EuroVector), BCR-684 (Institute for Reference
Materials and Measurements) and RM 8704 (National
Institute of Standards & Technology) materials. Results
indicated a good agreement between certified and deter-
mined values and the recoveries ranged from 93 to 110 %.
Results and discussion
Total organic carbon
The results of the TOC levels are summarized in Fig. 2. As
can be observed, the nutrient levels varied significantly
between sampling points (21,470–86,584 mg kg-1), where
the highest concentrations were obtained at sampling
points 3 and 7 (86,584 and 71,765 mg kg-1, respectively).
Sampling point 3 displays a greater amount of vegeta-
tion on both banks of the stream. In this sense, the large
trees may provide lignin to the aquatic environment, while
the riparian and aquatic vegetation can provide cellulose.
Certain microorganisms act on both of these substances to
962 Environ Earth Sci (2013) 69:959–968
123
form humic compounds, which can then undergo coagu-
lation and subsequent sedimentation (Steinberg and Melzer
1982; Schafer 1984; Giovanela et al. 2010). Thus, the high
TOC content at this sampling point may be linked to the
presence of OM with high degrees of humification. When
considering local geological features, the slightly acidic
nature of the water promotes the precipitation of humic
acids in the aquatic ecosystem (Esteves 1998).
On the other hand, at sampling point 7, the wetland area
near the sampling region, which consists mainly of grasses
and other decomposing materials, can possibly act as a
source of TOC for the sediment of the Marrecas Stream,
causing this sampling point to also have a high concen-
tration of this nutrient. This may be due to the effects of
rainfall and soil infiltration that carry organic materials to
the water body.
For the other sampling sites, the surrounding vegetation
may represent a less significant source of allochthonous
material, as compared to sampling points 3 and 7. Several
factors may contribute to the lower TOC concentrations in
the other sampling sites. For example, aerobic bacteria that
decompose OM may release a significant amount of less
chemically complex compounds that are rich in carbon and
are possibly dissolved in the water column rather than
being incorporated in the sediment. Additionally, the lim-
ited depth of the Marrecas Stream possibly favors the
elimination of carbon dioxide (produced by respiration of
aquatic organisms) to the atmosphere (Schafer 1984).
Total nitrogen
As can be observed in Fig. 2, the concentrations of TN in
the sediments are practically constant along the examined
river course, ranging from 2,806 to 5,233 mg kg-1. With
respect to this nutrient, the main natural sources include
rain, inorganic allochthonous materials and atmospheric air
(Esteves 1998). Biological fixation of this element, per-
formed by some algae and bacteria, results in the formation
of organic nitrogen (ON). This form of nitrogen may pre-
cipitate and be incorporated into the bottom sediment
(particulate ON) or remain in solution (dissolved ON).
Ammonia and the nitrite and nitrate ions, the main forms of
inorganic nitrogen, are also present in the aquatic envi-
ronment (Steinberg and Melzer 1982).
Because nitrogen is mineralized faster than carbon and
phosphorus, many reduced nitrogenated compounds are
found in the sedimentary column (Anderson and Jensen
1992; Agemian 1997). Therefore, nitrogen can be absorbed
into this environmental compartment, and when it is
summed with the resistant organic nitrogen compounds, it
constitutes the TN measured in the bottom sediment of the
Marrecas Stream.
According to Golterman (2004), nitrogen is encountered
predominantly in the sedimentary column ([90 %) in its
organic form. Thus, one would expect that the TN level for
sediment samples from the Marrecas Stream would be
equivalent to the ON content, as reported in other studies
(Froehner and Martins 2008). However, the sediments
analyzed in this study did not present TN concentrations
equal to the ON concentrations, as shown in Fig. 3.
In this context, nitrogen fixation is possibly more
effective in water than in sediment from the stream. This
would occur because the entire water column of the sam-
pling points analyzed in the Marrecas Stream is illuminated
due to its shallow depth and the low turbidity of water.
Under these conditions, the nitrogen fixing plankton is
more abundant and occupies a greater volume in the system
(Esteves 1998). After the fixation of nitrogen, the process
known as ammonification may follow. In this case, the
Fig. 2 TOC and TN contents (mg kg-1) in the sediment samples:
Black rectangle 1; little gray rectangle 2; rectangle with upper rightto lower left fill 3; rectangle with orthogonal crosshatch fill 4;
rectangle with diagonal crosshatch fill 5; rectangle with vertical fill 6;
dark gray rectangle 7
Fig. 3 Relation between TOC and TN concentrations (mg kg-1) for
sediment samples from the Marrecas Stream microbasin
Environ Earth Sci (2013) 69:959–968 963
123
sediment is the main active site, resulting in the formation
of ammonia. According to Esteves (1998), ammonia is
converted to the ammonium ion in slightly acidic pH and is
then easily assimilated by phytoplankton.
Furthermore, nitrification corresponds to the biological
oxidation of reduced nitrogenated compounds to nitrate
and occurs only in essentially oxygenated environments,
such as in the water column and sediment surface. In the
stream evaluated in this study, the nitrification process may
be hampered by the slow movement of its waters, mainly
caused by the low rainfall during the time of sampling.
According to the Civil Defense of the Rio Grande do Sul
State (Defesa Civil do Estado do Rio Grande do Sul 2011),
the average rainfall in the sampling month was only
52.5 mm. Finally, denitrification, like ammonification,
occurs in the sediment column due to its low oxygen
conditions and the significant amount of organic substrate
(Wetzel 2001).
Total, inorganic and organic phosphorus
The levels of TP, IP and OP in sediments of the Marrecas
Stream are summarized in Fig. 4. It can be seen that
the concentrations of TP (488–1,083 mg kg-1) and IP
(103–505 mg kg-1) varied significantly between sampling
points, whereas the OP levels (381–578 mg kg-1)
remained almost constant. Furthermore, OP concentrations
were greater than those of IP.
Because the levels of OP are greater than those of IP in
the sediments analyzed, Ruttenberg and Goni (1997)
affirmed that this characteristic might be linked to the vast
riparian vegetation adjacent to the sampling points.
According to these authors, this results in better
phosphorus retention by live OM and, therefore, more
effective processing of IP into OP.
In contrast, Mater et al. (2004) have reported that
phosphorus is usually in its inorganic form in the sediment
when the water body does not suffer significant anthropo-
genic interference. According to these authors, the fraction
of IP in relation to TP in these cases is approximately
60 %. However, the sediments analyzed in this study pre-
sented a greater contribution of OP in the TP (Table 1).
Moturi et al. (2005) and Froehner and Martins (2008) have
confirmed that high OP values in river sediments could be
attributed to the discharge of urban sewage. Therefore, one
cannot rule out the possibility that human interference
affects the phosphorus levels in the Marrecas Stream. The
lower ratio IP/TP observed for the sediment collected in the
sampling point 2, for example, suggests a greater amount
of OP in this sample. This behavior can be possibly
attributed to an inflow of domestic sewage that resulted
from recreational activities (camping) and from the resi-
dences situated in the study area.
Taking into consideration the variation in OP concen-
trations, it is possible that there is an inflow of domestic
sewage to the river between sampling points 1 and 2, as
previously mentioned. Below sampling point 2 and through
sampling point 4, the concentration of OP decreases due to
the probable uptake of this nutrient by microorganisms and
the reduced inflow of effluents in this region. Due to the
low depth of the stream and the fact that there is a decrease
in slope between sampling points 2 and 4, it is possible that
the turbulence of the water favors remobilization of OP
from the sediments to the water column, which may assist
in decreasing the concentration in the sedimentary column.
From sampling point 5, the stream begins to receive the
rainwater drainage from the city of Vila Seca (Caxias do
Sul, Rio Grande do Sul State, Brazil), likely including the
domestic sewage of this city and the contribution of waste
from a poultry farm located near the sampled region. These
factors may contribute to the increased concentration of OP
in the stream, especially at sampling point 7.
Physico-chemical interferences on the concentrations
of nutrients in sediments
The content of OM and fine material (silt–clay) and the
concentration of metal species, Al, Fe and Mn, in the
sediment samples are summarized in Table 2. The sedi-
ments that were analyzed presented OM contents ranging
from 10.1 to 29.3 %, which allows their classification as
organic sediments (Esteves 1998; Belo et al. 2010). Based
on the results obtained for the TOC and OM, it is possible
to observe that the TOC concentrations in sampling points
1–5 follow a behavior similar to those obtained for OM.
Moreover, sampling point 3 has the highest levels of TOC
Fig. 4 P species contents (mg kg-1) in the sediment samples: Blackrectangle 1; little gray rectangle 2; rectangle with upper right tolower left fill 3; rectangle with orthogonal crosshatch fill 4; rectanglewith diagonal crosshatch fill 5; rectangle with vertical fill 6; darkgray rectangle 7
964 Environ Earth Sci (2013) 69:959–968
123
and OM. This is because, at this sampling point, a signif-
icant amount of organic material possibly suffers slow
decay as a result of oxygenation of the medium. Sample
point 6 contains a greater OM content and lower TOC
concentration than sample point 7. This may be because
there is a greater dilution of this nutrient at sample point 6
due to increased water turbulence (Froehner and Martins
2008).
The amount of OM in the sediment may also influence the
nitrogen concentration, especially with regard to the deni-
trification step (Esteves 1998). Typically, the highest per-
centage of nitrate associated with the sedimentary column is
eliminated in the form of nitrogen gas (Spooner and Maher
2009). It should be noted that this nitrate can also undergo the
ammonification process and that the resulting ammonium
may be adsorbed by clay minerals from the oxidized portion
of the sediment (Schafer 1984). In the context of the Marr-
ecas Stream, the behavior of the OM content was similar to
TN in sampling points 1–5, while the fine material behavior
was similar to TN in sampling points 4 and 5. A direct
relation between OM and TN and fine material and TN
concentrations was observed. As for the last two points, the
TN concentration may be influenced more substantially by
other factors, such as water oxygenation and temperature
variations, as stated by Schafer (1984).
In addition to the OM and the fine material content
present in the sedimentary column and the aeration and
temperature conditions of the water, there are other inter-
fering factors that can act in nutrient concentrations. In the
case of phosphorus, for example, it is suggested that min-
eralogical characteristics of the area under study (basalts
and rhyolites) contribute to the behavior of this nutrient in
the sampling points of the stream. This is because the rocks
present in the Marrecas Stream microbasin favor the
presence of Fe, Al and Mn in the water column. These
metal species aid in the precipitation process of the
phosphorus with subsequent accumulation in the sediment,
as can be observed by the direct relation of the Al (sam-
pling sites 5 and 6), Fe (sampling sites 1, 2, 4, 5, 6 and 7)
and Mn (sampling sites 4, 5, 6 and 7) concentrations to the
IP content. Finally, as Al, Fe and Mn contents increased at
these sampling points, the IP concentrations also increased
(Agemian 1997; Esteves 1998; Schafer 1984).
Molar ratios between nutrients and their possible
sources
Molar ratios between the concentrations of nutrients have
been used to identify the origin of OM present in a given
ecosystem and to estimate the possible sources of nutrient
input to the environment (Ruttenberg and Goni 1997;
Froehner and Martins 2008). In the case of sediments
whose characteristics may have been influenced by riparian
vegetation present in the water body, TOC/OP levels
between 300 and 1,300 indicate that OM originates from
the tissue of small plants. TOC/OP ratios greater than 1,300
indicate that the OM is derived from wood. Table 3 pre-
sents the results for the TOC/OP molar ratios for sediments
of the Marrecas Stream.
Only sampling points 3 and 7 showed TOC/OP ratios
greater than 300 (520.1 and 320.2, respectively), which
may be linked to the contribution of small terrestrial plants.
For the molar ratios of the other sampling sites, it is sug-
gested that the contribution of domestic sewage to the
stream contributes to an increase in the concentration of OP
and therefore to a decrease in the TOC/OP molar ratio.
This is illustrated by sampling point 5, where the TOC/OP
ratio was the lowest (132.7) compared to the other sam-
pling points. At this location, the stream begins to receive
water from the storm drainage of Vila Seca and domestic
effluents from the same location, which may contribute to
the uptake of OP in the water body.
However, according to Wetzel (2001), the TOC/OP
ratios should be less than 350 for streams, shallow lakes
and reservoirs with low residence time (less than 6
months). Thus, although the stream in question possibly
receives domestic effluents, the region does not seem to
Table 1 Fraction of IP in the content of TP
Sediment samples 1 2 3 4 5 6 7
IP/TP (%) 50.0 17.6 37.2 21.8 35.8 52.4 46.6
Table 2 Results of the organic
matter content, silt–clay
percentage and Al, Fe and Mn
concentrations for the sediment
samples collected in the
Marrecas Stream microbasin
Sediment samples Silt–clay (%) OM (%) Al (g kg-1) Fe (g kg-1) Mn (g kg-1)
1 34.9 11.4 ± 0.15 19.8 ± 0.96 38.3 ± 0.76 0.69 ± 0.01
2 43.2 10.1 ± 0.13 20.6 ± 1.15 34.8 ± 1.28 0.94 ± 0.01
3 39.1 29.3 ± 0.02 19.4 ± 6.63 16.0 ± 0.36 0.17 ± 0.01
4 66.5 15.9 ± 0.02 21.9 ± 1.62 21.5 ± 0.53 0.31 ± 0.01
5 36.8 14.2 ± 0.11 19.4 ± 0.82 24.8 ± 0.77 0.35 ± 0.01
6 30.4 19.2 ± 0.04 19.5 ± 0.96 31.6 ± 0.88 0.66 ± 0.01
7 26.0 17.0 ± 0.11 18.5 ± 1.08 35.5 ± 0.69 0.96 ± 0.02
Environ Earth Sci (2013) 69:959–968 965
123
present high phosphorus contamination that could result in
its eutrophication over the medium or long term.
During the collection of sediments, it should be noted
that a direct observation at each sampling point showed
that the Marrecas Stream displayed no visual aspects of a
eutrophication process, such as growth of macrophytes or
high water turbidity. It should also be noted that the oxy-
genation of water and its temperature, which is relatively
low, could discourage this process. However, the condi-
tions of the aquatic ecosystem in question will probably be
modified after the construction of the reservoir complex. In
this context, in the case that the release of potential
anthropogenic sources of carbon, nitrogen and phosphorus
nutrients continues or intensifies during construction of the
complex, the eutrophication process will probably be
favored in the constructed lentic system.
Comparison of nutrient concentrations
with the literature
Many studies have addressed the quality of sediments by
determining the concentration of nutrients; however, these
studies show different focuses. Thouvenot et al. (2007), for
example, emphasize the modeling of the dynamics of
nutrients at the sediment–water interface in rivers. Wang
et al. (2003a, b) have followed the same approach, but they
emphasize the dynamics of phosphorus instead. Moreover,
the speciation of phosphorus in lake sediments is also
discussed by researchers such as Zhou et al. (2001) and Bai
et al. (2009). Other authors have also studied the behavior
of this nutrient in estuarine sediments (Aviles et al. 2000;
Plagliosa et al. 2005; Marins et al. 2007).
Thus, it can be seen that there are many studies on the
dynamics of nutrients in sediments from various types of
ecosystems. Considering that these studies are quite het-
erogeneous and specific for each environment assessed and
that Brazil does not yet have a law on sediment quality,
comparing the results obtained for the Marrecas Stream
microbasin with the literature is quite difficult. Therefore,
the nutrient concentrations in sediments of the Marrecas
Stream were compared with levels reported for the bottom
sediments of the Joao Correa and Lino streams, and the
Barigui and Itajaı-Acu rivers (Table 4). These environ-
ments were chosen for comparison because they are also
located in southern Brazil, like the area studied in this
work. Additionally, all environments correspond to lotic
environments. Therefore, they may present similar physi-
cochemical and hydrodynamic characteristics.
The Joao Correa Stream is located in the municipality of
Sao Leopoldo (Rio Grande do Sul State, Brazil), a metro-
politan area of Porto Alegre. This stream receives domestic
and industrial effluents, discharges from the pipes of a
waste treatment plant, and part of the urban surface runoff
(Silva 2008). The Lino Stream microbasin, on the other
hand, is located in the municipality of Agudo (Rio Grande
do Sul State, Brazil) and is influenced by the production of
tobacco, which requires intensive soil tillage and the use of
fertilizers and pesticides (Pellegrini et al. 2008).
The Itajaı-Acu River is located in the municipality of
Blumenau (Santa Catarina State, Brazil) and receives
domestic, commercial and industrial wastewater with and
without treatment (Silva et al. 2010). The Barigui River is
located in the metropolitan region of Curitiba (Parana
State, Brazil); the basin area is affected by rural use and the
release of raw sewage in the most urbanized region
(Froehner and Martins 2008).
Comparing the TOC content of sediment from the
Marrecas Stream (21,470–86,584 mg kg-1) with the Lino
Stream (14,000–19,000 mg kg-1) and Barigui River
(5,141–32,359 mg kg-1), it can be seen that the sediments
of the Marrecas Stream are more enriched in this nutrient.
Such behavior may be because the Marrecas Stream is
located in an undeveloped region, with the presence of vast
riparian vegetation along the course of the stream where
the sediment samples were collected. Furthermore, the low
flow rate of the water body results in deposition of fine
material, which contributes to the accumulation of OM
and subsequent humification, a factor that hinders the
Table 3 Molar ratio between TOC and OP concentrations
Sediment
samples
1 2 3 4 5 6 7
TOC/OP
molar ratio
267.3 185.0 520.1 288.0 132.7 278.2 320.2
Table 4 Comparison of the results for TOC, TN and TP in different
bottom sediments and water bodies in Brazil
Sediment source TOC
(mg kg-1)
TN
(mg kg-1)
TP
(mg kg-1)
Marrecas Streama
(Rio Grande do Sul
State)
21,470–86,584 2,806–5,233 488–1,083
Joao Correa Streamb
(Rio Grande do Sul
State)
n.d. n.d. 58–1,077
Lino Streamc (Rio
Grande do Sul State)
14,000–19,000 n.d. 1,070–1,310
Itajaı-Acu Riverd
(Santa Catarina
State)
n.d. 350–2,100 62–378
Barigui Rivere
(Parana State)
5,141–32,359 363–1,779 362–1,586
n.d. not determineda This work, b Silva (2008), c Pellegrini et al. (2008), d Silva et al.
(2010), e Froehner and Martins (2008)
966 Environ Earth Sci (2013) 69:959–968
123
mineralization of organic carbon and facilitates its inter-
action with the sediment (Agemian 1997).
Regarding the results obtained for TN (2,806–5,233 mg
kg-1), the Marrecas Stream is also rich in this nutrient
compared to the Itajaı-Acu (350–2,100 mg kg-1) and
Barigui rivers (363–1,779 mg kg-1). In the Marrecas
Stream, it is probable that the ammonification and deni-
trification processes are more effective due to the low rates
of oxygenation in the sedimentary column. However, in
both rivers, it is suggested that nitrification is the nitrogen
cycling stage that is most facilitated by the hydrodynamic
conditions of these ecosystems, possibly due to greater
aeration. Thus, large amounts of nitrate may remain dis-
solved, not adding to the TN levels in the sedimentary
column (Esteves 1998).
Regarding the TP content, the lowest concentration
obtained for sediments of the Marrecas Stream
(488 mg kg-1) was greater than the lower concentrations
obtained for the Joao Correa Stream (58 mg kg-1) and the
Itajaı-Acu and Barigui rivers (62 and 362 mg kg-1,
respectively). The highest concentration obtained for the
sediments of the Marrecas Stream (1,083 mg kg-1) was
higher than the highest concentration of TP in the Joao
Correa Stream (1,077 mg kg-1) and Itajaı-Acu River
(378 mg kg-1). In contrast, the Barigui River showed a
maximum TP limit (1,586 mg kg-1) higher than that
obtained for the Marrecas Stream. Only the Lino Stream
showed both minimum and maximum concentrations
(1,070 and 1,310 mg kg-1, respectively) that were greater
than the limits obtained for the Marrecas Stream.
The high TP levels in the Marrecas Stream sediment
samples, compared to those of the Joao Correa Stream and
the Itajaı-Acu and Barigui rivers, may be due to the fact
that the Marrecas Stream is located in a region with
chemical, physicochemical and hydrodynamic character-
istics favoring the precipitation of phosphorus (with sub-
sequent accumulation in the sediment), such as the
presence of fine material (silt–clay) and OM, as well as Fe,
Al and Mn species (Esteves 1998). Finally, the high TP
concentrations reported for sediments of the Lino Stream
may be associated with agricultural influence on the
microbasin region, as shown previously.
Conclusions
The purpose of this preliminary study was to assess the
levels of TOC, NT, TP, IP and OP in sediments that were
collected from a southern Brazilian microbasin. The results
indicated that the physico-chemical properties of the
samples act directly on the concentration of the nutrients.
The OM can influence the TOC and TN nutrients while the
grain size, in turn, may interfere with the TN contents. The
metal species, on the other hand, can favor the increase of
IP concentrations in the sedimentary column.
Furthermore, a direct relation was observed of the TOC
and IP concentrations to the vast riparian vegetation pres-
ent in areas adjacent to the sampling points and to the
physico-chemical properties of the water and sedimentary
columns, respectively. Moreover, the results obtained for
TN suggest that its concentration possibly suffers inter-
ference from the temperature of the water and its oxy-
genation, in addition to other biological activities. On the
other hand, one cannot rule out human interference, mainly
in the levels of OP, possibly due to the inflow of domestic
sewage to the stream. Compared to some studies in liter-
ature, the Marrecas Stream microbasin showed high levels
of TOC, TN and TP, suggesting significant interference
from the vast riparian vegetation and possible inflow of
domestic sewage and waste from a poultry farm located
near the sampled region.
Acknowledgments The authors acknowledge the Conselho Nac-
ional de Desenvolvimento Cientıfico e Tecnologico (National Council
for Scientific and Technological Development—CNPq) for its
financial support and the Fundacao de Amparo a Pesquisa do Estado
do Rio Grande do Sul (Foundation for Research Support of the State
of Rio Grande do Sul—FAPERGS) for the scientific initiation
scholarship.
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