The fluctuation of dissolved and particulate trace metals in a small,
enclosed, and shallow bay
M. LADAKIS, M. DASSENAKIS AND C. BELIAS
University of Athens, Faculty of Chemistry, Laboratory of Environmental Chemistry
Panepistimioupolis 157 71 Athens, GREECE
Abstract
The small, isolated and shallow bays of the Greek coastline differ significantly from the open sea in the degree
of eutrophication, the fluctuation of hydrological parameters and the concentration of pollutants, like trace
metals. Those characteristics can create interesting environmental conditions that may affect trace metals’
behaviour and accumulation to algal mats or to surface sediments.
The variations of dissolved and particulate forms of Al, Cd, Cu, Fe, Mn, Ni, Pb and Zn along with the
variations of pH, salinity, water temperature and eutrophication degree at a bay near to Athens, are studied in
this paper.
Monthly water samplings and in situ measurements for pH, salinity and temperature were carried out for a
period of one year (July 2000 – June 2001) at two points inside and one outside the under study bay.
The results of the various determinations showed that the waters inside the bay are more eutrophicated
compared to the open sea, whereas there is no significant difference in the pH, temperature and salinity.
The heavy metals’ concentrations of the bay’s water (in both dissolved and particulate form) are directly
affected by the exterior marine environment and by freshwater incomes. The determined metal concentrations
into the cove are rather favourable than obstructive for the phytoplankton growth. This conclusion in
combination with the absence of a limiting factor for the primary production create a favourable environment
for the development of a layer of algae mat that extends through the bottom of the bay.
Key-Words: Isolated bays, Algal mat, Particulate metals, Dissolved metals
1 Introduction
The Greek coastline, with a total length of about
15,000 Km, has a remarkable variability. There are
a lot of small, enclosed and shallow bays, which
differ from the open sea in the degree of
eutrophication, the rate of water renewal, the
fluctuation of temperature and the concentration of
pollutants like trace metals.
Fig 1
The area under research is a closed bay at Anavissos
on the coast of Saronikos Gulf, 50 Km away from
Athens, with an area of about 20,000 square meters
(Figure 1). A line of beachrocks shuts the bay’s
muzzle, obstructing the water’s renewal. A
remarkable reciprocation of the cove’s waters due to
the wind is also recorded. The south winds create a
flood and the north ones a withdrawal of the cove’s
waters. The outside of the cove is used as an
anchorage for small fishery and recreation crafts. At
the shallow bottom of the cove (max. depth of about
0.6 meters) there is a layer of green algae with a
thickness of 0.2–2 mm, which extends through the
bottom of the bay. No significant pollutant sources
were detected.
The renewal of the under study cove’s water is
partly obstructed by a line of beachrocks that shuts
its muzzle. On the other hand, freshwater enters
occasionally from the mainland into the cove.
Additionally, the mass of its water is small, due to
the shallowness of the bottom, resulting in a
significantly high rate of temperature fluctuation.
2 Problem Formulation
Coastal areas like the ones described above,
although small, can have specific interest because
the conditions prevailing there differ from the
neighbouring ones.
In
those
environments,
the
values
of
physicochemical as well as the concentration of
chemical parameters (i.e nutrients, metals, pigments,
pollutants, e.t.c) are expected to differ in values and
temporal fluctuation in comparison to the ones of
the adjusted coastal areas. In addition, such
environments seem to encourage the development of
algal mat on the surface of the bottom.
On the other hand, the external marine
environment’s influence to the metals concentration
at the bay’s water is expected to be considerable.
This study deals with the variations of dissolved and
particulate metals together with the variations of pH,
salinity, water-temperature and eutrophication
degree at the bay’s water.
The Flame and Graphite Furnace Atomic
Absorption Spectrometry were used for the
determination of both particulate and dissolved
forms of Al, Cd, Cu, Fe, Mn, Ni, Pb and Zn.
3 Results and Discussion
3.1 Physicochemical parameters
The variation of the pH was between 7.97 and 8.27
at all sampling points. No remarkable difference in
values between the interior and the exterior side of
the studied area was noted. The seasonal fluctuation
of pH in all 3 sampling points was similar.
Salinity ranged between 34.5 and 39.8 in the cove
(points A and B) and between 35.5 and 38.4 in the
external point (point C), with the exception of one
case (March 2001), where salinity was very low in
both points A and B inside the cove (18.2 and 22.2
respectively). This was probably due to freshwater
income at this time. Nevertheless, the values of
salinity (represented in figure 2) indicate that there
is no permanent freshwater income into the cove.
2.1 Materials, Methods and apparatus
Salinity
40,00
35,00
30,00
S
Monthly water samplings and in situ measurements
of pH, salinity and temperature were carried out for
a period of one year (July 2000 – June 2001) at two
points inside the cove, named point A and point B.
At the same time, similar measurements and
samplings were taken from a point outside the bay,
to be used as a reference, named point C.
The physicochemical parameters (pH, salinity and
temperature) were measured by the use of a portable
salinometer which was calibrated with a pH buffer
solution before every measurement.
The water samples for nutrient analysis were
collected in plastic bottles (pre-treated overnight
with 1N HCl solution) and stored in –18oC until the
time of analysis. Standard spectrophotometric
methods [1] were used for the determination of
nutrients by the use of a Carry-100 double beam
spectophotometer.
The water samples for metal analysis (volume of 2 l
each) were collected in glass bottles (pre-treated
overnight with 2N HNO3) and conserved until the
time of analysis by adding a few drops of
concentrated HNO3.
The samples were filtered through pre-weighted
nitrocellulose filters (Milipore 0.45 μm) in order to
separate the particulate from the dissolved form of
metals. The filters were treated with 40ml 1:1 HNO3
in teflon bakers and after their complete dissolution,
the volume was adjusted to exactly 50 ml.
The dissolved metals were pre-concentrated by
passing the sample through Chelex 100 resin [2] and
eluting them by 50 ml nitric acid 2N.).
25,00
20,00
15,00
point A
point B
point C
Jun- Jul- Aug- Sep- Oct- Nov- Dec- Jan- Feb- Mar- Apr- May- Jun00 00
00 00 00
00 00 01
01 01
01
01 01
months
Fig 2
The water temperature varied between 14.7 (in
January) and 33.2oC (in July) inside, and between
14.6 and 26.8oC outside the cove, respectively.
During the summer, the water was warmer inside
the cove than outside.
3.2 Eutrophication degree
The Karidis et al. criteria [3] have been applied to
the nutrient concentration values in order to
characterize the area’s eutrophication degree.
The annual min, mean and max values of the area’s
nutrient concentration are presented in table 1.
Table 1. Nutrients concentration (mean values in
parenthesis – all values in μgion/l)
Inside the bay
Outside the bay
[NO3]
0.62 - 2.27 (1.27)
0.58 - 1.82 (1.16)
[NO2]
0.04 - 0.13 (0.06)
0.01 - 0.07 (0.04)
[NH4]
0.14 - 1.75 (0.69)
0.02 - 1.47 (0.63)
[PO4]
0.03 - 0.48 (0.14)
0.02 - 0.26 (0.13)
According to those criteria, the water inside the bay
was in the Upper Mesotrophic level during 8 of the
12 months of the period, while Lower Mesotrophic
level characterize the water outside the bay during 8
of the 12 months of the period. No nutrient limiting
factor for the phytoplankton growth was found
according to the Justic et al (1995) criteria [4],
except for the months October and November,
where Phosphorus was the limiting factor.
the fluctuation of particulate Cd and Ni in the cove’s
water, as shown in figures 3 and 4:
3.3 Dissolved and particulate metals
The studied metals were separated in three groups:
a) Pollutants (which include Cd, Ni and Pb),
b) Biologically importants (which include Cu, Mn,
Fe and Zn) and
c) Metals derived from geological sources (which
include Al and Fe).
a) The pollutants
The dissolved forms of Cd ranged between 0.08 and
0.59 μg/l inside the cove and between 0.01 and 0.59
μg/l outside. The mean annual values were 0.32 and
0.28 μg/l respectively. A fair correlation in the
fluctuation of dissolved Cd inside and outside the
cove (r = 0.71 for p < 0.05, statistically important
according to the t-test), was detected.
Particulate Cd (figure 3) was found to be even
lower, as annual mean values were 0.12 and 0.08
μg/l inside and outside the cove respectively. On the
other hand, a significantly high value (0.75 μg/l)
was recorded during July 2000. Nevertheless, the
values of both dissolved and particulate forms of Cd
are low for coastal waters.
The values of dissolved Ni inside the cove were
found to be less than 1.55 μg/l, with the exception of
two cases (July 2000 and April 2001 with values of
2.39 and 3.63 μg/l respectively). The mean value
outside the cove was 0.95 μg/l.
Fig 3
The particulate Ni was recorded at the same levels
with the dissolved one, both inside and outside the
cove, with the exception of July 2000, when a
significantly high value (12.9 μg/l) was recorded in
the cove’s water. In general, there is a similarity in
Fig 4
The dissolved form of Pb ranged between 1.45 and
10.59 μg/l inside the cove and between 0.37 and
6.51 μg/l outside. The highest values were recorded
during the hottest period of the year with the
exception of August.
Fig 5
Fig 6
A good correlation in the fluctuation of dissolved Pb
inside and outside the cove (r = 0.88, statistically
important according to the t-test) was also detected,
as shown in figure 5. A rather random fluctuation
was detected for particulate Pb, as it is indicated by
figure 6.
In general, the cove’s water is enriched with Pb
when compared with the water outside.
b) The biologically importants
The fluctuation of the dissolved Cu both inside and
outside the cove is presented in figure 7.
Fig 7
A slight increase of its concentration is observed
during the hot period of the year. The relatively high
value that was recorded outside the cove in October
2000 (10.3 μg/l) was accompanied by a respectively
high value inside the cove (4.64 μg/l). The
concentration of the particulate Cu was less than 1
μg/l both inside and outside the cove.
The concentrations of dissolved Zn ranged between
0.6 and 8.6 μg/l both inside and outside the cove. A
remarkable similarity in the monthly fluctuation of
Zn inside and outside the cove was recorded (r =
0.71, statistically important according to the t-test).
As extracted from figure 8, the dissolved Zn
concentration increases during the hottest period of
the year and decreases during winter.
Fig 9
c) Metals originated from geological sources
The abundance of particulate Al in coastal waters is
well known, as it usually originates from the
corrosion of argillaceous minerals. As extracted
from figure 10, the fluctuation of particulate Al is
random and the concentration inside the cove is
higher than prevailing in the outside water.
Fig 10
A strong correlation between particulate Al and Fe
was observed inside the cove (r = 0.94 for p < 0.05),
as shown in figure 11, indicating the mineral origin
of Fe in the cove’s water.
Fig 8
The concentration of particulate Zn was found to be
lower than 2.5 μg/l in most cases and a slight
increasing trend during the hot period of the year
was noted (figure 9). A peak of particulate Zn was
observed during March 2001 in the waters outside
the cove and was reflected in the interior waters.
The water inside the cove was found to be enriched
in dissolved Mn, but, on the other hand, a fair
correlation of its monthly fluctuation between those
two water masses occurred (r = 0.76 for p < 0.05,
statistically important according to the t-test).
A strong correlation between particulate Mn and Fe
was observed both inside and outside the cove (r =
0.91 and 0.95 respectively for p < 0.05).
Fig 11
The dissolved metals’ concentration of the under
study area is much higher, compared to the values
prevailing in various areas of the open Saronikos
gulf [8], as extracted from table 2. The specific
morphological characteristics and the coastal
character of this area, contribute to elevated values
of dissolved metals’ concentration.
Table 2. Concentration of dissolved metals at the
open Saronikos gulf (values in μg/l).
Area
Cd Cu Μn Νi Pb Ζn
W. Saronikos gulf 0.05 0.16 0.20 0.33 1.13 3.14
S. Saronikos gulf 0.02 0.09 0.12 0.25 0.11 1.29
E. Saronikos gulf 0.05 0.13 0.16 0.29 0.35 2.53
Points A & B
Point C
0.32 3.13 3.75 1.31 4.71 4.23
0.28 2.80 1.19 1.48 2.85 4.21
4 Conclusions
The small and semi-isolated marine ecosystems
have special characteristics when compared with
other coastal areas. They present a high degree of
complexity and sensitivity in physical perturbations
and
human
pollution.
Various
coastal
microenvironments, such as the Vouliagmeni lake in
the peninsula of Attica and the Agios Nikolaos lake
in east Crete, have also been studied [5,6]. The
common
result
extracted
is
that
each
microenviromnent has its own characteristics.
The general results for the studied small gulf are:
The salinity decreases occasionally, due to
freshwater incomes from the mainland.
The metal concentration of the cove’s waters (in
both dissolved and particulate form) is directly
affected from the exterior marine environment.
A good correlation in the fluctuation of some metals
concentration inside and outside the cove occurs
(dissolved Zn, Pb, Mn and Fe as well as particulate
Zn).
Surcharge events outside the cove reflect directly at
a respective high concentration in the internal waters
(dissolved Cu in October 2000, dissolved Zn in
April 2001, particulate Zn in March 2001,
particulate Al in September 2000).
The determined metal concentrations into the cove
are more favourable than obstructive for the
phytoplankton growth as extracted from table 3.
Table 3. Normal, favourable and restrictive
concentration of some dissolved metals for the
phytoplankton growth [7].
Concentration of metals (μg/l)
Normally at the
favorable
restrictive
open sea
[Al]
1,500-2,000
[Cd]
0.11
[Cu]
2
6 - 200
[Fe]
3.4
0.006 - 10
[Mn]
1.9
0.05 - 50
[Ni]
2
[Pb]
0.03
[Zn]
2
6.5
500-5,000
This conclusion, in combination with the upper
mesotrophic level of the cove’s water, its
shallowness (up to 0.6 m), the high level of sunlight,
the fluctuation of the water’s temperature -that is
maintained between 14.7 and 33.2 oC during the
year- and the absence of a limiting factor for the
primary production (photosynthesis) create a
favourable environment for the layer of algae mat
development. This mat covers the whole surface of
the cove’s bottom and reaches to the upper point of
the flood.
References:
1. K. Grasshoff, and K. Kremlin: Methods of
Seawater Analysis, III edition, Wiley-VCH
Torondo 1997, pp 159 – 226
2. Riley, J.P. and Taylor, D. (1968). Chelating resins
for the concentration of trace elements from
seawater and their analytical use in conjunction
with A.A.S. Anal. Chemical Acta, 40, 479 – 484.
3. M.Karidis, L. Ignadiades, A Mouriki, G.Tsirtsis
and D. Kitsiou: Quantitative assessment of
eutrophication: Criteria development for the
management of coastal waters (1988)
4. D.Justic, N.N. Rabalais and R.E. Turner
Stoichiometric nutrient balance and origin of
eutrophication. Marine Pollution Bulletin 30(1)
(1995), pp 41 – 46.
5. M.Scoullos, A.Pavlidou, M.Dassenakis, P.Beza,
Environmental studies in a complex brakish
system: The Bouliagmeni lake, Greece,
International Conference on Restoration and
Protection of the Environment III, Chania, August
1996, Proc.pp.149-157
6. N.Michopoulos, M.Dassenakis, G.Anastasakis,
M.Scoullos, Physical and chemical characteristics
of a Mediterranean coastal microenvironment, the
salty lake of Agios Nikolaos, Crete, Greece. Global
Nest: the International Journal. Vol 2, No 2, pp
167-178, 2000.
7. Skinner B.J., and Turekian K.K., (1973), Man and
the Ocean, Prentice-Hall, Englewood Cliffs, New
Jersey.
8. Med-Pol project for the monitoring of Saronicos
gulf. Dissolved metals’ concentration data for the
year 2000.