Anomalous Po River flood event effects on sediments and the water

CLIMATE RESEARCH
Clim Res
Vol. 31: 151–165, 2006
Published July 27
Anomalous Po River flood event effects on
sediments and the water column of the northwestern
Adriatic Sea
F. Frascari1, F. Spagnoli2,*, M. Marcaccio3, P. Giordano1
1
CNR-ISMAR, Sezione di Geologia Marina, Via Gobetti 101, 40129 Bologna, Italy
2
CNR-ISMAR, Sede di Ancona, Largo Fiera della Pesca 2, 60125 Ancona, Italy
3
ARPA Emilia Romagna, Via Triachini 17, 40138 Bologna, Italy
ABSTRACT: The aim of this study was to investigate the spreading pattern and trophic impact of the
anomalous Po River flood in the fall of 1994 in the marine area offshore of the Po River delta. The
study was carried out by surveying the areal distribution of physical and biogeochemical parameters
(pH, redox potential [Eh], water content, grain-size, mineralogy, organic and inorganic C, total N,
total organic and inorganic P) in surficial and sub-surficial sediments, and physical-chemical properties (salinity, temperature and dissolved O2) of the water column. Water column investigations highlighted a fresh, turbid and relatively cold Po River water wedge on the basin surface that extended
more than 40 km offshore, well above the usual limits of the Po River plume influence, which was a
result of slow geostrophic currents and no wave motion in the basin. The distribution of minerals in
sediments (such as serpentine and dolomite), derived from river catchments, provided cues on the
maximum extension of Po and northern river influences. Biogeochemical tracers such as organic C
and organic P, together with C:N ratios, provided indirect evidence on the development of algal
blooms owing to the Po River flood run-off. Indeed, they indicated areas where there was the deposition of autochthonous reactive organic matter, derived from fresh plankton biomass. Their location
suggests that the maximum development of plankton blooms occurred along the external edge of the
plume, where warm basin waters mixed with colder nutrient-rich waters from the river. The data also
suggest that significant amounts of newly formed and degrading organic matter reached bottom
waters at the centre of the basin, thus increasing the degree of hypoxia.
KEY WORDS: Adriatic Sea · Po River · Organic matter · Biogeochemical tracer · Algal bloom · Flood
Resale or republication not permitted without written consent of the publisher
To better understand how the spreading mechanisms
of Po River waters and their particulate load affect the
primary production dynamics in the northern Adriatic
Sea, it is important to improve our knowledge of dispersion mechanisms of Po River inputs into the early impact zones of the North Adriatic basin in various discharge regimes and under various seasonal conditions.
One of the main obstacles encountered when investigating the northwestern Adriatic Sea is the difficulty
of identifying, with in situ observations, the impact
zones and maximum expansion processes of Po River
inputs towards the centre of the basin during exceptional floods in different seasons. Usually such extreme
events cannot be foreseen, and thus marine surveys
cannot be planned a priori. For the same reasons it is
difficult to investigate how and where algal blooms
develop when such exceptional events occur, and with
what mechanisms and at what depths the settling
autochthonous organic matter degrades and consumes
oxygen in the water column, which eventually affects
early diagenesis on the bottom sediments (Berner
1980, Barbanti et al. 1992). Actually, the autochthonous
organic matter is particularly reactive and sensitive to
a partial mineralization already present in the water
*Corresponding author. Email: [email protected]
© Inter-Research 2006 · www.int-res.com
1. INTRODUCTION
152
Clim Res 31: 151–165, 2006
2. STUDY AREA
column, where it consumes dissolved oxygen. Furthermore, the organic matter, which is deposited together
The study area extends about 40 km offshore from
with fine inorganic particles on the bottom, feeds the
the Po River delta; it is delimited to the north by the
bacterial degradation processes that are first oxic
Adige River mouth, and to the south by the Reno River
and later anoxic (i.e. when degradation becomes more
mouth (Fig. 1).
intense or takes place at greater depths in the sediFrom a hydrodynamic point of view, the marine area
ments) (Froelich et al. 1979, Berner 1980, Orel et al.
in front of the Po River delta is characterised by
1993). In this manner, degradation processes consume
summer water column stratification, with weak geodissolved oxygen in bottom waters and cause the slow
strophic currents that form both counter-clockwise and
release of nutrients. Indirect indications of deposition
clockwise gyres, and an autumn-winter structure in
and degradation of organic matter, relative to a single
which the water column stratification disappears and a
event or averaged over seasonal, annual or multiannual periods, may be obtained from
bottom sediment studies. Bottom sediments record both the offshore dispersion of suspended river organic
and inorganic particulate and the deposition of autochthonous organic
materials. However, in order to be
able to discriminate single sedimentation or reworking processes, seabottom sediment investigations are
not enough; we need observations
that are less averaged out over time,
namely those that take place in the
water column.
From 8 to 21 November 1994, a survey cruise (PR94) was conducted
within the framework of the PRISMA
1 National Programme (Frascari et al.
1998). The initial purpose of the cruise
was the deployment of 3 automatic
oceanographic measurement stations,
but it happened to coincide with an
anomalous Po River flood. As a consequence, we tried to obtain functional
data to understand the processes
related to the Po River flood in the
marine area in front of the Po River
delta by using all available instruments on board. To this aim, we performed both water column chemicalphysical measurements and bottom
sediment samplings and analyses.
The scope of this work is to show the
sediment and water column processes
and their extension that took place in
the marine offshore area in front of
the Po River delta during the November 1994 flood event, as deduced from
the chemical-physical parameters of
the water column and from the bioFig. 1. Study area. Numbered dots: multiparametric (temperature, salinity and disgeochemical, mineralogical and sedi- solved oxygen) water column profiles and box-corer stations. Solid lines: tracks
mentological composition of bottom of multiparametric transects discussed in text (Transects A, B and C). Bathymetric
contour interval: 10 m
sediments.
Frascari et al.: Po River anomalous flood event
north-south geostrophic current, the stronger north
Adriatic current (N-Ad), occurs (Franco et al. 1982,
Malanotte-Rizzoli & Bergamasco 1983, Artegiani et al.
1989, Orlic et al. 1992). In this way, on a seasonal basis,
Po River inputs extend further offshore in summer,
whilst during winter they tend to be more confined
along the western coast of the basin. As a general
result the Po River inputs are conveyed almost entirely
southwards.
The bottom sediment grain-sizes in the investigated
area (Brambati et al. 1983) are the result both of the
general hydrodynamics of the northern Adriatic Sea
and of the geological evolution of the last 20 000 yr
(Colantoni et al. 1979b, Trincardi et al. 1994). Along
the coast there is a thin coastal belt of sandy sediments,
up to a depth of about 7 to 8 m, as a result of inputs of
coarse material from rivers and coastal wave reworking; this is followed offshore by pelitic sediments in a
belt along a north-south axis, deriving from suspended
material inputs both from the Po River (between 18 ×
106 t yr–1 [Dal Cin 1983] and 26 × 106 t yr–1 [IRSA 1977]),
and to a lesser extent from other minor rivers. Towards
the centre of the basin there is a gradual change to
mainly sandy relict sediments (Colantoni et al. 1979a).
Po particulate inputs are composed of rock fragments and minerals of heterogeneous origin with the
presence of mainly silico-clastic elements, whilst the
solid load transported by rivers north of the Po has a
largely carbonate composition (Guerzoni et. al. 1984).
The phytoplankton biomass and primary production
dynamics in the northern Adriatic Sea are characterised by a permanent high production, especially in
the coastal belt along the western coast (Fonda Umani
et al. 1992). The area with the higher production is
quantified off the Po River delta and related to the
spreading of its plume. In this area, a marked west-toeast gradient of the standing crop and production is
observed (Smodlaka & Revelante 1983). The phytoplankton standing crop in the northern Adriatic is
related to thermohaline distribution: during periods of
reduced vertical mixing and conspicuous river inputs,
the surface community presents a cell density that is 25
times the bottom layers, dominated by microflagellates
and diatoms; in contrast, when the Po River outflow is
particularly reduced, phytoplankton density is relatively homogeneous throughout the water column and
is always dominated by microflagellates and diatoms.
The South Po River delta coast is characterised by a 6
to 10 km belt of spring diatom blooms and dinoflagellate summer monospecific blooms (Marchetti 1983)
Generally, these blooms are linked to a highly stratified system that often reoccurs at the beginning and
end of the summer period, but in almost every summer
since 1975 they have given rise to red tide phenomena
(Fonda Umani et al. 1990).
153
3. MATERIALS AND METHODS
During the PR94 cruise (8 to 21 November 1994), in
order to study the unforeseen flood event that took
place at the Po River mouths between approximately 6
and 24 November, temperature, dissolved oxygen and
salinity profiles of the water column were measured
using a multiparametric probe (SBE 911 plus), and
sediment box-corers were collected to sample bottom
sediments. Stations were located in the main marine
impact zones of the Po River flood inputs, along transects perpendicular to the coast line, with a frequency
distance between stations of each transect of about 5
nautical miles near the Po River mouth and 12 nautical
miles at the farthest extent (Fig. 1). Unfortunately, it
was not possible to measure turbidity and chlorophyll a
profiles owing to the lack of necessary equipment on
board. The multiparametric profiles were conducted
within a few days in order to have a synoptic view of
the physical-chemical properties of the water column,
with the main aim of evaluating the persistence of
water column stratification in a season that is usually
marked by high hydrodynamics, with constant values
of temperature and salinity throughout the whole
water column (Hendershott & Rizzoli 1976, Franco
1983, Franco et al. 1983, Fonda Umani et al. 1990,
Artegiani et al. 1997).
As far as bottom investigations are concerned, it
should be pointed out that we decided not to sample
coastal sands; our main purpose was to evaluate the
extension mechanisms (in the direction of the open
sea) of suspended material coming from the Po River
during the flood, and to assess evidence on the bottom
of the autochthonous organic matter being deposited.
Sampling extended to zones further out to sea,
where relict sands outcrop (Brambati et al. 1983), to
evaluate the maximum extension of fine material
deposition during exceptional floods. Each sediment
box-corer was first described macroscopically to identify sedimentary structures, grain-size, bioturbation
and macrofauna presence. In particular, the thickness
of the recently deposited material, recognisable by the
high degree of hydration and ochre colour, were
recorded. Next, sub-samples were collected at 2 levels
(surficial and sub-surficial) in each box-corer. As far as
possible, the thickness of the surficial layer (0.5 to 1 cm
thick) was chosen inside the thickness of the recently
deposited material. The sub-surficial sample (about
2 cm thick) was collected immediately below the flood
layer. This sampling strategy was based on the different information that surficial and sub-surficial samples
can give. In fact, while surficial sediments provide
information on the last sedimentological event (on the
condition that sampling is carried out very soon after
the event and that other processes, such as currents or
154
Clim Res 31: 151–165, 2006
wave motion, did not rework the sediment), sub-surficial samples provide information on more sedimentological events, averaged over time, because of the different reworking processes that act on sediments.
Physical and chemical parameters (redox potential
[Eh] and pH) were measured in each sub-sample
immediately after the collection, and then each sample
was subdivided into aliquots for sedimentological,
mineralogical and geochemical analyses.
Water content, grain-size and mineralogical composition of sediment samples were determined on an
aliquot stored at 4°C. Organic C, total N, total, inorganic and organic P content analyses were performed
on an aliquot stored at –20°C and then freeze dried.
The water content was calculated as the difference
between the weight of the wet and dried sediment
samples; samples were dried at 70°C until they reach
a constant weight (Gallignani & Magagnoli 1972).
Grain-size analyses were conducted by wet sieving, in
order to separate the finest fractions (< 63 µm) from the
coarser fractions (> 63 µm), and then by X-ray sedigraphy on the finer fractions. Mineralogical composition
was determined through X-ray-diffrattometry, and
percentages of the most abundant minerals were
evaluated (Cook et al. 1975).
Total and organic C and total N (mainly organic N;
Giordani & Angiolini 1983) were determined by means
of a CHNS elemental analyser. Organic C was determined by decarbonisation with HCl 1 M and drying at
60°C for 2 h (Froelich 1980, Hedges & Stern 1984).
Inorganic P was determined on the extract of sediment samples that were stirred at room temperature
for 16 h with HCl 1 M (Aspila et al. 1976). Total P was
determined on the extract after burning to ashes at
550°C for 2 h and stirring for 16 h with HCl 1 M. Reactive phosphates in all extracts were determined using
colorimetric technique (Strikland & Parson 1972,
Griffiths 1973). The organic P content was calculated
as the difference between total and inorganic P.
finished about 24 November (2270 m3 s–1) (Fig. 2); the
maximum flood discharges, reached on 10 November,
was 8630 m3 s–1; and average flood flow was 5479 m3
s–1, which was considerably above the average of the
Po River’s discharge between 1917 and 1994 (1500 m3
s–1, Ufficio Idrologico e Mareografico pers. comm.) and
that of the average discharge for 1994 (1870 m3 s–1).
The flood brought into the sea 5.1 × 106 t of suspended
solids (equal to 48% of the annual amount), 3297 t of
total P (26%) and 27 600 t of N (25%) (Marchetti et
al. 1996).
In the survey period (8 to 21 November 1994), which
coincided with the arrival at the sea of the flood waters,
the weather-sea conditions of the northern Adriatic
Sea were characterised by generally low hydrodynamic with regard to both geostrophic current intensity and wave motion, as observed by other field investigations in the same period in the northwestern
Adriatic Sea (ELNA Project cruise; Hopkins et al. 1999,
Hopkins 2001).
The salinity, temperature and oxygen profiles measured in the water column allowed us to reconstruct
the state of the basin at the moment of the flood discharge. Salinity, temperature and oxygen data were
elaborated to obtain longitudinal transects located perpendicularly to the coastline, immediately to the south
of the Po River delta (Transect A, Fig. 3), in front of the
delta (Transect B, Fig. 4) and to the north (Transect C,
Fig. 5) and also surface and bottom distributions
of these parameters in front of the Po River delta
(Figs. 6 & 7).
The salinity and temperature transect just south of
the Po River delta (Transect A, Figs. 1 & 3a,b) highlights
a strong stratification of the water column, with a surface layer (thickness ~10 m) of colder and less saline
water, relative to underlying water. The temperature
and salinity values inside the upper layer increase
gradually both from the surface down towards the
lower layer and in a land-to-sea direction (Figs. 3a,b &
6a,b). This layer extends for over 40 km offshore in the
zone to the southeast of the Po River delta (Fig. 6a,b)
4. RESULTS
10
m3 s–1 (103)
The November 1994 Po River flood was caused by
intense rainfall in a zone to the southwest of the Po
River’s drainage basin, in Piedmont (northwest Italy).
In this region, precipitation reached values of between
50 and 175 mm in 24 h (Autorità di Bacino del Fiume Po
1994) between 5 and 6 November 1994. Such intense
rainfall caused a huge flood in the upper reaches of the
Po River that was slightly reduced when it arrived at
the sea mouths for normal discharges of tributaries into
the lower part of the Po River. The flood reached the
Po mouths 1 d after the rainfall began. The runoff into
the sea began around 6 November (2290 m3 s–1) and
Po River discharge
8
6
4
2
0
2 Nov
11 Nov
18 Nov
26 Nov
4 Dec
12 Dec
Days (1994)
Fig. 2. Po River flood runoff (5 to 25 November 1994) with
annual (dashed line) and 1917–94 means (solid line)
12
16
20
24
25B
25
24
23
22B
32
28
36 5
.
36
37.0
–10
37.5
0
A1
a
22A
Frascari et al.: Po River anomalous flood event
–20
Transect A
–30
Salinity
PSU
12 16 20 24 28 32 36 40
–40
b
0
12
14
1615
15
16
Depth (m)
–10
17
17
17
–20
17
Transect A
–30
Temperature
°C
12 13 14 15 16 17 18 19 20
–40
0
c
5
6
6
6
5
–10
4
5
–20
4
–30
Transect A
Oxygen
2
2
mg l–1
0 1 2 3 4 5 6 7 8 9 10
3
3
3
4
–40
Fig. 3. (a) Salinity, (b) temperature and (c) dissolved oxygen distribution along
Transect A
155
while it is confined to the coast, with
a less accentuated stratification in
zones in front of and immediately
north of the delta (Figs. 4a,b, 5a,b &
6a,b). This situation is similar to that
shown by Artegiani et al. (1997) for
the autumn season, and by Franco
(1983) with regard to the buoyancy of
river waters over basin water, but
with a major offshore extension of the
less salty water front owing to the exceptional character of the flood relative to the averaged data of Artegiani
et al. (1997). Moreover, the temperature transects show that in the
deeper and eastern zones, an additional layer near the bottom is
characterised by lower temperatures
(Figs. 3a, 4a & 5a). The deep colder
water layer is also visible in the
central part of the basin in the bottom temperature areal distribution
(Fig. 7a). Over the whole area, the
salinity between the intermediate
and deeper waters increases with a
more gradual and regular trend
than does variation in temperature
(Figs. 3a, 4a, 5a & 7a), reaching a
maximum in the eastern part of the
studied area and forming a deep
layer with both high salinity and low
temperature. The dissolved oxygen
distributions along the transects
(Figs. 3c, 4c & 5c) allow us to note an
oxygen-rich surface layer that extends as far as the external limits of
the flood plumes (Fig. 6c) and a bottom hypoxic layer that corresponds
to a north-south elongated area
extending to the external limits of
the flood plume (Fig. 7c). Both the
deep hypoxic layer and the welloxygenated surface layer tend to become thicker and more evident in the
frontal zones where the Po River
fresh waters mix with the saltier
waters of the basin (Figs. 3c, 4c & 5c).
The distribution of water content in
surficial sediments (Fig. 8a) shows 2
areas characterised by higher values.
The 2 areas correspond to the 2
mouths of Po di Goro and Po della
Pila. The first of these areas extends
south-southeast, whilst the second—
after initially moving towards the
16B
17
–20
5
37.
–30
Transect B
Salinity
–40
0
b
13
–10
16
–20
Depth (m)
Depth (m)
17
18
17
18
Transect B
Temperature
–20
17
°C
12 13 14 15 16 17 18 19 20
–40
0
12 13 14 15 16 17 18 19 20
c
Transect C
Temperature
18
°C
–40
0
16
17
–30
–30
Transect C
Salinity
PSU
PSU
–10
37.0
37.5
12 16 20 24 28 32 36 40
12 16 20 24 28 32 36 40
–40
0
7
36
0
37.
–20
b
6
–10
36.5
35.5 36
36.
5
5
35.
12
34.5
–10
–30
5
0
4
a
3
16BIS
15C
0
144
a
Clim Res 31: 151–165, 2006
15TRIS
156
6
c
5
–10
–10
5
–20
5
4
–20
5
4
43
3
–30
2
Transect B
Oxygen
–30
Transect C
Oxygen
mg l–1
mg l–1
0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10
–40
Fig. 4. (a) Salinity, (b) temperature and (c) dissolved oxygen
distribution along Transect B
–40
Fig. 5. (a) Salinity, (b) temperature and (c) dissolved oxygen
distribution along Transect C
157
Frascari et al.: Po River anomalous flood event
a 45° 45’
N
b
Salinity
surface data
Temperature
surface data
PSU
45° 30’
-20
Venezia
Chioggia
Adige
River
28
°C
Chioggia
Adige
River
Po di Goro
20
28
16
Po Pila
Po di Goro
24
44° 45’
13
14
-40
Reno
River
20
32
44° 30’
14
15
28
Ravenna
Ravenna
Cervia
Cervia
44° 15’
12°00’E
c 45° 45’
N
15
-40
24
Reno
River
0
0
32
15
-2
Po
River
Po Pila
20
19
18
17
16
15
14
13
12
-20
Venezia
36
45° 00’ Po
River
-2
Latitude
45° 15’
40
36
32
28
24
20
16
12
12°30’E
13°00’E
Longitude
Oxygen
surface data
Fig. 6. Surface (a) salinity, (b) temperature and (c) dissolved
oxygen distribution around the Po River delta
mg l–1
45° 30’
Chioggia
Adige
River
45° 00’ Po
River
54
5
4
0
-2
Latitude
45° 15’
8
7
6
5
4
3
2
1
-20
Venezia
Po Pila
44° 45’
5
5
Po di Goro
4
6
-40
Reno
River
5
44° 30’
Ravenna
6
7
Cervia
44° 15’
12° 00’ E
12° 30’ E
Longitude
13° 00’E
open sea—heads southeast. They mark the main dispersion path into the sea of the Po River fine sediment
inputs distributed from these 2 mouths; in fact, highly
hydrated sediments indicate fine particles that had
settled shortly before and were thus not greatly compacted. The thickness of this layer ranged from about
20 cm in the area near the Po River mouths to 1 or 2 cm
near the farther border of the study area. In the subsurficial sediments (Fig. 8b), the water content was
lower because of their older deposition and hence
higher compactness.
The grain-size fine-fraction distribution in the surficial sediments (Fig. 9) shows a prevalence of clay fractions (< 8 φ in the same areas in which highly hydrated
sediments deriving from the Po River were deposited.
The mineralogical analyses performed on surficial
and sub-surficial sediment samples confirm the presence of (1) a silico-clastic facies (Dinelli et al. 1997)
deriving from the Po River, in front of and south of the
Po River delta, and (2) a carbonate facies, deriving
from rivers further north. Serpentine and dolomite are
among the minerals that can be used as tracers of these
158
Clim Res 31: 151–165, 2006
a
45° 45’
N
b
Salinity
bottom data
Temperature
bottom data
PSU
45° 30’
42
40
36
32
28
24
20
16
12
10
-20
Chioggia
Adige
River
Po Pila
37.
2
8
36.
16
17
13
16 16
-40
-40
17
Reno
River
.6
37
44° 30’
Reno
River
17
Po di Goro
38
44° 45’
20
19
18
17
16
15
14
13
12
0
Po di Goro
Chioggia
Adige
River
Po
River
.6
37
0
Po Pila
°C
-20
Venezia
-2
45° 00’ Po
River
-2
Latitude
45° 15’
Venezia
18
.2
37
Ravenna
Ravenna
Cervia
44° 15’
Cervia
12°00’E
c 45° 45’
N
12°30’E
13°00’E
Longitude
Oxygen
bottom data
Fig. 7. Bottom (a) salinity, (b) temperature and (c) dissolved
oxygen distribution in the study area
mg l–1
45° 30’
45° 15’
Chioggia
2
3
0
-2
Latitude
Adige
River
45° 00’ Po
River
8
7
6
5
4
3
2
1
-20
Venezia
Po Pila
Po di Goro
2
4
2
3
44° 45’
3
Reno
River
2
44° 30’
3
Ravenna
Cervia
44° 15’
12° 00’ E
12° 30’ E
Longitude
13° 00’ E
-40
2 facies. The former prevails in the fine Po River inputs
and the latter in the particulate of rivers north of the
Po River (Nelson 1971, Dinelli et al. 1997, Tomadin &
Varani 1998). The serpentine distribution, in both surficial (Fig. 10a) and sub-surficial (Fig. 10b) sediments,
has higher concentrations in an area in front of and
south of the Po delta and in another area further offshore, to the southeast; in a northeasterly direction,
concentrations lower than those in the first 2 areas are
found in an intermediate north-south belt. In this belt
the dolomite concentration increases, marking the
southward transition zone of northern river sediments.
In the sub-surficial sediments, the serpentine distribution pattern shows that the belt with greater concentrations becomes more limited towards the coast, in front
of the delta mouths, whilst to the southeast it is almost
absent (Fig. 10b).
The distribution of organic C (which includes both
terrigenous and autochthonous organic matter) in surficial sediments (Fig. 11a) shows a high concentration
zone in the area in front of the delta, which extends
both northwards and southwards in the central areas
159
Frascari et al.: Po River anomalous flood event
a
b
ISMAR ñ MARINE GEOLOGY
0
10
45° 30’
N
20
30
40 km
ISMAR ñ MARINE GEOLOGY
0
10
40 km
Chioggia
Chioggia
Latitude
30
Venezia
Venezia
45° 00’
20
H2O (%)
-40
-40
44° 30’
60
60
50
50
40
40
Ravenna
30
30
Cervia
20
12° 00’ E
-10
Ravenna
20
-20
12° 30’ E
12°00’E
13° 00’E
Cervia
-10
12°30’E
-20
13°00’E
Longitude
Longitude
Fig. 8. Water content distribution in (a) surficial and (b) sub-surficial sediments around the Po River delta
ISMAR ñ MARINE GEOLOGY
0
10
45° 30’
N
20
30 40 km
Venezia
Latitude
Chioggia
45° 00’ CLAY (%)
-40
70
60
50
40
44° 30’
30
Ravenna
20
10
12° 00’ E
Cervia
-10
12° 30’ E
-20
13° 00’ E
Longitude
Fig. 9. Clay content distribution in surficial sediments around
the Po River delta
of the northern Adriatic basin. The highest concentrations are found in the most easterly and southerly zone
of the study area. In sub-surficial sediments, organic C
has the same distribution pattern but with less pronounced southward and northward lobes (Fig. 11b).
Furthermore, to distinguish the nature and origin of
the organic matter, the organic C:total N ratio was
considered: it indicates, for high values (> 9 to 10), a
continental origin or an advanced degradation of
organic matter, and, for low values (< 7 to 8), an
autochthonous marine organic matter with limited
degradation (Müller 1977, Müller & Mathesius 1999).
The C:N ratio presents a zone in surficial sediments
(Fig. 12a) with high values — representative of prevalently terrigenous organic matter — that is located in
front of the river mouths and is extended further
offshore than in sub-surficial sediments (Fig. 12b).
Low surficial sediment C:N ratio values are present in
areas far from the Po River mouths.
Organic P shows a different distribution between
surficial and sub-surficial sediment. In surficial sediment (Fig. 13a), the organic P presents 2 enrichment
areas: one in front of the Po River delta with a southeast protuberance, and another offshore, characterised
by a south-southwest extension of the limits of the
muddy deposits distributed from the Po River. The subsurficial sediments have their maxima in the areas to
160
Clim Res 31: 151–165, 2006
a
0
10
45°30’
N
Latitude
b
ISMAR ñ MARINE GEOLOGY
20
30 40 km
ISMAR ñ MARINE GEOLOGY
0
10
Venezia
45°00’
Chioggia
Chioggia
SERPENTINE
SERPENTINE
-40
-40
-4
3.0%
2.5%
2.5%
2.0%
2.0%
1.5%
1.5%
Ravenna
1.0%
Ravenna
1.0%
0.5%
Cervia
12°00’ E
30 40 km
Venezia
3.0%
44°30’
20
-10
0.5%
-20
12° 30’ E
13° 00’ E
-10
Cervia
12° 00’ E
-20
12° 30’ E
13° 00’ E
Longitude
Longitude
Fig. 10. Serpentine content distribution in (a) surficial and (b) sub-surficial sediments around the Po River delta
a
b
ISMAR ñ MARINE GEOLOGY
0
10
45°30’
N
20
0
30 40 km
Latitude
10
20
30 40 km
Venezia
Venezia
Chioggia
45°00’
ISMAR ñ MARINE GEOLOGY
Chioggia
ORGANIC C
ORGANIC C
1.5%
1.5%
-40
44°30’
-40
1.3%
1.3%
1.1%
1.1%
0.9%
0.9%
0.7%
0.7%
0.5%
Ravenna
0.3%
0.5%
0.1%
12°00’ E
Cervia
0.3%
-10
0.1%
-20
12° 30’ E
Longitude
13° 00’ E
12° 00’ E
Ravenna
-10
Cervia
12° 30’ E
-20
13° 00’ E
Longitude
Fig. 11. Organic C content distribution in (a) surficial and (b) sub-surficial sediments around the Po River delta
161
Frascari et al.: Po River anomalous flood event
a
b
ISMAR ñ MARINE GEOLOGY
0
10
45°30’
N
20
ISMAR ñ MARINE GEOLOGY
0
30 40 km
30 40 km
Chioggia
45°00’ C/N
C/N
-40
11
44°30’
20
Venezia
Venezia
Chioggia
Latitude
10
-40
11
10
10
9
9
8
8
7
7
6 Ravenna
6 Ravenna
5
5
Cervia
4
12°00’ E
-10
12° 30’ E
Cervia
4
-20
13° 00’ E
12° 00’ E
-10
-20
12° 30’ E
Longitude
13° 00’ E
Longitude
Fig. 12. C:N molar ratio distribution in (a) surficial and (b) sub-surficial sediments around the Po River delta
a
0
10
45°30’
N
Latitude
b
ISMAR ñ MARINE GEOLOGY
20
ISMAR ñ MARINE GEOLOGY
0
30 40 km
10
20
Venezia
Venezia
Chioggia
Chioggia
ORGANIC P
–1
45°00’ (µg g )
ORGANIC P
(µg g–1)
495
495
-40
445
44°30’
-40
445
395
395
345
345
295
295
245
245
195
195
145 Ravenna
145 Ravenna
95
95
45
12°00’ E
30 40 km
Cervia
-10
45
-20
12°30’ E
Longitude
13° 00’ E
12° 00’ E
Cervia
-10
-20
12° 30’ E
13° 00’ E
Longitude
Fig. 13. Organic P content distribution in (a) surficial and (b) sub-surficial sediments around the Po River delta
162
Clim Res 31: 151–165, 2006
Table 1. Mean values (range) of parameters analysed in surficial and sub-surficial sediments collected during the PR94
cruise
Parameter
H2O (%)
Silt (%)
Clay (%)
Serpentine (%)
Organic C (%)
C:N
Organic P (µg g–1)
Surficial
sediments
Sub-surficial
sediments
47.2 (23.3–64.7)
42.8 (25.9–60.3)
36.5 (5.9–87.1)
37.6 (4.6–80.9)0
32.4 (0–71.5) 0
32.3 (0–69)0000
1.02 (0–4)0000
1.07 (0–3)00000
0.85 (0.2–1.5)0
0.86 (0.2–1.7)00
8.02 (4.5–12.2)
8.34 (5.1–12.9)0
245.3 (67.5–757.0) 239.2 (83.3–666.4)
the south and offshore of the Po River delta (Fig. 13b).
These areas are located in the same areas where
organic C is also high. The maximum values of organic
P in surficial and sub-surficial sediment are mainly distributed along the edges of the various plumes visible
from the areal distribution of surface salinity and temperature (Fig. 6a,b).
Table 1 shows mean values and ranges, in the
surficial and sub-surficial sediments, of parameters
discussed in the text.
5. DISCUSSION
The surface water salinity is minimal near the Po
River mouths and becomes gradually higher offshore
for the continuous mixing of river and basin waters
(Fig. 6a).
The temperature transects (Figs. 3b, 4b & 5b) and
bottom temperature areal distribution (Fig. 7b) highlight a vertical stratification in the water column. The
stratification shows a division into 3 layers that are
very clear in Transect A (Fig. 3b): (1) the surface layer
presents cold waters coming from the Po River; (2) the
intermediate layer is characterized by the warmest
waters, which are still affected by the marine summer
warming; and (3) the deepest and eastern layer again
represents cold waters, corresponding to the dense
water of the central northern Adriatic Sea characterised by low temperature and high salinity (Franco et
al. 1982, Malanotte Rizzoli & Bergamasco 1983, Orel et
al. 1993), which had remained confined to the bottom
from the previous winter. The salinity and temperature
surface stratifications are consequences of the fresh
water from the Po River that floats offshore and
fans out over the basin waters, mainly eastwards and
southwards (Figs. 3, 4 & 6). The strong floating and the
spreading eastward and southward of the fresher and
colder river waters are consequences of the high speed
and quantity of the Po River runoff in a basin characterised by low hydrodynamics, with no geostrophic
currents and wave motion. In fact, the latter cause a
disruption of the water column stratification when they
become established in fall (Hendershott & Rizzoli 1976,
Franco 1983, Franco et al. 1983, Fonda Umani et al.
1990, Artegiani et al. 1997).
The dissolved oxygen concentration pattern could be
used as an indicator of depositional processes of
decomposing organic particulate, mainly from primary
production. In fact, the low oxygen concentrations in
the bottom waters are ascribed to oxygen consumption
by the microbic degradation of reactive organic matter.
These hypoxic conditions are more intense and extend
upwards in the zones where the Po River and basin
waters mix together (Figs. 3c & 4c). This is an indication that oxygen consumption is due mainly to the
degradation of newly formed organic material settling
on the bottom, the latter being generated by the surface algal blooms in the mixing zones of the Po River
nutrient-rich waters with the warmer basin waters.
This increase in surface primary production in the
frontal zones of the river plume is confirmed by an
increase in dissolved oxygen in the surface layer near
to the front zones (Figs. 3c & 4c).
The parameters measured in surficial sediments
allow us to obtain direct information on depositional
processes, as well as indirect observation and confirmation of the processes that took place in the water
column when the survey cruise was carried out and the
flood was underway. In contrast, the same parameters
measured in the sub-surficial sediments allow us to
deduce the processes that occurred in the study area,
averaged over time, before the flood occurred.
The muddy material of early deposition from the river
plume is very rich in water, because it is the result of
flocculation that occurs when fresh water mixes with
salt water (Olsen 1982). Generally, the flocculated material is deposited in the proximal part of the prodelta
area (Barbanti 1989). In our case, owing to the fact that
fresh river water was floating on salty basin water, the
fine and flocculated material contained in the floating
water was spread out to sea in directions of river water
distribution currents, and deposited all over the area
covered by the flood plume as more hydrated material.
Indeed, the water content distribution map of the surficial sediments (Fig. 8a) can be seen as traces of the
flood plumes of the Po della Pila and Po di Goro mouths,
which develop southward and south-southeastward.
The origin of these zones with high water content is
confirmed by the sub-surficial sediments, which are
less hydrated over the whole area, having not been influenced by recent floods. Furthermore, the elevated
thickness of the flood layer (between 20 cm near the Po
River mouths and 1 to 2 cm near the farther borders of
the study area) indicates a very high particulate load
coming out from the Po River during the flood event.
Frascari et al.: Po River anomalous flood event
These observations are also confirmed by the clay
and serpentine surficial distributions (Figs. 9 & 10a),
which show—while deposition is underway— a higher
offshore extension, which is unlike that under normal
conditions when higher geostrophic currents occur
and the fine Po River load is deposited near the coast.
The spatial irregularities of the serpentine surficial distribution and, in particular, the lobed northward extension, in coincidence with the northward protuberance
of clay and organic C (as traces of plume extension),
indicate the low strength of general circulation currents during the flood that allowed the formation of an
anti-cyclonic secondary gyre.
In contrast, the organic C distribution in the surficial
sediments (Fig. 11a) and its relationship with surficial
N concentrations (Fig. 12a) highlights algal bloom process formation that is not related to the flood plume
distribution pattern. The maximum organic C values,
concomitant with low C:N ratios encountered in the
zones most easterly and southerly of the Po River
prodelta, may be explained by the deposition of
organic matter of primary production. The production
of organic matter is fostered by the mixing of nutrientrich river waters with the warmer basin waters along
the plume front, as can be seen by the high oxygen
value distribution pattern; this mixing also favours the
depositional processes in the front zones due to the disappearance of the pycnocline, which maintains the
particulate in suspension (Franco et al. 1989). Depositional processes are also favoured in the frontal area
owing to the retarded intruding river currents, which
reach minimum velocities in this region.
The distribution of organic P in surficial sediments
(Fig. 13a) confirms the presence of newly formed
organic matter at the plume front. Furthermore, the
high organic P concentrations, coinciding with high
organic C contents and concomitant with low C:N
ratios in surficial sediments, are found in areas of low
bottom oxygen concentrations — namely where newly
produced degrading organic matter is settling. Organic
P and organic C are thus excellent tracers, not only for
identifying zones affected by the flood plume but also
for defining the areal limits of the plume itself and of
the main processes of primary production in fall. These
processes produce, in the presence of a stratified water
column, a general hypoxia or anoxia in the dense
bottom waters.
The distribution of the C:N ratio in surficial sediments (Fig. 12a) shows high values in a zone near the
river mouths, which extend southwards; these high
values indicate the zones subject to the deposition of
organic matter of continental origin, as a result of the
early deposition of coarser material.
In light of our findings deduced from the surface
sediment parameter distributions and the temperature
163
and salinity distributions in the water column, it is possible to reconstruct the depositional processes of the Po
River suspended particulate during the 1994 flood. The
difference in salinity between the surface layer and the
deeper basin waters, the high velocity of the river
water inputs (rich in suspended solids) and the low
hydrodynamics of the basin have favoured the buoyancy of the fresh river waters over the salty basin
waters that are spread out towards the central basin
areas. This has increased the surface transport of particulate coming from the river, which has deposited
along the plume dispersion axes and particularly at the
fronts where fresh water and salt water mix and where
the reducing current speed, the disappearance of the
pycnocline and the higher weight of the flocculated
material favour the settling of the particulate. In this
manner, only a small portion of the finer suspended
particulate of river origin has undergone a process of
early deposition that usually occurs just outside the
Po River mouths as a result of flocculation processes
initiated by the mixing of fresh and salt water.
6. CONCLUSION
It can be seen from the PR94 cruise data and also
from the literature (Hopkins et al. 1999, Hopkins 2001)
that the geostrophic north-south current, generally
present in this area, was very slow during the 1994
Po River flood and, therefore, that the typical cyclonic
autumn-winter Adriatic circulation had not yet set in.
This is deduced in particular from the strong temperature and salinity stratification shown in the landoffshore transects — in fact, the north Adriatic Sea
water column stratification is disrupted when the N-Ad
current is present (Hendershott & Rizzoli 1976, Franco
1983, Franco et al. 1983, Fonda Umani et al. 1990,
Artegiani et al. 1997). The fresh and cold waters coming from the Po River spread out offshore, floating
above the basin waters and undergoing subjacent and
frontal mixing processes at the pycnocline limit. The
main fresh water branch, coming out from the Po della
Pila (as deduced from sediment and water column
data), tends first to be distributed directly offshore, as
far as ~40 km from the coast, and then to split into 2
branches: the main branch proceeds southwards while
the less pronounced branch heads northwards. Waters
coming from mouths south of the Po della Pila are distributed southeastwards and south-southeastwards.
The low hydrodynamic of the basin together with the
high speed and high amount of Po River runoff favour
the large extension of the Po River plume into the
basin,
The Po River water distribution pattern in the basin
is confirmed by a comparison of the parameters mea-
164
Clim Res 31: 151–165, 2006
sured in the surficial and sub-surficial sediments. The
distribution of high values of water content, serpentine,
organic C and organic P in the surficial sediments
(compared to sub-surficial sediments) in areas extended
southeastwards and eastwards mark the fresh deposition of terrigenous particulate. In particular, the area
occupied by the main plumes and the frontal masses of
flood waters can be superimposed on the fine highly
hydrated surficial sediments.
The elevated thickness and extension of the freshly
deposited hydrated sediment shows that water coming
from the Po River during the flood must have been particularly rich in suspended particulate. Furthermore,
because of the considerable concentration of organic
matter (high organic C) with a low C:N ratio and high
organic P content, whose maxima were found in the
bottom sediments in areas at the frontal zones, it is
hypothesised that water coming from the Po River
flood was rich in nutrients. In these areas, the fresh and
cold nutrient-rich river waters mix on the surface with
the saltier and warmer basin waters, and this favours
the growth of algal blooms.
The formation of algal blooms in the surface waters
along the plume fronts, and their subsequent remineralisation within the water column through the pycnocline down to the bottom waters and the bottom sediments, is confirmed by the (1) gradually decreasing
dissolved oxygen concentration from bottom water
to the surface plume fronts, and (2) accumulation of
organic matter with low C:N ratio and high organic P
contents in the surface sediment of the area located at
the plume fronts.
The reduced oxygenation of the confined bottom
waters is increased by the fresh organic mater mineralization processes. The persistence of the stratification
of the water column after this event (Regione Emilia
Romagna 1994) has led to a generalised anoxia of the
bottom waters of the central Adriatic basin. The anoxia
of the bottom water was resolved only with the early
fall storms and with the onset of the general winter
Adriatic Sea circulation, which disrupted the water
column stratification.
In contrast, the lack of zones containing high concentrations of organic C, a low C:N ratio and high concentrations of organic P in the sub-surficial sediments indicate
that, in the medium term, the particulate that accumulates in front of the Po River delta is reworked and redistributed by the currents and wave motion in more extensive areas, especially to the south. In this way, the Po
River prodelta bottom sediments act as temporary reservoirs of autochthonous organic matter and inorganic
terrigenous particulate. These solid materials are then
redistributed to other parts of the basin located further
south, after degradation processes of the more reactive
organic matter had already partially taken place.
Acknowledgements. This work was conducted under the
PRISMA I Project program. We thank Dr. Cristina Bergamini
and Dr. Barbara Garrone for their field and laboratory support and for advice on interpretation, Vladimiro Landuzzi,
Gabriella Rovatti, Angelo Magagnoli and Maurizio Mengoli,
for their analyses, and Dr. Fabio Zaffagnini for help in
constructing figures. This paper is Contribution No. 1380 of
ISMAR, Sezione di Geologia Marina, CNR, Bologna, Italy.
LITERATURE CITED
Artegiani A, Azzolini R, Salusti E (1989) On the dense water
in the Adriatic Sea. Oceanologica Acta 12:151–160
Artegiani A, Bregant D, Paschini E, Pinardi N, Raicich F,
Russo A (1997) The Adriatic Sea general circulation. Part II:
baroclinic circulation structure. J Phys Ocean 27:97–114
Aspila KI, Agemian H, Chau ASY (1976) A semiautomated
method for the determination of inorganic, organic and
total phosphate in sediments. Analyst 101:187–197
Autorità di Bacino del Fiume Po (1994) Indicazioni per lo
sviluppo del piano di bacino conseguenti all’evento alluvionale del 4–6 Novembre 1994. Autorità di Bacino del
Fiume Po, Parma
Barbanti A (1989) Comportamento geochimico del fosforo e di
alcuni metalli pesanti in ambiente fluviale e marino:
indagini alla foce del fiume Po. PhD thesis, University of
Bologna and Modena
Barbanti A, Bergamini MC, Frascari F, Miserocchi S, Ratta M,
Rosso G (1992) Early diagenesis and nutrient benthic
fluxes in an area South of Po River Delta, Northern Adriatic Sea, Italy. Rapp Comm Int Mer Méditerr 33:321
Berner RA (1980) Early diagenesis: a theoretical approach.
Princeton University Press, Princeton, NJ
Brambati A, Ciabatti M, Fanzutti GP, Marabini F, Marocco R
(1983) A new sedimentological textural map of the Northern and Central Adriatic Sea. Boll Ocean Teor Appl 1:
267–271
Colantoni P, Gallignani P, Lenaz R (1979a) The sediments of
the Po river delta and the adjacent continental shelf. Rapp
Comm Int Mer Méditerr 25/26:127–128
Colantoni P, Gallignani P, Lenaz R (1979b) Late Pleistocene
and Holocene evolution of the north Adriatic continental
shelf Italy. Mar Geol 33:41–50
Cook HE, Johnson PD, Matti C, Zemmels I (1975) Methods of
sample preparation and X-ray diffraction data analysis.
X-ray mineralogy laboratory, University of California,
Riverside, Initial Report DSDP 28:999–1007
Dal Cin R (1983) I litorali dal delta del Po alle foci dell’Adige
e del Brenta: caratteri tessiturali e dispersione dei sedimenti, cause dell’arretramento e previsioni sull’evoluzione futura. Boll Soc Geol 102:9–56
Dinelli E, Frascari F, Marcaccio M, Matteucci G, Roffi C,
Spagnoli F (1997) Caratteristiche composizionali dei sedimenti del Mare Adriatico: alcuni risultati del progetto di
ricerca PRISMA I PLINIUS. Suppl Ital all’Eur J Mineral
18:99–101
Fonda Umani S, Franco P, Ghirardelli E, Malej A (1990) Outline
of oceanography and the plankton of the Adriatic Sea. In:
Colombo G, Ferrari I, Ceccherelli VU, Rossi R (eds) Marine
eutrophication and population dynamic. Proc 25th Eur Mar
Biol Symp. Olsen & Olsen, Fredensborg, p 347–366
Franco P (1983) L’Adriatico settentrionale: caratteri oceanografici e problemi. Atti V Congresso AIOL, Stresa, p 1–27
Franco P, Jeftic L, Malanotte Rizzoli P, Michelato A, Orlic M
(1982) Descriptive model of the Northern Adriatic. Oceanol Acta 5:379–389
Frascari et al.: Po River anomalous flood event
165
Franco P, Rabitti S, Cioce F (1989) Adriatico settentrionale
in condizioni di stratificazione. 2. Distribuzione del materiale sospeso e delle proprietà ottiche (1983–1984). Boll
Oceanol Teor Appl NS:77–87
Frascari F, Bergamini MC, Marcaccio M, Matteucci G (1998)
Relazione conclusiva. Sottoprogetto ‘Flussi da e verso i
fondali’ (PRISMA 1). ISMAR Tech Rep, Sezione di Geologia Marina, Bologna
Froelich PN (1980) Analysis of organic carbon in marine sediments. Limnol Oceanogr 25:242–248
Froelich PN, Klinkhammer GP, Bender M, Luedtke NA, Hartmann B, Mainard V (1979) Early oxidation of organic matter
in pelagic sediments of the eastern equatorial Atlantic: suboxis diagenesis. Geochim Cosmochim Acta 43:1075–1090
Gallignani P, Magagnoli A (1972) Metodologie e tecniche di
sedimentologia fisica. Rapp Tec No. 1, CNR Laboratorio
per la Geologia Marina, Bologna
Giordani P, Angiolini L (1983) Chemical parameters characterizing the sedimentary environment in a NW Adriatic
coastal area (Italy). Estuar Coast Shelf Sci 17:159–167
Griffiths EJ (1973) Environmental phosphorus handbook.
John Wiley & Sons, New York
Guerzoni S, Frignani M, Giordani P, Frascari F (1984) Heavy
metals in sediments from different environments of a
northern Adriatic Sea area, Italy. Environ Geol Water Sci
6:111–119
Hedges JI, Stern JK (1984) Carbon and nitrogen determinations of carbonate-containing solids. Limnol Oceanogr 29:
657–663
Hendershott MC, Rizzoli P (1976) The winter circulation of
the Adriatic Sea. Deep-Sea Res 23:353–370
Hopkins T (2001) Abiotic variabily and biocomplexity in the
northern Adriatic Sea, some research perspectives. Biol
Mar Med 8:39
Hopkins T, Artegiani A, Kinder A, Pariente R (1999) A discussion of the northern Adriatic circulation and flushing as
determined from the ELNA hydrography. In: Hopkins TS,
Artegiani A, Cauwet G, Degobbis D, Malej A (eds) The
Adriatic Sea, ecosystem research report No. 32. European
Commission, Brussels, p 85–107
IRSA (1977) Indagine sulla qualità delle acque del Po.
Quaderno 32. Istituto di Ricerca Sulle Acque, Milano
Malanotte Rizzoli P, Bergamasco A (1983) The dynamics of
the coastal region of the northern Adriatic Sea. J Phys
Oceanogr 13:1105–1130
Marchetti R (1983) Quadro di sintesi delle indagini svolte dal
1978 sul problema dell’eutrofizzazione nelle acque costiere
dell’Emilia Romagna. In: Eutrofizzazione dell’Adriatico.
Ricerche e Linee d’Intervento, Regione Emilia-Romagna,
Bologna, p 39–75
Marchetti R, Baraldi O, Crosa G, Garibaldi L, Varallo A (1996)
I carichi di fosforo e azoto del Po durante la piena del
novembre 1994. Acqua Aria 5:499–503
Müller PJ (1977) C/N ratios in Pacific deep-sea sediments:
effect of inorganic ammonium and organic nitrogen compounds sorbed by clays. Geochim Cosmochim Acta 41:
765–776
Müller A, Mathesius U (1999) The paleoenvironments of
coastal lagoons in the southern Baltic Sea, I. The application of sedimentary C org/N ratios as a source indicators
of organic matter. Palaeogeogr Palaeoclim 145:1–16
Nelson BW (1971) Mineralogical differentiation of sediments
dispersed from the Po Delta. In: Stanley DJ (ed) The
Mediterranean Sea: a natural sedimentation laboratory.
Dowden, Hutchinson & Ross, Stroudsbury, PA, p 441–453
Olsen CR, Cutshall NH, Larsen IL (1982) Pollutant-particle
association and dynamics in coastal marine environments:
a review. Mar Chem 11:501–533
Orel G, Aleffi F, Umani Fonda S (1993) Ipossie e anossie
di fondali marini. L’Alto Adriatico e il Golfo di Trieste.
Regione autonoma del Friuli Venezia Giulia, Trieste,
p 46–77
Orlic M, Gacic M, La Violette PE (1992) The currents and
circulation of the Adriatic Sea. Oceanol Acta 15:109–124
Regione Emilia Romagna (1994) Rapporto sullo stato di
eutrofizzazione delle acque costiere dell’Emilia Romagna
nel 1994. Assessorato Territorio, Programmazione e Ambiente. Servizio Promozione, Indirizzo e Controllo Ambientale U.O.O. DAPHNE II, Cesenatico
Smodlaka N, Revelante N (1983) The trends of phytoplankton
production in the Northern Adriatic Sea; A twelve year
survey. Rapp Comm Int Mer Mediterr 28:89–90
Strickland JDH, Parsons TR (1972) A practical handbook of
sea-water analysis. Fisheries Research Board Canada,
Ottawa
Tomadin L, Varani L (1998) Provenance and downstream
mineralogical evolution of the muds by the Po River
(Northern Italy). Miner Petrogr Acta 61:205–224
Trincardi F, Corregiari A, Roveri M (1994) Late Quaternary
trasgressive erosion and deposit in a modern epicontinental shelf: the Adriatic semienclosed basin. Geo-Mar Lett
14:41–51
Submitted: November 21, 2004; Accepted: March 20, 2006
Proofs received from author(s): July 11, 2006

Download Report