Pirates and Smugglers of all times (in the Ebro Delta)
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Biological portfolio 2- Activity 1
1. LOCATION AND GEOLOGICAL DESCRIPTION OF
THE DELTA OF THE RIVER EBRO
The delta of the
River Ebro is on the north-eastern coast of Spain, in the province of
Tarragona, in the Autonomous Community of Catalonia. It is the main coastal
delta on the Iberian peninsula and one of the largest in the
Mediterranean.
The Ebro delta was once considered a
micro-tidal delta dominated by the river regime and wave action (Galloway,
1975). Due to the loss in intensity of the influence of the River Ebro, the
role of the waves has increased and its development and morphology are now
dominated largely by wave action. Delta of the River Ebro has a coastal length
of approximately 50km.
(1) However, the interventions carried out have enabled the elimination
of man-made barriers impeding the natural development of the delta system;
reducing and regulating activities and uses causing its degradation and
stimulating natural processes supporting its recovering.
Geological mapping
of the delta shows that the delta plain is occupied by quaternary Holocene
sediments, deposited on a gravel base, largely made up of coarse and medium
sand, muddy clays and mud, and with an upper layer of medium and fine sand. The
subsidence of the area is estimated at
0.20cm/yr (ITGE, 1996).
2.
HISTORICAL EVOLUTION OF THE EBRO DELTA SHORELINE
3.
WHY IS THE EBRO DELTA RECEDING?
A.
The last
28km of the River Ebro run through the delta plain, showing notably different
characteristics to the ones it has upstream, where it has been considerably
altered during the second half of the 20th century. (2)These changes are
largely due to the construction and use of numerous dams throughout its basin,
particularly those at the River Ebro.
The River Ebro
basin is 97% regulated (Varela et al., 1986) and it is estimated that
nowadays it discharges less than 1% of what the river used to discharge at the
beginning of the 20th century. It is
basically a plain, not exceeding a height of 4 or 5m above sea level, with an
emerged surface extending over approximately 325km2 (Rodríguez, 1999), while the submerged surface
(prodelta) extends over approximately 2,172km2 (Serra,
1997). (3).Consequently, certain sections of the delta are
receding (Rodríguez, 1999).
4.
INTRUSION
OF SALT WATER IN THE EBRO DELTA
The reduction in flow encourages the
intrusion of a wedge of salt water that penetrates the river underneath the
fresh water. This salt wedge alters the capacity to transport solids and
reduces the depth of the layer of fresh water, making it more difficult for the
delta’s agricultural operations to use it.
5.
EROSION PROCES IN THE EBRO DELTA
There are various
factors with a direct impact on the erosion process in the Ebro delta.
Firstly, the
reduction in river flow and therefore in the sediments that arrive at the mouth
due, on one hand, to the regulation of the river by means of dams and, on the
other, to the diversion of the water for irrigation and water supplies. (4) This
reduction in flow also causes the salt water wedge to penetrate further and
further, affecting the river’s power to transport solids
Secondly, the
regulation of the river also weakens the flood regime, preventing the
contribution of sediments to the delta plain compensating for the subsidence of
the delta and the rise in sea level.
6. ERODING SITES
A.
The morphological
configuration of the Ebro Delta leads to the existence of areas that behave
differently in terms of coastal dynamics. (5) If
to this is added the effect of the dams and the fall in precipitation in the
Ebro’s drainage basin, as well as diversions of the course for irrigation, the
result is a considerable decrease in the transport of sediments.
. The longitudinal
transport system along the coast is responsible for the distinctive
configuration, with sedimentation and erosion effects.
Northern Hemi-delta
This is made up almost completely of
sand, which forms the beaches and dunes that run along the coastal fringe of
the Fangar spit and the beaches of La Marquesa and Pal (see aerial view in
Figure 2).
Southern Hemi-delta
The southern hemi-delta, situated on the south side of
the river mouth, is favoured by net sedimentation as a result of coastal
transport processes (see aerial view in Figure 3).
7. PREVENTION TASKS
The various actions
and objectives shown by the schemes mentioned above are summarised below:
- Construction of walkways on the dunes to prevent
deterioration and preserve the natural defence they provide against erosion
(example: Riumar, Pal, Marquesa and Fangar beaches).
- Regeneration of dunes, fixed with the help of
stakes and dune vegetation (example: Trabucador Bar).
- Removal of infrastructure located on the shore
that prevents the normal
development of the
coastal dynamic (example: La Marquesa and Pal Beaches).
- Organisation of uses in the coastal area which
involve actions ranging from the building of car parks, preventing the
dunes being used for this purpose (example:Marquesa and Fangar beaches),
to the compulsory purchase of agricultural land (rice fields) located on
the edge of the beach (Pal beach) and limiting wheeled vehicle traffic in
the dunes (example: Fangar bar) and the creation of new alternative beach
accesses and the conservation of nesting areas by staking them off.
- Putting up signs near areas of landscape,
environmental and cultural interest.
- Respect for the cultural values of the area
(examples: throughout the delta).
- Construction of landscape viewpoints that allow
the contemplation, study and control of the protected environment
(examples: Fangar, Riumar, mouth of the Mitjorn, La Marquesa beach, La
Alfacada lagoon, Los Eucaliptus beach – the last three at the plan stage).
- Experimenting with a new method of coastal
defence called the Beach Drainage System which encourages the deposition
of sand on the beach by installing drainage and a pumping system (example:
Riumar beach).
8. EFFECTS RELATED TO EROSION
B.
The
evaluation of the effects of interventions on the delta system can only be
attempted in the medium and long term because they have been aimed at
protecting and maintaining the beach, the dune ecosystems and the recovery of
natural environments, like the lagoons and banks of the River Ebro. (6) There are
beaches with a marked erosional nature and beaches whose tendency is accretion
The interventions planned in the area have
been characterised by minimising building activity within it, being directed
towards regulatory intervention policies that basically cover the organisation
of the land, affecting land use and the exploitation of the existing natural
resources. Direct effects on the delta ecosystems can be quantified from the
censuses of species colonising it and also from the growth of the surface area
of the delta affected by protective regulations. This is included as an area
that can be colonised by natural species living there and using the delta
seasonally for reproduction or as a transit area on migration.
9. INVADER SPECIES
A.
APPLE SNAIL
Hundreds of thousands of snails that grow to the size of a golf ball are not only taking over and eating the Ebro delta rice fields but also threaten to destroy the delta ecosystem. At the moment, the snails have taken over the rice fields on the left bank, occupying a third of the 32,000 hectares of Natural Park, and have begun to spread to the other side.
The economic
losses are not significant at the moment, but rice farmers fear serious
consequences in the medium term if not remedied soon.
The
ravages of Pomacea insularum, scientific name of the apple snail species
identified in the delta, were previously known only in countries of South
America and Asia. The snail is one of many invasive species located in the
final stretch of the Ebro and a Government report warns of the risk that
"Delta will become the gateway for invasive species of this kind in
Europe."
Most of the plague is concentrated in about 100 hectares of the Left Bank. The drying will occur mostly on this side, but is also likely to be implemented in about 900 hectares on the right bank. Last year 4,000 hectares were left without water for longer than usual, but the move did not deter the snails, which reproduce with extraordinary rapidity in the mouths of canals and irrigated fields. (7) Some endemics species of iberian barbels, genus Barbus in the Cyprinidae, having once been abundant especially in the Ebro river.
Most of the plague is concentrated in about 100 hectares of the Left Bank. The drying will occur mostly on this side, but is also likely to be implemented in about 900 hectares on the right bank. Last year 4,000 hectares were left without water for longer than usual, but the move did not deter the snails, which reproduce with extraordinary rapidity in the mouths of canals and irrigated fields. (7) Some endemics species of iberian barbels, genus Barbus in the Cyprinidae, having once been abundant especially in the Ebro river.
Another
measure is to change the field drains, because the snails find the best living
conditions in them. The measure will affect about 3,500 farmers and 6,000
plots. The farmers are required to install in each of them a new underground
pipe with a PVC elbow to impede the progress of the mollusc.
B. WELS CATFISH
The wels catfish
(Silurus glanis) is a fresh-watercatfish recognizable by its broad, flat head
and wide mouth. The mouth contains lines of numerous small teeth, two long
barbels on the upper jaw and four shorter barbels on the lower jaw. It has a
long anal fin that extends to the caudal fin, and a small sharp dorsal fin
positioned relatively far forward. It uses its sharp pectoral fins to capture
prey: with these fins, it creates an eddy to disorient its victim, which it
then simply engulfs in its enormous throat. It has very slippery green-brown
skin. Its belly is pale yellow or white. Wels catfish live at least thirty
years and have very good hearing .
The female
produces up to 30,000 eggs per kilogram of body weight. The male guards the
nest until the brood hatches, which, depending on water temperature, can last
from three to ten days.
The wels
catfish lives on annelid worms, gastropod, insects, crustaceans, and fish; the
larger ones also eat frogs, mice, rats and aquatic birds like ducks.
The wels catfish lives in large, warm lakes and deep,
slow-flowing rivers. It prefers to remain sheltered in places such as holes in
the riverbed, sunken trees, etc. It consumes its food in the open water or on
the bottom, where it can be recognized by its superior mouth. Wels catfish are
food fish and are also kept in fish ponds. Most wels catfish are only about
1.30 to 1.60 meters long; fish longer than 2 meters are normally extremely rare.
(8) Only under exceptionally good living circumstances can the wels catfish
reach lengths of more than two meters.
This giant
was surpassed by some even larger specimens from France, Spain (in the River
Ebro), Italy (in River Po), and Greece, where this fish was released a few
decades ago. It grows very well at that location thanks to the mild climate,
lack of competition, and good food supply.
Since its introduction in the reservoir Mequinenza in
1974 - has spread to other parts of the Ebro basin over Ebro and its
tributaries, especially river Segre. (9) In order to halt their advance and destroy them, the
farmers have applied the drastic measure of leaving 9,500 hectares of paddy
fields dry for six months instead of the usual three.
Competition and predation by wels catfis has caused
its complete disappearance in the middle channel Ebro around 1990. The ecology
of the river also, has now a major development in the amount of aquatic
vegetation, seaweed and algae. Barbel species from mountain stream tributary of
the Ebro that wels catfis has not colonized, were not affected.
C. AMERICAN CRAYFISH
The American crayfish , Procambarus clarkii,
is called cranc americà in catalan. It is an invasive species in the Ebro delta
and many other wetlands in Europe. Originally introduced for food
it quickly escaped and has out competed the native species and carrys a fungus
which kills the native species.
There are concerns about the ecological impact of
introduction of foreign species that is almost always a burden, affecting much
of the original ecosystem
introduced species rapidly caused the extinction of numerous indigenous species. The introduction of
American crayfish has resulted in economic losses, introduced elsewhere for
cultivation, its success is attributable to its ability to colonise disturbed
habitats that would be unsuitable for the edible iberian crayfish.
.
Biological portfolio 2- Activity 2
2. Use all this information to make a Piktochart
Presentation about the topic : “BIOLOGICAL PROBLEMS OF DELTA
DEL EBRO : EROSION , INTRUSION OF SALT AND INVADER SPECIES”. You
have to talk about all the points explained, make special attention
to the real situation of Delta nowadays, and what we can expect in a
future.
Biological Portfolio 2 - Activity 3
Complete the fig. 2 and fig.3 adding the name of the principal lagoons of Ebro Delta.
Biological Portfolio 2 - Activity 5
Explain the meaning of subsidence,
ecosystem and extinction
.
Subsidence: The gradual caving in or sinking of an area of land
Ecosystem: Biological community of organisms and their physical
environment.
Extinction: Disappearance of a species.
Biological Portfolio 2 - Activity 6
Reasons
of recesion of Delta del Ebro.
The reduction of the river flow
and, therefore, in the sediments that arrive at the mouth due, on one hand, to
the regulation of the river by means of dams and, on the other, to the
diversion of the water for irrigation and water supplies.
The regulation of the river also weakens the
flood regime, preventing the contribution of sediments to the delta plain
compensating for the subsidence of the delta and the rise in sea level.
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