European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
SESSION 2
50
Poster Presentation
European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
COMPARATIVE ECOPHYSIOLOGICAL STUDY OF THE EFFECT OF
FLOODING ON THREE SALT MARSH PLANT SPECIES GROWING IN
NATURAL AND ARTIFICIAL ENVIRONMENTS
R. Samson, L. Lambregts, S. Camerlynck, R. Lemeur
Laboratory of Plant Ecology, Ghent University, Coupure Links 653, 9000 Gent, Belgium
(roeland.smson@rug.ac.be)
A CONTRIBUTION FROM THE ELOISE PROJECT: ISLED
The effect of a sea level rise on salt marsh vegetation was studied on three test
species : Spartina anglica, Aster tripolium and Triglochin maritima.
The effect of flooding was studied in the greenhouse, and on three different field
sites in the estuary of the river Scheldt with a different distance to the mouth of the
river. In the greenhouse flooding of the plants resulted in an increase in length growth
and biomass of A. tripolium and T maritima (Lambregts et al. 1999), whereas in the
field the reverse was observed. In the greenhouse flooding increased also specific leaf
area, shoot/root ratio and leaf water content.
Comparing the different salt marshes, it was concluded that both flooding and salt
had a negative effect on length growth of T. maritima and A. tripolium, and it was
shown that the decrease in length growth in non-flooded conditions in the greenhouse
was due to the accumulation of salt.
As well in the greenhouse as in the field net photosynthesis rate was highest for S.
anglica, due to the C4-metabolism of this species, whereas the other two studied species
have a C3-metabolism. Maximal photosynthesis in the greenhouse was lower than in the
field.
Because maximal photosynthesis increased further from the river border (Table 1),
and by comparing the different salt marshes, it was concluded that salt stress had a
higher impact on photosynthesis and biomass production than flooding.
SESSION 2
51
Poster Presentation
European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
Table 1 Light saturated photosynthesis rate (Amax, µmol CO2 m-2 s-1), dark respiration (Rd,
µmol CO2 m-2 s-1), light compensation point (Ic, µmol photons m-2 s-1) and quantum efficiency
(, mol CO2 mol-1 photons) of two salt marsh species growing close to (1) and more distant
from the water line (2) in the salt marshes of Ritthem (R)(close to the mouth of the river) and
Waarde (W)(further away from the mouth of the river); significant differences (Duncan, p<0.05)
are indicated with the superscripts a, b, c and d.
Amax
Aster tripolium
Ic

W 1
14.2  1.9
-1.17  0.53ab
17  6ab
0.068  0.017bcd
2
15.4  2.9
-0.85  0.31b
11  4a
0.079  0.003d
1
12.1  3.0
-1.03  0.20b
16  3ab
0.065  0.017bcd
2
13.2  3.5
-0.97  0.14b
23  11ab
0.049  0.024abc
W 1
21.7  3.7
-1.79  0.47a
25  5ab
0.072  0.016cd
2
12.7  8.3
-0.65  0.46b
18  17ab
0.042  0.014ab
1
20.6  7.6
-1.32  0.36ab
32  15b
0.044  0.010abc
2
22.3  8.5
-0.60  0.20b
18  5ab
0.033  0.003a
R
Spartina anglica
Rd
R
It can be concluded that it was difficult to compare observations, conducted in the
greenhouse and salt marsh species, as salt marsh conditions were difficult to mimic in
the greenhouse. The observed differences between the species were mainly explained by
the C4-metabolism of S. anglica and the C3-metabolism of A. tripolium and T. maritima,
and salt stress had a higher impact on photosynthesis and biomass production than
flooding.
References
Lambregts L, Samson R & Lemeur R (1999) Effect of flooding on the ecophysiology of salt
marsh plants. Med. Fac. Landbouww. Univ. Gent, 64(5), 147-150.
SESSION 2
52
Poster Presentation
European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
SALT MARSH VEGETATION CHANGE DETECTED BY AIRBORNE
REMOTE SENSING IN THE WESTERSCHELDE ESTUARY, NETHERLANDS
FOR THE ISLED PROJECT
A.G. Thomson
Section for Earth Observation, Centre for Ecology and Hydrology, Monks Wood,
Abbots Ripton, Huntingdon, Cambridgeshire, PE28 2LS, UK (agth@ceh.ac.uk)
A CONTRIBUTION FROM THE ELOISE PROJECT: ISLED
The Westerschelde estuary is the only major uncontrolled estuary in the south of the
Netherlands. More than 15 000 ships per year use it to access the Belgian port of
Antwerp. A major dredging operation along the Westerschelde, completed in 2000, has
changed the tidal regime and increased tidal inundation of the salt marshes at high tide.
The ISLED Project (Influence of rising Sea Level on Ecosystem Dynamics of salt
marshes) has examined the consequences of this increased flooding frequency. Airborne
remote sensing (CASI) was acquired in 1998 and 2000 for three salt marsh sites in the
Westerschelde estuary and an additional dataset exists for one site for 1993. The digital
airborne datasets have been classified into maps of salt marsh vegetation. These provide
an input for GIS-based modelling of sediment erosion/accretion. These maps of
vegetation classes and vegetation indices permit change detection: successional change
of salt marsh vegetation is clearly demonstrated. The 1993, 1998 and 2000 data show a
successional trend between 1993 and 1998 prior to the change in tidal regime with an
increase in the extent of upper marsh classes. This trend has, in part, reversed between
1998 and 2000 in accordance with the original hypothesis that the salt marsh will respond
to increasing frequency of tidal inundation by changing its species composition to favour
low and mid-marsh classes at the expense of upper marsh classes. Data also showed
significant erosion of the salt marsh edge. Data are being used to extrapolate field
measurements and help produce sediment budgets for the individual salt marshes.
Airborne remote sensing is demonstrated to be capable of detecting changes in salt
marsh vegetation over a two year period.
SESSION 2
53
Poster Presentation
European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
CLIMATE CHANGE? LONG-TERM CHANGES IN MARSH EXTENT AT
TWO SITES IN THE WESTERSCHELDE ESTUARY, NETHERLANDS, FOR
THE ISLED PROJECT
R. Cox
Centre for Ecology and Hydrology, Monks
Cambridgeshire, PE28 2LS, UK (rcox@ceh.ac.uk)
Wood,
Abbots
Ripton, Huntingdon,
A CONTRIBUTION FROM THE ELOISE PROJECT: ISLED
Sets of aerial photographs from the period 1944 to 1998 were obtained for two salt
marsh sites, Ellewoutsdijk and Waarde, in the Westerschelde estuary, Netherlands. The
seaward limit of the salt marsh was digitised from these photographs after they had been
georegistered and rectified to the Dutch National Grid. Comparison of the extents of the
marshes at nine time points revealed that the areas of both marshes had fluctuated over
this 55 year period because of both advances and retreats of the seaward marsh edges
(Fig.1). These advances and retreats appeared to be approximately synchronised in time,
although the largest areal changes occurred at Ellewoutsdijk where the rate of retreat
was up to 10 metres per year. The period 1944–1980 was a phase of continuous advance
on the eastern (upstream) ends of the marshes and stability or decline on the western
ends. After that period the retreat accelerated in the west and commenced in the east.
Figure 1. Position of seaward limit of marsh 1944-1998, Ellewoutsdijk.
SESSION 2
54
Poster Presentation
European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
A range of possible explanations were investigated, including changes in the size and
number of ships using Antwerp, dredging activities, channel realignment and climatic
trends.
Changes in the frequency and direction of winter storm force winds coupled with a
small but significant increase in wave height in the Northeast Atlantic would seem to be
the most important factors which have affected the balance between erosion and
accretion at these two sites.
SESSION 2
55
Poster Presentation
European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
MICROALGAL BIOMASS AND PRODUCTION IN TOP LAYER SEDIMENT
IN NATURAL AND ARTIFICIAL ENVIRONMENTS: RESPONSE TO SEA
LEVEL RISE
B. Le Rouzic and V. Creach
UMR 6553 "ECOBI0", Bât. 14, Université de Rennes 1, Avenue du General Leclerc, F-35042
Rennes, France
A CONTRIBUTION FROM THE ELOISE PROJECT: ISLED
The plant shadow, the sediment input and the submersion frequency are physical
factors affecting epilepic microalgal communities in the two salt marshes studied. Along
a longitudinal gradient from the high salt marshes level to the limit of the mud flat, two
locations were sampled under the vegetation cover. Biomass and activity of microalgae
in the top layer sediment appear to be directly linked to the grain size which was
different for the two salt marshes. Evolution of chlorophyll a breakdown products and
photosynthetic activity measured for microalgae presented contrasted tendency. While
photosynthetic activity became more homogeneous along the three years studied, the
breakdown products of chlorophyll a presented a higher variability. In a first approach,
it can be interpreted as a change in the ecosystem functioning. In artificial salt marshes,
associated or not to plants, epilepic microalgae of the intertidal zone have been affected
by a variety of flooding frequency. Parameters chosen to describe the community
indirectly characterised the respective control of the biomass by the resource availability
and the grazing intensity. Associated to the light availability, we can observe a strong
relationship between biomass and photosynthetic activity. It clearly point out the direct
control of the biomass by the nutrient availability. Moreover, numerous similarities in
the microalgal biomass observed between the two plant associations realised in each
mesocosm were due to the water transfer of chemical elements. While the grazing
activity can be considered as null, constant or, at the most, proportional to the
photosynthetic activity, the resource availability generally explain the microalgal
biomass of the top layer sediment.
SESSION 2
56
Poster Presentation
European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
VARIATIONS OF BACTERIAL ACTIVITIES AND PRODUCTIONS IN TOP
LAYER OF SEDIMENT IN NATURAL AND ARTIFICIAL ENVIRONMENTS:
RESPONSE TO SEA LEVEL RISE
V. Creach and B. Le Rouzic
UMR 6553 "ECOBIO", Bât. 14, Université de Rennes 1, Avenue du General Leclerc, F-35042
Rennes, France
A CONTRIBUTION FROM THE ELOISE PROJECT: ISLED
In the ISLED study, we investigated the influence of sea level rise on
micro-organism activity in top layer of sediment where a substantial part of organic
matter is degraded and assimilated by heterotrophic bacteria. This degradation depends
on the quantity and quality of organic matter produced by microalgae and halophytic
plants submitted to abiotic parameters. We measured bacterial number (Sybr-green
stain), enzymatic activity (MUF-substrates), net uptake and respiration rate of
'4C-glucose and production (3H-leucine). Two systems with different flooding
frequencies were studied: 1. an artificial environment in mesocosms and 2. natural salt
marshes in Westerschelde Estuary (Netherlands). The enzymatic activity
((3-glucosidase and leucine aminopeptidase) and bacterial number were correlated with
the quantity of organic carbon in sediment in both systems. This relationship seems
dependent on the dynamic of the salt-marsh. Additionally, we showed a high correlation
between the bacterial measurements (enzymatic activity) and the active bacteria. This
part of the community were determined by CTC staining. However, this dye is still
difficult to use because the conditions for its application are unclear. Generally, the
bacterial production was not related to either enzymatic activity or bacterial number
whatever the studied systems. In mesocosms, we showed a more higher impact of
dissolved organic matter and nutrients on bacterial activity than the flooding frequency.
Other ecosystems (eutrophic lake, salt marsh in France) have been studied. In these
ecosystems, the bacterial production and number were correlated with the percentage of
sedimentary organic carbon, too. In conclusion, we did not show an immediate impact
of the flooding frequency change on the microbial loop. But it could modified in
long-term other parameters such as the grain size as well as the quantity and quality of
organic matter which are the most important factors for bacterial community.
SESSION 2
57
Poster Presentation
European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
EVALUATING THE IMPACT OF CLIMATE CHANGE AND DAMMING
ACTIVITIES ON THE SEDIMENTARY BUDGET OF THE SEBOU RIVER
AND THE ESTUARINE ZONE (MOROCCO)
S. Haida ', M. Snoussi², J.L. Probst ³
(') Université Ibn Tofail, Faculté des Sciences, Dept de Géologie, Kénitra, BP 133, Marocco
(souad_hs_haida@yahoo.com)
(²) Université Mohammed V, Faculté des Sciences, Dept des Sciences de la Terre. BP 1014,
Avenue Ibn Battota, Rabat, Morocco. (snoussi@fsr.ac.ma)
(³) Laboratoire des Mécanismes de Transferts en Géologie, CNRS/Université Paul Sabatier, 38
rue des 36 Ponts, 31078 Toulouse Cedex, France (jlprobst@lucid.ups-tlse.fr)
The Sebou catchment area covers around 40 000 km2 and contains a population of
about 5 million people. It is funnel shaped and runs from the Atlantic coast between
two mountain ranges, i.e. the Rif to the North and the Middle Atlas range to the South.
These two ranges differ in terms of their hypsometry, size and lithological composition,
thus explaining the differences in rainfall distributions and flow regimes in the northern
and southern parts of the Sebou basin. Moreover, hydroclimatic patterns for the 19401979 period, as defined by annual discharge rates, indicated an alternation of short dry
periods and long humid periods (lasting 3 to 9 years). The basin was affected by a long
dry period that began in 1980 when water resources were not sufficient to meet needs
during this period. The discharge versus rainfall curve plotted for this period confirms
the marked discrepancy (fig 1).
This situation could be explained by the extensive use of surface waters during the
dry period and the construction of hydroelectric dams on Sebou River and tributaries
(Haida et al., 1999).
The natural vulnerability of the area has been magnified. by the magnitude and
extent of socio-economic activities, impacts and interventions that increase since the
1973s. It is important therefore to know that construction of the large dams,
supplemented by changes in rainfall regimes, has led to sharp reduction of water inflow
and sediment discharge Haida et al. (submitted). It is estimated that the increasing
degree of environmental pressure has reduced the water discharge of Sebou River by
about 70% and the sediment flux of nearly 95%.As result of these intensified pressures,
water and sediment discharges led to a decline in the estuarine zone. In this case, with
the decrease of the fluvial competence, the Sebou estuarine zone will become the site of
enhanced siltation and the defensive structures could induce important modifications in
the natural evolution of the coast.
SESSION 2
58
Poster Presentation
European Land-Ocean Interaction Studies
4th ELOISE Conference
5-7 September 2001, Rende, Italy
Figure 1 Relationship between the annual water discharge and the annual rainfall on the
Sebou river at Azib Es Soltane during the two periods of 1962 to 1973 to 1995 before and
after dam constructions, respectively.
Annual discharge rates (Km 3/yr.)
6
5
(1): 1962-1972
(2): 1973-1994
y1 = 0,0074x - 1,1476
R1 = 0,92
4
(1)
3
y2 = 0,0016x + 0,3365
R2 = 0,37
2
1
0
200
(2)
300
400
500
600
700
800
Annual rainfall (mm/yr.)
References
Haida, S., Probst, J. L., Ait fora, A. et Snoussi, M. 1999- Hydrologie et fluctuations
hydroclimatiques dans le bassin versant du Sebou entre 1940 et 1994. Rev. Sécheresse. n°3,
vol. 10, 221-228.
Haida S., Probst J.L., Snoussi. (submitted)- Impact of the construction of dams on the water
and the sediment discharge in the Semi-arid basin: The Sebou (Morocco). Regulated river.
Haida S. 2000- Transports de matières et bilan de l’érosion mécanique et de l’altération
chimique dans un bassin versant de zone semi-aride: Le Sebou. Imapcts des variations
climatiques et des activités humaines. Thèse Doct. Etat., Univ. Ibn Tofail. Kénitra, Maroc,
253p.
SESSION 2
59
Poster Presentation