L’OLIGOTROFITZACIÓ CULTURAL DELS RIUS OCCIDENTALS I ELS CANVIS A L’ECOSISTEMA FLUVIAL: EL CAS DE L’EBRE.
Seminari Dept Ecologia - UB per Carles Ibañez (IRTA-Sant Carles de la Ràpita) el 18/01/2013
Recombinant DNA technology (Immunological screening)
C ibanez sem_eco_gener2013
1. Regime shift in a large river: top-down versus
bottom-up effects
C. Ibáñez, C. Alcaraz, N. Caiola, A. Rovira, R. Trobajo, C. Duran, A. Munné
and N. Prat
IRTA Aquatic Ecosystems, Sant Carles de la Ràpita, Catalonia, Spain;
carles.ibanez@irta.cat
Confederación Hidrográfica del Ebro, Zaragoza, Aragón, Spain.
Agència Catalana de l’Aigua, Barcelona, Catalonia, Spain.
Departament d’Ecologia, Universitat de Barcelona, Catalonia, Spain.
2. Characterization of the recent ecosystem
changes in the lower Ebro River.
Analysis of the causes and consequences of
these changes.
Role of the top-down versus bottom-up
factors.
Implications for the conservation and
management of the ecosystem.
OBJECTIVES
3. A NOVEL ECOSYSTEM SHIFT ?
New conditions: less nutrients, lower discharge and alien species
Potamogeton pectinatus
Silurus glanis
Corbicula fluminea
Simulium erytrhocephalum
Dreissena polymorpha
4. DISSOLVED P AND N TRENDS (concentration)
Data from Confederación Hidrográfica del Ebro
Ascó
Tortosa
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
Year
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Phosphates(mg/L)
1987-1995
1996-2004
Ascó Tortosa
Site
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Phosphates(mg/L)
Ascó
Tortosa
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
Year
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
Nitrates(mg/L)
1987-1995
1996-2004
Ascó Tortosa
Site
0.0
2.0
4.0
6.0
8.0
10.0
Nitrates(mg/L)
6. CHLOROPHYLL TRENDS (concentration)
Change of total chlorophyll concentration (μg/L) from 1990 till 2005. Missing years are 1993, 1995,
1998, 1999. Regular data collection of chlorophyll concentration since 1990 by Consorci d’Aigües
de Tarragona. Apart of the clear seasonal trend in each year the total chlorophyll concentration
decreased significantly during the 90’s (Beta=-0.71; p<0.01) from 44,17 μg L-1 average total
chlorophyll concentration in 1990 to an average of 3,79 μg L-1 in 2005.
0
20
40
60
80
100
120
1990-
01
1991-
01
1992-
01
1993-
01
1994-
01
1995-
01
1996-
01
1997-
01
1998-
01
1999-
01
2000-
01
2001-
01
2002-
01
2003-
01
2004-
01
2005-
01
Date
μg Ch /L
11. Increased water transparency (phytoplankton
decline) due to:
Lower eutrophication (bottom-up)
Ibáñez et al. (2008). Changes in dissolved nutrients in the
lower Ebro River: causes and consequences.
Limnetica 27(1): 131-142.
Colonization of Zebra mussel (top-down)
Sabater et al. (2008). Longitudinal development of
chlorophyll and phytoplankton assemblages in a
regulated large river (the Ebro River).
Science of the Total Environment 404: 196-206.
More regular and lower discharge (light penetration,
velocity, temperature)
HYPOTHESIS TO EXPLAIN THE ECOSYSTEM SHIFT
The aim of this study was to elucidate which are the final causes of decrease
in chlorophyll, and the subsequent spreading of submerged macrophytes
occurred in the lower Ebro River, including data from zebra mussel density
(top-down effects).
Ibáñez et al. (2012). Science of the Total Environment 416: 314-322.
12. Several sources of data were used to collect time
series of different sites from the lower Ebro River:
1) hydrology and water quality: the Ebro Water
Authority (CHE) database and the Water
Consortium of Tarragona (CAT) database (for total
chlorophyll and phytoplankton);
2) zebra mussel density: the Grup Natura Freixe
(GNF) database for zebra mussel density in the
lower Ebro river and reservoirs.
3) macrophyte cover: several sampling surveys
of the whole study area carried out using a digital
echosounder;
STUDY AREA AND DATA ANALYSIS
Lower Ebro River, from Mequinença reservoir
to the Ebro estuary (80 km)
Mequinença
Reservoir
Dam
Mequinença
Faió
Ribarroja
Reservoir
Dam
Flix
Ascó
Móra
Garcia
Matarranya
River
N
FlixReservoirDam
SPAIN
PORTUGAL
FRANCE
Mediterranean
Sea
6000 m
Xerta
Tortosa
Amposta
Deltebre
St. Jaume
FangarBay
Alfacs Bay
Móra
la nova
CAT sampling point
CHE sampling point
Zebra musselsampling stretch
Macrophyte sampling sections
Benifallet
Miravet
The global database was used to analyze the
relationship between total chlorophyll concentration
(dependent variable) and a total of 33 independent
variables, along a period of 16 years, from 1990 to
2005. Machophyte cover was not included in the
global statistical analysis, since data is not available
all along the study period.
13. DATA ANALYSIS
A Principal Components Analysis (PCA) was carried out in order to explore patterns of
association among limnological variables in the lower Ebro River. Kaiser-Meyer-Olkin’s
(KMO) measure of sampling adequacy and Bartlett’s test of sphericity were used to
assess the usefulness and adequacy of the PCA. Pearson’s correlation coefficient (r)
was used to test the relationship between the limnological variables and the temporal
variation.
An analysis of Generalized Additive Models (GAMs) was carried out in order to model
the response of chlorophyll concentration to temporal variation. GAMs are an extension
of the generalized linear models that, unlike more conventional regression methods, do
not require the assumption of a particular shape for the variable response. The model
complexity of the GAM analysis was selected by the stepwise selection procedure using
the Akaike’s information criterion (AIC).
The association of chlorophyll concentration with the independent variables was then
analyzed with Generalized Linear Models (GLMs), assuming a Gaussian error and the
identity link function. An information-theoretic approach was used to find the best
approximating models describing the relationship between chlorophyll concentration and
limnological variables, in order to avoid model selection based on stepwise
regression methods, which have been used traditionally.
14. Results: Principal Component Analysis
-1.0
-0.5
0.0
0.5
1.0
-1.0 -0.5 0.0 0.5 1.0
Demanda biològica d’oxigen
SRPClorofil·la
Terbolesa
TSSTOC
Plàncton
Fluorats
Coliforms totals
Fe
N–NO2
N–NH4
N–NO3
N Kjeldahl
Tª de l’aigua Cu
Q
Q Max
O2 dissolt
Dies Q ≥ 1000 m3/s
Zn
Densitat de musclo zebrat
pH
SiO2
Tensoactius
HgPb
Alcalinitat
Na
SO4
Clorats
Conductivitat
CaMg
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
Any
4
2
0
-2
-4
-2-4 6 82 40
PCAcomponent2
PCA component 1
KMO = 0.802PCA1 = 21.3%; PCA2 = 18.1%
15. GAMs: changes in total chlorophyll (monthly
data)
El musclo zebrat al tram final de l'Ebre i els
seus impactes
Non-linear F1, 189 = 4.74, P =
0.031
Null model deviance = 45.8
Model deviance = 20.6
Model F2, 189 = 115.6, P <
0.0001
A slight change of tendency is
observed around the year
2000
Zebra mussel ?
0.0
0.5
1.0
1.5
2.0
Log(Chlorophyllconcentration(µg/L))
Month
Jan 92 Jan 96 Jan 00 Jan 04
24 48 72 96 120 144 168 1921
16. El musclo zebrat al tram final de l'Ebre i els
seus impactes
Log(Chlorophyllconcentration(µg/L))
0.0
0.5
1.0
1.5
2.0
1.6 1.8 2.0 2.2 2.4 2.6 2.8
Log(SRP concentration (µg/L))
r = 0.72
Full model r = 0.84
AICc best model r = 0.83
Averaged model r = 0.84
0.0
0.5
1.0
1.5
2.0
2.01.51.00.50.0
Predicted - Log(Chlorophyll concentration (µg/L))
0.0
0.5
1.0
1.5
2.0
0.3
Log(N―NO2 concentration (µg/L))
0.7 1.1 1.5 1.9
r = 0.25
3.0
Log(Silicates concentration (µg SiO2/L))
0.0
0.5
1.0
1.5
2.0
3.2 3.4 3.6 3.8 4.0
r = -0.43
GLMs results (monthly data)
17. GAMs: changes in total chlorophyll (annual
data)
El
Non-linear F1, 13 = 5.26, P =
0.039
Null model deviance = 2.38
Model deviance = 0.14
Model F2, 13 = 104.3, P <
0.0001
Again, a change in tendency is
observed around the years
1999-2000
Zebra mussel ?0.25
0.75
1.25
1.75
Log(Chlorophyllconcentration(µg/L))
1990 1992 1994 1996 1998 2000 2002 2004
Year
18. Variable
Model mensual
(Complet) N = 29
Model mensual
(Pre-) N = 52
Model mensual
(Post-) N = 207
Model anual
N = 25
β SP Bias β SP Bias β SP Bias β SP Bias
Constante 1.792 0.150 1.360 0.260 2.889 -0.413 -3.777 2.472
Periode de disminució -0.306 1.000 0.021 -0.108 0.037 -0.656
Cabal promig (m
3
/s) -0.141 0.460 -0.048 -0.242 0.621 -0.088 -0.255 0.419 0.333 -0.215 0.008 -2.395
SRP(µg/L) 0.719 1.000 -0.012 0.577 1.000 -0.020 0.857 0.935-0.129 0.961 0.989 0.252
N–NO2 (µg/L) 0.412 1.000 -0.033 0.417 0.983 -0.040 0.388 0.722-0.117 1.629 0.485 0.019
N–NO3 (µg/L) 0.252 0.342 0.074 0.355 0.395 0.095 -0.336 0.217 0.692 0.796 0.023 0.666
N–NH4 (µg/L) -0.144 0.796 -0.001 -0.085 0.369 0.023 -0.463 0.903-0.025 -0.401 0.373 0.549
TOC (µg C/L) 0.082 0.257 -0.113 0.152 0.268 -0.203 -0.130 0.176-0.700 1.067 0.301 2.136
Silicats (mg/L SiO2) -0.523 1.000 0.025 -0.532 1.000 0.005 -0.244 0.274 0.289 -0.505 0.145 0.036
TSS (mg/L) -0.029 0.255 0.475 -0.083 0.300 0.444 -0.086 0.205 0.195 0.529 0.787 -0.326
Tª de l’aigua (ºC) 1.010 1.000 0.023 1.200 1.000 0.019 0.468 0.493 0.254 1.655 0.047 1.609
Cond. (µS/cm 20ºC) -0.680 1.000 -0.121 -0.610 0.906 -0.099 -0.908 0.992-0.062 -1.147 0.289 -0.672
Musclo zebrat (ind/m
2
) No seleccionat -0.047 0.330 0.276 -0.073 0.071 0.498
GLMs: response of chlorophyll to the
independent variables
In the annual model SRP is the independent variable that mostly explains
the change in total clorophyll; the zebra mussel is selected but his
explanatory importance is ≈14 time lower that the SRP.
In the monthly model the zebra mussel is not selected (no effect on
chlorphyll). SRP, NO2, SiO2, Tº and Conductivity are the most rellevant
variables.
19. El musclo zebrat al tram final de l'Ebre i els
seus impactes
0.25
0.75
1.25
1.75
Log(Chlorophyllconcentration(µg/L))
Full model r = 0.99
AICc best model r = 0.98
Averaged model r = 0.99
1.750.25 0.75 1.25 1.6 1.8 2.0 2.2 2.4
Predicted - Log(Chlorophyll concentration (µg/L)) Log(SRP concentration (µg/L))
0.25
0.75
1.25
1.75
r = 0.93
r = 0.85 r = 0.79
0.25
0.75
1.25
1.75
1.2 3.5 3.7 3.9 4.1 4.3
Log(N―NO2 concentration (µg/L)) Log(Total suspended solids (µg/L))
0.25
0.75
1.25
1.75
1.3 1.4 1.5
GLMs results (annual data)
20. Discussion: why the Zebra mussel is not the cause of the
decrese in total chlorophyll?
Density of zebra mussel is only high in some locations and in some years,
but in average is low.
The volume (reservoirs) and turnover (river) of the water is high.
When the zebra mussel (or another filterer) is the main cause of
phytoplancton decrease, dissolved phosphorus uses to increase, but in
the Ebro it has decreased.
Phytoplancton decrease and macrophyte spreading has also occured
upstream the reservoirs, where there was no Zebra mussel and Corbicula.
Dissolved phosphorus explains most of the chlorophyll variation. SRP has
decreased all along the Ebro basin (90% of the monitoring stations).
Actually, it looks like the decrease in SRP has prevented a stronger
invasion of the zebra mussel.
21. Discussion: oligotrophication in rivers
Causes of phytoplankton decrease and macrophyte spreading are better studied and understood in
lakes than in rivers (Ibáñez et al., 2008).
Changes in dissolved nutrients in the lower Ebro river: causes and consecuences. Limnetica 27(1): 131-142.
The conclusion that physical factors such as light limitation and short hydraulic residence times will
always prevent any algal responses to nutrient enrichment in rivers are no longer tenable (Smith et al.
2006).
Eutrophication of freshwater and marine ecosystems. Limnology and Oceanography 51(1): 351-355.
There is surprisingly little information about how the trophic state of US streams has changed over the
past several decades, especially in response to changes in nutrient enrichment. Despite statistically
significant declines in nutrient concentrations at many monitoring sites from 1975 to 1994,
improvements in trophic state occurred at only about 25% of the sites (Alexander & Smith, 2006).
Trends in the nutrient enrichment of U.S. rivers during the late 20th century and their relation to changes in probable
stream trophic conditions. Limnology and Oceanography 51(1): 639-654.
Chételat et al. (2006) concluded that both nanoplankton and total potamoplankton biomass were
significantly correlated with water column total phosphorus concentrations, even though this response
was hysteretic.
Potamoplankton size structure and taxonomic composition: Influence of river size and nutrient concentrations.
Limnology and Oceanography 51(1): 681-689.
Reductions in wastewater loading led to significant declines in mean summer TP and Chl concentration
in two large rivers (Rhine and San Joaquín) despite their initially shallow (< 2m) euphotic depth and
continually high (> 40 mg m-3
) SRP concentration. The results suggest that TP was the principal
determinant of Chl and that the control of P loading may be an effective tool for managing
eutrophication in rivers with relatively high (10-100 mg m-3) SRP concentrations (van Nieuwenhuyse,
2007).
Response of summer chlorophyll concentration to reduced total phosphorus concentration in the Rhine River
(Netherlands) and the Sacramento – San Joaquín Delta (California, USA). Canadian Journal of Fisheries and
Aquatic Sciences 64: 1529-1542.
22. REFERENCE CONDITIONS
Natural flow regime
Discharge ↑
Sediments ↑
Phytoplankton ↓?
Macrophytes ↓?
Benthos ?
XIX Century
HUMANIZED RIVER
Altered flow regime
Discharge ↓
Regulation ↑
Eutrophycation ↑
Pollution ↑
Alien species ↑
Altered flow regime
Discharge ↓↓
Regulation ↑↑
Eutrophycation ↓
Wastewater treatment
Pollution ↓?
Alien species ↑↑
Sediments ↓
Phytoplankton ↑
Macrophytes ↓
Sediments ↓
Phytoplankton ↓
Macrophytes ↑
Benthos
↑Filterers
XX Century ~ 2000
Benthos
↓Filterers
23. CONSEQUENCES FOR THE ESTUARY
Phytoplankton P
Nutrient retention
Summer hypoxia
Nutrient and POM uptake
Low residence time
Less POM, more light
Less R, more PP & O2
24. CONCLUSIONS
Recent changes in the trophic status of the lower Ebro River are basically due
to a significant decrease in dissolved phosphorus. Zebra mussel plays a minor
role.
This has caused a quick regime shift from a phytoplankton to a macrophyte
dominated river ecosystem.
Low and regular river discharge conditions and lack of suspended sediments
(after dam construction) may facilitate the colonization and spreading of
macrophytes, but its possible effect was shaded by the eutrophication in the
70’s and 80’s.
Present ecosystem structure and dynamics is completely new, with local
species controlling primary production (macrophytes) and alien species
controlling secondary production (Zebra mussel, Corbicula, Silurus, Alburnus,
etc.).
The way back to reference conditions and good ecological status is not
possible without the recovery of floods and suspended sediments. However,
the effects of invasive species and climate change make impossible the full
recovery of original conditions.
Phosphorus reduction in the Ebro river (mostly point source) was an effective
way to reduce eutrophication in the river and the estuary.
25. FURTHER RESEARCH
To which extent the cultural oligotrophication is unfolding in rivers worlwide
and in particular in Western rivers ? What are the most common effects of this
process ?
To which extent the response of rivers to nutrient changes is different from
lakes ? Is different the response in large rivers and streams ?
To which extent the response of rivers to cultural oligotrophication is different
between calcareous and siliceous basins ? Is it just a quantitative difference or
it is qualitative one ?
To which extent the response of Mediterranean rivers is different from other
river types ?
What is the relationship and feed-backs between oligotrophication, river
regulation and invasive species ?. What is the effect of climate change ?
What is the expected evolution of our fluvial ecosystems under this scenario ?
