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Eric Struyf Kris Bal Sofie Van Belleghem Patrick Meire. Top-bottom investigation of water and nutrient fluxes to the coastal zone through a lowland river basin. Introduction. - PowerPoint PPT Presentation
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Top-bottom investigation of water and Top-bottom investigation of water and nutrient fluxes to the coastal zone through nutrient fluxes to the coastal zone through
a lowland river basina lowland river basin
Eric Struyf
Kris Bal
Sofie Van Belleghem
Patrick Meire
Introduction
The accurate quantification of fluxes of water and fluxes of dissolved constituents throughout whole river basins is of major importance.
This study can act as the working tool for river managers and modellers to anticipate future changes in hydrology due to climate change and development of vegetation throughout the Schelde basin (France, Belgium, The Netherlands)
Overview
Focus on two research projects within the total framework of integrated river basin management
1. The effect of vegetation on drainage in upper river basin sub catchments
2. The possible effect of changing external forcing conditions (increasing discharge) on the eventual transport of water and nutrients towards the coastal area through estuarine ecosystems
Dendermonde
Vlissingen
Gent
Temse Antwerp
Belgian-Dutch borderNorth Sea
Sche
lde
Schelde
Schelde
Dender
Rupel
Durme
Channel Gent-Terneuzen
North sea
The Schelde estuary
-Entire salt gradient-Highly eutrofied-Highly industrialized
Nete sub-catchment
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
Part 1 :Part 1 :
The effects of mowing on The effects of mowing on the discharge capacity the discharge capacity
of lowland riversof lowland rivers
Increased nutrient fluxes towards the river stimulate plant growth :
- discharge capacity will decrease
- possibility that adjacent valuable land will flood
Pro’s and cons of watervegetation
Pro :
- Vegetation acts as a sieve for suspended solids and nutriënts
- Vegetation acts as refugia areas for organisms during
extreme discharge conditions.
- Vegetation has a positive effect on the diversity of
organisms within and outside a river
Contra :
- increases the resistance
- often seen as a nuisance in waterways (perception)
This study
- Partial removement of macrophytes in three different mowing patterns for three different macrophytes
- Patterns with the most ecological potential
This as a compromise between the drainage and life support function of waterways
Pattern 1 Pattern 3
Pattern 2 : two sides of macrophytes
In-situ determination of biomass
Biomass Grote Caliebeek
0
0,5
1
1,5
2
Jan March April June Aug Okt Nov
Month
fres
hw
eig
ht
(kg
/m2)
Biomass Wamp
0
0,1
0,2
0,3
0,4
0,5
0,6
Jan March April May June Aug Okt Nov
month
fres
hw
eig
ht
(kg
/m2)
Biomass Slootbeek
0
0,1
0,2
0,3
0,4
0,5
0,6
Jan March April May June Aug Okt Nov
Month
Fre
shw
eig
ht
(kg
/m2)
Biomass Aa
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
Jan March May June July Aug Sept Okt Nov
Month
fre
sh
we
igh
t (k
g/m
2)
In-situ determination of biomass
Biomass Grote Caliebeek
0
0,5
1
1,5
2
Jan March April June Aug Okt Nov
Month
fres
hw
eig
ht
(kg
/m2)
Biomass Wamp
0
0,1
0,2
0,3
0,4
0,5
0,6
Jan March April May June Aug Okt Nov
month
fres
hw
eig
ht
(kg
/m2)
Biomass Slootbeek
0
0,1
0,2
0,3
0,4
0,5
0,6
Jan March April May June Aug Okt Nov
Month
Fre
shw
eig
ht
(kg
/m2)
Biomass Aa
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
Jan March May June July Aug Sept Okt Nov
Month
fre
sh
we
igh
t (k
g/m
2)
Streamvelocity within the patterns (ex-situ)vegetationVelocity is higher for pattern 2 (all species)
Ranunculus aquatilis
00,020,040,060,080,1
0,120,140,16
0 0,05 0,1 0,15
discharge (m3 s-1)
aver
age
stre
am v
elo
city
(m
s-1
) pattern 1
pattern 2
pattern 3
Callitriche species
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0 0,05 0,1 0,15
discharge (m3 s-1)
aver
age
stre
am v
elo
city
(m
s-1
) pattern 1
pattern 2
pattern 3
Potamogeton natans
00,020,040,060,080,1
0,120,140,16
0 0,05 0,1 0,15
discharge (m3 s-1)
aver
age
stre
am v
elo
city
(m
s-1
)
pattern 1
pattern 2
Open water
Velocity in pattern 2 is slightly higher then in the other
patternsPotamogeton natans
0
0,05
0,1
0,15
0,2
0,25
0 0,05 0,1 0,15
discharge (m3/s)
aver
age
stre
am v
elo
city
(m
/s) pattern 1
pattern 2
Ranunculus aquatilis
0
0,05
0,1
0,15
0,2
0,25
0,3
0 0,05 0,1 0,15
discharge (m3/s)
aver
age
stre
am v
elo
city
(m
/s) éénkant
tweekant
dambord
Callitriche species
00,050,1
0,150,2
0,250,3
0,350,4
0 0,05 0,1 0,15
discharge (m3/s)
aver
age
stre
am v
elo
city
(m
/s)
pattern 1
pattern 2
pattern 3
Determination of the resistance ex-situ
Pattern 2 had the highest Km values especially in the higher discharge
range Km = V*(R2/3*S1/2)-1
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0,16
0,18
0 10 20 30 40 50 60
Km (m1/3 s-1)
dis
char
ge
(m3/s
ec)
pattern 2
pattern 1
pattern 3
Pattern influence
Km values of pattern 1
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0 20 40 60 80 100
Km (m1/3 s-1)
Dis
char
ge
(m3/s
ec)
Ranunculus aquatilis
Potamogeton natans
Callitriche species
Species influence
- species with their biomass at the watersurface have higher Km values
Km values of pattern 2
0
0,05
0,1
0,15
0,2
0 20 40 60 80
Km (m1/3 s-1)
dis
char
ge
(m3/s
ec)
Ranunculus aquatilis
Potamogeton natans
Callitriche species
Conclusion
- Pattern two has the lowest resistance despite of higher biomasses
- Plant architecture influences the resistance :
* species with high leaf areas (Callitriche sp.) and branched leaves (Ranunculus aquatilis) have high resistances
* concentration of biomass at the surface will impede the water flow less
- The patterns have a better relative drainage at higher discharges
Part 2: Part 2: the effects of hydrological the effects of hydrological changes on nutrient changes on nutrient fluxes throughout fluxes throughout estuarine waters to the estuarine waters to the coastal zonecoastal zone
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
Changes in hydrological conditions throughout the Changes in hydrological conditions throughout the river shed eventually influence discharge conditions in river shed eventually influence discharge conditions in estuarine waters and can result in:estuarine waters and can result in:
- major changes in nutrient fluxes towards brackish major changes in nutrient fluxes towards brackish and salt estuarine and coastal watersand salt estuarine and coastal waters
- major changes in nutrient concentrations in the major changes in nutrient concentrations in the freshwater part of estuarine watersfreshwater part of estuarine waters
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
Why is nutrient flux towards and through estuarine waters so important?
-Estuarine and coastal waters are the main fishery grounds on EarthEstuarine and coastal waters are the main fishery grounds on Earth
-Diatom communities are fundamental in estuarine food webs and play Diatom communities are fundamental in estuarine food webs and play an essential role in productivityan essential role in productivity
-The optimal balance between diatom communities and less preferred The optimal balance between diatom communities and less preferred fytoplankton communities (e.g green algae) is dependent on nutrient fytoplankton communities (e.g green algae) is dependent on nutrient ratios within coastal watersratios within coastal waters
- Increase in N and P fluxes to coastal waters can induce eutrophication Increase in N and P fluxes to coastal waters can induce eutrophication (explosive growth of algae e.g. (explosive growth of algae e.g. PhaeocystisPhaeocystis) and subsequent negative ) and subsequent negative effects as oxygen depletion, fish kills, foam production...effects as oxygen depletion, fish kills, foam production...
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
Picture taken from: http://staff.science.uva.nl/~dcslob/lesbrieven/TomTahey/bovenbouwtekst3.htm
Eutrophication
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
This case study
-1996-2000: a period characterised by steadily increasing 1996-2000: a period characterised by steadily increasing discharges in the Schelde estuary discharges in the Schelde estuary
-The period 1996-2000 was taken as a reference period for The period 1996-2000 was taken as a reference period for possible major future changes in hydrological conditionspossible major future changes in hydrological conditions
- Vegetation in upper catchments- Vegetation in upper catchments- Global change- Global change- Urbanisation- Urbanisation
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
0
10
20
30
40
50
60
70
80
1996 1997 1998 1999 2000
Year
Dis
cha
rge
(m3 .s
-1)
Discharge from freshwater part towards brackish and coastal waters increased 2 to 3 fold in between 1996-2000.
73 m3.s-1
28 m3.s-1
Yearly average discharge in the freshwater zone of the estuary
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
0
20
40
60
80
100
120
140
160
jan-96 jan-97 jan-98 jan-99 jan-00
Date
Dis
char
ge
(m3.s
-1)
Increasing discharge apparent in both winter and summer: absolute discharge increase was higher in winter
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
0
5000
10000
15000
20000
1996 1997 1998 1999 2000
Dis
ch
arg
ed
lo
ad
(to
ns) ammonia
nitrate
nitrite
Increase in nitrate loadings
0
10
20
30
40
50
60
70
80
1996 1997 1998 1999 2000
Year
Dis
cha
rge
(m
3 .s-1
)
Nitrate input from the freshwater to the brackish increased Nitrate input from the freshwater to the brackish increased concurrently with discharge, ammonia loadings were stableconcurrently with discharge, ammonia loadings were stable
Discharges in the freshwater estuary
Dissolved nitrogen output doubled Dissolved nitrogen output doubled between 1996-2000between 1996-2000
8000 tons
16500 tons
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
Higher run-off
0
50000
100000
150000
200000
250000
300000
350000
1996 1997 1998 1999
Year
Dis
char
ged
SS
(to
ns)
0
5000
10000
15000
20000
25000
1996 1997 1998 1999 2000
Year
N (
ton
s)
Nitrate discharge Antwerp Agriculture loss
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
Non-point pollution (mainly agriculture) towards the estuary increased
Discharged suspended solids towards the estuary: indicator for surface run-off
Similar patterns in nitrate discharge and loss from agricultural soil, nitrate mainly originates from agriculture, ammonia relates
to point-pollution.
Estimates show a big increase
90000 tons
340000 tons
Source: AWZ Source: VMM
0
1000
2000
3000
4000
1996 1997 1998 1999 2000
Dis
char
ged
lo
ad (
ton
s)totP
DRP
0
5000
10000
15000
20000
1996 1997 1998 1999 2000
Dis
char
ged
lo
ad (
ton
s) DSi
P and Si discharge
Dissolved silica export tripled
Phosphorus export was less influenced
Hydrology changes can have major impact on
nutrient ratiosStruyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 0,5 1 1,5 2 2,5
log (discharge+1)
log
(n
itra
te+
1)
winter-autumn
spring-summer
0
0,2
0,4
0,6
0,8
1
1,2
0 0,5 1 1,5 2 2,5
log (discharge+1)
log
(am
mo
nia
+1)
winter-autumn
summer-spring
Nitrogen in the freshwater zone
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
In winter, nitrate concentrations In winter, nitrate concentrations increase with discharge, in increase with discharge, in summer they decrease.summer they decrease.Relations were opposite for Relations were opposite for ammonia.ammonia.
winter
summer
summer
winter
The natural, seasonal cycle The natural, seasonal cycle appears to be flattened out by appears to be flattened out by increasing dischargeincreasing discharge
The amount of nitrate in the Schelde however is alsoinfluenced by the presence or absence of macrophytes in the upper sub-catchments (Nete)
Aa November 2003
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
10:00 22:00 10:00
time
tot
N (
mg
/l)
stuw 3
halfway
stuw 4
When macrophytes are present (Summer) total N concentrations are lowered. When the plants decay (Winter) N is released which causes an increased N flux towards the upper sub-catchment and eventually the schelde
Aa Augustus 2003
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
0:00 12:00 0:00
time
tot
N (
mg
/l)
stuw 3
halfway
stuw 4
Data S. Van Belleghem
0
0,2
0,4
0,6
0,8
1
1,2
0 0,5 1 1,5 2 2,5
log (discharge+1)
log
(D
Si+
1)
winter-autumn
spring-summer
summer
winter
Silica in the freshwater zone
Diatoms: summer - spring: uptake of DSi winter - autumn: no uptake
With increasing discharge, summer concentrations approach winter concentrations
Diatom communities appear not adapted to high discharges
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
Impact on management
Higher discharges appear to:
- dilute pollutants and nutrients
- increase nutrient loadings towards coastal zone
Dilution effect masks the problem of increasing loadings from non-point pollution.
Dilution could affect political and public perception about the effectivity of pollution reducing measures
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
0
50
100
150
200
250
300
350
400
Ex
pe
ns
es
(1
06 €)
1989 1991 1993 1995 1997 1999
Year
Flemish government has drastically increased investments in point-pollution reduction in the last decade to REDUCE nutrient loadings.
Due to hydrological changes, the nutrient loadings have increased over the same period.
Source: VMM
Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press
General conclusion
* Global change will increase discharge. Consequently nutrient run-off towards coastal zones will increase.
* Vegetation however increases the residence time of water due to higher resistances. Self purifying capacity of the river is restored through the stimulation of ecosystem processes.
* Vegetation management is a tool which can buffer the fluctuations in discharge in the river basin.
AcknowledgementsWe like to thank L. Clement for analyzing our water samples.
We especially like to thank Flanders Hydraulics and AWZ for their cooperation
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