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Functions of hydro-morphological structures in large river-ecosystems with
fine sediments, and impacts by shipping and
river training structures
Martin Pusch
Leibniz-Institut für Gewässerökologieund BinnenfischereiInstitute of Freshwater Ecology and Inland FisheriesBerlin E-mail: pusch@igb-berlin.de
Questions
Which ecosystem functions are going on in rivers?
Why should we care?
What are the governing factors for riverine
ecosystem functions?
Relationship between ecosystem function and biodiversity
Impacts by shipping and river training
Conclusions / Issues for discussion
Case study: The Elbe River in Germany
Length: 1091 km
Waterways: 940 km
Slope: 0.021 %
Mean discharge: 350 m3/s
The River Elbe -
now one of the best studied
large river systems of the
world
Inputs of plant nutrients
(Grafik: FZ Jülich)
56 % 68 % 12 000 t/a Phosphorus
32 % 74 % 230 000 t/a Nitrogen
Retention of inputs
in river systemDiffuse inputs
Total inputs
Behrendt (2005) EUROCAT WP4 Report
Surface waters may retain a significant
proportion of nutrient inputs (retention of
matter and self purification)
As diffuse inputs can hardly be reduced
on the short term, river management
should seek to maximize in-stream
retention of matter
Contaminants
Inputs of badly treated sewage water
(saprobic contamination) ()
Biologically undegradable organic
compounds (Xenobiotics)
Pharmaceuticals and hormone-like
substances
Heavy metals
Phytoplankton
Plant nutrients N and P
Eutrophication
Recent human impacts on rivers
Morphology
River-floodplain connectivity
River morphology
Dynamic riverine channel structures and their ecological functions…
Habitat
Metabolism of matter
Retention
Transport
Human use and modification of riverine functions
…in rivers used for navigation…
…will partially be reduced by shore protection..
…or totally disappear
Historical river training on the Elbe
Overlain maps of Elbe section from 1792 and 1893 (red)
Current river morphology of the Elbe
Construction of groynes (and impoundment of upper Elbe
section) initiated strong depth erosion in some reaches:
max. 1.6 m in 120 a, currently 2 cm/a.
Bedrock ’grows’ out of the river bottom at 2 places, acting as
obstacles for navigation.
In erosional reaches groynes are now situated much too
high.
Self-acceleration of depth erosion, acceleration of flood
peaks.
Currently artificial bedload addition of 80 000 t/a (planned,
but not fully implemented because of practical problems).
Depth erosion process is currently still out of control.
Elbe bei Wittenberge
Loire near Bréhémont (Fluss-km 794)
Riverine morphological structures in the Elbe und Loire rivers
6000 groynes built on the
Elbe,
mostly in 1880s and 1930s
Sampling the central river sediments
with a diving bell ship
Degradation of matter in lowland rivers
Percentage of sediments in total riverine metabolism
Fischer, Pusch (2001) Freshwater Biology
after Wilczek, Fischer, Pusch ( 2005) Microbial Ecology
Elbe Spree Winter Summer Winter Summer
Bacterial production
Extracellular enzyme activity
96 % 90 % 94% 95%
Water columnAquatic plantsSediment
Riverine microbial metabolism is mainly
related to the river bottom
after Wilczek, Fischer, Pusch ( 2005) Microbial Ecology
Seasonal dynamics of microbial activities
Elbe sediments 2001-2002
Feb 20.0
30
40
50May
Jun
Jul
Aug
Sep
Dec
Jan
Mar
AprFloodPhosphatas
e[% of cumulativeenzyme activity in 0-5 cm and
15-20 cm depth]
Algal bloombreakdown
Input of terrestrialPOM containing PNov
Fischer, Kloep, Wilczek, Pusch (2005) Biogeochemistry
120
100
80
60
40
20
0
0 0.5 1.0 1.5 2.0 2.5 3.0
Dresden river bottom
Bacterial production [g C cm-3 h-1] S
ed
imen
t d
epth
[cm
]
Dresden river shore
Coswig groyne fields
Coswig river bottom
x 10-6
r2 = 0.83
r2 = 0.93
r2 = 0.86
r2 = 0.98
Bacterial production in Elbe sediments
In river sediments stabilized by groynes
microbial activity is restricted to the
surface.
• Infiltration of water and FPOM• High microbial activity
• Exfiltration• Low input and activities
VHG
O2O2
O2
Flow velocity
POM quality
POM pool
Bacterial density
Extracellular enzyme activity
Comm. respiration
HierarchicalcontrolHydro-dynamics andmorpho-dynamics
Input oflabile microbialsubstrates
Microbialactivity
MeasuredVariable
O2 DO
FPOM input O2
Wilczek, Fischer, Brunke, Pusch (2004) Aquatic Microbial Ecology
Hydrodynamics and microbial activity in a subaqueous dune
30 m
1 m
• Trapping of POM• High microbial activity
Lee sideLuff side Plateau Hydrodynamic coupling of water column and
sediments is crucial for significant microbial
activity
Central channel sediments – the ‚river‘s liver‘Bottom sediments swiftly overflown by river
water
form a hot spot of microbial activity
Fischer, Kloep, Wilczek, Pusch (2005) Biogeochemistry
Distribution of sedimentary metabolismStable discharge
conditions
Laterale
Konnektivität
Permanent vertical connectivity
by advective transport
Central channel sediments
Distribution of sedimentary metabolism
Discharge and water level fluctuations
Laterale
Konnektivität
Parafluvialsediments
Parafluvialsediments
Temporarylateral connectivity
by advective transport
Permanent vertical connectivity
by advective transport
Central channel sediments
Temporary lateral connectivityby advectivetransport
Intensive particle sedimentation in groyne fields
Isolines of water residence timein a groyne field
(Sukhodolov et al. 2004)
-3000
-2000
-1000
0
1000
199919981997
D
iffe
ren
z S
chw
ebst
off
frac
ht
[t/d
]
-500
-400
-300
-200
-100
0
Dif
fere
nzs
um
me
Sch
web
sto
fffr
ach
t [k
t]
Balance of suspended solids load between the two stations Wittenberge (Elbe-km 455) and Hitzacker (Elbe-km 523) (Schwartz et al. 2004)
Intensive particle sedimentation in groyne fields
1889 1990
Groyne fields are sites of intensive sedimentation
processes
This results in the disappearance of shore habitat
diversity
and in huge accumulations of contaminants
(e.g. 50kg Pb in 1 groyne field)
Retention of matter – balances and regulation
- Sedimentation of suspended solids in groyne fields: c. 2,5 t per river kilometer and day in winter
- In summer c. 1,4 % of OC load is degraded per river km
- Denitrification rate c. 10-20 t NO3-N per river km and year
Aerobic and anaerobic microbial metabolism is governed by hydrological connectivity of sediments with the water column.
Hydrological connectivity is governed by channel morphology and dynamics
Reduction in functionality due to river training cannot be estimated to date because of lack of reference reaches in the Elbe
River Quality Model QSIM
Bundesanstalt für
Gewässerkunde
(Federal Agency of Hydrology)
Koblenz, Germany
Human impacts on rivers can be modelled / predicted
concerning hydrodynamics, sediment transport, water
quality,
as well as habitat availability for fish and invertebrates.
Aquatic organisms as indicators of ecosystem health
Fish
Benthic invertebrates
Habitat quality of several shore protection types
Standard groyne field
Zoobenthosbiomass
ZoobenthosDiversity
-
Shore without groynes
Nearshore pool at low flow
Parallel groyne
Parallel groyne at low flow
Biomass Diversity
Biomass Diversity
Pool phase
Habitat quality of several shore protection types
Shore without groynes
Nearshore pool at low flow
Parallel groyne
Parallel groyne at low flow
Habitat quality of several shore protection types
In sand-bed rivers, ecosystem metabolism reaches its
maximum in constantly mobile central sediments,
while invertebrate diversity reaches its maximum in
temporally stable nearshore areas.
Hot spots of ecosystem functions and biodiversity
do not necessarily coincide spatially in river systems.
Both ecosystem functions and biodiversity depend on
typical riverine dynamics (floods, sediment transport,
morphological dynamics.
Effects of ship-induced waves on river margins
Passage of cruise ship „Victor Hugo“ on the Elbe near Coswig
Increase of
zoobenthos drift
by 3x – 30x
Brunke, Sukhodolov, Fischer, Wilczek, Engelhardt, Pusch (2002): Verh. Int. Verein. Limnol.
Parallel groyne
Modified groyne with
central opening
?
?Unaltered shore
morphology
Is an ecological optmization of river training measures feasable and
effective?
Modelling of habitats before and after planned alterations necessary
Synopsis of groyne effects River training by the construction of groynes is expensive both in installation and maintenance.
The construction of groynes may result in uncontrollable depth erosion, and in higher subaqueous dunes (due to faster flow), thus potentially reducing navigational depths at low flow.
In large rivers, aquatic invertebrates and fish mostly live near the river margins. Modification of these margins strongly affects these organisms.
The construction of groynes fosters storage processes (incl. contaminants) and reduces microbial metabolism.
Issues influencing Danube management strategy
Navigation in unstable river channels is largely facilitated by the Radarpilot device, which integrates Radar observa-tions of other ships, GPS and a digital river map.
Radar pilot
Issues influencing Danube management strategy
Navigation in unstable river channels is largely facilitated by the Radarpilot device, which integrates Radar observa-tions of other ships, GPS and a digital river map.
The Black Sea is a highly sensitive ecosystem which needs strong reduction of inputs especially in plant nutrients.
The European Water Framework Directive does not allow impedement of the ecological status of a river.
The European Commission could possibly require ecological mitigation of planned river training measures.
European R&D projects aiming to integrate objectives for the development of the Danube concerning- Navigation in rivers with limited depth- Hydropower generation- Flood control- Water Framework Directive- EU Habitat Directive- Socio-economic development of regions bordering the Danube
Co-ordinated implementation of river training measures
What is needed
Goodecological statusModerate ecological statusBad ecological status
Restoration of secondary channels in the lower River Rhine / Waal (NL)
Reconstruction of typical riverine structures from a highly altered state is very expensive, if possible at all.
MaßnahmenvorschlägeThank you for your
attention !
For those who want to
read even more on the
ecology of the Elbe
River I recommend this
book (in German) …
Vol. 5 of book series on the Elbe
Weissensee-Verlag, Berlin
ISBN 3-89998-011-5
Recommended