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