Transcript les flux particulaires et dissous des continents aux oceans

LES FLUX PARTICULAIRES ET DISSOUS
DES CONTINENTS AUX OCEANS,
EVOLUTION RECENTE DUES AUX
EFFETS ANTHROPIQUES
M. MEYBECK
UMR Sisyphe, CNRS / Univ. Paris VI
• Changement global du système terre
• Global change context within Earth System
• Pressions sur les systèmes fluviaux
• Man and rivers: growing pressures
• Distribution globale des changements fluviaux
•Mapping global river changes
• Interactions homme - fleuve, passées, présentes, futures
• Man / river interactions: past, present, future
Académie des Sciences, Septembre 2003
PRISTINE RIVER CHEMISTRY
ALASKA PRISTINE RIVER BASIN
BE1
• True pristine basins, with very limited land use and minimum contaminated
atmospheric fallout, are now uncommon in the temperate zone
• Such Alaska and Southern Chile sites are selected by scientists to study the natural N
and P cycles, sediment transfers, natural river chemistry, etc...
PRISTINE RIVER CHEMISTRY
VARIABILITY OF NATURAL RIVER CHEMISTRY
AND LITHOLOGY
Sum of cations (µeq/L)
Dominant ions
Example
50
Ca2+, Cl-
Rio Negro * (Amazonia) quartz sands
70
Na+, HCO3-
Rio Tefe * (Amazonia) quartz sands
500
Mg2+, Ca2+, HCO3-
Basaltic basins
600
Mg2+, HCO3-
Peridotite basins
4 000
Ca2+, HCO3-
Carbonated basins
5 000
Mg2+, SO42-
Coal schists
9 000
Na+, SO42-
Semliki R. Rift Valley
20 000
Na+, SO42-
Bituminous Shale (Montana)
50 000
Na+, Cl-
Urubamba tributary (Amazonia)
* Rain and vegetation control
There is no mean river water that can be used as a global or
even regional reference
PRISTINE RIVER CHEMISTRY
GLOBAL OCCURENCE (% of area) OF WATER TYPES AND
THEIR ORIGINS (Pristine rivers model)
Origin
Type
% Total
Rock dominated
Rain
Evaporated
dominated Sili cate Carbonate Pyrite Evaporites

Na2SO4
3,2
NaCl
6,8
Na2CO3
3,6

MgCO3
2,4

MgSO4
2,0
MgCl2
0,1
CaSO4
5,2
CaCO3
76,9
Total
100











2,6


 
35,4
45,1



5,2
3,6
8,2
• Ionic types in pristine rivers are more diverse than originally thought by
Gibbs (1972)
• CaCo3 is dominating in 77% of rivers (area weighted)
• Rain and vegetation recycling is dominating over 2.6% of the continents
area and the evaporation over 8.2% (rheic realm only, runoff > 3 mm)
• Rock weathering control extends over 89% of the continents area
• Evaporated waters may result in many chemical types
PRISTINE RIVER CHEMISTRY
PRISRI : GLOBAL DISTRIBUTION OF DIC
MEDIUM-SIZED BASINS
3 500 - 200 000 km2, rheic basins (n = 480)
%
DIC CONCENTRATION
% HCO3- / -
DIC EXPORT
RARE
99,5
99
UNCOMMON
90
COMMON
75
VERY COMMON
50
25
COMMON
10
UNCOMMON
1
0,5
0,1
RARE
1
10
DIC mg/L
10
50
100
In 50% of basins
HCO3- exceed 80% of
anions
0,5
1
10
DIC concentration ranges
over 2 orders of
magnitude
50
g C.m-2.y-1
100
DIC export ranges over
3 orders of magnitude
GLOBAL CHANGE
WHAT IS GLOBAL CHANGE?
• Global Change is more than Global Climate Change
• It has natural PLUS human/social dimensions
• A constellation of changes, many global in domain
For example, we see large changes in:
Richards (1991), WRI
(1990)
Mackenzie et al (2002)
Reid & Miller (1989)
U.S. Bureau of the Census
NOAA
Vitousek (1994)
GLOBAL SYNDROMES OF RIVERINE CHANGES
(examples)
Flow regulation (Nile)
• River course fragmentation (Volga, Colorado)
• Neoarheism (Colorado, Amu Darya, Nile)
• Salinization (Rhine, Don, Murray, Colorado, Amu Darya)
• River bed silting (Huang He)
• Chemical contamination
asphixiation (Thames, Seine, Rhine)
inorganic contamination (Tinto, Seine, St Lawrence)
xenobiotics occurence
• Acidification (Scandinavia, SE Canada)
• Eutrophication (Loire)
• (Microbial contamination) (Ganges)
• (Aquatic species introduction & invasion)
•
PRESSURES ON HYDROSYSTEMS
TROPICAL FOREST CLEARING
PD9
• Forest clearing is one of the major land use change of the last 50 years
• Short term impacts on river fluxes include high supply of eroded material and loss of nutrients (although very
limited compared to other human impacts)
• Long term impacts are likely to occur for aquatic biota diversity and for the water balance
MAN AND WATER INTERACTIONS : NOTHING NEW
IMPERIAL ROME APPARTMENT BUILDING IN OSTIA
(200 AD)
FB2
• Such building had drinking water supply up to the first floor,
common flush toilets, and collected sewage
• Roof runoff and street runoff were also collected in drains
PRESSURES ON HYDROSYSTEMS
BLAST FURNACE AT COPCA MICAS (RUMANIA,
1970 ’s)
Environmental regulations and
surveys were abundant in
Former socialists countries
although barely enforced, thus
resulting in pollution hotspots
PF1
Nat. Geogr. Mag., June 1976
PRESSURES ON HYDROSYSTEMS
AGROCHEMICALS, FERTILIZERS AND OLIGOELEMENTS (Zn, Cu, Mo, B, …)
PF34
EMC
Agrochemicals may increase soil metal contents
Fertilizers leaks provide nitrate and total phosphorous
Global impacts of reservoirs on land to oceans
fluxes
• Most major rivers are impounded (neocastorization, Vörösmarty et al.,
1997)
- North Am : Columbia, Churchill, Colorado, Rio Grande,
Missouri, James Bay
- South Am : Caroni, Parana, Tocantis
- Africa : Volta, Nile, Zambezi, Orange, Niger
- Europe : Volga, Danube, Don, Dniept, Dniestr, Spain
- Asia : Yang Tse, Yellow, Indus, Tigris, Euphrate
- Australia : Murray
• Global reservoirs area : 500 000 km2
• Global impacts
- biodiveristy : loss of connectivity, regulated rive regimes
- biogeochemistry : retention of DOC, POC, N, P and silica
- hydrology : river aging (up to 2 y), hydrograph distortion
- geomorphology : river bed changes downstream dam,
sediment starving in coastal zone and related erosion
PRESSURES ON HYDROSYSTEMS
COLORADO HOOVER DAM (1935)
FA50
US Geol. Survey
(Nat. Water Summary,
1984)
• The first giant dam ever built
• South California and Arizona economies have greatly depended on
Hoover dam
NEOARHEISM
A VANISHED RIVER : THE COLORADO RIVER MOUTH
• All river water is used in the
basin including the water left at
the US/Mexico border and
desalinized at Yuma according to
the bilateral treaty
• Local indian culture in the
Colorado delta does not longer
exist
QB2
Nat. Geogr. Mag., 1979
NEOARHEISM
RIVER FLUXES TRENDS AFTER DAMMING THE
COLORADO EXAMPLE (1910-1960)
A : annual water flow
B : annual sediment flux
• Colorado changes are some of the
most dramatic change documented
in a river system
• This evolution was triggered by the
construction of the Hoover Dam in
1936
TE17
SEDIMENT TRANSFER
HIGHLY TURBID RIVER IN HIMALAYA
PD34
• Due to very active tectonic uplift and glacial abrasion Himalayan rivers are
naturally very turbid (1 < TSS < 10 g/L)
• Such rivers would be qualified as unsuitable for most water uses in most water
quality scales
RIVER BED SILTING
YELLOW RIVER COURSE CHANGES OVER THE
LAST 2000 Y
Pohai Sea
Yellow Sea
Yang Tse Kiang
AE33
Due to the high sediment load (natural, then enhanced) the Huang He has
changed its river mouth location over 975 km, thus flooding several times
its enormous flood plain
The last dike outbreak in the 1930’s, due to war action, has caused one
million casualties, mostly due to famine
SEDIMENT TRANSFER
SOURCES, SINKS AND TRANSFERS OR RIVER PARTICULATES
NATURAL VS ANTHROPOCENE CONDITIONS
Head waters
Ocean
• Sediment transfer in fluvial systems is a complex set of erosion/sedimentation/remobilization processes
• Human activities may completely modify and control sediment transfer quantity and quality (e.g. reservoirs,
pollution)
SEDIMENT TRANSFER AND RIVER BED SILTING
Sediment transfer : solving contradictions
• There is world wide evidence of increased erosion and transport in headwaters as
a result of land use change
- forest clearing
- agriculture
- urbanisation
• The Huang He sediment flux has increased 10 times between 1000 AD and 1950
• Yet most long term records of suspended sediment fluxes in large river do not
present significant increase (Walling et al., 2002)
• Most of the generated sediment is stored within basins from slopes to floodplains
and in lakes. This retention is also accelerated by reservoir construction
• The natural retention is minimal in small and steep basins as those encountered in
SE Asia. The world sediment budget to oceans is now taking it into account
(Milliman & Syvitski, 1992)
• Sediment sources and pathways and their associated carbon, nutrients and
pollutants loads are now more and more generated and controlled by human
activitites
SALINIZATION
GLOBAL SALINITY HAZARD
PC26
WD Williams
(Ambio)
• Salinity hazard, linked to the water balance, is wide spread on all continents
• Unadequate irrigation may result in salt-build up in soils, long-term
salinization of ground waters, and of rivers, thus limiting downstream water
uses
• Endorheic regions (e.g. Central Asia) are particularly concerned
• Climate change may augment this risk
GLOBAL SYNDROMES OF RIVERINE CHANGES
Dumping into the Rhine (kg/sec)
CHLORIDE POLLUTION OF THE RHINE RIVER BY
POTASH MINES (1945-2000)
UG53
During this period the daily release of NaCl has been
regulated so that Cl- did not exceed 200 mg/L
ASPHIXIATION AND FAECAL CONTAMINATION
IMPERIAL ROMA BIGGEST SEWAGE COLLECTOR :
THE CLOAQUA MAXIMA
• Urban water supply and
sanitation was at its best in
Imperial Roma
• It has been probably
unequalled until modern
sanitation (e.g. London) in the
late 1800 ’s
GG9
XIXth cent. drawing
ASPHIXIATION
RHINE RIVER ASPHIXIATION (1960-1995)
River Rhine near Lobith, oxygen saturation
percentage
average
minimum
OG17
1950
60
70
80
90
95
The O2 minimum period lasted 15 years until sewage
collection and Oxygen Demand treatment was implemented
(1960-1975)
R. Breukel
CONTAMINATION
SCHEMATIC TRENDS OF SEDIMENT CONTAMINATION
IN ESTUARINE CORES
TE3
• Heavy metals (A) have peaked in the 1960 ’s (USA) to the 1980 ’s (some W. Europe rivers),
their trends are barely documented on other continents
• Carcinogenic polyaromatic carbons may still increase in some regions
• Polychlorinated biphenyls do not exist in nature (xenobiotics) : they trace the modern
human pressure
• Both PAHs and PCBs are inadequately surveyed in rivers
XENOBIOTICS OCCURENCE
ATRAZINE HERBICIDE USE MAP IN THE USA
SC22
The Corn Belt is the essential user of herbicides which are carried
some 2000 km downstream to the Gulf of Mexico through the
Mississippi system
EUTROPHICATION
Discharge
∆pH
RIVER EUTROPHICATION : DAILY pH CYCLES IN
THE LOIRE RIVER(AT DAMPIERRE)
PA68
F. Moatar (1999,
Univ. Tours)
• During spring and summer algal blooms (chloro A > 100 µg/L) the daily pH cycles
may reach 1.2 pH units
• Such events can only be noted during stable low flows : they are destroyed by
floods
EUTROPHICATION
A SUCCESS STORY : NUTRIENTS CONTROL IN THE
RHINE R.
mg P /L
mg P /L
Van Dijk & Marteijn, 1993
• The major effort of sewage collection was between 1960 and 1975 : it
resulted in particulate P abatment and NH4+ decrease
• P-PO43- control then decrease was only achieved after the 1985 ban of P
detergents and the dephosphatation in most treatment plants
EUTROPHICATION
NITRATE TRENDS IN WORLD RIVERS
Thames
From 1960 to 1990 nitrate
has increased in most large
rivers
Maximum rates are observed
in smaller catchments
exposed to intensive fertilizer
use
Seine
Rhine
Danube
Mississippi
SD11
EUTROPHICATION
IRRIGATION, RESERVOIRS &
EUTROPHICATION :
THE SILICA RETENTION
• Already 4 000 km3/y (= 5% world runoff) loss through irrigation
(Shiklomanov, 1998)
• The retention of nutrients by reservoir eutrophication, as for silica,
combined with increased N and P loads in the last 50 y has generated
major changes of N:P:Si ratio in some riverine fluxes to coastal zone,
hence causing dystrophy as for the Danube and Mississippi coastal zone
Si:N (g/g) trend in Mississippi
1900
48
2000
0,9
TOWARDS GLOBAL PICTURES OF
RIVERINE CHANGES
• Geographic Information systems provide a new tool permitting the
combination of multiple informations layers
• Information layers are now available at fine resolutions (1 to 50 km) for
most Earth system components (runoff, river network, relief, lithology...) to
map past natural river state
• Socio-economic layers (water uses, environmental pressures, water needs)
are still being developed or available at coarser resolutions
• First global maps of present river state are coming out
COASTAL ZONE SEGMENTATION
THE NATURAL CONNEXION BETWEEN CONTINENTS AND OCEANS
THROUGH RIVERS IS COMPLEX
• Some river basins are presently not active as in Sahara (arheism)
• Some rivers are flowing to internal water bodies as Caspian Sea, Aral Sea, Chad Lake (endorheism)
• Some rivers can still be somewhat connected to oceans (Okawango-Zambezi, Kerulem-Amur)
• Some endorheic basins are mostly dry (Tarim, Lake Eyre)
GLOBAL MAPPING
COASTAL ZONE SEGMENTATION : AVERAGE RUNOFF PER SEGMENT
(mm/y)
• Coastal basins morphology
is highly variable from
narrow strips (Peru-Chile) to
very deep basins
(Mississippi-Amazon)
• Mean runoff in coastal
basins range over 3 orders of
magnitude as for other river
fluxes (sediments, carbon,
nutrients)
• Mediterranean seas as
Hudson/Foxe/Ungawa and
Golf of Mexico/Caribean may
intercept a major portion of
riverine fluxes to oceans
GLOBAL MAPPING
COASTAL ZONE SEGMENTATION:
AVERAGE POPULATION DENSITY PER SEGMENT (p/km2)
Population pressure within coastal basins varies over more than 2 orders of
magnitude from 0.3 inhab/km2 for the Laptev Sea or the Gulf of Carpentaria to
more than 300 inhab/km2 in South and East Asia
Global nitrogen fluxes through rivers : preindustrial vs contemporary
• The global N fluxes (tot N) have increased more than 3 times
• Regionally the fluxes have increased more than 10 times
• Agriculture and urbanization are the two major N sources
Green et al. 2003
UNH
POSSIBLE FUTURE OF RIVER SYSTEMS
• Understanding the Past Man and River interactions is a clue to future
scenarios
• Interactions are complex depending on local natural condition, water
needs, water literacy, heritages (pressures, mental,...), econmic factors
• Interactions should consider far-reaching impacts (teleconnections) and
long-term impacts, particularly on Earth system (climate, biogeochemical
cycles, coastal zone, aquatic biodiversity)
MAN AND RIVER RELATIONS
WORKING HYPOTHESES ON THE EVOLUTION OF
WATER QUALITY ISSUES IN WESTERN EUROPE
(accelerated scale)
WESTERN EUROPE
SEVERE IMPACT
CL
Faecal
Metals
MODERATE IMPACT
Radionucl.
CR
NEGLIGIBLE IMPACT
Nitrate
CN
Xenobiotics
PRISTINE
- 2000
0
1000
1492
1900
LOCAL IMPAC TS
1950
REGIONAL GLOBAL
1970
2000
ANTHROPOCENE
Meybeck, 2003, Philosophical transaction
• There is no simultaneity of water quality issues
• New issues have occured in the last 50 years
• Some issues have no been handled (e.g. faecal and organic pollutions)
Anthropocene evolution
PRESSURES ON AQUATIC SYSTEMS AND
ENVIRONMENTAL
RESPONSES
REGULATIO
N/RES
TO RATIO
N
REGULATIO
N/RES
TO RATIO
N
REGULATIO
N/RES TO RATIO N
RES
PO
RESNSES
PO NSES
RES PO
ES
REGULATIO N/RES
TONS
RATIO
N
RESPO NS ES
HUMAN PRES
SURES PRES SURES
HUMAN
HUMAN
PRES
S URES
HUMAN
PRES
SURES
LIMATEVARIABILITY
VARIABILITY
CCLIMATE
C LIMATE VARIABILITY
CLIMATE VARIABILITY
00
0
0
EC O L. EC
FARMING
O L. FARMING
EC
O L.GW
FARMING
ART.
REC
HARGE
ART.
GW
REC HARGE
EC
O
L.
FARMING
ART.
GW
REC
HARGE
ENVIR.ART.
REGUL.
GW
REC HARGE
ENVIR.
REGUL.
ENVIR. ENVIR.
REGUL.REGUL.
ATM. PO
LL. C
O LL.
NTRO
L NTRO L
ATM.
PO
CLO
ATM. PO
LL. CPO
O NTRO
ATM.
LL. C O
NTRO L
RENATUR.
/ RES TO//RES
R.
RENATUR.
RES
TOR.
R.
RENATUR.
TO
RENATUR. / RES TO R.
S
EW
AGE
C
O
LL.
/TREAT.
SEW
AGE
C
O
LL.
/TREAT.
S EW
C O LL. /TREAT.
S EW AGE
C OAGE
LL. /TREAT.
AGRO C HEMIC ALS
AGROCC
HEMIC
ALS
AGRO
HEMIC
ATM.
PO
LLUTIOALS
N
AGRO
CALS
HEMIC
ATM.PO
PO
LLUTIOIMPAC
N
MINING
TS
ATM.
LLUTIO
N
ATM.
POPO
LLUTIO N
URBAN
MINING
IMPACTS
TS P. IMPAC TS
MINING
IMPAC
RIVER ENGINEERING
IMPAC
URBANMINING
POP.
P.IMPAC
IMPAC
TS TS
URBAN
PO
TS
LAND
USE
URBAN
PO P. IMPAC TS
RIVER
RIVERENGINEERING
ENGINEERING
RIVER
ENGINEERING
LAND
LANDUS
USEE
LAND US E
TIME
1950
2000
1000
1800
1900
1950
2000 TIME
1000
1800
1900
1950 1950 2000 TIME
1800
1900
2000
1000 1000
1800
1900
Meybeck, 2001
TIME
< 0,1% gl obalare a affe cte d
< 0,1% gl obalare a affe cte d
0,1 to
1% AFFECTED
< 0,1% GLOBAL
<AREA
0,1%
gl obalare a affe cte d
0,1
to
1%
1
to
10
%
0,1 to 1%
1 to 10 %to 1%
1 to 10 % 10 t o 0,1
50 %
1
10
t
o
50
10 to 50 % > 50 % to%10 %
> 50 %
> 50 %
10 t o 50 %
> 50 %
Natu ral clim ate variabi lity
Natu ral clim ate variabi lity
NATURAL C LIMATE VARIABILITY
Natu
clim
variabi
An th ropoge
n i cral
clim
ateate
variabi
litylity
ANTHRO
GENIC
Anthropoge
ni c PO
clim
ate variabi lity
CAnthropoge
LIMATE VARIABILITY
ni c clim ate variabi lity
Human responses to environmental impacts are usually delayed
MAN AND RIVER RELATIONS
SCHEMATIC POSITIONS OF CONTINENTAL AQUATIC SYSTEMS
SHARED BY SOCIO-SYSTEMS AND EARTH SYSTEM
FUNCTIONS
USE
HUMAN
DRIVERS
CONTINENTAL
AQUATIC
SYSTEMS
RESOURCE
SERVICES
PRESSURE
GLOBAL
CHANGE
DRIVERS
CONTROL
EARTH
SYSTEM
RESPONSE
SOCIETAL
RESPONSES
SHORT TERM
REACTION
EARTH
SYSTEM
COMPONENTS
RIVERINE
SYNDROMES
LONG TERM
REACTION
SOCIAL AND
ECONOMIC
IMPACTS
EARTH SYSTEMS
CHANGES
SOCIO-SYSTEMS
EARTH SYSTEM
• The Driver-Pressure-State-Impact-Response cycle in socio-systems is generally
observed at short to medium periods (10-50 y)
• The parallel Environmental impacts-Earth System response- Regional to Global
Change is a long term reaction (100-1000 y) still poorly known
MAN AND RIVER RELATIONS
EVOLUTION OF CONTINENTAL AQUATIC
SYSTEMS FROM HOLOCENE TO ANTHROPOCENE
STATE INDICATOR
MODELS SCENAR IOSŹ/Ź
PROJEC TIONS
DIRECT SU RVEY S
ARCH EOLOGI CALŹ/ŹHISTORICALŹDATA
EN VIRONMENTAL ARCH IVES
100Ź000
10Ź000
1Ź000
1Ź800
1Ź950
2Ź000
2Ź050
TIME
RESPONSES OF CONTINEN TAL AQUATIC SYSTEMS TO CLIMATE
VARIABILITY, LAN D COVER CHA NGE & DIREC T HUMAN PRE SSURES
STATE INDICATOR
RESPONSES OF C.A.S. TO WATER US ES & LAND USE
A
QM
HM
B
C
P
Hm
Qm
100Ź000
10Ź000
1Ź000
BP
BP
AD
1Ź800
1Ź950
2Ź000
2Ź050
HOLOCENE
ANTHROPOCENE
TIME
Possible scenarios
A : stabilized level, major Earth
System change, unmanageable
for Human development (laissezfaire)
B : stabilized level with maximal
acceptable risk for Human
development and marked Earth
System change (suppression of
most polluted sites)
C : stabilized level : acceptable
risk for Human development
with minimal Earth System
change (precaution principle)
P : return to pre-anthropocene
level
CONCLUSIONS
• Only 30% of continents is actively exposed to river transfer
(92% of fluxes)
•Regional and local references must be looked for
• Present-day natural chemistry and fluxes are variing over 2 to
3 orders of magnitude
• Locally Humans may have modified some ionic and nutrient
fluxes by one order of magnitude
• Half of the world rivers are not any more in pristine state
• Such global scale evolution confirms the occurrence of a new era
where Human controls on Earth System match the natural ones :
the Anthropocene (Vernadski, Crutzen)