burial and evasion in European lakes and reservoirs:
a contribution to the search for the missing sink
PD Dr. Adam Vecsei
Prof. Dr. M. Hinderer (TU
It has become a generally
accepted fact that the anthropogenic release of greenhouse gases like CO2
has a significant effect on our climate. Since early industrialization to
now the atmospheric CO2 content increased from 280 ppm to over 360 ppm due
to burning of fossil fuels and changes in land use. Man has become a global
ecological force. Possible consequences are global warming, sea level rise
an increasing frequency of climatic extreme events with strong implications
for all domains of human life.
Large parts of the biogeochemical process are as yet not well understood.
A key to this problem is the global carbon cycle. Estimates have been made
for marine and terrestrial carbon budgets. These estimates are still very
rough and contain major errors. Anyway, these calculations suggest an unknown
carbon sink of ca. 1 Gt/a: the missing sink.
Lakes and artificial water bodies have been neglected in most calculations.
Although lakes and reservoirs cover only about 2 % of the land surface,
they seem to play a significant role within the global carbon cycle. Lakes
and reservoirs have high carbon accumulation rates compared to the ocean
and they are naturally oversaturated with CO2 relative to the atmosphere.
Thus, they seem to have an ambivalent function as carbon sink and source.
Lakes and reservoirs in Europe. Presentation is limited by the resolution
of the image and the used dataset.
Furthermore the rising
numbers of rivers affected by damming necessitate more investigations. About
half of all rivers are dammed and supposed 800'000 artificial waterbodies
exist worldwide. Most of them are insufficiently documented. Their effects
on the water and carbon cycles are still a point of discussion.
Appearance of lakes and reservoirs
In Europe most lakes are
of glacial origin and therefore related to Pleistocene ice cover. High density
of lakes can be found in Scandinavia, northwest Russia and eastern Germany.
Tectonic, volcanic and other origins are minor. Lakes are generally geologically
young. Lakes reaching ages of several million years are very rare in Europe.
Different distribution of lakes in European regions: The western alps with
large lakes within the foreland (left) and numerous lakes covering the south
of Finland. Cut-Out from Landsat satellite images.
The distribution of reservoirs depends
on demand, political and social circumstances, and geomorphology. The common
applications of reservoirs are: irrigation, public water supply, flood control,
hydropower, low flow enhancement and fish farming.
The Lago di Vogorno (Switzerland) features the highest retaining wall
in Europe (220 m).
Reservoirs are numerous
in states with semi-arid regions, e.g. Spain. Also in mountainous regions
dams are often used for hydropower (Austria, Switzerland). Beside large
dams there are countless small artificial waterbodies like fire water ponds
which are difficult to quantify.
Carbon in lakes and reservoirs
Carbon in lakes and reservoirs
appears in different forms: as Dissolved Inorganic Carbon (DIC), Dissolved
Organic Carbon (DOC) and Particulate Organic Carbon (POC).
Simplified model of the main relevant carbon fluxes within a lake.
DOC is generally the dominant
species in lakes and is delivered from the catchment area. Major source
are carbon rich soils, e.g. peatlands.
The stable phase of DIC in most water is bicarbonate (HCO3-). It is either
produced by rock weathering or by decomposition of organic material within
the lake or the catchment. About half of the DIC from weathering of carbonate
rocks is of atmospheric origin. The rest is derived from dissolution of
carbonate minerals. Silicate weathering produces DIC of nearly entirely
POC is transported into the lakes through rivers and air. It is also generated
autochthonously by primary production within the lake. POC that is not lost
by decomposition or outflow is buried in lake sediments and thereby withdrawn
from the carbon cycle for a presumable long time. Reservoirs have much higher
sedimentation rates compared to lakes and are for that reason of special
Carbon can be stored in lake sediments as carbonate or organic matter.
This depends basically on alkalinity, primary production, water hardness
and sedimentation rates which are in turn related to other parameters like
catchment characteristics or climate.
Carbon is emitted from the lake through the outflow or by degassing. The
mainly released gases are CO2 and methane from decomposition of organic
matter. The lake surface is generally not in equilibrium but several times
oversaturated in CO2 with the atmosphere.
Water transport, degassing and burial make lakes and reservoirs important
carbon exchange sites.
The aim of the study is
to make a reliable estimate for the carbon budget of European lakes and
Thus, a database of relevant facts of European lakes, reservoirs and related
catchment areas will be created. This includes all available information
on water geochemistry, catchment characteristics, hydrological conditions
and sediment composition. Data will be implemented into a GIS and tested
for correlations among parameters. These results will be used for extrapolations
of carbon burial in and emission from all European lakes, including error
The result of the study should allow important insights into the role of
lakes and reservoirs within the carbon cycle. We intend to continue the
study on a global scale at a later date.