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structural EPS domains was low in the investigated
streams, and calcium carbonate crystals were
detected in all of them. However, a clear association
of calcium carbonate crystals with diatoms or their
stalks
'Biodiversity and DNA-Taxonomy of Algae and Cyano-
bacteria in calcifying Biofilms'(Fr 905/13, Ar 335/6),
'Control of Mineralization Processes by heterotrophic
and autotrophic Prokaryotes in high-PCO
2
-Biofilms of
tufa systems'(Ar 335/5, Sta 184/19), 'In situ Structure
and Function of Biofilm-Systems during Mineralization
of Carbonates' (Ne 904/2), and 'Influence of Temperature,
Oxygen Concentration and Concentration of organic
Substrates on marine microbial Carbonate Dissolution'
(Be 2167/7). NB, KIM and TF thank Gabriele Schauer-
mann and Ajoze Marrero-Cal´co for their skilful assistance
in the sequencing work, Jessica Ramm for provision of yet
unpublished results, as well as Regine Jahn, FU Berlin, for
SEM support and training of NB in diatom identification.
The work of TF was also supported by the German
Federal Ministry of Education and Research, BMBF
(AlgaTerra project, grant 01 LC 0026) within the
BIOLOG program. SC and ES thank Evelyne Brambilla,
DSMZ, for the skillful isolation of isolates from water
and tufa. We thank Christine Heim for providing the
field image of the Erasbach rivulet.
Two anonymous reviewer provided detailed and helpful
comments and suggestions.
was
not
detectable
during
any
of
the
sampling periods.
(5) Microsensor measurements demonstrate
that tufa biofilm calcification is, contrary to previ-
ous assumptions, controlled by the photosy-
nthetic activity of the biofilms. Cyanobacterial
tubes in karstwater streams therefore reflect
photosynthesis-induced precipitation, not passive
impregnation due to high external supersaturation
as a result of physicochemical CO
2
degassing.
Mass balance calculations, however, suggest that
biofilm photosynthesis is responsible for only 10
to 20% of Ca
2þ
loss in the stream, while remaining
Ca
2þ
loss may derive from physicochemical
precipitation on branches, leaves and fine-grained
calcite particles.
(6) Annual laminae couplets of tufa stromatolites
in the investigated karstwater streams reflect seaso-
nal changes, mainly driven by temperature and
irradiation: Porous microspar layers formed by
winter - spring biofilms with abundant diatoms
and scattered cyanobacteria alternated with dense
microcrystalline calcite layers formed by summer -
autumn biofilms with erect cyanobacterial filaments.
(7) Photosynthesis-induced microgradients in
tufa-forming biofilms do not cause
12
C-depletion
in the precipitated carbonate. Consequently, stable
carbon isotope values of tufa stromatolite carbo-
nate reflect that of water column, underlining the
potential of tufa stromatolites for palaeoclimate
reconstructions.
(8) Slowly or discontinuously growing tufa
stromatolites are subject to early neomorphism,
i.e. palisade crystal formation, within the calcite
supersaturated stream and laterally moving pore
waters, once biofilm exopolymeric matrix is
removed. Therefore, only fast and continuously
growing tufa crust appear to be suitable for palaeo-
climate reconstructions.
(9) While photosynthesis is the major mechanism
in cyanobacterial calcification and tufa stromatolite
formation within the karstwater streams, hetero-
trophic activity including exopolymer-degradation
and secondary Ca
2þ
-release rather decreases calcite
saturation, contrary to settings high in dissolved
inorganic carbon such as soda lakes. Consequently,
tufa stromatolites show cyanobacteria-related cal-
cification fabrics, while soda lake microbialites
show fabrics related to exopolymer degradation,
possibly analogous to marine counterparts.
Appendix: methods
Hydrochemistry: Water samples for titration of total
alkalinity were collected in Schott glass bottles, and for
determination of main anions and cations (Ca
2þ
,Mg
2þ
,
Na
þ
,K
þ
) in pre-cleaned PE-bottles. Samples for cation
analysis were filtered in the field through 0.8 mm
membrane filters (Millipore) and fixed by acidification.
Samples were stored cool and dark until laboratory
measurements. Temperature, electrical conductivity, pH,
and redox potential of water samples were recorded
in-situ using a portable pH meter (WTW GmbH) equipped
with a Schott pH-electrode calibrated against standard
buffers (pH 7.010 and 10.010; HANNA instruments),
and a portable conductivity meter (WTW GmbH).
Dissolved oxygen was analysed titrimetrically following
the Winkler method. Total alkalinity was determined by
acid-base titration immediately after sampling using a
hand-held titrator and 1.6 N H
2
SO
4
cartridges as titrant
(Hach Corporation). Main cations (Ca
2þ
,Mg
2þ
,Na
þ
and
K
þ
) were analysed either by flame AAS (atomic absorp-
tion spectroscopy, Philips-Unicam) in case of Reinsgraben
and Erasbach, or by ion chromatography with suppressed
conductivity detection (Dionex Corporation) in case of
Westerh¨ fer Bach and Deinschwanger Bach. ICP-OES
(Perkin Elmer) was used to determine Sr
2þ
and Ba
2þ
.
Anion concentrations (Cl
2
,SO
22
and NO
3
2
) were
measured either by ion chromatography with indirect
photometric detection (Waters) in case of Reinsgraben
and Erasbach, or by ion chromatography with suppressed
conductivity detection (Dionex Corporation) in case of
Westerh¨ fer Bach and Deinschwanger Bach. Dissolved
phosphate and dissolved silica concentrations were
measured by spectrophotometric methods (Unicam).
Measured values were processed with the computer
program PHREEQC (Parkhurst & Appelo 1999) in order
The study is part of the research unit 'Geobiology of
Biofilms' (DFG - FOR 571; publication #47), funded by
the German Research Foundation, with the subprojects
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