20 pages,7 figures, 6 tablesUsing electron microscopy techniques (SEM, LTSEM) coupled with analytical methods (XRD and
EDS) the role of phosphorus has been assessed in the formation of freshwater calcite deposits (tufa) in
a small pond of the Ruidera Lakes (Spain). Differences between the cell walls and sheaths of bacteria
and eukaryotic algae as well as the existence of additional layers of extracellular polymeric substances
(EPS) were features that lead to differences in the process of induced calcite biomineralization. Phosphorus
has influence in the biomineralization of the EPS, sheaths and cell walls of cyanobacteria allowing
for fossil preservation whereas does not participate in the calcite precipitation around algae and
mosses. This variability may explain the different positive or negative roles played by natural or artificial
inputs of phosphorus in hard water lakes and the different morphological features of calcite precipitates
associated with eukaryotic and cyanobacteria picoplankton found in natural environments. The
biomineralization observed is in agreement with the isotopic composition of the tufa layers that reflect
the variations in environmental conditions around biological communities.Work by V S-E and A de los R, was supported by the Spanish Ministry of Education and Science
through the programPeer reviewe