Microbial influence on macroenvironment chemical conditions in alkaline (tufa) streams: perspectives from in vitro experiments - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 68

Fig. 4. Data for Experiment 1. Mean and 1s data for stacked diurnal macroenvironmental conductivity over
the 1 month period shown in Figure 1 (the same period as used for compilation of fig. 2). (a) Flume 1; (b) Flume 2;
(c) Flume 3; (d) Flume 4.

macroenvironmental temperature. An approxi-
mately 5 mS variability in these systems indicates
temperature changes of c. 0.8 8C, assuming that
conductivity changes by c.2%8C 21 , as is generally
the case for naturally occurring solutions (Sorensen
et al. 1987). This variability will be induced by the
thermal regime of the building in which the flume
systems are housed, though it is heavily damped
by our precautions to thermally buffer these
systems. Flumes 1 and 2 (colonized), which are in
the same room as Flumes 3 and 4 and therefore
experience the same diurnal variability in air temp-
erature, do not demonstrate the same thermally-
driven cycling. Consequently, some additional
process must be occurring within these systems
that provides sufficient diurnal variability to over-
whelm this physical control on conductivity.
Minimum conductivity in both systems is achieved
after the lights have switched on in the morning,
and maximum conductivity in the middle part of
the day.

cold conditions (compare 'mid-summer' with
'mid-winter' and 'cold summer' in Figs 5 & 6).
Relative changes in pH values are presented as
offset values for treatment data from mid-summer
data, so that negative offsets indicate lower pH in
the treatment. This reflects the higher solubility of
CO 2(aq) at lower temperature, and consequently is
a predictable component of the response of all of
these systems (Weyl 1958). Less predictably, the
pH changed in both flumes under reduced light
conditions, with Flume 3 showing an offset of 0.1
(Fig. 5) and Flume 4 an offset of 20.2 (Fig. 6).
Colonized flume (1 and 2) pH data remain domi-
nated by photosynthetic cycles, regardless of the
experimental conditions (Figs 7 & 8). However,
changing both light and temperature conditions
alter the state of this diurnal cycle profoundly.
Under 'Cold summer' conditions, both flumes water
experience a drop in night-time pH (Flume 1
0.1 and Flume 2 0.15) relative to 'mid-summer'
(Figs 7 & 8), which are similar to the offsets
found within sterilized systems (Figs 5 & 6).
Daytime pH is increased by 0.1 in the data for
Flume 1 (Fig. 7) and by 0.25 for Flume 2 (Fig. 8).
'Warm winter' conditions result a slight increase
in night-time pH (,0.1) for Flume 1 (Fig. 7) and
c. 0 change for Flume 2 (Fig. 8). However, in both
flumes day-time pH is increased, by 0.15 for
Flume 1 (Fig. 7) and 0.2 for Flume 2 (Fig. 8).
Despite differences between the flumes in other
experiments, both colonized systems show the

Investigation of the independent and combined
impacts of temperature and photoperiod
length (Experiment 2)

The impact of the experimental treatments on
ambient water pH in sterilized systems are shown
in Figures 6 and 7. The results for sterilized
flumes (3 and 4) show lower pH under relatively