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 66

amplitude of diurnal changes in the earliest few days
of the experiment reflect the high buffering capacity
of the water, rather than low microbial activity.
After c. 10 days, approximate equilibrium in terms
of dissolved calcium concentration was reached
and the amplitude of diurnal variability in pH in
Flume 1 stabilized at approximately the same time.
However, the amplitude of pH variability in Flume
2 continued to increase until 30 days, after which it

began to reduce. The sterilized Flumes 3 (Fig. 1c)
and 4 (Fig. 1d) show an early period of raised pH fol-
lowed by a smooth fall to a position of equilibrium.
Some variability around this equilibrium can be
found in both flumes, but this is essentially random
noise. This experiment was fully replicated, with
similar results.
The pH data presented in Figure 1 and sub-
sequent figures can be viewed as a proxy for the

Fig. 1. Data for Experiment 1. Macroenvironmental pH evolution of flume systems subsequent to addition of water
from Welton Beck. The red vertical line indicates the start of the experiment. (a) Flume 1; (b) Flume 2; (c) Flume 3;
(d) Flume 4; (e) [Ca 2þ

(aq) ] in all four flumes. The decrease in [Ca 2þ (aq) ] and corresponding increase in the amplitude of

pH variability in Flumes 1 and 2 over the first 2-3 weeks reflect declining buffering capacity in the ambient water.