Sampling design
We began to sample the experimental units 23 days from the beginning of
the experiment. We removed one control and three treatment AS (F1, F2
and F3) from each stream, also using a hand sieve, and collected a total
of four experimental units per stream per sampling activity. Other four
AS were again removed four days later until the 39th day of the
experiment, when the fifth and last AS was removed from each stream. At
this stage of the experiment the AS were always collected before
applying the disturbance. The experimental units amounted to 200 after
the frequency and intensity experiments (20 units per stream, 5 streams
and 2 experimental batteries).