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).