Samples were taken where irrigation water entered (considered
clean and pesticide free) and exited both treatments. Macroinvertebrates
were collected from July 2003 to August 2004, using
the artificial substrate method (Castillo, 2000). Each substrate
consisted of a concrete block (20 cm × 12 cm × 6 cm) inside a nylon
mesh bag (Trama et al., 2008), which was placed under the water
for colonization by macroinvertebrates for 1 month. Two blocks
were placed in the irrigation channel (entrance into the field) and
two more blocks were placed into the drainage channel(water exit)
on each treatment (organic or conventional). Each bock was considered
as a an individual sampling unit and the total sampling
effort consisted of four blocks sampled every month for 1 year
(2003–2004) on each cultivation site (48), for a total of 96 blocks
sampled for the study.
In order to collect macroinvertebrates, the blocks and mesh
were scrubbed with brush and water over a 500 m sieve. The
passed content was placed into 90% Ethanol until identified.
Macroinvertebrates were separated in multi-plates by morpho
types, and then classified by species if possible, or by genus or