Colonization and production of macroinvertebrates on artificial substrata: upstream-downstream responses to a leaf litter exclusion manipulation

1. Macroinvertebrate colonization dynamics were examined on artificial substrata in a stream with terrestrial litter inputs excluded, downstream of the litter-exclusion treatment, and in a reference stream. 2. Short-term examination of the rates of organic matter accrual and invertebrate colonization demonstrated significantly lower accumulation of leaf detritus and invertebrates in the litter-excluded reach and a short distance downstream of that reach. 3. All major fractions of organic matter and invertebrates declined on artificial substrata during the 3-year litter exclusion. Further, secondary production on artificial substrata in the litter-excluded reach decreased from 6.2 to 1.5 g AFDM m(-2) year(-1) from pretreatment to the third pear of litter exclusion, respectively. 4. Downstream, fine particulate organic matter on artificial substrata decreased during litter exclusion, and there was a significant reduction in colonization of collector-filterers. Total secondary production downstream of the litter exclusion declined >70%, demonstrating that downstream colonization dynamics are linked to upstream detritus inputs and processing by stream invertebrates.