Assessing Organic Matter Breakdown and Associated Macroinvertebrate Community Structure in Headwater Streams: Effects of Hydrologic Gradients and Upland Timber Harvesting

摘要

I examined the effects of hydrologic gradients and upland timber harvesting with different streamside management zone widths on yellow-poplar (Liriodendron tulipifera) processing and the associated macroinvertebrate community structure in the Cumberland Plateau ecophysic region, U.S.A. Prior to upland timber harvesting, 5.0 ± 0.1 g yellow-poplar leaf packs were constructed, zip-tied to gutter nails, and placed into 7 perennial and 6 temporary stream reaches with similar physiochemical and geomorphic characteristics. From December 2007 to May 2008, 3–5 leaf packs were collected per reach monthly. I found significant differences in the functional feeding group composition. Temporary reaches contained higher shredder, gathering-collector, predator, and total macroinvertebrate abundances. Shredder and total macroinvertebrate biomass was also higher in the temporary stream reaches. Gathering-collector biomass along one measurement was higher in the temporary streams. Perennial and temporary stream reaches contained similar macroinvertebrate diversity. Logging operations occurred from May 2008–December 2008. After logging operations ended, yellow-poplar leaf packs were placed into the perennial and temporary reaches of 3 control and 3 treatment streams (2 with same SMZ width, 1 different). From December 2008–May 2009. Leaf packs were collected monthly. Within the temporary and perennial stream reaches, no significant differences were detected between control and treatment yellow-poplar processing rates. No significant differences were detected between the control and treatment functional feeding group composition in abundance and biomass. Post-harvest, taxon richness increased in both the perennial control and treatment streams, while richness declined in the temporary control and increased in the temporary treatment. My findings indicate that when water is present, organic matter processing will function similarly to downstream reaches that have continual water flow. During seasonal flow patterns, macroinvertebrate communities associated with organic matter are present in temporary streams and may exceed perennial stream reaches in their density and biomass. This indicates that temporary streams are physically suitable habitats for macroinvertebrate fauna and contribute to a stream’s form and function. Overall, no observed distinct response in yellow-poplar processing rates or the associated macroinvertebrate community structure was detected within the perennial or temporary streams. Macroinvertebrate community structure varied spatially and temporally. On the taxonomic level, increases in taxa-specific abundance and biomass remain to be explained. Future research assessing interactions on the taxonomic level might help explain increases or decreases in abundance and biomass in relation to treatment effects. This study documented the response of organic matter breakdown and associated macroinvertebrate community structure during the 1st 5 months after logging. Thus, it is only a snapshot of stream ecosystem response to disturbance. Long-term studies are needed to evaluate full ecosystem response and recovery. Due to uncontrollable factors, I was not able to evaluate the success of different SMZ widths. Results documented should be treated with hesitancy, until full ecosystem response has been documented.