Benthic detritus dynamics in a mountain stream

The dynamics of sedimentary detritus was examined over a 17-month period in a third-order mountain stream in Colorado. Autumnal and vernal peaks in total detritus standing crop (197 g and 165 g AFDW m⁻², respectively) were associated with leaf abscission and ice out. The flushing action of snowmelt runoff rapidly reduced benthic detritus to 14 g AFDW m⁻². Detrital size classes differentially contributed to temporal fluctuations in total detritus. The autumnal maximum was largely comprised of coarse particulate organic matter (CPOM), primarily leaf litter. The large increase following ice out was mainly due to fine detritus (FPOM, 0.45–75 μm) which accounted for > 50% of benthic detritus during 9 months of the year. Evidence suggests that changes in standing crop and particle size distribution during the extended period of ice cover (November-March) resulted from in situ processing rather than transport. Despite major differences in climate, geochemistry and hydrology, the Colorado stream exhibited patterns of detrital dynamics remarkably similar to an eastern deciduous forest stream.