Streams are constantly subject to downstream movement of materials. The role of fallen leaves in resisting downstream transport of particulates is largely unquantified. The litter exclusion study at Coweeta presented the opportunity to study a stream without litter input. I expected removal of leaf litter to reduce the capacity of the stream to retain fine particulate organic matter, FPOM. However, leaves are also a major source of FPOM. I studied the effect of leaf exclusion on FPOM transport by field sampling and by generating computer simulations of particle transport in the stream.

Sampling of suspended particles during storms showed that although litter inputs and subsequent particle generation were greatly decreased (Wallace et al. 1997), storm exports did not differ significantly from those of the reference stream. This suggested that the effect of litter exclusion was to reduce FPOM retention. Although there was no new organic matter entering the stream during the exclusion period, entrainment of stored material compensated for it.

The computer simulations predicted higher concentrations of FPOM for storms after litter exclusion than I actually measured except during heavy rains that greatly increased discharge. These results suggested that after litter exclusion, low-intensity storms exported lower concentrations than before exclusion. However, after exclusion, intense storms that greatly increased discharge entrained higher concentrations of FPOM.

Both field studies and computer models indicated that stability of the litter-excluded streambed was lower compared to the reference and pre-treatment streams, and stability was further reduced with increased discharge.