Particle transport and transient storage along a stream-size gradient in the Hubbard Brook Experimental Forest

The transport and deposition of fine particulate organic matter (FPOM) is an important flux linking upstream and downstream reaches of stream ecosystems. However, few studies have attempted to identify physical controls on particle transport. One reason has been the lack of relatively simple, inexpensive methods. We describe a new technique for measuring fine particle transport in streams using fluoresently labeled yeast as FPOM analogs. We used steady state injections of yeast and a conservative tracer (C1) in 6 reaches along a stream continuum at the Hubbard Brook Experimental Forest to explore the relationship between hydrologic properties of stream reaches and particle transport. The yeast technique is relatively easy and inexpensive, and measures of fine particle transport derived from this approach were comparable to those obtained for natural seston and other seston analogs in similarly sized streams. The transport distance of yeast particles (S_p) increased along the stream continuum. S_p was negatively correlated with relative transient storage (k₁/k₂) and positively correlated with hydrologic exchange rates of the main channel (k₁) and transient storage (k₂). The depositional velocity of yeast (v_dep), which normalizes average transport distances for stream velocity and depth, showed no trend along the continuum and was not related to k₁, k₂, or k₁/k₂. Together, these results suggest that velocity and depth were the most important factors in determining differences in particle transport along the continuum.