Influence of two-stage restoration on substrate composition and sediment flux in an agricultural stream

Conventionally-managed agricultural streams are generally disconnected from their floodplains and are characterized by high nutrient and sediment export, and unstable banks.  Two-stage ditch restoration has been developed to mitigate these issues through the construction of floodplain benches within formerly trapezoidal ditch configurations.  We implemented a two-stage manipulation over 620m in a northern Indiana stream in November 2007.  We are examining the effect of bench restoration on stream hydrology and channel substrate composition by quantifying habitat cover and measuring continuous turbidity before and after restoration. We predicted the two-stage would reduce turbidity through lower stream velocities. Additionally, decreases in stream channel fine sediments would be accompanied by increased organic matter content of bench soils. Post-restoration, we found decreased baseflow turbidity and mean daily sediment flux compared to the upstream control reach.  Largest declines occurred in autumn, coinciding with lowest stream discharges.  There were no significant differences in reach-scale coverage of sand or fine benthic organic matter suggesting that sediments were being deposited on benches.  However, bench organic matter content was variable and showed no significant increase post-restoration.  Results suggest that the mechanism for enhanced nitrogen removal associated with two-stage restoration may not be related to changes in sediment distribution or composition.