Abstract
Mountain meadows are unique wetland features on the landscape that provide a host of ecosystem services including water quality benefits. A large proportion of the meadows around the world are considered degraded due to past and present anthropogenic activities. Channel incision is a major contributor to meadow degradation and results in an unequal sediment load balance where more sediment is removed than is replenished. Increased hillslope surface runoff and sediment load transport are known to increase after wildfires, affecting the downstream water quality. This analysis was conducted as a paired watershed study and took place in the Upper Feather River Basin of northern California where severe wildfires are prevalent, and many meadows are considered impaired. Process-based restoration utilizing beaver dam analogs (BDAs) and other log structures on a burned and unburned degraded meadow stream were compared to an unrestored burned meadow to evaluate the effectiveness of restoration with post-wildfire sediment aggradation. Both restored meadows had higher percentages of pool sediment (63% & 23%) compared to the unrestored meadow (12%). Middle Creek, the restored-burned meadow, contained the most sediment (63%). Calculated suspended sediment load was reduced from upstream to downstream by 511 tonnes or 69%. BDAs were also effective at capturing sediment bound phosphorus, a known water quality pollutant and were reduced by 314 kg or 58%. Phosphorus enrichment ratio increased from upstream to downstream (p= 0.03) due to beaver dam analogs operating like sieves that settle out coarser materials and pass the finer sediments.
A Water Erosion Prediction Project (WEPP) model comparison of the measured streamflow, sediment, and total phosphorus loading resulted in over-prediction of streamflow (34%) and total phosphorus (65%) during both study years combined. However, the WEPP simulated sediment load for both years matched that of the measured load (1046 tonnes and 1044 tonnes, respectively). These findings suggest that this model has the potential to be used as a tool to estimate the sediment load necessary for process-based meadow restoration methods.