| Sediment is the main pollutant associated with forest management. Once sediment reaches a water body there is potential for biotic stress, stream habitat alteration, and water quality degradation, but there is little understanding of how forest operations alter sediment delivery. Consequently, a 9-year paired watershed study was conducted on the Cheat Ranger District of the Monongahela National Forest in Tucker County, West Virginia to quantify sediment delivery occurring prior to disturbance (fall 1999-June 2001), during haul road construction (July 2002-Oct. 2003), and during road stabilization and two-age timber harvesting (Sept. 2003 to Oct. 2006; harvesting was intermittent during this period) on a 32.7-ha watershed. A control watershed remained undisturbed throughout the study. Silt fence was constructed along the entire stream channel in each watershed to collect the mineral material eroded from the adjacent hill slopes. Because effects to aquatic organisms are exacerbated by fine sediment, the collected mineral material was sieved into six particle size classes (>4 mm, 2-4 mm, 1-2 mm, 0.125-1 mm, 0.063-1 mm, and <0.063 mm) to further focus on the masses associated with fine mineral material. Mineral mass in essentially every particle size class collected during the road construction period was significantly greater than during pretreatment or road stabilization/harvesting (e.g., p = 0.0372 for < 0.063 mm). Approximately 60 percent of the mineral mass collected during the first year of road construction came from only 152.2 m of silt fence out of the 2414.0 m of total fence length in the treatment watershed. Harvesting did not significantly change when compared to the previous years of collection for any particle size class (p = 0.9347 for < 0.063 mm). In the control watershed, the same time period (2003 and 2004) was not significantly different from the all other years' of collection for any particle size class (e.g., p = 0.1896 for < 0.063 mm). Total precipitation, total number of days > 2.54 cm of precipitation, and spring days with precipitation greater than 2.54 cm explained a significant amount of the variability of the total mineral masses collected. By constructing the haul road at the stream crossings using a full bench construction method, mechanical delivery of sediment to the stream from the fillslopes approaching the stream crossings would have been avoided. |
