Water Quality Response to Forest Biomass Utilization
Forested watersheds provide approximately 80% of freshwater drinking resources in the United States (Fox et al. 2007). The water originating from forested watersheds is typically of high quality when compared to agricul¬tural watersheds, and concentrations of nitrogen and phosphorus are nine times higher, on average, in agricultur¬al watersheds when compared to forested watersheds (Fox et al. 2007). Silvicultural activities typically occur on a low percentage of forested lands in any one year, and effects on water quality from silvicultural operations are typically localized and short-lived (Bethea 1985; Dissmeyer 2000). The effects of silvicultural activities on water quality have been reviewed on several occasions, and the findings are remarkably consistent. Throughout the United States, silvicultural activities have minimal effects on water quality, and potential effects from harvest operations are largely mitigated by the widespread adoption of best management practices (BMPs) (Binkley and Brown 1993; Fulton and West 2002; Grace III 2005; Stednick 2010; Ice et al. 2010). Silvicultural activities that may compromise water quality are typically nonpoint source and include road construction, ground disturbance from whole-tree skidding, mechanical site-preparation activi¬ties, herbicide application, and fertilizer application (Fulton and West 2002). In this chapter, we briefly review the current effects of silvicultural activities on water quality and then assess the potential effects of increased demand for biomass, based on select scenarios from the 2016 Billion-Ton Report (BT16), on several water-quality indicators including sediment, nitrate (NO3-), and total phosphorus (TP) load. The literature documenting the specific effects of biomass removal from forests on water quality is sparse at best. However, the majority of biomass would be harvested using harvest systems that mimic current silvicul¬tural practices. Therefore, it is reasonable to relate the potential effects of traditional forest-harvest operations to what we might expect from the removal of biomass.