Restoration effects on N cycling pools and processes
Over the past several years, there has been an acceleration of restoration efforts to mitigate the consequences (i.e., ground and surface water chemical pollutants, erosion, etc.) of degraded ecosystems and enhance structural and functional components of watershed ecosystems that regulate biogeochemical cycling and associated aquatic components. Biogeochemical processes are complex because they operate at a variety of spatial and temporal scales (e.g., near instantaneous soil chemical reactions vs. bedrock weathering). Large-scale assessments of the integrity of these fine-scale processes would be a dauntingtask; however, our knowledge of ecosystem processes at larger scales (e.g., stands, watersheds, basins) suggests emergent (and measurable) properties that integrate these finer-scale processes. For example, nutrient budgets are key indicators of watershed health and have proven useful for evaluating response and recovery to a variety of disturbances and management activities (Swank and Vose 1997; Swank et al. 2001). Since water moves nutrients through the system, hydrologic, aquatic, and biogeochemical processes are tightly linked. Nutrient budgets are comprised of inputs (e.g., atmospheric deposition, fixation), internal pools and cycling (e.g., soil, litter, and vegetation pools and cycling rates), and outputs (e.g., stream chemistry, seepage or groundwater chemistry, denitrification) (Figure 5.1). The nutrient cycling components shown in Figure 5.1 serve as a focal point for identifying ecosystem nutrient pools or processes requiring restoration to enhance biogeochemical processes and aquatic systems. However, pool sizes and cycling rates can vary considerably among ecosystems (Table 5.1). This variation makes general assessments of restoration effects on biogeochemical cycling difficult because similar types of ecosystem degradation (e.g., insect-related mortality) may not have similar impacts on nutrient pools and processes among ecosystems. Similarly, this variation also implies that restoration treatments applied in one ecosystem may not have similar results in another. Despite these complexities, it is important to develop and apply restoration practices that restore biogeochemical cycling processes in degraded ecosystems, and to develop methods, metrics, and approaches for assessing the recovery of biogeochemical cycling pools and processes among contrasting ecosystem types. This chapter focuses primarily on developing metrics and approaches for assessing the recovery of biogeochemical cycling pools and processes.