Soil biogeochemistry
Soils are deep, highly weathered, and generally Inceptisols or Ultisols (Boccheciamp 1977; Soil Survey Staff 1995). Soils are high in clay content and regolith extends to 10s of meters below the soil surface (Buss et al. 2017). Organic matter, nutrients, and exchangeable cations vary with lithology (volcaniclastic vs granitoid; McDowell et al. 2012), geomorphic position (ridge vs valley; McDowell et al. 2012), and position in the drainage network (higher soil cations below knickpoints in the granitoid terrain; Porder et al. 2015). Soils on middle to high elevations are very strongly acidic with low base saturation (<20%) due to a strong leaching environment (Ping et al. 2013). Weathering rates are very rapid, and the well-studied Icacos watershed is the fastest weathering granitic terrain on Earth (White et al. 1995). Soils show strong temporal and spatial variability in redox regime (Liptzin et al. 2010, Liptzin and Silver 2015), with drought causing large increases in average oxygen concentration at all topographic positions except riparian valleys (O’Connell et al. 2018). Landscape movement on uplands through landslides, slumps and fluvial/alluvial proc­esses has a significant effect on variation of C stores (Ping et al. 2013). Earthworms play a major role in soil nutrient cycling as well as in maintaining soil infiltration (Larsen et al. 2012).