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Table 1. Soil horizon mass, carbon (C) and nitrogen (N) pools, C and N concentrations, and C:N ratios in organic and mineral (0-10cm) soil horizons on adjacent old-growth and second-growth forest hillslopes at the Fraser Experimental Forest, CO. Values are means with standard errors (n=10 per hillslope type). Within each depth, * and ** denote differences at p<0.01 and <0.001 using a Student’s parametric t-test.
Table 2: Discharge, dissolved organic carbon (DOC), total dissolved nitrogen (TDN) concentrations and annual fluxes in subsurface flow from adjacent old-growth and second-growth hillslopes at the Fraser Experimental Forest, CO. Values are means with standard errors for the 2016, 2017, and 2018 snowmelt seasons. Sample numbers for DOC and TDN were n=36 for the old-growth and n=48 for second-growth. Differences between hillslope treatments are noted by ** at p<0.001 using a Welch-Satterthwaite non-parametric t-test.
Figure 1. Average daily subsurface flow (A) from adjacent old-growth and second-growth hillslopes at the Fraser Experimental Forest for 2016, 2017 and 2018. Dissolved organic carbon (B) and total dissolved nitrogen (C) in subsurface flow (old-growth n = 36; second-growth n = 48).
Figure 2. Components of fluorescing DOM (FDOM) in subsurface flow differentiated by fluorescence regional integration (FRI) modeling. Values are means from 2016, 2017 and 2018 for adjacent old-growth (n=23) and second-growth (n=35) hillslopes. Differences between FRI regions (RI-RV) were identified on logit transformed data at * and ** at p<0.01 and 0.001 using a Welch-Satterthwaite non-parametric t-test.
Figure 3. DOM quality and reactivity in subsurface leachate for adjacent old-growth and second-growth hillslopes. DOM quality examined through fluorescence index (A), and humification index (B) for samples collected during 2016, 2017, and 2018 flow periods (n=23 for second growth and n=35 for old-growth). Biological oxygen demand assays of DOM reactivity report oxygen consumption during the 2018 flow period (C).
Figure 4. Reactivity measured as oxygen consumption rates for DOM extracted from O-horizon litter inputs and subsurface flow exports (n=10 per each hillslope treatment with standard error bars). The dashed line shows oxygen consumption for a sample of the native microbial culture without hillslope DOM added (experimental control). Differences between hillslope treatments are noted by ** at p <0.001 using a Student’s parametric t-test.