Ecological Archives E096-110-A1

Philip G. Taylor, William R. Wieder, Samantha Weintraub, Sagy Cohen, Cory C. Cleveland, and Alan R. Townsend. 2015. Organic forms dominate hydrologic nitrogen export from a lowland tropical watershed. Ecology 96:1229–1241. http://dx.doi.org/10.1890/13-1418.1

Appendix A. Supplementary figures showing scaling between carbon and nitrogen in soil and stream water, a simplified watershed nitrogen budget, and a table showing seasonal changes in carbon and nitrogen within a small watershed in Costa Rica.

Fig. A1. Scaling between dissolved (black circles) and particulate (white circles) organic carbon and nitrogen in stream water. Inset shows the full range of POC and PON values collected during baseflow and storm flow. The average C:N stoichiometry of potential sources of organic matter, including microbial biomass and products (Cleveland and Liptzin 2007), mineral soil organic matter and leaf litterfall (Wieder et al. 2009) are shown as solid lines and labeled to the right of Fig. A2. The dashed lines are best-fit linear relationships.

Fig. A2. Scaling between lysimeters and stream water (A) DOC and (B) NO₃- illustrating the difference in concentrations between soil solution and stream water. Open and closed circles represent chemistry from lysimeters installed at 15 and 50 cm depth, respectively. Dashed line is 1:1 ratio.

Fig. A3. Nitrate as a function of dissolved organic carbon in shallow (white circles) and deep (black circles) soil solution as well as stream water (diamonds). The solid lines represent molar ratios of DOC:NO₃-, which included for visual illustration.

Fig. A4. Simplified input – output budget of the watershed N cycle with emphasis on N stocks and key internal fluxes (gross and net rates, respectively) in the top 10 cm of soil. Fixation from Reed et al. 2007, soil N from Cleveland et al. 2003, gross N fluxes from Wieder et al. 2013, N₂O fluxes from Wieder et al. 2011, net nitrogen processing, N deposition and hydrologic N losses from this study. Litterfall N calculated as the product of litterfall (this study) and average fresh litter C:N ratio (Wieder et al. 2009). Symbiotic N fixation, dry N deposition and N₂ flux remain unmeasured, though preliminary data for symbiotic N fixation from neighboring mature forests suggest relatively low rates (Sullivan and Cleveland, unpublished data). Units in kg N·ha^-1·y^-1.

Table A1. Seasonal mean and standard deviation of DOC, DON, and DIN in soils and stream water.

* BD: Below analytical detection (3 μg/L)
** Averages reflect flow-weighted mean concentrations at collected during baseflow.

Literature cited

Cleveland, C. C., A. R. Townsend, S. K. Schmidt, and B. C. Constance. 2003. Soil microbial dynamics and biogeochemistry in tropical forests and pastures, Southwestern Costa Rica. Ecological Applications 13:314–326.

Cleveland, C. C., and D. Liptzin. 2007. C:N:P stoichiometry in soil: is there a "Redfield ratio" for the microbial biomass? Biogeochemistry 85:235–252.

Reed, S. C., C. C. Cleveland, and A. R. Townsend. 2007. Controls Over Leaf Litter and Soil Nitrogen Fixation in Two Lowland Tropical Rain Forests. Biotropica 39:585–592.

Wieder, W. R., C. C. Cleveland, P. G. Taylor, D. R. Nemergut, E.-L. Hinckley, L. Philippot, D. Bru, S. R. Weintraub, M. Martin, and A. R. Townsend. 2013. Experimental removal and addition of leaf litter inputs reduces nitrate production and loss in a lowland tropical forest. Biogeochemistry 113:629–642.

Wieder, W. R., C. C. Cleveland, and A. R. Townsend. 2009. Controls over leaf litter decomposition in wet tropical forests. Ecology 90:3333–3341.

Wieder, W. R., C. C. Cleveland, and A. R. Townsend. 2011. Throughfall exclusion and leaf litter addition drive higher rates of soil nitrous oxide emissions from a lowland wet tropical forest. Global Change Biology 17:3195–3207.

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