Similarities between N and S Loading/Biogeochemistry of Forested Ecosystems

1. Ecological Perspectives on Critical Loads - Linkages between Biogeochemical Cycles and Ecosystem Change Differences and Similarities in N and S Cycling with an Emphasis on Forested Ecosystems in the United States by Myron J. Mitchell SUNY-ESF Syracuse, NY

2. Similarities between N and S Loading/Biogeochemistry of Forested Ecosystems

3. Wet Deposition Dry Deposition Nitrogen Loading Litter Inputs Gaseous N Losses Uptake Organic Nitrogen Immobilization Dissimilatory Reduction Of NO3- Mineralization NH4+ NH4fixation Nitrification Clays Abiotic N Retention NO3- Leaching to Surface Waters DON

4. Wet Deposition Dry Deposition Sulfur Loading Litter Inputs Uptake Gaseous S Losses Organic Sulfur Mineralization Immobilization Oxidation Dissimilatory Reduction Adsorbed Sulfate Desorption Adsorption SO42- SO42- Sulfur Minerals Leaching to Surface Waters Weathering DOS

5. Differences between N and S Loading/Biogeochemistry of Forested Ecosystems

6. Unique or important attributes Wet Deposition Dry Deposition Litter Inputs Gaseous N Losses Uptake Organic Nitrogen Immobilization Dissimilatory Reduction Of NO3- Mineralization NH4+ NH4 fixation Nitrification Clays Abiotic N Retention NO3- Leaching to Surface Waters DON

7. Wet Deposition Dry Deposition Unique or Important Attributes Litter Inputs Uptake Gaseous S Losses Organic Sulfur Mineralization Immobilization Oxidation Dissimilatory Reduction Adsorbed Sulfate Desorption Adsorption SO42- SO42- Sulfur Minerals Leaching to Surface Waters Weathering DOS

8. We know that in general sulfur loadings are more closely linked to sulfate losses than nitrogen loadings to nitrate loss.

9. Johnson & Mitchell, 1998

10. Aber et al. (2003) BioScience 60 WV CAT 50 ADK VT 40 NH ME 30 20 10 0 4 6 8 10 12 4 6 8 10 12 Threshold Response Spring (n=216) Summer (n=354) NO3- (mmol/L) Estimated N Deposition (kg ha-1 yr-1) Summer nitrate = 2.5 * N Deposition – 14.4, R2 = 0.30, P < 0.0001 Spring nitrate = 6.7 * N Deposition – 40.7, R2 = 0.38, P < 0.0001

11. What causes variation in relationships between S loadings and SO4 losses in drainage waters? • Generally relationship is better with highest S loadings. • Sulfate adsorption relationships have a major influence spatial patterns. • Weathering contributions can be important in some watersheds. • With decreasing loading internal S sources become more important (weathering and organic S mineralization).

12. Soils with high SO42- adsorption Rochelle et al. (1987)

13. Low pH (from nitrification) enhances SO42- adsorption (Mitchell et al., 1989) Harvest followed by enhanced nitrification

14. [SO42-] 0 Days Discharge Drier conditions result in higher SO42- concentrations in Ontario, Canada (Eimers and Dillon, 2002)

15. What causes the spatial variation associated with N loadings • Land use history including harvesting and fire. • Forms of N input (NH4 versus NO3). • Types of vegetation affecting N mineralization and nitrification rates. • More closely linked with other biotically regulated processes including soil freezing (disrupts fine root uptake) and carbon dioxide availability. • Also seems to be highly sensitive to climatic effects including overall temperature effects and the role of the snow pack.

16. Campbell et al.,2004 DIN INPUT-OUTPUT BUDGETS AT THE MOST INTENSIVELY MONITORED WATERSHEDS SR HB9 9 EBB HB6 BSB 8 CP HW 7 LR kg DIN ha-1 yr-1 6 F10 5 F4 F13 4 3 2 Input 1 Output 0 Substantial variation in DIN losses even for sites with similar DIN inputs

17. More sugar maple more nitrate Concentration of nitrate in B-horizon soil solution in mixed-species stands in the Adirondack Mountains plotted against the percentage of sugar maple in the stand (Lovett and Mitchell, 2004)

18. Ca rich site has greater proportion of sugar maple resulting in higher NO3- generation in two adjacent watersheds in Adirondacks (Christopher et al., 2006).

19. Importance of biotic cycling of N and S Stable isotopic results

20. Catskills of New York State

21. NO3- Isotope Data (Burns & Kendall 2002) Microbial processing of N

23. Loch Vale nitrate isotopes, 1995 100 60 20 -20 -4 -2 0 2 4 6 d15N (NO3) Winter snow Rainfall Snowmelt d18O (NO3) Spring snow Streams Groundwater Microbial nitrate (Campbell et al., 2002)

24. At Sleepers River, VT: values of 34S and 18O of SO4 in streams between bedrock and precipitation (Shanley et al., 2005) . 12 10 8 O of sulfate, ‰ 6 4 18 2 d 0 Precipitation Streamwater

25. How do S and N responses affect estimates of critical loading? • Importance of weathering as sources of SO4. • Adsorption/Desorption reactions need to be considered for SO4, but not for NO3. • Dissimilatory reduction reactions can have substantial effects on S and N. • Substantial gaseous loss of N, but not S. • Mobilization of previously reduced S with changing hydrology (wetlands).

26. How do S and N responses affect estimates of critical loading? (continued) • Biotic regulation • More important for N versus S. Tree species, soil organic matter dynamics, nutrient demand, etc. need to be considered for N. • Both N and S show substantial amounts of biological cycling before being released into drainage waters and these processes become especially important at lower N and S loadings.