Hi all,
I’m running a regional RegCM-CLM4.5 (CN + nitrification/denitrification enabled) simulation over Asia. After a long spin-up, the 2020 warm-season soil N₂O emissions from both nitrification and denitrification become near zero over Southeast China (105–125E, 18–32N), while North China shows reasonable/large emissions. This seems inconsistent with the fact that N deposition input and early-season mineral N pools are not particularly low.
Below I summarize area-weighted regional means from monthly CLM h0 outputs (Feb–Jul 2020, pre-modification). Key findings:
Questions to the community:
Any suggestions or similar experiences would be greatly appreciated. I can share more detailed daily diagnostics if helpful.
Thanks!
Input - Substrate - Competing sink Comparison (SE vs North China)
Process Intensity versus N₂O (SE vs North China)
I’m running a regional RegCM-CLM4.5 (CN + nitrification/denitrification enabled) simulation over Asia. After a long spin-up, the 2020 warm-season soil N₂O emissions from both nitrification and denitrification become near zero over Southeast China (105–125E, 18–32N), while North China shows reasonable/large emissions. This seems inconsistent with the fact that N deposition input and early-season mineral N pools are not particularly low.
Below I summarize area-weighted regional means from monthly CLM h0 outputs (Feb–Jul 2020, pre-modification). Key findings:
- N deposition entering soil (NDEP_TO_SMINN) in SE China is of the same order as North China through the period (SE: ~14–33 kgN/ha/yr; NC: ~22–32 kgN/ha/yr).
- Mineral N pools collapse in SE China in Jun–Jul:
- SMIN_NH4 drops from ~0.14 gN/m³ (Feb–May mean) to ~7.4e-4 gN/m³ (Jun–Jul mean).
- SMIN_NO3 drops from ~6.3e-3 gN/m³ to ~1.6e-4 gN/m³, essentially a “NO3 vacuum.”
Meanwhile, North China SMIN pools increase strongly in summer.
- Process suppression appears in SE China only in summer:
- F_NIT/POT_F_NIT declines from ~1 in Feb–May to 0.68 in Jun and 0.15 in Jul.
- F_DENIT/POT_F_DENIT declines from ~0.9 to 0.47 in Jun and 0.06 in Jul.
North China stays near 1 for both ratios.
- Consistent with (2–3), total soil N₂O in SE China drops by ~100× in Jun–Jul, while North China peaks.
- SE China also shows very large microbial immobilization (ACTUAL_IMMOB) relative to deposition in late spring–summer (IMMOB ~50–59 kgN/ha/yr vs NDEP_TO_SMINN ~14 kgN/ha/yr), suggesting strong competition for mineral N. However, even with relatively high deposition, the summer “mineral-N vacuum + scalar suppression” seems to shut down nitrification/denitrification.
Questions to the community:
- Has anyone seen a similar summer collapse of SMIN pools and N₂O fluxes in humid/forested subtropical regions in CLM4.5-CN/ND?
- Which diagnostics would you recommend to pinpoint the bottleneck?
- Are there known parameter settings that can lead to excessive immobilization or overly strong moisture/anaerobic suppression in warm wet regions?
Any suggestions or similar experiences would be greatly appreciated. I can share more detailed daily diagnostics if helpful.
Thanks!
Input - Substrate - Competing sink Comparison (SE vs North China)
| month | SE NDEP→SMINN (kgN/ha/yr) | NC NDEP→SMINN | SE IMMOB (kgN/ha/yr) | NC IMMOB | SE Plant uptake (kgN/ha/yr) | NC Plant uptake | SE SMIN_NH4 (gN/m3) | NC SMIN_NH4 | SE SMIN_NO3 (gN/m3) | NC SMIN_NO3 |
|---|---|---|---|---|---|---|---|---|---|---|
| 202002 | 32.9 | 23.9 | 26.5 | 1.59 | 10.5 | 0.0157 | 0.189 | 0.246 | 0.00991 | 0.00175 |
| 202003 | 21.0 | 22.0 | 0.0272 | 6.14e-06 | 3.79 | 0.00426 | 0.294 | 0.267 | 0.000764 | 3.3e-05 |
| 202004 | 11.6 | 31.6 | 28.2 | 19.4 | 4.38 | 11.7 | 0.0634 | 0.525 | 0.0107 | 0.0105 |
| 202005 | 16.4 | 27.6 | 46.4 | 20.5 | 6.76 | 14.7 | 0.0124 | 0.660 | 0.00388 | 0.0379 |
| 202006 | 14.3 | 23.9 | 50.4 | 21.0 | 7.23 | 16.6 | 0.00104 | 0.713 | 0.00031 | 0.148 |
| 202007 | 13.8 | 22.6 | 58.5 | 22.0 | 7.68 | 15.5 | 0.000438 | 0.507 | 9e-06 | 0.369 |
Process Intensity versus N₂O (SE vs North China)
| month | SE N2O_nit (kgN/ha/yr) | NC N2O_nit | SE N2O_denit (kgN/ha/yr) | NC N2O_denit | SE total N2O | NC total N2O | SE F_NIT/POT | NC F_NIT/POT | SE F_DENIT/POT | NC F_DENIT/POT | SE TSOI_10CM (K) | NC TSOI_10CM |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 202002 | 0.00261 | 0.000327 | 0.144 | 0.0103 | 0.147 | 0.0106 | 1.00 | 1.00 | 0.925 | 0.970 | 273.8 | 262.5 |
| 202003 | 5.71e-05 | 1.26e-06 | 7.11e-05 | 9.78e-08 | 0.000129 | 0.000001 | 1.00 | 1.00 | 0.679 | 1.00 | 264.5 | 254.8 |
| 202004 | 0.000369 | 0.00144 | 0.0822 | 0.0476 | 0.0826 | 0.0490 | 0.998 | 1.00 | 0.966 | 0.958 | 273.4 | 268.6 |
| 202005 | 0.000130 | 0.00533 | 0.0289 | 0.1169 | 0.0290 | 0.122 | 0.972 | 1.00 | 0.935 | 0.977 | 281.2 | 273.2 |
| 202006 | 1.30e-05 | 0.0153 | 0.00117 | 0.194 | 0.00118 | 0.209 | 0.681 | 1.00 | 0.468 | 0.983 | 287.4 | 281.9 |
| 202007 | 7.35e-07 | 0.0198 | 7.87e-05 | 0.153 | 8.08e-05 | 0.172 | 0.150 | 1.00 | 0.0583 | 0.973 | 290.2 | 290.2 |