6.8. jules_soil_biogeochem.nml

This file sets options and parameters for soil biogeochemistry.

If using the single-pool or RothC soil models, all soil parameters are read from this file.

If using the ECOSSE soil model, most soil parameters are read from a separate file (jules_soil_ecosse.nml).

6.8.1. JULES_SOIL_BIOGEOCHEM namelist members

JULES_SOIL_BIOGEOCHEM::soil_bgc_model

Type:integer Permitted:1, 2 or 3 Default:1

Choice for model of soil biogeochemistry.

Possible values are:

1. A single-pool model of soil carbon turnover in which the pool is not prognostic (not updated).

   This must be used when the TRIFFID vegetation model is not selected (l_triffid = FALSE).
2. A 4-pool model of soil organic carbon and nitrogen, originally based on the RothC model, with a single pool of inorganic N.

   Historically this was bundled with the TRIFFID vegetation model.

   This can only be used if the TRIFFID vegetation model is selected (l_triffid = TRUE).
3. A 4-pool model of soil organic carbon and nitrogen, and 2 inorganic N pools (ammonium and nitrate), based on the ECOSSE model (Smith et al., 2010).

   This can only be used if the TRIFFID vegetation model is selected (l_triffid = TRUE).

   This can also be run without nitrogen (l_soil_n = FALSE).

Warning

The ECOSSE model in JULES is still in development and is not fully functional in this version. The code is included to allow further development. Users should not try to use ECOSSE.

See also

References:

• Smith et al., 2010, Estimating changes in Scottish soil carbon stocks using ECOSSE. I. Model description and uncertainties, Climate Research, 45: 179-192, doi: 10.3354/cr00899.

Parameters for the single-pool model (only used if soil_bgc_model = 1)

JULES_SOIL_BIOGEOCHEM::kaps

Type:real Default:0.5e-8

Specific soil respiration rate at 25 degC and optimum soil moisture (s^-1).

See Hadley Centre Technical Note 24 Eq.16.

Parameters for the single-pool and RothC models (only used if soil_bgc_model = 1 or 2)

JULES_SOIL_BIOGEOCHEM::l_q10

Type:logical Default:T

Switch for use of Q10 approach when calculating soil respiration.

TRUE

Use Q10 approach.

Note

This is always enforced if the single-pool model is selected (soil_bgc_model = 1) and was used in JULES2.0.

FALSE

Use the approach of the RothC model.

JULES_SOIL_BIOGEOCHEM::l_soil_resp_lev2

Type:logical Default:F

Switch affecting the temperature and moisture used for soil respiration calculation.

TRUE

Temperature and total (frozen+unfrozen) moisture content of the second soil layer are used.

FALSE

Temperature and unfrozen moisture content of the first (topmost) soil layer are used.

Note

If layered soil C is used (l_layeredc = TRUE) the temperature and moisture of each soil layer is used to calculation respiration from that layer.

JULES_SOIL_BIOGEOCHEM::q10_soil

Type:real Default:2.0

Q10 factor for soil respiration.

Only used if l_q10 = TRUE.

See Hadley Centre Technical Note 24 Eq.17.

Parameters for the RothC-based model (only used if soil_bgc_model = 2)

JULES_SOIL_BIOGEOCHEM::l_layeredc

Type:logical Default:F

Switch for using the layered soil carbon model.

If the RothC model is used (soil_bgc_model = 2 this uses the approach of Burke et al. (2016) and two extra parameters are required: tau_resp, tau_lit.

Layered soil nitrogen is also available if the nitrogen cycle is switched on (l_nitrogen = TRUE), but this is a highly experimental version which needs further evaluation and so should be used with extreme caution. One additional parameter is required for layered soil nitrogen: diff_n_pft.

TRUE

The number and thickness of layers in the soil carbon model are set equal to those in the soil moisture model (JULES_SOIL).

FALSE

There are no specific layers in the soil carbon model (a single, bulk pool).

See also

References:

• Burke, E. J., Chadburn, S. E., and Ekici, A.: A vertical representation of soil carbon in the JULES land surface scheme (vn4.3_permafrost) with a focus on permafrost regions, Geosci. Model Dev., 10, 959-975, doi:10.5194/gmd-10-959-2017, 2017.

JULES_SOIL_BIOGEOCHEM::kaps_roth

Type:real(4) Default:3.22e-7, 9.65e-9, 2.12e-8, 6.43e-10

Specific soil respiration rate for the RothC submodel for each soil carbon pool (biomass, humus, decomposable plant material, resistant plant material).

JULES_SOIL_BIOGEOCHEM::bio_hum_cn

Type:real Default:10.0

Parameter controlling ratio of C to N for BIO and HUM pools.

JULES_SOIL_BIOGEOCHEM::sorp

Type:real Default:10.0

Parameter controlling the leaching of inorganic N through the soil profile. A factor of 1 means that in a timestep all the inorganic N is available for leaching. The default value of 10 means that 10% of inorganic N is available for leaching.

JULES_SOIL_BIOGEOCHEM::n_inorg_turnover

Type:real Default:1.0

Parameter controlling the lifetime of the inorganic N pool. A value of 1 implies the whole pool will turnover in 360 days.

JULES_SOIL_BIOGEOCHEM::tau_resp

Type:real Default:2.0

Parameter controlling decay of respiration with depth (m-1). Only used with layered soil carbon (l_layeredc = TRUE).

JULES_SOIL_BIOGEOCHEM::diff_n_pft

Type:real Default:5.0

Parameter controlling the rate of re-filling of the available inorganic nitrogen pool (1/360 days). This parameter determines how quickly the inorganic nitrogen reaches the roots after the roots uptake from the soil around them. This should be quicker than the turnover rate of inorganic nitrogen. In addition, it has to be small compared with the triffid timestep (360/triffid_period) otherwise the available inorganic nitrogen becomes unstable. Hence the choice of the default value 5. Only used with layered soil carbon and nitrogen scheme (l_layeredc = TRUE and l_nitrogen = TRUE). When l_trif_eq = TRUE or diff_n_pft is greater than (0.5 * 360 / triffid_period) then all of the inorganic nitrogen pool is deemed to be available.

Parameters for the RothC- or ECOSSE-based models (only used if soil_bgc_model = 2 or 3):

JULES_SOIL_BIOGEOCHEM::tau_lit

Type:real Default:5.0

Parameter controlling the decay of litter with depth (m-1). With RothC, this is only used with layered soil carbon (l_layeredc = TRUE). With ECOSSE, this is only used with plant_input_profile = 2.

Methane parameters and switches. Can be used for any choice of soil_bgc_model.

Warning

Some parameters may need to be re-tuned for different soil biogeochemistry models, and most of those parameters are currently hard-coded.

JULES_SOIL_BIOGEOCHEM::l_ch4_tlayered

Type:logical Default:F

Switch to calculate methane emissions based on layered soil temperature.

TRUE

Methane emission is calculated from layered soil temperatures.

FALSE

Methane emission is calculated from top 1m average soil temperature (default).

JULES_SOIL_BIOGEOCHEM::l_ch4_interactive

Type:logical Default:F

Switch to couple the methane emission into the carbon cycle. In order to use this the methane must be calculated from layered soil temperature (l_ch4_tlayered = TRUE).

TRUE

Methane flux is subtracted from soil carbon stocks.

FALSE

Methane emission is only diagnostic (default).

JULES_SOIL_BIOGEOCHEM::ch4_substrate

Type:integer Permitted:1, 2 or 3 Default:1

Choice of substrate for wetland methane. This controls the calculation method for the methane flux that is used to update soil carbon (only if l_ch4_interactive = TRUE) and to populate the variable fch4_wetl (seen by the atmospheric model in coupled mode).

Possible values are:

1. Using soil carbon as substrate (default).
2. Using NPP as substrate.
3. Using soil respiration as substrate.

This replaces the previous switch l_wetland_ch4_npp.