6.8. jules_soil_biogeochem.nml

This file sets options and parameters for soil biogeochemistry.

6.8.1. JULES_SOIL_BIOGEOCHEM namelist members

JULES_SOIL_BIOGEOCHEM::soil_bgc_model

Type:integer Permitted:1 or 2 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 carbon and nitrogen, originally based on the RothC model.

   This must be used when the TRIFFID vegetation model is selected (l_triffid = TRUE).

   Historically this was bundled with the TRIFFID vegetation model.

Note

At present this variable is redundant because it can be inferred from l_triffid, but it was added to support future developments.

JULES_SOIL_BIOGEOCHEM::l_layeredc

Type:logical Default:F

Switch for using the layered soil carbon model, currently only relevant if TRIFFID is switched on (l_triffid = TRUE). Using the approach of Burke et al.(2016). Two parameters can be defined for this model - 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 et al (2016). A vertical representation of soil carbon for the UKESM Earth System Model with a focus on permafrost regions. Geoscientific Model Development Discussion

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 TRIFFID is switched off (l_triffid = FALSE) 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 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 RothC-based model (only used if soil_bgc_model = 2)

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.

Only used if using the RothC-based soil C model (soil_bgc_model = 2), in which case soil carbon is modelled using four pools (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::tau_lit

Type:real Default:5.0

Parameter controlling the decay of litter 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).