Contribution to the European database of relevés with measured soil parameters

The intention is to (a) extend the ICP-M&M network with habitat experts that can assist in improving site specific biotic and a-biotic information in databases relevant to European critical loads, dynamic modelling assessments, and (b) strengthen collaboration to the extent that such data can be considered for inclusion in a European data base for future vegetation modelling. More specifically, it is proposed that vegetation soil data also be included in a database constructed by Wieger Wamelink to relate plant species occurrence with soil parameters (see www.abiotic.

wur.nl). The resulting model en responses per species will be made freely available through the same website.

For this, you are invited to provide contacts to persons who have information on vegetation relevés/species lists which have been collected together with measured soil parameters. in your country. They should fulfil the following criteria:

Vegetation relevés/species lists made on a limited surface area (e.g. ranging from 1–200 m²), preferably, but not necessarily, made in the sense of Braun-Blanquet. The relevés have to be accompanied at least with: the coordinates, an estimate of the altitude, the species present in the plot (surface area cover is not necessary), and at least one measured soil parameter, e.g. soil pH, nitrate concentration in the soil, potassium concentration, base cations, total N content, C/N, moisture content etc.;

meteorological data are also welcomed. For each meas-urement the analysis method (especially the extraction method) is also necessary, as well as the sample depth.

Please enter the person and his/her coordinates into the access table ‘relcontact’.

References

De Vries W, Kros H, Reinds GJ, Wamelink W, Mol J, Van Dobben H, Bobbink R, Emmett B, Smart S, Evans C, Schlutow A, Kraft P, Belyazid S, Sverdrup H, Van Hinsberg A, Posch M, Hettelingh J-P, 2007.

Developments in deriving critical limits and modeling critical loads of nitrogen for terrestrial ecosystems in Europe. Alterra Report 1382, Alterra WUR, Wageningen, The Netherlands, 206 pp

www.pbl.nl/cce

Sverdrup H, Belyazid S, Nihlgård B, Ericson L, 2007.

Modelling change in ground vegetation response to acid and nitrogen pollution, climate change and forest management at in Sweden 1500–2100 A.D. Water, Air and Soil Pollution: Focus, 7: 163–179, DOI: 10.1007/

s11267-006-9067-9

Appendix B

From VSD to VSD+

In this Appendix we summarise the mathematical formulations of those processes in VSD+ that constitute its upgrade from VSD (Posch and Reinds 2009). A complete description of the processes modelled in VSD+ can be found in Bonten et al. (2010). What distinguishes VSD+

from the VSD model is the much more detailed modelling of carbon (C) and nitrogen (N) pools and fluxes; and in the following we give a description of the processes modelled as well as the new input variables needed.

Organic carbon model:

For modelling carbon dynamics, VSD+ uses a 4-compart-ment model consisting of the following C-pools (in g/m²):

easily degradable fresh litter (C_fe);

slowly degradable (recalcitrant) fresh litter (C_fs);

microbial biomass (C_mb);

slowly degradable humic material (C _hm).

Each C-pool has its own first-order turnover rate k_x (in yr^–1) and its own fixed C/N ratio CN_x (in g/g). The first three C-pools can be converted to a different C-pool according to the scheme in Figure B.1; and all four pools loose C in the form of CO₂.

The change in the four C-pools are given by:

(B-1) ^G

GW&IHDPOIuIUIHOIDPUWuIUIHUWu<NIHu&IH

(B-2) ^G

GW&IVDPOIuIUIVOIDPUWuIUIVUWu<NIVu&IV

(B-3) ^G

GW&_PEN_IHuIU_KXIHu&_IHN_IVuIU_KXIVu&_IV<N_PEu&_PE (B-4) ^G

GW&KPNPEuIUKXPEu&PE<NKPu&KP

where am_lf is the litterfall and am_rt is the root turnover flux (both in kg/m²/yr); fr_fe,lf and fr_fs,lf are the easily degradable and recalcitrant fraction of the litterfall, respectively;

analogously fr_fe,rt and fr_fs,rt for roots. The factor 500 converts from kg litterfall to g C (assuming a C-content of 50%). k_x is the turnover rate of pool x=fe,fs,mb,hm, and fr_hu,x (x=fe,fs,mb) is the fraction of the total turnover of a C-pool converted to another C-pool (and (1–fr_hu,x )·k_x·C_x is released as CO₂).

Litterfall and root turnover are distributed over the easily degradable and recalcitrant fractions depending on the C:N ratios of litterfall (CN_lf) and root turnover (CN_rt) according to:

(B-5) ^IU^IHOI^u^&1^IH^IU^IVOI^u^&1^IV^&1^OI IUIHOIIUIVOI

(B-6) ^IU^IHOI^u^&1^IH^IU^IVOI^u^&1^IV^&1^OI IUIHOIIUIVOI

The turnover rates k_x are calculated from maximum turnover rates k_x,max by correcting for pH, temperature, wetness and drought according to:

(B-7) N[N[PD[uUIPLS+uUIPL

where the modifying functions rf_mi,pH and rf_mi (dependent on temperature, wetness and drought) are described below (see section ‘Correction of mineralization and (de) nitrification for environmental conditions’; note that earlier these functions were called ‘reduction functions’).

N processes:

Nitrogen processes implemented in VSD+ are depicted in Figure B.2; and the numbers indicate the calculation sequence.

Inputs of N in VSD+ are NH₄ and NO₃deposition, litterfall, root turnover and N fixation. N input by in litterfall, N_lf (eq/

m²/yr), is dependent on the deposition of N, N_dep=NH_4,dep+NO_3,dep (eq/m²/yr):

(B-8) 1_OIDPOI

FW1_OI_PLQFW1_OI_PD[<FW1_OIPLQu<H<H[S1OIGHSu1GHS where am_lf (kg/m²/yr) is the amount of litterfall (see below),

ctN_lf,min/ctN_lf,max (%) are the minimum/maximum N content of

litterfall, expNlfdep (m²yr/eq) is an exponent relating N deposition to N in litterfall, and the division by 1.4 converts from % to moles (=eq) of N. N input by root turnover, N_rt (eq/m²/yr), is computed as:

GW&IHDPOIuIUIHOIDPUWuIUIHUWu<NIHu&IH

Figure B.2 Nitrogen processes implemented in VSD+. The numbers indicate the calculation sequence.

1RUJ

GHSRVLWLRQ

SODQW XSWDNH 1IL[DWLRQ

12 GHSRVLWLRQ

QLWULILFDWLRQ

OLWWHUIDOOURRW WXUQRYHU

GHQLWULILFDWLRQ

OHDFKLQJ PLQHUDOL]DWLRQ

LPPRELOLVDWLRQ

(B-9) 1_UWDPUWu u&1UW

where am_rt (kg/m²/yr) is the amount of root turnover (see below), CN_rt is the C:N-ratio (g/g) of the roots, the factor 500 converts from kg biomass to g C (assuming a

C-content of 50%) and the division by 14 from g N to moles (=eq) of N.

N fixation, N_fix, is assumed constant (input). The immobili-sation/mineralization of N depends on the turnover of the C-pools:

(B-10) 1LP[

u&1[

6&[W ZLWK [IHIVPEKP

where N_im,x (eq/m²/yr) is the immobilisation of N in pool x, and ΔC_x,t=C_x,t–C_x,t–Δt (see eqs.B1-4). The total net N immobili-sation is:

(B-11) 1LP1LPIH1LPIV1LPPE1LPKP<1IL[<1OI<1UW

If N_im > 0, there is net N immobilization, otherwise net mineralization. The uptake of N by vegetation, N_u (eq/m²/ yr), is computed as:

(B-12) 1X6$P_W uFW1VW

where ΔAm_t=Am_st,t–Am_st,t–Δt is the growth increment at time-step t (in kg/m²/yr, see below) and ctN_st (%) is the N content of stems. If N_dep – N_im – N_u < 0, there is not enough N available for both immobilisation and uptake. In this case the turnover rate of the recalcitrant C-pool (k_fs) is reduced such that N_dep – N_im – N_up = 0. Total N uptake N_u is split into NH_4,u and NO_3,u – with preferential uptake of NH₄ – according to:

(B-13) ₁₊_X_PLQ

!

₁₊_GHS_<₁_LP₁_X

#

(B-14) ₁₂_X₁_X_<₁₊_X

where it is assumed that all N_im is in the form of ammo-nium. The next step in the fate of N is nitrification, N_ni (eq/

m²/yr):

(B-17) _IU_\_<_H[S

_<N_\_u_UI_\S+_u_UI_\ ^ZLWK ^\^QLGH

where k_y are user-supplied constants, and rf_y and rf_y,pH are modifying functions (see below).

The residual NH₄ and NO₃ will leach from the root zone (NH_4,le and NO_3,le in eq/m²/yr):

(B-18) ₁₊_OH₁₊_GHS_<₁_LP_<₁₊_X_<₁_QL (B-19) ₁₂_OH₁₂_GHS_<₁₂_X₁_QL_<₁_GH Vegetation growth:

For vegetation growth, VSD+ uses either a logistic growth-curve or user-prescribed growth and litterfall time series. In case of logistic growth, the amount of woody biomass (stems plus branches) in simulation year t, Am_st,t (kg/m²), is calculated as:

(B-20) $P_VWW $PVWP[

H[S<NJOuDJHYJW<W

where Am_st,mx is the maximum woody biomass (kg/m²), age_vg (yr) the initial age of the vegetation, t_½ (yr) the half life-time, and k_gl (yr^–1) the logistic growth rate constant.

The litterfall in year t, am_lf,t (in kg/m²/yr), approaches its maximum value faster and is calculated as:

(B-21) DP_OI_W DP_OI_P[

H[S<uNJOuDJHYJW<W

where am_lf,mx is the maximum amount of annual litterfall.

The generic shapes of Am_st,t/Am_st,mx and am_lf,t/am_lf,mx are shown in Figure B.3; it shows that maximum litterfall is already reached with about 10% of the biomass.

Figure B-3: Generic shapes of the (relative) amount of woody biomass Am_st,t/Am_st,mx (brown curve) and the amount of litterfall am_lf,t/am_lf,mx (green curve) as given be eqs.B-20,21.

Root turnover, am_rt,t (kg/m²/yr), is computed from litterfall by a vegetation-dependent – but time-independent – ratio ncf:

(B-22) DPUWWQFIuDPOIW

Correction of mineralization and (de)nitrification for environ-mental conditions:

Mineralization and (de)nitrification rates (called ‘turn-over rates’ above) depend on soil pH, temperature, wetness and drought, and are computed as follows:

pH: The modifying functions for mineralization and (de) nitrification due to pH, rf_mi,pH, are modelled as:

(B-23) UIPLS+

H[Su<S+

(B-24) UIQLS+

H[Su<S+

(B-25) UIGHS+

H[Su<S+

where pH is the soil solution pH.

Temperature: The modifying function of mineralization due to temperature, rf_mi,T, is modelled as:

(B-26)

UIPL7H[S 7<

7< 7<

¤² ¥

¦´

µ 7^F&

where T (°C) is the soil temperature. For nitrification and denitrification VSD+ uses the same modifying function as for mineralization:

(B-27) UIQL7UIGH7UIPL7

Wetness: The dependence of the decomposition rates on wetness is based on the aerobic/anaerobic zone concept.

Mineralization is proportional to the relative size of the aerobic zone in a soil. This size can be estimated from the dependency of denitrification on the water-filled pore space (= θ/θ_sat), under the assumption that denitrification only takes place under anaerobic conditions. The modify-ing function of denitrification due to wetness, rf_de,θ, is modelled as:

(B-28) _UI_GHe

IRU e eVDW

eeVDW<

²²

´´

IRU ) e eVDW

)

where θ (m³/m³) is the soil water content and θ_sat (m³/m³) is the total pore space (soil moisture at saturation). In VSD+,

due to wetness is defined as one minus the correction for denitrification (i.e. the size of the aerobic zone):

(B-29) UIPLe<UIGHe

(B-30) _UI_QLe_<_UI_GHe

Drought: The correction of mineralization due to drought stress, rf_mi,dr, is modelled as (Vleeshouwers and Verhagen 2002):

(B-31) _UI_PLGU

IRU e ) eZS

ue <eZS

eIF<eZS

IRU eZS e eIFeZS

IRU e *eIFeZS

««

where θ_fc (m³/m³) is the moisture fraction at field capacity and θ_wp (m³/m³) the moisture fraction at wilting point. For nitrification and denitrification VSD+ uses the same modifying functions as for mineralization:

(B-32) UIQLGUUIGHGUUIPLGU

Since soil temperature and moisture can be highly variable within a year, average modifying factors are calculated from daily (or weekly) values as follows:

(B-33) UI[ UI[euUI[7uUI[GUu 6W

WR 7

-

^6W

WR 7

Im Dokument Progress in the Modelling of (Seite 170-174)