----- Version 01.08.2014 ----Guidance Document on National
Nitrogen Budgets – Forest and seminatural vegetation (Annex 5)
Content
1
Introduction ..................................................................................................................................... 3
1.1
2
Nitrogen species ...................................................................................................................... 4
Internal structure ............................................................................................................................ 5
2.1
Sub-pool Forest ....................................................................................................................... 5
2.2
Sub-pool Other land ................................................................................................................ 6
2.3
Sub-pool Wetland .................................................................................................................... 6
2.4
Stocks & Stock Changes ........................................................................................................... 6
Stock changes in forest land ............................................................................................ 6
Stock changes in other lands ......................................................................................... 10
Stock changes in wetlands............................................................................................. 10
Biomass stock changes on land converted to other land-use ....................................... 10
Suggested Data sources................................................................................................. 11
3
Flows: Calculation guidance .......................................................................................................... 11
3.1
Forest Land ............................................................................................................................ 12
Atmospheric N deposition (A1) ..................................................................................... 12
Biological N fixation (A2) ................................................................................................ 13
Emissions (FS1) ............................................................................................................... 13
Leaching (FS2) ................................................................................................................ 15
Industrial timber (FS4).................................................................................................... 16
Energy wood (FS5).......................................................................................................... 16
Wood export (FS3) ......................................................................................................... 16
Wood growth (FS6) ........................................................................................................ 16
3.2
Other Land ............................................................................................................................. 17
Atmospheric N deposition (A1) ..................................................................................... 17
Leaching (FS2) ................................................................................................................ 17
1
3.3
Wetland ................................................................................................................................. 17
Atmospheric N deposition (A1) ..................................................................................... 17
Biological N fixation (A2) ................................................................................................ 17
Runoff (AG1)................................................................................................................... 17
Emissions (FS1) ............................................................................................................... 17
Plant uptake (FS1) .......................................................................................................... 17
4
Uncertainties ................................................................................................................................. 17
5
Tables............................................................................................................................................. 19
6
References ..................................................................................................................................... 24
2
1 Introduction
This document defines the pool “forest and semi-natural vegetation” to the annex of the “Guidance
document on national nitrogen budgets” (UN ECE 2013). It provides guidance on how to calculate
relevant nitrogen flows related to the pool forest and semi-natural vegetation, presents calculation
methods and suggests possible data sources.
The pool forest and semi-natural vegetation (FS) involves all natural and semi-natural terrestrial
ecosystems, according to the CORINE land cover class 3 “Forests and semi-natural areas” as well as
class 4 “Wetlands” (EEA, 2007). The main N flows between FS and other pools are presented in figure
1.
Figure 1: Flows connecting neighbouring pools with „Forest & Semi-Natural Vegetation“
Nitrogen input includes atmospheric deposition (mainly as ammonia (NH3) and nitrogen oxides
(NOX)) as well as biological fixation of elementary nitrogen (N2) (by microbes in a symbiotic
association with the roots of higher plants and soil heterotrophic microorganisms) as the most
significant inflows of nitrogen from the atmosphere to the biosphere (Leip et al., 2011). In case of
wetlands also runoff water from agriculture pool represents the biggest N source.
Nitrogen undergoes various transformation processes in the FS pool:


Ammonification (mineralization): During the decomposition of litter and soil organic matter,
different organic nitrogen compounds are mineralized to the ammonium (NH4+).
Nitrification: Ammonium can be oxidized by microbes to nitrite (NO2-) and further to nitrate
(NO3-).
3
The inorganic N species, ammonium (NH4+) and nitrate (NO3-) can either be taken up by plants or
immobilized by soil microorganisms in the form of an organic nitrogen compound. This is called
assimilation. Moreover, ammonium can also be adsorbed on the clay minerals and so precluded
from further transformation, known as adsorption. Hence uptake, immobilisation and adsorption
ensure for the N retention within the pool. Nitrate (NO3-), however, is easily soluble and cannot be
wholly consumed by plants and microorganisms and it is leached to the groundwater.


Denitrification: Under anoxic condition nitrite (NO2-) and nitrate (NO3-) are transformed into
gaseous compounds such as nitrogen oxide (NO), nitrous oxide (N2O) and elementary
nitrogen (N2) and are emitted back to the atmosphere.
Anammox (Anaerobic ammonium oxidation): Also under anoxic condition nitrite (NO2-) and
ammonium (NH4+) can be converted into dinitrogen (N2), which again is emitted.
Thus, leaching of nitrate (NO3-) into the hydrosphere and emission of denitrification products (N2O,
N2, NOX) to the atmosphere represent the significant outflows from the FS pool. In addition to these,
harvest/removal of the forest products and subsequent transformation in wood products as well as
losses through fire and other disturbances (e.g. insects, diseases) contribute to the N output.
Only quantitatively significant N flows (at least 100 t N per million inhabitants and year [10-2 Gg (106
capita)-1× a-1]) have been considered. There are no direct flow connections to the waste pool.
However, an indirect linkage is given via deposition processes (beschreiben). The FS pool is also
linked to the rest of the world (RW) through the export of wood products. The spatial boundary of
the system is given through the national border.
1.1 Nitrogen species
Nitrogen is distinguished between non-reactive nitrogen (N2) and reactive, bioavailable, nitrogen
(NOX, NO3-, NH3/NH4+, as well as organically bonded N) species.
Table 1 provides a descriptive overview of all potential nitrogen species involved. Data sources:
Pelletier & Leip, 2014; #
Table 1: Description of potential N species
Nitrogen
species
Atmospheric
Nitrogen
Nitrogen
organically
bounded
Nitrogen
oxides1
Nitrogen
dioxide
Nitrite
1
Molecular
Formula
N content
[%]
Aggregate
state
Occurrence
Inflow
N2
100.00
gaseous/not
reactive
atmosphere
biological
fixation by plant
and soil
R-NH2
#
solid
plant/microbes
NOx
30.43
gaseous
atmosphere/
soil
N2O
63.65
gaseous
soil
NO2-
30.45
dissolved
(ionic)
soil
internal N
circulation
Outflow
emission from
soil
to the
atmosphere
N content calculated based on NO2:NO as a ratio of 1:1
4
Ammonium
Nitrate
NH4+
NO3-
N in wood
78
dissolved
(ionic)
22.59
dissolved
(ionic)
soil
0.1-0.3
solid
plants
soil
leaching from
soil to the
hydrosphere
forest
products
2 Internal structure
The FS pool is divided into 3 sub-pools, namely forest, other land, and wetland where each sub-pool
involves two main sub-sub-pools, namely plant biomass and soil. Figure 2 shows the internal
structure of the pool and their specific connections to neighbouring pools.
Atmosphere
Agriculture
Humans &
Settlements
Wetland
Plant &Soil
Other land
Plant &Soil
Forest
Plant & Soil
Material and
Products in
Industry
Energy & Fuels
Waste
Hydrosphere
Figure 2: Internal structure of the pool FS
2.1 Sub-pool Forest
Atmospheric deposition and biological N fixation constitute the inflows of N to the system, while
harvested biomass, leaching, and denitrification account for the losses. Additionally, uptake by
growing plants and storage in biomass (wood growth) is counted as outflow from the soil. Thus, only
the fluxes into or out of the soil are included in the calculations, not the processes within the soil.
If only vertical percolation of precipitation to the groundwater is considered the N budget can be
calculated as:
5
∆ = 𝑫𝒆𝒑𝒐𝒔𝒊𝒕𝒊𝒐𝒏 + 𝑭𝒊𝒙𝒂𝒕𝒊𝒐𝒏 − 𝑯𝒂𝒓𝒗𝒆𝒔𝒕𝒊𝒏𝒈 − 𝑫𝒆𝒏𝒊𝒕𝒓𝒊𝒇𝒊𝒌𝒂𝒕𝒊𝒐𝒏 − 𝑳𝒆𝒂𝒄𝒉𝒊𝒏𝒈 −
𝑾𝒐𝒐𝒅 𝒈𝒓𝒐𝒘𝒕𝒉
2.1
2.2 Sub-pool Other land
The sub-pool "Other land" encompasses all other non-forested area including alpine pasture,
unproductive vegetation and bare land (Heldstab et al., 2010).
The atmospheric deposition is the main inflow to the sub-pool other land, while the leaching/runoff
represents the most relevant outflow. Biological N fixation as well as denitrification were assumed to
be very small and were thus neglected (J. Heldstab, personal communication).
∆ = 𝑫𝒆𝒑𝒐𝒔𝒊𝒕𝒊𝒐𝒏 − 𝑳𝒆𝒂𝒄𝒉𝒊𝒏𝒈
2.2
2.3 Sub-pool Wetland
The biggest N sources for wetland are runoff input from grazed, agricultural nearby and, atmospheric
deposition, and biological N fixation, while the important way of N attenuation are given by
denitrification and ANAMMOX processes as well as by wetland plant uptake.
∆ = 𝑹𝒖𝒏𝒐𝒇𝒇 + 𝑫𝒆𝒑𝒐𝒔𝒊𝒕𝒊𝒐𝒏 + 𝑭𝒊𝒙𝒂𝒕𝒊𝒐𝒏 − 𝑫𝒆𝒏𝒊𝒕𝒓𝒊𝒇𝒊𝒌𝒂𝒕𝒊𝒐𝒏 − 𝑨𝑵𝑨𝑴𝑴𝑶𝑿 −
𝑷𝒍𝒂𝒏𝒕 𝑼𝒑𝒕𝒂𝒌𝒆
2.3
Where Δ = accumulation (+) or loss (-).
In general, if the budget is negative it can be concluded that one or more of the mass balance terms
will eventually change since the output cannot be larger than input in the long term. Thus, measures
of stocks and stock changes are required in combination with the mass balance estimates.
2.4 Stocks & Stock Changes
Potential stock changes (i.e. variation over time of the respective accumulation, rather than the
nitrogen stock itself) result from the difference between inflows and outflows. When losses exceed
gains, the stock decreases, and the pool acts as a source; when gains exceed losses, the pools
accumulate nitrogen , and the pools act as a sink. With regard to carbon, IPCC reporting guidelines
distinguishes between plant biomass, dead organic matter (dead wood + litter) and soil N stocks
(IPCC, 2006,).
Stock changes in forest land
Under forest should be understood a forest land that have been under forest for over 20 years (IPCC,
2006).
6
2.4.1.1 Biomass stock changes
In this pool, biomass stock changes are related to plant growth, human activities (e.g. harvest,
management practices), and natural losses due to disturbance (e.g. windstorms, insects, and
diseases).
The calculation can be made by using the Stock-Difference Method or the Gain–Loss Method (IPCC
report, 2006).
(a) Annual changes in N stocks in biomass according to the Stock-Difference Method can be
calculated as follow:
∆𝑵𝑩 =
(𝑁𝑡2 −𝑁𝑡1 )
(𝑡2−𝑡1)
𝑵𝒕𝒏 = ∑{𝐴𝑖,𝑗 × 𝑉𝑖,𝑗 × 𝐵𝐶𝐸𝐹𝑠𝑖,𝑗 × (1 + 𝑅𝑖,𝑗 ) × 𝑁𝐹𝑖,𝑗 }
2.4
2.5
𝑖,𝑗
Where:
ΔNB = annual change in nitrogen stocks in biomass [t N y-1]
Nt2 = total N in biomass at time t2 [tonnes N]
Nt1 = total N in biomass at time t1 [tonnes N]
Ntn = total N in biomass for time t1 and t2
A = area of land [ha]
V = merchantable growing stock volume [m3 ha-1]
i = ecological zone (i = 1 to n)
j = climate domain (j = 1 to m)
R = ratio of below-ground biomass to above-ground biomass
NF = nitrogen fraction of dry matter, [tonnes N (tonnes d.m.)-1]
BCEFS = biomass conversion and expansion factor for expansion of merchantable growing stock volume to aboveground biomass. BCEFS transforms merchantable volume of growing stock directly into its above-ground biomass.
BCEFS values are more convenient because they can be applied directly to volume-based forest inventory data
and operational records, without the need of having to resort to basic wood densities. They provide best results,
when they have been derived locally and based directly on merchantable volume. However, if BCEFI values are
not available and if the biomass expansion factor (BEF) and basic wood density (D) values are separately
estimated, then the following conversion can be used: BCEFR = BEFR × D
(b) Annual changes in N stocks in biomass can also be calculated according to the Gain -Loss
Method:
∆𝑵𝑩 = ∆𝑵𝑮 − ∆𝑵𝑳
2.6
Where:
ΔNB = annual change in N stocks in biomass, considering total area [t N y-1]
ΔNG= annual increase in N stocks due to biomass growth, considering total area [t N y-1]
ΔNL = annual decrease in N stocks due to biomass loss [t N y-1]
Annual increase in biomass N stocks due to biomass increment (NG) is calculated:
∆𝑵𝑮 = ∑(𝑨𝒊,𝒋 × 𝑮𝑻𝑶𝑻𝑨𝑳𝒊,𝒋 × 𝑵𝑭𝒊,𝒋 )
2.7
𝒊,𝒋
7
Where:
ΔNG = annual increase in biomass N stocks due to biomass growth [t N y-1]
A= area of land [ha]
GTOTAL = mean annual biomass growth [tonnes d. m. ha-1 yr-1]
i = ecological zone (i=1 to n)
j = climate domain (j =1 to m)
NF = nitrogen fraction of dry matter [tonnes N (tonnes d.m.) -1], see table #
Average annual increment in biomass (GTOTAL) is calculated:
Tier 1
To estimate average annual biomass growth above and below-ground, the biomass increment data
of forest inventories (dry matter) can be used directly.
𝑮𝑻𝑶𝑻𝑨𝑳 = ∑{𝑮𝑾 × (𝟏 + 𝑹)}
2.8
Where:
GTOTAL = average annual biomass growth above and below-ground [t N d.m. ha-1y-1]
GW = average annual above-ground biomass growth for a specific woody vegetation type [t N d.m. ha-1y-1]
R = ratio of below-ground biomass to above ground biomass for a specific vegetation type. R must be set to zero
if assuming no changes of below-ground biomass allocation patterns.
Tier 2
Net annual increment data are used to estimate average annual above-ground biomass growth by
applying a biomass conversion and expansion factor.
𝑮𝑻𝑶𝑻𝑨𝑳 = ∑{𝑰𝑽 × 𝑩𝑪𝑬𝑭𝑰 × (𝟏 + 𝑹)}
2.9
Where:
GTOTAL = average annual biomass growth above and below-ground [t N d.m. ha-1y-1]
GW = average annual above-ground biomass growth for a specific woody vegetation type [t N d.m. ha-1y-1]
R = ratio of below-ground biomass to above ground biomass for a specific vegetation type
IV = average net annual increment for specific vegetation type [m 3 ha-1 y-1]
BCEFI = biomass conversion and expansion factor for conversion on net annual increment in volume (including
bark) to above-ground biomass growth for specific vegetation type, tonnes above-ground biomass growth [m3 net
annual increment]-1, see table #.
Tier 3
If BCEFI values are not available and if the biomass expansion factor (BEF) and basic wood density (D)
values are separately estimated, then the following conversion can be used:
𝑩𝑪𝑬𝑭𝑰 = 𝑩𝑬𝑭𝑰 × 𝑫
2.10
Where:
BCEFI = biomass conversion and expansion factor for conversion on net annual increment in volume (including
bark) to above-ground biomass growth for specific vegetation type, tonnes above-ground biomass growth [m3 net
annual increment]-1, see table #.
BEFI = biomass expansion factor –See page 4.13
D = basic wood density [oven-dry tonnes (moist m-3)]
Biomass loss (NL) is a sum of annual loss due to wood removals (Lwood-removals), fuel wood gathering (L
fuelwood) and disturbance (Ldisturbance).
2.11
8
∆𝑵𝑳 = 𝑳𝒘𝒐𝒐𝒅−𝒓𝒆𝒎𝒐𝒗𝒂𝒍𝒔 + 𝑳𝒇𝒖𝒆𝒍𝒘𝒐𝒐𝒅 + 𝑳𝒅𝒊𝒔𝒕𝒖𝒓𝒃𝒂𝒏𝒄𝒆
The annual N losses due to wood removals (Lwood-removals) are calculated as follow:
𝑳𝒘𝒐𝒐𝒅−𝒓𝒆𝒎𝒐𝒗𝒂𝒍𝒔 = {𝑯 × 𝑩𝑪𝑬𝑭𝑹 × (𝟏 + 𝑹 + 𝑩𝑬𝑭) × 𝑵𝑭}
2.12
Where:
Lwood-removals = annual N loss due to biomass removals [t N y-1]
H = annual wood removals, roundwood [m3 y-1]
R = ratio of below-ground biomass to above ground. R must be set to zero if assuming no changes of belowground biomass allocation patterns (Tier 1).
NF = Nitrogen fraction of dry matter [tonne N (tonnes d.m.)-1], see table #
BEF = biomass expansion factor
BCEFR = biomass conversion and expansion factor for conversion of removals in merchantable volume to total
biomass removals (including bark), tonnes biomass removal [m3 of removals]-1, see table #. However, if BCEFI
values are not available and if the biomass expansion factor (BEF) and basic wood density (D) values are
separately estimated, then the following conversion can be used: BCEFR = BEFR × D
The annual N losses due to fuelwood removal (Lfuelwood) are calculated as follow:
𝑳𝒇𝒖𝒆𝒍𝒘𝒐𝒐𝒅 = [{𝑭𝑮𝒕𝒓𝒆𝒆𝒔 × 𝑩𝑪𝑬𝑭𝑹 × (𝟏 + 𝑹) + 𝑭𝑮𝒑𝒂𝒓𝒕 × 𝑫} × 𝑵𝑭
2.13
Where:
Lfuelwood= annual N loss due to fuelwood removals [t N y-1]
FGtrees = annual volume of fuelwood removal of whole trees [m3 y-1]
FGpart = annual volume of fuelwood removal as tree parts [m3 y-1]
R = ratio of below-ground biomass to above ground. R must be set to zero if assuming no changes of belowground biomass allocation patterns (Tier 1).
NF = Nitrogen fraction of dry matter [tonne N (tonnes d.m.)-1], see table #
D = basic wood density [tonne N d.m.]-1
BCEFR = biomass conversion and expansion factor for conversion of removals in merchantable volume to total
biomass removals (including bark), tonnes biomass removal [m3 of removals]-1, see table #. However, if BCEFI
values are not available and if the biomass expansion factor (BEF) and basic wood density (D) values are
separately estimated, then the following conversion can be used: BCEFR = BEFR × D
The annual N losses due to disturbances (Ldisturbances) are calculated as follow:
𝑳𝒅𝒊𝒔𝒕𝒖𝒓𝒃𝒂𝒏𝒄𝒆 = {𝑨𝒅𝒊𝒔𝒕𝒖𝒓𝒃𝒂𝒏𝒄𝒆 × 𝑩𝑾 × (𝟏 + 𝑹) × 𝑵𝑭 × 𝒇𝒅}
2.14
Where:
Ldisturbance= annual other loss of N [t N y-1]
Adisturbances = area affected by disturbances [ha y-1]
BW = average above-ground biomass of land areas affected by disturbances [tonne N d.m.]-1
R = ratio of below-ground biomass to above ground. R must be set to zero if no changes of below-ground biomass
are assumed (Tier 1).
NF = Nitrogen fraction of dry matter [tonne N (tonnes d.m.)-1], see table #
fd = basic wood density [tonne N (tonnes d.m.)-1]
Note: The parameter fd defines the proportion of biomass that is lost from the biomass pool: as stand-replacing
disturbance will kill all (fd =1) biomass while an insect disturbance by only remove a portion (e.g. fd =0.3) of the
average biomass N density.
2.4.1.2 Dead Organic Matter stock changes
#
9
2.4.1.3 Soil stock changes
The soil nitrogen stock changes are largely determined by the forest productivity, the decomposition
of litter and its incorporation into the mineral soil and subsequent loss through mineralization.
The annual changes in N stocks in soil can be calculated by using the “Stock-Difference” Method:
∆𝑵𝑺 = 𝑵𝒕𝟐 − 𝑵𝒕𝟏
2.15
Where:
ΔNS=Changes in N stocks during the period t2-t1 [t N y-1]
Nt2,t1= total N stock during the year t2, t1, respectively [t N ha-1]
N stocks in soil are calculated on an area basis:
𝑵𝒕 = 𝑵 × 𝑩𝒅 × 𝒅 × 𝑯𝑺 × 𝟏𝟎
𝑯𝑺 = (𝟏 − (𝒔𝒕𝒐𝒏𝒆 𝒗𝒐𝒍𝒖𝒎𝒆 + 𝒓𝒐𝒐𝒕 𝒗𝒐𝒍𝒖𝒎𝒆) ÷ 𝒉𝒐𝒓𝒊𝒛𝒐𝒏 𝒅𝒆𝒑𝒕𝒉)
2.16
2.17
Where:
Nt= N stock per unit area [t N ha-1]
N= horizon N concentration [kg m-3]
Bd =bulk density [g cm-3]
d = thickness of soil layer [cm]
HS = is a dimensionless factor corrected the bulk density of the fine earth (<2mm) for stone and coarse root
volume
10 = is a unit conversion factor
However, in Swiss national N budget the soil N stocks changes were not included in budget since data
were not available (J. Heldstab, personal communication).
Stock changes in other lands
Nitrogen stock changes in other lands are assumed to be very small and were thus neglected.
Stock changes in wetlands
#
In general, N stocks changes can also be expected when other-lands or wetlands get converted to
forest lend either by natural or artificial regeneration. A default 20-year time interval is suggested
after the converted lands become forest (IPCC, 2006).
Biomass stock changes on land converted to other land-use
∆𝑵𝑩 = ∆𝑵𝑮 + ∆𝑵𝑪𝑶𝑵𝑽𝑬𝑹𝑺𝑰𝑶𝑵 − ∆𝑵𝑳
2.18
Where:
ΔNB= annual change in N stocks in biomass on land converted to other land-use category [t N y-1]
ΔNG= annual increase in N stocks in biomass due to growth on land converted to another land-use category [t N y1]
ΔNCONVERSION =initial change in N stocks in biomass on land converted to other land-use category [t N y-1]
ΔNL = annual decrease in biomass N stocks due to losses from harvesting, fuel wood gathering and disturbances
on land converted to other land-use category [t N y-1]
10
∆𝑵𝑪𝑶𝑵𝑽𝑬𝑹𝑺𝑰𝑶𝑵 = ∑{(𝑩𝑨𝑭𝑻𝑬𝑹𝒊 − 𝑩𝑩𝑬𝑭𝑶𝑹𝑬𝒊 ) × 𝑫} × ∆𝑨𝑻𝑶_𝑶𝑻𝑯𝑬𝑹𝑺𝒊 } × 𝑵𝑭
2.19
𝒊
Where:
ΔNCONVERSION= initial change in N stocks in biomass on land converted to other land-use category [t N y-1]
BAFTERi= biomass stocks on land type I immediately after the conversion, [t d.m. ha-1]
BBEFOREi =biomass stocks on land type I before the conversion, [t d.m. ha-1]
ΔATO_OTHERSi = area of land use I converted to another land-use category in a certain year [ha y-1]
NF = nitrogen fraction of dry matter, [tonne N (tonnes d.m.)-1]
i = type of land use converted to another land-use category
Suggested Data sources
CORINAIR landcover, contains information of the coverage and land use all over Europe:
www.eea.europa.eu; also FAO – www.fao.org
- IPCC 2006 guidelines (www.ipcc.ch) as well as EFDB (www.ipcc-nggip.iges.or.jp) provide
information on biomass and SON stocks, growth rates of N pools, biomass conversion and
expansion factors, wood density.
- National GHG inventory reports: http://unfeccc.int/national-reports/items/1408.php.
- National forest inventories: compiled at the European Forest Institute (EFI)
-
3 Flows: Calculation guidance
This section describes calculation methods and data sources to derive all relevant N flows in and out
of the pool Forest and Semi-Natural Vegetation and Soil. Figure 3 gives an overview on the flows
considered. In the following, the flows are grouped thematically:
-
Atmospheric deposition (A1) # Other land + wetland
Biological N fixation (A2)
Emissions (FS1)
Leaching (FS2)
Industrial timber (FS4)
Energy wood (FS5)
Wood export (FS3)
Wood growth (FS6)
11
I
I
AT4
AT5
Deposition
N2 fixation
I
AG1
Runoff
I
I
I
E
AT3
AT1
AT2
FS1
N2 fixation
Emission
(NH3, NOX,N2O,N2)
Deposition
Deposition
Forest
Plant & Soil
Plant & Soil
Plant & Soil
Emission/ANAMMOX
E
Energy wood
Wood Growth
WL2
WL1
Industrial timber
FS4
FS5
E
Plant uptake
FS3
Wood export
E
Other land
E
Wetland
FS6
OL1
Leaching/Runoff
FS2
Leaching/Runoff
E
E
Figure 3: Schematic overview on the considered flows. (Import symbols (I) depict both flows from actual imports and
from other pools, export symbols (E) depict outflows to other pools. Black and red colored arrows represent inflows and
outflows, respectively. The flow abbreviations refer to the relevant chapters below.
3.1 Forest Land
Atmospheric N deposition (A1)
Information on atmospheric N deposition is provided in annex 7- atmosphere. However, N deposition
to the soil varies between forest, open land and wetland due to effective sink of the forest canopies.
Thus, total N deposition in the forest land would be underestimated if throughfall, canopy uptake by
foliage, stems, epiphytic lichens, micro-flora, would not be taken into account. This means that total
deposition input on forest floor has to be corrected for the amount of the throughfall deposition.
Under the framework of the International Cooperative Programme on Assessment and Monitoring of
Air Pollution Effects on Forests (ICP Forest) the throughfall deposition has been monitored at several
hundred forest plots for more than 15 years with a precision of ±30% (95% significance level). The
mean annual inorganic nitrogen (NH4+-N and NO3--N) throughfall depositions [kg N ha-1 y-1] are
reported in Waldner at al., 2014.
For the countries without throughfall measurements, the throughfall deposition can be estimated by
an inferential approach:
𝑻𝑭 = 𝑻𝑫 − 𝑪𝑼 + 𝑪𝑳
𝑻𝑫 = 𝑾𝑫 + ∑(𝒗𝒅𝒆𝒑𝒊 × 𝒄𝒐𝒏𝒄𝒊 )
3.1
3.2
Where:
TF = throughfall [t N/year]
TD= total deposition in forested area [t N/year], see Error! Reference source not found.
12
CU= canopy uptake [t N/year], see Error! Reference source not found., see table #
CL = canopy leaching [t N/year], see table #
WD = wet deposition [t N/year], see 4.1.1.
Vdep_i = Depositionsgeschwindigkeit of coniferous and broad-leaved forests [#], see table #
Conc_i = concentration of the substance in the air [#]
At the plot scale in forest deposition monitoring, the total deposition of inorganic nitrogen (NH4+ and
NO3-) is calculated by using troughfall method in combination with the canopy budget model
developed by Ulrich 1983 and synthesized by Adriaenssens (2013).
3.1.1.1 Suggested Data sources
- CORINAIR landcover contains information on the coverage and land use all over Europe:
www.eea.europa.eu; www.eea.europa.eu/data-and-maps/data/corine-land-cover
- Transboundary nitrogen depositions are evaluated according to the country to country
blame matrices. The matrices are available in EMEP at the following link:
http://www.emep.int/mscw/SR_data/sr_tables.html
- Deposition monitoring on the ICP Forests Level II plots; http://icp-forests.net/page/datarequests
- National GHG inventory
Biological N fixation (A2)
For a rough estimation of biological N fixation (BNF) for several biome types, the N fixation rates are
provided in Cleveland et al. 1999; see table #. In this case, the N fixation rates for specific forest and
biome could be obtained after the default values have been related to the national forest area. It is
suggested, however, if relying on data reported in Cleveland et al., 1999, to use the lower percent
cover values of symbiotic N fixers over the landscape (i.e. 5%) and relate them to the actual
evapotranspiration (Galloway et al., 2004).
Biological N fixation can also be estimated as a difference between output (leaching, gaseous loss)
and input (deposition).
𝑩𝑵𝑭 = (𝑭𝑺𝟏 + 𝑭𝑺𝟐) − 𝑨𝟏
3.3
Where:
BNF = N2 fixed [t N/year]
FS1= outflow of N from denitrification [t N/year], see Error! Reference source not found.
FS2= outflow of N from leaching [t N/year], see Error! Reference source not found.
A1 = inflow of N from atmospheric deposition [t N/year], see 4.1.1.
In this context it must be stressed that such reverse calculation should be interpreted with caution
since both the deposition and leaching data are associated with high uncertainties.
3.1.2.1 Suggested data sources
- Cleveland et al. (1999)
- The European Nitrogen Assessment; Nitrogen process in terrestrial ecosystems. Sutton et
al., 2011. Cambridge University Press.
13
Emissions (FS1)
In most well drained and well-aerated forest soils, denitrification losses are <2 kg ha-1 y-1 of N (in
conifers often <0.5 kg ha-1 y-1) –Gundersen et al., 2005
3.1.3.1 Suggested data sources
#
14
Leaching (FS2)
Nitrate leaching occurs when N deposition (input) and net mineralization (status) exceed plant
demand (Gundersen et al., 2005). Hence, nitrate leaching is strongly dependent on the amount of N
deposited in througfall. No significant NO3- leaching could be expected when the throughfall fluxes
are under 8 kg N ha-1 y-1, while above 25 kg N ha-1 y-1 N leaching always occur (Dise et al., 2009;
Gunderson et al., 2006). Predicted rates on N leaching related to the throughfall N (95% confidence
intervals are ± 10 kg N ha-1 y-1) are given in the table #.
Also, a significant relationship was found between organic soil C:N ratios and leaching (Cools et al.,
2014). Threshold for elevated nitrate leaching is by a C:N ratio <25. However, in order to evaluate the
risk for nitrate leaching from the forest floor and topsoil thresholds of critical C:N ratios should be
taken into account according to tree species and the soil type (Cools et al., 2014) – see table #
Also, foliage N content as well as N density (total aboveground N input to the soil i.e. throughfall +
litterfall, excluding belowground root litter input) can be used as a proxy for the nitrate leaching
(Gundersen et al., 2006) –see table #. Finally, the N status of the system (limited vs. saturated) will
also determine its retention capacity. Basically, N-poor systems have a higher retention than N-rich
systems (Gundersen et al., 2006).
The IPCC guidelines propose a default leaching fraction of 0.3 # unit, i.e. it is assumed that 30% of
available nitrogen in the soil is reaching groundwater or surface water bodies (Rihm and Achermann,
2007).
At the plot level, leaching fluxes should be calculated by multiplying the measured soil solution
concentrations with simulated water fluxes. Water fluxes can be calculated with a monthly water
balance WATBAL model (Starr, 1999) or with a daily water balance Richard's model (van der Salm et
al., 2006).
For example, the nitrate leaching for dry sites with minimum denitrification and permanent plant
cover and a C:N ration ≤ 23 could be calculated as:
𝑭𝑺𝟐 = 𝑨𝟏 + 𝑨𝟐 − 𝟎. 𝟎𝟏
3.4
Where:
FS2 = outflow of N from leaching [t N y-1]
A1= inflow of atmospheric N deposition [t N y-1] [t N/year], see Error! Reference source not found.
A2= inflow of biological N fixation [t N y-1] [t N/year], see Error! Reference source not found.
0.01 = net plant uptake [t N y-1].
While for the soils with a C:N ratio >23, N leaching could be assumed to be zero (P. Gundersen,
personal communication).
3.1.4.1 Suggested data sources
- IFEF, Indicators of Forest Ecosystem Functioning, Dise et al., 1998b; contains data on inputoutput budgets published in scientific papers over the last decades for 250 forest sites.
- Level II database, expanded from De Vries et al.,2006 ; contains input-output budgets derived
from UN-ECE/EC intensive monitoring plots for the period 1995-2000 for approximately 110
forest sites.
15
- National forest inventory
- National soil inventory provides information on soil C:N ratio
Industrial timber (FS4)
All round wood felled or otherwise harvested and removed; it comprises all wood obtained from removals e.g.,
quatities removed from forests and from trees outside forests, including wood recovered from natural felling and
logging losses during a period. In the production statistics, it represents the sum of fuelwood, including wood for
charcoal, saw-and veneer logs, pulpwood and other industrial roundwood. In the trade statistics, it represents the
sum of industrial roundwood, and fuelwood, including wood for charcoal. It is reported in cubic meters
excluding bark. From IPCC 2006, Guidline for National Greenhouse Gas Inventories.
3.1.5.1 Suggested data sources
- national statistics
- EUROSTAT database:
http://epp.eurostat.ec.europa.eu/portal/page/portal/statistics/search_database
Energy wood (FS5)
Also wood-based fuels, wood-derived biofuels. All types of biofuels originating directly or indirectly from
woody biomass. According IPCC 2006, Guidlines for National Greenhouse Gas Inventories.
3.1.6.1 Suggested data sources
Wood export (FS3)
3.1.7.1 Suggested data sources
- FAOSTAT forestry database: http://faostat3.fao.org/download, are available from year
1961
- OECD database: http://www.oecd.org/statistics/, provides information on growing stock in
forest, forest land area and exports of forestry products
Wood growth (FS6)
Accumulation of organically bound N in forest comes up by annual biomass increments or
afforestation.
The annual increase in biomass can be estimated by comparing differences in biomass increments
from two different forest inventory periods or can be calculated as follow:
∆𝑵𝑮 = ∑(𝑨𝒊,𝒋 × 𝑮𝑻𝑶𝑻𝑨𝑳𝒊,𝒋 × 𝑵𝑭𝒊,𝒋 )
3.5
𝒊,𝒋
Where:
ΔNG = annual increase in biomass N due to biomass growth [t N y -1]
A= area of land [ha]
GTOTAL = mean annual biomass growth [tonnes d. m. ha-1 yr-1],see #
i = ecological zone (i=1 to n)
j = climate domain (j =1 to m)
NF = nitrogen fraction of dry matter [tonne N d.m. -1], see table #
16
3.1.8.1 Suggested data sources
- OECD database: http://www.oecd.org/statistics/, provides information on growing stock in
forest and forest land area
- Forest Europe: http://www.foresteurope.org/, has information on growing stock on forest
by forest type and member states from 1990-2011
- CORINAIR landcover, contains information of the coverage and land use all over the
Europe: www.eea.europa.eu; also FAO – www.fao.org
- IPCC 2006 guidelines (www.ipcc.ch) as well as EFDB (www.ipcc-nggip.iges.or.jp)
- National GHG inventory
3.2 Other Land
Atmospheric N deposition (A1)
3.2.1.1 Suggested data sources
Leaching (FS2)
3.2.2.1 Suggested data sources
3.3 Wetland
Atmospheric N deposition (A1)
3.3.1.1 Suggested data sources
Biological N fixation (A2)
3.3.2.1 Suggested data sources
Runoff (AG1)
3.3.3.1 Suggested data sources
Emissions (FS1)
3.3.4.1 Suggested data sources
Plant uptake (FS1)
3.3.5.1 Suggested data sources
4 Uncertainties
The quality of available data is diverse and for majority flows the uncertainties have to be estimated.
According to the IPCC reporting standard, for all fluxes 95% confidence interval should be stated. If
the error interval of the inflow overlaps the error interval of outflow, it can be assumed that the
balance is closed. In this context should be emphasized that geographic variations in climate, forest
types, ecology or species, forestry practices will require additional data and assumption. Moreover,
uncertainty originates from spatial and temporal variability of measured fluxes and difficulties when
upscaling point measurements to site and annual scales.
17
Zur Genauigkeit von WD von EMEP gegenueber WD gemessen an einem Punkt gibt es mehrere Publikationen.
This section specifies a general approach to assess uncertainties in the utilized data sets. The
uncertainties related with the pool HS are generally high, due to a lack of established and reliable
data sources. Many flows have to be determined as residuals from other flows within the pool, and
quantifications are frequently based on assumptions. This is why it is of particular importance to
indicate a range of uncertainty for all flows.
Analogous to Hedbrant and Sörme (2001), it is suggested to assign the data to a set of uncertainty
levels and the respective uncertainty factors (UF, see Table 2). These are compatible with the ratings
and typical error ranges from the EMEP/EEA air pollutant emission inventory guidebook 2013 (EEA
2013). Based on the likely value for a flow, the uncertainty interval can be derived by both
multiplying and dividing by the respective uncertainty factor2. Uncertainty levels can be assigned to
both N contents and mass flows of products. If two uncertain numbers with different uncertainty
factors are combined,3 the higher UF should be used for the result.
For some flows, uncertainties are already implicitly included in the calculation description (e.g.
emissions from human body – data used by Sutton et al. (2000) have a low estimate, high estimate,
and best estimate). In these cases, the UF that fits best to the given uncertainty interval should be
chosen.
Table 2: Levels of uncertainty (based on Hedbrant and Sörme 2001, Egle et al. 2014, Thaler et al. 2011)
Level
Uncertainty
Factor (UF)
1
1.1
2
1.33
3
2.0
4
4.0
Application
current official statistics, measurement
data, data from appropriate literature
expert estimates, outdated official
statistics, inofficial statistics,
presentations, industry reports
assumptions for which neither official
statistics nor expert estimates were
available often based on based on online data sources or publications
without accurate literature reference
an estimate based on a calculation
derived from assumptions only
Example, possible flows
FS1, FS2
N in materials with high variances in
their composition (e.g. PU, wood). FC1,
W1, P1, P2, W3, E1, E2, M3, M4
estimation on average N in tobacco,
based on diverse analytical literature of
different tobacco leaves with different
methods. G1, W2, M1
W2, E3, M2
2
e.g., for a likely value of 2530 t N/year with an UF of 1.33 the uncertainty interval would range from 1902 t N/year
(=2530/1.33) to 3365 t N/year(=2530*1.33)
3 Typically, this is for instance a multiplication such as: mass flow * N content = N flow
18
5 Tables
Table 3: N content factors for products referring to CPA 2008 Codes and CN Classes.
Table #: Ammonium to nitrate uptake ratios used for the calculation of the different canopy budget model versions,
based on the results of Adriaenssens et al., 2012
Period
Beech
Pedunculate oak
Scots pine
Oak-beech
Leaf development
2.1
2.9
93.6
2.6
Fully leafed
4.7
4.1
4.0
4.3
Leaf senescence
7.7
3.9
9.2
5.3
Leafless
4.3
5.1
39.6
4.8
Leafed
5.0
4.2
16.7
4.5*
Annual
4.8
3.7
49.2
4.1*
*approximate value, ratios used in the time trend analysis very between years depending on the
length of each period.
Table #: Reported ranges for biological N2 fixation in natural ecosystems (source: Butterbach-Bahl et al. 2011).
Ecosystem Type
Boreal forests and boreal woodland
Temperate forests and forested
foodplains
Natural grasslands
Mediterranean shrublands
N fixation rate
(kg N ha-1 yr-1)
1.5-2
Source
Cleveland et al., 1999
6.5-26.6
Cleveland et al., 1999
2.3-3.1
1.5-3.5
Cleveland et al., 1999
Cleveland et al., 1999
Table #: Predicted rates of NO3- leaching from forest (source: Macdonald et al., 2002)
Throughfall N
(kg ha-1 y-1)
10
10
20
20
30
30
C: N ratio
organic layer
≤25
>25
≤25
>25
≤25
>25
Leached N
(low/high 95% CI)
3 (0-11)
2 (0-11)
8 (0-18)
4 (0-14)
15 (5-25)
9 (0-18)
Table # An overview of ranges in N leaching as a function of the N status of the ecosystem (Source:
Gundersen et al., 2006).
Nitrogen status
Input [kg N ha-1y-1]
Needle N (in spruce) [%]
C:N ratio
Soil flux density proxy (litterfall +
throughfall) [kg N ha-1y-1]
Low status
(N-limited)
0-15
<1.4
>30
<60
Intermediate
15-40
1.4-1.7
25-30
60-80
High N status
(N-saturated)
40-100
1.7-2.5
<25
>80
19
Proportion of input leached
<10
0-60
30-100
20
Table #: Mean C:N ratios of the top soil (0-10 cm) with their 95% confidence interval (in brackets) grouped by WRB reference soil groups for the eight most
frequently recorded main tree species on ICP Forests (source: Cools et al., 2014)
Mean tree species
Scote pine
Reference soil
group
Arenosols
20.9
(20.4;21.4)
Cambisols
20.3
(19.3;21.5)
Gleysols
20.9
(18.7;23.4)
Histosols
30.7
(29.2;32.2)
Leptosols
20.2
(18.6;22.0)
Luvisols
16.4
(14.4;18.2)
Phaeozems
18.2
(16.6;20.3)
Podzols
23.6
(22.9;24.5)
Regosols
21.5
(20.8;22.2)
Stagnosols
21.3
(19.8;22.9)
Umbrisosl
16.1
(14.4;17.9)
Norway
spruce
20.8
(19.0;22.4)
18.3
(17.8;18.8)
18.3
(16.5;20.4)
26.4
(24.4;30.8)
18.4
(17.4;19.5)
14.9
(13.9;15.8)
17.2
(16.3;18.5)
20.8
(20.1;21.6)
19.4
(18.8;20.0)
19.3
(18.0;20.7)
18.0
(16.7;19.2)
Common
beach
15.7
(15.2;16.2)
Silver
birch
17.6
(16.0;20.2)
16.6
(15.4;18.4)
17.2
(14.7;21.5)
16.7
(15.1;18.4)
15.8
(14.7;17.6)
14.9
(14.2;15.7)
14.9
(14.0;16.2)
16.6
(14.9;18.5)
17.5
(16.0;20.2)
18.0
(16.7;19.2)
Pedunculate Holm oak
oak
19.4
(17.7;21.9)
15.3
(14.7;15.9)
Maritime
pine
Aleppo
pine
14.4
(12.9;16.0)
27.9
(23.0;32.8)
24.6
13.3
(21.6;30.1) (10.3;15.2)
13.5
(12.6;14.6)
17.0
(14.3;20.0)
13.7
(12.2;15.5)
30.5
(26.6;34.5)
23.8
15.1
(20.8;26.2) (11.3;20.2)
15.1
(14.2;16.1)
22.0
(19.4;25.4)
21.0
(18.3;24.2)
16.4
(14.7;18.2)
20.0
(18.0;22.0)
21
Table #: Estimated throughfall deposition according to geographic site and tree species (source: Nadelhoffer et al., 1999;
#)
Site
Sweden
Wales, UK
Switzerland
Denmark
Netherlands
Netherlands
Germany
France
Germany
Tree species
Picea abies
(Norway spruce)
Picea sichensis
(Sitka spruce)
Picea abies
(Norway spruce)
Picea abies
(Norway spruce)
Pseudothuga
menzieseii
(Douglas fir)
Pinus sylvestris
(Scots pine)
Picea abies
(Norway spruce)
Fagus sylvatica
(Common Beech)
Fagus sylvatica
(Common Beech)
Throughfall N
[kg ha -1 y-1]
13
Source
Nadelhoffer et al., 1999
15
Nadelhoffer et al., 1999
17
Nadelhoffer et al., 1999
20
Nadelhoffer et al., 1999
50
Nadelhoffer et al., 1999
58
Nadelhoffer et al., 1999
2.96
Rothe et al., 2002
7.6
Jussy et al., 2004
1.55
Rothe et al., 2002
Table # Default factors to convert from product units to nitrogen
1. Average wood density [ovendry tonnes m-3]
2. Nitrogen fraction [tonne N
(tonne d.m.)-1]
3. N factor (tonne N per m3 of
product or per air dry tonne of
product)
(row 1) x (row 2)
Roundwood
Temperate & Boreal tree
species
0.45
# from Luc
A=
22
BASIC WOOD DENSITY (D) OF SELECTED TEMPERATE AND BOREAL TREE TAXA
Taxon
D [oven-dry tones (moist m-3)]
Source
Abies spp.
0.4
2
Acer spp.
0.52
2
Alnus spp.
0.45
2
Betula spp.
0.51
2
Fagus sylvatica
0.58
2
Fraxinus spp.
0.57
2
Larix decidua
0.46
2
Picea abies
0.4
2
Picea sitchensis
0.4
3
Pinus pinaster
0.44
4
Pinus radiata
0.38 (0.33-0.45)
1
Pinus strobus
0.32
2
Pinus sylvestris
0.42
2
Populus spp.
0.35
2
Prunus spp.
0.49
2
Pseudotsuga menziesii
0.45
2
Quercus spp.
0.58
2
Salix spp.
0.45
2
Tilia spp.
0.43
2
Average
1
2
3
4
0.45
= Beets et al., 2001
= Dietz, 1975
= Knigge and Schulz, 1966
= Rijsijk and Laming, 1994
23
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Dentener, F., Drevet, J., Lamarque, J. F., et al., 2006. Nitrogen and sulfur deposition on regional and
global scales: A multimodel evaluation, Global Biogeochem. Cycles, 20, GB4003,
doi:10.1029/2005GB002672, 2006.
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This is a draft. For questions please contact:
Ika Djukic
ika.djukic@umweltbundesamt.at
Thomas Dirnböck
thomas.dirnboeck@umweltbundesamt.at
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