Soil subsidence is one of the major issues in the
management area of the water authority Amstel, Gooi and Vecht, including
emissions of greenhouse gases. This paper describes four different methods
to calculate these emissions in agricultural peat meadows, based on (1) the
mean lowest groundwater level, (2) the mean groundwater level, (3) the
subsidence rates and (4) general numbers. The emissions were calculated in
two polders (about 2600 ha peat meadow), these were comparable for all
methods, ranging from 42 up to 50 kton
Waternet is the executive agency of the regional water authority Amstel,
Gooi and Vecht (AGV). Soil subsidence is one of the major issues in the
management area of AGV, including emissions of greenhouse gases (GHG).
Different methods exist to estimate GHG emission from peat soils. In
Waternet, a literature study was done to estimate GHG emissions (Stoffels,
2009). Another estimation can be performed based on mean groundwater levels
(Jurasinski, 2016). In the model RE:PEAT,
The question was if calculations of GHG emissions based on these different
methods would give comparable outcomes. A method is developed to calculate
these emissions as a final step in groundwater modelling. It was
hypothesized that GHG estimations in part of the water management area would
be comparable for different methods (
Area of investigation Groot Wilnis-Vinkeveen and Wilnis-Veldzijde, with division into polder subunits (source of topographic underlayer: © Kadaster, 2016).
In this paper these methods are also used to evaluate GHG emissions of
different policies. It was expected that the formulated scenario's in this
study (passive rewetting, applying subsurface irrigation and lowering
surface water level at a rate of 6 mm yr
In this study, current GHG emissions in the agricultural peat lands of Groot-Wilnis Vinkeveen and Wilnis-Veldzijde are calculated (about 2600 ha peat meadows), see Fig. 1. The GHG in the water bodies or built area are not calculated.
It is common practice that the water authority lowers the surface water
levels in the same rate as the soil subsidence that has taken place since
the last level correction. In a part of Groot Wilnis-Vinkeveen a convenant
is made, meaning that the surface water levels will be lowered at a maximum
rate of 6 mm yr
GHG emissions were calculated for different policies in one polder in Groot-Wilnis Vinkeveen: polder subunit 9 (about 283 ha peat meadows).
Different methods were compared to calculate current GHG emissions (2015), which are shortly described in Table 1.
Methods used to calculate GHG emissions due to soil subsidence.
Figure 2 shows the
GHG emissions as a function of average lowest groundwater level (Stoffels, 2009).
Figure 3 shows the
Emissions of
GHG emissions and net GHG balance of peatlands depend on the average annual water table. The hairline graphs illustrate the 95 % confidence intervals, respectively (Jurasinski et al., 2016).
The estimation of the soil subsidence taking place per polder subunit based on historical values is used as an input for calculation of the GHG emissions for method 3.
For method 4, only peat meadow surface area is needed to estimate the
In the study area, four different policies were compared: (1) standard policy
(assumption: GHG emissions are not affected as the water authority lowers
the surface water levels in the same rate as the soil subsidence), (2)
passive rewetting (assumption: soil subsidence is not influenced by this
policy, while the (mean and lowest) ground water levels are affected), (3)
submerged drains (assumption: soil subsidence is half of measured soil
subsidence, meaning that only the
GHG estimations based on method 4 (peat meadow surface) are not influenced by policy scenario as the surface area is not affected.
Also for the polders Groot-Wilnis and Wilnis-Veldzijde GHG emissions are estimated for the policy passive rewetting and compared to standard policy (with the same assumptions as in case of only polder subunit 9).
The calculated total GHG emissions in Groot Wilnis Vinkeveen and surrounding
area were comparable for all methods, ranging from 42 upto 50 kton
Figure 5 shows the calculation of GHG emission in the research area (Groot-Wilnis Vinkeveen and Wilnis-Veldzijde) based on mean ground water level (Jurasinski et al., 2016) with a correction for clay cover.
Estimation of total GHG emissions in Groot-Wilnis Vinkeveen and surrounding area (for different methods: Table 1).
Calculated current
The methods to estimate GHG emissions differ. In case of applying method of
Waternet and Jurasinski, besides
However, methane emissions are expected at relatively high ground water levels and therefore are normally only a small portion of the total GHG emissions in agricultural peat meadows for both methods.
There is uncertainty about how accurate the different methods are,
especially regarding the
It is stated that the hairline graphs illustrate the 95 % confidence intervals for method 2, it seems however, that there is a high variability measured on GHG emissions (Jurasinski et al., 2016), see Fig. 3.
Note that the global warming potential in the Waternet method was not
updated of
Besides the presented methods in this paper, also other methods exist to
calculate GHG emissions from agricultural peat lands, for example
measurements of
Another method which is not shown in this paper is to use the land
subsidence model Phoenix in RE:PEAT, which determines land subsidence in
peat soils based on mean lowest groundwater level, in combination with the
In Fig. 6, the GHG emissions are shown for different methods for polder subunit 9.
GHG emissions with four different policies in polder subunit 9.
The estimations of the effect of different policies on GHG emissions differ, and these estimations are sensitive to the assumptions made. Therefore, the methods presented in this paper are rough concerning GHG emission estimations.
The estimation of GHG emissions based on general numbers (as used in the national counting), shows no effects of measures. This can be expected, as this estimation is only based on peat area and GHG emissions in peat area will only lower if soil types are changed, for small peat layers this means that if the peat disappears due to oxidation of the peat, also the GHG emissions will be lowered. This means that the efforts to lower soil subsidence and GHG emissions related to this soil subsidence will not show effect on the national counting.
Emissions are lowest in case of applying submerged drains, decreasing GHG
emissions by 35 %–50 % depending on the method applied (see Fig. 6). In
this estimation, the assumption is made that soil subsidence is lowered by
50 % and the
The value of the lower GHG emissions can also be quantified: the lower
emissions in this polder subunit in case of submerged drains represent a
value of about 550–930 EUR ha
The scenario passive rewetting leads to a decrease of about 12 %–21 % after
10 years, or 2–3 t
In this study, it is assumed that the soil subsidence is not influenced by
the policy of passive rewetting or maximum water level change (of 6 mm yr
The method of Jurasinski is based on mean groundwater levels (Jurasinski et al., 2016). However, it is expected that highest emissions take place in summer with lower groundwater levels.
For the whole polder Groot-Wilnis Vinkeveen and Wilnis Veldzijde, it is
expected that passive rewetting leads to 9 %–12 % GHG reduction compared to
standard policy after 10 years (results not shown), thus a reduction of
about 3.7–5.8 kton
Different methods were compared to estimate GHG emissions in agricultural peat land areas, which lead to comparable current GHG emission estimations. However, not all methods can be used to analyze effects of different policies on GHG emissions.
In this paper, different methods are used to analyze the effects of different policies on GHG emissions. This procedure will be used by the water authority AGV in the future to support water level management in areas with peat soils. It is recommended to update these methods regularly when new insights become available on GHG emissions in agricultural peat land areas.
In this paper, it was shown that different water management policies will affect GHG emissions in the study area. Within the scenario's compared, GHG emissions are expected to be decreased most by applying submerged drains. Estimations of GHG emission reductions depend on assumptions made.
The underlying research data is stored in a database of Waternet (not public).
AMMW took the lead in writing this paper. JB performed the groundwater modelling and contributed in writing the paper.
The authors declare that they have no conflict of interest.
This article is part of the special issue “TISOLS: the Tenth International Symposium On Land Subsidence – living with subsidence”. It is a result of the Tenth International Symposium on Land Subsidence, Delft, the Netherlands, 17–21 May 2021.
The idea of this work was given by Bart Specken. Corine van den Berg was the commissioner of the work. Johan Ellen provided the measured soil subsidence in Groot-Wilnis Vinkeveen and surrounding area. Marie-Josée Leloup provided the policy scenarios that were compared. Tim Pelsma helped on critical reviewing the work. Christian Fritz from Radboud University Nijmegen provided literature background on estimating GHG emissions.