Case Study Experiment - loss of organic matter in the organic soil
The researchers in Sweden are testing different crops, especially reed canary grass and Tall fescue and comparing them with the "usual" crop timothy, regarding yield and CO2 emissions.
|An aerial view of the case study site|
Penetration resistance (average of measurements at 10-20 cm depth) in July and October for Reed canarygrass(RCG), Timothy (T) and Tall fescue (TF).
The N2Oemission was quite low during the growing season and no significant difference between the crops could be found. The total yield from 2 cuts (t DM/ha) of T was 6.6. RCG yielded 9.3 and TF 8.6.
Broddbo (60.03o N, 17.4o E, 38 m a.s.l) is part of the peatland area, Bälinge mossar (1500 ha) that was firstly drained in 1899 and is now mainly managed as arable land and grassland with hay production. Mean annual air temperature is 5.3 oC and mean annual precipitation is 563 mm. Peat depth varies between <50 cm to up to several meters. The area is drained mainly by open ditches at 75 m spacings.
Main soil threat
Oxidation of agricultural peat soils causes a loss of organic matter and subsidence of land, which leads to deteriorating drainage and increased emissions of greenhouse gases. Agricultural peat soils represent only 7% of the agricultural land in Sweden but still have a significant effect on total national greenhouse gas emissions. The total emissions of CO2 and N2O from agricultural peat soils in Sweden have in 2003 been estimated to correspond to ~6–8% of total emissions of all greenhouse gases reported by Sweden (excluding the sink for land use, land use change and forestry - LULUCF).
Climate change, with its associated predicted higher temperatures in Sweden, will of course have a major effect on emission rates. The degradation products also pollute surface waters. With the subsidence of the peat, drainage levels are gradually getting shallower and farmers have to abandon the land, but emissions continue. Flooding agricultural peat soils is in many cases not possible without high costs, high (temporally extreme) GHG emissions and severe water pollution. Moreover, cultural and historic landscapes and meadow bird areas are lost. In some areas, regulating groundwater levels in dry summers to reduce peat oxidation can be an option. In areas where the possibility to regulate the water table is limited, the mitigation options are either to increase biomass production that can be used as bioenergy to substitute for some fossil fuel, to try to slow down the break-down of the peat by different amendments that inhibit microbial activity, or permanent flooding. Currently, farmers in the Case Study area are looking for alternatives to abandonment. There is a dire need for development of management strategies on peat and other organic soils to reduce subsidence and emission rates.
Other soil threats
Wind erosion of peat soils in arable agriculture can cause losses of 3 to 30 t ha-1 y-1 of peat material also causing subsidence, air pollution (fine organic particles) and pollution of surface waters. Soil degradation products such as nutrients, peat particles and dissolved organic matter (DOM) also pollute surface waters. With the subsidence of the peat, drainage levels are gradually getting shallower and farmers have to abandon the land, but emissions continue. Flooding agricultural peat soils is in many cases not possible without high costs, high (temporally extreme) GHG emissions and severe water pollution.
Location and Digital Elevation Model (DEM) of the Broddbo Case Study (Source: viewfinderpanoramas.org)
Geology & Soil formation
The Broddbo field site is located 750m west of a former field trial, Örke. The soil properties of Örke (Berglund et al., 2011) and Broddbo site (pH and loss on ignition) are shown in the table above. Values of pH in the Broddbo site are slightly higher than at Örke and old tree remains are visible in the soil - see below. The properties of the organic soils in the Bälinge Mossar area are quite representative of the cultivated peat soils in Sweden, with high organic matter content, high degree of decomposition and pH between 5 and 6. The properties of Swedish arable peat soils have been described by Berglund (1996).
|Depth [cm]||Degree of decomp.||
Loss on ignition
|pH (H2O)||Dry bulk density||Tot-C
|von Post*||Örke||Broddbo||Örke||Broddbo||g cm-3||% (w/w)||% (w/w)||ratio|
*von Post classification: H8: Thick mud, little free water, very strongly decomposed; H9: No free water, almost completely decomposed; H10: No free water, completely decomposed.
Soil types and Land Use in the Broddbo Case Study (Source: JRC, SMD Svenska Marktäckedata (classification based on CORINE Land Cover classification)).
The soil formation of Bälinge mossar is very well described by McAfee (1985): “After withdrawal of the Litorina sea, clay from the surrounding moraine was washed into deeper topographical areas. This clay consisted of irregular bands overlain by a layer of mixed Yoldia, Ancylus and Litorina clays.” The final withdrawal of water took place slowly, leaving relatively plane clay surfaces on which shore mud, possibly trapped in seaweed banks, was deposited. When the particular bay was cut off completely from the sea, conditions became calmer and two layers of gyttja (brackish water and fresh water) deposition began over the mud. Cascading flora and fauna gyttja deposited where the lake gradually gave its place to a marsh that gradually became covered by a Betula stand and achieved a more xerophilic nature. Taller evergreen trees with thicker trunks replaced Betula so that, at equilibrium, an almost totally coniferous forest reigned. The final stage in development of the profile was stagnation or the recurrence of marsh conditions. “In the domed mire area, Sphagnum colonies formed and began to spread. Trees died out as marsh conditions intensified and the moss colonies finally met up to cover the entire area. Material was classified as fen peat formed over a cascade of brackish water and fresh water gyttja deposits. “The lowest layer was Equisetum, which gave way to Carex remains. Above this was a thick layer of heterogeneous peat consisting of bush and tree remains. The uppermost layer of the domed mire consisted of Carex-Amblystegium at the edges with a thick mat of Sphagnum forming the dome. Södra Myren had a similar profile but in its case, it was impossible to distinguish between the two types of plankton gyttja. The gyttja was overlain by a brown, well humified mud instead of Scirpus and Phragmites gyttja. The remaining layers of the low moor profile consisted of a layer of forest peat, then finally a Carex-Amblystegium layer. The Södra Myren profile is a typical example of a fertile Swedish low moor or fen peat (Osvald, 1937).
The current surface level coincides with the sea level during the Stone Age so the ancient landscape is well visualized by the open landscape of today and many remains from that era and onwards can be found at higher elevations. It is therefore in the interest of the National Heritage Board that the current land use should be maintained. Farming - mainly grazing or grass production - is the main land use at Bälinge mossar today - see below.
The climate in this region is cold and temperate. The Köppen-Geiger climate classification is Dfb (humid continental climate with wet winters and summers). There is significant rainfall throughout the year, even during the driest month. The annual rainfall is about 551 mm (meteorological station in Uppsala). The average annual temperature during the last 30 years is 5.7°C but has increased in the last 10 years to 6.3°C - see below.
Drivers and Pressures
The major socio-economic driver for the reclamation and drainage of peat soils in Sweden has been the need for agricultural land, food production and intensified forest production. Fen peat soils are eutrophic or mesotrophic and therefore well suited for agricultural use, however, they have by nature a high water table, so they can be difficult to drain. Human activities with drainage and cultivation are important drivers for processes leading to decline in organic matter. In areas where horticulture and dairy farming is still profitable due to the good infrastructure and marketing opportunities cultivation is intensive but a large area of agricultural peat soils in less-favoured areas, where improved drainage might involve huge costs and also be restricted by legislation, are now abandoned. Land use and land management are also influenced political factors. For example, EU policies have an effect on the choices that farmers make regarding land use and crop. Some of these areas have been used as set-aside areas when this has been mandatory in EU CAP policies. Climate change, with its associated predicted higher temperatures in Sweden, will of course have a major effect on emission rates.
Status of soil threat
Since drainage of the Bälinge Mossar, the decline in surface levels due to peat subsidence has been determined by comparing surface elevations from the first survey in 1898 to those from surveys in 1938, 1964 and 1984 (McAfee, 1985). The average subsidence at the Broddbo field site has been estimated to about 1 cm/year during the last 40 years. At the Broddbo field site (below left) the peat depth is more than 100 cm and large areas in the region have peat depths greater than 3 m (McAfee, 1985). The subsidence in the area is about 1-2 cm/year and at some places within the Bälinge mossar region the peat depth is less than 20 cm and clay from the lower layers is being ploughed up. Areas close to the main channel are often flooded during the spring (below right). Drainage efficiency in many fields is very low and the bearing capacity is not high enough for modern machinery.
Maps on the current state of land use, soil degradation and soil conservation in the case study area have been produced using the WOCAT (World Overview of Conservation Approaches and Technologies) methodology
The steps of this process are as follows:
1) The area to be mapped is divided into distinctive land use systems (LUS). 2) The team gathers the necessary data on soil degradation and conservation for each LUS using a standardised questionnaire, in close consultation with local land users, and supported where possible by remote sensing or field data. 3) For each LUS, the soil degradation type, extent, degree, impact on ecosystem services, direct and indirect causes of degradation, as well as all soil conservation practices, are determined. 4) Once collected, the data is entered in the on-line WOCAT-QM Mapping Database from which various maps can be generated.
Following the principles of all WOCAT questionnaires, the collected data are largely qualitative, based on expert opinion and consultation of land users. This allows a rapid and broad spatial assessment of soil degradation and conservation/SLM, including information on the causes and impacts of degradation and soil conservation on ecosystem services.
More details about the methodology used to produce these maps and their interpretation can be found here.
Land Use (click on maps to expand)
The degree of degradation reflects the intensity of the degradation process, whilst the rate of degradation indicates the trend of degradation over a recent period of time (approximately 10 years).
The "effectiveness" of conservation is defined in terms of how much it reduces the degree of degradation, or how well it is preventing degradation. The Effectiveness trend indicates whether over time a technology has increased in effectiveness.
Effects of loss of organic matter on soil functions
The following table summarises and ranks the effects of loss of organic matter on the soil functions at the Broddbo Case Study.
|Functions of soil||Explanation||Effect|
Subsidence due to oxidation of the peat leads to lower bearing capacity reduced trafficability and oxygen deficiency for plants roots.
|Environmental interactions||Loss of peat results in loss of the storage of C, increased GHG emissions, mineralization and release of N, P and S and other minerals, dissolved OM (DOM) and peat particles towards surface waters.||VN|
|Gene reservoir/ Biodiversity pool||Depends on cultivation intensity. Higher biodiversity in permanent grasslands on the verge of abandonment compared to arable agriculture.||N/VN|
|Infrastructure||Roads and bridge culverts are negatively affected by the subsidence of the peat.||VN|
|Source of raw materials||The peat soil in the case study area is not suitable for peat harvesting.||Z|
|Cultural heritage||The National Heritage Board has declared The Bälinge Mossar area as a site of cultural significance since the Stone Age landscape is well visualized by the open landscape of today. It is therefore in the interest of the National Heritage Board that the current land use is maintained as much as possible.||P|
Administrative and socio-economic setting
There are approximately 135 landowners in the Bälinge Mossar area. The Case Study area is a small part of this area. The size of ownership varies, including many privately owned farms with only a few hectares of peatland each, to 30 hectares of peatland owned by the Bälinge parish, 80 hectares owned by the Uppsala University, and 160 hectares owned by one big farmer. Farming intensity can vary due to varying dependence on income from farming, distance between the farm centre and field plots out in the peatland area and/or type of production (cattle or not). Hence, small peatland ownerships are usually part of a farm that has its centre and buildings situated far from the main peatland area. These farmers will in general cultivate the peatland less intensively than farmers having the whole farm situated in the peatland area. Furthermore, different levels of intensity in farming create different demands for drainage intensity. Hence, big landowners such as the Uppsala University cultivate the peatland with a very low intensity and are not interested in new investments (deepening the ditches). All water management is regulated by the Swedish Environmental Code legislation and big drainage schemes are organised in associations (joint-ownership units). Current water management can be changed if more than 50% of the landowners (e.g. more than 50% of the area that will benefit from a changing water regime) reach consensus, provided it doesn’t harm 3rd party interests. Therefore this existing heterogeneity in land user priorities and preferences can create tension and conflict.
Relevant to water management, deepening the canals would also involve huge costs for lowering bridge culverts which is not in the interest of the Swedish National Road Administration. Another area of conflict has emerged due to the Act concerning Ancient Monuments and Finds. Some landowners want to plant their fields with trees (especially if the farm centre is situated far from the peatland area) but the National Heritage Board has declared The Bälinge Mossar area as a site of cultural significance since the Stone Age landscape is well visualized by the open landscape of today. It is therefore in the interest of the National Heritage Board that the current land use is maintained as far as possible. Still, some farmers have secured permission to plant limited areas with trees. Finally, large areas are abandoned due to drainage problems in combination with the declining economic viability in the agriculture sector. Since 1994, ditch levels are regulated by a legal document. Current land use should be maintained as far as possible, but in the long run the open landscape will gradually turn into forest if the drainage intensity is too low.
Strategies derived from the SWOT profile include: (a) peat extraction directed towards drained wetland to avoid GHG emissions in the long term, (b) introduction of agri-environment payments for peat preservation measures, (c) changes/simplification of legislation for water operations, (d) funding for more advanced after-treatment of pet extraction sites, and (e) establishment of culture reserves on peatlands (protection of landscape, land management and/or archaeological objects).
Relevant end-users and local stakeholder groups include;
- Land-owners in the area (private farmers, Uppsala University, Bälinge parish)
- The county council
- Agricultural societies and advisory organisations
- The public; local people and visitors
- The Swedish Board of Agriculture
- The Swedish Environmental Protection Agency
- The National Heritage Board.
Gender and stakeholder workshops
Berglund, K. (1996). Cultivated Organic Soils in Sweden: Properties and Amelioration. Reports and Dissertations PhD, Swedish University of Agricultural Sciences.
Berglund, Ö. (2011). Greenhouse gas emissions from cultivated peat soils in Sweden. AgrD. Doctoral Thesis, Swedish University of Agricultural Sciences.
Berglund, Ö. and K. Berglund (2011). "Influence of water table level and soil properties on emissions of greenhouse gases from cultivated peat soil." Soil Biology and Biochemistry 43(5): 923-931.
McAfee, M. (1985). The rise and fall of Bälinge mossar.69 pp pp. Institutionen för markvetenskap. Avdelningen för lantbrukets hydroteknik.http://pub-epsilon.slu.se:8080/721/01/mcafee_m_090506.pdf
Osvald, H. (1937). Myrar och myrodling. Stockholm, Kooperativa förbundets bokförlag.