Markytesänkning, växthusgasavgång och utlakning från dikad torvjord

Sammanfattning: Greenhouse gas emissions and land subsidence on four cultivated peat soils (Martebo, Örke, Kälkestad, Lidhult) have been investigated by measuring emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in field and lab. Greenhouse emitted gas (mg/h) from undisturbed soil cores was measured in lab. Measurements were performed at four different drainage depths. Soil cores were also kept incubated at constant drainage depth and emitted gas was measured with two-week intervals at three measurement occasions. Field measurements of CO2 emissions (mg/h/m2) were also performed. In addition to gas emissions, irrigation of soil cores has been carried out to investigate the risk of leaching of copper (Cu), phosphorus (P), nitrogen (N) and dissolved organic matter (DOC) during rewetting, and whether turbidity can be used as a measurement of DOC. Land surveying with GPS was done on three of the peat soils. This was to investigate how land subsidence can be related to CO2 emissions. On one of the sites different land surveying methods were used to assess their suitability for tracking land subsidence in peat soils. 30 year land surveying data from the sites have also been compiled and analyzed. The peat soils are part of a long-term experiment that was laid out in 1986. On each site one field was fertilized with copper and one was kept untreated as comparision. The purpose of the copper fertilizer was to reduce the activity of microorganisms. By doing so the degradation of soil organic matter could be reduced, thereby reducing the land subsidence. The results show that the ground surface at all four sites has subsided, but no difference is observed for copper-fertilized fields compared to untreated. Neither could an effect on CO2 emissions from copper fertilization be noted. The greatest land subsidence was observed for Martebo and the least for Kälkestad. By using data from the most recent time period the greatest subsidence was instead observed for Örke. This is consistent with Örke having the greatest CO2 emissions. CO2 emissions alone could not explain land subsidence. The results also show that emitted N2O was higher for nutrient-rich soils with the peak directly after saturation. CH4 was at its lowest initially, but then increased and emitted CH4 was greatest for the soils where easily biodegradable organic matter was available. Turbidity alone could not explain the DOC content in leachate from the irrigated soil cores. Conclusions drawn were that copper fertilization had no effect on land subsidence and CO2 emissions in this case. Copper did however still leach from the soils 30 years after addition. Emissions of CO2, N2O and CH4 varies greatly between the different soils. To be able to obtain reliable levels of greenhouse gas emissions from peat soils in climate models, more research is needed on how different peat soils react to water and nutrient content. It is important to have long time series when measuring land subsidence. Using the same measurement equipment will give better results. GPS for land surveying of peatland can be recommended if the results can be related to a fix point.