The influence of raised water table levels on carbon dioxide and methane production in ditch-dissected peat grasslands in the Netherlands

The impact of hydrological manipulation on the mineralisation rates, measured as carbon dioxide and methane production rates, in the soil of the land-water transition zone of an unfertilised, Dutch peat grassland area was studied. The hydrological manipulation involved raising the ditch and groundwater levels by admitting nutrient-poor, Ca-rich groundwater in the trial area. An adjacent, fertilised, field served as a control. On an annual basis the CO2 production rate was usually highest in the parcels, intermediate in the ditch banks and lowest in the ditch bottoms, ranging from 2496 to 598 kg C ha(-1) year(-1) in the wet field and from 2918 to 421 (kg C) ha(-1) year(-1) in the control field. The CH4 production rate was negligible in the parcels, low in the ditch banks and substantial in the ditch bottoms, ranging from 0 to 1175 (kg C) ha(-1) year(-1) in the wet field and from 2 to 241 (kg C) ha(-1) year(-1) in the control field. The CO2 production rate was significantly affected by pH, C:N ratio and by moisture content. It tended to be highest at pH 5.8, at a C:N ratio of 12, at a moisture content of 50% and at a temperature of 20 degrees C. The CH4 production rate was significantly affected by pH, organic matter content and C:N ratio. It tended to be highest at pH 6.7, at an organic matter content of >40% and at a C:N ratio of 17. A temperature effect was not apparent. It was estimated that the CO2 and CH4 production rates of typical Dutch peat grasslands are 2824.3 and 6.1 (kg C) ha(-1) year(-1) when used for agriculture, but 2435.5 and 20.8 (kg C) ha(-1) year(-1) when rewetted with nutrient-poor, Ca-rich artesian water. Thus, rewetting, e.g. for nature conservation purposes, may cause the production of CO2 to decrease by 14% but that of CH4 to increase 3.4-fold. Circumstances in which these gases are emitted were discussed. This study indicates that hydrological manipulation of typical Dutch peat-grassland areas ire which fertilisation has ceased has profound effects on the production of CO2 and CH4 of these systems and may lead to increased emission of methane to the atmosphere. (C) 1997 Elsevier Science B.V.