| Description: |
Peatlands cover about 3 % of the earth's land surface, while storing about 20 % of the total global soil organic carbon. These carbon stocks are largely at risk, as many peatlands have deteriorated since the Industrial Revolution due to conversion to agricultural land by drainage. Globally, peatland drainage is responsible for over 3.5 % of anthropogenic greenhouse gas emissions. Approximately 75 % of these emissions originate from warm climate regions. Mitigation of these emissions can be achieved by rewetting degraded peatlands. This study focuses on a warm Mediterranean sub-tropical climate peatland that has been cultivated for the past ∼70 years (Hula Valley, Israel). The historic marsh was drained in 1957 for agricultural use and underwent a hydrological restoration project for elevating and stabilizing groundwater table since 1994. This land management history resulted in a sedimentary peat column that can be divided into three distinct sub-sections: drained, rewetted and pristine peat. This setting enables studying the drainage and rewetting effects on soil organic matter (SOM) degradation and preservation under warm climates. For this purpose, five sediment cores, 4 m long each, were excavated from cropland located over the historic marsh area. Locations were chosen to match previous studies on this site. Each soil profile was characterized using Rock-Eval ® thermal analysis of the organic matter, and short-term soil aerobic respiration experiments. Integration of these results with historic SOM content data and with SOM modelling was used to explore the long-term process and rate of degradation. We found that the mean SOM content in the top one meter of the soil profile declined from 68±4 % to 21±2 % by weight over the past 66 years, excluding the compaction effect. In comparison to the drained section, the rewetted and pristine sub-sections have a mean SOM of 33±2 % and 64±2 %, respectively. A peak in pyrite concentration beneath the recent water table-level, was observed in most profiles, indicating ... |