Spatio-Temporal Variability of Peat CH4 and N2O Fluxes and Their Contribution to Peat GHG Budgets in Indonesian Forests and Oil Palm Plantations

Land-use change in tropical peatlands substantially impacts peat emissions of methane (CH4) and nitrous oxide (N2O) in addition to emissions of carbon dioxide (CO2). However, assessments of full peat greenhouse gas (GHG) budgets are scarce and CH4 and N2O contributions remain highly uncertain. The objective of our research was to assess changes in peat GHG flux and budget associated with peat swamp forest disturbance and conversion to oil palm plantation and to evaluate drivers of variation in trace gas fluxes. Over a period of one and a half year, we monitored monthly CH4 and N2O fluxes together with environmental variables in three undrained peat swamp forests and three oil palm plantations on peat in Central Kalimantan. The forests included two primary forests and one 30-year-old secondary forest. We calculated the peat GHG budget in both ecosystems using soil respiration and litterfall rates measured concurrently with CH4 and N2O fluxes, site-specific soil respiration partitioning ratios, and literature-based values of root inputs and dissolved organic carbon export. Peat CH4 fluxes (kg CH4 ha−1 year−1) were insignificant in oil palm (0.3 ± 0.4) while emissions in forest were high (14.0 ± 2.8), and larger in wet than in dry months. N2O emissions (kg N2O ha−1 year−1) were highly variable spatially and temporally and similar across land-uses (5.0 ± 3.9 and 5.2 ± 3.7 in oil palm and forest). Temporal variation of CH4 was controlled by water table level and soil water-filled pore space in forest and oil palm, respectively. Monthly fluctuations of N2O were linked to water table level in forest. The peat GHG budget (Mg CO2 equivalent ha−1 year−1) in oil palm (31.7 ± 8.6) was nearly eight times the budget in forest (4.0 ± 4.8) owing mainly to decreased peat C inputs and increased peat C outputs. The GHG budget was also ten times higher in the secondary forest (10.2 ± 4.5) than in the primary forests (0.9 ± 3.9) on the account of a larger peat C budget and N2O emission rate. In oil palm 96% of emissions were released as CO2 whereas in forest CH4 and N2O together contributed 65% to the budget. Our study highlights the disastrous atmospheric impact associated with forest degradation and conversion to oil palm in tropical peatlands and stresses the need to investigate GHG fluxes in disturbed undrained lands.

Contributions of methane and nitrous oxide to peat greenhouse gas emissions from forests and oil palm plantations in an Indonesian peatland

<p>Land-use change in tropical peatlands substantially impacts emissions of methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) in addition to emissions of carbon dioxide (CO<sub>2</sub>). However, assessments of peat GHG budgets are scarce and the contributions of CH<sub>4</sub> and N<sub>2</sub>O remain highly uncertain. The objective of our research was to assess changes in peat GHG flux and budget associated with peat swamp forest disturbance and conversion to oil palm plantation and to evaluate drivers of variation in trace gas fluxes. Over a period of one and a half year, we monitored monthly CH<sub>4</sub> and N<sub>2</sub>O fluxes together with environmental variables in three undrained peat swamp forests and three oil palm plantations on peat in Central Kalimantan. The forests included two primary forests and one 30-year-old secondary forest. We calculated the peat GHG budget in both ecosystems using soil respiration and litterfall rates measured concurrently with CH<sub>4</sub> and N<sub>2</sub>O fluxes, site-specific soil respiration partitioning ratios, and literature-based values of root inputs and dissolved organic carbon export. Peat CH<sub>4</sub> fluxes (kg CH<sub>4</sub> ha<sup>-1</sup> yr<sup>-1</sup>) were insignificant in oil palm (0.3 ± 0.4) while emissions in forest were high (14.0 ± 2.8), and larger in wet than in dry months. N<sub>2</sub>O emissions (kg N<sub>2</sub>O ha<sup>-1</sup> yr<sup>-1</sup>) were highly variable spatially and temporally and similar across land-uses (5.0 ± 3.9 and 5.2 ± 3.7 in oil palm and forest). Temporal variation of CH<sub>4</sub> was controlled by water table level and soil water-filled pore space in forest and oil palm, respectively. Monthly fluctuations of N<sub>2</sub>O were linked to water table level in forest. The peat GHG budget (Mg CO<sub>2</sub> equivalent ha<sup>-1</sup> yr<sup>-1</sup>) in oil palm (31.7 ± 8.6) was nearly eight times the budget in forest (4.0 ± 4.8) owing mainly to decreased peat C inputs and increased peat C outputs. The GHG budget was also ten times higher in the secondary forest (10.2 ± 4.5) than in the primary forests (0.9 ± 3.9) on the account of a larger peat C budget and N<sub>2</sub>O emission rate. In oil palm 96% of emissions were released as CO<sub>2</sub> whereas in forest CH<sub>4</sub> and N<sub>2</sub>O together contributed 65% to the budget. Our study highlights the disastrous atmospheric impact associated with forest degradation and conversion to oil palm in tropical peatlands and stresses the need to investigate GHG fluxes in disturbed undrained lands.</p>

Development of new drainage factor in ECOSSE model to improve water dynamics and prediction of CO2 fluxes from drained peatlands

<p>ABSTRACT</p><p>Drained peatlands often act as carbon source and their drainage characteristics can be challenging to accommodate in biogeochemical models. This study uses the ECOSSE process-based  biogeochemical model [to simulate water-table level and CO<sub>2</sub> fluxes (heterotrophic respiration) <sub>[1]</sub>], and empirical data from two Irish drained peatlands: Blackwater and Moyarwood, which were partly rewetted (both sites are extensively described in earlier studies <sub>[2]</sub>). Here we explain details on the development of a new drainage factor with seasonal variability Dfa(i) for drained peatlands, based on our recently published work <sub>[3] </sub> that we hope can contribute towards the potential future development of IPCC Tier 3 emissions reporting. The Dfa(i) was developed using empirical data from Blackwater drained bare-peat site (BWdr) and its application was further tested at the Moyarwood site under drained (MOdr) and rewetted conditions (MOrw) <sub>[3]</sub>. The development of the Dfa(i) was carried out in three main steps <sub>[3]</sub>: 1 - identification of the ‘wt-discrepancy event’; 2 - development of Dfa without seasonal variability, and 3 - accounting for seasonal variability and development of Dfa(i). Dfa(i) was then applied to the rainfall inputs for the periods of active drainage in conjunction with the measured water-table inputs <sub>[3]</sub>. As explained in our published work <sub>[3]</sub>, the results indicate that the application of Dfa(i) could improve the model performance to predict water-table level (BWdr: r<sup>2 </sup>= 0.89 MOdr: r<sup>2 </sup>=  0.94); and CO<sub>2</sub> fluxes [BWdr: r<sup>2</sup> = 0.66 and MOdr: r<sup>2 </sup>= 0.78) under drained conditions, along with ability of the model to capture seasonal trends <sub>[2]</sub>. The model simulation of CO<sub>2</sub> fluxes at MOrw site was also satisfactory (r<sup>2</sup>=0.75); however, the MOrw water-table simulation results suggest that additional work on the water model component under rewetted conditions is still needed <sub>[3]</sub>. We further discuss our insights into potential opportunities for future additional improvements and upgrading of the ECOSSE model water module.</p><p><strong> </strong></p><p><strong>Acknowledgements</strong></p><p>The authors are grateful to the Irish Environmental Protection Agency (EPA) for funding the AUGER: Project (2015-CCRP-MS.30) under EPA Research Programme 2014–2020. Full acknowledgements are provided in Premrov et. al (2020) <sub>[3]</sub>.</p><p> </p><p><strong>Literature</strong></p><p>[1] Smith, J., et al. 2010. ECOSSE. User Manual.</p><p>[2] Renou-Wilson, F., et. al. 2019. Rewetting degraded peatlands for climate and biodiversity benefits: Results from two raised bogs. Ecol. Eng. 127:547-560.</p><p>[3] Premrov, A., D. Wilson, M. Saunders, J. Yeluripati and F. Renou-Wilson (2020). CO<sub>2 </sub>fluxes from drained and rewetted peatlands using a new ECOSSE model water table simulation approach. Sci. Total Environ. (https://doi.org/10.1016/j.scitotenv.2020.142433; on-line 2020; in print Vol. 754, 2021; under CC BY 4.0).</p>

Temporary Confined Water-Induced Landslide in the Binary Structure of a Gentle Slope: A Case Study of the Fanshantou Landslide

With the increase in rainfall, landslides occur on many gentle slopes in the mountainous areas of southeast China. Gentle slopes have a particular dual geological structure, i.e., the lower part is a gravel soil layer with good water permeability, and the surface layer is clay soil with relatively poor water permeability. Under conditions of heavy rainfall, a gentle slope with this structure is likely to collect temporary confined water. The intermittent creep of the upper slope is caused by the floating force of the temporary confined water, which causes landslide disasters. The conditions that bring about temporary confined water are related not only to the stratum structure, but also to the rainfall intensity and the initial height of the water table level. On the basis of the characteristics of the stratum of the gentle slope landslide on the front of Fanshantou Mountain, we constructed a hydrological model in GEO-STUDIO. We investigated the effect of different rainfall intensities and initial water table levels on confined water under continuous rainfall conditions and conducted a corresponding stability analysis. The results show that when both the initial water table level and the rainfall intensity are high, temporary confined water is formed rapidly, increasing the chance of a landslide disaster. The research results provide a theoretical basis for the treatment of landslides on similar gentle slopes in the mountainous areas of southeast China.

Evolution of Salinity and Water Table Level of the Phreatic Coastal Aquifer of the Emilia Romagna Region (Italy)

The coastal aquifers of the Mediterranean region are highly susceptible to seawater intrusion due to a combination of challenges such as land subsidence, high aquifer permeability, urbanization, drainage, and an unsustainable use of water during the dry summer months. The present study is focused on a statistical analysis of groundwater data to evaluate the spatial changes of water level and electrical conductivity in the coastal phreatic aquifer of the Emilia-Romagna (Northeast Italy) for the period from 2009 to 2018. Data from 35 wells distributed across the entire regional coastal area are used to establish a temporal trend, as well as correlations between salinity, water table level, and rainfall. Water table and salinity distribution maps for the entire study area are discussed regarding surface geology and water management. Most of the wells are in the beach wedge sand unit, which allows for easy connectivity between groundwater and surface water. Surface water and groundwater salinization are enhanced along the surface water bodies connected to the sea. The lowest water table level occurs in the western and northern parts of the study area, because of the semiconfined behavior of the aquifer. Only in the northernmost, close to the Po River, and in the southernmost parts of the study area does the groundwater remain fresh for the whole period considered due to river aquifer recharge. In the rest of the region, the thickness of freshwater lenses, where present, is less than 4.5 m. The existence of a water table level below sea level and high saline water at the bottom of the aquifer in most of the study area suggest that the aquifer is in unstable hydrodynamic conditions and groundwater quality is not fit for human consumption or for irrigation. This study is the first to provide a regional overview of the state of groundwater level and salinization within the coastal aquifer of the Emilia-Romagna Region; it also suggests that, overall, the salinization trend has slightly decreased from 2009 to 2018.

Periodically inundated uvalas and collapse dolines of Upper Pivka, Slovenia

Within the area of Upper Pivka there is a number of intermittent lakes because of oscillation of water table level close to the surface i.e. shallow karst. Our survey was focused on morphogenetic interpretation of depressions hosting intermittent lakes by means of classic morphographic mapping and sediment analyses that was supported by electrical resistivity tomography. We can interpret at least two different morphogenetic types of depressions. One type are depressions which are periodically inundated uvalas positioned in-between conical hills. The second type are circular depressions within karst plain that are collapse dolines filled with extensive flood deposits up to several metres thick.