Abstract. Degradation of tropical peats is a global concern due to large Carbon emission and loss of biodiversity. The degradation of tropical peats usually starts when the government drains and clears peat forests into open peats used for food crops, oil palm and industrial timber plantations. Major properties of tropical peat forests are high in Water Contents (WC), Loss on Ignition (LOI) and Total Organic Carbon (TOC), and low in peat pH, Dry Bulk Density (DBD), and Total Nitrogen (TN). In this study, we investigated impacts of drainage and land use change on these properties. We collected peat samples from peat forests, logged over peat forest, industrial timber plantation, community agriculture, and oil palms. We used independent t-tests and oneway ANOVA to analyze mean differences of the research variables. We found that peat pH, DBD, and TN tend to increase. A significant decrease of C/N ratio in oil palm and agriculture sites importantly denotes a high rate of peat decompositions. Water contents, LOI, and TOC are relatively constants. We suggest that changes in pH, DBD, TN and atomic C/N ratio are important indicators for assessing tropical peat degradation. We infer that land use change from tropical peat forests intoCorrespondence to: G. Z. Anshari (gzanshari@live.untan.ac.id) cleared and drained peats used for intensive timber harvesting, oil palms and industrial timber plantations in Indonesia has greatly degraded major ecological function of tropical peats as Carbon storage.

Abstract. Estimation of belowground carbon stocks in tropical wetland forests requires funding for laboratory analyses and suitable facilities, which are often lacking in developing nations where most tropical wetlands are found. It is therefore beneficial to develop simple analytical tools to assist belowground carbon estimation where financial and technical limitations are common. Here we use published and original data to describe soil carbon density (kgC m −3 ; C d ) as a function of bulk density (gC cm −3 ; B d ), which can be used to rapidly estimate belowground carbon storage using B d measurements only. Predicted carbon densities and stocks are compared with those obtained from direct carbon analysis for ten peat swamp forest stands in three national parks of Indonesia. Analysis of soil carbon density and bulk density from the literature indicated a strong linear relationship (C d = B d ×495.14+5.41, R 2 = 0.93, n = 151) for soils with organic C content > 40 %. As organic C content decreases, the relationship between C d and B d becomes less predictable as soil texture becomes an important determinant of C d . The equation predicted belowground C stocks to within 0.92 % to 9.57 % of observed values. Average bulk density of collected peat samples was 0.127 g cm −3 , which is in the upper range of previous reports for Southeast Asian peatlands. When original data were included, the revised equation C d = B d × 468.76 + 5.82, with R 2 = 0.95 and n = 712, was slightly below the lower 95 % confidence interval of the original equation, and tended to decrease C d estimates. We recommend this last equation for a rapid estimation of soil C stocks for well-developed peat soils where C content > 40 %.

Estimation of soil carbon stocks in tropical wetlands requires costly laboratory analyses and suitable facilities, which are often lacking in developing nations where most tropical wetlands are found. It is therefore beneficial to develop simple yet robust analytical tools to assess soil carbon stocks where financial and technical limitations are common. Here we use published and original data to describe soil carbon density (gC cm⁻³; C_d) as a function of bulk density (g dry soil cm⁻³; B_d), which can be used to estimate belowground carbon storage using Bd measurements only. Predicted carbon densities and stocks are compared with those obtained from direct carbon analysis for ten peat swamp forest stands in three national parks of Indonesia. Analysis of soil carbon density and bulk density from the literature indicated a strong linear relationship (C_d = B_d × 0.49 + 4.61, <i>R</i>² = 0.96, <i>n</i> = 94) for soils with an organic C content >40%. As organic C content decreases, the relationship between C_d and B_d becomes less predictable as soil texture becomes an important determinant of C_d. The equation predicted soil C stocks to within 0.39% to 7.20% of observed values. When original data were included in the analysis, the revised equation: C_d = B_d × 0.48 + 4.28, <i>R</i>² = 0.96, <i>n</i> = 678 was well within the 95% confidence intervals of the original equation, and tended to decrease C_d estimates slightly. We recommend this last equation for a rapid estimation of soil C stocks for well developed peat soils where C content >40%

Climate change has been a prominent issue in the last decade. Climate change on a global scale does not necessarily have the same effect in different regions. Rainfall is a crucial weather element related to climate change. Rainfall trends analysis is an appropriate step in assessing the impact of climate change on water availability and food security. This study examines rainfall variations and changes at West Kalimantan, focusing on Mempawah and Kubu Raya from 2000-2019. The Mann-Kendall (MK) and Sen's Slope estimator test, which can determine rainfall variability and long-term monotonic trends, were utilized to analyze 12 rainfall stations. The findings revealed that the annual rainfall pattern prevailed in all locations. Mempawah region tends to experience a downward trend, while Kubu Raya had an upward trend. However, a significant trend (at 95% confidence level) was identified in Sungai Kunyit with a slope value of -33.20 mm/year. This trend indicates that Sungai Kunyit will become drier in the future. The results of monthly rainfall analysis showed that significant upward and downward trends were detected in eight locations. Rainfall trends indicate that climate change has occurred in this region.

Astiani D, Burhanuddin, Gusmayanti E, Widiastuti T, Taherzadeh MJ. 2018. Enhancing water levels of degraded, bare, tropical peatland in West Kalimantan, Indonesia: Impacts on CO2 emission from soil respiration. Biodiversitas 19: 472-477. The major drivers of deforestation in West Kalimantan have been the development for large or small-scale expansion of agricultural activities; the establishment of oil palm and other plantations; fire; and degradation of forests particularly from industrial logging. Our previous research findings have shown that such activities in affected peatland areas have lowered the water table levels (down to 0.5-1.0 m depths), and have significantly increased CO2 emissions from the peat soils. It has been demonstrated that unmanaged, lowered water tables in peatlands act as one of the main factors inflating soil carbon emissions - an issue that has assumed global significance in recent decades. Regulating peatland water tables has the potential to mitigate degraded peatland carbon emissions as well as improve the hydrological functions for communities who farm the peatlands. However, we are still uncertain exactly how much impact controlled raising of the peatlands water tables will have on reducing soil CO2 emissions. The research described here aimed to mitigate CO2 emissions by raising and regulating water levels on drained peatland to restore and enhance its hydrological functions. The results confirmed that raising the water table significantly decreases CO2 emissions and improves water availability and management for crop production in the coastal peatland of Kubu Raya district, West Kalimantan. Water levels previously at 60cm below the soil surface were regulated to raise the watertable up to just 30 cm below the surface and this reduced peatland carbon emissions by about 49%. However, longer-term monitoring is required to ensure that the hydrological benefits and CO2 mitigation can be sustained.

Indonesian peatland forest is considered a huge sink of tropical carbon and thereby make significant contribution to global terrestrial carbon storage. However, landcover and landuse changes in this ecosystem have incurred a synergistic exposure to drought and wildfires. Deforestation and forest degradation through combustion and decomposition of forest biomass and soil carbon have become global issues because of their greenhouse gas contribution to global climate change. Thus fire-driven carbon losses in these peatlands have increased the need to evaluate the impacts of fire at a landscape scale. In 6-10 week dry periods from January to April 2014 and in January 2015, wildfires burnt peatland forest in Kubu Raya, West Kalimantan province (Indonesian Borneo). An assessment was conducted to provide more reliable estimates of the effects of fire on aboveground and soil carbon losses and their dynamics in the coastal peatlands of the province. Carbon loss from combustion of both aboveground biomass and peat soil was substantial. Moreover, CO 2 emission from soil respiration at the burnt peat surface increased 46% over the first 9 months after the fire. This study clearly showed the magnitude of fire-driven carbon loss and the scale of CO 2 emission to the atmosphere arising from fire in tropical peatland forest.

Drainage is a major means of the conversion of tropical peat forests into agriculture. Accordingly, drained peat becomes a large source of carbon. However, the amount of carbon (C) loss from drained peats is not simply measured. The current C loss estimate is usually based on a single proxy of the groundwater table, spatially and temporarily dynamic. The relation between groundwater table and C emission is commonly not linear because of the complex natures of heterotrophic carbon emission. Peatland drainage or lowering groundwater table provides plenty of oxygen into the upper layer of peat above the water table, where microbial activity becomes active. Consequently, lowering the water table escalates subsidence that causes physical changes of organic matter (OM) and carbon emission due to microbial oxidation. This paper reviews peat bulk density (BD), total organic carbon (TOC) content, and subsidence rate of tropical peat forest and drained peat. Data of BD, TOC, and subsidence were derived from published and unpublished sources. We found that BD is generally higher in the top surface layer in drained peat than in the undrained peat. TOC values in both drained and undrained are lower in the top and higher in the bottom layer. To estimate carbon emission from the top layer (0–50 cm) in drained peats, we use BD value 0.12 to 0.15 g cm−3, TOC value of 50%, and a 60% conservatively oxidative correction factor. The average peat subsidence is 3.9 cm yr−1. The range of subsidence rate per year is between 2 and 6 cm, which results in estimated emission between 30 and 90 t CO2e ha−1 yr−1. This estimate is comparable to those of other studies and Tier 1 emission factor of the 2013 IPCC GHG Inventory on Wetlands. We argue that subsidence is a practical approach to estimate carbon emission from drained tropical peat is more applicable than the use of groundwater table.

Variabilitas curah hujan sangat erat kaitannya dengan perubahan iklim di suatu wilayah dan analisisnya sangat berguna dalam mengukur ketersediaan air untuk pertanian khususnya padi sawah. Penelitian ini bertujuan menganalisis variabilitas curah hujan dan hubungan curah hujan tahunan terhadap produktivitas padi di Kalimantan Barat.  Lokasi penelitian difokuskan di wilayah Kabupaten Mempawah dan Kubu Raya dengan menggunakan data yang tersedia pada tahun 2000-2019. Analisis datanya menggunakan persamaan variabilitas dan dilanjutkan dengan analisis korelasi dan komposit. Hasil analisis menunjukkan bahwa variabilitas curah hujan tahunan di Mempawah dan Kubu Raya termasuk dalam kategori rendah. Nilai variabilitas bulanan menunjukkan rentang yang bervariasi dari rendah hingga ekstrem di setiap lokasi. El Nino memiliki dampak negatif yang kuat terhadap curah hujan pada periode Juni-Juli-Agustus (JJA) dan September-Oktober-November (SON), sedangkanLa Nina memiliki dampak positif yang kuat terhadap curah hujan pada periode Juni-Juli-Agustus. Pada periode Desember-Januari-Februari (DJF) dan Maret-April-Mei (MAM), El Nino (La Nina) memiliki efek terhadap peningkatan (pengurangan) curah hujan. Dipole Mode Positif memberikan dampak pengurangan curah hujan pada periode SON dan MAM. Dipole Mode Negatif memberikan dampak bervariasi pada curah hujan pada periode JJA, SON dan DJF. Hubungan signifikan antara curah hujan tahunan dan produktivitas padi hanya ditunjukkan di Sungai Kunyit dan Sungai Kakap. Hal ini mengindikasikan bahwa curah hujan tahunan secara umum tidak berpengaruh signifikan terhadap produktivitas padi di sebagian besar wilayah penelitian. ABSTRACTRainfall variability is closely related to climate change in a particular region and it is useful in estimating the water availability for agriculture, especially lowland rice. This study examines the rainfall variability and correlation between annual rainfall and rice productivity in West Kalimantan. The research location is focused on the Mempawah and Kubu Raya districts in 2000-2019. The variability equation accompanied by correlation and composite analysis was used in the analysis. The result shows that the variability of annual rainfall in Mempawah and Kubu Raya falls in the low category. Monthly rainfall variability values mark a range that varies from low to extreme at each location. El Nino had a substantial negative impact on rainfall in the June-July-August (JJA) and September-October-November SON period. While, La Nina had a positive impact on rainfall only in the JJA period. In the December-January-February (DJF) and March-April-May (MAM) period, El Nino (La Nina) has an anomalous effect on increasing (reducing) rainfall. Positive Dipole Mode gives the negative impact in the SON dan MAM period. Negative Dipole Mode has a varied impact on rainfall in the JJA, SON and DJF periods. The significant corellation between annual rainfall and rice productivity was shown only at Sungai Kunyit and Sungai Kakap. This indicates that the annual rainfall generally has no significant effect on rice productivity in most areas.