Carbon Dynamics of Rewetted Peatlands Under Different Land Covers in Bengkalis Regency, Riau

Abstract

The deforestation and degradation of tropical peatland swamp forests (PSFs) followed by land conversion and drainage generate greenhouse gas (GHG) emissions. This changes PSFs from carbon sinks to carbon sources, thus contributing to climate change. The rewetting of degraded peatlands is expected to control soil respiration, encourage regrowth, and transform these landscapes back into carbon sinks. In this study, experimental plots were established to measure the effect of peatland rewetting on three different land cover types (a reforested area, an oil palm plantation and a rubber plantation) following the clearing of PSF land in Bengkalis Regency, Riau. Carbon dynamics were assessed by measuring total ecosystem carbon stocks (TECS) and GHG emissions in these experimental plots before and after the rewetting of the landscape.

Common tree species in the reforested area (including Ficus sp., Dyera polyphylla, Mezzetia parviflora, Callopyhllum teysmannii, Cratoxylon arborescens, Macaranga sp., Hevea brasiliensis, and Shorea uliginosa) have basal areas of 0.24 ± 0.02 m2 ha-1. Rubber trees in plantations have a basal area of 0.14 ± 0.02 m2 ha-1. The TECS were highest in the reforested area (3,983.08 ± 318.14 Mg C ha-1), followed by the oil palm area (3,523.90 ± 253.9 Mg C ha-1), and finally by the rubber plantation area (3,363.08 ± 207.8 Mg C ha-1).

In the reforested area and the oil palm area, the proportion of heterotrophic soil respiration (SRh; 48.91 ± 4.75 and 54.98 ± 1.53 Mg CO2 ha-1 yr-1) to total soil respiration (SRt; 49.68 ± 6.84 and 55.71 ± 5.54 Mg CO2 ha-1 yr-1) was roughly 98% before rewetting. On the other hand, SRh (67.67 ± 2.13 Mg CO2 ha-1 yr-1) was slightly higher than SRt (61.36 ± 7.28 Mg CO2 ha-1 yr-1) in the rubber plantation area. Overall, this shows that peatland rewetting can reduce the CO2 flux in these three land cover types.

Mean CH4 flux consistently increased after rewetting in the reforested area (-0.70 ± 0.28 to 0.84 ± 0.28 Mg CH4 ha-1 yr-1), oil palm area (0.37 ± 0.16 to 0.90 ± 0.61 Mg CH4 ha-1 yr-1), and the rubber plantation area (-0.57 ± 0.05 to 1.05 ± 0.37 Mg CH4 ha-1 yr-1). N2O flux in the reforested, oil palm, and rubber plantation areas was 0.12 ± 0.03, 0.15 ± 0.08, and 0.37 ± 0.12 Mg N2O ha-1 yr-1, respectively, and decreased to –0.06 ± 0.02, -0.10 ± 0.05, and 0.19 ± 0.07 Mg N2O ha-1 yr-1, respectively, after rewetting.

Deforestasi dan degradasi hutan rawa gambut tropis (PSF) yang diikuti dengan konversi penggunaan lahan dan drainase menghasilkan emisi gas rumah kaca (GRK). PSF sebagai reservoar kaya karbon berubah dari penyerapan menjadi emisi karbon ekosistem yang berkontribusi terhadap perubahan iklim. Pembasahan kembali lahan gambut yang terdegradasi sebagai bagian dari restorasi diharapkan dapat mengendalikan respirasi tanah, mempercepat pertumbuhan vegetasi, dan melindungi bentang alam agar tetap menyimpan karbon. Kami membuat plot percobaan untuk mengukur pengaruh pembasahan gambut di tiga tutupan lahan yang berbeda (kawasan revegetasi, perkebunan kelapa sawit dan karet) setelah konversi di Kabupaten Bengkalis, Riau. Kami menilai dinamika karbon dengan mengukur total stok karbon ekosistem (TECS) dan emisi GRK di tutupan lahan tersebut sebelum dan sesudah dibasahi-ulang.

Spesies umum di kawasan revegetasi adalah Ficus sp., Dyera polyphylla, Mezzetia parviflora, Callopyhllum teysmannii, Cratoxylon arborescens, Macaranga sp., Hevea brasiliensis, dan Shorea uliginosa memiliki luas dasar area 0,24 ± 0,02 m2 ha-1 dan perkebunan karet 0,14 ± 0,02 m2 ha-1. Total stok C ekosistem lebih tinggi di kawasan revegetasi (3.983,08 ± 318,14 Mg C ha-1), diikuti oleh kelapa sawit (3.523,90 ± 253,9 Mg C ha-1), dan perkebunan karet (3.363,08 ± 207,8 Mg C ha-1). Pada areal revegetasi dan kelapa sawit, proporsi respirasi heterotrofik tanah (SRh; 48,91 ± 4,75 dan 54,98 ± 1,53 Mg CO2 ha-1 tahun-1) terhadap respirasi total tanah (SRt; 49,68 ± 6,84 dan 55,71 ± 5,54 Mg CO2 ha-1 tahun-1) kira-kira 98% sebelum pembasahan ulang. Sebaliknya SRh (67,67 ± 2,13 Mg CO2 ha-1 tahun-1) sedikit lebih tinggi dibandingkan SRt (61,36 ± 7,28 Mg CO2 ha-1 tahun-1) di perkebunan karet. Secara keseluruhan, pembasahan gambut dapat mengurangi fluks CO2 di tiga tutupan lahan melalui pengukuran SRt dan SRh.

Rata-rata fluks CH4 meningkat secara konsisten setelah pembasahan di kawasan revegetasi (-0,70 ± 0,28 hingga 0,84 ± 0,28 Mg CH4 ha-1 tahun-1); kelapa sawit (0,37 ± 0,16 hingga 0,90 ± 0,61 Mg CH4 ha-1 tahun-1), dan perkebunan karet (-0,57 ± 0,05 hingga 1,05 ± 0,37 Mg CH4 ha-1 tahun-1). Sementara fluks N2O di kawasan revegetasi, kelapa sawit, dan perkebunan karet (0,12 ± 0,03; 0,15 ± 0,08; 0,37 ± 0,12 Mg N2O ha-1 tahun-1, berturut-turut) menurun menjadi –0,06 ± 0,02; -0,10 ± 0,05; 0,19 ± 0,07 Mg N2O ha-1 tahun-1, berturut-turut) setelah pembasahan.