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Soil greenhouse gas fluxes from tropical coastal wetlands and alternative agricultural land uses
Journal article   Open access   Peer reviewed

Soil greenhouse gas fluxes from tropical coastal wetlands and alternative agricultural land uses

N. Iram, E. Kavehei, Damien T Maher, S E Bunn, M. Rezaei Rashti, B. S. Farahani and Maria Fernanda Adame
Biogeosciences, Vol.18(18), pp.5085-5096
01/09/2021
DOI: https://doi.org/10.5194/bg-18-5085-2021
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Soil greenhouse gas fluxes from tropical coastal wetlands and alternative agricultural land usesView
Published (Version of record)CC BY V4.0,  Open

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Abstract

Coastal wetlands are essential for regulating the global carbon budget through soil carbon sequestration and greenhouse gas (GHG – CO2 , CH4 , and N2O ) fluxes. The conversion of coastal wetlands to agricultural land alters these fluxes' magnitude and direction (uptake/release). However, the extent and drivers of change of GHG fluxes are still unknown for many tropical regions. We measured soil GHG fluxes from three natural coastal wetlands – mangroves, salt marsh, and freshwater tidal forests – and two alternative agricultural land uses – sugarcane farming and pastures for cattle grazing (ponded and dry conditions). We assessed variations throughout different climatic conditions (dry–cool, dry–hot, and wet–hot) within 2 years of measurements (2018–2020) in tropical Australia. The wet pasture had by far the highest CH4 emissions with 1231±386   mg m - 2 d - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="56pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="9a351d59159677021c73cdc4349d131e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-5085-2021-ie00001.svg" width="56pt" height="15pt" src="bg-18-5085-2021-ie00001.png"/></svg:svg> , which were 200-fold higher than any other site. Dry pastures and sugarcane were the highest emitters of N2O with 55±9   mg m - 2 d - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="56pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="9e5722e5bcab6aa6a1a092c5b6ff7b79"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-5085-2021-ie00002.svg" width="56pt" height="15pt" src="bg-18-5085-2021-ie00002.png"/></svg:svg> (wet–hot period) and 11±3  m g m - 2 d - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="47pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="5c097377f94715c27c133a5814e4070b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-5085-2021-ie00003.svg" width="47pt" height="15pt" src="bg-18-5085-2021-ie00003.png"/></svg:svg> (hot-dry period, coinciding with fertilisation), respectively. Dry pastures were also the highest emitters of CO2 with 20±1   g m - 2 d - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="47pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="c0aab21059d0ee7939623231dab627b6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-5085-2021-ie00004.svg" width="47pt" height="15pt" src="bg-18-5085-2021-ie00004.png"/></svg:svg> (wet–hot period). The three coastal wetlands measured had lower emissions, with salt marsh uptake of - 0.55 ± 0.23 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="6441b7abd15f03ffdd21a117acd67400"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-5085-2021-ie00005.svg" width="64pt" height="10pt" src="bg-18-5085-2021-ie00005.png"/></svg:svg> and - 1.19 ± 0.08 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="e1975a3ba25cfd0f9036d25f0ca90dc4"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-5085-2021-ie00006.svg" width="64pt" height="10pt" src="bg-18-5085-2021-ie00006.png"/></svg:svg>   g m - 2 d - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="47pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="8521700b0b05a966a960bc5a0514c3d0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-5085-2021-ie00007.svg" width="47pt" height="15pt" src="bg-18-5085-2021-ie00007.png"/></svg:svg> of N2O and CO2 , respectively, during the dry–hot period. During the sampled period, sugarcane and pastures had higher total cumulative soil GHG emissions ( CH4+N2O ) of 7142 and 56 124  CO 2-eq kg ha - 1 yr - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="92pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="3404ea53ae88124f3c211523f4fcccc3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-5085-2021-ie00008.svg" width="92pt" height="17pt" src="bg-18-5085-2021-ie00008.png"/></svg:svg> compared to coastal wetlands with 144 to 884  CO 2-eq kg ha - 1 yr - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="92pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="716ab3705b9260c90ed57e50f15f05b0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-5085-2021-ie00009.svg" width="92pt" height="17pt" src="bg-18-5085-2021-ie00009.png"/></svg:svg> (where CO2-eq is CO2 equivalent). Restoring unproductive sugarcane land or pastures (especially ponded ones) to coastal wetlands could provide significant GHG mitigation.

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