Climate change mitigation and improvement of water quality from the restoration of a subtropical coastal wetland [Dataset]

Coastal wetland restoration is an important activity to achieve greenhouse gas (GHG) reduction targets, improve water quality, and reach the Sustainable Development Goals. However, there are still many uncertainties on achieving, measuring, and reporting success from coastal wetland restoration. We measured levels of carbon (C) abatement and nitrogen (N) removal potential of restored coastal wetlands in subtropical Queensland. The site was originally a supratidal forest comprised of Melaleuca spp. that was cleared and drained in the 1990s for sugarcane production. In 2010, tidal inundation was reinstated, and a mosaic of coastal vegetation (saltmarsh, mangroves, and supratidal forests) emerged. We measured soil GHG fluxes (CH4, N2O, CO2) and sequestration of organic C in the trees and soil to estimate the net C abatement associated with the reference, converted, and restored sites. To assess the influence of restoration on water quality improvement, we measured denitrification and soil N accumulation. We calculated C abatement of 18.5 Mg CO2-eq ha-1 y-1 when sugarcane land transitioned to supratidal forests, 11.0 Mg CO2-eq ha-1 y-1 when transitioned to mangroves and 6.2 Mg CO2-eq ha-1 y-1 when transitioned to saltmarsh. The C abatement was due to tree growth, soil accumulation, and reduced N2O emissions due to the cessation of fertilisation. Carbon abatement was still positive, even accounting for CH4 emissions, which increased in the wetlands due to flooding and N2O production due to enhanced levels of denitrification. Coastal wetland restoration in this subtropical setting effectively reduces CO2 emissions while providing additional co-benefits, notably water quality improvement.

滨海湿地修复是实现温室气体（GHG）减排目标、改善水质并达成可持续发展目标（Sustainable Development Goals）的重要举措。然而，滨海湿地修复的成效达成、效果测定与成果报告仍存在诸多不确定性。我们针对亚热带昆士兰州的已修复滨海湿地，测定了其碳减排量与氮移除潜力水平。该研究样地最初为潮上带森林（supratidal forest），由千层桃属（Melaleuca spp.）植物构成，于20世纪90年代被清伐并排水以种植甘蔗。2010年，该区域恢复潮汐淹没，进而形成了由盐沼（saltmarsh）、红树林（mangroves）与潮上带森林构成的滨海植被镶嵌群落。我们测定了土壤温室气体通量（CH4、N2O、CO2）以及树木与土壤中的有机碳固存量，以此估算参照样地、转化样地与修复样地对应的净碳减排量。为评估修复对水质改善的影响，我们测定了反硝化作用（denitrification）与土壤氮累积量。我们测算得出：当甘蔗种植地转变为潮上带森林时，碳减排量为18.5 Mg CO₂-eq·ha⁻¹·y⁻¹；转变为红树林时为11.0 Mg CO₂-eq·ha⁻¹·y⁻¹；转变为盐沼时为6.2 Mg CO₂-eq·ha⁻¹·y⁻¹。上述碳减排主要源于树木生长、土壤碳累积，以及因停止施肥而减少的N2O排放。即便计入因湿地淹水导致的CH4排放升高，以及反硝化作用增强催生的N2O生成，碳减排量仍为正值。此亚热带区域的滨海湿地修复可有效降低CO2排放，同时带来额外的协同效益，尤以水质改善最为显著。