Compositions of sequestrated soil carbon in constructed wetlands of Taiwan

Methanogens dominate methanotrophs and act as a methane source in aquaculture pond sediments

Aquaculture pond sediments act as hotspots for methane (CH4) emissions; however, knowledge gaps on the regulation of microorganisms hinder our further understanding of methane dynamics in aquaculture pond sediment. Using field sampling and molecular analysis, we examined CH4 fluxes, the methanogenic community composition, and their interaction with methanotrophs to comprehensively understand the methane cycling in sediments of aquaculture ponds in northern China. Compared with a fishing pond without feed inputs, the abundances of methanogens mcrA and methanotrophs pmoA genes increased significantly in aquaculture ponds sediments. The dominant methanogens were Methanothrix, Methanoregula, and Methanolinea, and the α-diversity indices of methanogens demonstrated higher levels in 0-5 cm surface sediment. The methanotrophs were dominated by Methylocystis, Methylocaldum, and Methylobacter, and the α-diversity indices of methanotrophs showed no significant difference. The total organic carbon (TOC) contents and oxidation reduction potential (ORP) were the key factors driving methanogenic and methanotrophic communities on methane cycle in aquaculture sediment. The inter-domain ecological network (IDEN) analysis revealed that total number of network nodes, links, connectances, and links per species in the aquaculture sediments presented relatively higher levels, whereas the IDEN modules were fewer. The methanogens dominated in the networks and the interaction of methanogens and methanotrophs was more competitive and complex in aquaculture sediments. These findings highlight the marked methane production in aquaculture sediment, primarily due to the abundance, diversity, and competitive advantage of methanogens over methanotrophic communities.

Variation in chemical property of asphalt immersed in varying aqueous solutions and its leachate property

The pavement asphalt properties are susceptible to deterioration under environmental factors, and the deterioration product will affect its surrounding aqueous environment. For this reason, the idealized asphalt-aggregate mixture was treated with coupled temperature, ultraviolet and aqueous solutions based on self-made multifactorial coupled simulation device. Subsequently, the deterioration of asphalt chemical properties was analyzed by fourier transform infrared spectroscopy and saturate-aromatic-resin-asphaltene tests. Meanwhile, the effect of environmental factors on leachate properties was explored based on organic matter contents and chemical elements. Based on that, the grey correlation method was adopted to correlate asphalt chemical properties and leachate properties. The results clearly showed that environmental factors increased the sulfoxide and carbonyl group content of asphalt and transformed the chemical components within it into polar substances. The asphalt chemical properties were gradually improved when coupling ultraviolet with sodium carbonate, sodium chloride and distilled water sequentially. Compared to neutral solution, alkaline solution exacerbated the effect of asphalt precipitates on leachate properties. The environmental factors increased the organic matter contents and chemical elements of leachate with time. The interaction mechanism between asphalt and aqueous environment involved the deterioration of asphalt properties caused by the presence of water, as well as the release of precipitates from aged asphalt into surrounding aqueous environment.

Assessing CO2 sources and sinks in and around Taiwan: Implication for achieving regional carbon neutrality by 2050

Taiwan has pledged to achieve net-zero carbon emissions by 2050, but the current extent of carbon sinks in Taiwan remains unclear. Therefore, this study aims to first review the existing nature-based carbon sinks on land and in the oceans around Taiwan. Subsequently, we suggest potential strategies to reduce CO2 emissions and propose carbon dioxide removal methods (CDRs). The natural carbon sinks by forests, sediments, and oceans in and around Taiwan are approximately 21.5, 42.1, and 96.8 Mt-CO2 y-1, respectively, which is significantly less than Taiwan's CO2 emissions (280 Mt-CO2 y-1). Taiwan must consider decarbonization strategies like using electric vehicles, renewable energy, and hydrogen energy by formulating enabling policies. Besides more precisely assessing both terrestrial and marine carbon sinks, Taiwan should develop novel CDRs such as bioenergy with carbon capture and storage, afforestation, reforestation, biochar, seaweed cultivation, and ocean alkalinity enhancement, to reach carbon neutrality by 2050.

Greenhouse gases emissions and carbon budget estimation in horizontal subsurface flow constructed wetlands with different plant species

Constructed wetlands (CWs) are pivotal for wastewater treatment due to their high efficiency and numerous advantages. The impact of plant species and diversity on greenhouse gas (GHG) emissions from CWs requires a more comprehensive evaluation. Moreover, controversial perspectives persist about whether CWs function as carbon sinks or sources. In this study, horizontal subsurface flow (HSSF) CWs vegetated with Cyperus alternifolius, Typhae latifolia, Acorus calamus, and the mixture of these three species were constructed to evaluate pollutant removal efficiencies and GHG emissions, and estimate carbon budgets. Polyculture CWs can stably remove COD (86.79 %), NH4+-N (97.41 %), NO3--N (98.55 %), and TP (98.48 %). They also mitigated global warming potential (GWP) by suppressing N2O emissions compared with monoculture CWs. The highest abundance of the Pseudogulbenkiania genus, crucial for denitrification, was observed in polyculture CWs, indicating that denitrification dominated in nitrogen removal. While the highest nosZ copy numbers were observed in CWs vegetated with Cyperus alternifolius, suggesting its facilitation of denitrification-related microbes. Selecting Cyperus alternifolius to increase species diversity is proposed for simultaneously maintaining the water purification capacity and reducing GHG emissions. Carbon budget estimations revealed that all four types of HSSF CWs were carbon sinks after six months of operation, with carbon accumulation capacity of 4.90 ± 1.50 (Cyperus alternifolius), 3.31 ± 2.01 (Typhae latifola), 1.78 ± 1.30 (Acorus calamus), and 2.12 ± 0.88 (polyculture) kg C/m2/yr. This study implies that under these operation conditions, CWs function as carbon sinks rather than sources, aligning with carbon peak and neutrality objectives and presenting significant potential for carbon reduction efforts.

Quantifying carbon pool in ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia

Ex-mining lake-converted constructed wetlands play a significant role in the carbon cycle, offering a great potential to sequester carbon and mitigate climate change and global warming. Investigating the quantity of carbon storage capacity of ex-mining lake-converted constructed wetlands provides information and justification for restoration and conservation efforts. The present study aims to quantify the carbon pool of the ex-mining lake-converted constructed wetlands and characterise the physicochemical properties of the soil and sediment. Pearson's correlation and a one-way ANOVA were performed to compare the different sampling stations at Paya Indah Wetland, Selangor, Malaysia. An analysis of 23 years of ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia, revealed that the estimated total carbon pool in soil and sediment accumulated to 1553.11 Mg C ha-1 (equivalent to 5700 Mg CO2 ha-1), which translates to an annual carbon sink capacity of around 67.5 Mg C ha-1 year-1. The characterisation showed that the texture of all soil samples was dominated by silt, whereas sediments exhibited texture heterogeneity. Although the pH of the soil and sediment was both acidic, the bulk density was still optimal for plant growth and did not affect root growth. FT-IR and WDXRF results supported that besides the accumulation and degradation of organic substances, which increase the soil and sediment carbon content, mineral carbonation is a mechanism by which soil and sediment can store carbon. Therefore, this study indicates that the ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia have a significant carbon storage potential.

Microbial community development in tropical constructed wetland soils in Taiwan

Constructed wetlands are widely used around the world as a low-cost wastewater treatment system that simultaneously provides various ecosystem services. Microorganisms in wetland soils serve as fundamental producers and decomposers that support wetland functions. However, few studies have documented the compositions of soil microorganisms in constructed wetland systems and even fewer have evaluated how soil microorganisms change after a wetland is constructed. In this study, soil samples were collected from four constructed wetlands of different ages and analyzed with a phospholipid fatty acid (PLFA) method to show how soil microbial communities change overtime. The results were that both the bacterial and fungal abundances increased with wetland age, and bacteria comprised about 90% of the soil microbial communities in all ages of constructed wetlands. Although the compositions of microbial communities remained similar among the wetlands, the stress indices showed that microbial stress may be affected by changes in the availability of in situ nutrients, e.g. ammonium, nitrate_, soluble organic nitrogen and total dissolved nitrogen.