Selection of areas for restoration should be based on cost‐effectiveness analysis to attain the maximum benefit with a limited budget and overcome the traditional ad hoc allocation of funds for ...restoration projects. Restoration projects need to be planned on the basis of ecological knowledge and economic and social constraints. We devised a novel approach for selecting cost‐effective areas for restoration on the basis of biodiversity and potential provision of 3 ecosystem services: carbon storage, water depuration, and coastal protection. We used Marxan, a spatial prioritization tool, to balance the provision of ecosystem services against the cost of restoration. We tested this approach in a mangrove ecosystem in the Caribbean. Our approach efficiently selected restoration areas that at low cost were compatible with biodiversity targets and that maximized the provision of one or more ecosystem services. Choosing areas for restoration of mangroves on the basis carbon storage potential, largely guaranteed the restoration of biodiversity and other ecosystem services.
Riverine wetlands are created and transformed by geomorphological processes that determine their vegetation composition, primary production and soil accretion, all of which are likely to influence C ...stocks. Here, we compared ecosystem C stocks (trees, soil and downed wood) and soil N stocks of different types of riverine wetlands (marsh, peat swamp forest and mangroves) whose distribution spans from an environment dominated by river forces to an estuarine environment dominated by coastal processes. We also estimated soil C sequestration rates of mangroves on the basis of soil C accumulation. We predicted that C stocks in mangroves and peat swamps would be larger than marshes, and that C, N stocks and C sequestration rates would be larger in the upper compared to the lower estuary. Mean C stocks in mangroves and peat swamps (784.5 ± 73.5 and 722.2 ± 63.6 MgC ha−1, respectively) were higher than those of marshes (336.5 ± 38.3 MgC ha−1). Soil C and N stocks of mangroves were highest in the upper estuary and decreased towards the lower estuary. C stock variability within mangroves was much lower in the upper estuary (range 744–912 MgC ha−1) compared to the intermediate and lower estuary (range 537–1115 MgC ha−1) probably as a result of a highly dynamic coastline. Soil C sequestration values were 1.3 ± 0.2 MgC ha−1 yr−1 and were similar across sites. Estimations of C stocks within large areas need to include spatial variability related to vegetation composition and geomorphological setting to accurately reflect variability within riverine wetlands.
Agriculture is a major contributor to marine nitrogen pollution, and treatment wetlands can be a strategy to reduce it. However, few studies have assessed the potential of treatment wetlands to ...mitigate nitrogen pollution in tropical regions. We quantify the nitrogen removal rates of four recently constructed treatment wetlands in tropical Australia. We measured denitrification potential (Dt), the inflow-outflow of nutrients, and tested whether the environment in these tropical catchments is favourable for nitrogen removal. Dt was detected in three of the four systems with rates between 2.0 and 12.0 mg m-2 h−1; the highest rates were measured in anoxic soils (ORP −100 to 300 mV) that were rich in carbon and nitrogen (>2% and >0.2%, respectively). The highest nitrogen removal rates were measured when NO3−-N concentrations were >0.4 mg L−1 and when water flows were slow. Treatment wetlands in tropical regions can deliver high removal rates of nitrogen and other pollutants when adequately managed. This strategy can reduce nutrient loads and their impacts on sensitive coastal zones such as the Great Barrier Reef.
Linear accumulation of C in bioretention soil with age (x axis) and within the soil profile (y axis).
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•Bioretention basins store carbon over the whole ponding area.•Top 5 cm of ...bioretention’s soil accounts for 32% of soil carbon stocks.•Age is the most influencing factor on soil carbon accumulation.•Low carbon density of the soil below 20 cm in depth and not influenced by age.•Bioretention basins can sequester carbon at a rate of 0.31 kg C m−2 yr−1.
Bioretention basins are a prominent type of vegetated stormwater infrastructure that provides various ecosystem services, such as carbon (C) sequestration. Despite the key role of organic matter in the performance of bioretention basins, there is little understanding of their C accumulation properties. Using detailed field studies, we investigated the spatial, temporal and vertical variation of C capture in the soil of 25 subtropical bioretention basins in Australia. A thirteen-year soil chronosequence was used to estimate C sequestration rate. It was observed that the bioretention basins displayed a spatially uniform depositional pattern of C in their ponding area. The mean areal C density of soil in the upper 20 cm was 3.8 ± 0.3 kg C m−2, from which 32% was associated with the top 5 cm of soil. There was a strong influence of age on C density only throughout the first top 20 cm of the soil profile with a C sequestration rate of 0.31 kg C m−2 yr−1. Carbon quickly accumulates in the top 5 cm layer while in the lower depths it accumulated at a more gradual rate. The results show that bioretention systems could be designed for the enhancement of their C sequestration potential, and amendments in their design, such as addition of a carbon source layer, are important for better managing carbon availability in the basins.
Wetlands can store large quantities of carbon (C) and are considered key sites for C sequestration. However, the C sequestration potential of wetlands is spatially and temporally variable, and ...depends on processes associated with C production, preservation and export. In this study, we assess the soil C sources and processes responsible for C sequestration of riverine wetlands (mangroves, peat swamp forest and marsh) of La Encrucijada Biosphere Reserve (LEBR, Mexican south Pacific coast). We analysed soil C and nitrogen (N) concentrations and isotopes (δ¹³C and δ¹⁵N) from cores dated from the last century. We compared a range of mangrove forests in different geomorphological settings (upriver and downriver) and across a gradient from fringe to interior forests. Sources and processes related to C storage differ greatly among riverine wetlands of the Reserve. In the peat swamp forest and marsh, the soil C experienced large changes in the past century, probably due to soil decomposition, changes in plant community composition, and/or changes in C sources. In the mangroves, the dominant process for C accumulation was the burial of in situ production. The C buried in mangroves has changed little in the past 100 years, suggesting that production has been fairly constant and/or that decomposition rates in the soil are slow. Mangrove forests of LEBR, regardless of geomorphological setting, can preserve very uniform soil N and C for a century or more, consistent with efficient C storage.
Wetlands of Melaleuca spp. in Australia form large forests that are highly threatened by deforestation and degradation. In America, Melaleuca has invaded large areas of native wetlands causing ...extensive damage. Despite their status as an endangered native ecosystem and as a highly invasive one, little is known about their C and N dynamics. In this study, we sampled five Melaleuca wetlands and measured their C and N ecosystem stocks (aboveground biomass and soil), tree accumulation rates, sedimentation rates, and soil stability. Melaleuca wetlands were highly heterogeneous, but most have large ecosystem C mean ± SE (range); 360 ± 100 (80–670) Mg C ha-1 and N 8100 ± 1900 (1600–13,000) kg N ha-1 stocks. Tree accumulation rates were 5.0 ± 2.1 Mg C y⁻¹ and 26 ± 14 kg N y⁻¹, and surface soil accumulation rates were 0.6 ± 0.2 Mg C ha⁻¹ y⁻¹ and 39 ± 1kgNy⁻¹. We found evidence of long-term C and N accumulation in the soil, but also of some level of organic decomposition. Overall, we found that Melaleuca wetlands store and accumulate large amounts of C, especially in their trees, and large amounts of N in their soils, suggesting an important role in coastal biogeochemical cycles.
•Age and sand content were the most influencing factors on the soil TN accumulation.•Denitrification potential and δ15 N values increased with the age of basins.•With the N limitation in young basins ...(≤ 3 years) N fixation is likely to occur.•Top 5 cm of bioretention's soil accounted for 29% of soil TN stocks.•C3 plants (e.g., bioretention plants) were the primary source of soil C.
Bioretention basins are one of the most commonly used green stormwater features, with the potential to accumulate significant levels of nitrogen (N) in their soil and to permanently remove it through denitrification. Many studies have investigated the N removal potential of bioretention basins through the assessment of inflow and outflow concentrations. However, their long-term N removal through soil accumulation and denitrification potential is less known. This study investigated the temporal variation of total N (TN) accumulation and denitrification potential in soils of 25 bioretention basins within a 13-year soil chronosequence, in a subtropical climate in Australia. The denitrification potential of a subset of seven bioretention basins was investigated in accompaniment with nutrient and soil characteristics. Additionally, stable isotopes (δ13C and δ15N) were used to assess temporal changes in the soil composition as well as to identify the sources of carbon (C) into these basins. Over 13 years of operation, TN accumulated faster in the top 5 cm of soil than deeper soils. Soil TN density was highest in the top 5 cm with an average of 1.4 kg N m−3, which was about two times higher than deeper soils. Site age and soil texture were the best predictors of soil TN density and denitrification (1 to 9.7 mg N m−2 h−1). The isotope values were variable among basins. Low δ15N values in young basins (-1.02‰) suggested fixation as the main source of N, while older basins had higher δ15N, indicating higher denitrification. Bioretention plants were the primary source of soil C; although the occurrence of soil amendment also contributed to the C pool. To improve the performance of these bioretention basins, we recommend increasing vegetation at initial years after construction, and enhancing more frequent anaerobic conditions in the high soil profile. These two conditions can improve denitrification potential, and thus the performance of these basins for improving water quality.
(a) Linear accumulation of TN in bioretention soil with age (x-axis) and within the soil profile (y-axis); (b) correlation matrix: positive and negative correlations are shown in red and blue color, respectively. The size of circles and the color intensity are proportional to the strength of the correlation; * and ** indicate significance at the level of 0.05 and 0.01, respectively. The bold black box represents the analysis on 25 bioretention basins, and the rest represent the analysis on a subset of seven bioretention basins. Display omitted
Nitrogen (N) from anthropogenic sources has been identified as a major pollutant of the Great Barrier Reef (GBR), Australia. We developed a conceptual framework to synthesise and visualise the fate ...and transport of N from the catchments to the sea from a literature review. The framework was created to fit managers and policymakers' requirements to reduce N in the GBR catchments. We used this framework to determine the N stocks and transformations (input, sources, and outputs) for ecosystems commonly found in the GBR: rainforests, palustrine wetlands, lakes, rivers (in-stream), mangroves and seagrasses. We included transformations of N such as nitrogen fixation, nitrification, denitrification, mineralisation, anammox, sedimentation, plant uptake, and food web transfers. This model can be applied to other ecosystems to understand the transport and fate of N within and between catchments. Importantly, this approach can guide management actions that attenuate N at different scales and locations within the GBR ecosystems. Finally, when combined with local hydrological modelling, this framework can be used to predict outcomes of management activities.
Wetlands are characterised by soils rich in organic matter that accumulate carbon, providing an important pathway for carbon dioxide sequestration. Nevertheless, not all the carbon fixed can be ...accumulated, and a proportion will decompose through microbial consumption and be partly released into the atmosphere. Rates of organic matter decomposition in tropical wetlands and the factors associated with this process are scarce. We conducted a 2-year field study in three
Melaleuca
wetlands in tropical and subtropical Australia using standardised tea litter substrates (green-labile and rooibos-recalcitrant) to measure organic matter decomposition and the microbial communities associated with this process. Decomposition rates were 4-fold higher in labile litter, which was low in carbon: nitrogen, compared to recalcitrant litter. The prokaryotic communities associated with the decomposing litter were unique at each site and different from the soil. They contained taxonomic groups adapted to anaerobic, high temperatures, acidic conditions and suggestive of slow anaerobic turnover. Microbial communities changed as decomposition progressed, with the latter characterised by taxa with cellulose-degrading functions. The decomposition of recalcitrant organic matter within
Melaleuca
soils was relatively slow, with half of the organic matter inputs remaining after two years, supporting long-term carbon sequestration.
Mangroves are one of the most carbon‐dense forests on the Earth and have been highlighted as key ecosystems for climate change mitigation and adaptation. Hundreds of studies have investigated how ...mangroves fix, transform, store, and export carbon. Here, we review and synthesize the previously known and emerging carbon pathways in mangroves, including gains (woody biomass accumulation, deadwood accumulation, soil carbon sequestration, root and litterfall production), transformations (food web transfer through herbivory, decomposition), and losses (respiration as CO2 and CH4, litterfall export, particulate and dissolved carbon export). We then review the technologies available to measure carbon fluxes in mangroves, their potential, and their limitations. We also synthesize and compare mangrove net ecosystem productivity (NEP) with terrestrial forests. Finally, we update global estimates of carbon fluxes with the most current values of fluxes and global mangrove area. We found that the contributions of recently investigated fluxes, such as soil respiration as CH4, are minor (<1 Tg C year−1), while the contributions of deadwood accumulation, herbivory, and lateral export are significant (>35 Tg C year−1). Dissolved inorganic carbon exports are an order of magnitude higher than the other processes investigated and were highly variable, highlighting the need for further studies. Gross primary productivity (GPP) and ecosystem respiration (ER) per area of mangroves were within the same order of magnitude as terrestrial forests. However, ER/GPP was lower in mangroves, explaining their higher carbon sequestration. We estimate the global mean mangrove NEP of 109.1 Tg C year−1 (7.4 Mg C ha−1 year−1) or through a budget balance, accounting for lateral losses, a global mean of 66.6 Tg C year−1 (4.5 Mg C ha−1 year−1). Overall, mangroves are highly productive, and despite losses due to respiration and tidal exchange, they are significant carbon sinks.
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