Browsing by Author "Rogers, K"
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- ItemAllochthonous and autochthonous contributions to carbon accumulation and carbon accumulation and carbon store in southeastern Australian coastal wetlands(Estuarine, Coastal and Shelf Science, 128, 84-92, 2013-08-10) Saintilan, N; Rogers, K; Mazumder, D; Woodroffe, CDEstimates of carbon store and carbon accumulation rate in mangrove and saltmarsh are beset by issues of scale and provenance. Estimates at a site do not allow scaling to regional estimates if the drivers of variability are not known. Also, carbon accumulation within soils provides a net offset only if carbon is derived in-situ, or would not otherwise be sequestered. We use a network of observation sites extending across 2000 km of southeastern Australian coastline to determine the influence of geomorphic setting and coastal wetland vegetation type on rates of carbon accumulation, carbon store and probable sources. Carbon accumulation above feldspar marker horizons over a 10-year period was driven primarily by tidal range and position in the tidal frame, and was higher for mangrove and saltmarsh dominated by Juncus kraussii than for other saltmarsh communities. The rate of carbon loss with depth varied between geomorphic settings and was the primary determinant of carbon store. A down-core enrichment in delta C-13 was consistent with an increased relative contribution of mangrove root material to soil carbon, as mangrove roots were found to be consistently enriched compared to leaves. We conclude that while surface carbon accumulation is driven primarily by tidal transport of allocthonous sediment, in-situ carbon sequestration is the dominant source of recalcitrant carbon, and that mangrove and saltmarsh carbon accumulation and store is high in temperate settings, particularly in mesotidal and fluvial geomorphic settings. © 2013, Elsevier Ltd.
- ItemEstablishing carbon retention and sequestration in a submerged mangrove using isotopic analysis(University of New South Wales and Australian Nuclear Science and Technology Organisation, 2015-07-09) Curran, J; Zawadzki, A; Mazumder, D; Rogers, KNot supplied to ANSTO Library.
- ItemImpacts of land reclamation on tidal marsh ‘blue carbon’ stocks(Elsevier, 2019-07-01) Ewers Lewis, CJ; Baldock, JA; Hawke, B; Gadd, PS; Zawadzki, A; Heijnis, H; Jacobsen, GE; Rogers, K; Macreadie, PITidal marsh ecosystems are among earth's most efficient natural organic carbon (C) sinks and provide myriad ecosystem services. However, approximately half have been ‘reclaimed’ – i.e. converted to other land uses – potentially turning them into sources of greenhouse gas emissions. In this study, we applied C stock measurements and paleoanalytical techniques to sediments from reclaimed and intact tidal marshes in southeast Australia. We aimed to assess the impacts of reclamation on: 1) the magnitude of existing sediment C stocks; 2) ongoing C sequestration and storage; and 3) C quality. Differences in sediment horizon depths (indicated by Itrax-XRF scanning) and ages (indicated by lead-210 and radiocarbon dating) suggest a physical loss of sediments following reclamation, as well as slowing of sediment accumulation rates. Sediments at one meter depth were between ~2000 and ~5300 years older in reclaimed cores compared to intact marsh cores. We estimate a 70% loss of sediment C in reclaimed sites (equal to 73 Mg C ha−1), relative to stocks in intact tidal marshes during a comparable time period. Following reclamation, sediment C was characterized by coarse particulate organic matter with lower alkyl-o-alkyl ratios and higher amounts of aromatic C, suggesting a lower extent of decomposition and therefore lower likelihood of being incorporated into long-term C stocks compared to that of intact tidal marshes. We conclude that reclamation of tidal marshes can diminish C stocks that have accumulated over millennial time scales, and these losses may go undetected if additional analyses are not employed in conjunction with C stock estimates. © 2019 Published by Elsevier B.V.
- ItemIsotopic tools for better management of aquatic environment and resources(Australasian Environment Isotope Conference, 2015-07-08) Mazumder, D; Saintilan, N; Kobayashi, T; Wen, L; Rogers, K; Hollins, SE; Johansen, MP; Walsh, C; Narimbi, J; Sammut, JWater is a vital resource that is under ever-increasing demand from population and industry growth, agricultural development, and environmental allocations that are crucial to sustain the natural ecosystems upon which we all rely. Analysis of naturally-occurring stable isotopes (d13C and d15N) have emerged as powerful techniques for addressing research and management-related questions in ecology and aquaculture. Our work on coastal wetlands has identified carbon and nutrient dynamics, the sequestration potential of saltmarsh and mangrove systems, and anthropogenic impacts on aquatic food chains. We compared trophic position and dietary sources in freshwater wetlands during a severe El Nino drought (2007) and following a subsequent series of wetter than average La Nina years (2013), and identified that food chains expand and contract with oscillations in climate phase in the absence of new sources of carbon. We applied isotopic tools in aquaculture, which is the fastest growing food-producing sector in Australia and around the world and accounts for one-third of global fish production. However, production and profitability from inland and coastal aquaculture are often low due to environmental constraints and the increasing cost of production. Our work to develop low-cost feeding strategies for PNG fish farmers suggests operational costs can be reduced by carefully utilising production inputs or changing the ingredients used in feed formulations. These results provide insights for further applications of stable isotopes in the aquatic ecosystem studies.
- ItemMangrove dynamics and blue carbon sequestration(The Royal Society Publishing, 2019-02-06) Rogers, K; Saintilan, N; Mazumder, D; Kelleway, JJWe monitored coastal wetland vertical accretion, elevation gain and surface carbon (C) at Homebush Bay, Australia over 18 years (2000–2017) in three settings initially characterized by saltmarsh, mixed saltmarsh–mangrove ecotone and mangrove-dominated zones. During this time, the saltmarsh transitioned to mixed saltmarsh–mangrove ecotone, and the mixed saltmarsh–mangrove ecotone transitioned to mangrove, consistent with vegetation transitions observed across the east Australian continent in recent decades. In spite of mangrove recruitment and thickening in the former saltmarsh zone, and the dominance of mangrove root material as a contributing C source, the rate of C accumulation in the former saltmarsh zone did not change over the study period, and there was no significant increase in surface elevation. This contrasted with the response of sites with a longer history of mangrove colonization, which showed strong accretion and C accumulation over the period. The result suggests that the C accumulation and surface elevation gains made as a result of mangrove colonization may not be observable over initial decades, but will be significant in the longer term as forests reach maturity. © 2019 The Author(s) Published by the Royal Society.
- ItemProductivity influences trophic structure in a temporally forced aquatic ecosystem(John Wiley & Sons, Inc., 2017-07-06) Mazumder, D; Saintilan, N; Wen, L; Kobayashi, T; Rogers, KPrevious studies on the relationship between ecosystem productivity, size and food-chain length have been restricted to comparisons between locations. We examined the effect of temporal variability in productivity on trophic structure of a floodplain ecosystem, hypothesising that during the wet-flood pulses, the increased resource availability might lead to higher food-chain lengths. We examined multiple common sampling locations and species during a severe El Niño drought which followed a consecutive series of historically wet La Niña years, comparing trophic position and dietary sources. While carbon stable isotopes showed no significant difference between the two phases, nitrogen stable isotopes indicated that most species were feeding higher in the food chain in the wet phase. The results suggest that oscillations in climate phase-driven changes have effects on food-chain lengths through changes in productivity, without the introduction of new sources of carbon or changes to the composition of higher-order predators. © 2017 John Wiley & Sons, Inc.
- ItemSpatial variability of coastal wetland carbon(Coastal & Estuarine Research Federation, 2017-12-09) Owers, CJ; Rogers, K; Mazumder, D; Woodroffe, CDBlue carbon ecosystems, particularly mangrove and saltmarsh, sequester more atmospheric carbon per unit area than any other natural system in the world. Variation in above and below-ground carbon storage, that relate to the expression of environmental processes across wetland landscapes, are yet to be adequately quantified. We proposed that vegetation structure was a significant control on some of the spatial variation in carbon storage, and that this was a function of the dynamic nature of vegetation change at a site. Initially vegetation structural complexity was delineated using innovative remote sensing techniques. Above-ground biomass of mangrove and saltmarsh were quantified by developing region-specific allometric relationships. Cores were extracted from wetlands on the basis of delineated vegetation complexity to characterise the variation in carbon storage within sediments to 2m depth. We found that above-ground biomass varied with vegetation structural complexity, such that tall mangrove contribute more than 65% of above-ground biomass at some sites. The influence of vegetation structure on below-ground carbon storage was only detected to a depth of 50 cm, however >50% of below-ground carbon exists below this depth. Spatial variation in below-ground carbon storage is primarily due to sedimentary factors associated with estuary evolution and geomorphic setting and the influence these factors have on vegetation distribution over the mid-late Holocene. Current approaches to carbon stock assessment, based on extrapolating mean values of carbon storage to national and global scales, oversimplify carbon stock variation and may significantly under or overestimate carbon storage. Systematic approaches to carbon stock assessments characterising carbon storage variation at various scales will provide required confidence necessary for carbon markets.
- ItemSpatial variation in carbon storage: a case study for Currambene Creek, NSW, Australia(Coastal Education and Research Foundation & Journal of Coastal Research, 2016-03-01) Owers, CJ; Rogers, K; Mazumder, D; Woodroffe, CDQuantifying carbon storage in coastal wetland environments is important for identifying areas of high carbon sequestration value that could be targeted for conservation. This study combines remote sensing and sediment analysis to identify spatial variation in soil carbon storage for Currambene Creek, New South Wales, Australia to establish whether vegetation structure influences soil carbon storage in the upper 30 cm. Wetland vegetation was delineated to capture structural complexity within vegetation communities using Light detection and ranging (Lidar) point cloud data and aerial imagery with an object-based image analysis approach. Sediment cores were collected and analysed for soil carbon content to quantify below-ground carbon storage across the site. The total soil carbon storage in the upper 30 cm for the wetland (59.6 ha) was estimated to be 3933 ± 444 Mg C. Tall mangrove were found to have the highest total carbon storage (1420 ± 198 Mg C), however are particularly sensitive to changes in sea-level as they are positioned lowest in the intertidal frame. Conservation efforts targeted at protecting areas of high carbon sequestration, such as the tall mangrove, will lead to a greater contribution to carbon mitigation efforts. © Coastal Education and Research Foundation, Inc. 2016
- ItemTemperate coastal wetland near-surface carbon storage: spatial patterns and variability(Elsevier B. V., 2020-04-05) Owers, CJ; Rogers, K; Mazumder, D; Woodroffe, CDCarbon mitigation services provided by coastal wetlands are not spatially homogeneous, nevertheless are commonly described on the basis of vegetation distribution within the intertidal zone. Distribution of mangrove and saltmarsh varies in response to frequency of tidal inundation, resulting in environmental gradients in edaphic factors that influence vegetation structure, and subsequently affect sedimentary carbon additions by vegetation and carbon losses by decomposition. Current sampling approaches and reporting do not adequately account for variability of carbon storage within a wetland, and assessments need to capture spatial variation associated with carbon storage to improve estimates of potential carbon mitigation services by natural ecosystems. This study quantifies the variation in near-surface carbon storage (i.e. upper 30 cm) across an intertidal gradient using a stratified sampling approach that recognises vegetation structure. Vegetation distribution and structure, as well as sedimentary controls on carbon content, explained variation in carbon storage. Saltmarsh near-surface carbon storage varied considerably between structural form. This was less evident for mangrove structural forms (i.e. tall, shrub, dwarf), which may be due to mangrove roots extending to depths beyond 30 cm. Sedimentary characteristics correlated with carbon content, demonstrating considerable influence on near-surface carbon storage within a wetland. The principal finding of this study was that variation within a wetland corresponds to the variation between sites. Stable carbon isotopes offer a means to identify previous vegetation contributions to sediment, associated with an earlier stage of wetland development, likely reflecting previous environmental conditions. A stratified sampling approach that recognises vegetation structure provides the capacity to account for variability of carbon within a wetland that is inadequately described by current sampling protocols. © 2020 Elsevier B.V.
- ItemVegetation persistence and carbon storage: implications for environmental water management for Phragmites australis(American Geophysical Union, 2015-07-14) Whitaker, K; Rogers, K; Saintilan, N; Mazumder, D; Wen, L; Morrison, RJEnvironmental water allocations are used to improve the ecological health of wetlands. There is now increasing demand for allocations to improve ecosystem productivity and respiration, and enhance carbon sequestration. Despite global recognition of wetlands as carbon sinks, information regarding carbon dynamics is lacking. This is the first study estimating carbon sequestration for semiarid Phragmites australis reedbeds. The study combined aboveground biomass assessments with stable isotope analyses of soils and modeling of biomass using Normalized Digital Vegetation Index (NDVI) to investigate the capacity of environmental water allocations to improve carbon storage. The study considered relationships between soil organic carbon (SOC), carbon sources, and reedbed persistence in the Macquarie Marshes, a regulated semiarid floodplain of the Murray-Darling Basin, Australia. SOC storage levels to 1 m soil depth were higher in persistent reedbeds (167 Mg ha−1) than ephemeral reedbeds (116–138 Mg ha−1). In situ P. australis was the predominant source of surface SOC at persistent reedbeds; mixed sources of surface SOC were proposed for ephemeral reedbeds. 13C enrichment with increasing soil depth occurred in persistent and ephemeral reedbeds and may not relate to flow characteristics. Despite high SOC at persistent reedbeds, differences in the rate of accretion contributed to significantly higher rates of carbon sequestration at ephemeral reedbeds (approximately 554 and 465 g m−2 yr−1) compared to persistent reedbeds (5.17 g m−2 yr−1). However, under current water regimes, rapid accretion at ephemeral reedbeds cannot be maintained. Effective management of persistent P. australis reedbeds may enhance carbon sequestration in the Macquarie Marshes and floodplain wetlands more generally. © 2015 American Geophysical Union
- ItemWetland carbon storage controlled by millennial-scale variation in relative sea-level rise(Springer Nature Limited, 2019-03-06) Rogers, K; Kelleway, JJ; Saintilan, N; Megonigal, JP; Adams, JB; Holmquist, JR; Lu, M; Schile-Beers, L; Zawadzki, A; Mazumder, D; Woodroffe, CDCoastal wetlands (mangrove, tidal marsh and seagrass) sustain the highest rates of carbon sequestration per unit area of all natural systems1,2, primarily because of their comparatively high productivity and preservation of organic carbon within sedimentary substrates3. Climate change and associated relative sea-level rise (RSLR) have been proposed to increase the rate of organic-carbon burial in coastal wetlands in the first half of the twenty-first century4, but these carbon–climate feedback effects have been modelled to diminish over time as wetlands are increasingly submerged and carbon stores become compromised by erosion4,5. Here we show that tidal marshes on coastlines that experienced rapid RSLR over the past few millennia (in the late Holocene, from about 4,200 years ago to the present) have on average 1.7 to 3.7 times higher soil carbon concentrations within 20 centimetres of the surface than those subject to a long period of sea-level stability. This disparity increases with depth, with soil carbon concentrations reduced by a factor of 4.9 to 9.1 at depths of 50 to 100 centimetres. We analyse the response of a wetland exposed to recent rapid RSLR following subsidence associated with pillar collapse in an underlying mine and demonstrate that the gain in carbon accumulation and elevation is proportional to the accommodation space (that is, the space available for mineral and organic material accumulation) created by RSLR. Our results suggest that coastal wetlands characteristic of tectonically stable coastlines have lower carbon storage owing to a lack of accommodation space and that carbon sequestration increases according to the vertical and lateral accommodation space6 created by RSLR. Such wetlands will provide long-term mitigating feedback effects that are relevant to global climate–carbon modelling. © 2019 Springer Nature Limited