Browsing by Author "Kelleway, JJ"

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    Carbon isotope fractionation in the mangrove Avicennia marina has implications for food web and blue carbon research
    (Elsevier B. V., 2018-05-31) Kelleway, JJ; Mazumder, D; Baldock, JA; Saintilan, N
    The ratio of stable isotopes of carbon (δ13C) is commonly used to track the flow of energy among individuals and ecosystems, including in mangrove forests. Effective use of this technique requires understanding of the spatial variability in δ13C among primary producer(s) as well as quantification of the isotopic fractionations that occur as C moves within and among ecosystem components. In this experiment, we assessed δ13C variation in the cosmopolitan mangrove Avicennia marina across four sites of varying physico-chemical conditions across two estuaries. We also compared the isotopic values of five distinct tissue types (leaves, woody stems, cable roots, pneumatophores and fine roots) in individual plants. We found a significant site effect (F3, 36 = 15.78; P < 0.001) with mean leaf δ13C values 2.0‰ more depleted at the lowest salinity site compared to the other locations. There was a larger within-plant fractionation effect, however, with leaf samples (mean ± SE = −29.1 ± 0.2) more depleted in 13C than stem samples (−27.1 ± 0.1), while cable root (−25. 8 ± 0.1), pneumatophores (−25.7 ± 0.1) and fine roots (−26.0 ± 0.2) were more enriched in 13C relative to both aboveground tissue types (F4, 36 = 223.45; P < 0.001). The within-plant δ13C fractionation we report for A. marina is greater than that reported in most other ecosystems. This has implications for studies of estuarine carbon cycling. The consistent and large size of the fractionation from leaf to woody stem (∼2.0‰) and mostly consistent fractionation from leaf to root tissues (>3.0‰) means that it may now be possible to partition the individual contributions of various mangrove tissues to estuarine food webs. Similarly, the contributions of mangrove leaves, woody debris and belowground sources to blue carbon stocks might also be quantified. Above all, however, our results emphasize the importance of considering appropriate mangrove tissue types when using δ13C to trace carbon cycling in estuarine systems..© 2018 Elsevier Ltd
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    Effect of acidification on elemental and isotopic compositions of sediment organic matter and macro-invertebrate muscle tissues in food web research
    (Wiley-Blackwell, 2010-10-30) Mazumder, D; Iles, J; Kelleway, JJ; Kobayashi, T; Knowles, L; Saintilan, N; Hollins, SE
    Stable isotope techniques in food web studies often focus on organic carbon in food sources which are subsequently assimilated in the tissue of consumer organisms through diet. The presence of non-dietary carbonates in bulk samples can affect their δ13C values, altering how their results are interpreted. Acidification of samples is a common practice to eliminate any inorganic carbon present prior to analysis. We examined the effects of pre-analysis acidification on two size fractions of sediment organic matter (SOM) from marine and freshwater wetlands and pure muscle tissue of a common freshwater invertebrate (Cherax destructor). The elemental content and isotopic ratios of carbon and nitrogen were compared between paired samples of acidified and control treatments. Our results showed that acidification does not affect the elemental or isotopic values of freshwater SOM. In the marine environment acidification depleted the δ13C and δ15N values of the fine fraction of saltmarsh and δ15N values of mangrove fine SOM. Whilst acidification did not change the elemental content of invertebrate muscle tissue, the δ13C and δ15N values were affected. We recommend to researchers considering using acidification techniques on material prepared for stable isotope analysis that a formal assessment of the effect of acidification on their particular sample type should be undertaken. Further detailed investigation to understand the impact of acidification on elemental and isotopic values of organic matter and muscular tissues is required. © 2010, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
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    Equivalence of trophic structure between a tropical and temperate mangrove ecosystem in the Indo-Pacific
    (CSIRO Publishing, 2019-05-22) Mazumder, D; Saintilan, N; Yusoff, FM; Kelleway, JJ
    In this study we compared ecosystem trophic structure between a tropical mangrove forest at Matang, Malaysia, and a temperate mangrove forest near mangrove poleward limits at Towra Point in south-east Australia. These forests are separated by 8500 km of ocean over 45° of latitude and are of contrasting size, productivity and diversity. However, we observed a marked degree of similarity in food chain length (approximately four trophic levels in both forests), the taxonomy of key intermediate members of the food chain and the isotope signature of primary carbon sources, suggesting a strong contribution of surface organic matter rather than mangrove detritus. Common families were represented among dominant grazing herbivores, zooplanktivorous fishes, decapod crustaceans and top predators. These similarities suggest that there is some consistency in trophic interactions within two mangroves on opposite sides of the Indo-Pacific, despite a degree of evolutionary divergence in the assemblage. © CSIRO 2019
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    Geochemical analyses reveal the importance of environmental history for blue carbon sequestration
    (American Geophysical Union (AGU), 2017-07-07) Kelleway, JJ; Saintilan, N; Macreadie, PI; Baldock, JA; Heijnis, H; Zawadzki, A; Gadd, PS; Jacobsen, GE; Ralph, PJ
    Coastal habitats including saltmarshes and mangrove forests can accumulate and store significant blue carbon stocks, which may persist for millennia. Despite this implied stability, the distribution and structure of intertidal-supratidal wetlands are known to respond to changes imposed by geomorphic evolution, climatic, sea level, and anthropogenic influences. In this study, we reconstruct environmental histories and biogeochemical conditions in four wetlands of similar contemporary vegetation in SE Australia. The objective is to assess the importance of historic factors to contemporary organic carbon (C) stocks and accumulation rates. Results from the four cores—two collected from marine-influenced saltmarshes (Wapengo marine site (WAP-M) and Port Stephens marine site (POR-M)) and two from fluvial influenced saltmarshes (Wapengo fluvial site (WAP-F) and Port Stephens fluvial site (POR-F))—highlight different environmental histories and preservation conditions. High C stocks are associated with the presence of a mangrove phase below the contemporary saltmarsh sediments in the POR-M and POR-F cores. 13C nuclear magnetic resonance analyses show this historic mangrove root C to be remarkably stable in its molecular composition despite its age, consistent with its position in deep sediments. WAP-M and WAP-F cores did not contain mangrove root C; however, significant preservation of char C (up to 46% of C in some depths) in WAP-F reveals the importance of historic catchment processes to this site. Together, these results highlight the importance of integrating historic ecosystem and catchment factors into attempts to upscale C accounting to broader spatial scales. ©2017 American Geophysical Union - Open Access
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    Grazing kangaroos act as local recyclers of energy on semiarid floodplains
    (CSIRO Publishing, 2010-08-25) Iles, J; Kelleway, JJ; Kobayashi, T; Mazumder, D; Knowles, L; Priddel, D; Saintilan, N
    On Australian semiarid floodplains, large herbivores such as kangaroos have a role in the cycling of energy (carbon) through the mechanism of feeding and defaecation of vegetative material. The degree to which kangaroos are vectors of energy within this system is not fully understood. This study describes the stable carbon isotope signature of floodplain plants and kangaroo scats at two close study sites. Kangaroos were found to deposit scats that mirrored the forage composition at each particular feeding site. Scats were 3.94‰ higher in δ13C values at the site where C4 grasses were available, indicating that this grass contributed ~25–30% of the diet of these kangaroos. The difference in diet due to the relative availability of C3 and C4 forage, detectable in the carbon stable isotope signature of scats, is used to demonstrate that kangaroos are recycling and redistributing energy locally, rather than transporting it more broadly across the floodplain. © 2010, CSIRO Publishing
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    Incorporation of local dissolved organic carbon into floodplain aquatic ecosystems
    (Springer Nature Limited, 2021-03-31) Saintilan, N; Kelleway, JJ; Mazumder, D; Kobayashi, T; Wen, L
    Environmental flow releases in lowland Australian rivers are currently timed to avoid high-carbon production on floodplains. Moreover, return flows (water draining from floodplains back into rivers) are avoided if there exists a risk of introducing deoxygenated “blackwater” into the main channel. This concern has restricted the range of possible watering scenarios being considered by environmental flow managers. We utilised a series of blackwater flows in the lower Murrumbidgee floodplain, Australia, in 2016 and 2017 to determine the origin and trophic contribution of blackwater dissolved organic carbon (DOC) in a floodplain wetland. We demonstrate a consistent difference in the isotope signature of blackwater DOC compared to both dissolved inorganic carbon (DIC) and river water DOC, explained by the greater contribution of floodplain vegetation (including the river red gum Eucalyptus camaldulensis) to blackwater DOC. Stable carbon isotope signatures suggest a contribution of blackwater to algal production, whereby microbial-mediated conversion of blackwater DOC into DIC may create opportunities for primary autotrophic productivity. This carbon signature was incorporated by the common yabby Cherax destructor. In the main river channel, C. destructor, the native gudgeon Hypseleotris spp. and the introduced European carp Cyprinus carpio may utilise the same basal carbon source. The use of small to moderate floodplain inundation with return flow to the river, properly monitored, would ameliorate the risk of hypoxia while providing the benefit of floodplain-derived DOC and associated increases to in-stream productivity. © The Author(s), under exclusive licence to Springer Nature B.V. 2021
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    Mangrove dynamics and blue carbon sequestration
    (The Royal Society Publishing, 2019-02-06) Rogers, K; Saintilan, N; Mazumder, D; Kelleway, JJ
    We 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.
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    Seventy years of continuous encroachment substantially increases ‘blue carbon’ capacity as mangroves replace intertidal salt marshes
    (John Wiley & Sons, 2016-03-22) Kelleway, JJ; Saintilan, N; Macreadie, PI; Skilbeck, CG; Zawadzki, A; Ralph, PJ
    Shifts in ecosystem structure have been observed over recent decades as woody plants encroach upon grasslands and wetlands globally. The migration of mangrove forests into salt marsh ecosystems is one such shift which could have important implications for global ‘blue carbon’ stocks. To date, attempts to quantify changes in ecosystem function are essentially constrained to climate-mediated pulses (30 years or less) of encroachment occurring at the thermal limits of mangroves. In this study, we track the continuous, lateral encroachment of mangroves into two south-eastern Australian salt marshes over a period of 70 years and quantify corresponding changes in biomass and belowground C stores. Substantial increases in biomass and belowground C stores have resulted as mangroves replaced salt marsh at both marine and estuarine sites. After 30 years, aboveground biomass was significantly higher than salt marsh, with biomass continuing to increase with mangrove age. Biomass increased at the mesohaline river site by 130 ± 18 Mg biomass km−2 yr−1 (mean ± SE), a 2.5 times higher rate than the marine embayment site (52 ± 10 Mg biomass km−2 yr−1), suggesting local constraints on biomass production. At both sites, and across all vegetation categories, belowground C considerably outweighed aboveground biomass stocks, with belowground C stocks increasing at up to 230 ± 62 Mg C km−2 yr−1 (± SE) as mangrove forests developed. Over the past 70 years, we estimate mangrove encroachment may have already enhanced intertidal biomass by up to 283 097 Mg and belowground C stocks by over 500 000 Mg in the state of New South Wales alone. Under changing climatic conditions and rising sea levels, global blue carbon storage may be enhanced as mangrove encroachment becomes more widespread, thereby countering global warming. © 2015, John Wiley & Sons Ltd.
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    Thirty-year repeat measures of mangrove above- and below-ground biomass reveals unexpectedly high carbon sequestration
    (Springer Nature Limited, 2019-06-13) Lamont, K; Saintilan, N; Kelleway, JJ; Mazumder, D; Zawadzki, A
    Mangrove ecosystems store large quantities of organic carbon for long periods of time. This study explores organic carbon stock change through the first comparative study of radiometric analysis and repeat field measures over a multi-decadal period in a mangrove system. Examining one tall gallery forest of Avicennia marina, and an adjacent interior scrub mangrove of mixed Avicennia marina and Aegiceras corniculatum, radiometric analysis estimated a soil organic carbon accumulation rate of 4.3 ± 0.6 Mg C ha−1 y−1 in the tall gallery forest and 2.2 ± 0.5 Mg C ha−1 y−1 in a stunted mangrove. Repeat measures of root carbon separated by 30 years estimated an increase of 5.06 Mg C ha−1 y−1 in the tall forest and 6.63 Mg C ha−1 y−1 in the stunted forest—suggesting an underestimate of carbon accumulation by radiometric dating of 15% and 67% in the tall and stunted forest, respectively. A higher carbon stock in the interior forest was attributed to root mass increase, associated with landward mangrove encroachment. Extrapolated to the entire region of NSW we estimate that mangrove encroachment has contributed at least about 1.8 Tg C sequestration over the 70 years for which this has been observed in New South Wales, Australia. © 2019 Springer Science+Business Media, LLC, part of Springer Nature
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    Trophic structure of benthic resources and consumers varies across a regulated floodplain wetland
    (CSIRO Publishing, 2010-04-27) Kelleway, JJ; Mazumder, D; Wilson, GG; Saintilan, N; Knowles, L; Iles, J; Kobayashi, T
    Riverine food webs are often laterally disconnected (i.e. between watercourses) in regulated floodplain wetlands for prolonged periods. We compared the trophic structure of benthic resources and consumers (crustaceans and fish) of the three watercourses in a regulated floodplain wetland (the Gwydir Wetlands, Australia) that shared the same source water but were laterally disconnected. The crustaceans Cherax destructor (yabby), Macrobrachium australiense (freshwater prawn), the exotic fish Cyprinus carpio (European carp) and Carassius auratus (goldfish) showed significantly different δ13C values among the watercourses, suggesting spatial differences in primary carbon sources. Trophic positions were estimated by using δ15N values of benthic organic matter as the base of the food web in each watercourse. The estimated trophic positions and gut contents showed differences in trophic positions and feeding behaviours of consumers between watercourses, in particular for Melanotaenia fluviatilis (Murray–Darling rainbowfish) and M. australiense. Our findings suggest that the observed spatial variation in trophic structure appears to be largely related to the spatial differences in the extent and type of riparian vegetation (i.e. allochthonous carbon source) across the floodplain that most likely constituted part of the benthic resources. © 2010, CSIRO Publishing
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    Using isotopic techniques to assess trophic structure in northern Murray-Darling Basin wetlands
    (CSIRO Publishing, 2010-04) Kelleway, JJ; Mazumder, D; Wilson, G; Kobayashi, T
    Floodplain wetlands provide habitats for many species of terrestrial and aquatic biota (Junk et al. 1989; Junk and Wantzen 2004). Their overall productivity and biodiversity is closely linked to patterns of flooding (Kingsford and Thomas 1995; Kingsford 2000; Arthington and Pusey 2003) which mobilise resources such as carbon and nutrients from the floodplain surface and upstream watercourses. These resources are subsequently utilised by a range or organisms, from bacteria to predatory fish and waterbirds over a range of temporal and spatial scales. For example, microbial components such as bacteria and algae develop within days of inundation of the floodplain sediments (Kobayashi et al. 2009) and are then utilised by higher-level consumers such as zooplankton and fish (Lindholm et al. 2007; Burford et al. 2008). Understanding the flow of nutrients and energy, as well as the trophic linkages within food webs, is essential for developing ecological models for sustainable management of aquatic ecosystems. However, food web connections are often complex and are likely to be influenced by the dynamics of physico-chemical processes. For example, the relative contribution of energy to food webs by autochthonous (derived within the watercourse, e.g. algae) and allochthonous (derived outside the watercourse, e.g. riparian leaf litter) primary sources varies between wetlands, influenced by factors such as climate, discharge regime, canopy cover, nutrient concentrations and other abiotic characteristics(Vannote et al. 1980; Bunn 1986; Lake et al. 1986; Reid et al. 2008). Identifying linkages between sources of primary production to lower and higher trophic-order consumers and detrital pathways (e.g. bacteria and detritivores) is fundamental to our understanding of ecosystems, and ultimately their conservation. Carbon and nitrogen stable isotope ratios (δ13C and δ15N) provide an important tool with which to model trophic connectivity between species and ecosystem resources. In this chapter, we review the ecological applications of stable isotope techniques to freshwater food web research and present findings from two key wetland systems in the northern Murray-Darling basin. © 2010, CSIRO Publishing
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    Wetland 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, CD
    Coastal 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