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Browsing by Author "Kobayashi, T"

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Carbon uptake in surface water food webs fed by paleogroundwater
(American Geophysical Union, 2019-04-05) Mazumder, D; Saintilan, N; Hollins, SE; Meredith, KT; Jacobsen, GE; Kobayashi, T; Wen, L
The use of 14C to elucidate sources of carbon within freshwater aquatic ecosystems is challenging the assumption that modern autochthonous carbon dominates energy flows. We measured the uptake of old carbon through several trophic levels of a wetland fed by groundwater of the Great Artesian Basin, Australia, the largest artesian basin in the world. Stable isotopes (δ13C and δ15N) and radiocarbon (14C) were used to quantify food chain links and connection between groundwater and surface water food webs. Our results suggest that old groundwater was the dominant carbon source even at the highest trophic levels, with predatory fish returning apparent carbon ages of up to 11 ka. Stable isotope analysis (δ13C and δ15N) identified trophic links between fish, aquatic insects, and algae with smaller contributions from particulate organic matter to the food webs. As natural mound springs and associated wetlands are the only source of reliable water during dry periods over vast areas of the western Great Artesian Basin, the result has potential implications for the interpretation of archaeological artefacts associated with indigenous passage within the interior. ©2019. ANSTO, Macquarie University, Commonwealth of Australia.
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
Environmental flow water and aquatic consumer food web structure: temporal aspects
(NSW Department of Environment, Climate Change and Water, and the CSIRO Water for a Healthy Country Flagship, 2010-05-11) Iles, J; Kobayashi, T; Knowles, L; Saintilan, N; Mazumder, D
We examined the structure of a consumer food web in a swamp on the Lowbidgee floodplain which was inundated by an environmental flow for nine months. The food web structure was measured as a two-dimensional space (polygon) formed by mean δ13C and δ15N values of consumer species. The change in the food web structure was assessed by examining the shape and area of polygons. We found marked temporal changes in the consumer food web structure with the development of the swamp. The mean δ13C value of the consumer population decreased within the swamp indicating a consumer shift to a more 13C depleted food source. The amount of niche space occupied by the consumer population reduced although the nearest neighbour distance between species increased. We conclude that floodplain habitats such as inundated swamps in the Lowbidgee provide a broader range of food items to consumer species for relatively longer periods of time, enabling the food web structure to develop following an environmental flow.
Food webs in freshwater floodplain wetlands inundated with environmental flows during drought conditions
(Australian Nuclear Science and Technology Organisation, 2010-08-09) Mazumder, D; Johansen, MP; Saintilan, N; Iles, J; Knowles, L; Kobayashi, T; Wen, L
In the present study we used δS13C and δS15N stable isotope ratios in basal sources, primary producers, and a variety of invertebrate and fish consumers to gain better understanding of the sources of energy and trophic positions for aquatic species at floodplain water bodies within Yanga wetlands, Murrumbidgee floodplain, Australia. We compared δ13C and δ15N data from conditions of higher water levels and volumes that occurred in summer following a managed environmental flow, with data from winter conditions of lower water levels and volumes. Mass-balance mixing models were used to examine relative food source contributions to consumer diet. We also employed probabilistic simulation modelling to better understand trends of trophic positions, diet shifts and varying contributions from sources to consumers in water bodies of the Yanga wetlands. The data indicated contraction in the trophic position of Hypseleotris spp. in winter consistent with shrinking water volumes that induced greater competition, particularly between endemic Hypseleotris spp and and exotic Cyprinus carpio, for overlapping, and more limited varieties of food sources. Data indicated that the δ13C values for fish and insects from the low-water sampling period were typically -2-4%0 depleted compared to the corresponding high-water values. The δ13C values for one basal source (algae) depleted up to 25%0 between the sampling periods, while a second basal source (SOM) depleted less than 4%0. This study provided modelling results that indicated shifts in energy source and trophic position related to water fluctuations were consistent between adjacent water bodies and changes in food availability increased competition among species that may adversely impact population of endemic species.
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
Hydrological connectivity and ecological functional processes in inland floodplain wetlands: nutrient and carbon cycling
(Australian Society for Limnology, 2013-12-03) Wassens, S; Ralph, TJ; Ryder, DS; Saintilan, N; Mazumder, D; Wen, L; Hunter, S; Kobayashi, T
Floodplain wetlands have intricate multi-channeled networks and unpredictable wet and dry phases related to variable hydrological regimes and geomorphic processes such as sedimentation and erosion. Hydrological reconnection of river channels with outer floodplain and wetland habitats initiates mobilisation and transformation of nutrients and carbon in inland floodplain wetlands. In this study, we aim to show habitat-dependent patterns of mobilisation and transformation of nutrients (total and dissolved nitrogen and phosphorus) and dissolved organic carbon (DOC) following environmental water releases, based on the available data from the Murrumbidgee Wetlands, Macquarie Marshes and Gwydir Wetlands. In general, concentrations of nutrients and DOC are lower within channels and higher on the floodplain and in wetlands where shallow inundation and mixing of topsoil with water occurs. Higher concentrations of nutrients and DOC on the floodplain represent a combination of supply from channels coupled with in situ releases from the water-soil interface. The volume, timing, depth, rate of rise and fall, and spatial distribution of water being introduced to floodplain wetlands influence the amount and distribution of nutrients and carbon in these systems. Rates of ecological functional processes such as primary productivity and respiration (or decomposition) are closely related to concentrations of nutrients and DOC. We propose a nutrient-DOC framework, combined with hydrological regimes and geomorphic processes, to better predict and understand the relationship between hydrological connectivity and ecological responses of inland floodplain wetlands. © The Authors
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
Inherent variation in carbon and nitrogen isotopic assimilation in the freshwater macro-invertebrate Cherax destructor
(CSIRO Publishing, 2016-01-05) Mazumder, D; Wen, L; Johansen, MP; Kobayashi, T; Saintilan, N
Individual variability in diet source selection has often been cited as the main factor for intra-specific variation of isotopic signatures among food-web consumers. We conducted a laboratory study to test how well the individual variability of the δ13C and δ15N ratios in the muscle of an omnivore consumer (yabby: Cherax destructor) corresponded to the variability of various diet types and diet combinations. We found that C. destructor muscle isotope signatures varied in concert with the composition of single-source diets, and that this variability was low. However, when fed the same proportional mixture of multiple diet sources, comparatively high isotopic variability was observed among specimens. Results suggest that a substantial component of isotopic variability in wild populations may be owing to inherent differences in uptake, absorption, and sequestration among individuals, which is distinct from behaviourally driven individualised diet selection. Considering the potential of such individual variability in assimilation to be present in many different consumer populations, we suggest further testing for a range of species and inclusion of this source of variation, for interpretation of isotopic data for trophic ecology. © CSIRO 1996-2020
Isotopic 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, J
Water 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.
Longitudinal spatial variation in ecological conditions in an in-channel floodplain river system during flow pulses
(Wiley-Blackwell, 2011-05-01) Kobayashi, T; Ryder, DS; Ralph, TJ; Mazumder, D; Saintilan, N; Iles, J; Knowles, L; Thomas, R; Hunter, S
A field survey was conducted during flow pulses to investigate the longitudinal spatial patterns in water quality, dissolved inorganic and organic matter, phytoplankton, planktonic bacteria, zooplankton, gross primary productivity (GPP) of phytoplankton and planktonic respiration (PR) in channels of the large floodplain system (similar to 124 km in length) of the Macquarie Marshes, south-eastern Australia. Four river reaches (areas) with distinct hydrogeomorphological characteristics within the distributary zone of the lower Macquarie River were chosen for analysis of abiotic and biotic variables in their in-stream environments. The results showed marked longitudinal spatial variation in the values within and among the measured environmental variables including such functional aspects as primary productivity and PR. The variables that tended to have increasing values in a downstream direction were conductivity, total nitrogen (TN), total phosphorus (TP), dissolved reactive phosphorus (DRP), dissolved silica, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP), ratio of DOC/DON and counts of planktonic bacteria. Conversely, the values that tended to decrease downstream were the ratios of TN/TP, DIN/DRP, DOC/DOP, DON/DOP and GPP/PR. Variables that had a localized peak(s) were dissolved oxygen, turbidity, dissolved inorganic nitrogen, GPP, PR and counts of cyanobacteria, diatoms, green algae, cryptomonads, protozoans, rotifers, copepods and cladocerans. Overall, two distinct ecological zones were identified within the broader distributary functional process zone (FPZ): these being the upstream zone with relatively high levels of DO, turbidity, diatoms and GPP/PR ratio, and the downstream zone with relatively high levels of nutrients, dissolved organic matter, cyanobacteria, planktonic bacteria, protozoans and cladocerans. The results of this study describe the spatial connectivity of ecological processes related to hydrogeomorphological factors within a FPZ of a riverine ecosystem, and support the predictions of the riverine ecosystem synthesis framework that ecological patterns and processes can be discontinuous on a longitudinal spatial scale. Copyright (C) 2010 John Wiley & Sons, Ltd.
Macro-charcoal accumulation in floodplain wetlands: problems and prospects for reconstruction of fire regimes and environmental conditions
(PLOS, 2019-10-24) Graves, BP; Ralph, TJ; Hesse, PP; Westaway, KE; Kobayashi, T; Gadd, PS; Mazumder, D
Floodplain wetland ecosystems respond dynamically to flooding, fire and geomorphological processes. We employed a combined geomorphological and environmental proxy approach to assess allochthonous and autochthonous macro-charcoal accumulation in the Macquarie Marshes, Australia, with implications for the reconstruction of fire regimes and environmental conditions in large, open-system wetlands. After accounting for fluvial macro-charcoal flux (1.05 ± 0.32 no. cm-2 a-1), autochthonous macro-charcoal in ~1 m deep sediment profiles spanning ~1.7 ka were highly variable and inconsistent between cores and wetlands (concentrations from 0 to 438 no. cm-3, mean accumulation rates from 0 to 3.86 no. cm-2 a-1). A positive correlation existed between the number of recent fires, satellite-observed ignition points, and macro-charcoal concentrations at the surface of the wetlands. Sedimentology, geochemistry, and carbon stable isotopes (δ13C range -15 to -25 ‰) were similar in all cores from both wetlands and varied little with depth. Application of macro-charcoal and other environmental proxy techniques is inherently difficult in large, dynamic wetland systems due to variations in charcoal sources, sediment and charcoal deposition rates, and taphonomic processes. Major problems facing fire history reconstruction using macro-charcoal records in these wetlands include: (1) spatial and temporal variations in fire activity and ash and charcoal products within the wetlands, (2) variations in allochthonous inputs of charcoal from upstream sources, (3) tendency for geomorphic dynamism to affect flow dispersal and sediment and charcoal accumulation, and (4) propensity for post-depositional modification and/or destruction of macro-charcoal by flooding and taphonomic processes. Recognition of complex fire-climate-hydrology-vegetation interactions is essential. High-resolution, multifaceted approaches with reliable geochronologies are required to assess spatial and temporal patterns of fire and to reconstruct in order to interpret wetland fire regimes. © 2019 Graves et al. This is an open access article distributed under the terms of the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproductionin any medium, provided the original author and source are credited.
Productivity 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, K
Previous 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.
Stable isotopes to understand trophic interactions in floodplain wetlands of semi-arid Australia
(Australian Nuclear Science and Technology Organisation, 2015-07-08) Kobayashi, T; Wen, L; Mazumder, D; Saintilan, N
We use stable isotopes (δ13C and δ15N) and gut-content analysis to understand the trophic interactions among aquatic and terrestrial consumers such as crustaceans, fish and kangaroos in floodplain wetlands of semi-arid Australia. Our results indicate the importance of water flow regimes in both spatial and temporal patterns in the trophic interactions among consumers. For example, by using δ13C and δ15N values of sample specimens, we found significant spatial differences in dietary items and trophic positions of consumers in watercourses that share the same source water but are laterally disconnected (Kelleway et al., 2010). We found shifts in dietary sources and trophic positions for two fish species (one native and one introduced) that co-occur in shallow water bodies during water withdrawal, providing evidence that flow reductions in wetland systems could increase the dietary overlap between native and introduced fish species (Mazumder et al., 2012). With these findings, we are assessing further applications of stable isotopes to better understand the trophic interactions among aquatic and terrestrial consumers in floodplain wetlands of semi-arid Australia.
Trophic shifts involving native and exotic fish during hydrologic recession in floodplain wetlands
(Springer Nature Limited, 2011-12-28) Mazumder, D; Johansen, MP; Saintilan, N; Iles, J; Kobayashi, T; Knowles, L; Wen, L
Stable isotopes (δ13C and δ15N) and gut contents were analysed for two species of co-occurring native and exotic fish in three shallow water bodies within an Australian riparian wetland system. During a period of hydrologic recession we found depletions in δ13C of up to −25‰ for algae and −2‰ for sediment organic matter (SOM). The native Hypseleotris sp. (carp gudgeon) and the exotic Cyprinus carpio (common carp) were depleted in δ13C up to −3.2‰, indicating that the SOM was the dominant dietary source of carbon for the two species of fish in both high- and the receded low-water conditions. In the low-water conditions, however, there was a five-fold increase in the occurrence of insects in the gut of the exotic C. carpio and the trophic positions of C. carpio and Hypseleotris sp. were more similar in all three water bodies than at high-water conditions. Our results indicate that there were shifts in dietary sources and trophic positions during hydrologic recession and provide evidence that flow reductions in wetland systems can increase the dietary overlap between native and exotic fishes. © Society of Wetland Scientists 2011
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
The use of stable isotope techniques for long-term monitoring of Australian Freshwater Wetlands
(University of New South Wales and Australian Nuclear Science and Technology Organisation, 2015-07-10) Prentice, E; Mazumder, D; Kobayashi, T; Saintilan, N
Not provided to ANSTO Library.
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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