Browsing by Author "Knowles, L"

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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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    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.
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    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.
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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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    Isotopic and modelling studies of food web structure in wet and dry conditions, Yanga wetlands NSW, Australia
    (CSIRO, 2010-05-11) Mazumder, D; Johansen, MP; Saintilan, N; Iles, J; Knowles, L; Kobayashi, Y; Wen, L
    Floodplain wetlands provide habitat for a diverse range of aquatic biota, as well as performing other important ecosystem functions such as transformation of nutrients, providing breeding and nursery grounds for numerous species. Overall productivity and biodiversity of floodplain wetlands are closely linked with water availability, and in particular to the reliable reoccurrence of water inflows. Alteration of wetland inflow and outflow regimes can greatly impact the functioning of food-webs through biodiversity loss, diversion of energy flow and ecosystem functionality. In the present study stable isotope ratios (δ13C and δ15N) of primary producers, sediment organic matter (SOM) and a variety of invertebrate and fish species are used to gain better understanding of the food-web relations at various waterholes in wetter and drier conditions in Yanga National Park, in the lower Murrumbidgee floodplain. Mass-balance mixing models were used to examine relative food source contributions to consumer diet. We also employed probabilistic simulation software to better understand trends of trophic positions, diet shifts and varying contributions from sources to consumers in waterholes of the Yanga wetlands. We compared δ13C and δ15N data from wetter (greater surface water area and depth) conditions in February, with data from the drier (smaller surface water area an depth) conditions in August. The data indicated contraction in the trophic position of Hypseleotris spp. (carp guudgeon) in August consistent with shrinking waterholes where species were forced into competing for overlapping, and a more limited variety, of food sources. In particular the endemic Hypseleotris spp. appears to be forced into greater competition with the exotic C. carpio (carp). Data also indicated that energy source of consumer species varied with changing water levels among all waterholes. The drier (August) δ13C values for fish and insects were typically shifted ~1-3‰ lower than the corresponding wetter (February) values. These shifts appear to correspond to depletion in the δ13C algal values, and appear to indicate a greater proportional contribution of δ13C from algae to the δ13C in consumers. This study provides δ13C and δ15N values for endemic and exotic aquatic species in Australian semi-arid wetlands. It provides modelling results indicating shifts in energy source and trophic position relative to water fluctuations and indicates increased competition among similar species that may adversely impact endemic species populations.
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    Isotopic studies of food-web properties in Yanga wetlands, NSW Australia
    (Australasian Environmental Isotope Conference, 2009-12-03) Mazumder, D; Johansen, MP; Kobayashi, Y; Iles, J; Saintilan, N; Knowles, L; Hollins, SE
    Floodplain wetlands provide habitats for a diverse range of species of terrestrial and aquatic biota, and perform important ecosystem functions. Overall productivity and biodiversity of floodplain wetlands is closely linked with water availability and environmental stability. Alternation flow regimes is a major threat to the functioning of food-webs and is responsible for a wide range of ecological responses, including biodiversity loss [1] diversion of energy flow [2] and is suspected to have influenced ecosystem functionality. Changes in land use, flow regulation and diversion for water resources, coupled with climate change have altered energy flow dynamics and structure of aquatic food webs. In the present study stable isotope ratios (δ13C and δ15N) of primary producers, sediment organic matter (SOM) and a variety of invertebrate and fish species are used to gain an understanding of the source of energy and trophic positions for aquatic species at various swamps in the Yanga National Park, lower Murrumbidgee River. A mass balance mixing model [3] was used to determine the fraction of food sources contributing to consumer diet. We also employed probabilistic simulation software (GoldSim) to better understand trends of trophic positions, dietary shifts and varying contributions from sources to consumers in swamps of the Yanga wetlands. We found that energy source varies between swamps in close proximity (in relative contribution of algae). Some trophic links are unaffected by this change (Fig.1) while for others a threshold may be crossed when diet shifts from predominantly benthic organic matter to algae. Over time food chain length is diminished as the floodplain wetland dries, drawing predators into competition. Natural systems are complex and highly variable thereby presenting difficulties and challenges for their effective management. Understanding the variability of the food web properties is important for effective management of the wetlands.
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    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.
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    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
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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