Browsing by Author "Ralph, TJ"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    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
  • No Thumbnail Available
    Item
    Late holocene fire history and palaeoecological conditions at Dunphy Lake, Warrumbungle National Park, New South Wales, Australia
    (New Zealand Freswater Sciences Society and Australian Society for Limnology, 2015-11-26) Konayasji, T; Ralph, TJ; Lobb, J; Gadd, PS; Theischinger, G
    There is a significant geographical and temporal gap in the Holocene environmental record of fire, hydrology and palaeoecological conditions in the region of the Warrumbungle Mountains in eastern Australia. Dunphy Lake (-31.3076°S, 149.0149°E) is a small, ephemeral freshwater wetland within Warrumbungle National Park, and the only example of its kind in this temperate -semiarid region. Late Holocene fire history and palaeoecological conditions at Dunphy Lake were determined using a multiproxy approach that incorporates geochronological, limnological and geochemical techniques. The sediment profile at Dunphy Lake is dominated by mud (< 63 µm) and the macrocharcoal record indicates that the largest local fire events have occurred since 1,793±28 years BP. Some distinct peaks in macrocharcoal are coincident with peaks in sand (63-2000 µm) content, suggesting that some fires occurred at similar times to episodes of significant runoff and sediment flux from the catchment. Recent palaeoecological conditions were conducive to a relatively complex aquatic food web, as shown by the presence of micro- and macro-invertebrate and diatom remains in the upper sediment facies. A geochemical record derived from ITRAX core scanning shows facies with elevated pedogenic (e.g. Mn, Ca) and detrital (e.g. Si, Ti) elements, but does not show a significant increase in anthropogenic elements at the surface. Altogether, this multiproxy approach yields a record of fire and aquatic conditions that can be used to place historical and contemporary fires and vegetation changes in this region into context.
  • No Thumbnail Available
    Item
    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.
  • Thumbnail Image
    Item
    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.