Browsing by Author "Dimovski, C"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Biokinetics and discrimination factors for delta C-13 and delta N-15 in the omnivorous freshwater crustacean, Cherax destructor
    (CSIRO Publishing, 2012-10-29) Carolan, JV; Mazumder, D; Dimovski, C; Diocares, R; Twining, JR
    Knowledge and understanding of biokinetics and discrimination factors for carbon-13 (delta C-13) and nitrogen-15 (delta N-15) are important when using stable isotopes for food-web studies. Therefore, we performed a controlled laboratory diet-switch experiment to examine diet-tissue and diet-faeces discrimination factors as well as the biokinetics of stable-isotope assimilation in the omnivorous freshwater crustacean, Cherax destructor. The biokinetics of delta C-13 could not be established; however, the delta N-15 value of C. destructor tissue reached equilibrium after 80 +/- 35 days, with an estimated biological half-time for N-15 of 19 +/- 5 days. Metabolic activity contributed to the turnover of N-15 by nearly an order of magnitude more than growth. The diet-tissue discrimination factors at the end of the exposure were estimated as -1.1 +/- 0.5% for delta C-13 and +1.5 +/- 1.0% for delta N-15, indicating that a delta N-15 diet-tissue discrimination factor different from the typically assumed +3.4% may be required for freshwater macroinvertebrates such as C. destructor. The diet-faeces discrimination factor for delta N-15 after 120 days was estimated as +0.9 +/- 0.5%. The present study provides an increased understanding of the biokinetics and discrimination factors for a keystone freshwater macroinvertebrate that will be valuable for future food-web studies in freshwater ecosystems. © 2012, CSIRO Publishing.
  • Thumbnail Image
    Item
    Groundwater residence time in the Kulnura-Mangrove Mountain Plateau (Gosford, NSW, Australia)
    (Australasian Environmental Isotope Conference, 2009-12-03) Cendón, DI; Hankin, SI; Williams, JP; Dimovski, C; Meredith, KT; Hughes, CE; Hollins, SE
    The Kulnura-Mangrove Mountain plateau consists of the catchments of Mangrove, Narara, Mooney Mooney, and Ourimbah Creeks, and Wyong River. Groundwater plays a key role in sustaining stream flow within these catchments. Estimates indicate up to 50% of annual stream flow is derived from baseflow. The local community water supply relies on the groundwater within the elevated Hawkesbury- Narrabeen sandstone plateau. Furthermore, the Gosford-Wyong Councils’ Water Authority (WSA) is the third largest in NSW and utilises many of the streams flowing from the sandstone plateau for municipal water supply. It is anticipated that the WSA will provide municipal water for 319 000 persons by the year 2010. The increasing volumes of groundwater being extracted and changing land use have the potential to cause damage to the fresh water aquifer through contamination and aquifer depletion. A hydrogeochemical survey (2006-2009) has been conducted in NSW Dept of Water and Energy (DWE) monitoring wells across the plateau in order to determine groundwater residence times. Groundwater was analysed for major ions, minor and trace elements, H2O 18O and 2H, 13CDIC, 87Sr/86Sr, 14CDIC, and 3H, and complemented with mineralogical and isotopic information obtained from soil and drill chips collected during well construction. Water stable isotopes confirm the meteoric origin of the groundwater with most values plotting on the local meteoric water line. Localised evaporative trends suggest recharge with evaporated groundwater stored in ponds. Shallow groundwaters have 3H and 14C activities consistent with modern recharge (Fig 1). Carbon “bomb pulse” signatures of up to 116.8 pmC are found in the central areas of the plateau. The thin soils, lack of carbonates in the intensely weathered near-surface Hawkesbury sandstone, and the shallow depth of the water samples is consistent with the 3H results measured, suggesting minimal dilution of the original 14C. Input of this data into a southern hemisphere bomb pulse model [1] suggest potential recharge during the 1990´s, coinciding with sustained wet conditions and above average rainfalls experienced during this period. Fig. 1. 14C vs 3H plot of groundwater samples in the Kulnura- Mangrove Mountain Plateau Deeper groundwaters have lower 14C and 3H activities in some cases close to background level (Fig. 1). The quantifiable 3H suggests residence times of <70 a. However, non-corrected 14C residence times are submodern (>500 a). This apparent discrepancy can be explained by either mixing with older waters or dissolution of carbonates. The good correlation of total dissolved inorganic carbon (TDIC) and Ca (R2=0.8), 13CTDIC in groundwater and mineralogy results from drill chips suggest that dissolution of dispersed carbonates is taking place. The deepest groundwaters show the most difference in residence time across the study area. The eastern and western plateaus yield old groundwater with 14C corrected residence times of around 9 ka and 4 ka respectively. However, the groundwater at equivalent depths in the central plateau was found to be considerably younger with residence times of <70 a.