Can the nitrogen and carbon stable isotopes of the pygmy mussel,Xenostrobus securis, indicate catchment disturbance for estuaries in northern New South Wales, Australia? |
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| Authors: | Stephanie K Moore Iain M Suthers |
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| Institution: | 1. Fisheries and Marine Environmental Research Laboratory, School of Biological, Earth and Environmental Sciences, University of New South Wales, 2052, Sydney, New South Wales, Australia
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| Abstract: | The nitrogen and carbon stable isotope ratios (δ15N and δ13C) of the pygmy mussel,Xenostrobus securis, were determined for three estuaries with varying levels of catchment disturbance in northern New South Wales, Australia.
The lower Manning River catchment supported the highest human population densities with 3% residential development and some
livestock agriculture (41%); the Wallamba River catchment was mostly livestock agriculture (56%) while the Wallingat River
catchment was mostly vegetated (79%). Mussels, estuarine particulate organic matter (POM), and livestock and human-derived
waste were collected in two stages during the austral summers of 2001–2002 and 2002–2003 for dual carbon-nitrogen stable isotope
analysis. The disturbed Manning and Wallamba River catchment mussels were enriched in15N by an average of 3.2‰ and 1.5‰, respectively, compared to the vegetated Wallingat River mussels. Mussel δ13C values ranged from −24.8‰ to −30.3‰ and showed an estuarine gradient becoming enriched with distance downstream within estuaries,
but were unable to distinguish patterns in catchment disturbance between estuaries. The δ15N and δ13C values of POM showed a similar pattern to mussels, indicating a direct link between them within each estuary. A multiple
regression model of mussel δ15N using the fractions of land used for livestock agriculture and residential development within 5 km zones from river networks
to a distance equivalent to a tidal ellipse from sites explained 67% of the variation in mussel δ15N with 95% of the differences lying within 1.6‰ of observed values. Increasing fractions of land used for livestock agriculture
depleted mussel δ15N values estimated by the regression equation, indicating the use of cow manure as a nutrient source with a value of 2.0‰.
Increasing fractions of land used for residential development enriched estimated mussel δ15N, indicating the use of human-derived waste with a value of 20.8‰. Pygmy mussels are a useful long-term bio-indicator for
the effects of anthropogenic catchment disturbance and nutrient enrichment in estuaries. |
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