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Baseline isotope data for Spirodela sp.: nutrient differentiation in aquatic systems
Jaclyn Marie Hill1, Sven Kaehler, Martin Patrick Hill
1Dept. Zoology and Entomology, Rhodes University, PO Box 94, Grahamstown 6140, South Africa. j.hill@ru.ac.za
Water Research
|April 25, 2012
Summary
Duckweed (Spirodela sp.) δ¹⁵N signatures can distinguish between nitrogen sources like KNO₃ and manure within two days. This suggests Spirodela may be a useful tool for monitoring long-term nitrogen loading in freshwater systems.
Area of Science:
- Environmental Science
- Biogeochemistry
- Ecotoxicology
Background:
- Excess nitrogen loading degrades aquatic ecosystems globally.
- Macrophyte δ¹⁵N signatures can indicate nitrogen input levels in aquatic systems.
Purpose of the Study:
- To assess Spirodela sp.'s feasibility as a biomonitor for anthropogenic nitrogen (N) loading.
- To investigate isotopic equilibration rates and concentration effects of different N sources on Spirodela sp.
Main Methods:
- Cultured Spirodela sp. with KNO₃ and cow manure solutions.
- Monitored δ¹⁵N, δ¹³C signatures, C/N ratios, %N, and %C over time.
- Analyzed isotopic differentiation and concentration effects.
Main Results:
- Spirodela δ¹⁵N signatures differentiated nutrient types within 2 days.
- KNO₃ resulted in depleted δ¹⁵N (-15‰ to -12‰), while manure yielded enriched δ¹⁵N (14‰ to 18‰).
- Higher N concentrations affected δ¹⁵N values; δ¹³C differences were minimal.
Conclusions:
- Spirodela sp. shows potential as an isotope monitoring tool for continuous N inputs, like sewage outfalls.
- A cyanobacterial-duckweed association impacts Spirodela's effectiveness in low-nutrient environments.
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