Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences

Short Communication: Elevated δ15N values in aquatic plants from cleared catchments: why?

James White Udy and Stuart Edward Bunn

Marine and Freshwater Research 52(3) 347 - 351
Published: 2001


δ15N values of plants and animals are being increasingly used to identify the flow of nitrogen through aquatic ecosystems. The δ15N values of crops, riparian trees, emergent and submerged aquatic vegetation in streams from both cleared (agricultural) and forested (rainforest) catchments were sampled. Riparian and aquatic plants had similar δ15N values in forested streams,suggesting a similar source of inorganic nitrogen.In cleared catchments, however, aquatic plants had δ15N values 4–8‰ higher than adjacent riparian vegetation and aquatic plants from streams in forested catchments. The elevated δ15N values of aquatic vegetation in streams with cleared catchments suggest that these plants either have access to a different source of N than those in undisturbed catchments or that high rates of microbial decomposition and nutrient cycling in the cleared catchments influence the δ15N value of available N. This also suggests that the aquatic plants in disturbed catchments are incorporating a different source of nitrogen than the adjacent riparian vegetation. This supports the proposal that in-stream processing of N affects the δ15N value of available N in streams with cleared catchments. These results begin to identify potential pathways for nitrogen transport to streams and the effect that internal cycling may have on a stream’s nitrogen load.

Keywords: nitrogen, stable isotopes, denitrification, catchment disturbance, riparian vegetation, sediment

© CSIRO 2001

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