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Catchment Influences on Carbon Stable Isotope Variation in Trout; Might It Be Methane?
Michael Hinchliffe1,2, Aimeric Blaud1,2, Peter Gilbert3,4
1Edinburgh Napier University, School of Applied Sciences, Edinburgh Napier University Edinburgh UK.
Ecology and Evolution
|May 1, 2026
Summary
Stable isotope analysis in brown trout reveals how land use impacts aquatic food webs. Poorly drained soils and pasture cover correlate with methane-derived carbon, influencing trout diet and ecology.
Area of Science:
- Ecology
- Environmental Science
- Stable Isotope Geochemistry
Background:
- Stable isotope analysis (SIA) is crucial for understanding ecological processes like species movement and food web dynamics.
- Brown trout (Salmo trutta) are ecologically significant, and their stable carbon isotope (δ13C) values can reflect catchment characteristics and food web structure.
- Variations in δ13C in aquatic organisms are linked to the base of the food web, with chemosynthesis (e.g., methane oxidation) yielding different values than photosynthesis.
Purpose of the Study:
- To investigate the relationship between catchment characteristics and δ13C values in brown trout fry.
- To determine if trout δ13C values serve as indicators of carbon processing within the aquatic ecosystem.
- To explore the role of methane-derived carbon in structuring upland stream food webs.
Main Methods:
- Collected δ13C isotope data from brown trout fry across 51 sites in the River Tweed tributaries, Scotland.
- Analyzed the correlation between trout δ13C values and various catchment features, including soil drainage and land cover.
- Sampled mayflies (Baetis spp.) at 26 sites to compare their δ13C values with those of trout fry.
Main Results:
- Soil drainage and pasture cover were the most significant predictors of trout fry δ13C values.
- Lower soil drainage and higher pasture cover were associated with lower δ13C values in trout.
- A strong positive correlation was found between the δ13C values of mayflies and trout fry, supporting the use of trout as bioindicators.
Conclusions:
- Catchment land use, particularly poorly drained soils and pasture, influences carbon sources in the aquatic food web.
- Methane-derived carbon, indicated by lower δ13C values, appears to play a significant role in the diet of brown trout in these systems.
- Stable isotope analysis of brown trout provides valuable insights into the impact of land management practices on freshwater ecosystem functioning.
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