Isotopically labelled macroalgae: A new method for determining sources of excess nitrogen pollution

Area of Science:

• Environmental Science
• Marine Biology
• Isotope Geochemistry

Background:

• Stable nitrogen isotopes (δ¹⁵N) are crucial for identifying nitrogen pollution sources in aquatic environments.
• Current methods using water nitrate face challenges due to temporal variations and high analytical costs.
• Developing alternative, cost-effective methods for nitrogen pollution source tracking is essential.

Purpose of the Study:

• To investigate the potential of isotopically labeled macroalgae as a novel tool for tracing nitrogen pollution.
• To assess the efficiency and feasibility of using Fucus vesiculosus (bladder wrack) for this purpose.
• To establish a low-cost, alternative method for monitoring nitrogen pollution in coastal waters.

Main Methods:

• Macroalgae (Fucus vesiculosus) were cultured in solutions with distinct, artificially enriched δ¹⁵N values (170‰ and -60‰).
• The experiment was conducted over 19 days under controlled laboratory conditions (temperature, light).
• Isotopic analysis (δ¹⁵N) of macroalgal tips was performed throughout the experiment.

Main Results:

• Fucus vesiculosus rapidly incorporated the isotopic signatures from the enriched seawater solutions.
• Significant isotopic enrichment was observed within 11–15 days, reaching 50% of the solution's value.
• Nitrogen isotope ratios were incorporated preferentially into the basal regions of the macroalgal tips.

Conclusions:

• Fucus vesiculosus effectively incorporates and reflects the δ¹⁵N of its surrounding water.
• Laboratory-created isotopically labeled macroalgae can be deployed to signal specific nitrogen sources in marine environments.
• This macroalgae-based approach presents an efficient and economical alternative for nitrogen pollution monitoring.