DNA metabarcoding effectively quantifies diatom responses to nutrients in streams.

Area of Science:

• Ecology
• Environmental Science
• Molecular Biology

Background:

• Nutrient pollution from human activities is a significant threat to stream ecosystems globally.
• Diatoms, a diverse group of unicellular algae, are sensitive indicators of nutrient concentrations in aquatic environments.
• Understanding diatom responses to nutrient enrichment is crucial for effective stream management and watershed protection.

Purpose of the Study:

• To quantify the ecological effects of total phosphorus (TP) and total nitrogen (TN) on stream diatom communities using DNA metabarcoding.
• To identify specific diatom operational taxonomic units (OTUs) and their responses along nutrient gradients.
• To establish potential thresholds for nutrient concentrations that trigger significant changes in diatom assemblages.

Main Methods:

• DNA metabarcoding was employed to analyze the diversity and abundance of stream diatoms.
• Threshold Indicator Taxa analysis (TITAN) identified indicator OTUs sensitive to TP and TN.
• Boosted regression trees and gradient forest analyses were used to model diatom responses to nutrient concentrations.

Main Results:

• Significant changes in diatom assemblage structure were observed, with notable shifts occurring around 20 µg TP/L.
• Low phosphorus-tolerant diatoms decreased, while high phosphorus-tolerant diatoms became dominant at concentrations above 150 µg/L.
• Diatom communities showed sensitivity to total nitrogen, with low nitrogen-tolerant diatoms declining and high nitrogen-tolerant diatoms increasing at concentrations above 525 µg/L.

Conclusions:

• Diatom metabarcoding provides a robust method for monitoring nutrient pollution in streams.
• Identified diatom responses to phosphorus and nitrogen can inform water quality protection and nutrient reduction strategies.
• Specific diatom groups can serve as valuable bioindicators for assessing stream health in relation to nutrient levels.