A diatom-based biological condition gradient (BCG) approach for assessing impairment and developing nutrient criteria...

Area of Science:

• Environmental Science
• Ecology
• Limnology

Background:

• Nutrient over-enrichment causes excess algal growth in rivers and streams, impacting biological communities.
• Establishing scientifically defensible nutrient criteria is crucial for protecting stream integrity.
• The Biological Condition Gradient (BCG) approach offers a framework for assessing ecological conditions.

Purpose of the Study:

• To develop a system for categorizing stream impairment using diatom assemblages and the BCG approach.
• To identify scientifically defensible nutrient criteria for protecting stream biotic integrity.
• To explore the relationship between BCG levels, nutrient concentrations, and watershed characteristics.

Main Methods:

• Applied the BCG approach to stream diatom assemblages to categorize sites by impairment level (1-6).
• Utilized Threshold Indicator Taxa Analysis (TITAN) to identify change-points in diatom communities along the BCG gradient.
• Analyzed relationships between BCG levels, total phosphorus, nitrogen, and watershed forest cover using data from New Jersey and Mid-Atlantic states.

Main Results:

• BCG levels strongly correlated with total phosphorus and watershed forest percentage, but not pH.
• A significant shift in diatom assemblages occurred between BCG levels 3 and 4.
• Sites with BCG levels 1-3 featured attached diatoms, while levels 4+ had motile diatoms.
• The identified diatom change-point corresponded to approximately 50μg/L total phosphorus.

Conclusions:

• The BCG approach effectively categorizes stream health based on diatom assemblages.
• A total phosphorus concentration of 50μg/L may serve as a critical threshold for stream health.
• Diatom community structure provides valuable indicators for assessing stream condition and informing nutrient criteria development.