Diatom Assemblage Changes in Agricultural Alluvial Plain Streams and Application for Nutrient Management

Area of Science:

• Ecology
• Environmental Science
• Limnology

Background:

• Agricultural activities, including nutrient application and altered hydrology, can lead to nutrient enrichment in small alluvial streams.
• Nutrient enrichment significantly affects algal assemblage structure and metabolism, impacting stream ecosystem health.
• Understanding stressor-response relationships is crucial for setting effective nutrient reduction goals in agricultural watersheds.

Purpose of the Study:

• To investigate the relationship between nutrient inputs (Phosphorus and Nitrogen) and diatom assemblage structure in agricultural streams of the Mississippi Alluvial Plain (MAP).
• To identify potential thresholds for nutrient concentrations that indicate ecological shifts in these aquatic ecosystems.
• To evaluate the utility of diatom assemblages as bioindicators for monitoring nutrient impacts and assessing agricultural best management practices.

Main Methods:

• Diatom assemblages were sampled from instream woody debris in 25 MAP streams with varying land management and nutrient inputs.
• Field nutrient concentrations (total Phosphorus and Nitrogen) and dissolved oxygen were measured.
• Ordination analysis was employed to identify gradients in species composition related to nutrient levels and environmental factors.

Main Results:

• A significant shift in diatom assemblage structure was observed when total Phosphorus concentrations exceeded 0.12 mg L-.
• Increasing Phosphorus was associated with a distinct set of indicator species, lower abundances of ubiquitous species, and higher abundances of tolerant and high-P indicator species.
• No significant relationships were found between Nitrogen concentrations and diatom assemblage measures or traits.

Conclusions:

• Diatom assemblage structure is sensitive to Phosphorus enrichment in MAP streams, serving as a valuable bioindicator.
• The study identified a potential P concentration threshold indicative of ecological change, informing nutrient reduction strategies.
• Diatom-based metrics can aid in setting benchmarks for reducing nutrient impacts and monitoring the effectiveness of agricultural best management practices.