# Developing a monitoring and assessment program with diatoms, an improved metric calculation method, and causal analysis for Big Cypress National Preserve, Florida (USA)

## TL;DR

This study develops a monitoring program using diatoms to assess wetland health in Big Cypress National Preserve, focusing on phosphorus levels and species composition.

## Contribution

The study introduces a novel relative abundance calculation method and applies causal analysis to improve diatom-based monitoring.

## Key findings

- Diatom assemblages in low phosphorus conditions are limited to a few taxa, while higher phosphorus allows more species to colonize.
- Metrics using TITAN-derived taxa traits and log-transformed relative abundances showed the strongest correlation with phosphorus levels.
- Diatom metrics were more closely related to distance from phosphorus sources than direct phosphorus measurements.

## Abstract

We used relationships between diatom species composition and phosphorus concentration in periphyton (mat P) to develop a monitoring and assessment program for wetlands in the Big Cypress National Preserve (BCNP) in Florida, USA. Cluster analysis and regression showed limitation of taxonomic composition of assemblages to a few low phosphorus (P) taxa in low mat P conditions, with additional species being able to colonize habitats having higher mat P concentrations. TITAN (Threshold Indicator Taxa Analysis) and regression respectively identified 11 and 8 low P taxa and both methods identified 47 high P taxa. Congruence of low and high P taxa traits determined in our study and results of prior phosphorus experiments confirmed P caused taxon responses. We varied taxa traits (low and high P taxa), method for determining traits, and trait calculation method to evaluate metric performance. Metrics of biological condition, whether using the low or high P taxa traits, were most highly related to mat P when using TITAN derived taxa traits and a novel relative abundance calculation using log-transformed relative abundances. Benchmarks for management targets were determined for minimally disturbed conditions and for greater than usual changes in assemblages along the P gradient. Diatom metrics were more highly correlated with distance from P sources than mat P, indicating species-based metrics have high value for monitoring and assessment. Our results can be used for a monitoring and assessment program with effects-based management targets in BCNP, and our methods provide examples for applications in other ecological settings.

The online version contains supplementary material available at 10.1007/s10661-026-15144-0.