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

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.