USING A MESOCOSM EXPERIMENT TO TEST HOW AMBIENT PH INFLUENCES PHOSPHORUS SENSITIVITY OF CALCAREOUS PERIPHYTON MATS

Limestone-based freshwater ecosystems, such as the Everglades in South Florida, are dominated by CaCO₃-rich periphyton mats that are sensitive to phosphorus (P) enrichment. Previous research shows pH also strongly influences diatom assemblages and is indistinguishable from P as a primary driver, highlighting the need for experiments to disentangle pH effects from P. Using a 10-day ex situ mesocosm experiment, we tested how ambient pH influences the P sensitivity of calcareous periphyton mats from Everglades National Park (EVER) and Big Cypress National Preserve (BICY). We applied low (6.0) and high (8.0) pH across a P gradient (0–1000 µg P/L) and assessed periphyton attributes and algal assemblage composition using a randomized block design. Low pH and higher P were associated with increased algal content (pH: β = 0.43, p = 0.03; P: β = 0.08, p = 0.04), mat total P (pH: β = 0.80; p < 0.001; P: β = 0.24; p < 0.001), and gross primary production on some days (Day 2 pH: β = 2.16, p = 0.002; Day 8 P: β = 0.42, p = 0.01) compared to the high pH and lower P treatments. The pH x P interaction was not significant, and neither pH, P, nor their interaction affected mat organic content or algal assemblage composition. EVER mats and assemblages responded more strongly to low pH and P than BICY mats, likely due to lower mineral content. These findings suggest low-pH environments may stimulate algal production and demonstrate the value of a mesocosm approach for testing stressor interactions that may be difficult to assess in observational studies or large-scale field experiments.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Kelsey Solomon, Florida International University (ksolomon@fiu.edu)

Authors:

Kelsey Solomon, Florida International University  (ksolomon@fiu.edu)

Gustavo Dominguez Saman, Florida International University  (gudoming@fiu.edu)

Katherine Johnson, Florida International University  (kajohnso@fiu.edu)

Evelyn Gaiser, Florida International University  (gaisere@fiu.edu)