Contrasting Responses of Periphyton Growth to Nutrient Amendment across the Littoral-Benthic Habitat of a Mesotrophic Subalpine Lake (Castle Lake, CA)

ALDO SAN PEDRO; FACUNDO SCORDO; CARINA SEITZ; ERIN SUENAGA; SUDEEP CHANDRA

Grand Rapids

Congreso; Joint Aquatic Sciences Meeting 2022 in Grand Rapids, Colorado; 2022

American Fisheries Society (AFS) - Association for the Sciences of Limnology and Oceanography (ASLO) - Coastal and Estuarine Research Federation (CERF) - Freshwater Mollusk Conservation Society (FMCS) - International Association for Great Lake Research

More frequent occurrences of filamentous algal blooms have been observed in the littoral zone of clear mountain lakes around the world. Periphyton often dominate the nutrient cycling and total lake production in clear mountain lakes, yet most studies have focused on open-water phytoplankton for nutrient limitation assessments. To assess nutrient limitation in the littoral-benthic habitat, we deployed nutrient-diffusing substrata (NDS) at 2.5 meter intervals, beginning at the shoreline (2.5 m) and ending in the euphotic zone (17.5m), in the late summer. NDS treatments were spiked with ammonium (NH4), nitrate (NO3), or phosphate (PO4), or combinations of NH4+PO4 or NO3+PO4. After 19 days of incubation, we retrieved the NDS and measured chlorophyll-α concentrations to gauge periphyton growth responses to nutrient amendments. Periphyton growth near the surface (2.5m, 5m) exhibited NH4, NO3 limitation and slight, but not statistically significant (p=0.09), suppression when PO4 was added alone. In contrast, periphyton growth below 10m was limited by PO4 and inhibited by variations of NH4, NO3, NH4+PO4, and NO3+PO4. Despite ample research documenting contrasting responses of phytoplankton to nutrient amendments across the entire water column, our study provides the first investigation into the nutrient limitations of periphyton growth across the littoral extent. Our results demonstrate that periphyton, like phytoplankton, exhibit differential responses to nutrient amendments across the breadth of their habitat. More experiments using benthic bioassays will allow us to better anticipate how periphyton communities will respond to anthropogenic and climate-driven nutrient regime shifts.