Sediment Resuspension Controls Light Attenuation and Ecosystem Function in a Large, Shallow, Eutrophic Lake

Abstract

Light limitation can constrain primary production and ecosystem recovery in shallow eutrophic lakes even when nutrients remain abundant. We evaluated the effects of reduced physical disturbance on underwater light availability in Utah Lake, Utah, USA, using large limnocorrals that reduced exposure to wave-driven disturbance and restricted access by benthivorous fishes. Water transparency was assessed using Secchi depth during 2022–2023 and vertical profiles of photosynthetically active radiation (PAR) during 2024; the two datasets were analyzed independently. The mean Secchi depth was approximately 81% greater inside than outside the limnocorrals (39.8 vs. 22.0 cm; p < 0.001). Similarly, PAR declined to a theoretical photosynthetic threshold of 0.01 µmol photons m−2 s−1 at an estimated depth of 101 cm inside the corrals compared with 81 cm outside the corrals, representing a 25% increase in potential photosynthetic depth. Phytoplankton biovolume was not a detectable predictor of Secchi depth after accounting for treatment and month (p = 0.996), although chlorophyll a and phycocyanin were associated with PAR at shallow depths and phytoplankton became more important during late-season bloom conditions. Total suspended solids (TSSs) were associated with PAR throughout the measured depth profile but differed only slightly between treatments (72.89 vs. 75.16 mg L−1; p = 0.08). Thus, the large optical response cannot be explained by changes in bulk TSS concentration alone and may instead reflect changes in the optically active suspended-particle fraction, including preferential settling of fine, strongly scattering particles; particle-size distributions and optical properties were not directly measured. These results demonstrate that reducing physical disturbance can substantially improve underwater light conditions in a large, shallow, nutrient-rich lake. Management approaches that reduce sediment resuspension and restore benthic light availability may therefore provide a direct pathway toward ecosystem reorganization, particularly where large internal nutrient stores and atmospheric inputs limit the effectiveness of external nutrient reductions alone.