The ecological structure and function of shallow coastal lagoons is susceptible to droughts through reductions in freshwater inputs and increases to evaporation rates which increase salinity. This can reduce submerged aquatic macrophyte (SAM) distribution and abundance through osmotic stress. Wind-induced sediment resuspension can further impact SAM growth through increased light attenuation. The aim of this study was to investigate the role of wind-induced sediment resuspension on light attenuation and its implications for SAM growth in the Coorong, a shallow coastal lagoon of both regional and international importance which has been degraded by prolonged drought. Two intensive field sampling campaigns were conducted to measure wind speed and direction, wave height and period, water velocity, suspended particle concentration and water column light penetration during diel wind cycles within the shallow (~ 0.5 m) littoral mudflats over the depth range (0.2–1m) of the SAM community. Wind was the primary driver of wave and current-induced benthic shear stresses which surpassed the estimated critical shear stress of the sediment. Particles were increasingly resuspended with sustained shear stresses above estimated particle thresholds and their concentrations peaked several hours after wind and shear stress subsided, likely the result of wind-mediated transport and circulation. Suspended particles increased light attenuation, impacting SAM growth over the reproductive cycle (spring-summer) when winds are strongest. This study highlights the prolonged negative consequences of drought on shallow coastal lagoon ecosystem health.

Primary Presenter: Daniel Chilton, The University of Adelaide (daniel.chilton@adelaide.edu.au)

Authors:

Daniel Chilton, Ecology and Evolutionary Biology, the University of Adelaide  (daniel.chilton@adelaide.edu.au)

Sally Macintyre, Ecology, Evolution and Marine Biology, The University of California, Santa Barbara  ()

Christopher Keneally, Ecology and Evolutionary Biology, The University of Adelaide  ()

Robert Reid, Ecology and Evolutionary Biology, The University of Adelaide  ()

Tyler Dornan, Ecology and Evolutionary Biology, The University of Adelaide  ()

Justin Brookes, Ecology and Evolutionary Biology, The University of Adelaide  ()