On the significance of wind event frequency for particulate resuspension and light attenuation in coastal waters

Wind-induced resuspension of particulate matter was investigated in a shallow coastal region off southwestern Australia, chosen for its isolation from the complexity of other confounding physical processes. The site had negligible river discharge, low nutrient concentrations and was largely devoid of tidal currents. Moorings were deployed in the micro-tidal waters to measure current speed, wave parameters, backscatter, subsurface irradiance and dissolved oxygen concentration. Two contrasting sites were chosen as representative of high and low wave-energy environments. Turbulent kinetic energy, recorded by the instruments, was dominated by the wind-wave signal. During wind events, at the most exposed site, bed shear stress exceeded the critical stress required to lift and resuspend sediments. At the most enclosed site, bed shear stresses only exceeded the critical stress required to suspend less dense material such as benthic fluff. Wind-waves were found to be the dominant mechanism driving the vertical redistribution of particulate matter. Low frequency storm events and high frequency (daily) sea breezes were found to differ significantly in their retention of particulate matter suspended in the water column. Long periods of calm generally followed the passage of a storm, allowing suspended particulate matter to settle out, while consecutive daily sea breezes were more effective in holding particulate matter in suspension. Linear correlations were found between the backscatter (a proxy for suspended particulate matter), light attenuation and dissolved oxygen concentration. Approximately half the variability in dissolved oxygen concentration could be attributed to the variability in light attenuation, with a decline in concentration during wind resuspension events. Variability in dissolved oxygen concentration was interpreted as a possible indicator of the moderation of pelagic phytoplankton productivity during wind events.

[1]  R. W. Sheldon,et al.  The Size Distribution of Particles in the OCEAN1 , 1972 .

[2]  D. Lawrence,et al.  Wind events and benthic-pelagic coupling in a shallow subtropical bay in Florida , 2004 .

[3]  J. Jiménez,et al.  Sediment resuspension across a microtidal, low-energy inner shelf , 2002 .

[4]  R. Preisendorfer,et al.  Principal Component Analysis in Meteorology and Oceanography , 1988 .

[5]  X. D. D. Madron,et al.  Sediment dynamics during wet and dry storm events on the Têt inner shelf (SW Gulf of Lions) , 2006 .

[6]  Lars Håkanson,et al.  Suspended Particulate Matter in Lakes, Rivers, and Marine Systems , 2006 .

[7]  R. Weiss.  The solubility of nitrogen, oxygen and argon in water and seawater , 1970 .

[8]  R. Benner,et al.  Bacterial utilization of different size classes of dissolved organic matter , 1996 .

[9]  G. Masselink.  The effect of sea breeze on beach morphology, surf zone hydrodynamics and sediment resuspension , 1998 .

[10]  M. J. Howarth,et al.  Resuspension of benthic fluff by tidal currents in deep stratified waters, northern North Sea. , 2002 .

[11]  David P. Hamilton,et al.  CDOM and its contribution to the underwater light climate of a shallow, microtidal estuary in south-western Australia , 2005 .

[12]  S. Jones,et al.  Dynamics of suspended particles in coastal waters (southern North Sea) during a spring bloom , 2002 .

[13]  J. Imberger,et al.  Dynamics of the Coastal Boundary Layer off Perth, Western Australia , 2007 .

[14]  P. Puig,et al.  Near-bottom suspended sediment variability caused by storms and near-inertial internal waves on the Ebro mid continental shelf (NW Mediterranean) , 2001 .

[15]  P. Negro,et al.  Diel microbial variations at a coastal Northern Adriatic station affected by Po River outflows , 2008 .

[16]  Charitha Pattiaratchi,et al.  Seasonal changes in beach morphology along the sheltered coastline of Perth, Western Australia , 2001 .

[17]  F. Dufois,et al.  In situ record of sedimentary processes near the Rhone River mouth during winter events (Gulf of Lions, Mediterranean Sea) , 2010 .

[18]  B. Osborne,et al.  Light and Photosynthesis in Aquatic Ecosystems. , 1985 .

[19]  M. Eliot,et al.  Sea level variability in south-west Australia: from hours to decades , 2009 .

[20]  C. Cerco,et al.  Modeling underwater light climate in relation to sedimentation, resuspension, water quality and autotrophic growth , 2001, Hydrobiologia.

[21]  J. Dunn,et al.  A mixed-layer nutrient climatology of Leeuwin Current and Western Australian shelf waters: Seasonal nutrient dynamics and biomass , 2006 .

[22]  Charitha Pattiaratchi,et al.  Mixing in Estuaries and Coastal Seas , 1996 .

[23]  R. D. Evans,et al.  Empirical evidence of the importance of sediment resuspension in lakes , 1994, Hydrobiologia.

[24]  J. Lumley,et al.  A First Course in Turbulence , 1972 .

[25]  Y. Azov,et al.  Seasonal patterns of phytoplankton productivity and abundance in nearshore oligotrophic waters of the Levant Basin (Mediterranean) , 1986 .

[26]  A. Shields,et al.  Application of similarity principles and turbulence research to bed-load movement , 1936 .

[27]  A. L. New,et al.  Factors affecting the quality of shipboard acoustic Doppler current profiler data , 1992 .

[28]  F. Fisher,et al.  Sound absorption in sea water , 1977 .

[29]  W. D. Wilson.  Equation for the Speed of Sound in Sea Water , 1960 .

[30]  G. G. Stokes.  On the Effect of the Internal Friction of Fluids on the Motion of Pendulums , 2009 .

[31]  Steven E. Lohrenz,et al.  Physical-Biological Coupling in Southern Lake Michigan: Influence of Episodic Sediment Resuspension on Phytoplankton , 2003, Aquatic Ecology.

[32]  X. D. D. Madron,et al.  Fine-grained sediment dynamics during a strong storm event in the inner-shelf of the Gulf of Lion (NW Mediterranean) , 2005 .

[33]  Peter D. Thorne,et al.  Comparison between ADCP and transmissometer measurements of suspended sediment concentration , 1999 .

[34]  T. Hellström,et al.  Redistribution of sediments in three Swedish lakes , 1990, Hydrobiologia.

[35]  S. Jones,et al.  Observation and modelling of the dynamics of benthic fluff resuspended from a sandy bed in the southern North Sea , 1998 .

[36]  C. Wentworth.  A Scale of Grade and Class Terms for Clastic Sediments , 1922, The Journal of Geology.

[37]  William L. Smith,et al.  A parameterization of ocean surface albedo , 2004 .

[38]  John Gould,et al.  Impact of sea-breeze activity on nearshore and foreshore processes in southwestern Australia , 1997 .

[39]  O. Madsen,et al.  Combined wave and current interaction with a rough bottom , 1979 .

[40]  J. Carleton,et al.  Pelagic production and respiration in the Gulf of Papua during May 2004 , 2007 .

[41]  K. Deines,et al.  Backscatter estimation using Broadband acoustic Doppler current profilers , 1999, Proceedings of the IEEE Sixth Working Conference on Current Measurement (Cat. No.99CH36331).

[42]  A. Sánchez-Arcilla,et al.  Near-bottom suspended sediment fluxes on the microtidal low-energy Ebro continental shelf (NW Mediterranean) , 2002 .

[43]  L. Håkanson,et al.  Suspended particulate matter (SPM) in the baltic Sea-New empirical data and models , 2005 .

[44]  Pd Craig,et al.  Wind-driven circulation of Cockburn Sound , 1983 .