- Author : Stephen Wayne Andrews
- Publisher :
- Release : 2010
- ISBN : 9781124508290
- Pages : pages
Measurement and Interpretation of Light Scattering by Suspended Particulates in an Oligotrophic Lake
Download or read book Measurement and Interpretation of Light Scattering by Suspended Particulates in an Oligotrophic Lake written by Stephen Wayne Andrews and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The accurate characterization of fine suspended particles is central to a wide range of limnological research areas, including microbial ecosystem function and dynamics, underwater light propagation, nutrient cycling, and drinking water quality. The goal of this work was to develop methods to measure and characterize suspended particles in the oligotrophic Lake Tahoe, California-Nevada, where light scattering by particulates is the dominant process controlling lake clarity. Suspended particle populations were characterized using an in situ laser diffraction particle size analyzer--the LISST 100X. A set of laboratory tests was first performed to assess the accuracy of the LISST over a wide variety of environmental particle shapes and compositions. Processing techniques based on Mie theory were developed which enabled the LISST to produce accurate size distributions on the majority of the samples tested. Analysis of field data showed the LISST to be highly sensitive to ambient sunlight, causing erroneous spikes in small particle concentrations at high light levels. Techniques were developed to post-process the data and remove light contamination based on independently measured or modeled light intensities. These data processing techniques were employed to examine the composition of particulates in Lake Tahoe. Measured ratios of backscatter by particles to total particle scattering were used to estimate the bulk index of refraction, a proxy for particle composition. Sampling was performed during four periods relevant to the seasonal clarity cycle. Scattering ratios on all sampling days were found to be consistent with dominance by particles of predominantly organic composition. Consequently, the late spring minimum in Lake Tahoe clarity was shown to be likely due to phytoplankton growth stimulated by streamborne nutrients. Phytoplankton communities in the summer period of intense lake stratification were found to exhibit photoacclimation, the process by which algal cells adapt to lower light deeper in the water column by increasing their cellular chlorophyll concentration. These findings suggest a greater role of organic particles in impacting lake transparency than was previously thought, and have implications for lake clarity management.