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Physical Processes in the Littoral Z...

Roberts, Derek Charles.

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Physical Processes in the Littoral Zone of a Large Lake and the Implications for Water Quality.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Physical Processes in the Littoral Zone of a Large Lake and the Implications for Water Quality./
Author:	Roberts, Derek Charles.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2019,
Description:	195 p.
Notes:	Source: Dissertations Abstracts International, Volume: 81-04, Section: B.
Contained By:	Dissertations Abstracts International81-04B.
Subject:	Environmental engineering. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13809292
ISBN:	9781085795166

Physical Processes in the Littoral Zone of a Large Lake and the Implications for Water Quality.
Roberts, Derek Charles.

Physical Processes in the Littoral Zone of a Large Lake and the Implications for Water Quality. - Ann Arbor : ProQuest Dissertations & Theses, 2019 - 195 p.

Source: Dissertations Abstracts International, Volume: 81-04, Section: B.

Thesis (Ph.D.)--University of California, Davis, 2019.

This item must not be sold to any third party vendors.

The littoral zone of large lakes is home to some of the greatest concentrations of freshwater biodiversity and represents the area of contact between the lakes and human activity. Despite the importance of this nearshore area, it is poorly understood, due, in part, to the diversity of superimposed processes governing water quality and ecosystem function in this highly complex and spatio-temporally variable area. This dissertation quantifies the role of several in-lake, physical processes in driving nearshore water quality variability in Lake Tahoe, CA/NV, including wind waves, upwelling, surface seiches, and inflow mixing dynamics. Given the unique characteristics of each lake's shoreline, there is no fully generalizable understanding of lake littoral zones; this dissertation may best serve as an example of the roles of various physical processes in the nearshore of one lake and of some approaches for quantifying their impacts in many lakes.Wind waves are shown to be the primary driver of elevated turbidity in the nearshore of Lake Tahoe. Two years of turbidity data collected at five littoral sites show that elevated nearshore turbidity is reasonably predicted by preceding wind speed and direction, and that these patterns are well delineated by a model-predicted threshold for sediment resuspension. Application of this model shows that nearshore sediment resuspension is more prevalent in the fall and winter months (October - March) and on the prevailing downwind north and east shores. These patterns vary interannually due to shifts in both the direction and magnitude of the prevailing winds. The dynamics of spring upwelling events are detailed using an array of temperature, current, and water quality measurements. Observations show that large magnitude upwelling (~80 m) may advect nitrate into the nearshore, but that these concentrations appear to downwell to depth prior to the arrival of post-upwelling internal wave fronts that would potentially dilute these concentrations, depositing a residual nutrient load in the littoral zone. Resonant, basin-scale surface oscillation modes are characterized using a finite-element numerical model and a spatially distributed set of high-frequency pressure measurements. The magnitude of these surface seiche oscillations is greatest on shallow shelves (on the order of 5 cm). Main-basin seiche modes are expressed in peripherally attached water bodies (marinas, wetlands, bays), implying the presence of a reversing flow at the mouths of these semi-enclosed areas. This reversing flow is directly quantified at the mouth of Emerald Bay, where low-magnitude surface oscillations play a major role in cross-sill flows. The impact of watershed loads is not directly quantified. However, a relationship between winter climate conditions and in-lake inflow mixing dynamics is established. Winters with lower snowpack are shown to lead to an increased proportion of annual inflows entering the lake at neutral to positive buoyancy, favoring nearshore and near-surface mixing of associated loads. Given trends toward warmer winters in the Tahoe basin, this trend should be considered in any appraisal of future nearshore conditions at Lake Tahoe. The chapters of this dissertation serve as building blocks toward a better understanding of lake littoral zones and, in particular, Lake Tahoe's nearshore area. Extended investigations of the processes described above are suggested in the conclusions section of this dissertation; the availability of data to support these investigations, collected as part of this dissertation, is also described.

ISBN: 9781085795166Subjects--Topical Terms:

548583
Environmental engineering.

Physical Processes in the Littoral Zone of a Large Lake and the Implications for Water Quality.
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245 1 0 $a Physical Processes in the Littoral Zone of a Large Lake and the Implications for Water Quality.
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300 $a 195 p.
500 $a Source: Dissertations Abstracts International, Volume: 81-04, Section: B.
500 $a Advisor: Schladow, Geoffrey.
502 $a Thesis (Ph.D.)--University of California, Davis, 2019.
506 $a This item must not be sold to any third party vendors.
520 $a The littoral zone of large lakes is home to some of the greatest concentrations of freshwater biodiversity and represents the area of contact between the lakes and human activity. Despite the importance of this nearshore area, it is poorly understood, due, in part, to the diversity of superimposed processes governing water quality and ecosystem function in this highly complex and spatio-temporally variable area. This dissertation quantifies the role of several in-lake, physical processes in driving nearshore water quality variability in Lake Tahoe, CA/NV, including wind waves, upwelling, surface seiches, and inflow mixing dynamics. Given the unique characteristics of each lake's shoreline, there is no fully generalizable understanding of lake littoral zones; this dissertation may best serve as an example of the roles of various physical processes in the nearshore of one lake and of some approaches for quantifying their impacts in many lakes.Wind waves are shown to be the primary driver of elevated turbidity in the nearshore of Lake Tahoe. Two years of turbidity data collected at five littoral sites show that elevated nearshore turbidity is reasonably predicted by preceding wind speed and direction, and that these patterns are well delineated by a model-predicted threshold for sediment resuspension. Application of this model shows that nearshore sediment resuspension is more prevalent in the fall and winter months (October - March) and on the prevailing downwind north and east shores. These patterns vary interannually due to shifts in both the direction and magnitude of the prevailing winds. The dynamics of spring upwelling events are detailed using an array of temperature, current, and water quality measurements. Observations show that large magnitude upwelling (~80 m) may advect nitrate into the nearshore, but that these concentrations appear to downwell to depth prior to the arrival of post-upwelling internal wave fronts that would potentially dilute these concentrations, depositing a residual nutrient load in the littoral zone. Resonant, basin-scale surface oscillation modes are characterized using a finite-element numerical model and a spatially distributed set of high-frequency pressure measurements. The magnitude of these surface seiche oscillations is greatest on shallow shelves (on the order of 5 cm). Main-basin seiche modes are expressed in peripherally attached water bodies (marinas, wetlands, bays), implying the presence of a reversing flow at the mouths of these semi-enclosed areas. This reversing flow is directly quantified at the mouth of Emerald Bay, where low-magnitude surface oscillations play a major role in cross-sill flows. The impact of watershed loads is not directly quantified. However, a relationship between winter climate conditions and in-lake inflow mixing dynamics is established. Winters with lower snowpack are shown to lead to an increased proportion of annual inflows entering the lake at neutral to positive buoyancy, favoring nearshore and near-surface mixing of associated loads. Given trends toward warmer winters in the Tahoe basin, this trend should be considered in any appraisal of future nearshore conditions at Lake Tahoe. The chapters of this dissertation serve as building blocks toward a better understanding of lake littoral zones and, in particular, Lake Tahoe's nearshore area. Extended investigations of the processes described above are suggested in the conclusions section of this dissertation; the availability of data to support these investigations, collected as part of this dissertation, is also described.
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