Masters Theses

Date of Award

3-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental Engineering

Major Professor

R. Bruce Robinson

Committee Members

Greg D. Reed, Bruce A. Tschantz

Abstract

An evaluation is presented of the factors controlling light attention and algal production in Boone Reservoir, a eutrophic reservoir located in upper east Tennessee. The study upon which this evaluation is based was conducted by TVA during the spring and summer of 1984. The basic equation for the attenuation of light underwater is the Beer-Lambert equation which expresses light attenuation as an exponential decay function:

Iz/Io = e-Kd

where Iz = irradiance at depth z (energy/m /s)

Io = irradiance just below water surface 2 (energy/m /s)

Kd = total light attenuation coefficient for vertical downward irradiance (1/m)

z = depth (m)

To determine the influence of variance light attenuating substances (algae, sediment, dissolved color, etc.) on the transparency of Boone Reservoir, the coefficient Kd can be partitioned in terms of the light attenuating substances present. Two approaches are used to partition Kd values. The first involves linear regression of Kd and measured concentrations of chlorophyll a and algal cell populations. The second approach utilizes relationships which express apparent optical properties (e.g. Kd) as functions of the inherent scattering and absorption coefficients (a and b, respectively). Regression of values of a and b against corresponding concentrations of light attenuating substances will permit an evaluation of the fractional contribution of each substance to a and b and hence to Kd. Statistical evaluation of each partitioning method showed that the first method (direct linear regression of Kd versus chlorophyll a) provided the best results for Boone Reservoir.

The value of partitioning the coefficient Kd is that it allows a determination of which substances control the transparency of a reservoir. This will provide guidance to reservoir management strategies directed at improving the aesthetic quality of a reservoir. By partitioning the light attenuation coefficients obtained on Boone Reservoir it was shown that algae are a major factor controlling the transparency of the reservoir with the fractional light attenuation by algae generally greater than 50 percent.

The quantification of the light attenuation by algae may also be useful as an input parameter in methematical models of algal production. Plans are currently under consideration to implement tertiary nutrient removal for the municipal wastewater dischargers to Boone Reservoir as a means of reducing the eutrophic state and excessive algal growth problems. The application of algal models should provide a cost effective means of evaluating the benefits derived from reservoir management strategies such as tertiary nutrient removal before funds are invested in implementation of such strategies.

Due to the significant role of algae in light transparency reductions in Boone Reservoir and other algal related water quality problems, an evaluation was also conducted of the photosynthetic response of the reservoir algal population to light. This was done primarily in an attempt to provide the light response variables (e.g. light-saturated production rate and the irradiance at which the photosynthetic rate is maximum) for use in algal production modeling. Limited success was achieved, however, in defining these variables due to inconsistencies in field measurements of algal production. These inconsistencies may have been due to the use of depth inte grated samples in measurements of algal production.

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