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In cooperation with the City of Houston

Light Attenuation in a Shallow, Turbid Reservoir, Lake Houston, Texas

By Roger W. Lee and Walter Rast

U.S. Geological Survey
Water-Resources Investigations Report 97–4064


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Contents

Abstract

Introduction

Characteristics of Light Attenuation in Surface Waterbodies

Effects of Constituents Contributing to Light Attenuation on Surface Waterbodies

Reservoirs and Natural Lakes

Study Area

Climate

Characteristics of Lake Houston

Land Use in the Drainage Basin

Light Attenuation in a Shallow, Turbid Reservoir

Site Selection and Data Collection

Light-Extinction Coefficients

Secchi Depth

Water-Quality Constituents Affecting Light Attenuation

Total Suspended Solids

Total Organic Carbon

Chlorophyll a+b

Color

Turbidity

Nutrients

Dissolved Phosphorus

Dissolved Nitrogen

Relation of Relevant Water-Quality Constituents to Light Attenuation

Water-Quality Constituents Contributing to Light Attenuation

Water-Quality Data Significant to Light Attenuation

Multiple-Regression Analysis

Conclusions

References

Figures

1.   Diagram showing Kimmel and Groeger model of reservoir gradients
2.   Map showing study area and locations of water-quality sampling sites on Lake Houston
3.   Graphs showing relation of light-extinction coefficients to sampling date for water at six sites in Lake Houston, 1989–90
4.   Boxplots showing distribution of light-extinction coefficients for water at six sites in Lake Houston, 1989–90
5.   Boxplots showing distribution of Secchi-depth transparency for water at six sites in Lake Houston, 1989–90
6.   Graph showing relation of light-extinction coefficients to computed depths of light penetration and Secchi-depth transparency for water at six sites in Lake Houston, 1989–90
7.   Graphs showing relation of total suspended solids to sampling date for water at six sites in Lake Houston, 1989–90
8.   Boxplots showing distribution of total suspended solids for water at six sites in Lake Houston, 1989–90
9.   Graphs showing relation of total organic carbon to sampling date for water at six sites in Lake Houston, 1989–90
10.   Boxplots showing distribution of total organic carbon for water at six sites in Lake Houston, 1989–90
11.   Graphs showing relation of chlorophyll a+b to sampling date for water at six sites in Lake Houston, 1989–90
12.   Boxplots showing distribution of chlorophyll a+b for water at six sites in Lake Houston, 1989–90
13.   Graphs showing relation of color to sampling date for water at six sites in Lake Houston, 1989–90
14.   Boxplots showing distribution of color for water at six sites in Lake Houston, 1989–90
15.   Graphs showing relation of turbidity to sampling date for water at six sites in Lake Houston, 1989–90
16–18.   Boxplots showing distribution of:
  16.   Turbidity for water at six sites in Lake Houston, 1989–90
  17.   Dissolved phosphorus for water at six sites in Lake Houston, 1989–90
  18.   Dissolved nitrogen for water at six sites in Lake Houston, 1989–90
19–21.   Graphs showing:
  19.   Relation of predicted light-extinction coefficients from water-quality data to measured light-extinction coefficients for water at six sites in Lake Houston, 1989–90
  20.   Spearman rank order correlation coefficients for the relation of light-extinction coefficients to total suspended solids, inorganic suspended solids, volatile suspended solids, chlorophyll a+b, total organic carbon, turbidity, color, and Secchi-depth transparency for water at six sites in Lake Houston, 1989–90
  21.   Relation of light-extinction coefficients to color and turbidity for water at six sites in Lake Houston, 1989–90

Tables

1.   Geometric means of selected characteristics of natural lakes and reservoirs in the United States
2.   Water-quality constituents and physical properties in water from Lake Houston, 1989–90
3.   Spearman rank order correlation coefficients for light-extinction coefficients in relation to water-quality constituents and physical properties in water from Lake Houston, 1989–90

Abstract

Results of measurements of light penetration at sites in Lake Houston near Houston, Texas, indicate that light-extinction coefficients during 1989–90 range from about 2.49 to 7.93 meters-1 and euphotic zone depth ranges from about 0.61 to 1.85 meters. The coefficients are largest near the inflow site of West Fork San Jacinto River (upstream) and decrease slightly toward the dam (downstream). Total suspended solids and total organic carbon concentrations also are largest at the upstream end. Chlorophyll a+b concentrations are smallest near the dam, increase slightly upstream, and are largest during growing-season months. Color and turbidity show the strongest correlations with light-extinction coefficients in Lake Houston. Dissolved phosphorus and nitrogen concentrations are greater than growth-limiting concentrations during the study period, indicating that nutrient availability did not limit primary productivity or the phytoplankton biomass in Lake Houston.

Light-extinction coefficients in relation to selected water-quality constituents indicate that more than one constituent affects the light-attenuating properties of Lake Houston. Attenuation of light in water depends on total suspended solids for predominant light scattering and on dissolved organic matter (color) and chlorophyll a+b for absorption of light.

A statistical analytical model using Spearman rank order correlation shows that color and turbidity are the most useful water-quality constituents sampled to determine light-attenuating properties of water in Lake Houston. Multiple-regression analysis of measured light-extinction coefficients as the dependent variable and measured color and turbidity as independent variables for water from Lake Houston produced the relation:

light-extinction coefficient (h) = 2.78 + 0.007 x color + 0.036 x turbidity,

with an average error of the computed coefficient to measured value of ±13 percent. The model can be useful in computing the thickness of the euphotic zone to determine primary productivity in the reservoir.




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