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Environmental Setting and the Effects of Natural and Human-Related Factors on Water Quality and Aquatic Biota, Oahu, Hawaii

U.S. Geological Survey Water-Resources Investigatons Report 03-4156

Prepared in cooperation with the

National Water-Quality Assessment Program

By Delwyn S. Oki and Anne M.D. Brasher

Download the accessible pdf file at wri03-4156.pdf (12,558Kb pdf file). Download Acrobat reader for free


Abstract

The island of Oahu is the third largest island of the State of Hawaii, and is formed by the eroded remnants of the Waianae and Koolau shield volcanoes. The landscape of Oahu ranges from a broad coastal plain to steep interior mountains. Rainfall is greatest in the mountainous interior parts of the island, and lowest near the southwestern coastal areas.

The structure and form of the two volcanoes in conjunction with processes that have modified the original surfaces of the volcanoes control the hydrologic setting. The rift zones of the volcanoes contain dikes that tend to impede the flow of ground water, leading to high ground-water levels in the dike-impounded ground-water system. In the windward (northeastern) part of the island, dike-impounded ground-water levels may reach the land surface in stream valleys, resulting in ground-water discharge to streams. Where dikes are not present, the volcanic rocks are highly permeable, and a lens of freshwater overlies a brackish-water transition zone separating the freshwater from saltwater. Ground water discharges to coastal springs and streams where the water table in the freshwater-lens system intersects the land surface.

The Waianae and Koolau Ranges have been deeply dissected by numerous streams. Streams originate in the mountainous interior areas and terminate at the coast. Some streams flow perennially throughout their entire course, others flow perennially over parts of their course, and the remaining streams flow during only parts of the year throughout their entire course.

Hawaiian streams have relatively few native species compared to continental streams. Widespread diverse orders of insects are absent from the native biota, and there are only five native fish, two native shrimp, and a few native snails. The native fish and crustaceans of Hawaii's freshwater systems are all amphidromous (adult lives are spent in streams, and larval periods as marine or estuarine zooplankton).

During the 20th century, land-use patterns on Oahu reflected increases in population and decreases in large-scale agricultural operations over time. The last two remaining sugarcane plantations on Oahu closed in the mid-1990's, and much of the land that once was used for sugarcane now is urbanized or used for diversified agriculture. Although two large pineapple plantations continue to operate in central Oahu, some of the land previously used for pineapple cultivation has been urbanized.

Natural and human-related factors control surface- and ground-water quality and the distribution and abundance of aquatic biota on Oahu. Natural factors that may affect water quality include geology, soils, vegetation, rainfall, ocean-water quality, and air quality. Human-related factors associated with urban and agricultural land uses also may affect water quality. Ground-water withdrawals may cause saltwater intrusion. Pesticides and fertilizers that were used in agricultural or urban areas have been detected in surface and ground water on Oahu. In addition, other organic compounds associated with urban uses of chemicals have been detected in surface and ground water on Oahu.

The effects of urbanization and agricultural practices on instream and riparian areas in conjunction with a proliferation of nonnative fish and crustaceans have resulted in a paucity of native freshwater macrofauna on Oahu. A variety of pesticides, nutrients, and metals are associated with urban and agricultural land uses, and these constituents can affect the fish and invertebrates that live in the streams.

CONTENTS

Abstract

Introduction

Purpose and Scope

Environmental Setting

Physical Setting

Climate

Temperature

Rainfall

Solar Radiation

Pan Evaporation

Geologic Setting

Waianae Volcano

Koolau Volcano

Geochemistry of the Volcanic Rocks

Geologic Modification Processes

Subsidence

Weathering and Erosion

Deposition

Hydraulic Conductivity of the Rocks

Soils

Surface Water

Drainage-Basin Characteristics

Streamflow Characteristics

Ground Water

Freshwater-Lens Systems

Dike-Impounded Systems

Perched Systems

Ground-Water Areas

Interaction of Ground Water and Surface Water

Aquatic Biota

Land Use

Zoned Land Districts

Mapped Land Use

Agriculture

Sugarcane

Pineapples

Other Row Crops and Orchards (Diversified Agriculture)

Horticulture and Shade Houses

Livestock Operations

Developed (Nonagricultural) Land

Residential Areas

Commercial and Industrial Areas

Social Services

Public Infrastructure

Open Space

Water Use

Ground Water

Surface Water

Recent Trends in Water Use

Effects of Natural and Human-Related Factors on Water Quality and Aquatic Biota

Rainfall

Surface Water

Natural Factors

Urban-Related Factors

Agriculture-Related Factors

Ground Water

Natural Factors

Urban-Related Factors

Agriculture-Related Factors

Aquatic Biota

Summary and Conclusions

References Cited

Citation: Oki, D.S., and Brasher, A.M.D., 2003, Environmental Setting and the Effects of Natural and Human-Related Factors on Water Quality and Aquatic Biota, Oahu, Hawaii: U.S. Geological Survey Water-Resources Investigations Report 03-4156, 98 p.




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