Tropical Stream Ecology

David Dudgeon

• Publisher: Academic Press
• Year: 2011
• eBook ISBN: 9780080557175
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

Tropical Stream Ecology describes the main features of tropical streams and their ecology. It covers the major physico-chemical features, important processes such as primary production and organic-matter transformation, as well as the main groups of consumers: invertebrates, fishes and other vertebrates. Information on concepts and paradigms developed in north-temperate latitudes and how they do not match the reality of ecosystems further south is expertly addressed. The pressing matter of conservation of tropical streams and their biodiversity is included in almost every chapter, with a final chapter providing a synthesis on conservation issues. For the first time, Tropical Stream Ecology places an important emphasis on viewing research carried out in contributions from international literature.- First synthetic account of the ecology of all types of tropical streams- Covers all of the major tropical regions- Detailed consideration of possible fundamental differences between tropical and temperate stream ecosystems- Threats faced by tropical stream ecosystems and possible conservation actions- Descriptions and synstheses life-histories and breeding patterns of major aquatic consumers (fishes, invertebrates)

1

Physical and Chemical Features of Tropical Flowing Waters

William M. Lewis, Jr.

Publisher Summary

This chapter discusses the physical and chemical features of tropical flowing waters. Tropical flowing waters typically show well-defined seasonality in depth and velocity of flow, water chemistry, and metabolic rates, but seasonality is based primarily on hydrology alone rather than hydrology in conjunction with temperature, as would be more typical of temperate latitudes. Because of high mean water temperature, the oxygen reserve at saturation is substantially lower for tropical waters at low elevations than for temperate waters averaged over the growing season. Dissolved forms of phosphorus and nitrogen in tropical streams and rivers are present in quantities sufficient to support moderate to high biomass of autotrophs even under pristine conditions. The main significance of temperature for flowing waters is through its effect on metabolism and the capacity of water to hold dissolved oxygen. Tropical flowing waters as a whole have a lower oxygen reserve and a higher potential oxygen demand for a given amount of organic loading than temperate waters, except when temperate waters briefly reach the height of summer warmth. Factors affecting both suspended and dissolved load and concentration include slope, annual precipitation, lithology, disturbance, and natural or anthropogenic impoundment. Tropical flowing waters in some ways differ as a group from their counterparts at higher latitudes, but in other respects latitudinal differences are weak or nil. Tropical streams and rivers are stable thermally but should show seasonality driven by hydrology.

Chapter Outline

I Introduction

II Climatic Organizing Principles

III Temperature

IV Precipitation

V Runoff

VI Suspended and Dissolved Solids

VII Phosphorus, Nitrogen, and Carbon

VIII Conclusions

References

Tropical latitudes offer an abundance of well watered landscapes because the Hadley circulation favors heavy seasonal rainfall, particularly within the migration area of the Intertropical Convergence Zone. Hydrographic seasonality typifies tropical streams and rivers, and to a large extent is predictable on the basis of latitude within the tropics. Because thunderstorms play an important role in the delivery of precipitation, hydrographs for small streams often show numerous intra-annual spikes in discharge, but these patterns are obscured through hydrographic averaging at the regional scale. Tropical flowing waters typically show well-defined seasonality in depth and velocity of flow, water chemistry, and metabolic rates, but seasonality is based primarily on hydrology alone rather than hydrology in conjunction with temperature, as would be more typical of temperate latitudes.

Total annual irradiance at tropical latitudes does not differ greatly from that of latitudes as high as 40° because of the high moisture content of tropical air. Because of high mean water temperature, the oxygen reserve at saturation is substantially lower for tropical waters at low elevations than for temperate waters averaged over the growing season. Metabolic rates of rivers within the tropics are affected by thermal variation related to elevation and percent moisture in the atmosphere.

Topography is the dominant control on suspended and dissolved solids of tropical streams and rivers. Concentrations of dissolved solids range from a few mg L⁻¹ in wet areas of low gradient and resistant lithology to 1000 mg L⁻¹ or more on high gradients with readily eroded lithologies, especially in the presence of disturbance. Seasonality in discharge is accompanied by seasonality in concentrations of dissolved and suspended solids, organic matter, and nutrients; seasonal ranges in concentration often reach an order of magnitude.

Dissolved forms of phosphorus and nitrogen in tropical streams and rivers are present in quantities sufficient to support moderate to high biomass of autotrophs even under pristine conditions. Concentrations of phosphorus (P), nitrogen (N), and dissolved organic carbon (DOC) show no obvious categorical contrast with those of higher latitude at similar elevations, but mechanisms for the delivery of P, N, and DOC from tropical watersheds to streams and rivers, and their subsequent processing within the aquatic environment, may differ in important ways that are not yet well understood.

I. INTRODUCTION

Generalizations about tropical streams and rivers are most easily approached through the influences of climate. A climatic perspective on tropical flowing waters also establishes a useful framework for comparisons between tropical waters and more familiar temperate waters and highlights the differences that are related to latitude by way of climate. Therefore, this chapter begins with an overview of tropical climatology and follows the climatic connections through hydrology and water temperature. Next is a presentation of water chemistry with a focus on suspended and dissolved solids as well as P, N, and C, which sets the stage for later chapters that deal with ecosystem functions and biotic communities.

Tropical climatology is a subject for books rather than chapters. Only a sketch of tropical climates can be given here, but a substantial narrowing of scope is justified by special re...

Table of contents

• Cover image
• Title page
• Table of Contents
• Contributors
• Preface
• Chapter 1: Physical and Chemical Features of Tropical Flowing Waters
• Chapter 2: Primary Production in Tropical Streams and Rivers
• Chapter 3: Organic Matter Processing in Tropical Streams
• Chapter 4: Macroinvertebrates: Composition, Life Histories and Production
• Chapter 5: Fish Ecology in Tropical Streams
• Chapter 6: Aquatic, Semi-Aquatic and Riparian Vertebrates
• Chapter 7: Riparian Wetlands of Tropical Streams
• Chapter 8: Tropical High-Altitude Streams
• Chapter 9: Are Tropical Streams Ecologically Different from Temperate Streams?
• Chapter 10: Tropical Stream Conservation
• Index