ABSTRACT

South East Asia is one of the most populated regions within the humid tropics and is fast becoming an enclave of industrial development. Geographically, it is endowed with a good source of water, due to its copious rainfall. However water resource problems often arise because of variations in distribution, timing and the small sizes of the catchments. The last few decades also witnessed the rapid deterioration of the available water due to anthropogenic activities causing pollution, reducing further the available water. Demands, on the other hand, have increased with rising urbanization and industrial development. In many countries, balancing a good water supply and demands is a major issue requiring more than environmental controls. It may require very stringent legislation to control the water sources. It is the aim of this chapter to examine some of those inherent problems so that scientists, mitigation planners and engineers can address them in their detailed resource planning.

INTRODUCTION

The humid tropics is a geographical region recognized by its climatic similarities. Quantitative definitions have been given by Chang & Lau (1983) as a region having a minimum of 4.5 wet months per year and an average minimum temperature of 18°C (See Appendix A, this volume). Vitousek & Sanford (1986) have defined it as an area lying 23° N and 23° S and receiving at least 1,600mm of annual rainfall. Within this broad region astride the equator lies an assortment of countries which could be categorized further, based either on economic status, geographical size or political alignment. The first is used by macro-economists to show the levels of development within and between regions, and will also be used in this chapter.

ABSTRACT

The paper presents the author's personal philosophy of hydrological methodology. It claims that the latter is biased toward mechanistic reductionism and an exaggerated orientation towards short-term technological solutions to water-related problems arising in the temperate climatic zone. It suggests that this bias stands out most clearly against the background of the specific natural conditions of the humid tropics. In this context, three aspects are emphasized as deserving major attention in the development of an adequate scientific basis for the hydrology of the region and for addressing its long-term environmental and water resource problems. These aspects are: 1) non- stationarity of the major geo- and biophysical/chemical processes, 2) a dynamically sound macrohydrology, and 3) quantitative eco-hydrology (i.e. the soil-vegetation-atmosphere interactions as mediated by energy and water).

A HISTORICAL PERSPECTIVE

Hydrology, as most everyone knows, is the science dealing with the dynamics of the hydrological cycle, i.e., with the circulation of water on planet Earth. Not everybody realizes, however, that this dictionary definition is more a statement of a program than a statement of fact. Hydrology has never been practised in a global water context. Such an approach has only recently been contemplated as feasible, and, indeed, as necessary. In spite of this realization, it is by no means clear how such a program can be executed or how much integration is desirable and necessary among the historically-formed autonomous sciences of oceanography, climatology, meteorology and atmospheric physics, glaciology, hydrogeology, and the hydrology of the land surface, i.e., hydrology in the narrow sense.

ABSTRACT

Over the past twenty years, economists and planners have questioned the benefits of water supply, while other health interventions have competed with the water sector for resource allocation. This has created a credibility gap which the medical profession and sanitary engineers have had difficulty in bridging. Evaluation of the health impact of water management in tropical developing countries has likewise been excessively oriented towards adverse effects, further impeding the development of the necessary resources. Despite the momentum created by the International Drinking Water Supply and Sanitation Decade, coverage of the world population with supply services is far from satisfactory. Progress can hardly keep pace with the increase in population. The majority of rural people in poor tropical countries are not served and there is little prospect of achieving universal coverage in the foreseeable future. Moreover, the generalization of cost mechanisms may shift resources from other vital sectors (nutrition, health) and so offset the benefits of a safe water supply.

Innovative approaches can overcome the professional barriers between health specialists and decision-makers. The main health benefits accrue from the availability of unlimited quantities of water, whatever its quality. Unnecessarily stringent quality standards may be counter-productive since they may reduce the quantities available, delay the supply or increase its cost. Recycling waste water is a necessity to increase the resources, and appropriate health safeguards can be developed with respect to each usage category, depending on selected application techniques.

Finally, engineering techniques and nonmedical interventions in water management can be shown as the most cost-effective measures for controlling diseases of economic importance. Examples of dracunculiasis and onchocerciasis illustrate the point.

ABSTRACT

The particular water management issues in the humid tropics arise from the hydrological features of this region (excess water, floods, greater variation of flows than in temperate zones), from the unique potential for hydro-power generation and from the traditional emphasis on growing irrigated rice. The central cause of water management problems is the rapid population growth with its increasing demand for water, food and energy, resulting in increasing pollution, and environmental and social problems. The capacity to deal with these problems is constrained by the limited availability of human and financial resources. Organizations at various levels, national and international, have been created to deal with the numerous issues, but the situation is far from satisfactory. Policy-makers and managers in the water sector should give special attention to the issues of institutional and water-sharing arrangements and make determined efforts to adopt modern tools and procedures to improve water development planning and implementation.

INTRODUCTION

Water utilization is on the increase as a result of rapid population growth. As rivers and lakes become more and more polluted, clean water becomes scarce; as public awareness of clean water dependency intensifies, so does the demand for efforts to protect this resource. But there is a disparity between official policies and plans for water resource utilization, and the actual implementation efforts, as is the case for resources in general. In view of these broad issues, there is a need to determine realistic water development policies for efficient, integrated and environmentally sound water resource utilization.

It is widely recognized that water is going to be one of the major issues confronting humanity at the turn of the century and beyond. We are already facing a crisis as regards the quantity and quality of water supply, but we have yet to experience the full social and political impact of that crisis. Water is the life-blood of living organisms, and a very potent factor in human behaviour. Where plentiful, water is accepted unreflectively as a gift of nature. But when scarcity makes it a precious commodity, it can become a source of dispute and even conflict between its users. We know that civilization has always been crucially dependent on water. It is essential to remember that the converse is also true: vital water resources depend upon civilization, or more precisely on the “civilized” use of a finite and vulnerable resource. Culture and tradition are therefore important dimensions to be taken into account in water conservation.

The interdependence of water and civilization highlights the need for close co-operation among all players in the water game, extending from the local through the regional right up to the global level. At the international level, one of the most important needs is for co-ordinated efforts to understand the processes occurring in the water cycle, to assess surface and ground water resources, and to promote attitudes conducive to maintaining the quality and quantity of water resources for generations to come. Recognition of the importance of these objectives led to the launching of the International Hydrological Decade (IHD) in 1964, the first truly international scientific and educational effort ever made in hydrology.

ABSTRACT

This paper reviews the current hydrological and water resources knowledge in Africa and some of the associated problems of the humid tropical region of Africa

Data availability and accuracy are identified as major constraints. Estimates of water resources vary widely. Knowledge about the lakes in the region is inadequate, apart from information on their physical characteristics. A generalized knowledge about the sediment yield for the African region has been put forward recently but is only tentative because of the data constraint. Subregional and regional syntheses are needed on water quality, droughts and low flows. Such a synthesis is available for groundwater, but needs updating with the large amount of data that has been made possible through the International Drinking Water Supply and Sanitation Decade. The impact of land degradation and climate variation on the hydrology and water resources of the region is an area of study that also needs urgent attention.

PHYSIOGRAPHY

Location

The location of the humid tropic region is the low-lying areas within the two tropics of Cancer and Capricorn – basically as defined by Chang and Lau (this volume). Figure 1 shows the African regional coverage which generally lies between latitudes 15°N and 20°S. The region is bounded on the west by the Atlantic Ocean, on the east by the Indian Ocean, on the north by the Sudano-Sahelian belt and Sahara Desert and on the south by the Kalahari Desert.

ABSTRACT

The characteristics and general ecology of tropical fresh waters are outlined, with reference to the physical and chemical regulation of aquatic environments and the differentiation and dynamics of their communities.

Solar radiation income is the most distinctive and driving variable which leads to relatively high and seasonally-maintained temperatures, with relatively small differentials with depth. This thermally controlled density stratification is sensitive to changes in the energy balance and wind stress, which, in turn, controls chemical and biological stratification. Indefinitely prolonged stratification is common in very deep lakes, and well developed seasonal cycles are frequent, even in equatorial water bodies.

The primary chemical inputs are dominated by rock weathering and atmospheric gaseous exchange, although numerous secondary pathways and controls exist. Dissolved constituents are separable into major, minor and trace elements; gases; and organic compounds. The total ionic content varies widely, but is generally low in the humid tropics. Important interactions between gaseous (CO2) and ionic constituents occur via the CO2/HCO3-/CO32- system, with implications for pH buffering, Ca2+ removal as CaCO3, P removal as apatite, and the biological supply of CO2. Inorganic forms of the nutrient elements N, P and Si are subject to biological depletion; in tropical regions low concentrations of nitrate and high ones of dissolved Si are prevalent. Anoxia is associated with accumulations of the chemically reduced gases CH4, H2S and NH3 with their derivatives, both in very deep and very shallow (swamp) waters. “Black water” rivers carry high concentrations of organic material. The relationship of concentration with river flow rate varies with different chemical constituents, as do upstream-downstream relationships.

Principles of reclaiming degraded land

There are large areas of land in the UK which have been rendered derelict by a variety of industrial activities. Dereliction from industrial processes in the UK commenced centuries ago but the rate of dereliction accelerated from the time of the Industrial Revolution (about 1750) onwards. We have a legacy of scarred landscapes resulting from industrial operations, for example wastes from coal mining, the iron and steel industries, and the mining and smelting of non-ferrous metals; toxic wastes from chemical industries; and the quarrying and digging of pits for the extraction of sand, gravel, brick- and china-clay and roadstone. The damage caused by new industries is much more closely regulated, but it was still possible to estimate that the rate of production of derelict land in Britain in 1980 was 1200–1600 hectares per year (Bradshaw and Chadwick (1980)). This figure is matched in some years by the rate of reclamation. Department of the Environment figures for 1982 indicated that over 117000 hectares of land remained derelict in England, Wales and Scotland.

The dereliction caused by different industries creates different problems for those given the task of repairing the damage, but there are some over-riding principles.

Levels of human impact on ecosystems

Before considering the needs for conservation and how ecosystems can be utilised to our long-term advantage, it is necessary to evaluate the impact that people have on ecosystems.

The level of impact on ecosystems should be viewed in relation to the landscape or habitat type that is being affected. A hierarchy of landscape and vegetation types against which impacts could be judged, described in 1971 by V. Westhoff in ‘Dynamic structures of plant communities’ (In Duffey, E. & Watts, A. S. (eds.) Scientific management of plant and animal communities for conservation, Blackwell Scientific), takes into account the degree of intervention in ecosystem processes and the consequences of that intervention on the structure (formation and physiognomy) of the plant communities. They are:

1. 1 Natural landscape

2. The flora and fauna are uninfluenced by people. (Westhoff suggests that this type no longer occurs in western and central Europe.)

3. 2 Subnatural landscape

4. The flora and fauna are similar to the potential natural vegetation in species composition and structure (and hence appearance), but the influence of people can be measured.

5. 3 Semi-natural landscape

6. The plant communities are to a large extent indigenous but the vegetation type has been essentially changed by human activity. The plant communities present a different structure and appearance to the expected natural vegetation. Examples of this in the UK are unimproved grasslands, heathlands and moorlands, which would all be expected to develop into woodland if not managed in some way.

7. […]

Phenomenon of desertification

Deserts are dry areas with few plants and can be conveniently separated from other vegetation types on the basis of rainfall and temperature. They are found where mean annual rainfall is below about 50 mm and mean annual temperature is above 15 °C. The term desertification was used initially (1949) in reference to the increasing extension of deserts into semi-arid lands. In the 1980s and 1990s, authorities have begun to question the extent or even existence of the desertification problem. The term desertification may imply a ‘once and for all’ process on a massive scale, but what seems to happen on the ground (in areas where desertification appears to be occurring) is the development of areas of land degradation, in some cases quite severe, but which with care and two or three good rainy seasons might return to their former status.

Here is the suggestion, discussed by J. A. Binns in ‘Is desertification a myth?’ (Geography 75:106–13 (1990)), that the phenomenon is linked with lack of rainfall (i.e. drought) and land utilisation of a kind that damages the environment. Perhaps the critical point, which is rarely stressed, is that the degradation (desertification) occurs in areas where rainfall is usually sufficient to support at least a sparse vegetation cover.

The ‘approximate desert boundaries’ in the Sudan (see figure 4.1) suggest the desert in Sudan moved south by about 120 km between 1958 and 1975.

This chapter is directed at ecosystem management on a local (in particular the UK) rather than a global scale. There has been considerable development in the understanding of ecosystem structure and functioning over the last few decades, particularly in the field of vegetation change. In many ecosystems and habitat types it is possible to be reasonably confident about the consequences of management interventions, thus achieving the objectives of management aims. There are a number of important principles which emerge from the problems that face environmental managers.

Problems of ecosystem management

Ecosystems are in a constant state of flux, but the degree to which and the speed with which changes occur relate to the ecosystem's successional stage. Succession is a more or less predictable change in vegetation type. In most of the UK it progresses from bare soil, through annual and biennial weed and grassland communities, to low and then tall scrub. Tall scrub then gives way to pioneer woodland species (e.g. birch (Betula spp.), ash (Fraxinus excelsior), pine (Pinus spp.) and alder (Alnus glutinosa)), but the exact nature varies according to environmental factors such as soil and climate. Finally the pioneer canopy species are replaced by tall oak (Quercus spp.) forest, the so-called climax type. The stable vegetation types found in fully developed ecosystems (the climax stage) change relatively little apart from local variations arising from death and replacement of their constituents.

This book is intended to be used in schools but would also serve as an introductory text for those interested in the environment in which we live. Much of the material is derived from lecture courses that I give to undergraduates at Worcester College of Higher Education.

The book examines environmental problems of the present day from the perspective of an ecologist concerned with impacts of human activities on the integrity of ecosystem function, energy flow and nutrient cycling. Global and local issues receive consideration and the impact of land-use changes, forestry operations and human pressures on semi-arid regions are assessed. The exploitation, conservation and management of biological systems forms a significant part of the second half of the book. The concluding chapter explores the principles and practice of reclaiming derelict land.

I am aware that it is not possible to be an expert on all the subjects covered in this text. I have depended very much, therefore, on the work of others and I am, accordingly, grateful for their painstaking research and hard work. I hope that, in selecting the material and distilling it into this form, I have not been guilty of misrepresentation or error. Furthermore, I hope that I will be forgiven if I have inadvertently cast my words in a form close to that of others.

I would like to thank Alan Cornwell and Cambridge University Press for the invitation to write this book and assisting me in its production.

Biogeochemical cycles

To understand the significance of some of the factors which cause environmental concerns, particularly on a global scale, it is necessary to understand biogeochemical cycles. Biogeochemical cycles are models of the position and behaviour of materials, usually elements or compounds, on a local or global scale under the influence of living organisms, physical earth processes and chemical earth processes. It is possible to distinguish between three types of cycle:

1. Local cycles involve the less mobile elements and have no mechanism of long-distance transport. They are characterised by the absence of leakage from one ecosystem to another. Examples of elements that participate in local cycles are phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), zinc (Zn), boron (B), molybdenum (Mo), manganese (Mn) and iron (Fe).

2. Global cycles have a gaseous component which allows the element or compound to be transported over great distances in the atmosphere. This includes elements and compounds which may also participate, in a different state, in local cycles. Elements of significance here are carbon (C), oxygen (O), hydrogen (H), sulphur (S) and nitrogen (N), often in a variety of gaseous compounds (e.g. carbon dioxide (CO2), water (H2O), oxides of nitrogen (NOx), methane (CH4), sulphur dioxide (SO2)).

3. Sedimentary cycles, in which particulate material of all sorts is transported by water or sometimes wind.