A GRASS MENAGERIE: II - The Inhabitants of the Grasslands

In essence, the smaller denizens of the grasslands (including the myriad of insects inhabiting this biome) live in a forest-like environment – not under a canopy of leaves and between tree trunks, but rather between the culms and the inflorescences of the taller grasses. Their environment is dense and provides for ample opportunities either to shelter or to escape from predators. 

Moreover, these smaller organisms, experience subtle stratification of the environmental factors (such as light intensity, temperature and humidity) from ground level upwards to the top layer of the grasses. These littlies can move up and down in their environment to modify, albeit very slightly, the influence on their tiny bodies of a few environmental factors. For example, any small motile animals living in the grasslands can escape the heat of a summer’s day by moving down to the shaded ground level; they can escape desiccating winds, again by sheltering at the bases of the grasses. Despite these advantages, the differences between day and night are significant and can prove to be challenging to the small inhabitants; at night the grasslands become much colder, as a lot of heat is re-radiated to outer space, while far less heat is trapped in the sparse biomass of the vegetation. Of course, for the larger animals the grasslands are essentially two-dimensional environments, with the subtle changes in environmental conditions proving insignificant (apart from changes from day to night).

For many animal species, the grasslands become uninhabitable during the winter seasons. In general, two responses have evolved to this challenge. Those motile organisms that can not cope with the prolonged dry, cold times will migrate to areas that are more amenable in environmental conditions. The larger herbivores often partake in long-distance migrations, following the patchy and intermittent rainfall. Many bird species are trans-equatorial migrants, using long-distance flight to inhabit grasslands only during the wetter summer months in both hemispheres.

Many of the smaller organisms that are not able to escape from the rigours of the winter season by migration over large distances enter a period of dormancy, often for significant stretches of time. In regions of the planet with warmer climates, many insects living exclusively in grasslands aestivate during the most arid months. Populations of active insects will fluctuate in number seasonally; moreover, the occurrence of large, stable populations of insects in local areas of grasslands tends to be less predictable than in other biomes. A number of insect taxa do cope well with the environmental conditions in grasslands. These include orders of insects such as the Orthoptera (including grasshoppers and locusts) and the Hymenoptera (including ants). The very successful insects consume the leaves of grasses themselves, or they harvest, store and consume the grass seeds.

For the much larger vertebrate herbivores that inhabit the grasslands, food is present in abundance, provided the animals can graze the grasses themselves, feed on the grass seeds or select the herbs nestling deeper down between the grasses. Although the biodiversity of grassland plants is generally very high, the vegetation types available for herbivores is limited to grasses and smaller, usually non-woody flowering plants that grow here. Consequently, the diversity of animal life that is supported by grasslands is impoverished (in general) when compared to other biomes like the woodlands and forests, at least in terms of the number of species that inhabit the grasslands. This is not necessarily the case in terms of the number of individuals that live in the grasslands, since adaptation to this periodic environment has occurred in many groups of organisms (such as the grasses themselves, and the flock-forming seed-eating birds and the herd-forming grazing antelopes).

Amongst the numerous antelope species living in grasslands and open savannas, an interesting correlation exists between the size of individuals of a species and the social behaviour that has evolved in that species. The smaller browsers and grazers require vegetable food sources of high nutritional quality. Their bodies have a small volume compared to their surface area. To keep fuelling the high rate of cellular respiration required to maintain a constant and high core body temperature, these small antelope must be highly selective in the food that they consume. Therefore, small antelope species are solitary or live in small family groups.

In the much bigger herbivores, the quality of the food is not that vital. Inherent in the large size is a decreased ratio between the surface area of the organism and its volume that allows for a slower basal metabolic rate than that found in smaller species. With a small surface area compared to volume, large organisms are not faced with excessive heat loss through their skin. At the same time, the larger volume allows for the digestion of the food to proceed at a slower pace. Large antelope can graze grasses and allow the digestion to take place over time; hence the evolution of multi-chambered stomachs and the behaviour of chewing the cud in the antelope species. The alternative strategy, seen in horses and zebras, for example, involves the evolution of a large caecum; in essence, this is a spacious storage vat in the hindgut in which vegetation can be decomposed by bacterial action. Whatever the anatomy of these larger herbivores, they can survive easily in vast herds since the food they consume is more easily available, albeit of low nutritional value.

Add to this another benefit: the relatively low height of the grassland vegetation allows for vigilance against predators for the larger animal species. Living in a large group means more eyes and ears, as well as a smaller chance that a particular attack by predators will result in the death of any one of the members of the group. (Of course, one of us will die, but the chance of it being I is lessened in a large group.) The ability to live in larger herds has necessitated some form of herd co-operation and control that is complex enough to promote social cohesion, especially during courtship and mating. So vast herds of large grazers occupy the grassland environment, tracking the intermittent rainfall in spectacular long-distance migrations. Their predators, too, follow the migrations, but to a lesser extent – territoriality between carnivores well-equipped with the weapons of their trade can be intense and will limit the movement of groups of predators.

Another feature vital for the survival of mammalian herbivores in grasslands is the production of precocial young, that is, babies that are fully functional very soon after birth. The gestation periods of grassland herbivores is lengthened, in general, and the newborn is able to be on its feet and run with the herd within minutes after birth. In the smaller herbivores, where no herd behaviour is found, the young are precocial nevertheless, although they will often hide in denser vegetation or denser patches of grassland near where the mother is feeding.

The lack of tall vegetation in which predators can conceal themselves has necessitated the evolution of larger carnivores that can run down their prey, rather than relying on concealment and a pounce at close quarters. Three strategies in hunting prey among the larger carnivores prevail in grasslands: sheer speed of pursuit, endurance of long-distance chasers or the use of elaborate hunting strategies in larger social units of predators. Predators that rely only on speed still live either as solitary individuals or in small family groups, usually a female and her offspring only. This is often not the case with the two other groups – the long-distance chasers and the strategic hunters both require the co-operation of several members of the group in order to kill prey. This interdependence of members of a group for effective hunting goes hand in hand with more complex and elaborate social behaviour. Maintaining co-operation in a pack or pride requires social interactions that promote group cohesion, such as appeasement behaviours and social ranking of individuals within the group. Invariably, a hierarchical social system develops in these predatory species.

For the rodents, the omnivores and the smaller carnivores of the grasslands, shelter from the harsh environment, concealment from predators, or safety during reproduction is often found in burrows. The grassland environment, with its relatively deep soils and the top layer of the soil knitted together by the adventitious root systems of the grasses allows deep tunnel systems to be excavated by many animals that have the strength and the equipment (such as large claws) to do so. Subsequent occupation of the burrows by a host of other species – comprising individuals that themselves can not dig effectively – means that these tunnel systems often stay in use for long periods.

Photographing wildlife in grasslands is challenging. The larger species (mammals and birds) will flee readily and they can not be approached without difficulty. The unpredictability of the occurrence in any specific area of larger animal species can be taxing too. For me, portraying the grasslands has remained a test that I accept with glee. To display the magnificence of this biome and its menagerie of inhabitants will remain a special privilege always – particularly so since I too am an original inhabitant of the Highveld’s grasslands.

A GRASS MENAGERIE: I - The Environment of the Grasslands

The world’s grasslands flourish in the middle latitudes of our planet, quite far north and south of the equator; hence, this biome is subjected to pronounced seasonal changes in environmental factors. Grasslands also tend to thrive in the drier interior of continents some distance from the oceans.

Grasslands generally receive moderate, often erratic rainfall, usually in late spring to early summer; the short wet season is followed by prolonged dry periods during which very little precipitation falls. Temperatures in grasslands can fluctuate annually from hot daytimes to very cold winters with significant bouts of frost (at least). Moreover, most grasslands occur on deep soils (often sandy or friable) that do not retain soil moisture for long.

The grasslands survive pronounced seasonal changes in a combination of environmental factors: sufficient warmth and sufficiently long day-lengths for growth, moist upper layers of soil, and frost-free nights in the summer months, with cold and frosty nights, dry soils, and short day-lengths in winter. This combination of factors gives rise to an obvious growing season for the vegetation in late spring and summer, followed by a lengthy dormant season.

In southern Africa, the grasslands are located chiefly in South Africa (on the Highveld (an elevated central plateau) and the inland areas of KwaZulu-Natal and the Eastern Cape) with much smaller, localised regions found particularly in the eastern highlands of Zimbabwe. In general, the topography is flat or undulating, but it includes the escarpment areas of the Highveld and the highlands of Zimbabwe too. The altitude of southern Africa’s grasslands varies from near sea level to close to 3000 metres in elevation.

A copious number of grass species dominates the grasslands extensively. Between the grasses also grow many non-woody flowering plants and many geophytes (bulb-producing plants); regularly woody shrublets can also survive the environmental and climatic conditions experienced in grasslands. Since the height of the vegetation is very low, plants in grasslands experience high light intensities (at least during the summer months); no true shade-plants survive here.

Taller shrubs and trees are generally absent from grasslands. There are several reasons for this absence. The deep and often well-drained soils of grasslands frequently become too dry at deeper levels for tree roots to be able to absorb sufficient moisture. In general, the leaves and smaller twigs of trees and shrubs are also not frost resistant; therefore, taller woody vegetation can not survive the lengthy cold, dry winter seasons. During the winters, fire too becomes a significant ecological factor in grasslands, removing dense old growth from the biome, making nutrients available again for the rapid growth of new grasses during the following growing season. Fire also prevents the encroachment of shrubs and trees into grassland areas.

In contrast to most woody vegetation, grasses can survive the challenging conditions of the dry seasons during which grasses become dormant. In winter, the grasses usually die back; that is, the above-ground culms dry out completely while the below-ground root systems survive the harshest of parched cycles. Alternatively, many grasses are annual plants rather than perennials – the adult lives for one season only, during which time the plant germinates from seed, grows rapidly, flowers and sets seed itself, only to die when the dry season commences. As long as the upper soil layer does not become too hot during a fire, the seeds of the previous summer can survive there and the grasslands can persist even through regular cycles of wildfires. The smaller non-woody herbs, flowering plants and the shrubs of the grasslands follow similar strategies.

Grasses form a special subset of the vegetable world in many ways. Their roots do not penetrate deep into the soil; rather, the many thin, fibrous roots spread out just under the soil surface, knitting together the top layer of soil. The decomposition of the dead leaves, culms and roots of grasses releases nutrients into the topmost, enmeshed and very fertile soil layer. The web of fibrous roots also captures much soil water before it percolates into the deeper strata following good rains. Sacrificing a long life for rapid growth, grasses with their strap-like leaves and thin culms have done away with thick trunks and large leaves. The strategy employed is one of grow, reproduce and set seed as rapidly as possible. In grasslands, plants that do not produce seeds are very rare.

Although they are flowering plants, grasses have done away with large, showy flowers. The grasslands, in general, are often too dry for much of the year to support a permanent, large insect population. There exist vast numbers of insects in grasslands, but their appearance in a local area may be unpredictable. Therefore, attracting a pollinator at the correct time – when the flowers have grown and matured, and are ready for pollination and fertilization – is a challenge for any flowering plant in a grassland environment. Instead, grasses have reverted to wind pollination and the flowers have become minute, but bright, splashes of colour in the inflorescences of grasses. Since most grasses grow to a more or less uniform height and the grass stalks are thin, wind can move over and through grasslands relatively unimpeded, except at ground level. Thus wind pollination is an effective strategy for plant reproduction in this environment.

In contrast to all other plants, the grasses possess a unique feature. In plants that are not grasses, cell division for growth of the organism takes place only in two regions of the plant: at the tips of the roots and twigs (where elongation of all plants takes place), and in woody plants just below the outer covering inside of the bark of larger shrubs and trees (so that an increase in the diameter of roots, trunks and branches can take place). In grasses, however, patches of undifferentiated tissues (the intercalary meristems) occur and cell division can take place at any regular point along the plant. As a consequence, grasses do not stop growing when their leaves and culms are grazed (that is, when the tips of the plants are removed); rather, growth of new plant material will take place from the intercalary meristems. In fact, grasses tend to thrive better if they are grazed to a certain extent. The saliva of the antelopes that graze the grasslands of Africa and elsewhere also stimulates grass growth, an interesting example of co-evolution between a predator and its prey in these two groups that evolved on our planet at the same time.

When people look at grasslands, they may conclude that the biodiversity of this biome is quite low. Grasslands look uniform – there seem to be only grasses present, and these tend to grow to the same length (more or less) in any particular area. However, in South Africa, this biome harbours a tremendously high biodiversity (second only to the fynbos biome of the southern Cape). The grasslands are often home to rare plants, particularly so in the higher-lying areas along the escarpment. These scarce species are often endangered; they comprise mainly endemic geophytes (bulb-producing plants) and dicotyledonous herbaceous plants. However, very few species of grasses are rare or endangered, almost certainly as a result of wind pollination and the production of small seeds.

All my life I have been a resident of the Highveld of South Africa. My earliest recollections of wilderness are intertwined intimately with the grasslands. As a very young photographer, I often lamented the fact that my family had not lived in a bushveld or coastal area – environments that seemed so much more photogenic in themselves and that appeared to be jam-packed with opportunities of capturing images of wildlife. However, the more I explored, the closer I looked at the grasslands surrounding my home, the more grew my appreciation of the spectacular expanses of the grasslands. Nowadays, I relish the challenge of portraying the grasslands in all their splendour; I cherish every opportunity of arresting, in an image, the fabulous grass menagerie.

THE WORLD OF WATER: A PERSONAL JOURNEY – Part V: When Sunlight Breaks

Like most children, I was a cloud-spotter from the knee-high stage onwards. The cloudscape above the South African veld made an indelible impression on me. Hours on end we children would lie on our backs, the hot sun baking our tanned faces, arms and legs, high above us cumulus clouds suspended in the heavenly blue: Big Ears-ears, Pinocchio-noses, old-man-faces, unicorns and other creatures and landscapes of mythopoeia. Add to that the seemingly endless wisps and stripes of high cirrus clouds, the towering walls of cumulonimbus castles. I imagined an enchanted world amongst the clouds, a world higher and greater than my own down below.

Alas, in contrast to almost all other children, my perception of the world around me has never changed. I still seek for, yearn for, the charmed and enchanting in an otherwise stultifying adult world. So I remain a cloud watcher, peepers pointed skyward, still searching for my fairy queen and yet another glimpse of that other world. Nowadays, however, looking is not enough. For me, as a photographer, clouds remain endlessly fascinating: in constant flux, never static in pattern or process, and especially the incessant wonderful play of light and shadow that arises.

Special excitement is provided by iridescent clouds. When thin cloud layers (particularly cirrostratus, altostratus and altocumulus clouds) are present in the sky, it can happen that sunlight shining through these clouds breaks apart into its rainbow colours. This phenomenon is observed best when the clouds occur in an arc of less than 20° from the sun. Since you are facing the sun, often the light is too bright then to observe the phenomenon or to capture an impressive image on film. It is better to photograph this singular spectacle at sunrise or sunset, especially when the sun is shielded by other clouds so that no light falls directly on the lens.

In general, iridescence appears when surfaces of objects are composed of multiple layers or the surfaces comprise a very thin film, as for example in soap bubbles or when oil is spilt on water. In these instances, the light that impinges on the object is reflected, not off one surface, but off several different tiers. If the incident light originates from a single source (as is the case with sunlight), iridescence occurs strongly since the wavelengths of the reflected light rays coming from different layers can interfere with each other. In this way, some wavelengths are either dampened or enhanced. With interference all the wavelengths reflected off an iridescent object added together no longer appear white (the total sum of all colours in sunlight), but parts of the object now show a colour cast. The resulting spectacle depends on the angle of view, of course.

In clouds specifically, several processes that occur simultaneously cause iridescence. When sunlight passes through a thin cloud layer, some light rays are absorbed; most rays, however, are scattered by the cloud particles, so that the cloud usually appears white. Some light rays pass between the water droplets or ice crystals and are thus diffracted. Other rays pass through the droplets and are then refracted and split into their constituent colours.

Whether sunlight passes through or between water droplets, whether it is diffracted, reflected or refracted, the light rays that finally travel towards the observer can still cause interference phenomena. Since sunlight originates from a single (point) source, all the light rays are still in phase with each other (even after the many changes that have occurred); therefore, two light rays can become superimposed one on the other to give rise to interference. With this, some colours may cancel out; others may become exaggerated, because the different wavelengths of light are affected differently during interference.

The result of this long journey by the light rays through the diaphanous cloud is iridescence. From the point of view of the observer, the angle between the cloud and the sun must be less than 20° for this phenomenon to be visible. In addition, the resulting colour spectacle is dependent on the density of the cloud or cloud layer. If the clouds are very thin and wispy, the colours that appear are washed out and indistinct; on the other hand, if the clouds are too dense, either too much light is absorbed or the rays are scattered too irregularly to result in iridescence. Other factors that modulate the appearance and intensity of iridescence include the size of the cloud's water droplets or ice crystals, the movement of the cloud and the way in which the sunlight impinges on the cloud surface.

Cloud iridescence is not a halo phenomenon, since the colours occur in bands rather than in concentric rings, as is the case with halos. Iridescent clouds also differ from the similar nacreous or polar stratospheric clouds and noctilucent clouds. Although the physical processes involved in all these cases are the same, iridescent clouds can be observed at most latitudes and during daylight hours. The cloud type involved in iridescence always comprises cirrus- or stratus-type clouds in the troposphere (the lowest layer of the atmosphere, starting at the earth's surface and extending to a height of between 7 km at the poles and 17 km at the equator). In contrast, nacreous clouds can only be observed at latitudes larger the 58° from the equator. Also, nacreous clouds are found in the stratosphere (up to 30 km above the earth's surface). In the case of noctilucence, high clouds in the mesosphere (between 50 km and 80 km above the planet surface) may still reflect sunlight after sunset (or before sunrise) during very deep dusk.

So, do I still spend time on my back these days? Of course! The only change that has occurred is that the bones complain when I attempt to stand up after a long sojourn in the magical, mythical realm of clouds.

THE WORLD OF WATER: A PERSONAL JOURNEY – Part IV: Cloudscapes

Ever since childhood the other world that exists, the one high above the grasslands and bushveld of South Africa, has enthralled and fascinated me with its endless watery vistas of cloudscapes. To find a workable photographic composition in this immense realm remains a challenge that I relish. The shapes of the clouds, their flow, their highlights and shadows, and their colours, from the customary white and greys at midday, through all the tints of the rainbow that compose sunlight earlier or later in the day.

Clouds are essentially vast collections of water droplets or ice crystals held up in air. The mass of water that is trapped within a typical cloud can reach several million tons. And yet, the density of the relatively warm air that holds the water droplets in suspension is low enough that air currents below and inside the cloud keep it hanging. Ice crystals are much lighter than water (after all ice floats on water) and can form clouds much higher in the atmosphere under freezing conditions.

Physical conditions within a cloud are never static. Formation of water droplets (around condensation nuclei such as dust or smoke particles) and re-evaporation of water droplets into vapour occur ceaselessly. If, like me, you are often compelled to look skywards, you too will have seen the miraculous-seeming condensation or evaporation of clouds as unseen masses of air pass and mix in the blue sky above you.

The type of cloud that can form at any one time and in any specific air mass depends on only a few local conditions of the atmosphere. The main ingredients for cloud formation are the presence in the air of sufficient water vapour, the turbulence or stability of the air in question, and the presence or absence of convective uplift (that is, the presence of warmer air that will rise in altitude). Essentially, all the different shapes and forms of clouds can be divided into only two categories: layered and convective cloud types. In unstable atmospheric conditions, convection of air predominates, giving rise to vertically-developed clouds, while more tranquil atmospheric conditions give rise to horizontal cloud layers that can extend over great distances.

When attempting to classify cloud types, almost the only other consideration is the height at which clouds form (remembering that the higher the altitude, the less the density of air itself is, and so too its ability to suspend a vast mass of water or ice). High clouds invariably are composed of tiny ice crystals, giving rise to wispy, layered cirrus-type clouds, often spread out in horizontal wind currents over enormous distances. Mid-altitude clouds are composed of water droplets, giving rise to denser, layered clouds or smaller clouds aggregated in cloud fields. At low altitudes in the atmosphere dense, layered stratus-type clouds or scraggly dense fields of low cumulus-type clouds form.

The most dramatic clouds develop in the presence of strong convection currents in the atmosphere. These vertical clouds have fierce internal up-draughts of air and rise above their bases formed at various heights in the atmosphere. These cauliflower- or anvil-shaped cumulus or cumulonimbus clouds, respectively, are often the harbingers of rainstorms or thundershowers.

As sunlight shines on clouds and travels through the mixture of water droplets or ice crystals and air particles, light rays are reflected, scattered, diffracted or absorbed by the bits of the clouds. The colour of the cloud, the wavelengths of light that are reflected from the cloud towards the observer, of course, depends on the colour of the light that is striking the cloud.

During midday hours the tops of clouds and the sides facing the sunlight appear white. The intense white light is reflected and scattered by the water droplets or ice crystals in all directions equally. Even if the light has been diffracted at the surface of cloud particles or inside the water droplets, the reflected light rays from the countless molecules in the cloud recombine to give the appearance of white light. The water droplets comprising a cloud tend to scatter light effectively, so the intensity of solar radiation passing through a cloud diminishes with depth into the cloud. Thus dense clouds show various shades of grey, especially towards their bases. The same greys also appear in areas of a cloud that are shielded from direct sunlight.

Rarely clouds may take on a tinge of colour other than the usual white shade. Most frequently large and very dense clouds will appear blueish-grey due to light scattering within the clouds; the short wavelengths (blues and greens) are more easily scattered, while the longer wavelengths (reds, oranges and yellows) are more easily absorbed. Therefore, blueish clouds indicate strong scattering of light by rain-sized droplets, meaning that a drenching may be imminent. Much less frequently, clouds appear greenish; invariably such clouds are composed of large ice crystals or hail stones that scatter strongly the green wavelengths of light. When clouds appear yellowish, the atmosphere usually contains a large proportion of smoke particles following large-scale fires, natural or man-made.

For a short while, twice a day, clouds are not white and grey or tinged by subtle hues of colour. At dawn and dusk, when the atmosphere and its floating clouds are still shaded from the sun by our planet itself, only the strongly scattered short wavelengths penetrate Earth’s shadow, painting any clouds present in intense hues of violet, indigo and dark blue. As the sun peeks above the horizon in the morning, or before it sets in the evening, clouds become a fiery spectacle of reds, oranges and yellows, as the sun’s rays travel through the air at a shallow angle, with the cooler colours temporarily subtracted from the light.

Whatever the time of day, whatever the atmospheric conditions, clear skies or storms, whatever the cloud types that form, for me the constant flux and flow and the play of light high in the atmosphere above me remain enchanting. Clouds are the manifestation of physical processes happening in the invisible air, giving rise ultimately to the patterns that represent an entire world other than the terrestrial one to which my feet are rooted. Rooted in body to Earth perhaps, but with my imagination skipping among the clouds.

THE WORLD OF WATER: A PERSONAL JOURNEY – Part III: Fresh Water

In a previous post I explained why water as a substance holds such fascination for me, particularly so as a photographer. As a child, I experienced real freedom, unfettered by over-protective parents – days spent out-of-doors in the immense Highveld grasslands, dry and dusty, far from home, in the company only of a small band of loveable rascals. Any encounter with water was a rare occurrence for us youngsters, be it a stream, a river, a dam or – on a few travels with our parents – the ocean. The coolness, the flow, water’s ceaselessly changing nature, its might, held us in thrall.

At school, I was taught that water, as a compound, is colourless and odourless. It took me quite a while to realise that the teachers were speaking of pure water, uncontaminated by any solutes and any suspended particles, a substance so pure that I had never been exposed to it. And, while the teachers were right, to me water has always remained a fascinating enigma. It is colourful by reflection and diffraction of sunlight or because it harbours cyanobacteria, algae and other organisms, or because it is mixed with countless other chemicals. It does smell too, again because water never occurs in its pure form in nature on our planet.

Water is weird. Although the atoms that comprise a water molecule (when taken together) are less massive than the atoms that make up a hydrogen sulphide molecule, water is liquid at room temperature rather than a gas. Water also clings: it coheres to itself (forming spherical raindrops and hailstones and suspended droplets on branches or grass culms following rain or dense mist) and it adheres to a multitude of other substances (a natural ‘glue’ that holds lumps of soil together, for example). Pure water has its highest density at 4°C, so that ice floats instead of sinking, and deep lakes never freeze all the way through to their bottom. Water heats up much more slowly, but, similarly, once heated, it also loses heat much more slowly than air or rock and sand. The presence of a large amount of water in the environment, either on the surface (as seas or large lakes), in the soil or stored inside vegetation (which also releases moisture into the atmosphere by evapotranspiration) tends to reduce the fluctuations in temperature of the terrestrial environment from day to night and from season to season. Water also has low viscosity, flowing easily down the slightest of slopes, or vanishing between the tiniest of cracks on rock or spaces in sandy soil. Moreover, water is a massive enough, incompressible liquid that scours, erodes, and sculpts even the hardest of rock surfaces.

As water evaporates from the vast surface of the oceans, clouds are formed and condensed water droplets, carrying no dissolved minerals, fall back to the surface as precipitation. Some of the moisture will be blown off course by winds and will fall, not back into the seas, but onto the solid surfaces of the islands and continents. This pure, fresh water will accumulate dissolved chemicals as it percolates downwards through the soil and porous rock strata, but it will never attain the much higher concentrations of solutes found in the oceans.

The water will continue to flow downwards, unless it is prevented from doing so by impervious rock strata. It will collect underground if trapped or it will emerge onto the surface of the slopes of the land as springs. From here it will continue its downward journey, forming rivulets and streams, or filling depressions in the landscape as pools and lakes.

As weird and wonderful as water is physically and chemically, for me it is the flow of this vital substance and its ability to reflect light that mesmerise. Silent, smooth, un-rippled and gentle in one instance, eliciting tranquil thoughts, moods and emotions; thunderous, dangerous, life-threatening on the next occasion, bringing forth excitement, bewilderment and even fear.

The speed and shape of the flow and the different colours of water seem interminable, and yet these bewitching phenomena are simply manifestations of the underlying action of the fundamental physical forces of the universe. The knowledge and experience that there exist substances, and interactions between substances, and actions of forces upon these substances and their interactions – actions and reactions, processes and patterns – that are at the same time fully explainable, determined and constrained by the forces of nature, and yet endlessly mutable as an outcome, to me have offered meaning, beauty and awe in equal measure throughout my life.

For humans and the vast majority of all the other terrestrial inhabitants of Earth fresh water is vital for continued existence. Only around 3% of the total quantity of water that can be found in the biosphere carries a dissolved mineral content low enough to be considered safe for the consumption by species that ply their trade on continents and islands. And this vital resource is diminishing rapidly as our own species continues to exploit and pollute any and all sources of fresh water on the planet surface, still believing, as we do, in ancient mythologies that professed that we, Homo sapiens, are the masters of it all and that Earth, and indeed the entire universe, exist because of us, for us. As our ceaseless slumber continues and we remain embedded and comforted by out-dated and misguided beliefs, as yet unpolluted, consumable sources of water are speedily becoming an exceptionally rare reserve planet-wide. And as this vital, life-supporting liquid dwindles on Earth’s surface, both in quality and quantity on our ever rapidly-heating planet, so too evaporate any hopes of a future for humankind that is meaningful, tolerable and peaceful. Fresh water is running out fast.