Great Sandy Geomorphology
Vast masses of fine siliceous sand, constitute both Fraser Island and Cooloola landforms. The sand masses account for well over half of the Great Sandy Region’s 350 000 hectares.
The dunes of Fraser Island and Cooloola are composed almost entirely of deep siliceous sand which has been carried to the region by littoral transport of wind and tide. The sand is then deposited on the dunes by the wind which then proceeds to work and rework the sand into a magnificent sculptured masterpiece of Nature. Here the natural processes continue so conspicuously. Watching the actions of the sandblows sculpturing the landscape is like witnessing the awesome action of mighty glaciers. There are however significant differences. Sandblows defy the forces of gravity and are driven uphill by the wind they are more like “glaciers in reverse.” The subtropical setting is another significant difference to the genuine glaciers.
The sandmasses have innumerable examples of large parabolic dunes, unique in the world. Hundreds of wind-driven sand dunes are part of a complex cycle eroding and restructuring the sandmass. This process is more developed than anywhere else in the world. The oldest age sequence of giant coastal sand dune systems yet recorded exist here. Some dunes may be 400 000 years old. It is this complexity and the active, dynamic nature of the dune system which excited one scientist to exclaim, “Fraser Island is for sandmasses of the World what the Great Barrier Reef is to coral reefs of the World”.
The complex interaction of the windblown sand and the flora and its decomposing organic material, results in impervious organically bound sand in wind-formed dune depressions, are unparalleled in the world. There are over forty perched dune lakes on Fraser Island which contain some of the freshest, purest water in the world.
The soil is composed predominantly quartz sands with overall much less than 2% of other minerals; mainly ilmenite, zircon and rutile with some feldspar. The quartz grains on the older surface beds are more weathered than their younger counterparts, and may contain up to 15% of silt and clay sized particles in some zones. The bulk of the sands are Pleistocene deposits and the Holocene sands form a thin veneer along with the eastern to middle sections. The sands have arrived on the coast via marine transport and have been derived from the river catchments of the Australian east coast to the south; the main source rocks were the granites, sandstones and metamorphic rocks of these areas. The sands have been deposited along the coast during episodic periods of dune building. Quarternary fluctuations in sea levels and intensity of onshore wind transport in the past served to pile the sands into sequences of giant dunes.
Surface morphology is an excellent guide to the history of the dune sands in the Great Sandy Region. The periods of dune building can be readily distinguished, each is comparable in appearance and sharp boundaries between groups of dunes of similar ages provide evidence of periodic sand accumulation. The least eroded dunes lie upwind of others with more degraded outlines and evidence that younger dunes have invaded older, already vegetated dunes, is common.
The sequence of dunes can be described briefly as follows:
sand dunes without vegetation;
strong dune relief without water-scoured channels;
strong dune relief with water-scoured channels;
subdued dune relief;
degraded sands with very few subdued dune remnants;
degraded sands without dune relief.
The predominant onshore winds from the south-east have brought new sand to the coast and this has invaded the existing sand masses. It is in this area where the wind has its highest energy that the sand is reworked, resulting in the formation of sandblows. Simultaneously, as the sand has been accumulated and reworked on the eastern side, the older dunes in the west have been leached and subdued.
Few of the periods of sand accumulation have yet been dated directly. The relationship between the dune sands and former beach lines provides an opportunity to relate the two. Slow uplift of the land was ensured that former beaches have been saved from subsequent wave attack. Evidence of this shore is apparent at Mudlow Rocks, Rainbow Beach, where it rises 3m above the present beach and is the highest Pleistocene shoreline yet recognised on the Queensland coast. Several attempts have been made to date the driftwood in this beach; some gave ages close to the radiocarbon limit and others showed the wood to be older than 40 000 years. A relatively great age is implied by the fact that the beach lies beneath the Teewah Sands.
Research work is yet to commence on an appraisal of variations in the magnetic fields which may be recorded in the iron pans of the Great Sandy Region.
Despite the enormity of the mass of the sand, Fraser Island is not without its rocky outcrops. However, they collectively cover only a few hectares. There are two different kinds of outcrop – igneous (crystallised from a molten state) and sedimentary (resulting from compaction and cementation of sediments).
Rock outcrops on the eastern coast are at Indian Head, Middle Rocks, and Waddy Point, and are mainly trachy rocks of Mesozoic (65 – 225 million years B.P) or Tertiary (2.5 – 65 million years B.P) age. The volcanic origin of Indian Head is exemplified by the large scale basaltic columnar jointing up to 10 metres in height on the north face.
These are thought to be tips of submarine volcanic outcrops. Sand has accumulated around them slowing down the weathering process of this rhyolite mass which was once probably more massive and more extensive.
Evidence indicating that the Indian Head rhyolite rock strata do not underlie a large area has come from oil drilling exploration carried out on Fraser Island during the 1950’s and early 1960’s. One drill near Wathumba Creek penetrated more than 2000 feet (over 300 metres) below sea level without encountering hard rock. That drilling was carried out a few kilometres from Waddy Point.
Rhyolite is a finely textured acidic rock characterised by its light natural colour, indicating a high proportion of quartz in the rock. Little of the rhyolite of these outcrops is thought to have been used in making some Aboriginal implements such as bowls. It was not used for making knives and scrapers..
A lesser known area of rocky outcrop occurs on the tidal estuary of Bun Bun Creek. Navigators of Great Sandy Strait will note an area of rocky rubble several hundred metres from the shore in a direct alignment with the axis of Big Woody Island. This outcrop, marked by a navigation beacon, is the only remnant of the folded sedimentary rock outcrop which is the basis of the two National Park Islands of Big and Little Woody Islands and the Duck and Picnic Islands at the head (northern end) of Great Sandy Strait. Some of the rock from these islands has been identified as being used in the stone implements found on Fraser Island. At no other part of Fraser Island is any natural rock evident.
The Quaternary sand rests on bedrock of the Maryborough Basin. The bedrock is believed to be sedimentary rocks of Cretaceous age (65 – 136 million years B.P), possibly the Burrum Coal Measures.
Origin of the Sand
Most of the sand in Cooloola and Fraser Island originally came from New South Wales. Scientists have discovered that a vast amount of it once filled what are now deep vallys of the Blue Mountains. The heavy rains falling on the eastern side of the Great Dividing Range has eroded away the sedimentary rocks and granites which chiefly comprise the mountains to the west of the coastal plains. The resulting sand is carried down to the sea to meet the next agent of transport, the sea, at the river mouth. The beaches have for millions of years been nourished by the continual flow of sand down our rivers.
The sand of The Great Sandy Region is of the Quaternary Period. It has accumulated and been deposited during the last 2 million years. The sand has had a long, interesting history of movement. It was initially released from solid rock which has been broken down by erosion and weathering to grains which are so small and so light they can be blown about by the wind. The size of the grains of sand vary considerably from 0.02mm to 1.00mm. The most common grain size found in the region is 0.18mm to 0.27mm.
Principal sources of nearshore sediment for coastal areas are streams and rivers which transport sand directly to the ocean. A small amount of sand is derived along the coastline by the gradual wearing away and weathering of rocky headlands along the shore. The sand is moved along the coast by wave action, wind and currents and this movement of sand along the coast is called longshore transport.
Because the prevailing winds in Eastern Australia are south easterlies the waves are mainly from that direction. Although the waves tend to straighten up to meet the coast face on, they rarely succeed, and most frequently waves observed from the beach break from the southern end first. This action of waves breaking from south to north on our eastern Australian beaches tends to move sand from south to north.
There is a continuous movement of sand. It is this longshore transportation which has carried Queensland’s most valuable import secretly and unnoticed along the beaches together with the rutile and zircon which originally mainly came from the granites of the New England Table in Northern New South Wales. Such man made structures as the Tweed River boat harbour disrupt the flow of sand and cause sand to pile up on the southern side of the obstacle. The beaches north of groynes and other artificial barriers are frequently starved for new sand as a result.
Zeta Curves are a product and function of the prevailing wind as it drives on to the coastline. Winds generally move obliquely towards the equator and off the South Queensland Coast the prevailing wind is a south-easterly. Given the average strength and direction of the wind and given fixed points such as Indian Head, Double Island Point and Noosa Head, the beaches will align themselves on parallel axes, running slightly obliquely to right angles to the wind hitting the coast.
Another result of the prevailing south-easterly wind in Eastern Australia is to form beaches in the shape of Zeta Curves or reverse “J’s” with a straight beach running from NNE terminating in either a rocky headland (e.g. Fraser Island at Indian Head and Sunshine Beach at Noosa Heads), or in a sand spit (Inskip Point or Breaksea Spit.) The tip of the hook is usually a rocky headland such as Double Island Point or a sand spit.
An extraordinary feature of Fraser Island is that on the eastern side of the island are two conventional zeta curves with the sand moving north but on the western side of the island a large zeta curve is headed in the opposite direction. The beach between Rooneys Point and Moon Point is only exposed to winds from the north and west. This changes the shape and direction of the zeta curve.
Common characteristics of zeta curves include sheltered bay with its series of sand bars and lagoons at the base and either a rocky headland or a sand spit at the terminal end. Inskip Point typifies the sandspits. Headlands often accumulate large volumes of sand heaped against them, often faster than the vegetation can keep up with it, as it does at Indian Head and especially at Double Island Point. This culminates in a huge sandblow, often isolating the rocky headland by a seemingly unstable isthmus of sand, which is difficult to negotiate in most wheeled vehicles. Often the sand moves overland at the back of the headland, as well as being swept around in the surf.
On a fine, calm, sunny day, any person standing at the summit of rocky headlands will see the sand seemingly suspended in an emulsion, being transported in the surf zone around almost 180 degrees around the headland, at the rate of hundreds, if not thousands, of tonnes per day. Even this longshore transportation can’t fully keep up with all the sand drifting north. Therefore, surplus sand accumulates and gets trapped behind the headland resulting in dunes exceeding 200 metres in height. Normally, sand dunes reach their greatest heights south-west of headlands at the top of Zeta Curves.
It is estimated that 500,000 tonnes of sand are annually moved along eastern Australia’s “ocean pipeline. Since European settlement of Australia, the building of dams and other man made structures on the streams has slowed down the rate of flow of the sand onto the beaches. This has serious consequences on sand replenishment. It is highlighted by the erosion problems of Queensland’s Gold Coast. The problems of the Gold Coast will be felt more and more in other areas because the supply of sand is now very limited and it has been disrupted through man’s activities. These not only reduce the flow of sand into the “ocean pipeline” but also interrupt its flow along the coast. The build up of sand on the southern side of the Tweed River breakwater is causing the Gold Coast beaches to be “starved” for sand.
The Great Sandy Region of a wind shaped wilderness. The whole origin and shape of the sand mass is indebted to the influence of the prevalent South East winds. The influence of the wind needs to be understood in almost every stage of the process of creating the wind shaped wilderness.
- The wind brings the rain that not only assists the weathering of the rocks, but also transports the sediments in the streams down to the sea.
- In the sea it is the wind which is the driving energy of the longshore transportation by directing the waves to break most commonly from South to North.
- The wind which determines also the amount of in the wave energy. That influence whether sand is deposited on the beach or whether the beach is depleted of its sand.
- The wind influences the shape of the beach and the function of its Zeta Curve.
- The wind transports sand off the beach to create berms and foredunes.
- The wind creates blowouts in the dunes and mobilizes the loose sand on the surface of the sandblows.
- The wind carries the rain and the aerosol nutrients to nourish the vegetation that stabilizes the dunes. It is because Fraser Island has always been a vegetated sandmass that it has elongated parabolic dunes aligned from south-east to north-west
The wind simultaneously carries the energy to rework and sculpture the dunes in the parabolic dunes. Ultimately wind and rain degrades the dunes, subduing their steep slopes into more gentle forms and which depletes the soil surface of its essential nutrients.
Ancient fossil remains of plants in the layers of sands along the shoreline have been discovered indicating how varying sea levels existed at different times in the earth’s long history.
During the four major glacial periods of the Pleistocene Age (up to two million years ago) the icecaps of the poles slowly expanded and sea levels dropped, stranding the sand plains of the ocean floor along the fringes of the great land masses.
Between the ice ages were warmer periods during which the sea levels rose. The greatest Interglacial period of 200 000 years, occurred between the second and third glacial epochs.
During the glacial periods winds of incredible velocity and strength whipped up the surface sediments and deposited them elsewhere. The coast sand plains of Eastern Australia, once covered by water were swept by the winds which deposited the sand on the high dunes. This was the glacial time which created the greatest era of dune building activity in the Great Sandy Region.
A second major burst of dune building took place in the windy spells of the “little ice ages” over the last 10 000 years. During these recent interglacial periods, the sea levels were high and sand on the sea floor was delivered to the beach by the sea where the wind carried it inland. Thus the coastal sand masses represent significant stages in the evolutionary history of the earth.
Peter Stanton in preparing the first Fraser Island Management Plan in 1975 developed a system of 19 “dune sands”, more detailed than land systems. He defined dune lands as areas possessing “a uniform geomorphological history, which is dominated by the one parent material, and which has a characteristics range and aggregation of the vegetation structural types”. Stanton subsequently prepared a similar system of classifications for the Cooloola Management Plan. These two systems provide us with the most comprehensive set of descriptions of land systems.
Fraser Island’s eastern shoreline of Fraser Island is almost entirely a broad sandy beach backed by low foredunes or at Sandy Cape mobile sand sheet complexes. In several places the sea has eroded the older and higher dune deposits to form cliffs at the shore.
Beaches are constantly changing, natural systems. Even apparently static beaches undergo constant change, with periods of erosion balanced by periods of deposition. On static beaches, such as the main Fraser Island beach, the natural processes are balanced over a long period of time. This balance is delicate and can easily be upset. Beach stability is determined by: the amount and type of sand, the intensity of the natural forces, and the stability of sea level.
A variation of any of three factors, energy, sediment or sea level, can alter the balance of erosion and deposition. Beach erosion is a natural process and becomes a serious problem only when man’s structures are placed in the path of shoreline recession.
Beaches recede when the capacity of the waves to transport sand exceeds the amount of new sand supplied by the system.
High energy storm waves erode sand from the beach. This sand is often deposited offshore as submerged sand bars.
During periods of calm weather low energy waves move sand from offshore sources and deposit it back on the beach to form a berm parallel to the shoreline.
The berm, or ridge of sand, is formed on the upper part of the beach, outside the reach of normal high tides, by the wash of incoming waves.
Waves shape the beach into a number of subtle ridges, bays and gutters. Cusps are defined by ridges of mobile sand running down to the water, which separate the beach into a series of mini-bays. Sometimes these bays are protected by a sand bar stretching out to cut off the surf and so establish a small gutter of quieter water.
Such gutters are sought by the fish because where the water is less turbulent, it is normally clearer so that the fish can more easily see their food. Because the fish seek out the gutters, so do the fishermen. However, gutters do not remain in the same place for any extended period. The whole beach usually changes to some extent with every tide.
Marine erosion of the eastern margins of the sandmasses forms sea-cliffs which expose the sands of the various dune systems and multi-coloured sands, particularly at Cooloola. Older sea cliffs and fossil beaches both at Fraser Island and Cooloola provide evidence of past high sea levels and are important in interpreting past geological events.
Types of Dunes
There are many types of dunes which are represented in the Great Sandy Region.
In calm weather low energy waves move sand up the beach to build a berm parallel to the shoreline.
Berms are increased in size by the addition of wind blown sand which has been trapped by debris and vegetation. During periods of shoreline advance the beach grows seaward to a point where waves do not reach the former berm and another berm is constructed seaward. A broad barrier consisting of series of parallel beach ridges separated by low swales may be constructed in this manner.
Berms develop well along most of the beaches during periods of calmer weather. These are many times, mainly during winter when the berms are quite high and the beach face is quite steep. At such times there are frequently developed lagoons at the top of the beach between the berm and foredune.
Foredunes are built up at the back of beaches on the crests of berms and beach ridges where vegetation or other obstructions trap wind blown sand. They become higher and wider as sand accretion continues.
Onshore winds of sufficient velocity to move sand particles erode sand from the dry parts of the beach and transport it landward. Sand is moved from beaches by wind. Individual sand grains are carried by the wind close to the surface in a series of short hops in a process termed “saltation”.
The grains of sand on the beach are sorted by the wind. The small particles may be completely removed from the beach/dune area while the largest particles remain. Sand grains removed from the beach by wind and deposited in dunes are of essentially one size (diameter ranges from 0.15mm to 0.30mm).
Vegetation plays a dominant role in determining the size, shape and stability of foredunes. The aerial parts of vegetation obstruct the wind and absorbs its energy. Wind velocity near vegetation is thus reduced below that needed for sand transport and the sand deposits around the vegetation.
Successive stages of plant growth and sand deposition result in increased width and height of the dune.
Foredunes act as barriers against the action of waves and tides, and are a source of sand for the beach during periods of erosion. They protect areas behind them from wave damage and salt-water intrusion during storms.
Foredunes are well developed in many places of the Great Sandy Region including the areas immediately behind most beaches which are not eroding the dunes to form steep cliff faces and along the western side of most of the larger lakes with sandy shores including Lake Lake Boomanjin, Lake Birrabeen and Lake McKenzie.
Parallel Dunes such as occur south of Dilli Village and east of Moon Point develop parallel to the shore during periods when the shores advance. There may be a series of parallel dunes.
The seaward margin of a foredune is trimmed back by storm waves. During calm weather waves build up a new beach ridge in front of and parallel to the original foredune, or to the trimmed margin of the foredune. As the new beach ridge develops a low-lying swale is formed between the developing ridge and the original foredune. Dune grasses colonise the new beach ridge, accumulate wind blown sand, and a new foredune is built up.
Sand beach ridges are generally less than 10m above sea level and are largely restricted to parts of the coastline and sand islands where wave action is only moderate such as Moon Point. They are therefore less liable to storm, wave and wind erosion. They tend to accumulate as the coastline advances forming a series of low sandy ridges and swales, often enclosing some lagoon and swamp areas.
Beach ridges perform the same function as foredunes. They act as a buffer against wave attack and are a source of sand to supply the beach during periods of coastline erosion.
Transgressive dunes take shape on any large surface of mobile sand. Large transgressive dunes have ridges aligned across the prevailing wind. These occur near Sandy Cape and south of Indian Head. Several sets of transgressive dune ridges are arranged roughly parallel to the ocean coast. Each ridge partly overlaps its predecessor and is stabilized beneath a cover of scrub and forest. The ridges range up to 30 – 60m above sea level and consist of silica sand blown from the beach in relatively recent geological time when sand supply was greater than at present.
Blowouts form when strong onshore winds erode a gap in a single foredune or series of beach ridges. The wind blows through the gap sweeping sand from the beach and dune (or beach ridge) in an inland direction.
Where foredunes or beach ridges have been cut back by wave action leaving an unvegetated cliff of loose sand, strong onshore winds may initiate blowout formation. Blowouts also develop in the foredune/beach ridge system where the stabilizing vegetative cover has been damaged or destroyed by natural causes (drought, fire, cyclones) or by human interference (grazing, clearing, heavy pedestrian and vehicular traffic).
Unless the gaps in the foredune/beach ridge system are repaired by sand accumulations colonised by stabilizing vegetation the blowouts increase in size and migrate inland under the influence of the prevailing winds. Series of consecutive blowouts developed in an unstable foredune/beach ridge system often grade into parabolic dunes.
Originally used to describe blowout dunes in Denmark in 1894 the term Parabolics have since been used to describe “U” or “V” shaped dunes exposed to the wind. Parabolic dunes normally form humid vegetated sand masses particularly those carrying woodlands and forests. The vegetation on either side of the bare drifting sand, traps some sand.
They are blowouts that have migrated inland under the influence of the prevailing winds but become stabilized by vegetation. They have an advancing nose of loose sand and trailing arms of sand which have been partially fixed and stabilized by vegetation. In this way the blowout develops into a parabolic or U-shaped dune. The dunes retain a parabolic form as long as they remain partly vegetated so that the trailing arms are held back by vegetation.
Parabolic dunes have three main geomorphic components: the slip-face at the dune apex, trailing arms along each side of the dune with steep external slip-slopes and usually moderate internal slopes, and concave (in cross-section) dune floor between the trailing arms. To these may be added inclusions of older dune remnants, occurring as ‘islands’ or truncated weathering profiles with iron or organic-cemented pans protruding through the dune floor, and secondary erosional features, such as gully heads, channels, and fans resulting from water erosion of steep external slopes, some internal slopes and parts of the dune floor.
Fraser Island and the adjoining Cooloola sandmass consist almost entirely of quartz sands that have accumulated during episodic periods of dune building in the Quaternary. Nine dune systems have been identified on Fraser Island marking separate episodes of deposition above sea level. Deposits also overlay older aeolian deposits below sea level.
Absolute age dating of dune systems is at an early stage but it shows that the youngest systems span 120,000 years while the oldest dunes may have formed 800,000 years ago. These dates show that the age sequence is by far the oldest on record.
Parabolic dunes, open to the onshore winds, dominate the five youngest dune systems. The older dune systems have been reduced to broad whale-back sandhills. The dune systems provide many examples of the various stages in development and degradation of parabolic dunes, from bare mobile dunes showing progressive degradation by water erosion, to the strongly degraded sandhills which have lost their initial aeolian shape. These form a time series, illustrating the long-term changes in surface morphology from aeolian deposition to advanced degradation.
Soils on the freely-drained vegetated dunes also show progressive development with age, forming a sequence from rudimentary podzols to giant podzols on the oldest dunes. The depth of podzol development and the dimensions of the soil horizons, far exceed those recorded elsewhere. The dimensions and age span of this podzol chronosequence is of considerable scientific importance, internationally and is invaluable to soil science.
Further, where seasonal water tables rise to the surface in dune corridors and on the coastal plains, a different soil process is involved, forming humus podzols. The black organic B horizon of these soils becomes hard and cemented with time and, where exposed along the beach is known as sandrock.
The sands contain low amounts of plant nutrients and in the raw sands these are mostly associated with sesqui-oxides on the sand grains and with small amounts of feldspar. As the sands are vegetated and the soils develop, plant nutrients are transferred from this source, and also from the rainfall, through the vegetation and the organic matter on the developing soil surface. The nutrients in the organic matter are weakly held and easily leached but are not readily avaible to the plants.
As the nutrient layer is progressively leached deeper into the soil profile the nutrients become more concentrated. This nutrient rich layer is known as the “B” horizon. The layer above it which has been leached of colour is known at the “A” horizon. The youngest sands are generally near Fraser Island’s east coast and have no soil profile or only a superficial one (Dune System 1). Moving west the soil profiles gradually become more pronounced and as they do the height of the forest canopy get higher until it reaches a maximum in the centre of the island. (Dune Stem 4) About here though the sand is much older and the “B” horizon is so deep in the soil profile that even the roots of the largest trees can no longer access mineral like potassium and Phosphate, so essential for plant growth. The result is that the height of the canopy rapidly tapers off and trees diminish in size and even grow in mallee form. (Dune System 6)
The nexus between the soil profile is well illustrated in the Fraser Island logo.
Ramifying through the sand beneath the dune vegetation are fine fungal threads called hyphae. They particularly abound in rainforest, but even bare sand near the sea contains fungal spores. Hyphae grow independently of but in association with plant roots. Hyphaecolonizing the youngest dunes. These fungi form mycorrhizae – intimate associations between roots and fungal hyphae in which the fungi transfer nutrients extracted from the sands for glucose from the plants. These in turn probably supply various organic compounds which the fungus, Hyphae have no chlorophyll and cannot photosynthesize and are dependant on plants for nourishment just as the plants survival is dependant on the minerals released by the hyphae.
Because of the differences in the rates of water erosion and sedimentation on each of the geomorphic components of vegetated coastal dunes, soil development varies from site to site. However, at all sites depth of soil development increases with the period of weathering (dune age) until it reaches a water table which alters soil forming processes. A podzol age sequence from rudimentary profiles (< 50cm thick) to giant forms (> 20m thick) has developed across the dune systems. The dune systems show that, with age, aeolian shapes are gradually lost, landforms due to water erosion become dominant, and weathering eventually proceeds to depths of >20 m. Both Cooloola and Fraser Island contain giant podzol profiles with depths in excess of 25m, far exceeding known depths of podzols development elsewhere.
The soils of the wet coastal plains and river flats are mainly humus podzols, humic gleys, and gleyed podzolic soils with some acid peats. Lateritic and gleyed podzolic soils are dominant on sandstone hills with smaller areas of soloths and lithosols.
As the number of people using the Great Sandy Region increases, pollution pressure is likely to increase. Various items of litter (cigarette butts, apple cores, fruit peelings), and human excreta may be deposited along pathways, which may spread and contaminate the verges of tracks and along the upper Noosa River; by changing the nutrient status of the soil. Nutrient enrichment alters the ecological balance in natural plant communities.
Although not enriching the soil, non-degradable littler such as glass, plastic and polystyrene have a visible environmental impact.