The Americans have, for almost fifty years, pioneered a soil erosion estimating system which requires the farmer to comply with required soil management techniques, if he wishes to continue receiving government support. The Food Securities Act of 1985 requires that farmers apply conservation measures to remain eligible to participate in certain government programmes.
The erosion risk (A=annual soil loss) is calculated from a number of factors that have been measured for all climates, soil types, topography and kinds of land used in the USA. This technique helps to predict erosion and shows farmers which farming methods to use. It also identifies erosion-sensitive areas.
The factors are combined in a number of formulas of the 'Universal Soil Loss Equation', which returns a single number, the tolerance factor, equivalent to predicted erosion in ton/ha: A = RKLSCP , where:
It is hoped that where no erosion estimating system is available, farmers and land owners, consider the above factors in the ways they manage their soils. Remember that sustainability of cropland is very difficult to attain.
(Source: W J Elliot, G R Foster, A V Elliot: Soil erosion: processes,
impacts and prediction. in Lal & Pierce Soil management for
|The International Geosphere-Biosphere
Program (IGBP) uses Relative Erosion Rates (RER) as per table on right,
for each type of land use. When taking land slope and rainfall into account,
they use the following formula for Relative Erosion Potential (REP):
^ 1.5 x RER x precipitation / 1000
The problem of this formula
is that it does not take evapotranspiration into account but it recognises
that erosion occurs mainly when the soil is saturated and rainfall is maximal,
with heaviest rains occurring in one month. Note how the RER for croplands
and urban areas is over ten times that of an evergreen forest. Watersheds
with REP less than 5 are under low threat; between 5 and 45 medium and
those above 45 high. A maximum REP of 1400 is possible for large rivers
with poor soil management.
water body, lake
evergreen broadleaf forest
evergreen needleleaf forest
deciduous needleleaf forest
croplands, natural mix
urban & built-up
barren or sparse veg.
the river water, loaded with sediment and nutrients, reaches the sea, it
forms a mud plume, the size of which increases gradually as the river flow
increases. The graph shows plume length (km) against river flow in thousands
of m3 per second, assuming that river plumes dissolve into the sea water
continuously and assuming there are no coastal currents to displace these
over huge areas. It is a pity that the plume is not expressed as surface
area or square km, but only as a distance extending out from the river's
mouth, hence the curve's flattening out.
The invisible plume of released nutrients is estimated to be far larger and longer lasting. Very little is known about these.
|Affecting the sea
Mud flowing into the sea, has a profound effect on it, although it is not precisely known how it all works. Here is my own idea:
Remember that clay is a very fine mineral consisting of layers made of aluminium, iron and silica. It carries a charge (negative) that binds positive ions (cations) that are important to the soil's fertility. As it washes into the sea, it is likely that its structure is affected, causing the release of iron and silica and the soil nutrients.
People often don't realise that the area of land causing the problems, is much larger than the area of coastal sea, which is often no more than a few hundred metres. From the air, one can see clearly how mud slicks stay close to the shore.
|For those interested,
the amount of land for each metre of shoreline, increases proportionally
with the diameter of the continent or island. Thus large continents potentially
have large coastal problems, depending also on climate and rainfall. New
Zealand, being small, has relatively small coastal problems.
Imagine the land a circle of surface pi x r x r. Its circumference is 2 x pi x r. Divide the first by the last, gives the ratio = r / 2 or diameter / 4. In relation to the surface area of a continent, coastal problems increase with the square root of continent size.
|The clay provides precisely all the nutrients that are in short supply in the sea, causing the plankton to bloom with gusto. Normally this would be beneficial to marine creatures, but there can be too much of a good thing. My thesis is that in the past 15 years (NZ), the sea has overstepped the line, resulting in problematic plankton blooms. It is called eutrophication or overfeeding. Of course these blooms are happening close inshore, where all our marine farming is and where a large part of our ocean's biodiversity is found. To make matters worse, the mud stays inshore for a long time, being stirred up by every swell or storm. Coastal currents transport it along the shore, exposing a much larger area to its ill effects.||
Could the sea become saturated? It would explain why problems are getting
worse, and why they are accelerating. Surely, this little amount of mud
and sewage from grazing stock and humans cannot saturate the ocean which
is so large and deep? The dust will just diffuse away, into the deep oceans
and currents will wash it away isn't it? Well, perhaps it does accumulate.
Although the world's oceans are immense and deep, the coastal margin around continents, the continental shelf, is narrow and shallow. Here is where most of the sea's productivity is found, most biodiversity, most of the fisheries, and ALL of our shellfish fisheries and marine farming. The diagram shows how nutrients cycle over the continental shelf.
|Clay, silt and sand (mud) enters the water. First it floats on the surface because of the large amounts of fresh water, but gradually it becomes mixed with salt water. The larger particles, the sand, settle out near the shore, the silt further out and the clay still further, but it takes a long time to get there. The sea bottom must be stirred many times, and as the bottom sinks deeper, such events become rarer and rarer (see oceanography/waves). Although exact figures are not known, it may take hundreds, perhaps thousands of years for clay to arrive at the continental shelf. It may need an ice age to lower the sea level by 100m, before the clay will move this far. This alone is a possible cause for the shelf to saturate. But there is more to it.|
In the chemistry of the sea bottom, organisms like those found in soil,
are doing what soil organisms would do: breaking down dead organisms and
organic matter and producing nutrients (pink), which feed the plankton,
once they move upward to the sunlight. As can be expected, the bottom organisms
will also store nutrients, causing the sea bottom to hold a large amount
of the total amount of nutrients on the shelf. All this can be expected
from the ways an ecosystem works, but none of these postulations have been
number of natural forces are at work to preserve the nutrients in the shallow
waters of the continental shelf where sunlight may reach the bottom. Winds
do not blow equally strong along the coast, which protects the water from
land winds. Thus the sea winds, blowing shoreward, outgun the land winds,
and water moves gradually shoreward. The ocean's currents that run along
the margins of continents, form eddies that herd the nutrients back over
the shelf, and deeper down they are found corkscrewing (in NZ counter-clockwise),
pushing nutrient-rich water up the continental slope and onto the shelf.
All these systems may work so well, that the continental shelf indeed saturates, or at least becomes richer with time.
It is almost poetic that the minerals which once formed soil on land,
now form the sea soil, containing similar organisms, and doing similar
tasks. The sea soil provides attachment for bacteria, and these create
micro environments that enable them to do their work. Worms tunnel around,
giving the sea soil structure, while allowing oxygen to reach deeper layers.
Animals with jaws (sea 'insects' like fleas and slaters, but also bristleworms)
are available to dissect dead organisms. But unlike the land soil, the
sea soil does not have plants with roots. Instead, the living canopy is
represented by a thin soup of microscopic floating plants, the phytoplankton.
These single-celled plants grow rapidly, die after only a few days, and
sink down. But during their fall, bacteria in the water already start breaking
them down, doing their best to recycle the nutrients close to the surface.
But in the end, it all ends up on the bottom, where the sea soil does the
final recycling. See also the separate section on plankton.
reason for researching this resource on the nature of soil, is the fact
that I have sound reasons to believe that mud from the land is the main
cause of the rapid deterioration in the seas around New Zealand. Having
made nearly 2000 dives here in 24 years, and living by the sea, close to
the first marine reserve of NZ, I have been able to make close observations.
By being under water so frequently, I have been able to see the changes
and to record these on movie film and photographs. I've seen that the only
thing that changed, was the amount of mud entering the sea. Every other
factor that could possibly be detrimental to the sea, has stayed reasonably
constant. I have now come to the conclusion that it is not possible to
save the sea without first saving the land.
In 1984 the reign of the New Right started, subjecting this country to the full storm of globalisation, destroying productive industries, making life difficult for farmers and selling the people's assets. Our politicians rode to victory on the promise of sustainable export-led growth. Today we can see that exactly the opposite was achieved: stagnation of income, burgeoning debt, unsustainable debt servicing, and a current account in deficit of over 30% of export revenue. For every dollar we earn, we now spend two. Worst for the sea, the Government abolished fertiliser subsidies, which resulted in hill country deteriorating and eroding at an ever faster pace, while poor foliage opened these soils to the damage from raindrops. In the past ten years I have observed that the clarity of the sea, its problems and erosion have multiplied almost three times. What can we expect in the next ten years? Ten times the problems? Obviously, something needs to be done, and fast.
As the land is becoming tired from lack of fertiliser, and farmers are pushed to the brink, also the climate is changing. We are now experiencing heavier and more frequent rainstorms than can be remembered. The ball game has changed and our opponent has become stronger. We have to play a smarter game.
You would ask: where is the data to support this? Yes, where is it? In their wisdom, scientists have forgotten to put a network of water quality monitoring stations in place, back in 1960 when interest in the sea began to accelerate and problems first started to show. Although efforts are now being made, the data is essentially missing and my own observations are perhaps the best we have. I hope that many will join me in the fight to retain what we once had.
The Seafriends website is now the ONLY place in the world that traces the problems in the sea from their very origins on the land. It even goes further by analysing what causes eutrophication of coastal waters, and how eutrophication works. We even discovered an entirely new method to measure the health of planktonic ecosystems. Follow the links from our decay section and study the degradation chapter. Everyone can now help to save our seas.
Floor Anthoni, 11 November 02000.
Wellington (NZ) discharges its untreated sewage straight into the sea, along its prettiest seashore and most desirable beaches. Obviously the health of the sea is not a priority!
|Least loss landscapes
In our fleeting moment of being alive on Earth, we are unable to see the slow earth processes at work, those that shaped the landscapes around us. We find it hard to believe that the last ice age ended only 4000-6000 years ago, and that the sea level rose by 100-120m in less than 2000 years. We can hardly imagine that our coasts as recently as 7000 years ago, stood at the margins of the continental shelves, some 10-100km out in sea. It is difficult also to understand that when the sea level stopped rising, about 4000 years ago, it stood precisely where it once was, hundreds of thousands of years ago, in one of the inter-glacial warm periods like today. It is also unimaginable that the sea coasts we see today are practically the same of that era. Up until the industrial era, sea coasts have been eroding only very slowly, and what we see today, is almost identical to what once was, a very long time ago.
Underlying each landscape, is the geological process of uplift and subduction,
compression and corrugation, tectonic and volcanic activity, shaping the
landscape in a gross way. This is a very slow process, taking millions
of years rather than thousands. Erosion then rounds these shapes, quickly
at first but gradually more slowly, until it stabilises at a rate of minimal
|Least Loss Landscapes
To further our thinking about landscapes and erosion, I like to introduce a new concept, that of least loss landscapes. My contention is that all landscapes around us, including the coasts and seascapes have stabilised into forms conducive to least loss of nutrients and soil. This natural law can be proved by assuming that if a part of the landscape did not conform, like being uplifted recently, this part would then erode more quickly until it reached a form of minimal erosion again. In this process, of course, the land cover of vegetation plays an important role, as it does also in the sea.
This law predicts, that when humans change the shape of the landscape, an increase in erosion will result, which is hardly newsworthy, since we see frightening examples of it everywhere, as discussed throughout this section on soil. The law also predicts that when humans change the original land cover, like changing forests into pasture, erosion will increase, but this is no news either. Conversely, by bringing eroding land back into forest, erosion will be reduced. However, the law also predicts that naturally bare land, when reforested, will cause a momentary increase in erosion and loss of nutrients, until its shape stabilises, which may take a millennium to complete.
More unexpectedly, the law also predicts that erosion and loss of nutrients will follow climate change, which affects not only the physical factors like moisture, rainfall, drought, frost and so on, but also the composition of the cover of vegetation and soil. An interesting consequence of this is that the layers of mudstone, formed in the sea, may well represent periods of climate change, and their thicknesses corresponding to the severity of such change.
Reader please note that the above is not mainstream science, but entirely my own thoughts - a new paradigm if you like. Use it to look at the landscapes you travel through, in order to understand more about them.
go to erosion index <===> go to erosion1 <===> go to erosion2