Soil erosion and conservation - part3

by Dr J Floor Anthoni (2000)
If the risk of erosion can be estimated in advance, farmers would be better prepared and can apply the proper soil conservation measures. A formula has been devoloped, the Universal Soil Loss Equation, with which the risk of unsustainability can be calculated. All soil eventually ends up in the sea, where it causes tremendous damage in mysterious ways.

estimating erosion Soil erosion can be predicted from the kind of soil, what it is used for, how it is farmed, the lay of the land, and size of the field.
affecting the sea Ultimately, all soil ends up in the sea. It is a natural process that brings nutrients to the sea where it fertilises the coastal fishery. But too much of a good thing causes problems.
least loss landscapes The landscapes we see today have existed for a very long time. Under the influences of climate and cover, they have formed into shapes that minimise the loss of soil and nutrients. A new look.
go to erosion index <===> go to erosion1 <===> go to erosion2


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Estimating erosion
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:

A ‘tolerance factor’ of 4-11 ton/ha/yr is aimed for, which is still much larger than natural soil formation, but which does not appear to affect productivity. If the tolerance factor exceeds sustainability of productivity, different cover management practices or supporting practices are selected and enforced.

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 sustainability, 1991)

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):

REP= slope ^ 1.5 x RER x precipitation / 1000 
where slope ^1.5 means slope to the power 1.5 (less than squared).
rainfall precipitation is the mean monthly rainfall for the peak rainfall month, in mm.

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.
Refer also to the diagram for erosion rate as a function of land slope soil63.gif

Land category
water body, lake
evergreen broadleaf forest
evergreen needleleaf forest
deciduous needleleaf forest
closed shrubland
open shrubland
woody savanna
permanent wetlands
croplands, natural mix
urban & built-up
barren or sparse veg.
river plume vs river flowOnce 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.


Muddy seas:
  • kill deep seaweeds
  • suffocate filter feeders
  • affect shellfish
  • cause problem blooms
  • damage beaches
  • pollute shores
  • 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.
    Contributing factors:
  • mud stays inshore
  • is stirred up often
  • currents shift it
  • 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.
    nutrient cycling on the continental shelfClay, 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 proved (yet).
    currents herding nutrients onto the shelfA 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.

    The very 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.

    muddy sea in the marine reserve
    Since 1990, the sea has become much dirtier. This photo was taken in the winter of 1996. It shows the first marine reserve in New Zealand, near Goat Island (in the picture). A heavy rain storm colours the sea deep brown with visibility less than 10cm. Such densities of mud damage sea life. Before 1990, such events were unknown but now they occur 2-4 times yearly.
    mud in Leigh Harbour
    Sights like these, of mud filling coastal embayments, are now common world-wide. This picturesque harbour of Leigh, New Zealand, has a very small catchment area with well tended farms and properties. Yet, a single rain storm today, brings more mud to the sea than ever before in history.
    Noctiluca scintillans plankton bloom
    Drifts of orange plankton blooms of the sea spark Noctiluca scintillans are now common all year round, whereas before 1990 some would be noticed in warm summers. The sea spark is not poisonous, inflicting little damage to the environment.
    Dense plankton bloom West Coast
    This is not oil, nor mud, but a very dense plankton bloom at New Zealand's northern west coast. The visibility in the water would be less than 5 cm! Blooms like these are a very recent phenomenon. Some plankton blooms cause mortality in marine animals. Shellfish fisheries are closed due to the presence of high levels of Paralytic Shellfish Poisoning.
    biotoxin alert
    Health warning signs like these are now found where they have never been before. The sea has been changed profoundly.

    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!

    sewage! no swimming!.
    Pilchard mass mortality
    In June 1995, a mass mortality of pilchards happened around New Zealand's north east coast. Pilchards feed on fine phyto and zoo plankton, and grow fast. They are a main source of food for higher organisms like commercial fish and dolphins. 
    Close-up of dead pilchards. Pilchards are one of the few fish capable of filtering very fine plankton, even phyto plankton (diatom strings), reason why they grow fast. They form the basis for a food web of fish and even dolphins. When pilchards are threatened, a chain of other species is threatened too.
    a sea cucumber mopping up the dust
    Dust settling on marine algae, shades them from the sunlight which is already weak under water. But sea cucumbers come to their rescue. With ten sticky mops in their mouths, they mop up the dust, thus providing a mobile cleaning service. Notice how the area around the cucumber has been cleaned. While moving from left to right, it leaves a long trail of compacted waste behind.
    seasquirt mats in Parengarenga Hr
    Parengarenga Harbour in New Zealand's far north, located furthest away from the ill effects of population, was renowned for its clear water and rich sea life. Now a caricature of its former glory, its shores are covered in fast growing seasquirts and other opportunistic organisms. Its biodiversity has plummeted.
    scyphistoma of jellyfish on rocks
    These white polyps are the scyphistoma of jellyfish. Each produces dozens of small jellyfish, adding up to a plague of them. The polyps could establish themselves, because spots on the rocks, like this one, fell bare because the organisms once living there, died by poison from plankton.
    carpet tube worms
    Carpet tubeworms, covering the sandy bottom with wall to wall white, living carpet, were once fairly common. Of the five spots known to me, only one can still be found today.
    washup of parchment worm
    Parchment worms
    The sea bottom has suddenly been colonised by these parchment tubeworms, washed up on this beach after a storm. Although the tube worm may have lived in New Zealand long before, it suddenly found reason to take over, destroying scallop beds and altering the sea bottom. Without these worms, scallop beds have already been disappearing because of overfishing and pollution.

    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 erosion.

    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