Salinity and Pollution

This section is still under construction as we get our ideas together. We just can't help thinking many scientists are wrong - and that some permaculture practitioners may be right. If you disagree with us please contact us only if you can explain why.

Even though the climate over the last 10- 12,000 years had been relatively mild and predictable compared with the many millions of years previously when the god Chaos ruled the earth, during this period we have been systematically destroying our aquifers and our land. There is irrefutable evidence that we are also affecting our climate, at least since the industrial revolution began. The sequence: agriculture, irrigation, salinity and desertification has all too often been repeated in too many places. It is plain to see that our failure to understand and live with nature and understand the natural water cycle cannot continue. We must change the way with think to solve the problem.

In years gone by forests and grassland covered most of our planet. When it rained much of the water naturally percolated though soils that performed vital functions of providing albido and microclimate, slowing down the rate of transport to rivers and streams, purifying the water and replenishing natural aquifers. Our legacy has been to plough or pave, redirecting the water that fell as rain as quickly as possible to the sea. In dryer times the consequence is that we use up the natural freshwater lense non our ancient aquifer which are replaced with water that has traveled thereby picking up salts and pollution. Given global water shortages, problems with salinity, pollution, volume and rate of flow of runoff we need to change our practices so as to mimic the way it was for so many millions of years before we started making so many changes.

Our reading of the current literature indicates a failure to understand the water dynamic. Salinity and pollution are connected by a fundamental truism that does not seem to emerge in the literature which is that the more water travels through ground - the more salt it picks up as it will dissolve anything that is soluble and salts are by definition soluble. The more it travels through built up areas the more soluble pollution it can gather. The faster it travels the more energy it has to carry mud, silt and and macro pollution. Because they are controlled by the same water dynamic we discuss salinity and pollution together in this section.

 

The Water Dynamic with Respect to Salts and Pollution

How to Combat Pollution

Storm water = Rainwater + Pollution

Water is a scarce resource and it makes little sense to allow it to pick up pollution, yet this is what we not only allow to happen, it is what we make happen by bad engineering. It seems obvious to us that the solution to pollution of rainwater is to not let water gather volume and speed. This can easily be achieved by immediately capturing, filtering, cleaning and storing water and the only way to do so in urban and built up areas is to use pervious pavement. For this purpose we have designed Permecocrete which not only performs these functions but, because it uses Eco-Cement as the binder sets by absorbing CO2. Depending on whether capture during manufacture has been achieved or not the Eco-Cement used can either be close to carbon neutral or a carbon sink. In rural areas strategies include retaining and creating natural mulches, deep drainage, appropriate vegetation and reforestation.

Roads are conduits not just for traffic and a more detailed discussion of the merits of permecocrete is available in our product area and in papers for download.

For those skeptics who think that pervious pavement will rapidly become blocked by silt and macro-pollution - there are machines available that can clean pervious pavement just like we clean deep pile carpet. Besides, it is better to deal with pollution on our streets because once it gets into our water ways it is impossible to do anything much about it.

How to Defeat Salinity

The dynamics of water that affect pollution affect salinity in a similar way so we explain salinity differently to many others who work in the area and have different ideas about how to solve the problem. How we differ is that we believe that all salinity is related to the simple dynamic graphically set out above and is best explained in relation to it.

A major cause of salinity is irrigation. To the extend that irrigation is usually practiced in hot dry areas to add to the available water and thus allow plants to grow then it is also true that evaporation is greater than in cooler areas. Where irrigation is practiced other ground cover is lacking such as trees and associated leaf litter and the water does not therefore stay, much of it evaporates partly due to the sun's action but substantially also due to more rapid air movement at ground level as a consequence of the lack of vegetative cover in the form of bushes and trees. Water also flows through the soil into subterranean aquifers or along our plough furrows into drains and usually back to a source of irrigation water for others. The more water travels through ground the more salt it picks up. Much of the irrigation water used upstream returns to a stream or river and every time it recycles in this way it becomes saltier. The externality is a gradual build up of salt in the soil that does not express in real time economics and so the practice which will in the short term produce valuable corps is continued. In the longer term the external cost is poisoning of the land by salt for future generations.

The solution to irrigation salinity is to minimise added water requirements by increasing retention (and thus the water available for use) and reducing recycling which increases the distance traveled in accordance with the water dynamic. Another solution is deep drainage but this is not always possible especially in low lying areas. Retention can be increased by swales and appropriate planting and mulching and land that has already been ruined by salination can even be recovered in this way as has been recently demonstrated by the PunderZoie company. An excellent flash movie is available from the ABC North Coast on our sustainability links page that promotes permaculture which embraces these strategies.

Salination in dry country that is cleared and cropped without irrigation is explained by the Australian government and CSIRO in terms of lower evaporation and consequently rising water table that brings salt with it. We think this explanation confuses both cause and effect. The cause is higher evaporation through loss of ground cover and higher wind loads at ground level not lower evaporation as suggested. The effect is that rain that falls no longer replenishes underground aquifers which previously would have had a lense of fresh water on top. When this lens goes than saltier water can come to the surface in the manner described.

The solution is similar to that for irrigation salinity and includes appropriate planting reducing loss through evaporation, swales etc. in a similar manner.

Salination also occurs naturally such as in low lying areas with poor drainage or where water travels a long way through strata that contains salt and that is why the dead sea is for example salty.

Salt and the Demise of Civilisations

Irrigation is implicated in the fall of many civilizations and Mesopotamia is the example most often used. When large-scale irrigation began in the Tigris and Euphrates river valleys, it was accompanied by urban growth, writing, empires, monumental construction, and such technological innovations as the wheel. The former desert prospered and was central to the growth of human population and influence for about 4000 years. The former desert land became known as the Fertile Crescent. Today this so called Fertile Crescent is mostly desert again.

Salinity was the main cause of desertification however we believe that the analysis most often given which is that the process of irrigation reversed the normal flow of water through the soil is over emphasized. According to this analysis salt free fertile areas with reasonable rainfall are watered mainly by rain that carries salt in the soil deeper into the ground whereas evaporation in an irrigated desert causes water in the soil to move from lower levels toward the top of the soil as the sun dries out upper layers of fresher water and such movement carries salt toward the surface. Compared to the Australian government and CSIRO description above this explanation is more plausible, however there is another explanation we prefer which is best described by the water dynamic which applies in all cases and will always result in the correct explanation. In the case of irrigation reuse of the same water causes it to travels further through soil, and the water dynamic dictates that it will as a consequence pick up more salt. Irrigation causes more salinity the more the same water is used.

Most plants do not grow in salty soil and the Romans, appreciating this, sowed salt on the ruins of Carthage after its defeat to prevent it from returning to power. Flooding can reverse the effects of irrigation by washing the salt back into lower regions of the soil and out to sea. Egypt and China, subject to floods, have had fewer problems with salty soil than has Mesopotamia. In Egypt, however, damming of the Nile in 1964 prevented flooding but also started a buildup of salt in the soil.

The Maya practiced irrigation in a rain forest, where salt buildup would seem less likely than in a desert. Nevertheless, it appears that they too managed with irrigation to reverse the normal flow of minerals through the permeable limestone soil of Central America, contributing to the collapse of their civilization.

Today farmers in other irrigated regions, such as Australia, Pakistan and the San Joaquin Valley in the United States, face similar buildup of salt in the soil.


printer friendly

[1] Source:Illustration by John M. Evans USGS, Colorado District (http://ga.water.usgs.gov/edu/watercyclegraphichi.html)