Sinking and Disappearing Soils
By James Sanner
What it Means for Food Availability
The issues outlined in this article are specific to the Everglades, but the problems and concerns around aspects of soil subsidence is something impacting soils across the planet. In the article ‘Are sinking soils in the Everglades related to climate change’ [1], recently published in the American Society of Agronomy journal, there is discussion around the causes and the effects relating to the soils sinking in the Everglades.
Draining swamps leads to significant ecological problems
In the Everglades the problems began around a hundred years ago when people worked to drain and divert water from parts of the swamps. Where this may have increased the things that people could do with that land, it dramatically changed the nature of the affected soils. Swamps have a special kind of soil known as a hydric soil. This typically waterlogged soil creates conditions in the soil where there is little to no oxygen, so the decomposition of plants is minimal.
Healthy hydric soils can be organic matter accumulators
As plants growing in these wet places die and are buried over time, much of the carbon making up those plants remains, because of how little decomposition occurs. [6] One way to think of decomposition is consumption and redistribution. Things that decompose act as a food source for some other micro or macro organism. The bacteria, fungi, protozoa nematodes and arthropods may snack on parts of the dead plant matter, move around some, and are then themselves snacked on by something else in the old web.
In nature everything is food for something else
The process of metabolism is one which takes some food and converts it into energy. Just like a cooking fire needs oxygen to burn, most metabolic processes need oxygen to make energy. So when there is no oxygen in a soil, like waterlogged hydric soils, there is not much metabolism going on consuming the carbon food, and the carbon accumulates there. These carbon sources over time accumulate to form peat, and over a longer time continue on becoming brown coal, and if left in appropriate conditions with enough time, they would turn into a hard black coal like anthracite.
Soils are sinking an inch a year
When canals are cut in and swamps’ soils are drained, as that water drains out, spaces open up in the spongy organic matter which are able to be filled with air. When all of the organic matter now becomes exposed to oxygen it creates great conditions for a bacteria decomposer feeding frenzy. With the help of the oxygen, the bacteria begin eating the carbon, and giving off as a byproduct carbon dioxide. Bacteria are taking carbon from the soil, and releasing it into the atmosphere. This transferring of soil carbon to atmospheric carbon has been occurring in the Everglades for decades and has been measured as reducing the soils an inch a year. [1] With the problems caused by the high levels of atmospheric carbon, it is unfortunate that there continues to be policies which support practices that move so much carbon out of the ground and into the sky.
Sinking Soils are Elsewhere for Different Reasons
On the other side of the United States there are issues around ground subsidence, but for very different reasons. A few years ago it became increasingly apparent that the ground in California’s central valley was sinking. As the measurements came in it was found that vast areas were sinking up to two inches per month, with areas having sunk over time nearly thirty feet.
Nature abhors a vacuum
This was in the height of one of California’s worst droughts, and farmers were pumping as much well-water up as they could to keep their crops going. The problem escalated due to the huge voids that all that removed water was creating. Some of the snow melt coming off the western slopes of the Sierra Nevada mountain range percolates down through the ground, finding its way into vast aquifers. These aquifers are like underground caves, and as the water was removed, the water pressure was no longer pushing the top of the cave roof up and the aquifers began to compress underground, and the soil began to sink up on the surface.
When somethings are gone, they will never again return
The problem of shrinking aquifer volume is significant, because this is not something which is able to be recovered, meaning that the overconsumption of water has left those areas with less available future water. Regardless of how much future snow melt water comes off the mountains it will not have the force necessary to raise the ground back up and increase the volume of the aquifers.
Irrigating arid soils often leads to problems with too much salt
The changes in this area have also had negative impacts on the soils as well. Plants need water, light and nutrients to grow. In a region where there is very little rainfall a common practice is to irrigate so as to help plants get the water they need. Water is a polar molecule which means it has a positively charged side and a negatively charged side. This is what leads to water being called the universal solvent, because just about everything dissolves into water. These properties are what enable so many solids to combine with water and turn into a liquid solution. This is why our oceans are salty, rain water dissolves salts in and on the ground and those salts accumulate as they are washed down to and deposited into the sea.
1/10 of the world’s irrigated land has been damaged by salt [5]
When an area gets just a little water, like from that of irrigation in arid regions, some of the minerals in the soil may dissolve. However, instead of being leached or drained away those minerals are drawn up to the surface as the water evaporates. Given enough time with irrigation water being applied to an area which doesn’t receive enough rainfall to flush things out, the soils in an area can actually develop a salty crust over them. This salt accumulation creates conditions which makes it nearly impossible for most plants to grow in.
Permaculture’s First Principle is to Observe
By closely observing an area you will know if you are doing harm. So, what does this all point to? Practices making historically wet areas dryer and dry areas wetter both have negative impacts on the soil’s ability to help growing plants. Soil carbon is of tremendous benefit for the growth of plants due to its ability to hold and make available water and nutrients. Places like wetlands or prairies can have a deep stores of built up carbon, but interventions which break open those soils, with practices like plowing, adding in oxygen, and reducing constant cover of the soil, can turn places like the Everglades to bare rock and the Great Plains into a dust bowl.
Earth has lost a third of arable land in the past 40 years [3]
Practices which degrade the soil are not new. Some argue that as long as agriculture has existed, the rate of soil loss has been greater than it would have been without human interference. In David Montgomery’s wonderfully researched book, Dirt: The Erosion of Civilization, he points out how it has specifically been the destruction of healthy soils which has led to the downfall of nearly every major past civilization. Society needs food to eat, food grows from the soil, when the soil is gone either the society falls apart or they find new soil to work with.
By 2050, we’ll need an estimated 50% more food for 9 billion people [3]
Our current society is a global society, so when problems occur in one area there is no ‘over there’ that we can run to and find a fresh new area to work with. The old adage goes, ‘when one is in a hole it is first good to stop digging.’ Identifying the causes of the problems leading to these soils failing is critically important. Plowing, leaving land barren, spraying or covering it with artificial or toxic chemicals, inappropriate grazing practices and the mismanagement of water and wastes are a few of the factors leading to major soil losses.
Mother Earth supplies an abundance for all creatures to thrive
Fortunately, there are alternatives to all of these ill-advised practices. With regenerative agriculture practices soil carbon concentrations are able to be increased instead of continuing to decrease, with that soil carbon actually being sequestered out from the atmosphere. Through the switching over to perennial crops the need for tilling and/or leaving fields bare is able to be done away with. Not every annual currently has a perennial, but through the care and attention of plant breeders this is changing with increasing perennial plant availability. There is inspiring plant breeding work being done at places like the Land Institute where they are working to increase perennial crop availability. In addition, if holistic range management were to be employed, with rotational grazing not allowing an area to exceed its holding capacity, the presence of the animals on the land not only doesn’t harm the land, but it can positively benefit it.
Where we do what we do matters as much as what we do
And finally, the mantra of real estate needs to be considered in the scope of agriculture; it's all about location, location, location. Not all areas are suited for agriculture, the side of a mountain, edge of a desert or polar tundra come to mind. And many of the places which are best suited for agriculture have been developed over the years with roads, houses or buildings. Once established it is a difficult thing to ask someone to move, because there is a different plan for their land. However, as history has pointed out, when the food runs dry people are often forced to move to areas better suited for getting their needed resources. Some of these difficult social issues will likely be addressed at some point in the future, thankfully from the standpoint of how to act as good stewards of the land, there are many people showing the way for how to live in harmony with the soil.
Footnotes
[1] American Society of Agronomy, Press Release, Sinking Soils Related to Climate Change, https://www.agronomy.org/news/media-releases/releases/2020/0115/1145
[3] https://www.theguardian.com/environment/2015/dec/02/arable-land-soil-food-security-shortage
[5] Food and Agriculture Organization (FAO). Training Manual, “Salty Soil” Chapter 7, https://www.fao.org/3/r4082e/r4082e08.htm
[6] This process is more thoroughly explained in the soil blog article from December 3rd. https://weplantitforward.org/blog/soilcansaveus