Published on April 5th, 2018 | by James Ayre0
Fossil Water Depletion, Groundwater Contamination, Saltwater Intrusion, & Permanent Subsidence — The Great Freshwater Depletion Event Now Underway
April 5th, 2018 by James Ayre
Much of the modern world’s agricultural productivity, industrial activity, and high degree of urbanization is dependent upon the pumping and exploitation of limited freshwater resources. In some regions the water that is being relied upon is so-called fossil water — that is, water that was deposited many millennia ago and is mostly not being replenished for whatever reasons, such as lack of rainfall or impermeable geologic layers like heavy clay or calcrete laid on top.
As these fossil water reserves are depleted, there is often nothing to replace them (the one notable exception being the possibility of desalination in some regions), with the eventuality often being large populations, industrial infrastructure, and farmland that is untenable in the regions in question, to be followed by mass migrations out of such regions.
Particularly notable regions that are dependent upon fossil water are the American Great Plains (the Ogallala Aquifer), northeastern Africa (the Nubian Sandstone Aquifer System), and central-southern Africa (the Kalahari Desert fossil aquifers).
The situation as regards to fossil water depletion in some regions is compounded by extensive development (and paving over) of aquifer-recharge areas in regions where rainfall is otherwise sufficient to replenish aquifers, and further so simply by unsustainable usage rates which draw down reserves.
As groundwater in regions with the possibility of recharge is pumped at unsustainable rates, though, what generally also occurs is ground subsidence. In plain language, the ground sinks due to the lack of support previously provided by groundwater that is no longer there. Subsidence in this context is notable because it leaves the ground and aquifer in question far less capable of storing water, due to compaction. In other words, excess groundwater pumping permanently removes the ability of many aquifers to store water, leaving total aquifer capacity far lower than previously, and thus contributing to the drying out of the region in question.
Going back to the issue of over-paving watersheds that have been developed, another issue that follows from this is the eventuality of large flood events (due to the lack of open ground-space to run down into), and thus further soil erosion which itself leaves the land in question less capable of holding and retaining water/moisture.
All of these above issues are themselves further compounded by saltwater intrusion in coastal regions due to the pumping of groundwater creating a vacuum-effect that draws nearby saltwater into the aquifers, and also due to ground subsidence, general sea level rise, and groundwater contamination in many regions, which is often the direct result of the industrial and agricultural activities that are themselves drawing the most water.
So what we have in the modern world, when we take a step back, is the convergence of growing problems of: fossil water depletion; the destruction of the ability of many aquifers to retain water due to over-pumping as the result of ground subsidence; saltwater intrusion of aquifers caused by over-pumping and sea level rise; widespread groundwater contamination due to industrial and agricultural activities; and ever growing population numbers and food/agricultural needs.
With that in mind, the following is a basic overview of where things stand on different issues.
First, here are a couple of basic facts:
- More than 4 billion people around the world already experience extreme water scarcity at least 1 month every year.
- More than 500 million people around the world already experience extreme water scarcity essentially year-round. This number is expected to increase significantly over the coming decades.
- Well over half of the largest cities around the world now experience water scarcity occasionally.
- Fresh-water demand is estimated to exceed demand by at least ~40% by 2030.
- Deforestation and accompanying aridification and/or desertification are primary drivers of water scarcity in some regions due to decreasing atmospheric moisture and thus rainfall levels. This is largely driven by consumer demand for cheap meat and livestock-feed on the one hand, and by demand for timber products on the other. Other water-intensive crops play a part as well though, like cotton and various types of oil/tree-nut/fruit crops for instance.
- With “higher” standards of living, water use increases exponentially as people switch from a low-resource lifestyle to one of profligate use and waste. People in the wealthier countries of the world are known to use 10-50 times more fresh-water on an annual basis than those in the poorest.
- Over just the last century, more than half of the world’s wetlands and watersheds have been destroyed and no longer exist in any capacity. Unsurprisingly, this has resulted in the loss of a very large amount of biodiversity, and also of numerous fisheries. In the US and Europe the loss of historic wetlands over the last century is in the 80-95% range.
- A large majority of the groundwater now being pumped up from aquifers is being used by agriculture and industry.
- Many of the largest rivers of Asia could effectively be gone by as soon as the end of the century due to the current rapid melting of associated glaciers.
Overpumping, Ground Subsidence, & Saltwater Intrusion
The overpumping of freshwater from aquifers, as noted previously, is a direct cause of ground subsidence and saltwater intrusion in coastal areas. What wasn’t stated previously is that as aquifer levels are drawn down, the quality of the water being pumped is generally being lowered, with rising levels of salinity (via ground salts), and also rising levels of grit and contaminants also being observed.
Something else to note on that count is that as aquifers are diminished, the natural outflows of the region — springs, etc. — experience much reduced outflows, or simply cease to exist.
In relation to this, the aforementioned experience of ground subsidence results in sinking land, which increases the danger of flood events in addition to reducing the capacity of the aquifer in question to hold water. It’s notable, for instance, that in some of the land surrounding Houston, Texas, ground levels have dropped by as much as 9 feet in recent decades due to extensive groundwater pumping.
Despite all of this, resistance to a reduction in pumping rates is often high, with those involved in agriculture in particular often fighting hard to stop the imposition of such an approach.
Accompanying ground subsidence in coastal regions is often saltwater intrusion into the aquifers being pumped — thereby diminishing the quality of the water, and often demanding costly treatment processes to allow continued potability.
Generally speaking, freshwater pumping in coastal regions allows saltwater to flow further inland than is otherwise the case, as do agricultural drainage systems. Sea level rise itself does as well, of course, as do the storm surges that accompanying powerful storms. This is all especially true in coastal regions where the aquifers are highly porous — in parts of New Jersey and Florida, for instance.
Groundwater Contamination & Pollution
In addition to problems of sheer freshwater unavailability are the fast increasing problems of freshwater contamination. Groundwater contamination has become an increasingly common problem in recent decades as industrial and agricultural productivity levels have been brought to unsustainable levels.
While contamination that ultimately is the result of industrial and agricultural activities is the most common type, increasing urbanization is another, as population-dense regions are often unable to deal effectively with the waste products that result without expensive systems (which some regions can’t afford). Ineffective wastewater treatment facilities, landfills, and fueling stations, for instance, are often sources of groundwater contamination in urban regions. Some regions, it should be noted, feature groundwater with high levels of arsenic or fluoride regardless of human activity, and aquifer reliance in those regions is thus dangerous.
An example of a dangerous but common type of groundwater contaminant deriving from human activities is nitrates, which is generally the result of agricultural activities. Other, more dangerous, compounds are also common groundwater pollutants, including various types of solvents, PAHs, heavy metals, hydrocarbons, pesticides, herbicides, other artificial fertilizers, radioactive compounds, pharmaceuticals and their metabolites, and various types of persistent chemical pollution.
Before closing this section, I suppose that hydraulic fracturing (fracking) as a means of extracting fossil oil and gas reserves deserves a mention. While the practice itself does not inherently need to be a cause of groundwater contamination, in practice it often is due to the reality that it is often pursued carelessly and that e companies involved have a tendency to dissolve when problems arise (with those involved simply starting a new firm afterwords).
Loss Of Glaciers, Climate Change, Rising Temperatures, & Increasing Atmospheric Moisture
Accompanying the depletion and contamination of groundwater freshwater resources, the world’s above-ground freshwater resources — largely glaciers, winter snowpack, and high-altitude lakes — are rapidly disappearing as well in many parts of the world.
While the rapid melting of many glaciers in recent years has led to an increase in water availability in some regions — in particular in the parts of the world that ultimately source their freshwater from glaciers in South and Central Asia (via rivers originating there) — all that this means is that long-term supply is being compromised even faster than would otherwise be the case. As these glaciers disappear, there will be increased water scarcity affecting literally hundreds of millions to billions more people than is currently the case.
Also worth noting here, is that rising temperatures are themselves affecting freshwater supplies by increasing the rate of evaporation in many regions and thereby limiting the amount of surface water and the ability of aquifers to recharge. Accompanying this is the reality that as atmospheric moisture levels rise as a result, temperatures will continue rising even faster due to the reality that water vapor is itself a potent greenhouse gas.