Inland freshwater salinization historically was once thought to be a problem only in areas with arid and semi-arid climates, poor agricultural drainage practices, sodic soils and saline shallow groundwater. Certainly, when I was in school that is what we were taught. Today, inland freshwater salinization is on the rise across many cold and temperate regions of the United States.
Inland freshwater salinization is particularly notable in
the densely populated Northeast and Mid-Atlantic like here in Northern Virginia,
and agricultural Midwest regions of the country. It turns out that salt is the
fingerprint of mankind. We have disrupted the Earth's natural salt cycle in every
activity from the first seeds of agriculture to modern high-tech living. The
presence of mankind is marked by salt- the fundamental change in the chemistry
of the world’s inland waters and soils.
The first mark of this fingerprint appeared in ancient
Mesopotamia, the Cradle of
Civilization. To feed growing populations, the Sumerian people of
Mesopotamia (Modern day Iraq) engineered massive irrigation systems for their
arid lands. They used flood irrigation
and this over-irrigation of their caused the water table to rise, wicking
naturally occurring underground salts to the surface via capillary action.
As water evaporated,
it left behind a salt crust. Between 2100 BC and 1700 BC, soil salinity forced
a shift from wheat to the more salt-tolerant barley, eventually leading to
agricultural collapse and the migration of 60% of the population. This pattern
repeated itself across other civilizations across the globe.
As humanity expanded, and our population grew, so did the ways that the salt footprint that traveled
with our communities grew- through intensified land use and waste disposal. In regions like Australia, clearing
deep-rooted native trees for shallow-rooted crops stopped the natural drawdown
of groundwater, allowing saline water tables to rise and drown the soil in
salt. The land application of manure and modern fertilizers adds significant
salt ions (like potassium and chloride) to the soil, which eventually leach
into groundwater and rivers.
Mankind has a taste for salt. Wastewater from growing urban centers carries concentrated salts from our diets. This "fingerprint" is becoming even more indelible as we more widely adapt potable water reuse—recycling wastewater directly back into our taps. While recycling is a necessity to supplement supply for regions becoming more water scares or increasing population, it creates a salt loop that is difficult and expensive to break. Because traditional wastewater treatment cannot remove salts every time we use water, we add salt—from our diets, soaps, and water softeners. When that water is recycled and sent back to homes, those salt levels naturally rise for each cycle. To strip this salt out, cities must use Reverse Osmosis (RO). However, RO is energy-intensive and produces a highly concentrated "brine" waste that is difficult to dispose of without harming local ecosystems.
The scientists at the Occoquan Watershed Laboratory believe
that the sodium in UOSA’s wastewater comes from a variety of sources -watershed
deicers, water treatment processes (both household and Fairfax Water),
household products, commercial and industrial discharges, drinking water
treatment, and wastewater treatment. On the basis of data provided by UOSA they
estimate that 46.5% of the daily sodium mass load in UOSA’s reclaimed water is
from chemicals used in water and wastewater treatment (for pH adjustment,
chlorination, dichlorination and odor control), a single permitted discharge
from the Micron Semiconductor facility and human excretion (our diets are
salty). That still leaves 53.5% of the salt, and its source remains unknown.
The salt levels are also rising in the rivers and streams
that provide water to our region. In the modern era, the salt fingerprint has
become more complex, involving a "chemical cocktail" of salts used
for safety and comfort. For example, there is salt in soaps, cleaners, and
water treatment chemicals. To ensure
winter safety, millions of tons of chloride-based salts are spread on roads
annually. This salt doesn't just disappear; it migrates into lakes and streams,
where it can persist for decades.
In many regions, household water softeners are the largest
source of chloride to wastewater treatment plants, and also to the groundwater.
In Prince William County water softeners in homes connected to public water
supply are not tracked. However, the VA Tech tracks water softeners used by
well owners. In Prince William there about 16,000 private wells and over 40% are
estimated to have water softeners. Each one of these water softeners discharges
800-1,000 pounds of salt. This salt is
discharged directly into freshwater ecosystems.
Globally, human-caused salinization affects an estimated 2.5billion acres of soil—an area the size of the United States. It isn't just
a local agricultural nuisance; it is a chronic environmental
"syndrome" that mobilizes other toxins like lead and mercury,
threatens drinking water, and permanently alters the chemistry of our planet's
freshwater.
