How Groundwater Contamination Threatens Aquifer Life and Ecosystems

Field report

The invisible spread of chemicals through underground water layers is reshaping ecosystems beneath our feet.

Environmental Correspondent has covered water quality and freshwater ecology for outlets including National Geographic, The Guardian, and Audubon Magazine.

And August aims to deliver. We’ve got the rise of a rare blue supermoon, a planet glowing bright in opposition, dark skies for one of the best meteor showers of the year, and some peak beauty from the Milky Way.

Wishing you clear skies!

Nature Archives / Freshwater Ecology Collection

During the last century, modern agricultural chemicals were developed as part of an intensification of farming that sought to boost yields at any cost. After World War II, synthetic compounds ushered in a new era of chemical agriculture—one that conveniently ignored the collateral damage to creatures living in soil and water. The chemical industry expanded rapidly, pushing products everywhere it could, even with the knowledge that aquatic organisms, amphibians, and invertebrates were dying as a result.

Thankfully, we recognized the devastating effects of some of the worst chemicals, and several have been banned in much of the world. However, we are still enthusiastic about applying synthetic compounds to living systems. Currently, around 3 million tonnes of agricultural chemicals are used worldwide every year. In Imperial measurements, that's around 3.3 million tons or 6.6 billion pounds.

It is an enormous number, and here's the thing. We apply these vast amounts of chemicals to crops, but they don't just vanish once they've done their job of eliminating their intended targets.

Researchers now reveal that agricultural chemicals, in fact, travel far and wide after initial application, seeping into groundwater, rivers, springs, and soils far from where they were first spread.

The global study analyzed the geographic distribution of 92 of the most commonly used agricultural chemicals and found that approximately 70,000 tonnes (77,000 U.S. tons or 155 million pounds) of potentially harmful compounds leach into groundwater systems each year, impacting aquifer ecosystems and the freshwater resources that depend on them.

The shower, sometimes creating as many as 60 to 200 shooting stars per hour, is produced as Earth passes through debris left over from the orbit of Comet Swift-Tuttle. This 16-mile-wide periodic comet, which completes an orbit around the sun every 133 years, has been described as "the single most dangerous object known to humanity." This is because every instance of its return to the inner solar system brings it ever closer to the Earth-moon system. Though astronomers believe the comet bears no threat for at least the next 2,000 years, future impacts cannot be ruled out.

"Our study has revealed that these chemicals wander far from their original source," says lead author Federico Maggi from the University of Sydney's School of Civil Engineering. "In many cases these compounds end up a long way downstream and often, though in much smaller amounts, all the way to the ocean."

The researchers show that some 80% of applied chemicals degrade into byproducts ("daughter molecules") in the soil that surrounds crops.

"This degradation often occurs as a 'cascade' of molecules into the surrounding environment, which can persist in the environment for a long time and can be just as harmful as the parent compound or applied chemical. One such example is glyphosate. Although it is highly degradable, it breaks down into a molecule known as AMPA that is both highly persistent and toxic," says Maggi.

The study reveals that only a fraction of chemicals enter river systems. But once they are in the water, most of the active ingredients end up in the ocean. This puts at risk the very basis of marine and freshwater food chains," the authors explain, with potential negative impacts on aquatic insects, fish larvae, and the amphibians that depend on clean water for breeding.

August is peak Milky Way season in the northern latitudes, providing not only comfortable temperatures from which to gaze into our galaxy’s shimmering core but also great positioning in the night sky.

Dr. Federico Maggi, Dr Francesco Tabiella, Dr Fiona Tang

And indeed, it amounts to 730 tonnes (1.6 million pounds) of chemicals entering rivers alone each year. As the study explains, about 13,000 kilometers (8,100 miles) of rivers display chemical concentrations above safety limits for a number of aquatic plants and invertebrates—and nobody is sure about what kind of impact this has on the tiny creatures—mayfly nymphs, caddisfly larvae, freshwater mussels—that form the foundation of river food webs.

"Just because we don't see chemical residues in soil and water doesn't mean they're not there, impacting critical systems on land, rivers and oceans," says paper co-author Dr. Fiona Tang from Monash University.

With a rapidly expanding human population and the daunting logistics of growing enough food to feed everyone, the topic of agricultural chemicals can become contentious. Advocates argue that they are needed in order to grow adequate food. But Maggi points out that reducing chemical use worldwide is possible without threatening food security, as long as such initiatives are designed and implemented in consultation with food producers.

"Globally, there is a lot of room to increase efficiencies and yield while still supporting an abundant food supply through new technology and modern crop management practices," he says. In a separate paper, Maggi laid out recommendations to reduce chemical use, including calling for a reliable set of indicators and improved monitoring.

"It is important that national authorities disclose statistics on the use of agricultural inputs, be they fertilizers or crop protection, given the effect they have on the environment and ecosystem services."

The study, "Agricultural pesticide land budget and river discharge to oceans," was published in Nature.

Umetsu N, Shirai Y. Development of novel pesticides in the 21st century. J Pestic Sci. 2020 May 20;45(2):54-74. doi: 10.1584/jpestics.D20-201. PMID: 33132734; PMCID: PMC7581488.

Look for Earth's shadow (All year)

Ever wonder what causes the beautiful bands of color in the eastern sky at sunset or the western sky at sunrise? The dark blue band stretching 180 degrees along the horizon is actually the Earth's shadow emanating some 870,000 miles into space. The golden-red portion, nicknamed the "Belt of Venus," is Earth's upper atmosphere illuminated by the setting or rising sun.

Now that you know about this phenomenon, choose a night or morning sometime to try and pick it out. You'll need a western or eastern horizon that's fairly unobstructed to get a clear view of our planet's huge curved shadow.

Why Space Matters to Treehugger

Space is our planet’s home, and its wonders help us get outside and foster an appreciation of nature. Exploring space and the cosmos can also help us learn about what’s happening on Earth. Space-based technologies have helped us better understand climate change, water cycles, and even air quality.