A highly toxic insecticide used on cats and dogs to kill fleas is poisoning rivers and streams across the United States and the United Kingdom, according to two recent studies. The pollution is directly affecting water insects and the fish and birds that depend on them, the researchers warned.
Both studies focused on fipronil, a pesticide commonly used as an anti-flea substance for petsin many parts of the world. It has several properties that make it an attractive pest control agent (including high toxicity towards invertebrates and water solubility) — but those same properties also make it a nasty pollutant.
Despite being banned for agricultural use, fipronil is still commonly used in pets to treat fleas and ticks. In the UK alone, there are 66 licensed veterinary products that contain fipronil, including spot-on solutions, topical sprays, and collars impregnated with the active ingredient. Some require prescription and others don’t.
Researchers in the UK found fipronil in 99% of samples from 20 rivers and the average level of one particularly toxic breakdown product of the pesticide was 38 times above the safety limit. There are about 10 million dogs and 11 million cats in the UK, with an estimated 80% receiving flea treatments.
“Fipronil is one of the most commonly used flea products and recent studies have shown it degrades to compounds that are more toxic to most insects than fipronil itself,” Rosemary Perkins at the University of Sussex, who led the study, told The Guardian. “Our results are extremely concerning.”
This isn’t the first time researchers have sounded the alarm on this type of pollution. A study in 2017 by the conservation group Buglife had already warned over high levels of insecticides in rivers but didn’t include fipronil. Aquatic insects are highly vulnerable to such substances. Previous studies shown chronic waterway pollution led to sharp drops in insect numbers and falls in bird numbers.
With that in mind, Perkins and her team decided to review 4,000 analyses on samples in 20 English rivers. They found fipronil in 99% of the samples as well as a highly toxic breakdown product called fipronil sulfone in 97% of them. Average concentrations were 5 and 38 times higher than their chronic toxicity limits, respectively.
“I couldn’t quite believe the pesticides were so prevalent. Our rivers are routinely and chronically contaminated with these chemicals,” Dave Goulson, part of the study, told The Guardian. “The problem is these chemicals are so potent, even at tiny concentrations. We would expect them to be having significant impacts on insect life in rivers.”
Similar results were found in a recent study in the US. Researchers from Colorado State University. Researchers learned that fipronil and other related compounds were more toxic to stream communities than previous research had suggested, especially in the relatively urbanized Southeast region.
The insecticide is likely affecting stream insects and impairing aquatic ecosystems across the country. To make matters even worse, fipronil degrades into new compounds, some of which the study found to be more toxic than fipronil itself.
The researchers also found delayed or altered timing of when these insects emerged from streams, and the effects of this can cascade across the entire food chain.
“The emerging insects serve as an important food source,” Janet Miller, the lead researcher of the study, said in a statement. “When we see changes, including a drop in emergence rates or delayed emergence, it’s worrisome. The effects can reverberate beyond the banks of the stream.”
Miller said fipronil compounds were detected at unsafe concentrations in 16% of streams sampled across the U.S. and were most prevalent in streams of the Southeast region of the country. Scientists found fipronil compounds much less widespread in other regions, suggesting use patterns of the insecticide differ across the country.
Every time you bathe in the sea, you have geology to thank for the extra buoyancy that salty water provides. Large-scale geological processes bring salt into the oceans and then recycle it deep into the planet. The short answer to ‘why is the ocean salty’ sounds something like this:
Salts eroded from rocks and soil are carried by rivers into the oceans, where salt accumulates. Another source of salts comes from hydrothermal vents, deep down on the surface of the ocean floor. We say “salts” — because the oceans carry several types of salts, not just what we call table salt.
But the longer answer (that follows below) is so much more interesting.
In the beginning there was saltiness
As it is so often the case in geology, our story begins with rocks and dirt, and we have to go back in time — a lot. Billions of years ago, during a period called the Archean, our planet was a very different environment than it is today. The atmosphere was different, the landscape was different, but as far as ocean saltiness goes, there may have been more similarities than differences.
Geologists look at ancient rocks that preserved ancient water (and therefore, its ancient salinity); one such study found that Earth’s Archean oceans may have been ~1.2 times saltier than they are today.
At first glance, this sounds pretty weird. Since salt in the seas and oceans is brought in by river runoff and erosion, the salts hadn’t yet had time to accumulate in Earth’s earliest days. So what’s going on?
It is believed that while the very first primeval oceans were less salty than they are today, our oceans have had a significant salinity for billions of years. Although rivers hadn’t had sufficient time to dissolve salts and carry them to oceans, this salinity was driven by the oceanic melting of briny rocks called evaporites, and potentially volcanic activity. It is in this water that the first life forms on Earth emerged and started evolving.
“The ions that were put there long ago have managed to stick around,” says Galen McKinley, a UW-Madison professor of atmospheric and oceanic sciences. “There is geologic evidence that the saltiness of the water has been the way that it is for at least a billion years.”
The ancient salinity of oceans is still an area of active research with many unknowns. But while we don’t fully understand what’s going on with the ancient oceans, we have a much better understanding of what drives salinity today.
So how do the oceans get salty today?
Oceans today have an average of 3.5% salinity. In other words, 3.5% of the ocean’s weight is made of dissolved salts. Most, but not all of that is sodium chloride (what we call ‘salt‘ in day to day life). Around 10% of the salt ions come from different minerals.
At first glance, 3.5% may not seem that much, but we forget that around 70% of our planet is covered in oceans. If we took all the salt in the ocean and spread it evenly over the land surface, it would form a layer over 500 feet (166 meters) thick — a whopping 40-story building’s height of salt covering the entire planet’s landmass. That’s how much 3.5% means in this particular case.
All these salts come from rocks. Rocks are laden with ionic elements such as sodium, chlorine, and potassium. Much of this material was spewed as magma by massive volcanic eruptions and can form salts under the right conditions.
Because it is slightly acidic, rainwater can slowly dissolve, erode rocks. As it does so, it gathers ions that make up salts and transfers them to streams and rivers. We consider rivers to be “freshwater”, but that’s not technically true: all rivers have some salt dissolved in them, but because they flow, they don’t really accumulate it. Rivers are agents for carrying salts, but they don’t store salts themselves.
Rivers constantly gather more salts, but they constantly push it downstream. Influx from precipitation also ensures that the salt concentration doesn’t increase over time.
Meanwhile, the oceans have no outlet, and while they also have currents and are still dynamic, they have nowhere to send the salts to, so they just accumulate more and more salt. Which leads us to an interesting question.
So, are the oceans getting saltier?
No, not really. Although it’s hard to say whether oceans will get saltier in geologic time (ie millions of years), ocean salinity remains generally constant, despite the constant influx of salt.
“Ions aren’t being removed or supplied in an appreciable amount,” says McKinley. “The removal and sources that do exist are so small and the reservoir is so large that those ions just stay in the water.” For example, she says, “Each year, runoff from the land adds only 0.00005 percent of total ocean salts.”
A part of the minerals is used by animals and plants in the water and another part of salts becomes sediment on the ocean floor and is not dissolved. However, the main reason why oceans aren’t getting saltier is once more geological.
The surface of our planet is in a constant state of movement — we call this plate tectonics. Essentially, the Earth’s crust is split into rigid plates that move around at a speed of a few centimeters per year. Some are buried through the process of subduction, taking with them the minerals and salts into the mantle, where they are recycled. The movement of tectonic plates constantly recirculates material from and into the mantle.
With these processes, along with the flow of freshwater, precipitation, and a number of other processes, the salinity of the Earth’s oceans remains relatively stable — the oceans have a stable input and output of salts.
But isolated bodies of water, however, can become extra salty.
Why some lakes are freshwater, and some are *very* salty
Lakes are temporary storage areas for water, and most lakes tend to be freshwater. Rivers and streams bring water to lakes just like they do to oceans, so then why don’t lakes get salty?
Well, lakes are usually only wide depressions in a river channel — there is a water input and a water output, water flows in and it flows out. This is called an open lake, and open lakes are essentially a buffer for rivers, where water accumulates, but it still flows in and out, without salts accumulating. Many lakes are also the result of chaotic drainage patterns left over from the last Ice Age, which makes them very recent in geologic time and salts have not had the time to accumulate.
But when a lake has no water output and it has had enough time to accumulate salts, it can become very salty. This is called a closed lake, and closed lakes (and seas) can be very salty, much more so than the planetary oceans. They accumulate salts and lose water through evaporation, which increases the concentration of salts. Closed lakes are pretty much always saline.
We mentioned that world oceans are 3.5% salt on average. The Mediterranean Sea has a salinity of 3.8%. The Red Sea has some areas with salinity over 4%, and Mono Lake in California can have a salinity of 8.8%. But even that isn’t close to the saltiest lakes on Earth. Great Salt Lake in Utah has a whopping salinity of 31.7%, and the pink lake Retba in Senegal, where people have mined salt for centuries, has a salinity that reaches 40% in some points. The saltiest lake we know of is called Gaet’ale Pond — a small, hot pond with a salinity of 43% — a testament to just how saline these isolated bodies of water can get.
It’s important to note that lakes are not stable geologically, and many tend to not last in geologic time. Some of the world’s biggest lakes are drying up, both as a natural process and due to rising temperatures, drought, and agricultural irrigation.
Salt can also come from below
We’ve mentioned that rock weathering and dissolving makes oceans salty, but there is another process: hydrothermal vents.
A part of the ocean water seeps deeper into the crust, becomes hotter, dissolves some minerals, and then flows back into the ocean through these vents. The hot water brings large amounts of minerals and salts. It’s not a one-way process — some of the salts react with the rocks and are removed from seawater, but this process also contributes to salinization.
Lastly, underwater volcanic eruptions can also bring salts from the deeper parts to the surface, affecting the salt content of oceans.
It’s harder to imagine a more imposing river than the Nile. Stretching over 6,650 km (4130 miles) long and serving as an essential water source since time immemorial, the Nile is a lifeline across northern Africa. Ancient Egyptians considered the Nile river to be the source of all life, and believed the river to be eternal.
Recent research seemed to back that idea up — well, maybe the Nile wasn’t eternal, but it was around for a few million years — which is eternal by humanity’s standards.
The Nile has a surprisingly steady path, nourishing the valleys of Africa for millions of years and shaping the course of civilizations. But for geologists, that was weird.
Why is the Nile so steady when rivers (particularly larger rivers in flat areas) tend to meander so much?
Now, researchers at the University of Texas at Austin believed they’ve cracked that mystery, and it has a lot to do with movement inside the Earth’s mantle.
“One of the big questions about the Nile is when it originated and why it has persisted for so long,” said lead author Claudio Faccenna, a professor at the UT Jackson School of Geosciences. “Our solution is actually quite exciting.”
The team traced the geologic history of the Nile, correlating it with information from volcanic rocks and sedimentary deposits under the Nile Delta. They also carried out computer simulations that recreated tectonic activity in the area over the past 40 million years.
They linked the Nile’s behavior to a mantle conveyor belt.
“We propose that the drainage of one of the longest rivers on Earth, the Nile, is indeed controlled by topography related to mantle dynamics (that is, dynamic topography).”
The Earth’s interior is dominated by the mantle, and the mantle is not static. Large swaths of the mantle are moved around by convection. Sometimes, parts of that are pushed towards the surface. This upwelling magma has been pushing up the Ethiopian Highlands, helping to keep the river flowing straight to the north instead of wending its way sideways. This uplift, researchers conclude, is responsible for the gentle and steady gradient that keeps the Nile on a consistent course.
Getting to this conclusion, however, was not straightforward — and it wouldn’t have been possible without state-of-the-art geophysical modeling. This proved to be the glue that pieced the entire theory together.
“I think this technique gives us something we didn’t have in the past,” said Jackson School scientists Petar Glisovic, one of the authors who is now a research collaborator at the University of Quebec.
As a consequence of this study, the researchers also showed that the Nile must be at least as old as the Ethiopian highlands — so this puts its age at 30 million years, which is several times more than previous estimates.
Rivers are essential to mankind. Almost all major cities have been established around rivers. They have been used as a source of water and food since pre-history, and to this day, they are vital for settlements, often serving as an easy means of disposing of wastewater and as a channel for navigation.
Yet much like any other ecosystem, rivers are also affected by the climate. Researchers have known this for a while, but they’ve struggled to detect the influence of climate on the formation and evolution of rivers.
Rivers typically flow somewhere higher to somewhere lower. If you’d make a profile of a river, you’d end up with a path that descends in elevation — that’s pretty straightforward gravitationally, but the shape of this gradient is quite important.
According to conventional wisdom, these river profiles have a concave-up shape (similar to the inside of a bowl), with fluctuations serving as markers of interference from climate, tectonics, lithology, or human impact. However, not all rivers play by this rule. Some rivers have profiles with an almost zero concavity — in other words, they have almost ramp-like straight profiles.
It’s not exactly clear why this variation in profile shape happens, but a new study might shed some light on that. The new research suggests that the shape of the river is essentially a signature of the long-term climate in the area: humid climates have more concave profiles whereas arid rivers have ramp-like profiles.
Lead author Shiuan-An Chen from the University of Bristol’s School of Geographical Sciences, said this comes as no surprise:
“The long profile is formed gradually over tens of thousands to millions of years, so it tells a bigger story about the climate history of region. We would expect climate to affect the river long profile because it controls how much water flows in rivers and the associated force of water to move sediment along the riverbed.”
It has traditionally been suggested that these shape variations are connected to climate, which makes sense. After all, climate directs rainfall, which in turn affects runoff and erosion, and further influences sediment deposition. But up until now, researchers lacked a systematic dataset of river profiles, spanning all the areas of Earth. Chen and colleagues produced this database (also making it freely available for anyone to use and study).
The data for the river profiles came from NASA satellites and includes observations on over 330,000 rivers from all across the globe. It’s the first study which shows distinct river shapes across the different climate zones.
In humid regions, rivers tend to have consistent flow all-year-round. This means they continuously bring up sediment and erode the profile to a more concave shape until an equilibrium is reached. As the climate becomes drier, rivers cause less erosion, and in the aridest climates the flow is very inconsistent. Using a numerical model which simulates river evolution, researchers were able to back up their observations and confirm that indeed, the climate is the main driver of this change.
Dr. Katerina Michaelides, also from Bristol’s School of Geographical Sciences, who led the research, added:
“Traditional theory included in textbooks for decades describes that river long profiles evolve to be concave up. Existing theories are biased towards observations made in humid rivers, which are far better studied and more represented in published research than dryland rivers.”
“Our study shows that many river profiles around the world are not concave up and that straighter profiles tend to be more common in arid environments.”
However, Michaelides also draws attention to the fact that most studies on rivers focus on areas where people tend to live — as a result, we know less about the rivers in the driest areas.
“I think dryland rivers have been understudied and under-appreciated, especially given that drylands cover ~40% of the global land surface. Their streamflow expression gives unique insights into the climatic influence on land surface topography,” she adds.
There is another important takeaway in this study: with the advent of both satellite data and high-power computing, researchers have unprecedented access to tools to study the Earth.
The study ‘Aridity is expressed in river topography globally’ by S-A. Chen, K. Michaelides, S. Grieve and M.B. Singer, has been published in Nature.
Flowing through rivers and oceans, plastic waste has become an important environmental threat across the globe. Trying to deal with the problem, researchers in Australia developed a way to purge water sources of microplastic without harming microorganisms, using a set of magnets.
Microplastics are ubiquitous pollutants. Some are too small to be filtered during industrial water treatment, such as exfoliating beads in cosmetics, while others are produced indirectly when larger debris like soda bottles or tires weather amid sun and sand.
“Microplastics adsorb organic and metal contaminants as they travel through water and release these hazardous substances into aquatic organisms when eaten, causing them to accumulate all the way up the food chain,” said senior author Shaobin Wang, a professor at the University of Adelaide (Australia).
Wang and the research team generated short-lived chemicals, called reactive oxygen species, which trigger chain reactions that chop the polimers (long molecules) that makeup microplastics into tiny and harmless segments that dissolve in water. The study was published in the journal Matter.
The problem was reactive oxygen species are often produced using heavy metals such as iron or cobalt, which are dangerous pollutants in their own right and thus unsuitable in an environmental context. To get around this, they used carbon nanotubes laced with nitrogen to help boost the generation of reactive oxygen species.
“Having magnetic nanotubes is particularly exciting because this makes it easy to collect them from real wastewater streams for repeated use in environmental remediation,” says Xiaoguang Duan, a chemical engineering research fellow at Adelaide who also co-led the project.
The carbon nanotube catalysts removed a significant fraction of microplastics in just eight hours while remaining stable themselves in the harsh oxidative conditions needed for microplastics breakdown. Their coiled shape increased stability and maximized reactive surface area. Chemical by-products of this microplastic decomposition, such as aldehydes and carboxylic acids, aren’t major environmental hazards. The team, for example, found that exposing green algae to water containing microplastic by-products for two weeks didn’t harm the algae’s growth.
The next step of the research will be to ensure that the nano springs work on microplastics of different compositions, shapes, and origins, as all microplastics are chemically different. They also think that the byproducts of microplastic decomposition could be harnessed as an energy source for microorganisms.
“If plastic contaminants can be repurposed as food for algae growth, it will be a triumph for using biotechnology to solve environmental problems in ways that are both green and cost-efficient,” Wang says.
In certain cases, rivers have lost as much as 50% of their flow.
Image via Pixabay.
New research led by a hydrologist at the University of Arizona warns that massive groundwater pumping since the 1950s is bleeding rivers dry. The findings can help shape policy for the proper management of U.S. water resources, the authors say, and should be of interest especially for states such as Arizona that manage groundwater and surface water separately.
“We’re trying to figure out how that groundwater depletion has actually reshaped our hydrologic landscape,” said first author Laura Condon, a University of Arizona assistant professor of hydrology and atmospheric sciences.
“What does that mean for us, and what are the lasting impacts?”
According to Condon, this is the first study to look at the impact of past groundwater pumping across the entire U.S. Other research has dealt with this issue, but only on smaller scales.
The team started by using computer models to see what the state of U.S. surface waters would have been today in the absence of human consumption. They then compared that with surface water changes recorded since large-scale groundwater pumping first began in the 1950s.
The model maps ground and surface waters onto a grid of squares (0.6 miles per side) that covers most of the U.S., excluding coastal regions. It included all the groundwater down to 328 feet (100 meters) below the land surface. The analysis focused primarily on the Colorado and Mississippi River basins and looked exclusively at the effects of past groundwater pumping because those losses have already occurred.
Estimates from the U.S. Geological Survey (USGS) place the loss of groundwater volume between 1900 and 2008 at 1,000 cubic kilometers. “The rate of groundwater depletion has increased markedly since about 1950,” it adds, peaking between 2000 and 2008 “when the depletion rate averaged almost 25 km3 per year (compared to 9.2 km3 per year averaged over the 1900–2008 timeframe).” One thousand cubic kilometers of water corresponds to one billion liters or 264.170.000 gallons.
“We showed that because we’ve taken all of this water out of the subsurface, that has had really big impacts on how our land surface hydrology behaves,” she said. “We can show in our simulation that by taking out this groundwater, we have dried up lots of small streams across the U.S. because those streams would have been fed by groundwater discharge.”
Too much of a good thing
Groundwater is a very valuable resource across the world. When surface water sources are scarce, absent, or overtaxed, groundwater is pumped to supply our domestic and economic needs. When misused, it can lead to enormous crises, likethe one facing India today.
Among other things, it is also used for agriculture and provides hydration for wild vegetation. Some native vegetation like cottonwood trees will eventually die if the water table drops below their roots. In the United States, it is the source of drinking water for about half the total population and nearly all of the rural population, and it provides over 50 billion gallons per day for agricultural needs, according to the same article from USGS.
The team found that streams, lakes, and rivers in western Nebraska, western Kansas, eastern Colorado and other parts of the High Plains have been particularly hard hit by groundwater pumping. Those findings agree with other smaller-scale studies in the region.
“With this study, we not only have been able to reconstruct the impact of historical pumping on stream depletion, but we can also use it in a predictive sense, to help sustainably manage groundwater pumping moving forward,” says Reed Maxwell, the paper’s co-author.
“We can do things with these model simulations that we can’t do in real life. We can ask, ‘What if we never pumped at all? What’s the difference?'”
The regions that were most sensitive to a lowering water table are east of the Rocky Mountains, where the water table was initially shallow (at the depth of 6-33 feet or 2-10 meters). Ground and surface waters are more closely linked in these areas, so depleting the groundwater is more disruptive for streams, rivers, and by extension, vegetation. The western U.S. has deeper groundwater, so reducing their volume didn’t have as powerful an effect on surface waters.
Condon says that other research has shown that the areas of the Midwest where precipitation used to equal evaporative demand — i.e. where irrigation wasn’t required for crops — are becoming more arid. Those are some of the regions where groundwater pumping has reduced surface waters.
“In the West, we worry about water availability a lot and have many systems in place for handling and managing water shortage,” Condon said. “As you move to the East, where things are more humid, we don’t have as many systems in place.”
The paper “Simulating the sensitivity of evapotranspiration and streamflow to large-scale groundwater depletion” has been published in the journal Science Advances.
Water flew intermittently — but very intensely — on Mars, for billions of years.
A photo of a preserved river channel on Mars. Color shows different elevations (blue is low, yellow is high). Image credits: NASA/JPL.
The case for Mars having water in the past is already very strong, and this latest study brings even more evidence to support that idea. Mars is dry today but it used to have a thick atmosphere in the past and it could have supported liquid water. Remote sensing data has revealed numerous valleys which appear to be precipitation-fed former rivers.
Edwin Kite, Ph.D., first author of a new paper says that not only did Mars have rivers and lakes, but they were pretty big, and they were around for billions of years, over several geological periods.
Kite and colleagues used images from NASA’s Mars Reconnaissance Orbiter, characterizing over 200 such systems. They used the number of craters around to estimate the age of these rivers and used the visual data to calculate the intensity of the river runoff.
While some channels have eroded over the eons, many are still clearly visible due to the very slow erosion currently taking place on Mars. Ironically, the lack of water and atmosphere responsible for this slow erosion allowed researchers to better study these former rivers.
It’s unclear how deep these rivers were, but they were wide — on average, they were wider than those on Earth. They also appear to be evenly distributed across the Martian surface. The team’s results suggest that these rivers flower intermittently (probably fed by precipitations), but intensely.
“Using multiple methods, we infer that intense runoff production [..] persisted until <3 billion years (Ga),” researchers write in the study. “[The] precipitation-fed runoff production was globally distributed, was intense, and persisted intermittently over a time span of >1 Ga.”
There’s another interesting find: it’s not just that these rivers were active for billions of years, but they were active until the very period when Mars almost completely dried up.
“You would expect them to wane gradually over time, but that’s not what we see,” Kite said in a statement. “The wettest day of the year is still very wet.”
According to our current climate models of Mars, that just shouldn’t happen — there’s no way the thinning Martian atmosphere could have supported such rivers. It’s not clear where the problem lies, and it’s also not clear exactly when and why Mars dried up. Understanding that could offer us a new understanding of whether Mars what habitable.
“Our work answers some existing questions but raises a new one,” Kite said in the statement. “Which is wrong: the climate models, the atmosphere evolution models or our basic understanding of inner solar system chronology?”
The Curiosity Rover currently roaming Mars and NASA’s upcoming 2020 Mars rover will probably offer crucial puzzle pieces to solve that question — and more.
The study “Persistence of intense, climate-driven runoff late in Mars history” has been published in Science Advances.
Lenght isn’t everything so today, we’re taking a look at which river can boast being the widest.
Sunset over the Amazon River. Image credits Oscar Castillo.
Earlier this week, we looked at which river is the longest in the world — a deceptively tricky question to answer, as my colleague Tibi showed. Width, by contrast, should be much more straightforward, shouldn’t it?
Well, not really; but let’s get into it.
Widest of the wide
Before we bite into the issue, let’s take a moment to talk estuaries.
Rivers that flow out to sea in tidal regions tend to form wide mouths known as estuaries. The Thames, the Loire, La Plata, Saint-Lawrence, Ob-Irtysh, the Tagus rivers, are some of the rivers that form estuaries. Due to tidal movements on the one hand and the river’s outflow on the other, estuaries tend to hold brackish water — a mixture of sweet and salt water brought in by the tides. The same motions that mix these two also flush out silt and other sediment flowing out to sea. In effect, this prevents the river from forming new deposits at its mouth.
Satellite image of the Amazon River estuary (Brazil), with Marajó Island in the center, and the cities (in red) of Macapá (left) and Belém (right). Image credits NASA / LandSat / Geocover 1990 via Wikimedia.
Estuaries, then, resemble deltas sans the solid bits. This is quite relevant in the context of the discussions we’re having today, as deltas tend to be wide, fan or funnel-shaped structures.
Since estuaries aren’t technically rivers, I’m not going to include them in the comparison to follow (sorry, estuaries). To give you an idea of how massively wide such structures can get, the St. Lawrence River (on the Canada-US border) estuary — the widest in the world — boasts over 140 km in width. That’s wider than the state of New Hampshire, and simply dwarfs anything a river can reach.
With that out of the way, we’re left with five candidates for the title of “World’s Widest River”: the Missouri, Amazon, Mekong, Huanghe, and Congo rivers.
Function of circumstance
The length of a river may be tricky to measure because there are many ways to go about it. Their width, however, is hard to gauge because it changes over time.
A river’s length is mostly a product of geography — where it springs, where it flows out to sea, and the terrain between these two points. Their width is mostly a function of volume — i.e. how much water it carries. Geography tends to stay constant; volume likes some variety.
However, since volume weighs so heavily, a likely victor appears: the Amazon.
The Amazon has the largest drainage system (the surface it draws water from) in the world, covering a large part of South America — some 350,000 sq kilometers. Even better, that drainage system includes vast expanses of rainforest, which tend to be very humid environments that see large quantities of precipitation.
This bountiful fief makes the Amazon a leviathan. It single-riverly supplies 20% of all the fresh water that drains into oceans on Earth. Its average output — of 209,000 cubic meters (7,381,000 cubic ft) per second — exceeds the average output of the next seven riverscombined.
All that water helps make the Amazon the widest river in the world. During the dry season, it is about 11 kilometers (6.8 miles) wide at its widest points. During the wet season, it explodes to some 40 kilometers (24.8 miles) in width. In terms of surface (width times length), the Amazon covers around 110,000 sq km (42,400 sq miles) during the dry season, and it more than triples during the wet season to 350,000 sq km (135,000 sq miles), according to Extreme Science.
The Amazon currently holds the Guinness World Record for the widest river in the world — 11 kilometers (7 miles) at its widest point, measured on the 18th of March, 2005.
Measuring the world’s longest river is actually not as simple as it sounds. The process is far more complicated than finding the source and the mouth then measuring the distance between them. Rivers often join together in river systems making it very difficult to pinpoint where an individual river begins and where it ends.
How do you measure a river? It’s not as simple as using a ruler
Today, most hydrologists agree that the most accepted method is to measure the longest possible along-thalweg continuous distance from the headwaters of the 1st order stream to the mouth of a river. The thalweg is a line connecting the lowest points of successive cross-sections along the course of a valley or river. A 1st order stream is a stream without any tributaries entering. When two 1st order streams meet, they form a 2nd order stream and when two or more 2nd order streams meet, they form a 3rd order stream — and so on. In other words, to find the longest river, you have to measure the length of the longest continuous river channel in a given river system.
That’s still a gross oversimplification because, in practice, things can get very tricky. For instance, for most rivers, the mouth is easy to determine and measure, but for very large rivers like the Amazon, which flows into the ocean, placing the mouth can be less concrete — and can make all the difference in terms of river length. Another example of murky measurement is the Mississippi, whose headwaters are considered by the USGS to be Lake Itasca in Minnesota, yet if its longest tributary is taken into account (the Jefferson and Missouri rivers), it becomes three times as long.
I know what you’re thinking — get to the damn question already.
Well, there are two ways to think about the largest river. One is length, where the Nile takes the crown, and the other is volume, where the Amazon clearly stands out among all other river systems in the world.
The Nile — the longest river in the world
According to the U.S. National Park Service, the river Nile is the longest in the world, spanning 4,135 miles (6,650 kilometers). Though it mostly runs through Egypt, from its source in Burundi to its delta on the Mediterranean Sea, the Nile also passes through nine other African countries: Sudan, Eritrea, Ethiopia, Uganda, Kenya, Tanzania, Rwanda, Burundi and the Democratic Republic of Congo.
The biggest lake in Africa, Lake Victoria, was historically regarded as the source of the river Nile. A waterfall known as Ripon Falls on the northern edge of the lake pours water through a narrow opening, which many claim this to be the very beginning of the Nile. But if that’s the case, what’s the source of Ripon Falls? Lake Victoria is surrounded by mountains riddled with streams which tumble down into the lake. The largest tributary of Lake Victoria is the Kagera River, which has its headwater in Burundi. It is from here that the Nile is measured as the world’s longest river.
Some 300 million people depend on this river for their water supply and for food crop irrigation.
There’s even a dam that harnesses the Nile’s energy — the Aswan High Dam. After it was completed in 1970, for some years it used to provide half of the electricity demand of Egypt, though this figure has steadily decreased as the nation increased its electricity demand. It now supplies around 20% of the country’s electricity. The dam also controls summer flooding.
At the other side of the spectrum, officially, the shortest river is the D River in Oregon, USA, which is just 37 meters long.
The Amazon — the largest river in the world by water volume
Credit: Maps of the World.
It’s not even close: the Amazon is considered the 2nd longest river in the world, spanning 3,980 miles (6,400 kilometers). However, it holds the title of the world’s largest river by volume. On average, 120,000 cubic meters (about 20 swimming pools’ worth) of water flows out of its mouth every second. It contains a staggering 20% of the world’s fresh water supply. Some parts of the river can exceed 120 miles (190 kilometers) in width when the Amazon swells during the wet season. Even in dry conditions, the Amazon is so wide throughout its length that to this day, no bridge spans it.
From its source in Peru, the Amazon, or Rio Amazonas in Portuguese and Spanish, flows mostly through Brazil and empties into the Atlantic Ocean. The Amazon also forms the world’s largest river drainage basin that includes Brazil, Bolivia, Peru, Ecuador, and Colombia.
The source of the Amazon has also been hard to pin down over the centuries. Scientists and explorers have attempted to establish the river’s source ever since the 1600s. Over the years, five rivers in southwestern Peru were given the honor and for nearly a century the headwaters of the Apurímac River on Nevado Mismi was considered as the Amazon’s most distant source. But a 2014 study found it to be the Cordillera Rumi Cruz at the headwaters of the Mantaro River in Peru.
However, some geographers have disputed this — according to them, Mantaro stays dry for about five months of the year when the Tablachaca dam, built in 1974, diverts its water through a 12-mile (20 km) tunnel. And to make the dispute even more interesting, if the Mantaro River really is the source, that would add 47 to 57 miles (75 to 92 kilometers) to the length of the Amazon.
Does being the longest even matter?
In 2007, Brazilian researchers announced they had identified a new source and a new mouth, measuring the Amazon 4,225 miles (6,800 kilometers) long and toppling the Nile as the longest river. The mouth of the Amazon is traditionally thought to be located on the north side of the Marajó Island, which is about the size of Switzerland. The rather hefty area means that the side of the island the mouth is on can matter a lot when measuring the Amazon’s length. The Brazilian study, which was not peer-reviewed and immediately proved controversial, put the mouth on the south side of the island to the Pará River then out into the ocean. After more recent studies, experts seem to agree that, although there’s indeed some of the Amazon’s water in the Pará, the latter river is distinct from the Amazon. The Nile is still king for now, but as new sources are discovered and mouth areas are redefined, the crown could get swapped between the two rivers — and possibly more than once.
At the end of the day, ‘the longest river’ title doesn’t even matter all that much. As the constant juggling of measurements throughout the centuries show, there will always be some researcher or team that will claim they’ve made some more precise readings. And of course they will — the coastline paradox states that measuring something with a complex geometry, such as a coastline is not possible because the length actually increases the more granular the measurement gets. Huh? I know that sounds shocking, but this counterintuitive concept has been proven mathematically and arises from the properties of fractal-like geometries, which includes rivers. Rivers have a lot of curves and the more you zoom in, the more bends and twists you see.
So, keeping the coastline paradox in mind, a lot of scientists have long ago stopped caring about measuring river length. What’s far more interesting and scientific — not to mention a lot easier and precise — is to look at the drainage area, which is an area of land where precipitation collects and drains off into a common outlet, such as into a river or a bay. By this measure, the Amazon is clearly the largest river in the world with a drainage area of 6.3 million square kilometers, while the Nile makes it only to the fifth spot, trailing behind Congo, the Mississippi, and the Ob.
There are a lot of rivers on Earth — many more than we’ve assumed.
Image credits Alex Hu.
Previous estimations of river- and stream- cover on our planet haven’t exactly been accurate, according to new research from the University of North Carolina. Excluding land covered with glaciers or ice sheets, our planet is braided with about 300,000 square miles (773,000 square kilometers) of rivers and streams — 44% more area than previously estimated.
My river runneth over
To find out just how much ‘river’ you need to make one ‘Earth’, the team — University of North Carolina hydrologists George Allen and Tamlin Pavelsky — drew on thousands of images recorded by NASA’s Landsat satellite. Using software that Pavelsky designed specifically for this task, they took over 58 million measurements of rivers, streams, and other similar waterways. The researchers estimated river shapes by measuring their widths. Finally, they added all of them up to calculate the total surface area they cover.
To make sure that the software wouldn’t foul the measurements, the team recruited “a small army of undergrads” to monitor the program as it went about its task. One of the team’s main concerns was that roads or other similar structures could be treated as rivers by the program, but this turned out not to be the case.
Aside from finding those extra 300,000 square miles of river (roughly the same size of Texas, to put it into perspective), the researchers also report that rivers were both narrower and more sparse in developed areas. This could come down to seasonal variations, water drainage for agriculture, habitat removal (such as drainage of swamps), or the corraling of rivers for hydroelectricity. The team can’t say for sure what the cause is, however, and call for further research into the area.
Not only will the findings send fishing enthusiasts cheering for their rods, it also has some more worrying implications. Namely, it influences how we study and deal with climate change. Waterways are a prime source of greenhouse gas exchange between the surface and the atmosphere, especially when waters are polluted.
For a very long time, people were content to let rivers soak up pollutants completely secure in the belief that these compounds will wind up in the ocean. It was a simpler time when we thought we could afford this. Over the past decade, however, researchers have wisened up to the fact that rivers instead help break down this waste, and release greenhouse gasses into the atmosphere. Some of the most common river-borne pollutants are fertilizers, sewage, and drainage from soils — and the wet, relatively oxygenated, and biodiverse backdrop of a river is an excellent place for these to break down. As they break down, they release gasses such as methane, nitrous oxide, and carbon dioxide into the atmosphere. Even if they do wind up in the ocean, that is by no means a get out of jail card.
If rivers cover up more area than we assumed (and the 44% more this paper reports on is significantly more) then our current calculations regarding how much greenhouse gas they release need to be re-crunched.
“If you look around the world, rivers look different from place to place,” Allen told Gizmodo. “They might be braided, or sinuous, or meandering. And for the most part, current technology doesn’t take into consideration the actual morphology of rivers. This data set is the first of its kind to do this at a global scale on high resolution.”
This global map of rivers might also help predict floods and it will be an invaluable resource in the future, when we’re trying to keep track of how rivers behave as the Earth warms up.
The paper “Global extent of rivers and streams” has been published in the journal Science.
We all see garbage in our daily routine, be it on the way to work, school, or just on the streets. But most people just choose to ignore it; after all, what difference could one man possibly do? Well, Tommy Kleyn didn’t think like that when he was walking pass a polluted river to work. He took a bag of garbage every day after work, and managed to clean up a river – by himself.
Netherlands is known as one of the most environmentally friendly countries in the world – but even the Dutch have their pollution problems (who doesn’t, these days?). Tommy Klein decided to take matters into his own hands and clean the river he passed by every day on his way to work. In just six days, he managed to make a noticeable difference, and – here’s where it gets even cooler – the neighbors also started to chip in. Everyday, Klein monitored the changes to the river, taking pictures and sharing them on Facebook: Project Schone Schie.
“The idea is to motivate people to fill one garbage bag with litter each year. It only takes 30 minutes, it really makes a difference and you will be amazed about how good you feel afterwards,” he said.
After five weeks, the river was clear sparkling clean, and he made his point – just as clearly.
“I want to show how easy it is to remove the clutter,” he added. “Hopefully there will come a time when manufacturers are thoughtful and their products are no longer wrapped in layers of plastic.”
Not long after that, his story went viral, as it should – the Facebook page has grown and has inspired numerous people who now share their own clean-up stories. Klein actually challenges people to spend no more than 30 minutes a year to fill a trash bag with litter, and see what a difference they can make.
“It feels great and you’ll make a big impact,” he wrote. People are free to share their ‘before’ and ‘after’ pics on the page. The challenge has caught on, with people in countries as far as Taiwan responding with their own photos and stories!
So the take-away message here is that we can all make a significant difference in our community – after all, if one man managed to clean a river by himself in five weeks, then what would all of us be able to do, if we really worked for it, even just 30 minutes a year?
Caño Cristales is a river located in Northern Columbia, with a length of almost 100 km and a width of under 20 meters. If you look at it, you’d be tempted to think this is some sort of illusion or photographic trick, but you’d be wrong.
Photo by Mario Carvajal.
It’s quite remote, and you can get there only by foot, horses and donkeys, but that doesn’t stop tourists from flooding in. There were so many of them that visiting it was actually forbidden for several years. Now it’s open, but within reasonable limits. The river is a rainbow of colors, changing from corner to corner.
Photo by Mario Carvajal.
Photo by Mario Carvajal.
The hard rocks which make most of the bottom of the river are covered with moss, which most of the year have a dull green or brown colour. In the rainy season the water is too deep for the colours to bloom, and in the dry season there’s just not enough water to support all the moss.
Photo by Mario Carvajal.
Photo by Mario Carvajal.
However, there is a window during these seasons when the water level is just right, and the dazzling display of colours appears to delight the eye.
Nature has its own way of protecting itself, and we should have already learned this (the hard way), because so many catastrophes have happened as a result of man’s destructive work. Look at the damage caused by the recent tsunamis; they would have been almost neglectable if we hadn’t destroyed the plankton, which has a very protective action. Also, despite the numerous experiements and studies, we have yet to find a solution to this issue.
The case of cleaning nitrogen caused by human activities seems to be similar in many ways, as scientists haven’t come up with a viable plan of cleaning it yet, except for an easy, natural way: maintaining healthy river systems. That’s right, healthy river streams with vibrant ecosystems play a critical role in removing excess nitrogen caused by human activities, according to a recent major study published in nature.
The study was led by a team of 31 aquatic scientists across the United States and it was the first to explain how much nitrogen that rivers and streams can filter through tiny organisms or release into the atmosphere through a process called denitrification.
“The study clearly points out the importance of maintaining healthy river systems and native riparian areas,” said Stan Gregory, a stream ecologist in the Department of Fisheries and Wildlife at Oregon State University, an a co-author of the study. “It also demonstrates the importance of retaining complex stream channels that give organisms the time to filter out nitrogen instead of releasing it downstream.”
The study was conducted after analyzing 72 streams across the United States and Puerto Rico that spanned a diversity of land types, including urban, rural, agricultural and forests. They found out that if the river was healthy, it cleansed roughly 40 to 60 percent of nitrogen within 500 meters of the source. This happens because small organisms, such as algae, fungi and bacteria that may live on rocks, pieces of wood, leaves or streambeds can absorb the nitrogen.
“Streams are amazingly active places, though we don’t always see the activity,” said Sherri Johnson, a research ecologist with the U.S. Forest Service, and a courtesy professor of fisheries and wildlife at OSU.. “When you have a healthy riparian zone, with lots of native plants and a natural channel, the stream has more of an opportunity to absorb the nitrogen we put into the system instead of sending it downriver.”