Scientists have found a (partial) explanation for the ‘blood rain’ in Spain

Rain showers can sometimes take a bizarre turn: in very rare cases, animals such as fish and frogs have been known to fall from the sky alongside water droplets, and around the world, people have experienced what’s known as blood rain, where the water has a peculiar red tinge.

Reports of blood rain have been recorded for centuries – back before humans knew any better, it was believed the sky was actually spitting out blood. Nowadays, we have the technology to analyse the composition of blood rain so we no longer have to jump to any crazy conclusions, but scientists are only just figuring out how and why it occurs. And now a new study has put forward an explanation for a recent incident in Zamora, a city in northwestern Spain.

The people of Zamora and several nearby villages noticed blood rain falling from the sky late last year: was it chemical pollution? Was it some kind of deliberate sabotage? Was it a sign from God? A concerned resident sent a sample of collected rainwater to scientists at Spain’s University of Salamanca to see if they could come up with any answers. And now the results are in.

The researchers say a freshwater green microalgae called Haematococcus pluvialis is to blame – this microalgae is capable of producing a red carotene pigment called astaxanthin when in a state of stress, perhaps caused by getting caught up in a rain-cloud.

That matches up with previous studies of blood rain, one of which found the microalgae  to be the cause of an incident in Kerala in India– different kinds of microalgae, but the same root cause.

Astaxanthin in H. pluvialis. Credit: Frank Fox/Wikimedia

What’s less clear is how these microalgae spores are travelling. H. pluvialis is not native to Zamora or any of the neighbouring regions, and before the Kerala incident, T. annulata was thought to only exist in Austria – a long way from India. So now the researchers have to figure out exactly how these mysterious microorganisms are making their way across the globe.

Hitching a ride on global wind currents would be a good bet, but so far researchers have been unable to find any concrete proof of this. The researchers identified a prevailing current that could’ve carried the microalgae out from North America to Spain, but have yet to pinpoint the exact source. Their work has been published in the Spanish Royal Society of Natural History Journal.

In the meantime, there’s no cause for panic if you’re caught in a blood rain shower: H. pluvialis is non-toxic and is often used as a food source for salmon and trout to give them a more pinkish hue. Indeed, motorcycle company Yamaha recently used the microalgae to reduce carbon dioxide emissions from its factories.

Blood rain puddle from Zamora. Credit: Joaquín Pérez

Source: Scientists have found a (partial) explanation for the ‘blood rain’ in Spain

First map of Earth’s hidden groundwater reserves shows we’re using them too quickly

An international team of hydrologists has come up with the best estimate yet for Earth’s total supply of groundwater, saying that nearly 23 million cubic kilometers of groundwater is contained in hidden reserves under the surface of the planet. And while that might sound like a lot, it’s not enough to sustain us if we keep consuming it as fast as we are right now.

The study suggests that less than 6 percent of groundwater in the upper 2 kilometers of the Earth’s landmass is renewable within a human lifetime. That statistic is concerning, not only because the uppermost water is what we can access for drinking, but also because the lengthy renewal cycle is slower than our consumption habits.

“This has never been known before,” said lead researcher Tom Gleeson of the University of Victoria in Canada. “We already know that water levels in lots of aquifers are dropping. We’re using our groundwater resources too fast – faster than they’re being renewed.”

To come up with their global groundwater map, the researchers compiled multiple data-sets, including data from almost a million watersheds and more than 40,000 groundwater models. Of the nearly 23 million cubic kilometers of total groundwater on the planet, approximately 0.35 million cubic kilometers is younger than 50 years old.

The distinction between young and old groundwater is important. Young (or modern) groundwater lies closer to the surface and is more likely to be drinkable. In comparison, older groundwater – which can date as far back as millions of years – lies deeper in Earth’s landmass, and may contain arsenic or uranium. It’s often stagnant and saltier than seawater, and as such, is only usually suitable for agricultural or industrial purposes.

Young groundwater’s proximity to the surface means it’s easier for us to access it and also easier to renew with fresh rainwater – but it’s also more readily exposed to human contamination and more vulnerable to environmental risks like climate change.

The researchers’ map reveals that most of Earth’s groundwater reserves are stored in tropical and mountain regions, including the Amazon Basin, the Congo, Indonesia, and in North and Central America. Arid regions, as one might presume to be the case, don’t have as much water underground.

“Intuitively, we expect drier areas to have less modern groundwater and more humid areas to have more, but before this study, all we had was intuition,“ said one of the team, Kevin Befus, who is now with the United States Geological Survey. ”Now, we have a quantitative estimate that we compared to geochemical observations.”

The researchers hope their findings, published in Nature Geoscience, will help water managers, policy developers, and scientists to better manage Earth’s remaining groundwater in more sustainable ways. In the meantime, Gleeson will be leading a new study, designed to track depletion rates on a global scale.

“Since we now know how much groundwater is being depleted and how much there is, we will be able to estimate how long until we run out,” he said.

Source: First map of Earth’s hidden groundwater reserves shows we’re using them too quickly