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Watching over water, Earth's most precious resource
Satellites are helping Europe protect its lakes, lagoons and rivers.
It is early morning on the Razelm-Sinoe lagoon in Romania when a small boat sets out with instruments and probes. The researchers on board are collecting water samples and measurements to bring to the laboratory for analysis.
Located on the shores of the Black Sea, Lake Razelm is part of the most extensive wetland in Europe and of a World Heritage site: the Danube Delta.
Close up and afar
The researchers are part of an EU-funded project called CERTO tracking water quality along coasts and in places that transition between fresh and saltwater like lagoons, estuaries and large rivers. The team gets support not just from waterborne transport but also from something much more distant: a satellite network.
"Traditionally, people have gone out in boats and sampled," said Professor Steve Groom, CERTO coordinator and head of science/earth observation at Plymouth Marine Laboratory in the UK. "But it's expensive and they can't be everywhere along the coast on the same day. We're moving towards using satellites to complement in situ monitoring."
The Razelm-Sinoe lagoon was almost closed off from the Black Sea during the 1970s as part of a plan to create a freshwater source for agriculture.
Nowadays it only has one sea inlet. The limited water exchange with the sea, combined with mineral and nutrient run-off from nearby farms, led in the 1990s to excessive plant and algal growth and low-oxygen levels that harmed fish and wildlife in the lagoon.
The lagoon's diversity, including varying water depths and levels of salinity, makes for a valuable study site—and the interest is not just academic. Ensuring the health of coastal waters is vital both for ecosystems and for people who make a living from activities such as fishing, farming and tourism.
The skyward help that the CERTO researchers receive is through Copernicus, the Earth observation part of the EU's space program. Copernicus uses satellite data to observe water quality and quantity.
"CERTO puts the use of satellite data in the spotlight," said Adriana Maria Constantinescu, technical leader of a Razelm-Sinoe lagoon case study. "We can get good-quality data from satellite images and the work we do in situ helps improve algorithms."
CERTO is using on-site measurements and satellite-observation data in six places. Among them are also the world-famous lagoon in Venice, Italy and the Curonian lagoon in Lithuania.
The project, due to end this September after almost four years, is investigating ways to classify water.
"The technical term is optical water types, but it's really just a way of saying 'this water is a bit muddy' or 'this area is nice and blue,"' said Groom.
The term categorizes bodies of water based on the color of the light they reflect.
Murky green ponds, for example, contain more organic matter such as algae than clear ponds and reflect less blue light. Murky water also indicates a surplus of nutrients that could be harmful to fish and wildlife.
In this way, using satellites to measure how much light bodies of water reflect can help determine their health without needing to go out in a boat and take samples. It also gives scientists a database to draw on when analyzing waters classified as the same type.
"The value is that you don't necessarily have to take in situ measurements to validate your algorithms everywhere," said Groom. "We're trying to go from lakes all the way to oceans and come up with a common set of water types for all those waters."
CERTO also wants to make it easier for scientists to use the available information on water quality and bridge existing gaps in the data.
At present three Copernicus services, each using different approaches, provide information on water quality, making it hard for scientists to have an overview. In addition, some areas such as transitional waters aren't covered by any service at all.
The project's legacy will be prototype software that can be plugged into existing Copernicus services as well as popular open-source software called SNAP that's used more widely in the research community.
Constantinescu, the head of a Razelm-Sinoe study, expects the CERTO work to lead to more research at the lagoon. The filtering properties of reed beds or their role in attenuating wind waves could be some of the nature-based solutions investigated to deal with coastal erosion.
Satellite data is also used to keep an eye on Europe's groundwater.
The EU-funded G3P project tracked variations in vital groundwater reserves for three years through 2022.
The project used data both from Copernicus and from a joint US-Germany satellite mission known as GRACE that, since its start in 2002, has transformed scientists' view of how water moves and is stored around the planet.
"Groundwater is one of the major resources for humankind," said Professor Andreas Güntner, who coordinated G3P and works at the GFZ German Research Centre for Geosciences in Potsdam.
Groundwater accounts for almost a third of total freshwater resources worldwide. In the EU, it supplies 65% of drinking water and a quarter of water for agricultural irrigation.
Groundwater has also been declared an essential climate variable—a critical indicator of how the Earth's climate is changing—by an international non-governmental organization known as the Global Climate Observing System.
Copernicus doesn't yet provide consistent, worldwide data on groundwater reserves and how they're evolving.
The G3P team built a new dataset to fill that gap.
The researchers relied on information from GRACE, which has featured twin satellites. An initial GRACE mission lasted 15 years and a follow-up one began in 2018.
The distance between the two satellites changes constantly depending on the mass distribution below them. For example, when one approaches heavy masses such as mountains, ice sheets and large groundwater reserves, it speeds up and the distance from the other satellite increases.
By tracking the gravitational push and pull on the spacecraft as they fly over different landscapes, scientists were able to map out the distribution of water on and below Earth's surface and how it's changing.
Knowing more about groundwater reserves, their changes and how they are affected by human activities such as farming is essential as countries seek to improve the management of water resources generally.
"In some areas of the world, taking water from aquifers for irrigation has led to more withdrawal than replenishment—in other words unsustainable use," Güntner said. "The first global observation-based groundwater dataset is really an amazing thing."
Still, plenty more research lies ahead to make greater use of the dataset.
"The next step is in-depth analysis of the groundwater data we obtained to try to understand how groundwater resources have changed over the last 20 years, how those changes may be related to climate change, changing rainfall and how much is due to human interference," said Güntner.
Provided by Horizon: The EU Research & Innovation Magazine