From space everything looks different. In fact, distance allows us to distinguish strange shapes, such as the Great Dam of Zimbabwe or the eye of the saharabut also colors that go more unnoticed at ground level. Thus, on June 7, 2021, an Expedition 65 astronaut aboard the International Space Station pointed his camera toward the southeast of Spain and took a photograph that looks like a watercolor: Mediterranean blue, a muted green and an intense pink reminiscent of quartz. The color palette is finished off by the white reflection of the sun.
The three colors correspond to bodies of water a few kilometers from each other, in Alicante: the Mediterranean, and the saline lagoons of La Mata and Torrevieja. What seems like an aesthetic coincidence is actually chemistry visible from orbit. Each tone reveals something: the degree of salinity, which microorganisms dominate the water, and in what fragile balance they coexist.
The lagoons of La Mata and Torrevieja. The Torrevieja lagoon has been used as a salt mine since the 13th century and today are the largest salt producer in Europe, with an average of 650,000 tons per year, a figure that varies depending on solar radiation, wind and precipitation. It does not function as a natural lagoon, but as an industrial system where water moves according to production needs.
The La Mata lagoon acts as a prior concentration chamber: receive sea water through artificial channels and runoff from intermittent streams of the Sierra de San Miguel de Salinas. From there, the water is pumped to the Torrevieja salt mine, where brine from the Pinoso salt diapir through a 55 kilometer pipeline. The result is that the concentration of salt in the Torrevieja lagoon can overcome 260 grams of salt per liter, much more than the 38.5 g/liter Mediterranean that bathes its coast. Two adjacent lagoons but with completely different chemical worlds.
Why do they have such different colors?. Each time water of different composition is pumped to produce salt, the chemistry of the system is altered, which determines What organisms can live and in what quantity. Two lagoons a kilometer apart, two different microbial communities and two opposite colors.
The pink color of the Torrevieja lagoon is produced by microorganisms. More specifically, in conditions of high salinity and intense solar radiation, the microalgae Dunaliella salina accumulates β-carotene as protection against light. The halophilic archaea that share the lake reinforce that tone: they have red pigments distributed throughout their cell membrane, which makes them visually more decisive in the final color of the water. In La Mata, the lower concentration of salt favors a different microbiota where chlorophyll predominates over carotenoids: that explains the green color.
Context. The salinity gradient between both lagoons goes beyond chemistry: it is what allows a different and exceptional biodiversity. The wetland houses up to 400 taxaten species of threatened birds and one of the most important Audouin’s gull breeding colonies in the Mediterranean. Without that difference in salinity, many of those ecological niches would disappear.
The NASA image is also more than a photograph: it portrays the fragile balance between industry, microbiology and conservation that climate change is already testing as temperatures rise and salinity fluctuations alter the living conditions of Dunaliella salinaor what is the same, that that striking pink color seen from space could disappear.
Why is it important. Dunaliella salina is the organism that supports the base of the food chain in hypersaline lakes around the world. Since 1966 it has been grown commercially to produce β-carotene, which has applications in pharmacology and cosmetics. But it is also an organism that NASA has on the radar because it constitutes a form of life in extreme conditions. It should be remembered that the data from the Perseverance rover indicates that there were hypersaline waters in the Jezero crater of Mars. Studying life in these types of lakes helps understand the potential in these old Martian lakes. What makes Torrevieja pink is the best laboratory we have to know what to look for on another planet.
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