thumb|Salt evaporation pond in [[Manaure, La Guajira, Colombia]]

A salt evaporation pond is a shallow artificial salt pan designed to extract salts from sea water or other brines. The salt pans are shallow and expansive, allowing sunlight to penetrate and reach the seawater. Natural salt pans are formed through geologic processes, where evaporating water leaves behind salt deposits. Some salt evaporation ponds are only slightly modified from their natural version, such as the ponds on Great Inagua in the Bahamas, or the ponds in Jasiira, a few kilometres south of Mogadishu, where seawater is trapped and left to evaporate in the sun.

During the process of salt winning, seawater or brine is fed into artificially created ponds from which water is drawn out by evaporation, allowing the salt to be subsequently harvested.

The ponds also provide a productive resting and feeding ground for many species of waterbirds, which may include endangered species. However, Ghanaian fisheries scientist RoseEmma Mamaa Entsua-Mensah also noted that salt winning can destroy mangrove forests and mudflats, altering the environment and making it unproductive for other development or fish growth. The ponds are commonly separated by levees. Salt evaporation ponds may also be called salterns, salt works or salt pans.

Metrics and energetics

thumb|Minimum least work of evaporation from saline water to atmosphere, as a function of [[specific humidity (ω), temperature (T), and salinity (C, mass fraction salt)

Evaporation systems are also often evaluated by the water evaporation rate per unit area. When the energy is largely provided by sunlight, these are often evaluated with a solar efficiency, (<math>\eta_{\rm sol}</math>), which is a thermal efficiency that compares incoming light energy to the enthalpy of vaporization. This is the same as the gained output ratio (GOR) in desalination. including Charleston Slough. Cargill has since ended salt production in the area, and most of the ponds are being restored to a more natural state.

  • South Bay Salt Works in San Diego, California.
  • The Dead Sea salt ponds in the West Bank, Israel and Jordan.
  • The salt ponds in Salina, Malta. The name of the village is the Maltese word for salt pan.
  • The Port Hedland, Dampier, Lake McLeod, Useless Loop and Onslow salt ponds in Western Australia.
  • Yellow Walls, Malahide, Ireland; active from 1770 to 1837.
  • Lake Grassmere in New Zealand
  • The ancient salt pans in Marsala and Trapani, Sicily. Salt has been farmed here since the Phoenician period, with archaeological evidence still present in nearby Motya.
  • The Nature reserve of Margherita di Savoia, in Apulia, Italy. Known since antiquity, it's one of the largest in Europe. Flamingos often nest in the area.
  • The salt works on the island of Great Inagua owned by Morton Salt.
  • The salt harvesting by the Tsonga women of Baleni on the Small Letaba River, Limpopo, South Africa.

Until World War II, salt was extracted from sea water in a unique way in Egypt near Alexandria. Posts were set out on the salt pans and covered with several feet of sea water. In time the sea water evaporated, leaving the salt behind on the post, where it was easier to harvest.

Production

Salt pans are shallow and open, and metal pans are often used to evaporate brine. They are usually found close to the source of the salt. For example, pans used in the solar evaporation of salt from seawater are usually found on the coast, while those used to extract salt from solution-mined brine will be found near the brine shaft. In this case, extra heat is often provided by lighting fires underneath.

History

Archaeology

Archaeology is difficult and fragmentary: sea-level rise, deliberate demolition of furnaces, and repeated breakage of containers obscure direct traces.

Evidence for marine salt making in western Europe reaches back to the 5th millennium BCE, where seasonal coastal lagoons behind low sandy–silty shores likely served as proto-salterns that pre-concentrated brine before heating.

In China

In China, archaeological and chemical analyses at Zhongba (Three Gorges) demonstrate significant salt production by the first millennium BCE, with indications of earlier activity and brine-boiling as a primary technique.

On the north China coast (southern Laizhou Bay, Shandong), late Neolithic through Shang–Zhou saltmaking sites (e.g., Shuangwangcheng, Nanheya) show sea-salt manufacture adapted to coastal flooding and Holocene shoreline change. Multi-proxy evidence further reconstructs prehistoric sea-salt manufacture on the East China coast as an adaptation strategy to coastal flooding.

In India

In India, coastal settlements on the Saurashtra–Gulf of Khambhat littoral show direct archaeological evidence for sea-salt manufacture: the Harappan site of Padri (Kerala-no-dhoro) is interpreted as a specialised salt-producing centre in the Mature Harappan period (ca. 2200–2000 BCE). A geoarchaeological synthesis notes that Padri's economy “depended on salt manufacturing” in a stable estuarine setting close to present sea level.

In Mesopotamia and Sumer

In Mesopotamia (including Sumer), cuneiform sources attest salt as Sumerian mun (sign MUN) and Akkadian milḫu (salt). Procurement drew mainly on natural salines and brines of the alluvial plain and marshlands; the direct archaeological visibility of purpose-built evaporation complexes is limited.

In America

At El Salado (central Veracruz), salt production shows two major occupational phases: an Early Formative phase (ca. 1400–1000 BCE) and a Late Classic phase (ca. AD 650–1000), identified through stratified features and residues associated with brine evaporation and salt making.

Marine salterns in antiquity

Across the classical civilizations of the Mediterranean, the ancient Middle East, India and Han China, antiquity transformed salt use less through new technology than through administration and literacy: conservative production know-how persisted while political (west) and bureaucratic (east) management, enabled by classical literate elites, widened output, distribution and consumption.

Within this framework, marine salterns took on greater importance: sea-salt exploitation expanded, waterborne transport increasingly displaced overland routes, and by about AD 500 sea salt supplied the larger share of salt consumption—no longer a luxury but a staple closely tied to fish processing.

By classical antiquity, extensive marine salterns (salinae) operated around the Mediterranean. Seawater was channelled by gravity into connected, shallow evaporation ponds where brine concentration increased stepwise before crystallisation and harvest.

Across the ancient Near East—including Phoenicia, Egypt, Mesopotamia and Israel—salt held ritual, symbolic and legal significance: it was prescribed for offerings at the Jerusalem Temple; invoked in “covenants of salt” and other treaty formulae; used to curse conquered lands by salting the soil; and, in the Second Temple period, supplied to the Temple as a tax-free ration by imperial rulers. Rabbinic texts describe substantial salt usage and a dedicated storehouse for Temple sacrifices, while early Christian writings employ salt as a moral metaphor (“salt of the earth”; speech “seasoned with salt”). Some traditions also linked salt to fertility and to Aphrodite.

Where conditions allowed, salt-evaporation ponds were laid out in sheltered coastal lagoons and low-energy shorelines, using networks of shallow, graded basins linked by canals and sluices to concentrate seawater by solar evaporation before crystallization and harvest.

Marine salterns in middle-age

On the French Atlantic seaboard (Guérande–Batz, the Baie de Bourgneuf/Marais breton, and Saintonge/Brouage), purpose-built solar saltern landscapes took shape from the early Middle Ages.

In the Guérande basin, marsh-based pond systems are securely attested by the 9th century (with earlier know-how) and became the dominant mode of production.

In Saintonge/Brouage, sheltered lagoonal settings were engineered into étier-fed, graded ponds. The 1478 rent survey for the prévôté d’Hiers records renewed exploitation and organisation in the Saintonge marshes.

Studies of distribution and river/coastal routes show Atlantic “bay salt” circulating widely from Merovingian/Carolingian times toward northern France and the British Isles.

Outside France, medieval salterns are widely attested: in England, the Domesday Book (1086) records over 1,195 “salinae,” mostly on the south and east coasts. In Portugal, a 959 donation charter by Countess Mumadona Dias mentions lands “in Alavario et salinas” at Aveiro, indicating early-medieval salt pans on the Ria de Aveiro.

From early modern reorganization to industrialization

After the Middle Ages, European saltmaking saw both the expansion of coastal solar salterns and the rationalization of inland brine works. In the northern Adriatic, the Piran/Sečovlje system was reorganised under Venetian rule (regular sequences of evaporation and crystallisation basins) and, during a 15th-century wave of salt-pan destructions elsewhere, Piran's pans remained active and entered a prolonged “golden age.”

<gallery>

File:2014 Cape Verde. Sal. Saltkratern (2).JPEG|Natural salt evaporation ponds at Pedra de Lume, Sal island, Cape Verde

File:Marakkanam Salt Pans.JPG|A salt pan worker in a salt evaporation pond in Tamil Nadu, India.

File:Lithium mine, Salar del Hombre Muerto, Argentina.jpg|Salt evaporation ponds at a lithium mine in Argentina. The brine in this salar is rich in lithium, and the mine concentrates the brine in the ponds.

File:Lanzarote salt pans.jpg|Contemporary solar evaporation salt pans on the island of Lanzarote at Salinas de Janubio

File:Solar Evaporation Ponds, Atacama Desert.jpg|Solar evaporation ponds in the Atacama Desert

File:Fundacion Valle Salado511.JPG|Solar evaporation ponds in the Salt Valley of Añana, Spain

File:Vallesaladoanana.jpg|Solar evaporation ponds in the Salt Valley of Añana, Spain

Aerial image of the Pag salt evaporation ponds (view from the south).jpg|Salt evaporation ponds at Pag, Croatia

Aerial image of the salt evaporation ponds in Margherita di Savoia (view from the west).jpg|Aerial view of the Saline di Margherita di Savoia, Italy

Aerial image of the salt evaporation ponds in Ston (view from the southwest).jpg|Aerial view of the salt evaporation ponds in Ston, Croatia

Salinas grandes-pala oxidada.jpg|Salt pile in Argentina

</gallery>

See also

  • Solar desalination
  • Seawater greenhouse
  • Evaporite

References

Video

  • Short BBC documentary on the salt evaporation ponds of Pedra de Lume, Cape Verde [https://www.bbc.com/reel/video/p0hjd77r/cape-verde-s-stunning-salt-mines]
  • NASA page on salt ponds
  • Information on the San Francisco Bay salt ponds
  • Interactive satellite view
  • "Salt, Grown On Sticks Harvested From Sea" Popular Science, March 1933