Asalt evaporation pond is a shallow artificialsalt pan designed to extractsalts fromsea water or otherbrines. 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 onGreat Inagua inthe Bahamas, or the ponds in Jasiira, a few kilometres south ofMogadishu, where seawater is trapped and left to evaporate in the sun.
During the process ofsalt winning, seawater or brine is fed into artificially created ponds from which water is drawn out byevaporation, allowing the salt to be subsequently harvested.[1]: 517 [2]
The ponds also provide a productive resting and feeding ground for many species ofwaterbirds, which may includeendangered species.[3] However, Ghanaianfisheries scientistRoseEmma Mamaa Entsua-Mensah also noted that salt winning can destroymangrove forests andmudflats, altering the environment and making it unproductive for other development or fish growth.[4] The ponds are commonly separated bylevees. Salt evaporation ponds may also be calledsalterns,salt works orsalt pans.
There is an associated loss of available energy when evaporating into dry air. ThisGibbs Free Energy becomes positive when the salinity is high enough (or air humid enough) for the salt solution to cause water to condense into it. That is how liquid desiccants work.[5]
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, (), which is athermal efficiency that compares incoming light energy to the enthalpy of vaporization. This is the same as the gained output ratio (GOR) in desalination.[5]
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Due to variablealgal concentrations, vivid colors (from pale green to bright red) are created in the evaporation ponds. The color indicates the salinity of the ponds.Microorganisms change their hues as thesalinity of the pond increases. In low- to mid-salinity ponds, green algae such asDunaliella salina are predominant, although these algae can also take on an orange hue.Halobacteria, a type of halophilicArchaea (also known asHaloarchaea), are responsible for changing the color of middle to high-salinity ponds to shades of pink, red, and orange. Otherbacteria such asStichococcus also contributetints.[citation needed]
Notable salt ponds include:
UntilWorld War II, salt was extracted from sea water in a unique way in Egypt nearAlexandria.[12] 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.
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.
Archaeology is difficult and fragmentary: sea-level rise, deliberate demolition offurnaces, and repeated breakage of containers obscure direct traces.[13]
Archaeological evidence indicates that early European salt making (from theNeolithic through theIron Age) relied mainly on inland brine sources and fuel-evaporation techniques (briquetage), with production systems adapted to local environments; large coastal solar ponds were best suited to warmer, arid regions.[14]
Evidence for marine salt making in western Europe reaches back to the5th millennium BCE, where seasonal coastallagoons behind low sandy–silty shores likely served as proto-salterns that pre-concentrated brine before heating.[13]
By the3rd millennium BCE in France'sCentre-Ouest, the hypothesis of organized salt production is validated archaeologically, with distinctive ceramic forms signalling brine-heating installations; this does not exclude prior solar concentration in littoral lagoons such asLocmariaquer/Carnac (Morbihan) andVarna (Bulgaria).[13]
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.[15]
On the north China coast (southernLaizhou Bay,Shandong), late Neolithic through Shang–Zhou saltmaking sites (e.g., Shuangwangcheng, Nanheya) show sea-salt manufacture adapted to coastal flooding andHolocene shoreline change.[16] Multi-proxy evidence further reconstructs prehistoric sea-salt manufacture on the East China coast as an adaptation strategy to coastal flooding.[17]
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).[18] A geoarchaeological synthesis notes that Padri's economy “depended on salt manufacturing” in a stable estuarine setting close to present sea level.[19]
InMesopotamia (includingSumer), cuneiform sources attest salt asSumerianmun (sign MUN) andAkkadianmilḫu (salt).[20][21] 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.[22]
AtEl Salado (centralVeracruz), 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.[23]
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.[24]
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.[25]
Byclassical 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.[14]
Sea-salt production in antiquity was fundamental tofood preservation, animal husbandry and crafts, yet the archaeological footprint of the salt pans (salinae) themselves is comparatively scarce, making the reconstruction of production landscapes and practices challenging.[26]
Across the ancient Near East—includingPhoenicia,Egypt,Mesopotamia andIsrael—salt held ritual, symbolic and legal significance: it was prescribed for offerings at theJerusalem 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.[27]
Where conditions allowed, salt-evaporation ponds were laid out in sheltered coastal lagoons and low-energy shorelines, using networks of shallow, graded basins linked bycanals andsluices to concentrate seawater by solar evaporation beforecrystallization and harvest.[26]
On theTyrrhenian seaboard, including the environs of theTiber mouth, exploitation of lagoonal wetlands provided early, enduring settings for salt making within broader coastal economies and transport systems.[26]
Documented Romansalterns include complexes at O Areal (Vigo, NW Iberia),Kaunos (southern Turkey), and the lagoonal systems nearMaccarese–Fiumicino (Rome), which preserve characteristic arrays of ponds, channels and working surfaces for marine salt production.[26]
Along Israel's Mediterranean coast, particularly the WesternGalilee and northernCarmel, surveys by theIsrael Antiquities Authority have recorded ancient salt-producing installations, including sequences of shallow evaporation basins and channels.[27]
From the lateRepublic through the first two centuries CE, ownership and management were diverse: some salinae were state property leased out to tax-farming companies, but many were run under municipal or private control; a universal statemonopoly is not supported by the available evidence.[26]
InOceania, archaeologically attested solar-evaporation salterns are documented at theSigatoka Sand Dunes (Viti Levu,Fiji), where seventh-century AD installations used large flanged clay dishes to evaporate seawater—the first prehistoric salt-working identified in thePacific.[28]
On the FrenchAtlantic seaboard (Guérande–Batz, the Baie deBourgneuf/Marais breton, andSaintonge/Brouage), purpose-built solar saltern landscapes took shape from the early Middle Ages.[29][30][31]
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.[29][32]
In Saintonge/Brouage, sheltered lagoonal settings were engineered into étier-fed, graded ponds.[30] Late-medieval documents—Blanchet family accounts (1463–1512) in the Bourgneuf area—detail ownership, restructuring and renewed exploitation after mid-14th-century disruption.[33] The 1478 rent survey for the prévôté d’Hiers records renewed exploitation and organisation in the Saintonge marshes.[34]
Studies of distribution and river/coastal routes show Atlantic “bay salt” circulating widely from Merovingian/Carolingian times toward northern France and the British Isles.[35]
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.[36] 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.[37]
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.”[38]
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Also written milḫu … (CAD M/2: 69).
…Countess Mumadona Dias donated "terras alavario et salinas" to the monastery of Guimarães in 959.
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