Saltpans

The Strunjan saltpans are historically part of the Piran saltpans. The latter were indirectly mentioned in the proceedings of the Placitum of Riziano in 804, while the first written source in which they are specifically recorded is the Piran town statutes from 1274. These documents, which listed the saltpans in Sečovlje, Lucija and Strunjan, defined the ordinance on the regulation of the saltpans and on the rights of the town of Piran to produce and trade in salt.

In 1358, all of the Piran saltpans, inspired by a new salt-making method from Pag, Croatia, started producing salt on a microbiological substrate called petola, which prevents the salt from mixing with the sea mud, thus keeping it clean and white.

In 1460, the Piran saltpans became the largest and most important in the north-eastern Adriatic and the Republic of Venice. With the income from abundant harvests, Piran was able to carry out important infrastructural works, securing a solid economic position for itself for the following 300 years. Therefore Piran is said ‘to have grown on salt.’

Upon the fall of La Serenissima in 1797, the Istrian saltpans passed to the administration of the Austrian monarchy, which in 1814 declared a state monopoly of the salt trade. This expanded the markets of Piran and with that the Strunjan saltpans. At the same time, the Austrians increased the number of crystallization ponds and built salt warehouses, which stand to this day.

In early 20^th century, the salt-fields in the Strunjan saltpans, which were privately owned by 19 local families, were bought out by the Austro-Hungarian monarchy in 1903, as they took ownership over the whole of the Piran saltpans. It employed hydrologists, maintenance and salt workers, thus replacing the family with state-operated salt manufacture. It reorganised the saltpan facilities, introduced the use of the Beaumé scale to measure the density of the brine and the removal of salt by wheelbarrow, as well as modernizing the wind pumps.

With the collapse of the Austro-Hungarian Empire in 1918, the Piran saltpans passed under Italian administration and underwent further changes. In 1945, they were incorporated into the Free Territory of Trieste. After becoming part of Yugoslavia in 1947, they were renovated one last time in 1957, when they were already losing their battle with salt mines.

In 1960, the Mining Authority at the Secretariat of the Executive Council for Industry of the People’s Republic of Slovenia declared the Strunjan saltpans to be part of the area designated for mineral (sea salt) extraction for commercial purposes and issued to the company Piranske soline, Portorož, a license for their exploitation.

Between 1961 and 1988, the Piran saltpans underwent a few modifications, closed some of the salt-producing areas and kept improving the infrastructure, but no major changes (for the better) came from that.

In 1990, the municipalities of Izola and Piran established Landscape Park Strunjan in the territory of the Peninsula of Strunjan, which also comprises the Strunjan saltpans.

Saltpan Structure and Operation

The Strunjan saltpans were built on the flood plain of the Roja stream. The alluvial deposits at the mouth of the Roja raised the stream bed and created the conditions necessary for the formation of salt fields.

In the saltpans, marine salt is obtained through natural crystallisation in the process of solar and wind evaporation. For that to occur, the seawater, or brine, has to complete the entire course of the saltpans, guided through salt ponds in which it becomes progressively denser.

Based on their function, the ponds can be divided into three types: supply, evaporation and crystallisation ponds. The water from the sea is led through a series of ponds to allow the evaporation of water and thus increase the salt concentration in the brine. The precipitation of salt takes place at the end of the course in the crystallisation ponds, where crystals of sodium chloride settle out from the oversaturated brine. This occurs when the share of sodium chloride (NaCl) in the brine reaches approximately 26 %; i.e., when the density of the brine is exactly 25.5 °Bé.

Circulation and Transport of Water

For the purposes of salt manufacture, seawater from the Bay of Strunjan is supplied with the tidal flow. Unwanted inflow of external waters is prevented by the outlying channels and levees. The system of water circulation and transport consists of a network of inlet and outlet channels, pumping sites, sluices for regulating the flow rates and a main sluice gate with two-way directional valves for filling the ponds with water or discharging it directly into the sea or the channels connected with it.

The channels for moving the water around the Strunjan saltpans are built from the sediments of the alluvial deposits by the Roja stream and susceptible to erosion, which is especially rapid during heavy rainfalls and when caused by wind-waves in the flooded ponds. To limit the erosion, the levees are partly lined with wood or stone, and the sparse and uneven vegetation covering the larger surfaces helps to some extent.

The saltpans are a technological facility that must be constantly maintained in a suitable state of repair. The protective levees in the saltpans are at the same time protective structures for the surfaces inland, the residential areas and agricultural terrain, and the important road route that connects them.

Cultivation of Petola

While the brine-producing ponds in the evaporation area have a clay base, the beds in crystallisation ponds are covered by a layer of petola.

Petola is a 1 to 2 cm thick hard substrate consisting of cyanobacteria (Microcoleus chthonoplastes) and other microorganisms, gypsum, carbonate minerals, algae and, to a smaller extent, clay. It plays a double role, preventing the sea mud at the floor of the crystallisation pond mix with the salt, and acting as a biological filter by inhibiting the incorporation of iron and manganese ions into the salt.

The salt-making method based on the artificially grown microbiological substrate, which was brought to us in the 14^th century from the Isle of Pag, Croatia, marked perhaps the major development milestone in the history of Piran saltpans.

In fact, the changeable weather in our area dictates the custom of daily harvests of salt. The crop has to be gathered as soon as possible to prevent the frequent afternoon showers from ruining it. A day-old salt surface is only one crystal thick and by raking the salt from the floor of the crystallisation ponds the crop is often sullied by pieces of the clay substrate.

In petola-based salt-making method, the mud applied to the beds of crystallisation ponds is, in a matter of weeks, colonised by algae and cyanobacteria, which in the form of a crust-like protective layer prevents the salt from coming into direct contact with the mud and thus enables the manufacture of white, pure salt free from impurities even in an environment in which a daily harvest is a necessity.

Working Tools and Methods

The tools used by the salt workers for their daily chores are made of chemically untreated and uncoated wood. On occasion, aluminium shovels are used to load and unload the salt.

Where the difference in height is insufficient for the water to move from a higher to a lower location by force of gravity, it is transferred by electric pumps. In the work in the crystallisation area, traditional manual techniques are employed in the preparation of clay terrain and the cultivation of petola.

The Job of a Salt Worker

In the Strunjan saltpans, the salt is only harvested in summer in the smallest crystallisation ponds, but the care for it is a year-round task.

In mid-March, when the conditions are suitable for growing a thick algal carpet, the salt workers start applying a layer of sea mud over the beds of crystallisation ponds. The mud coating has to be completed by the fourth week of April, when it is time to reinforce the substrate in the crystallisation ponds (or cavedini, in salt-making jargon) and prepare the salt fields for the season. Before and after the mud coating, the salt workers also regulate the water flows so as to achieve the perfect growth of the algal carpet.

The salt-making season extends from May to mid-September. Once the new algal carpet has developed, it is time to clean the crystallisation ponds by washing and scrubbing them with a wooden scraper (the so called gavero). By this time, the petola, interlaced by microorganisms, calcium carbonate and gypsum, has become brown-black, rough and compact (firm and elastic).

The salt harvesting season, which lasts from June to mid-September, is the result of previous efforts and a time of worries about the weather. If rain comes, all work and costs will have been for nothing – such is the nature of traditional salt-making. But normally, the salt worker daily uses the wooden gavero to rake up the salt into several low and wide piles, allowing it to drain a little, then carefully moving it onto a cart (cariola) and taking it away to unload it with a shovel and leave it to dry completely.

Old salt workers did not say in vain that ‘the salt is made in winter.’ At the end of summer, after-season works begin: water management in the crystallisation area through regulation of wooden sluices and utilisation of gravity-led or pump-aided flows; earth, maintenance and repair works in the salt fields; replacement of worn out or damaged wooden equipment; maintenance of infrastructure…These activities take place from mid-September to mid-March, and then the circle of chores starts again.

There are several types of salt, based on the time of formation, the concentration of the brine, and content of sodium chloride (NaCl), calcium and magnesium in the dry matter.

First salt

This grows at the beginning of the season or longer if the season is frequently interrupted by rain. The concentration of brine in crystallisation ponds, with a continuous supply of saturated brine, ranges roughly between 25 and 27° Bé, the minimum NaCl content is 97 % on a dry matter basis, the maximum combined share of calcium and magnesium 0.4 %.

Traditional salt

This forms when the salt production has stabilised thanks to a period of stable weather conditions and a steady flow of concentrated brine into the supply ponds. The concentration of the brine in the crystallisation ponds, with a continuous supply of saturated brine, reaches roughly up to 29° Bé, the minimum NaCl content is 95 % on a dry matter basis, the minimum combined share of calcium and magnesium 0.4 %.

Piran salt

The production of this salt is enabled by longer periods of dry weather. The concentration of the brine is higher, ranging between 28 and 31° Bé, which allows for the precipitation of large quantities of various minerals (calcium, magnesium, potassium, bromine, iron). The harvesting is difficult, as the small size of the crystals makes it difficult to amass the salt into mounds. The minimum NaCl content is 95 % on a dry matter basis, the minimum combined share of calcium and magnesium 0.55 %.

The quality and the mineral composition of salt can vary. They depend on how well the petola substrate has been prepared, on the concentration of the brine readied for crystallisation and on the concentration of the brine in the ponds at the very time of crystallisation, which, in turn, depends largely on the weather and the proficiency of the salt workers.

Fleur de Sel

In periods of no wind, fleur de sel forms on the surface of the brine as a thin, delicate crust of white to pale pink salt crystals, arranged in a typical inverted pyramid structure. It can form anywhere in the crystallisation area, but the best grows at higher concentrations of brine. The minimum NaCl content is 96 % on a dry matter basis, the minimum combined share of calcium and magnesium 0.22 %.

Fleur de sel typically has a very low bulk density and requires twice as much space as the same mass of evaporated salt. The finer the crystals, the finer the quality of fleur de sel. If it sits for a long time, it starts to cake. Fleur de sel is distinguished from other types of salt by its airiness and fragility, as it readily crumbles between the fingers.

Fleur de sel was made famous by French chefs, but it is now appreciated by bon vivants all over the world for its mild taste when added just before serving to accentuate the flavours on the plate.

The area of the Strunjan saltpans and lagoon has been included in Natura 2000, the European network of areas of environmental importance, as the local activity of salt-making is a major factor in the biodiversity of this exceptionally important type of ecosystem: the salt wetland.

The sub-Mediterranean climate, the high salinity of the water in the shallow ponds and the traditional salt-making methods create specific ecological conditions in which only the best-adapted organisms can survive.

To preserve this valuable biotope, the Regulation on the Landscape Park Strunjan prescribes the maintenance and renovation necessary to ensure a constant water regime in the saltpans and thereby the diversity of plant and animal habitats characteristic of saltwater, brackish and freshwater coastal wetlandsa.

The Stjuža lagoon and the Strunjan saltpans are an important living environment for birds. Following is a quick review of the aquatic bird community in the saltpan area:

• The reed bunting (Emberiza schoeniclus) is, of course, common in reed beds, but also found in drier habitats and gardens. In Slovenia, it is classified as a rare, year-round bird species with a population of 200‒400 pairs in summer and 1,000‒2,000 pairs in winter.
• The common greenshank (Tringa nebularia) is a greyish wader of marshes and estuaries, easily recognisable by its long green legs and elongated, slightly upturned grey bill. In Slovenia, it is a regular migratory species, most numerous in autumn.
• The black-winged stilt (Himantopus himantopus) is a black and white wader with extremely long legs, a prettily rounded head and a long, thin and straight pointed bill. In flight, its pink legs extend far back. This is a summer species of prevalently coastal areas of Europe with a preference for salt marshes. In recent years, it has been regularly nesting in the Strunjan saltpans.
• The little egret (Egretta garzetta) is a regular guest of the Stjuža lagoon and the Strunjan saltpans. It is readily identified by its stabbing black bill and black legs with yellow feet, its elegance and a gracefully curved neck. The great egret (Ardea alba), a much rarer sight, differs from its smaller cousin in size, of course, but also in the colour of bill and legs, both yellow. Especially in winter, the two egret species are often joined by the grey heron (Ardea cinerea), a difficult bird to miss around our parts.
• The Mediterranean gull (Ichthyaetus melanocephalus) has a pale plumage, a heavy red bill with a hooked tip, and red legs. In summer, the adult displays a black hood that extends down the nape and shows a distinctive white eye crescent; in winter the hood is largely lost, but the dark streaking around it, and behind the eye, remains. In the Strunjan saltpans, the Mediterranean gulls are a genuine eye-catcher in summer, as it is possible to see as many as 300 of them flocked together. In addition to Mediterranean gulls, the area is also visited by yellow-legged gulls (Larus michahellis) and black-headed gulls (Chroicocephalus ridibundus). The latter is frequently confused with I. melanocephalus. The main difference between the two species is the wing tip colour: white in the Mediterranean and black in the black-headed gull.
• The mallard (Anas platyrhynchos) is a common, widespread water bird, which can be seen year-round in very different water habitats, from remote marshes and watercourses to ponds in urban environments. The breeding male mallard’s plumage is distinctly different from the more modest female’s. The male has a bottle-green head, white collar and a brown chest, its back and wings are light grey. The female mallard shares its coloration with most female surface-feeding ducks. It can be identified by the dark brown crown, dark eye-stripe and orange bill. The female’s plumage is typically mottled to provide protection, especially in the egg-laying period.
• The common kingfisher (Alcedo atthis) is a peculiar bird, a living jewel, elusive enough to only be perceived as a bright blue creature flying low over the water. It is limited to rivers and creeks, but in winter it can also be seen in the Strunjan saltpans and lagoon. It has a beautiful iridescent plumage, with blue-green upperparts, a bright blue rump and rich orange-red underparts.

But birds are not the only residents of the saltpans. The shallows are home to a host of smaller animals, such as polychaetes, shrimp and crabs, molluscs, larvae of certain flies and other creatures tempting the palates of the local feathered population.

• The lagoon cockle (Cerastoderma glaucum) colonizes soft sediments with shell debris. It usually forms dense populations in lagoons, estuaries, ponds and saltpan channels, where it burrows right under the surface of the sand, its upper part sticking out. When dislodged onto the shore by wave action, the bivalve jumps back in by bending and straightening its muscular foot. The shell is thick and rounded, up to 5 cm in size, with conspicuous radiating ribs, its colour ranging from white to off-grey, and olive green in the posterior. The bivalve is widespread throughout the Mediterranean and is economically significant. Though edible, it is more often used as fish bait and in the production of souvenirs.
• The Mediterranean mud shrimp (Upogebia litoralis) lives in the mud burrows it mostly digs in clayey, only slightly inclined shores, such as the level and bare surfaces around the Istrian saltpans and the lagoon floor, which are exposed at low tide. Normally, it only leaves its burrows at night-time. The elongated body is soft and white, rarely pink or bluish. The shrimp variety present in the Slovene sea grows up to 5 cm in size.
• Ephydra riparia is a greenish brine fly with a metallic sheen, most often found in saltpans and on shores with dead algae washing up. The brine fly family comprises about 1,000 species, mostly tropical and North-American flies, with some 200 species recorded in Europe. Adult specimens populate the grass and other vegetation on seashores or around inland stagnant and running waters; the larvae also mine the stalks and leaves of aquatic plants in salt and freshwater.
• Notomastus latericeus is a member of sedentary polychaetes, by far the most widespread group in the Capitellidae family of marine worm, and is present throughout the Slovene sea. It prefers the soft sedimentary seabed floor into which it digs temporary spiral holes, thereby turning and aerating the upper layer of the substrate. N. latericeus is a detritivore, feeding on organic detritus (also called marine snow) that it consumes mostly intermixed with sand and silt, thus accelerating the return of decomposed material into the cycle of life.
• The South European toothcarp (Aphanius fasciatus) is a small fish (up to 5 cm in size) living in saltpans, ditches near the sea and river mouths. Its diet consists of mud shrimp and other small invertebrates. The male toothcarp is colourful, with dark bars on a silvery background, yellow fins and a prominent submarginal stripe in the caudal fin. Especially in the period of spawning, its bold appearance sharply contrasts with the discrete silverish colouration of the female. In summer, the population of this species in the saltpans can build up to several hundred thousands. The main predators of A. fasciatus include herons, egrets and gulls. The fish spends the winter buried in the soft mud or under the dense algal carpets of the saltpans.

Halophytes are plants adapted to living in an environment characterised by considerably higher concentrations of minerals compared to ordinary types of soil. Saline soils can be encountered both on the continent as well as on the seashore.

Throughout geological history, continental salt flats formed as a consequence of extremely dry climates. The tectonic shifts moved them underground and nowadays they are exploited as salt mines. In modern times, many terrains have become salinized due to man’s exploitation of soil through intensive agriculture and irrigation. As there are no continental salt flats in Slovenia – the ones nearest to us are situated in the most arid regions of the Pannonian Plain, for example in central Hungary and in Vojvodina, Serbia – we only encounter halophytic plants on our coast.

While the most beautiful plant communities have developed in saltpans (in Strunjan and Sečovlje) and in coastal wetlands (Škocjanski zatok, the surroundings of Ankaran), it is possible to come across individual specimens also on the natural rocky shore and on the breakwaters, in older ports and on other forms of anthropogenic coast.

The prevailing type of salt in Slovene halophyte sites is sodium chloride. Ordinary plants are sensitive to higher contents of NaCl (and other mineral substances) in the soil, as the consequent build-up of osmotic pressure prevents the transfer of water from the environment into plant cells. High concentrations of salt can even be poisonous to a plant, for the salt ions hinder some of the biochemical processes taking place in it. Halophytic plants have adapted to such conditions and are able to eliminate excess salt through the glands on their leaves, and regulate osmosis inside their cells in order to control the amount of salt in their tissues.

• The shrubby swampfire (Sarcocornia fruticosa) is a succulent perennial plant with vestigial leaves reduced to scale-like blades. Its main stems are slightly woody. The plant blooms from July to October. Though not particularly noticeable in the flowering period, as the tiny inflorescences are completely embedded in the fleshy shoots, with only the stamens sticking out, it certainly catches the eye in autumn, when it turns red.
• The common glasswort (Salicornia europaea) is the most widespread halophytic annual in the Strunjan saltpans. As the young shoots of the plant are tender and juicy, the salt workers used to include glasswort in their diets, preparing it as a toothsome salad. It blooms from July to September, as discretely as swampfire.
• The golden samphire (Inula crithmoides) traditionally grows on rocky shores. In Slovenia, where other types of coast prevail, it usually flourishes in manmade coastal landforms, such as ports and docks. In the Strunjan saltpans it is found in tufts along large and dry levees and large channels, but also occurs individually in the ruins of old saltpan houses. Blooms last from June to September.
• Sea lavender Limonium angustifolium is an herbaceous perennial with a strong rhizome, sturdy and fleshy evergreen leaves and small violet flowers, which bloom from July to September. The glands secrete excess salt, which in dry weather takes the shape of cubic crystals. L. angustifolium used to be picked for dry flower bouquets to the point of threatening the species with extinction.
• The bluish wormwood (Artemisia caerulescens) is a halophyte of somewhat arid soils, commonly found anywhere along the Slovene shore, particularly in associations with sea lavender and sea purslane (Atriplex portulacoides). It may look a lot like sea purslane to the untrained eye, but the aroma of a leaf crushed between the fingers quickly gives wormwood away. The plant blooms in September and October.
• The sea aster (Aster tripolium) is a common seashore species typical of brackish waters. It grows well on saltpan levees, though never building large stands. Asters bloom from June to October, thus providing food to the last of the butterflies that persist until the arrival of the cold weather, but it is not uncommon to find blooming specimens even in the dead of winter.
• The rock samphire (Crithmum maritimum) is a common species growing on rocky coasts, in rock and wall crevices regularly sprayed by seawater. It blooms in June and July. Each flower produces an oval, flat aromatic seed, which can be used as condiment. However, picking rock samphire is prohibited in Landscape Park Strunjan, as it is – like all other plants of this area – protected.
• The opposite-leaved saltwort (Salsola soda) grows on the edges of embankments. In the past, it was an important source of sodium carbonate (or soda ash), widely used until the 19^th century in soap- and glassmaking. In fact, the ‘Levantine soda ash’ is famed to have bestowed particular malleability to the celebrated Murano glass, allowing Venetian glassblowers to fully express their creativity. Nowadays, more than by glassmakers, the saltwort is appreciated by gourmets, who pick it wild or buy it grown as ordinary vegetables. It blooms from July to October.
• The spear-leaved orache (Atriplex prostrata) is a widespread species colonising all types of coast, even those under strong anthropogenic impact. It is easily recognisable by its lanceolate leaves. In October and November, the seeds of this plant are an important food source to numerous granivorous birds. This blooms from July to October.

The salt-tolerant marine phanerogams in Landscape Park Strunjan include the annual seablite (Suaeda maritima), which grows in almost all types of plant communities. Unlike the majority of halophytes in Slovenia, it has not made the IUCN Red List of Threatened Species, on which we can find almost all previously presented plants, as well as the lesser sea spurrey (Spergularia marina), the Puccinellia palustris grass species and the curved sicklegrass (Parapholis incurva).