Saltmarshes

Introduction		Click here to watch the saltmarsh 360°
Saltmarshes typologies
	- Lagoon edge saltmarshes
	- Internal saltmarshes
	- Saltmarshes along the old Lagoon tributaries
	- Saltmarshes along the Lagoon waterways
	- Paleo saltmarshes
Saltmarshes zonation
	- Low saltmarsh
	- Medium saltmarsh
	- High saltmarsh
Adaptation of the organisms		Curiosities and interesting findings!	Discover the saltmarsh profile Let's think about it...
	- Plants - Invertebrates

Introduction

Saltmarshes are the most common geomorphologic form in the Lagoon; nowadays they cover the 8% of its surface, compared to a 25% at the beginning of the century (from Various authors, “La Laguna di Venezia”, CIERRE, Verona, 1995).
According to Boerio (1856), their name comes from “baro”, the vernacular term indicating a thick group of bushes or an uncultivated marshy land.
They look like a flat and small island, whose substrate is mainly made up of silt-clayey sediments (from Rallo G., “Guida alla natura nella Laguna di Venezia - Itinerari, storia e informazioni naturalistiche”).
Saltmarshs are constantly visible, except when the tide rises. High tide represents the limiting factor to their vegetal association in terms of salinity, water availability, lighting, etc.

Other systems characterising the saltmarshs are the ghebi, the velme, the chiari, the paciare.
The velme are shallow beds that emerge only when the tide lowers. Several types of phanerogams characterise the velme:Cymodocea nodosa, Zostera noltii, Zostera marina. Particularly, the Zostera marina dwells in the external velme, the velme fronting the Lagoon waterways; the Zostera noltii characterises the internal velme, those fronting the marshes.
The chiari and the paciare sono delle depressioni are ground depressions where salty water accumulated during high tide mixes with meteoric water, thus forming small lakes. These environments go on developing and come out from the dynamic balance of sediments, currents, and vegetation.
Saltmarshes are crucial in the fight against eustacy: the plants growing on them catch sediments and debris, thus making the soil thicker and taller.

Saltmarshes typologies

Saltmarshes are classified according to both the ways they have been formed and their own evolution. Each kind of saltmarsh is characterised by a stratification of sediments and the zonizing of the distinctive vegetation.

Lagoon edge saltmarshes
Some saltmarshes are the remaining visible part of the coastal plain. They are so permeated with salty water that only the halophyle vegetation, adapted to such an inhospitable environment, can grow on them.
This kind of saltmarshes are located along the Lagoon edge towards the mainland, like the ones between Campalto and the Dese area. These saltmarshes show their nature through some continental indicators that can be detected both on the surface and few centimetres in depth.
Originally saltmarshes were directly influenced by the mainland, which continuously provided sediments and plants. When the lagoon boundary stopped the sediments provision, a demolition process began.

Internal areas saltmarshes
The saltmarshss sited in the internal parts of the Lagoon have had a more complex history. They were initially wetted by salty waters; later on, due to the rivers flowing into the Lagoon, they started developing fresh water marshes and peat-bog. Eventually, after the waterways were diverted towards the sea (see: deflection of the Lagoon tributaries), they reassumed Lagoon features.

They are mostly sited in the South Lagoon, between Marghera and Chioggia. The lack of sediments provision, caused by waterways diversion, brought to a graduate lowering of saltmarshes, worsened by the erosion due to wave motion and to the subsidence.
The history of this kind of saltmarshes can be traced back through the underground sediments: in fact, stratigraphy underlines the succession of the Lagoon indicators - indicators of fresh environment - saltmarshes indicators - indicators of Lagoon environment.

Saltmarshes along the old tributaries to the Lagoon
Another kind of saltmarshes can be found along the old waterways flowing into the Lagoon and they were formed by ancient drifts.
On the maps of the Lagoon, they are often indicated by the phrase “points of the lovi”, the word “lovo” probably coming from “alluvium” (flood), thus revealing their origin. As they are easily accessible from the mainland, they have been often turned into agricultural fields.

Saltmarshes along the Lagoon waterways
The saltmarshes along the Lagoon waterways have a different origin: they were formed by sediments brought about by the marine current; because of their slow flowing speed, the sediments dropped some suspension material. A smaller amount of sediments come from the erosion caused by the marine current on the canals beds.
They can be considered original ecotopes , as they have been only slightly influenced by man. Consequently, their flora and fauna, as well as the sediments structure and its dynamisms, have not altered their original features much.
This kind of saltmarsh is typical of the North Lagoon (S. Erasmo, San Felice, San Lorenzo, and Burano) where many sediments are dropped after flowing into the Lagoon from the Lido lagoon inlet by a reduced current speed.
The edge of these saltmarshes is taller on the side of the supplying canal, while it becomes shorter as it moves away from it, turning into a velma.
Even in this case the underground sediments reveal the evolution of the place: at the beginning of the stratigraphic series a large amount of Lagoon indicators can be detected, but gradually they are replaced by saltmarshes indicators.
This type of saltmarsh cannot be found in the Malamocco and Chioggia lagoon inlets, because the water flowing into them does not carry an amount of sediments large enough to form" Lagoon waterways saltmarshes".
The main problem affecting this kind of saltmarshes is the erosion given by the wave motion due to heavy water traffic.

Paleo saltmarshes
In the Venice Lagoon there are also some paleo saltmarshes, whose long-lasting presence has been proved by traces of oxidation and of developing vegetal remains: their appearance was not due to a storage of sediments but to the lowering of the sea level (from Cavazzoni S., “La Laguna: origine ed evoluzione“ in “La Laguna di Venezia“, CIERRE, Verona, 1995 and from Favero V., Serandrei Barbero R., “Origine ed evoluzione della laguna di Venezia. Bacino meridionale“, in “Lavori, vol. 5, Venetian Society of Natural Sciences, Venice, 1980).
Being characterised by three association of perennial plants (Spartineto, Limonieto, Puccinellieto) saltmarshes vegetation is stable.These associations can exploit environmental resources at their best without turning into more complex ones. An excessive salinity,blocking the vegetation natural series, prevents their coming to a climax (from Pignatti S., “La vegetazione alofila della laguna veneta“).

Saltmarshes zonation

Despite their origin, three different layers can be distinguished in the saltmarshes, corresponding to three levels of elevation.

- Low saltmarshes: they are slight downwards slopes linking the velma to the proper saltmarsh.
They host the Spartinetum strictae, a vegetal association which is mainly formed by the saltmarshes common cord grass (Spartina maritima) and, to a lesser extent, by glasswort (Sarcocornia fruticosa), sea lavender (Limonium narbonense), and puccinellia (Puccinellia palustris).

The low saltmarsh salinity is quite high (25 – 35 ‰), its terrain loose, rich in organic matter , and soaked in water. Vegetal association is stable; as a matter of fact, both the sea lavender and the common cord grass of the saltmarshes are perennial plants, thus exerting their consolidating action in an efficient and ongoing way.
The glasswort is said to be a pioneer plant, since it is the first to grow in the velme. It starts consolidating the sediments that will host the common cord grass, the real stabiliser of the saltmarshes.

- Medium saltmarshes:their typical association is the Limonietum venetum. According to Pignatti (1966), about the 90% of saltmarsh surface is covered by this vegetal association. It is composed of sea lavender, glasswort, puccinellia, annual sea-blite (Suaeda marittima), sea aster (Aster tripolium), sea rush (Juncus maritimus).
This biodiversity is really important for the defence of saltmarshes as different species can use environmental resources in various ways, thus assuring a consolidating vegetal presence in any condition.
The soil on which the limonietum grows must be clayey, very moist or even soaked, not much airy, with a high salinity, and periodically submerged by high tide.

Adaptation of organisms

Plants
Saltmarshes plants show an adaptation ability that makes them survive in such a peculiar environment.
One of the main problems for plants living in these places is water absorption, which occurs by osmotic pressure difference: therefore, water moves from where the concentration of solutes is low towards an area where their concentration is higher.
Saltmarshs salt concentration is quite high, thus preventing plants from absorbing water from the ground.
Saline concentration in the tissue of halophyle plants can even reach a 10%; this makes the absorption of water and of nutritional substances possible. Salt storage and the photosynthesis occur in the branches, being salicornia leaves extremely short or even absent.
Other adaptation features are:
- a vegetative part which is poorly developed and very short in order to resist wind;
- well developed roots to absorb as much nourishment as they can from such a dry and salty terrain;
- flowers set in small niches not to let the wind scatter pollen.
Sea lavender stem and leaves have glands that release extra salt.
The sea purslane (Halimione portulacoides) leaves, like those of other plants, are succulent or small to limit water loss caused by evapotranspiration.
In the saltmarshs there are some depressions, like the chiari and the paciare, where salty water mixes with meteoric water thus diminishing salinity. These less prohibitive conditions let also the wigeongrass (Ruppia marittima), grow; it provides important nourishment for the common coots (Fulica atra) and anatidae. In fact, saltmarshes are inhabited by limicolous birds, particularly in winter and in the migration time. The anatidae coming from North European countries find a favourable climate and spend the winter here.

Invertebrates
Some terrestrial invertebrates adapted to this environment by adopting special strategies: some insects dig tunnels in the substrate, breathing in air bubbles while immersing in the saltmarsh; some others follow the tide flow and shelter on top of the plants when the tide rises; they get back to the soil when the tide lowers (da Torricelli P., Bon M., Mizzan L., “Aspetti naturalistici della laguna e laguna come risorsa” Parte Prima: Aspetti naturalistici della laguna).