THE MOST ANCIENT DUNES IN THE 'DELTA DEL LLOBREGAT'

Claire Fontaine & The Grandma in Gavà

Today, Claire Fontaine and The Grandma have visited the Delta del Llobregat beaches from El Prat to Gavà.

The Grandma is a great fan of dunes and it's a great privilege to contemplate them near her home in this wonderful natural place next to El Prat Airport.

The most amazing thing about dunes is not only their capacity of formation but the vegetation that can grow in them and the great quantity of animals that can live in them.

Claire and The Grandma have relaxed on the beach thanks to a great sunny day and the warm temperatures. While Claire was swimming, The Grandma has studied a new lesson of her First Certificate Language Practice manual (Vocabulary 2).

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The Llobregat Delta, in Catalan Delta del Llobregat, is the delta of the Llobregat river, located near the city of Barcelona, Catalonia. The current delta has been altered by farming, urban development, industrialisation and transport infrastructures such as the Port of Barcelona and the Barcelona El Prat Airport.

The Natural Areas of the Llobregat Delta, in Catalan Espais Naturals del Delta del Llobregat, is a network of protected areas established in 1987 that belongs to the municipalities of El Prat de Llobregat, Viladecans, Gavà and Sant Boi de Llobregat. It encompasses more than 900 hectares over the right margin of the river that have been declared a Special Protection Area as a designation under the European Union Directive on the Conservation of Wild Birds.

Claire takes sun in Gavà

In physical geography, a dune is a hill of loose sand built by aeolian processes, wind, or the flow of water. Dunes occur in different shapes and sizes, formed by interaction with the flow of air or water. Most kinds of dunes are longer on the stoss, upflow, side, where the sand is pushed up the dune, and have a shorter slip face in the lee side. The valley or trough between dunes is called a slack. A dune field or erg is an area covered by extensive dunes.

Dunes occur in some deserts and along some coasts. Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach. In most cases, the dunes are important in protecting the land against potential ravages by storm waves from the sea.

Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds. Dunes can form under the action of water flow, fluvial processes, and on sand or gravel beds of rivers, estuaries and the sea-bed.

The modern word dune came into English from French c. 1790, which in turn came from Middle Dutch dūne.

Dunes form where the beach is wide enough to allow for the accumulation of wind-blown sand, and where prevailing onshore winds tend to blow sand inland. Obstacles, for example, vegetation, pebbles and so on, tend to slow down the wind and lead to the deposition of sand grains. These small incipient dunes or shadow dunes tend to grow in the vertical direction if the obstacle slowing the wind can also grow vertically.

More information: Espais Naturals del Delta del Llobregat

Coastal dunes expand laterally as a result of lateral growth of coastal plants via seed or rhizome. Models of coastal dunes suggest that their final equilibrium height is related to the distance between the water line and where vegetation can grow. Additionally the height of coastal dunes is impacted by storm events, which can erode dunes. Recent work has suggested that coastal dunes tend to evolve toward a high or low morphology depending on the growth rate of dunes relative to storm frequency. In certain conditions, both low and high dunes are possible, dunes are a system that shows bistable dynamics.

As a dune forms, plant succession occurs. The conditions on an embryo dune are harsh, with salt spray from the sea carried on strong winds. The dune is well drained and often dry, and composed of calcium carbonate from seashells. 

The Grandma & Claire on the beach, Gavà

Rotting seaweed, brought in by storm waves adds nutrients to allow pioneer species to colonize the dune.

These plants are well adapted to the harsh conditions of the foredune typically having deep roots which reach the water table, root nodules that produce nitrogen compounds, and protected stoma, reducing transpiration.

Also, the deep roots bind the sand together, and the dune grows into a foredune as more sand is blown over the grasses. The grasses add nitrogen to the soil, meaning other, less hardy plants can then colonize the dunes. Typically these are heather, heaths and gorses. These too are adapted to the low soil water content and have small, prickly leaves which reduce transpiration.

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Heather adds humus to the soil and is usually replaced by coniferous trees, which can tolerate low soil pH, caused by the accumulation and decomposition of organic matter with nitrate leaching. Coniferous forests and heathland are common climax communities for sand dune systems.

Young dunes are called yellow dunes and dunes which have high humus content are called grey dunes. Leaching occurs on the dunes, washing humus into the slacks, and the slacks may be much more developed than the exposed tops of the dunes.

It is usually in the slacks that more rare species are developed and there is a tendency for the dune slacks soil to be waterlogged and where only marsh plants can survive. These plants would include: creeping willow, cotton grass, yellow iris, reeds, and rushes. As for the species, there is a tendency for natterjack toads to breed here.

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One billion grains of sand come into existence in the world each second. That's a cyclical process. As rocks and mountains die, grains of sand are born. Some of those grains may then cement naturally into sandstone. And as the sandstone weathers, new grains break free. Some of those grains may then accumulate on a massive scale, into a sand dune.

Magnus Larsson