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The dunes of Doñana are formed as follows. The tides carry sand and shells to the beach, pushed inward by ocean winds. When the sand meets up with a plant, a dune begins to be formed. The buried plant then dies and the dune begins to move inward.
The movable dunes form dune ropes or trains which move between 5 and 6 meters every year in a direction perpendicular to the coastline. Between two trains of dunes “corrals” appear as vegetation oases in this sandy world.

The elevated insolation of southern Spain increases the ground temperature of the dunes. Reptiles and amphibians, cold-blooded animals, take advantage of this circumstance to set their archaic metabolism in motion and they can frequently be found among the white sand. However, the heat which favours cold-blooded animals is a deterrent to mammals, and very few enter the sand dunes while the sun is shining. But everything changes at night. An infinite number of footprints demonstrate that hunters have been stalking during the night, or simply moving through the sand to enter in one of the corrals, or even further in the ferocious world of the thicket or the marsh.

From a biological standpoint, the marsh is the most important area of Doñana and undoubtedly the most productive, i.e., that which produces the greatest quantity of living matter per unit of time and surface.
The floor of the marsh is composed of clayish sediments and becomes inundated every year between autumn and spring by rain and nearby floodwaters.
It is thus a system which depends very heavily on water and undergoes season transformations which mark, to a great extent, the rhythm of the entire Park. The marsh changes from a lake in wintertime to a fertile meadowland in springtime. Finally, in the summertime, it is converted into a land scorched by the sun and the lack of rain.

In one way or another, water is Doñana’s lifeblood and therefore its Achilles heel. Growing urbanisation which draws water from the aquifers and dumping into the rivers which nourish the marshes threaten the conservation of the most important national park in Europe. Life and death are thus summed up in a single word: water.

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