Landscape Ecology

The birth of an island

The North Sea island of Spiekeroog is a huge he great wilderness natural laboratory: over the past century its begins behind the eastern part, the “Ostplate”, has been trans- National Park Centre Wittbülten. The red formed from a small sand flat into a vast, wild brick building, where visitors can learn landscape of sand dunes and salt marshes. A Tabout the flora and fauna of the Wad- team of researchers led by Gudrun Massmann den Sea, roughly indicates the point where the island of Spiekeroog used and Luise Giani has studied how groundwater to end around 1950. At that time, there and soil develop on this young stretch of land was nothing but a few small white heaps of sand – and behind them, a bare, dry sand flat and the sea stretch- ing all the way to the horizon. Nowa- days you can walk eastwards from the National Park Centre for hours on solid ground. Behind the building a trail begins that winds its way between a chain of dunes and flat salt marshes crisscrossed by tidal creeks for about seven kilometres, until it reaches the end of the island. The inconspicuous path, which vis- itors are only allowed to use during the winter months because of the numer- ous birds breeding here in spring, leads through one of the most untouched landscapes in Germany – the ”Ost- plate” or eastern flat of Spiekeroog Is- land. The new part of the island, like the rest of the East Frisian Islands, has been a protected area since 1971. Since

28 EINBLICKE 2020/21 With every high tide, the North Sea washes new sediment into the salt marshes of Spiekeroog's Ostplate. The tides, the wind, and the storm surges keep the soil "young".

1986, when the Wadden Sea National groundwater and creating contiguous of the island, the first dunes began to Park of Lower Saxony was established, bodies of freshwater. grow on it 60 years ago, and 30 years it has been part of the most strictly It was these processes that Mass- later a seven-kilometre chain of dunes protected restricted zone. ”There are mann, Giani and Dr. Thomas Poll- covered with marram grass and a wide no coastal management measures of mann, Dr. Tobias Holt and Dr. Stephan strip of flat salt marshes had formed. any kind, no construction. The land- Seibert, who were still doing their PhDs The focus of the hydrological project scape is just left to itself – it’s the jewel at the time, rigorously studied from part was freshwater. A special feature of the national park,” enthuses Prof. 2015 to 2019. Their project, funded by of the East Frisian islands is that de- Dr. Gudrun Massmann, head of the the German Research Foundation spite their small size they have their Hydrogeology and Landscape Hydrol- (DFG), was titled ”Chronosequential own freshwater reservoirs, so-called ogy working group at the University initial evolution of soils and freshwater freshwater lenses, which are fed by of Oldenburg. The only forces at work resources of a barrier island.” rainwater and float above denser saline here are the tides, the wind and the groundwater. The lens in the western weather. Storm tides repeatedly break Accelerated part of Spiekeroog, for example, is al- through the young dunes, depositing most 50 metres thick and supplies res- growth new sand and flushing salt water into idents and tourists with drinking wa- the gaps between them. ter. But until now very little was known All this makes the Ostplate a unique The history of the Ostplate began at the about how and at what speed these experimental laboratory: ”You can end of the nineteenth century when bodies of water are formed, how large literally watch how the landscape the last remnants of what was once they are, what determines their chem- evolves, how the dunes grow higher the Harlebucht (Harle Bay) were diked. ical composition and what role the soil and higher and the vegetation chang- Originally fifteen kilometres wide, in plays in this process. ”The Ostplate is es,” explains Prof. Dr. Luise Giani, who the sixteenth century the bay stretched the only place where it is possible to heads the Soil Science working group about ten kilometres inland, almost study the initial stages of freshwa- at the university. Less visible are the all the way to what is now the city of ter-lens formation,” says Massmann, changes below the surface, which are Jever. ”The flow patterns in the tidal even if there are no plans to extract crucial to turning the former sand flat flats changed so much as a result of water there. into a piece of new land. Here, various the diking that sand accumulated east The team had to make regular visits chemical reactions occur, substanc- of Spiekeroog at a breath-taking pace,” to Spiekeroog to conduct their inves- es redistribute, and rainwater seeps explains Massmann. Around 1920 a tigations. The researchers took hun- into the dunes, displacing the saline sandflat appeared at the eastern end dreds of soil and water samples over

29 Salt-tolerant plants such as Salicornia and common cordgrass Hard work: Tobias Holt (right) and Stephan Seibert had to rely on are found in the pioneer zone of the salt marshes. In autumn, the their own muscle power to bring the equipment for groundwater shoots turn bright red. sampling to the Ostplate.

the course of a year, installing fifteen arate freshwater lenses already ex- creating new compounds such as the new groundwater measuring points ist beneath the dunes of the Ostplate, iron mineral pyrite. ”The oldest water with built-in data loggers. The instru- the formation of which probably be- in the main lens in western Spiekeroog ments still continually record water gan around 1975, they differ from the is about 50 years old,” explains Seibert. levels and salinity all the way down to large lens in the western part of the The smaller lenses on the Ostplate a depth of fifteen metres today. ”The island: ”These freshwater lenses are proved to be much younger and more sampling was of course carried out in only two to four metres thick, much dynamic by comparison. The water close consultation with the National thinner than the one in the west,” Holt there was no more than five years old. Park administration and the rangers; explains. His models also predicted The team also found that, unlike in we had to comply with strict regula- that under the current circumstances textbook illustrations, fresh and salt tions,” emphasises Giani. they are unlikely to expand any time water are not clearly separated there soon. ”They have already reached the but that instead there is a broad tran- A transitional area maximum possible size and are in a sition zone: ”It is here that oxygen-rich, kind of equilibrium,” the researcher salty seawater meets freshwater that between land and sea explains. Although precipitation fills contains no oxygen or nitrate, but does up the freshwater lenses, the winter contain dissolved iron, for example. Working in the nature reserve was a storm tides limit their growth: sea- Some minerals precipitate, others dis- unique experience for everyone: ”The water regularly seeps into the subsoil solve,” Seibert explains. Ostplate is a world of its own,” says north and south of the dunes, causing Chemical reactions also take place Pollmann. The team was under con- fresh groundwater to become saline in the soil above the groundwater. Poll- stant time pressure during the long and lenses to shrink again. In this way, mann's measurements showed that, marches to the measuring points be- the lenses grow and shrink in a sea- contrary to expectations, soils in the cause the salt marshes are partially sonal rhythm. Only if the dunes of the new part of the island hardly seem to flooded at high tide. The researchers Ostplate continue to grow, giving rise, age at all: the dunes and salt marshes also had to transport their equipment – for example, to another chain of dunes, in the western part of the Ostplate spades, drilling rigs, cameras, pumps could the lenses increase in size. were formed earlier than those fur- and measuring devices, etc. – on foot, Using samples from the groundwater ther to the east, but from a pedological and also carry the samples they had measuring points on the Ostplate and viewpoint they are at the same stage of collected in their backpacks. It was not from wells in the western part of the development. ”Tides, wind and storm unusual for each of them to be carrying island, Seibert studied the chemical tides are currently working against soil twenty kilograms or more at a time. processes that occur as the rainwater formation, they keep the soil in a young The data they collected on the new passes through the dunes, as well as state”, the researcher explains. part of the island (and also on the old inside the freshwater lenses them- As the project results show, the Ost- part for comparison) revealed that the selves. His measurements show how the plate is still a dynamic landscape which, Ostplate is still a transitional area be- chemical composition of the ground- in the absence of coastal protection tween land and sea that is shaped by water changes as it ages. For example, measures, is constantly changing. But tides and storm surges. Holt's meas- microbes break down organic material how will the East Frisian Islands de- urements and models showed, for with the help of reactive substances velop in the future if the sea level con- example, that although several sep- such as oxygen, nitrate or sulphate, tinues to rise and heavy storm tides

30 EINBLICKE 2020/21 Redox potential measurements show whether aerobic or anaero- Luise Giani, Thomas Pollmann, Gudrun Massmann and geoeco- bic conditions prevail in the soil. logist Holger Freund (from left) don't just conduct research on Spiekeroog, they also organize a landscape ecology excursion for students every autumn.

become more frequent? As part of a protective dunes would be particularly groundwater discharge is ”unstable newly initiated joint project, the Old- problematic,” Gudrun Massmann ex- and in the worst case irretrievable” – as enburg hydrogeology team wants to plains. ”If they cause seawater to seep on Langeoog, where several storm tides determine how climate change will af- from above into a freshwater lens that in the eighteenth and nineteenth cen- fect freshwater lenses – and how these is used to supply drinking water, this turies divided the island and its fresh- resources, which are so important for resource could be rendered useless for water lens. The lens has not recovered the islanders, can be managed sustain- decades.” The balance between precipi- to this day and is still divided into two ably. ”Storm tides that break through tation, water extraction and submarine separate water bodies. (uk)

BACKGROUND

Research in the backyard

For the marine and environmental ratory for social science and ecological two national networks for long-term researchers at Oldenburg University, research. In all projects, the university environmental measurements. Spiekeroog is the island “on their works closely with the National Park Underwater sensors continuously doorstep” – their first port of call when Administration as well as the Natio- record the temperature, electrical researching tidal flats and the North nal Park Centre Wittbülten and the conductivity and pressure of seawa- Sea. It all started in 2001 with the Hermann Lietz School. Laboratories ter at various depths, as well as the research group "BioGeoChemistry of and seminar rooms are available at the direction of the current and its nutrient Tidal Flats" at the Institute for Chemistry Wittbülten Research Centre, located concentrations. A radar measures the and Biology of the Marine Environment next to the National Park Centre. height of the waves, while meteoro- (ICBM), which was funded for almost The University runs several permanent logical sensors record weather data ten years by the German Research monitoring stations on Spiekeroog, and solar radiation. Foundation (DFG). It aimed to study including the fifteen groundwater All this makes Spiekeroog one of the the influence of tides, weather and measuring points on the Ostplate most intensively studied German North microorganisms on the biogeochemis- (see text), twelve experimental islands Sea islands. The various measuring try of tidal flats, with a particular focus in the Wadden Sea and the “Time-Series stations in combination with regular on the Janssand sandbank. Since then, Station Spiekeroog” – also known as teaching and research activities make Oldenburg research on Spiekeroog has the “Messpfahl” – in the strait be- up the Spiekeroog Coastal Observato- covered topics such as invasive plant tween the islands of Spiekeroog and ry (SCO) at the ICBM. The Oldenburg species, the spread of plastic waste neigh-bouring Langeoog. Built in 2002, researchers aim to investigate this and submarine groundwater discharge. this bright yellow construction pro- turbulent transition zone between land In an ongoing project on coastal protec- trudes about fifteen metres out of the and sea even more comprehensively in tion, the island serves as a field labo- sea and has since been integrated into the future.

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