Unerwartete Unterstützung aus der Natur: Marschlandschaften wachsen mit dem Meeresspiegel mit

Der NDR übte sich am 10. Mai 2017 in Klimaalarm und gab eine Pressemitteilung heraus, in der angebliche Geheiminformationen aus einem internen Papier des Bundesamtes für Seeschifffahrt und Hydrographie zitiert werden:

Bundesamt für Seeschifffahrt und Hydrographie befürchtet stärkeren Anstieg des Meeresspiegels

Das Bundesamt für Seeschifffahrt und Hydrographie (BSH) befürchtet, dass der Meeresspiegel in den kommenden Jahrzehnten deutlich stärker ansteigen könnte als bislang gedacht. Das geht nach Recherchen des NDR aus einem internen Schreiben hervor, das die Behörde im März an das Bundesministerium für Verkehr und digitale Infrastruktur (BMVI) gesandt hat, dem es untersteht. In dem Papier, das der NDR einsehen konnte, warnt das BSH davor, dass die bisherigen Anstiegsszenarien des UN-Klimarates zu optimistisch sein könnten. Das Schreiben trägt den Titel “Aktualisierung von Informationen zum Meeresspiegelanstieg” und gibt den Stand aktueller Klimastudien wieder. Das BSH warnt das Ministerium davor, dass “ein höherer Anstieg des Meeresspiegels deutlich über einen Meter hinaus bis hin zu 1,70 Metern bis zum Ende des Jahrhunderts mittlerweile nicht mehr ausgeschlossen zu sein scheint”.

Weiterlesen beim NDR.

Man muss kein Graphologe sein, um die Potsdamer Handschrift hier zu erahnen. Irgendwie müssen Vertreter der extremen Meeresspiegelszenarien Zugang zum Führungszirkel des BSH gefunden haben, um dieses Papier zu initiieren. Zu gerne würden wir die wissenschaftliche Basis überprüfen, auf der die Behauptungen fußen. Da das Papier ‘intern’ ist, bleiben die Thesen unüberprüfbar. So wird Politik am wissenschaftlichen Begutachtungssystem vorbei gemacht: Interne Papier werden wissenschaftlich ungeprüft an Ministerien gesandt, die diese dann möglicherweise direkt in politische Entscheidungen umsetzen, einfach unglaublich. Die neue Strategie der Alarmisten ist es offenbar, unterhalb des Radars zu fliegen und hierbei persönliche Kontakte spielen zu lassen.

Fakt ist: Der Großteil der Meeresspiegelforscher teilt die wilden BSH-Szenarien nicht:

Was gibt es Neues aus der Meeresspiegelforschung? Kirwan und Kollegen (2016) legten in Nature Climate Change dar, dass Küstenmarschlandschaften deutlich weniger in Gefahr sind als angenommen. Sie können nämlich aufschlicken und in gewissen Grenzen mit dem Meeresspiegel mitwachsen:

Overestimation of marsh vulnerability to sea level rise
Coastal marshes are considered to be among the most valuable and vulnerable ecosystems on Earth, where the imminent loss of ecosystem services is a feared consequence of sea level rise. However, we show with a meta-analysis that global measurements of marsh elevation change indicate that marshes are generally building at rates similar to or exceeding historical sea level rise, and that process-based models predict survival under a wide range of future sea level scenarios. We argue that marsh vulnerability tends to be overstated because assessment methods often fail to consider biophysical feedback processes known to accelerate soil building with sea level rise, and the potential for marshes to migrate inland.

Hier die dazugehörige Pressemitteilung der Virginia Institute of Marine Science vom 24. Februar 2016:

Study predicts salt marshes will persist despite rising seas

Traditional assessment methods overestimate vulnerability

A new study in Nature Climate Change contends that traditional assessment methods overestimate the vulnerability of salt marshes to sea-level rise because they don’t fully account for processes that allow the marshes to grow vertically and migrate landward as water levels increase.

The persistence of salt marshes despite rising seas would be a rare bit of good news for coastal ecosystems, which are under threat from a host of factors including nutrient pollution, invasive species, and development. Healthy marshes buffer coasts from storms, improve water quality, provide habitat for commercial fisheries, and help fight global warming by trapping carbon. Lead author Matt Kirwan, a professor at the Virginia Institute of Marine Science, says “Catastrophic predictions of marsh loss appear alarming, but they stem from simple models that don’t simulate the dynamic feedbacks that allow marshes to adapt not only to present rates of sea-level rise but the accelerated rates predicted for coming decades. Marsh soils actually build much faster as marshes become more flooded.”

More frequent flooding carries more mud into the marsh and also encourages the growth of several common marsh plants. Together, these processes raise the marsh soil in concert with rising waters. By not accounting for these feedbacks, Kirwan and his co-authors argue, traditional assessments greatly underestimate marsh resilience. Joining Kirwan on the study were Stijn Temmerman of the University of Antwerpen, Emily Skeehan of VIMS, Glenn Guntenspergen of the U.S. Geological Survey, and Sergio Fagherazzi of Boston University. The team conducted their study by compiling and re-analyzing 179 previously published records of change in marsh elevation from sites in North America and Europe. “Our study shows that soil accretion rates more than double as marshes become more flooded, suggesting a strong ability for marshes to survive accelerations in sea-level rise,” says Kirwan.

“The most common models greatly overestimate marsh vulnerability to sea-level rise,” adds Guntenspergen. “These models assume that marshes rise, but only at a rate equal to recent measurements of marsh accretion. This approach leads inevitably to marsh drowning, and predictions that most tidal wetlands will be inundated by the end of the current century.” The researchers say the few models that do incorporate dynamic feedbacks indicate that marshes can generally survive 10 to 50 millimeters of sea-level rise per year. That far exceeds current annual rates of about 3 millimeters of globally averaged sea-level rise, and mostly exceeds even the higher-end rates of 8 to 17 millimeters per year predicted by U.N. climate scientists for 2100.

The team suggests that use of these more advanced models will help ecosystem managers assess marsh vulnerability more accurately, and should be encouraged. They also recommend that researchers expand their current focus on the vertical adaptability of marshes by mounting studies that help clarify the processes that control the horizontal migration of marsh boundaries through time. Looking at recent history, the researchers note that the feedbacks built into the dynamic models also help explain the observed stability of many salt marshes in the mid-Atlantic and elsewhere during recent decades, and the relative rarity of marshes that have already drowned. Where drowned marshes do occur—think the Mississippi delta or Venice lagoon—the culprit is a reduced sediment supply, due to dam or levee building, or increased subsidence due to groundwater withdrawal and other factors. “Marshes fail to survive current rates of sea-level rise only where people have restricted sediment delivery or where the tidal range is very low,” says Kirwan.    

The researchers temper their optimism regarding vertical marsh growth with a cautionary note about the importance of allowing salt marshes to migrate horizontally as rising seas push them landward. They note that in low-lying areas of the U.S. Atlantic Coast, migration into nearby forests could offset most of the loss of existing salt marshes. But marsh migration isn’t possible where obstructed by coastal cliffs or human barriers. “Almost 20% of the Chesapeake Bay shoreline is hardened by riprap, seawalls, and other structures,” says Kirwan, “and similar structures border almost all marsh areas in northwest Europe. We suggest that the availability of low-lying land for wetland migration is a first-order determinant of marsh fate.”

Der Schutz der Küsten-Salzmarschen unterstützt daher auch den Küstenschutz, worauf die University of the Basque Country am 30. Juni 2017 in einer Pressemitteilung hinweist:

Restoring saltmarshes, a cost-effective strategy to counteract the rise in sea level

A piece of research led by the UPV/EHU-University of the Basque Country has shown that in only 10 years it is possible to regenerate some of these coastal wetlands on the eastern Cantabrian coast

Saltmarshes cushion the energy of the waves and act as natural barriers against high-energy climate phenomena. That is why restoring the currently occupied saltmarshes could be a cost-effective adaptation strategy to counteract the effects of the rise in sea level. This is one of the conclusions of a piece of research led by the UPV/EHU and which sets the time needed by several saltmarshes on the eastern Cantabrian coast to regenerate at less than 10 years.In the current scenario of global warming and the acceleration in the rise in sea level, “the study of the saltmarshes is of great interest in developing adaptation strategies to tackle the consequences of climate change in the coastal area”, explained Ane García-Artola, researcher in the UPV/EHU’s Department of Stratigraphy and Palaeontology and who is currently on a post-doctoral internship at the Rutgers University (USA). She is the lead author of the paper Agricultural fingerprints in salt-marsh sediments and adaptation to sea-level rise in the eastern Cantabrian coast (N. Spain), published by the Estuarine, Coastal and Shelf Science journal. The UPV/EHU lecturers Alejandro Cearreta and María Jesús Irabien, as well as researchers at East Carolina University and the National Autonomous University of Mexico also participated in the work.

On the eastern Cantabrian coast many of these coastal wetlands had been occupied for agricultural purposes since the 17th century and in particular from the second half of the 19th century onwards until the 1950s when agricultural activity experienced a decline.  The lack of dyke maintenance allowed water from the estuary to enter and it invaded these zones that had been artificially cut off, thus encouraging them to regenerate and be recolonised by halophytic vegetation, in other words, of the type that can survive in saline environments.

This work explored the regeneration process of the saltmarshes located in the Santoña, Plentzia and Urdaibai estuaries using the variation in the abundance of typical salt-marsh microfossils (foraminifera) and the sand content. “The agricultural horizon could be identified by the almost total absence of microfossils, whose number gradually increased during the regeneration process until becoming highly abundant once the saltmarsh had already regenerated,” explained Garcia-Artola. At the same time, the sand content increased as the regeneration took place, which indicates a greater tidal influence on the saltmarsh as the environment was being restored.

To be able to work out the age of the sedimentary layers and determine the build-up rates, the activities of short-lived radioisotopes, pollution peaks and historical aerial photography were analysed. From a regional perspective, the environmental regeneration of these three saltmarshes took place mainly in the Santoña estuary between 1950 and 1960 and in some zones, even before the 1940s; between 1950 and 1960 in the Urdaibai estuary; and, finally, from the 1970s and 1980s onwards, in the estuary of Plentzia. In all the cases, the regeneration process was very fast (less than 10 years), owing to the high rates of sedimentation that took place (14-18 mm per year). The availability of abundant sediment material in the estuarine waters was crucial in the regeneration of the saltmarshes.

The study of the environmental transformation of these coastal zones is crucial when it comes to making predictions about the coastal evolution of the region. So the saltmarshes on the eastern Cantabrian coast are expected to adapt to the increase in the ongoing rise in sea level (1.9 mm per year during the 20th century), bearing in mind the high sedimentation rates observed during the regeneration process of the previously occupied areas. “The restoration of currently occupied saltmarshes in temperate zones with an abundant input of sediments could be put forward as a strategy of cost-effective adaptation to counteract the effects of the rise in sea level,” pointed out Ane García-Artola.

Bibliographical reference
García-Artola, A, Cearreta, A, Irabien, MJ, Leorri, E, Sanchez-Cabeza, JA, and Corbett, DR, 2016. Agricultural fingerprints in salt-marsh sediments and adaptation to sea-level rise in the eastern Cantabrian coast (N. Spain) Estuarine Coastal and Shelf Science 171, 66-76. http://dx.doi.org/10.1016/j.ecss.2016.01.031