From Polder to Saltmarsh Saltmarsh Restoration in Noarderleech (Wadden Sea)
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FROMFROM POLDERPOLDER TOTO SALTMARSHSALTMARSH SALTMARSHSALTMARSH RESTORATIONRESTORATION ININ NOARDERLEECHNOARDERLEECH (WADDENSEA)(WADDENSEA) ANAN EXPERIMENTEXPERIMENT FROM POLDER TO SALTMARSH SALTMARSH RESTORATION IN NOARDERLEECH (WADDEN SEA). AN EXPERIMENT. Published by: Olterterp 2007 Altenburg & Wymenga Report 1020 A&W-report 1020 CONTENTS 1 Summary................................................................................................................................3 2 Struggle and Rise ...................................................................................................................5 3 Historical Background.............................................................................................................6 4 Reclaim and Retreat................................................................................................................8 5 Saltmarsh Dynamics..............................................................................................................10 6 Saltmarsh Restoration Elsewhere ..........................................................................................13 7 Management of Noarderleech..............................................................................................14 8 The Intervention ...................................................................................................................15 9 Research...............................................................................................................................17 10 Monitoring ...........................................................................................................................18 11 Tidal Flooding and Salinisation .............................................................................................19 12 Vertical Accretion .................................................................................................................21 13 Vegetation............................................................................................................................22 14 Birdlife..................................................................................................................................25 15 Evaluation and Perspectives ..................................................................................................27 16 Sources.................................................................................................................................28 2 A&W-report 1020 1 SUMMARY Human habitation along the edges of the Wadden these breaches, the area will be flooded fourteen Sea dates back to long before Roman times. During times a year on average during storm tides. the Middle Ages, the inhabitants of this region A monitoring programme was set up to study the began to reclaim land from the Wadden Sea. From salinisation of the groundwater and soil and the the seventeenth century onwards ditch systems vertical accretion in grazed and ungrazed condi- were developed to stimulate accretion on the tions, in the abiotic environment. Monitoring of the saltmarshes, and this essentially continued as a biotic environment involved studying the vegetation ‘farmer’s method’ of land claim well into the twen- development and assessing the numbers of winter- tieth century. By embanking the elevated saltmarsh- ing and staging geese and breeding birds in relation es, between 1897 and 1939 summer polders with to trends in the wider environment. an area of 1100 ha were created in Noarderleech. Land reclamation was undertaken in an ever more Against all expectations, salinisation of the ground- professional manner and, eventually, responsibility water, soil and soil moisture proved to evolve only was assumed by the national Directorate-General of gradually. After four years the levels of salinity were Public Works and Water Management, the still below those seen in the adjacent natural salt- Rijkswaterstaat. During the nineteen seventies and marshes. There was no massive die-off of non-salt eighties, people’s ideas and attitudes changed as tolerant vegetation as a result of ‘salt shock’, and land reclamation became increasingly expensive and no salinisation was established in the adjacent the natural values of unembanked saltmarshes summer polder. Vertical accretion varied from 0.3 – were appreciated more and more; so much so, that 36.7 mm per year. It was highest in the lower-lying new large-scale targets were formulated to restore parts of the trial area and higher in ungrazed areas summer polders which had been reclaimed from than in grazed areas, because taller ungrazed the sea back into saltmarshes, and to open them vegetation traps more sediment. Vertical accretion up to tidal influence again. Noard-Fryslân in Noarderleech is more than adequate to keep Bûtendyks (North Friesland ‘outside the dikes’) pace with land subsidence and the rise in sea level. would then become the largest saltmarsh area in Europe. Processes such as accretion and erosion in Over time the vegetation gradually changed into relation to the sediment balance of the whole of that which is typical of a saltmarsh with many salt- the Wadden Sea are very complex and rarely ob- tolerant species, resulting in a clear increase of the vious. Because the consequences of saltmarsh species targeted by the restoration project. Grazing restoration cannot be predicted with any certainty, has proved to be a very important factor in attain- the nature conservation society It Fryske Gea began ing the target scenario. In ungrazed areas (exclo- an experimental saltmarsh project in 2001 in an sures) the plant cover developed towards species- area measuring 135 ha. Researchers carefully moni- poor Couch-grass vegetation. The availability of tored the results until the end of 2005 to learn food plants for Brent and Barnacle Geese still lags about future de-embankments, adding to the body behind expectations and was lower than it was in of knowledge about saltmarsh restoration already the adjacent summer polders and saltmarshes. The gained in various countries around the world. It food situation will probably recover as the salt- Fryske Gea would like to see rich and varied salt- marsh vegetation continues to develop. No changes marsh vegetation being created in Noard-Fryslân were observed in the numbers of breeding birds in Bûtendyks with good foraging opportunities for the trial area. geese; to achieve this a semi-natural grazed salt- marsh would be the most appropriate land use. In In summary, the experimental saltmarsh restoration 2001, the summer dike was breached in three in Noarderleech can already be considered a places after a very natural-looking but artificial success, and the prospects for continued saltmarsh winding creek system had been dug to stimulate restoration in Noarderleech and the rest of Noard- the supply of seawater and sediment. Through Fryslân Bûtendyks are good. 3 A&W-report 1020 4 A&W-report 1020 2 STRUGGLE AND RISE Traditionally, the Dutch have had to fight the sea to thought about in relation to agriculture, nature and survive and they are known for this characteristic all other uses, i.e., in terms of what we call integrated over the world. The motto of the province of water management. Interestingly, and perhaps typi- Zeeland, Luctor et emergo – I struggle and rise – cally, the Dutch have managed to turn this into a could well be their national motto; it is a source of global export product too, as other countries national pride. The Dutch have been exporting their including the USA and China also have enormous knowledge of drainage and land reclamation for water management problems; the Dutch ‘polder- centuries and Dutchmen are involved in drainage men’ have again taken the lead in finding solutions and embankment projects across the globe. But as they continue to struggle and rise. It is in keep- now, out of the blue, they are breaching dikes in ing with this change in attitude to breach dikes and several places in their own country to allow the sea expose agricultural land to the influence of rivers, into land that was reclaimed from it earlier at great estuaries and inland seas again, replacing polders effort and cost. How on earth can this be? It is no by saltmarshes in a managed way, which is often wonder that many people, especially in the referred to on the European continent as Netherlands, find it hard to understand; and no de-embankment (or depoldering, ontpolderen in wonder that, deep in their hearts, many people are Dutch). hostile to it, especially those who live in places where it is happening, where families have striven Saltmarshes in the Dutch part of the Wadden Sea for generations to claim and secure farming land, can be found on the mainland side of the Wadden and where older people have sharp memories of Sea islands and along the mainland coasts of catastrophic dike breaches and floods. We might Friesland and Groningen. The largest continuous just have a thing or two to explain to them. area of saltmarsh in the whole of the Wadden Sea lies in the Noard-Fryslân Bûtendyks area. It Fryske The world around us is changing, but it’s not just Gea has obtained extensive tracts of this area over that: we ourselves are changing as well and our the past few years for the purpose of improving views on nature, agriculture and water manage- their natural values. To achieve this, the plan is to ment have changed. In the Netherlands until half a breach summer dikes in certain places on a large century ago, nature was something that