Ecological Engineering 66 (2014) 82–90 Contents lists available at ScienceDirect Ecological Engineering journal h om epa ge: www.elsevier.com/locate/ecoleng How helophytes influence the phosphorus cycle in degraded inundated peat soils – Implications for fen restoration Dominik Zak a,∗ , Jörg Gelbrecht a , Stefan Zerbe b , Tom Shatwell a , Martin Barth c , Alvaro Cabezas a , Peggy Steffenhagen d a Department of Chemical Analytics and Biogeochemistry, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, D-12587 Berlin, Germany b Faculty of Science and Technology, Free University of Bozen, I-39100 Bolzano, Italy c Faculty of Agricultural and Environmental Sciences, University of Rostock, Germany d Luftbild Umwelt Planung GmbH (LUP), Große Weinmeisterstraße 3a, D-14469 Potsdam, Germany a r t i c l e i n f o Article history: Received 12 December 2012 Received in revised form 27 September 2013 Accepted 2 October 2013 Available online 4 November 2013 Keywords: Leaching Phosphorus retention Phragmites australis Top soil removal Redox interface Rewetting a b s t r a c t When severely degraded fens are rewetted, they often become shallow lakes with an average water depth of less than 1 m. The additional high nutrient availability in highly decomposed peat soils of these newly formed ecosystems favours the fast establishment of a small number of helophytes while the return of lost target species like low sedges and brown mosses could be delayed for decades. We hypothesise that the phosphorus (P) uptake of the newly developed vegetation substantially influences the P cycle in rewetted fens. Therefore, we investigated how much of the P released in upper degraded peat soils is pumped across the redox-interface between the soil and surface water (=‘P barrier’) during the growing season (∼150 days) by six helophytes (Phragmites australis, Typha latifolia, Glyceria maxima, Carex acutiformis, Carex riparia, and Phalaris arundinacea) in five rewetted fens. We then assessed how this would affect the different plant-available P fractions in the rooted degraded peat layers. The highest P uptake during the growing season (duration 150 days from May to September) was recorded for T. latifolia and G. maxima (3.0 and 2.8 g m -2 , respectively). Overall, the P uptake was in the range of the P mobilisation rates we measured in highly decomposed peat soils (range: 0.8–15.6 g P m -2 , n = 30), but four to 10-fold higher than diffusive net P fluxes at the interface between soil and surface water. Accordingly, helophytes are able to compensate for the high P mobilisation in degraded peat soils during the growing season, by incorporating this P into biomass. On the other hand a large part of the plant-P stock is released after die back through leaching and mineralisation, which increases the P load of these newly formed shallow lakes and possibly also of adjacent water courses. We estimated that it would still take 20–50 years to exhaust the large pool of plant-available P in highly decomposed peat soils if aboveground biomass was removed. Without any further management apart from fen rewetting it is unlikely that the fens will return to low nutrient levels within a human life time. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. 1. Introduction The eutrophication of lakes and rivers is still a problem in most regions of Central Europe due to non-point source phos- phorus (P) pollution from intense agricultural land use (Lamers ∗ Corresponding author at: Department of Chemical Ananlytics and Biogeochem- istry, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, D-12587 Berlin, Germany. Tel.: +49 3064181730; fax: +49 3064181682. E-mail addresses: zak@igb-berlin.de (D. Zak), gelbr@igb-berlin.de (J. Gelbrecht), Stefan.Zerbe@unibz.it (S. Zerbe), shatwell@igb-berlin.de (T. Shatwell), Martin.Barth@uni-rostock.de (M. Barth), acabezas@ymail.com (A. Cabezas), peggy.steffenhagen@lup-umwelt.de (P. Steffenhagen). et al., 1998). One important strategy to improve water quality as required by the EU Water Framework Directive (2000) is to restore natural nutrient sinks like minerotrophic peatlands, i.e. fens. Orig- inally, they covered about 495,000 km 2 of Europe, or 5% of the total land area. An even higher proportion of more than 10% was found in northern Germany where fens once acted as important buffer zones between the mineral soils of uplands and water ways (Fig. 1). However, drainage and intensified agricultural use of fen areas led to the loss of the sink function and other ecosystem services, thus increasing the load of phosphate and other nutri- ents entering adjacent surface waters (Kalbitz and Geyer, 2002; Kieckbusch and Schrautzer, 2007). Today ∼60% of European peat- lands are drained or suffer from lowered groundwater tables in 0925-8574/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2013.10.003