In this study we address the question of the extent to which iron may be a limiting factor in restoring rich fens in the temperate climate zone of Europe. Rewetted fens that were heavily degraded in the past by draining over a long period, were compared with pristine fens or fens with slightly altered hydrological systems. The chemical composition of peat and of pore water was analysed and related to the composition of the vegetation of the fens. The species composition and chemistry of the topsoil of restored fens differed markedly from that of the other fens, while the chemistry of the pore water from deeper layers showed only minor differences. Multivariate analysis revealed that differences in species composition between both categories were strongly related to the concentration of Fe in the pore water in the topsoil. Restored sites with high iron concentrations in the pore water (> 100 mu mol.L-1) lacked many vascular plants and mosses typical of peat forming fens. Iron and inorganic phosphorus pools in the topsoil of most restored fens were much greater than in the reference fens. A higher soil phosphorus pool originated mainly from the iron-bound fraction. We conclude that these differences are strongly governed by local processes and not by regional differences in climate, which were associated with geographical distribution of the different fens studied. The strong accumulation of iron and phosphorus in restored fens is attributed to a long history of drainage, which enhanced the accumulation of oxidized iron in the topsoil and also lowered the concentrations of calcium, magnesium and sulphur through drainage-caused reoccurring oxidation-reduction and leaching processes. A high iron and associated high phosphorous content appears to be an important and possibly irreversible bottleneck to restoring biodiversity and accumulation of peat with a low degree of humification in degraded fens. If a degraded fen has a low iron content then it is more likely to be restorable.

Traditional grasslands are often of high conservation value, but depend on non-intensive management like mowing for their preservation. During the 20th century, traditional agricultural usage was either heavily intensified or abandoned due to socio-economic reasons. In Eastern Europe, land abandonment mainly took place in regions with qualitatively bad soils. This large scale land use change lead to secondary succession. In fens and fen meadows, this may lead to a decrease in species richness and a replacement of specialist species by more generalist ones. The main objective of the present study is to examine if and how mowing cessation interacts with hydrology in determining species and trait distribution in a fen meadow. In the Upper Course of the Biebrza National Park, Poland, we selected 15 sites along four transects, with plots in mown and abandoned parcels. In these plots we measured plant abundance, aboveground biomass and relative light intensity, while plant traits were selected from different trait databases. The relationship between these plot characteristics and the different traits was assessed using concordance analysis. Mowing cessation resulted in reduced moss cover and light availability, while vegetation height increased and higher litter deposition and tussock development were observed. This altered environment not only resulted in decreased species richness and evenness in abandoned plots but also caused shifts in plant trait distribution. Most of the significantly linked traits responded more strongly to mowing cessation than to the hydrologic gradient. Traits related to light competition, such as light requirements, plant height and shoot growth form, especially responded to mowing cessation. This stresses the importance of light competition as a major factor determining species and trait distribution in fen systems.

The Berg River is one of the main rivers in the Cape Region; it is essential for the local economy and ecology, as it supplies water to agriculture and industries, provides drinking water for the greater Cape Town region, and supports rich aquatic ecosystems.The Berg River is impacted by both diffuse pollution from agricultural run-off and point-source pollution from urban and industrial wastewater.Construction of a dam on the headwaters of the Berg River in 2007 has changed the hydrology of the upper catchment.Pelagic nutrient dynamics in the Berg River are well documented.The opposite is however true for riparian nutrient dynamics.We studied changes in riparian nutrient storage over a gradient in elevation (a proxy for flooding frequency and drought) and human influence (the Berg River dam and lateral nutrient and pollutant input).Our results show that nutrient concentrations in the riparian sediments reflect nutrient concentrations in the river.N concentrations in the sediment increased up to 1 000%, while P concentrations rose up to 200% with increasing human influence.For biogenic Si, we found generally low concentrations throughout the whole gradient sampled (all < 0.5 mg BSi g -1 sediment).Sediments closer to the river appear to have more efficient recycling and export of nutrients into the river.Overall, we conclude that the observed patterns indicate the necessity of incorporating nutrient status and management of riparian habitats in the Berg River monitoring strategy.

1. Macrophytes in running waters experience an often dynamic and harsh environment. To avoid breakage, plants have to reduce the experienced drag force. However, by reducing leaf area, photosynthetic production is less. Aquatic plants therefore have to find a balance between reducing drag and maintaining photosynthetic capacity.2. In the experiments in this study, we assessed to what extent different morphological strategies (emergent vs. submerged) were able to minimize drag while maximizing leaf area.3. From our measurements, it is clear that with increasing water velocities, emergent plant species have a drag value three to four times higher than submerged species.4. To test the versatility of leaves, leaves were removed and their effect on drag and bending was investigated. Almost 60% of the drag is contributed by the leaves, and stems bend less when leaves are removed.5. Because high submerged leaf area increases not only plant drag but also photosynthetic yield, a trade-off between both parameters was investigated in the function of stream velocity. Emerged species had a more favourable trade-off at low stream velocities. However, with increasing stream velocity, submerged species could reduce their drag more in comparison with blunt objects. Within these submerged species, a clear distinction was seen between those (Potamogeton natans) concentrating their leaf area on or just beneath the water surface (Stuckenia pectinata) and those with more or less evenly distributed biomass (Callitriche platycarpa and Ranunculus penicillatus).6. These results indicate that aquatic plants with an emergent strategy are able to take better advantage of zones with reduced hydraulic forces than submerged plants. Additionally, this plant occurrence will be determined by the relationship between total plant drag and root strength.

Despite the growing concern about the importance of silicon (Si) in controlling ecological processes in aquatic ecosystems, little is known about its processing in riparian vegetation, especially compared to nitrogen (N) and phosphorus (P). We present experimental evidence that relative plant uptake of N and P compared to Si in riparian vegetation is dependent on mowing practices, water-logging and species composition. Results are obtained from a controlled and replicated mesocosm experiment, with a full-factorial design of soil water logging and mowing management. In our experiments, the Si excluding species Plantago lanceolata was dominant in the mown and non-waterlogged treatments, while Si accumulating meadow grasses and Phalaris arundinacea dominated the waterlogged treatments. Although species composition, management and soil moisture interacted strongly in their effect on relative Si:N and Si:P uptake ratios, the uptake of N to P remained virtually unchanged over the different treatments. Our study sheds new light on the impact of riparian wetland ecosystems on nutrient transport to rivers. It indicates that it is essential to include Si in future studies of the impact of riparian vegetation on nutrient transport, as these are often implemented as a measure to moderate excessive N and P inputs.

*Although silica (Si) is not an essential element for plant growth in the classical sense, evidence points towards its functionality for a better resistance against (a)biotic stress. Recently, it was shown that wetland vegetation has a considerable impact on silica biogeochemistry. However, detailed information on Si uptake in aquatic macrophytes is lacking. *We investigated the biogenic silica (BSi), cellulose and lignin content of 16 aquatic/wetland species along the Biebrza river (Poland) in June 2006 and 2007. The BSi data were correlated with cellulose and lignin concentrations. *Our results show that macrophytes contain significant amounts of BSi: between 2 and 28 mg BSi g(-1). This is in the same order of magnitude as wetland species (especially grasses). Significant antagonistic correlations were found between lignin, cellulose and BSi content. Interestingly, observed patterns were opposite for wetland macrophytes and true aquatic macrophytes. *We conclude that macrophytes have an overlooked but potentially vast storage capacity for Si. Study of their role as temporal silica sinks along the land-ocean continuum is needed. This will further understanding of the role of ecosystems on land ocean transport of this essential nutrient.

Vegetation and proximity to the river control amorphous silica storage in a riparian wetland (Biebrza National Park, Poland) E. Struyf, W. Opdekamp, H. Backx, S. Jacobs, D. J. Conley, and P. Meire Lund University, GeoBiosphere Science Centre, Department of Geology, Sölvegatan 12, 22362 Lund, Sweden University of Antwerp, Department of Biology, Ecosystem Management Research Group, Universiteitsplein 1c, 2610 Wilrijk, Belgium Received: 17 September 2008 – Accepted: 19 November 2008 – Published: 15 January 2009 Correspondence to: E. Struyf (eric.struyf@geol.lu.se) Published by Copernicus Publications on behalf of the European Geosciences Union.

Wetlands can modify and control nutrient fluxes between terrestrial and aquatic ecosystems, yet little is known of their potential as biological buffers and sinks in the biogeochemical silica cycle. We investigated the storage of amorphous silica (ASi) in a central-European riparian wetland. The variation in storage of ASi in the soil of an undisturbed wetland was significantly controlled by two factors: dominance of sedges and grasses and distance to the river (combined R-2=78%). Highest ASi storage was found near the river and in sites with a dominance of grasses and sedges, plants which are well known to accumulate ASi. The management practice of mowing reduced the amount of variation attributed to both factors (R-2=51%). Although ASi concentrations in soils were low (between 0.1 and 1% of soil dry weight), ASi controlled the availability of dissolved silica (DSi) in the porewater, and thus potentially the exchange of DSi with the nearby river system through both diffusive and advective fluxes. A depth gradient in ASi concentrations, with lower ASi in the deeper layers, indicates dissolution. Our results show that storage and recycling of ASi in wetland ecosystems can differ significantly on small spatial scales. Human management interferes with the natural control mechanisms. Our study demonstrates that wetlands have the potential to modify the fluxes of both DSi and ASi along the land-ocean continuum and supports the hypothesis that wetlands are important ecosystems in the biogeochemical cycling of silica.

1. To encourage more project assessment and reporting of restoration outcomes, Palmer et al. (2005) propose five criteria for assessing the ecological success of river restoration. They also suggest that these criteria should help to clarify which activities should qualify for ecological restoration funding and facilitate consistency about what constitutes an ecologically successful restoration project. 2. We critique the five criteria and agree they all merit inclusion in an assessment of successful river restoration. However, the practical application of measuring self-sustainability (resilience) following restoration is potentially problematic and an explicit timeframe is needed to evaluate the results of the restoration. 3. A sixth criterion is proposed that encourages specific hypotheses and/or a conceptual model of the ecological mechanisms by which the proposed activities will achieve their target. This would enhance our understanding of the mechanisms at play for successful river restoration, and provide a more powerful deductive framework likely to lead to appropriate practices that can be applied across rivers. To explore the potential practical applicability of these six criteria, we applied them to a recently published example of river restoration to ascertain its ecological success. 4. Synthesis and applications. We agree with the criteria proposed by Palmer et al. (2005), although the problems of measuring resilience and defining a timeline for recovery should be addressed. We suggest strengthening the deductive framework of restoration projects by formulating some sort of conceptual model. This step could involve scientists, and be a useful way of involving science more explicitly in restoration activities. Agreed-upon criteria for successful restoration will greatly facilitate evaluation of river ecosystem recovery at the critical broader scales where our knowledge is still limited.

Nanocyperion plant communities occur on wet, more or less nutrient-poor and sparsely vegetated soils in temperate climates and are characterized by tiny, very short-lived plant species. Most of these have become locally extinct. It is generally assumed that drainage and eutrophication were the most important reasons for this decrease. However, chemical analysis of soil pore water from plots on growth sites of these ephemerals showed that phosphorus availability was relatively high.In a greenhouse experiment, the growth of ephemeral species was strongly limited by the amount of available phosphorus, whereas there was little or no limitation to the growth of other plant species from this habitat. At low phosphorus concentrations, the ephemeral species reached their reproductive phase within the same period, but showed a strong reduction in the amount of flowers that were produced. We concluded that ephemeral species in particular require a minimum amount of phosphorus for reproduction. Other species on nutrient-poor, wet soils have a longer life span and can postpone flowering in nutrient-poor soils.In contrast to other short-lived plant species from the same habitat, the growth of ephemeral species was barely stimulated by enhanced nitrogen availability. Apparently, the ephemerals are adapted to low nitrogen concentrations. The occurrence on nitrogen-poor and relatively phosphorus-rich soils suggests that this community may be very sensitive to nitrogen deposition. Reduced phosphorus availability below the minimum requirements of ephemerals. for example at I ter acidification or the exclusion of human activities, has possibly contributed to the decrease of ephemeral plant species.